European Journal of Clinical Investigation (1992) 22, 562-568
Renal reserve filtration capacity in growth hormone deficient subjects R. P. F. DULLAART*, S. MEIJERt, P. MARBACHS & W.J. SLUITER* Department of Internal Medicine, Divisions of Endocrinology* and Nephrologyt, University Hospital Groningen, The Netherlands, and Sandoz Pharma Ltd.,S Basel, Switzerland Received 10 January 1992 and in revised form 19 March 1992; accepted 26 March 1992
Abstract. In normal subjects, the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) acutely increase in response to infusion of amino acids and to low doses of dopamine. It is uncertain whether circulatory growth hormone (GH) is a permissive factor for these stimulatory effects. G F R and ERPF (constant infusion technique using 1251-iothalamate and 1311-hippuran,respectively) were measured before and during the infusion of dopamine and amino acids in 8 G H deficient subjects. The clearance study was repeated during concomitant administration of octreotide to investigate whether this somatostatin analogue would modify the amino acid and dopamineinduced renal haemodynamic changes. Dopamine increased baseline GFR from 89 f3 (mean f SEM, n = 8 ) to 102+4 ml min-' 1.73 m P 2and ERPF from 352k 19 to 476f26 ml min-' 1.73 m-2, Pc0.001 for both. During amino acid infusion G F R and ERPF increased to 108k3 and 415f23 ml min-' 1.73 m-2, respectively, Pc 0.001 for both. Octreotide did not significantly decrease baseline and dopamine-stimulated renal haemodynamics but lowered the amino acid-stimulated GFR (98f4 ml min-I 1-73 mT2, PcO-05) and ERPF (381f18 ml min-I 1-73 mP2, P c 0.05). Basal plasma glucagon concentrations were not suppressed by octreotide, whereas the amino acidinduced increments in plasma glucagon were partially inhibited. It is concluded that G H is not a necessary factor for the stimulatory effects of amino acids and dopamine on renal haemodynamics. The renal reserve filtration capacity in GH deficiency was at least as large as previously documented in normal subjects. It is likely that there is a functional antagonism between the effects of amino acids and octreotide on renal haemodynamics in G H deficiency. Keywords. Amino acids, dopamine, growth hormone, octreotide, renal haemodynamics.
Correspondence: R. P. F. Dullaart MD, Department of Internal Medicine, University Hospital Groningen, PO Box 30.001,9700 RB Groningen, The Netherlands.
562
Introduction It is well established that the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) acutely increase in response to a protein load or amino acid infusion in human subjects [1-41, The mechanisms involved in these renal haemodynamic changes are still poorly understood. Hormonal and humoral factors as well as a tubuloglomerular feedback mechanism might be involved [4-71. Some investigators have assigned an important role to glucagon in the amino acid-induced increase in G F R and ERPF [5,6], but this has been disputed by others [8,9]. It is beyond doubt that growth hormone (GH) is important in the maintenance of glomerular filtration. G H stimulates renal function indirectly via insulin-like growth factor I (IGF-I) [lo]. GFR and ERPF are low in G H deficient subjects [l 11, whereas acromegalic patients show glomerular hyperfiltration [ 11,12,13]. Whether circulatory G H is necessary for the acute rise in renal haemodynamics following protein loading or amino acid-infusion is controversial. In G H deficient subjects, the proteininduced rise in GFR was obliterated [14]. Other studies have shown a normal rise in GFR and ERPF during arginine infusion and an increase in creatinine clearance after a protein load in G H deficient subjects [ 15,161. Native somatostatin, which profoundly suppresses the secretion of glucagon, G H as well as other hormonal substances, has been shown to abolish the amino acid-induced increase in G F R and ERPF in normal subjects [6,17]. Long-term administration of the somatostatin analogue, octreotide, did not prevent the rise in G F R and ERPF during amino acid infusion in acromegalic patients [13]. In this situation, amino acid-stimulated plasma glucagon was not significantly reduced. Apart from amino acids, the renal reserve filtration capacity, i.e. the increment in renal function in response to certain stimulatory factors, can be tested using low-dose dopamine infusion [3,18,19]. Amino acids and low-dose dopamine infusion enhance renal function by different mechanisms and their effects are additive [3,18,19]. The possible permissive role of G H in the renal haemodynamic effect of dopamine is unknown.
RENAL RESERVE CAPACITY IN GROWTH HORMONE DEFICIENCY
563
respectively [21]. The G F R and ERPF were corrected to 1.73 mP2 of body-surface area. The filtration fraction was calculated as the ratio GFR/ERPF and expressed as a percentage. On each study day, a 3.5-h equilibration period was taken from 07.30 to 11.00. On day 1, the baseline GFR and ERPF were determined over a 2-h clearance period from 1 1.OO to 13.00. This baseline measurement was followed by a 2-h clearance period during which dopamine was infused at a rate of 1-5-2.0 pg kg-' min-' (Braun Unita I1 pump, Melsungen, Germany). Infusion of an amino acid solution (Vamin NQ, 7% weight volume-', Kabi Vitrum, Limoges, France) was started at 18.00 at a rate of 83 ml h-'. The amino acid infusion was maintained overnight and on day 2 the effect of amino acids was determined over a 2-h clearance period from I 1.OO to 13.00, followed by a 2-h clearance period during the combined infusion of amino acids and dopamine. On both days Ringerslactate, the vehicle for octreotide, was infused at a rate of 1 ml h-' after a bolus of 2 ml at 07.30. This was done to make the procedure similar to that during the octreotide administration. The participants were readmitted after 2-6 weeks to repeat the clearance studies with concomitant octreotide administration. On these study days, designated days 3 and 4, octreotide was administered intravenously to prevent fluctuations in octreotide concentrations during the clearance studies. Octreotide was diluted in Ringers-lactate (10 pg ml-I). After a 20 pg bolus injection at 07.30, octreotide was infused at a rate of 10pg h- I . The infusion was stopped at 15.00. In addition, subcutaneous octreotide injections of 100pg were administered at 17.00 and 23.00 on the day prior to day 3 and on day 3. Normal values in our laboratory for GFR and ERPF and the increments induced by dopamine, amino acids and their combined infusion are: GFR 103f3 (mean k S E M , n = 17), range 79-123 mlmin-' 1.73 mP2andERPF429+ 18, range310-554mlmin-' 1.73 mP2; dopamine induced increment in GFR 13.5f2.2% and in ERPF 36.1 f3-8%; amino acidinduced increment in G F R 13.2 & 2.7% and in ERPF 10.6f 3.2%; combined dopamine and amino acidinduced increment in G F R 22.3 f2.2% and in ERPF 40.6+55% [19].
The purpose of the present study was to investigate the renal haemodynamic response to amino acid and low-dose dopamine infusion in G H deficient subjects. Secondly, we assessed whether concomitant administration of octreotide would alter the effects of these stimuli on G F R and ERPF. Patients and methods Patients Eight adult patients with severe G H deficiency were included in the study (Table 1). The diagnosis of severe GH deficiency was made on the basis of a peak serum GH concentration below 1.5 pg I - ' in response to insulin-induced hypoglycaemia [20]. In 4 patients an arginine-infusion test was also performed showing a maximal GH response below 1.5 pg I-'. The mean plasma IGF-I concentration was 0.18 (range 0.120.40) kU 1-' (reference values for adults 0.34 to 2.2 kU 1-I). The patients suffered from either congenital or acquired multiple hypothalamo-hypophyseal hormonal deficiencies. Supplementation therapy with various hormones was given if necessary and continued during the study (Table I). Two patients had been previously treated with human GH. G H administration was discontinued at least 5 years before the study. None of the patients had hypertension (systolic blood pressure 2 160 mm Hg and/or diastolic blood pressure 2 9 5 mm Hg) or renal disease. All participants consented to the procedure after explanation of the purpose of the study. Procedure The patients were hospitalized for the renal haemodynamic and hormonal investigations. The participants were studied after an overnight fast. A diuresis of at least 100 ml h-' was maintained by the oral administration of water. Supine glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured simultaneously, using '251-iothalamate and '3'I-hippuran, respectively according to a previously described procedure [21]. After a priming dose, 1251iothalamate and I3'I-hippuran were infused at a constant rate of 3.6 pCi h-' (133 kBq h-') and 4.5 pCi h-' (167 kBq h-I), respectively. The coefficients of variation of the GFR and the ERPF were 2.2% and 50%, Table 1. Clinical characteristics Age (years) 33 28 53 32 45 52 37 41
Sex
Original diagnosis
F M M F M
primary hypopituitarism primary hypopituitarism non-functioningpituitary adenoma primary empty sella non-functioningpituitary adenoma non-functioningpituitary adenoma primary hypopituitarism primary hypopituitarism
F
M F
Height (m)
I .29 I .41 1.93 1.59 1.82 1.68 1.65 1.46
Replacement therapy 39 53 93 13 93 88 51 55
thyroxine, cortisone acetate thyroxine, growth hormone+ thyroxine, cortisone acetate, sex steroids thyroxine, cortisone acetate thyroxine, cortisone acetate thyroxine, cortisone acetate, desmopressin thyroxine,cortisone acetate, sex steroids, growth hormone+ thyroxine, sex steroids
F denotes female; M denotes male. * Growth hormone therapy discontinued 5 years (patient no. 2) and 18 years (patient no. 7) before study.
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Blood pressure was measured at 120 min intervals using a standard sphygomomanometer, Korotkoff phase 5 was taken as the diastolic blood pressure. Mean arterial blood pressure (in mm Hg) was calculated at 0.67 x diastolic pressure+O.33 x systolic pressure. Five blood samples were drawn from an intravenous catheter for the measurement of GH, glucagon, glucose and octreotide on each study day. Laboratory analysis The serum and plasma samples were frozen at -20°C until assay. Serum GH was measured by radioimmunoassay (Farmos Diagnostica, Turku, Finland). The lower detection limit was 0.5 pg 1-I. Plasma glucagon was measured by radioimmunoassay (antibody 30K, Prof R. H. Unger, Dallas, Texas, USA) [22]. Plasma octreotide was measured at Sandoz Laboratories (Basel, Switzerland) using a previously described radioimmunoassay [23]. IGF-I was determined with a commercially available kit (Nichols Institute of Diagnostics, San Juan Capistrano, CA, USA). Blood glucose was measured with a hexokinase method (Autoanalyzer 11, Technicon Instruments Corporation, Tarrytown, NY,USA). The respective intraand interassay coefficients of variation were 4% and 9% for GH, 5% and 15% for glucagon, 5% and 10% for octreotide, and 5% and 10% for IGF-I. Statistical analysis
The results are expressed as mean fSEM. Data were compared by using the Wilcoxon-rank-sum-test for paired observations and a two-way analysis of variance according to Friedman [24]. Adjustment for multiple comparisons was carried out using Duncan's method [25]. Correlation coefficients were analysed using Spearman's rank test. Averaged correlation coefficients were computed after Z-transformation of correlation coefficients obtained in individual participants. A two-sided P-value of c0.05was considered to be significant.
Results Renal haemodynamics and blood pressure The GFR, ERPF and filtration fraction during each of the clearance periods and the effect of concomitant octreotide infusion are shown in Fig. 1. Baseline GFR and ERPF were low in the GH deficient subjects. Dopamine infusion induced a significant increase in GFR and ERPF, whereas the filtration fraction decreased. The infusion of amino acids also resulted in a significant rise in GFR and ERPF, but with this stimulus the filtration fraction increased. The increments in GFR and ERPF resulting from the combined infusion of amino acids and dopamine were larger than during the separate infusion of these stimuli. These
effects of dopamine and amino acids were at least as large as previously documented in normal subjects 1191. The GFR and ERPF did not significantly decrease during infusion of octreotide. The increments in GFR and ERPF induced by dopamine infusion were similar and the values achieved were not different from those without octreotide infusion. During octreotide amino acid infusion still induced a significant rise in GFR and ERPF, but the values achieved were lower than those before octreotide infusion. The filtration fraction did not increase during concomitant amino acid and octreotide infusion. The mean arterial blood pressure was 93.5 & 3.1 mm Hg, 92.5f3.1 mm Hg, 93.8f2.2 mm Hg and 89.5 f2.6 mm Hg on days 1,2,3 and 4 of the clearance studies, respectively, indicating no significant effect of either amino acid or octreotide infusion on blood pressure. The change in mean arterial blood pressure during dopamine infusion was also not significant (1.7f 3.5 mm Hg on day 1, NS and - 1.9 3.2 mm Hg on day 3, NS). Metabolic assessment
GH was undetectable (c0-5pg 1-I) in all serum samples taken during the 4 study days. To evaluate the effect of amino acid and octreotide infusion on plasma glucagon concentration, the 5 samples from each patient obtained on each study day were averaged. The glucagon levels are shown in Fig. 2. The mean plasma glucagon concentrations were 234 f24 ng 1- I , 397 f23 ng I-', 221 f20 ng 1-' and 3 14f 21 ng 1-' on days 1,2, 3 and 4 of the clearance studies, respectively. Plasma glucagon concentrations increased significantlyduring amino acid infusion, both before ( P c 0.001) and during octreotide infusion ( P c 0.001). Octreotide did not decrease plasma glucagon on day 3, but the amino acid induced increment in glucagon concentrations was diminished with concomitant octreotide administration on day 4 (163118 ng 1-' vs. 94f21 ng 1-I, P c 0.02). To investigate the possible relationship between the amino acid-induced rise in plasma glucagon and in renal haemodynamics, the correlation coefficients between plasma glucagon and GFR or ERPF were assessed. In each subject, the 4 datasets from the baseline and the amino acid clearance periods, with and without concomitant octreotide infusion were used. Both GFR (averaged Rs=0.96, P c 0.00 1) and ERPF (averaged Rs = 0-86, P c 0.00 1) were significantly related to plasma glucagon. Octreotide levels increased shortly after the start of octreotide infusion and then remained constant during the clearance periods (Fig. 3). The mean octreotide levels were similar on both days (2.27 f0.27 pg 1-' vs. 2.04 f0.23 pg 1- I , NS). The mean blood glucose concentrations were not different on the 4 study days (3.56f0.11 mmol l - l , 3.91 f0.08 mmol 1-I, 3.65f0.08 mmol l-' and 3.79f0.15 mmol 1-' on days 1, 2, 3 and 4 respectively, NS).
RENAL RESERVE CAPACITY IN GROWTH HORMONE DEFICIENCY
6
-
Effective renal plasma flow
m
L
40
r: 600
5z w L U
Glornerular filtration rate 50
700
30
400
20
300
10
w
34 C
0
.
Filtration fraction 28
1
T
565
9.11
Effective renal plasma flow
T
60 +I
50 40
30 20 10
0 baseline
dopamine amino acids amino adds + dopamine
dopamine
amino acids
amlno acids + dopamine
Figure 1. Renal reserve filtrationcapacity. Data are given in mean & SEM (n = 8). GFR glomerularfiltration rate; ERPF effective renal plasma flow. Open bars: before octreotide; hatched bars: during octreotide. A Absolute values. B relative increments in YO change from baseline. P
Renal reserve filtration capacity in growth hormone deficient subjects R. P. F. DULLAART*, S. MEIJERt, P. MARBACHS & W.J. SLUITER* Department of Internal Medicine, Divisions of Endocrinology* and Nephrologyt, University Hospital Groningen, The Netherlands, and Sandoz Pharma Ltd.,S Basel, Switzerland Received 10 January 1992 and in revised form 19 March 1992; accepted 26 March 1992
Abstract. In normal subjects, the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) acutely increase in response to infusion of amino acids and to low doses of dopamine. It is uncertain whether circulatory growth hormone (GH) is a permissive factor for these stimulatory effects. G F R and ERPF (constant infusion technique using 1251-iothalamate and 1311-hippuran,respectively) were measured before and during the infusion of dopamine and amino acids in 8 G H deficient subjects. The clearance study was repeated during concomitant administration of octreotide to investigate whether this somatostatin analogue would modify the amino acid and dopamineinduced renal haemodynamic changes. Dopamine increased baseline GFR from 89 f3 (mean f SEM, n = 8 ) to 102+4 ml min-' 1.73 m P 2and ERPF from 352k 19 to 476f26 ml min-' 1.73 m-2, Pc0.001 for both. During amino acid infusion G F R and ERPF increased to 108k3 and 415f23 ml min-' 1.73 m-2, respectively, Pc 0.001 for both. Octreotide did not significantly decrease baseline and dopamine-stimulated renal haemodynamics but lowered the amino acid-stimulated GFR (98f4 ml min-I 1-73 mT2, PcO-05) and ERPF (381f18 ml min-I 1-73 mP2, P c 0.05). Basal plasma glucagon concentrations were not suppressed by octreotide, whereas the amino acidinduced increments in plasma glucagon were partially inhibited. It is concluded that G H is not a necessary factor for the stimulatory effects of amino acids and dopamine on renal haemodynamics. The renal reserve filtration capacity in GH deficiency was at least as large as previously documented in normal subjects. It is likely that there is a functional antagonism between the effects of amino acids and octreotide on renal haemodynamics in G H deficiency. Keywords. Amino acids, dopamine, growth hormone, octreotide, renal haemodynamics.
Correspondence: R. P. F. Dullaart MD, Department of Internal Medicine, University Hospital Groningen, PO Box 30.001,9700 RB Groningen, The Netherlands.
562
Introduction It is well established that the glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) acutely increase in response to a protein load or amino acid infusion in human subjects [1-41, The mechanisms involved in these renal haemodynamic changes are still poorly understood. Hormonal and humoral factors as well as a tubuloglomerular feedback mechanism might be involved [4-71. Some investigators have assigned an important role to glucagon in the amino acid-induced increase in G F R and ERPF [5,6], but this has been disputed by others [8,9]. It is beyond doubt that growth hormone (GH) is important in the maintenance of glomerular filtration. G H stimulates renal function indirectly via insulin-like growth factor I (IGF-I) [lo]. GFR and ERPF are low in G H deficient subjects [l 11, whereas acromegalic patients show glomerular hyperfiltration [ 11,12,13]. Whether circulatory G H is necessary for the acute rise in renal haemodynamics following protein loading or amino acid-infusion is controversial. In G H deficient subjects, the proteininduced rise in GFR was obliterated [14]. Other studies have shown a normal rise in GFR and ERPF during arginine infusion and an increase in creatinine clearance after a protein load in G H deficient subjects [ 15,161. Native somatostatin, which profoundly suppresses the secretion of glucagon, G H as well as other hormonal substances, has been shown to abolish the amino acid-induced increase in G F R and ERPF in normal subjects [6,17]. Long-term administration of the somatostatin analogue, octreotide, did not prevent the rise in G F R and ERPF during amino acid infusion in acromegalic patients [13]. In this situation, amino acid-stimulated plasma glucagon was not significantly reduced. Apart from amino acids, the renal reserve filtration capacity, i.e. the increment in renal function in response to certain stimulatory factors, can be tested using low-dose dopamine infusion [3,18,19]. Amino acids and low-dose dopamine infusion enhance renal function by different mechanisms and their effects are additive [3,18,19]. The possible permissive role of G H in the renal haemodynamic effect of dopamine is unknown.
RENAL RESERVE CAPACITY IN GROWTH HORMONE DEFICIENCY
563
respectively [21]. The G F R and ERPF were corrected to 1.73 mP2 of body-surface area. The filtration fraction was calculated as the ratio GFR/ERPF and expressed as a percentage. On each study day, a 3.5-h equilibration period was taken from 07.30 to 11.00. On day 1, the baseline GFR and ERPF were determined over a 2-h clearance period from 1 1.OO to 13.00. This baseline measurement was followed by a 2-h clearance period during which dopamine was infused at a rate of 1-5-2.0 pg kg-' min-' (Braun Unita I1 pump, Melsungen, Germany). Infusion of an amino acid solution (Vamin NQ, 7% weight volume-', Kabi Vitrum, Limoges, France) was started at 18.00 at a rate of 83 ml h-'. The amino acid infusion was maintained overnight and on day 2 the effect of amino acids was determined over a 2-h clearance period from I 1.OO to 13.00, followed by a 2-h clearance period during the combined infusion of amino acids and dopamine. On both days Ringerslactate, the vehicle for octreotide, was infused at a rate of 1 ml h-' after a bolus of 2 ml at 07.30. This was done to make the procedure similar to that during the octreotide administration. The participants were readmitted after 2-6 weeks to repeat the clearance studies with concomitant octreotide administration. On these study days, designated days 3 and 4, octreotide was administered intravenously to prevent fluctuations in octreotide concentrations during the clearance studies. Octreotide was diluted in Ringers-lactate (10 pg ml-I). After a 20 pg bolus injection at 07.30, octreotide was infused at a rate of 10pg h- I . The infusion was stopped at 15.00. In addition, subcutaneous octreotide injections of 100pg were administered at 17.00 and 23.00 on the day prior to day 3 and on day 3. Normal values in our laboratory for GFR and ERPF and the increments induced by dopamine, amino acids and their combined infusion are: GFR 103f3 (mean k S E M , n = 17), range 79-123 mlmin-' 1.73 mP2andERPF429+ 18, range310-554mlmin-' 1.73 mP2; dopamine induced increment in GFR 13.5f2.2% and in ERPF 36.1 f3-8%; amino acidinduced increment in G F R 13.2 & 2.7% and in ERPF 10.6f 3.2%; combined dopamine and amino acidinduced increment in G F R 22.3 f2.2% and in ERPF 40.6+55% [19].
The purpose of the present study was to investigate the renal haemodynamic response to amino acid and low-dose dopamine infusion in G H deficient subjects. Secondly, we assessed whether concomitant administration of octreotide would alter the effects of these stimuli on G F R and ERPF. Patients and methods Patients Eight adult patients with severe G H deficiency were included in the study (Table 1). The diagnosis of severe GH deficiency was made on the basis of a peak serum GH concentration below 1.5 pg I - ' in response to insulin-induced hypoglycaemia [20]. In 4 patients an arginine-infusion test was also performed showing a maximal GH response below 1.5 pg I-'. The mean plasma IGF-I concentration was 0.18 (range 0.120.40) kU 1-' (reference values for adults 0.34 to 2.2 kU 1-I). The patients suffered from either congenital or acquired multiple hypothalamo-hypophyseal hormonal deficiencies. Supplementation therapy with various hormones was given if necessary and continued during the study (Table I). Two patients had been previously treated with human GH. G H administration was discontinued at least 5 years before the study. None of the patients had hypertension (systolic blood pressure 2 160 mm Hg and/or diastolic blood pressure 2 9 5 mm Hg) or renal disease. All participants consented to the procedure after explanation of the purpose of the study. Procedure The patients were hospitalized for the renal haemodynamic and hormonal investigations. The participants were studied after an overnight fast. A diuresis of at least 100 ml h-' was maintained by the oral administration of water. Supine glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured simultaneously, using '251-iothalamate and '3'I-hippuran, respectively according to a previously described procedure [21]. After a priming dose, 1251iothalamate and I3'I-hippuran were infused at a constant rate of 3.6 pCi h-' (133 kBq h-') and 4.5 pCi h-' (167 kBq h-I), respectively. The coefficients of variation of the GFR and the ERPF were 2.2% and 50%, Table 1. Clinical characteristics Age (years) 33 28 53 32 45 52 37 41
Sex
Original diagnosis
F M M F M
primary hypopituitarism primary hypopituitarism non-functioningpituitary adenoma primary empty sella non-functioningpituitary adenoma non-functioningpituitary adenoma primary hypopituitarism primary hypopituitarism
F
M F
Height (m)
I .29 I .41 1.93 1.59 1.82 1.68 1.65 1.46
Replacement therapy 39 53 93 13 93 88 51 55
thyroxine, cortisone acetate thyroxine, growth hormone+ thyroxine, cortisone acetate, sex steroids thyroxine, cortisone acetate thyroxine, cortisone acetate thyroxine, cortisone acetate, desmopressin thyroxine,cortisone acetate, sex steroids, growth hormone+ thyroxine, sex steroids
F denotes female; M denotes male. * Growth hormone therapy discontinued 5 years (patient no. 2) and 18 years (patient no. 7) before study.
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R. P. F. DULLAART et al.
Blood pressure was measured at 120 min intervals using a standard sphygomomanometer, Korotkoff phase 5 was taken as the diastolic blood pressure. Mean arterial blood pressure (in mm Hg) was calculated at 0.67 x diastolic pressure+O.33 x systolic pressure. Five blood samples were drawn from an intravenous catheter for the measurement of GH, glucagon, glucose and octreotide on each study day. Laboratory analysis The serum and plasma samples were frozen at -20°C until assay. Serum GH was measured by radioimmunoassay (Farmos Diagnostica, Turku, Finland). The lower detection limit was 0.5 pg 1-I. Plasma glucagon was measured by radioimmunoassay (antibody 30K, Prof R. H. Unger, Dallas, Texas, USA) [22]. Plasma octreotide was measured at Sandoz Laboratories (Basel, Switzerland) using a previously described radioimmunoassay [23]. IGF-I was determined with a commercially available kit (Nichols Institute of Diagnostics, San Juan Capistrano, CA, USA). Blood glucose was measured with a hexokinase method (Autoanalyzer 11, Technicon Instruments Corporation, Tarrytown, NY,USA). The respective intraand interassay coefficients of variation were 4% and 9% for GH, 5% and 15% for glucagon, 5% and 10% for octreotide, and 5% and 10% for IGF-I. Statistical analysis
The results are expressed as mean fSEM. Data were compared by using the Wilcoxon-rank-sum-test for paired observations and a two-way analysis of variance according to Friedman [24]. Adjustment for multiple comparisons was carried out using Duncan's method [25]. Correlation coefficients were analysed using Spearman's rank test. Averaged correlation coefficients were computed after Z-transformation of correlation coefficients obtained in individual participants. A two-sided P-value of c0.05was considered to be significant.
Results Renal haemodynamics and blood pressure The GFR, ERPF and filtration fraction during each of the clearance periods and the effect of concomitant octreotide infusion are shown in Fig. 1. Baseline GFR and ERPF were low in the GH deficient subjects. Dopamine infusion induced a significant increase in GFR and ERPF, whereas the filtration fraction decreased. The infusion of amino acids also resulted in a significant rise in GFR and ERPF, but with this stimulus the filtration fraction increased. The increments in GFR and ERPF resulting from the combined infusion of amino acids and dopamine were larger than during the separate infusion of these stimuli. These
effects of dopamine and amino acids were at least as large as previously documented in normal subjects 1191. The GFR and ERPF did not significantly decrease during infusion of octreotide. The increments in GFR and ERPF induced by dopamine infusion were similar and the values achieved were not different from those without octreotide infusion. During octreotide amino acid infusion still induced a significant rise in GFR and ERPF, but the values achieved were lower than those before octreotide infusion. The filtration fraction did not increase during concomitant amino acid and octreotide infusion. The mean arterial blood pressure was 93.5 & 3.1 mm Hg, 92.5f3.1 mm Hg, 93.8f2.2 mm Hg and 89.5 f2.6 mm Hg on days 1,2,3 and 4 of the clearance studies, respectively, indicating no significant effect of either amino acid or octreotide infusion on blood pressure. The change in mean arterial blood pressure during dopamine infusion was also not significant (1.7f 3.5 mm Hg on day 1, NS and - 1.9 3.2 mm Hg on day 3, NS). Metabolic assessment
GH was undetectable (c0-5pg 1-I) in all serum samples taken during the 4 study days. To evaluate the effect of amino acid and octreotide infusion on plasma glucagon concentration, the 5 samples from each patient obtained on each study day were averaged. The glucagon levels are shown in Fig. 2. The mean plasma glucagon concentrations were 234 f24 ng 1- I , 397 f23 ng I-', 221 f20 ng 1-' and 3 14f 21 ng 1-' on days 1,2, 3 and 4 of the clearance studies, respectively. Plasma glucagon concentrations increased significantlyduring amino acid infusion, both before ( P c 0.001) and during octreotide infusion ( P c 0.001). Octreotide did not decrease plasma glucagon on day 3, but the amino acid induced increment in glucagon concentrations was diminished with concomitant octreotide administration on day 4 (163118 ng 1-' vs. 94f21 ng 1-I, P c 0.02). To investigate the possible relationship between the amino acid-induced rise in plasma glucagon and in renal haemodynamics, the correlation coefficients between plasma glucagon and GFR or ERPF were assessed. In each subject, the 4 datasets from the baseline and the amino acid clearance periods, with and without concomitant octreotide infusion were used. Both GFR (averaged Rs=0.96, P c 0.00 1) and ERPF (averaged Rs = 0-86, P c 0.00 1) were significantly related to plasma glucagon. Octreotide levels increased shortly after the start of octreotide infusion and then remained constant during the clearance periods (Fig. 3). The mean octreotide levels were similar on both days (2.27 f0.27 pg 1-' vs. 2.04 f0.23 pg 1- I , NS). The mean blood glucose concentrations were not different on the 4 study days (3.56f0.11 mmol l - l , 3.91 f0.08 mmol 1-I, 3.65f0.08 mmol l-' and 3.79f0.15 mmol 1-' on days 1, 2, 3 and 4 respectively, NS).
RENAL RESERVE CAPACITY IN GROWTH HORMONE DEFICIENCY
6
-
Effective renal plasma flow
m
L
40
r: 600
5z w L U
Glornerular filtration rate 50
700
30
400
20
300
10
w
34 C
0
.
Filtration fraction 28
1
T
565
9.11
Effective renal plasma flow
T
60 +I
50 40
30 20 10
0 baseline
dopamine amino acids amino adds + dopamine
dopamine
amino acids
amlno acids + dopamine
Figure 1. Renal reserve filtrationcapacity. Data are given in mean & SEM (n = 8). GFR glomerularfiltration rate; ERPF effective renal plasma flow. Open bars: before octreotide; hatched bars: during octreotide. A Absolute values. B relative increments in YO change from baseline. P
