Clinical Endocrinology (19901, 33, 187-192
THE EFFECT OF GALANIN ON BASELINE AND GHRH-INDUCED GROWTH HORMONE SECRETION IN OBESE CHILDREN S. LOCHE, S. PINTUS, S. G . CELLA, M. BOGHEN, S. VANNELLI, L. BENSO, E. E. MULLER, R. CORDA A N D C. PINTOR Department of Pediatrics, University of Cagliari; Department of Pharmacology, University of Milan; Pierrel Medical Department, Milan; and 2nd Department of Pediatrics, University of Turin, Italy (Received 31 October 1989; returned for revision I I December 1989;fmaIIy revised 5 February 1990; accepted 14 February 1990)
SUMMARY
We have evaluated the effect of the administration of galanin (Gal), a newly identified hypothalamic peptide, on baseline and GHRH-induced GH rise in five obese children and in seven controls. The GH response to GHRH (hpGRF(1-29), 1 pg/kg i.v.), and to Gal (15 pg/kg/h for 1 h), evaluated both as the maximum GH peak and as integrated area under the curve (AUC), was significantly lower in the obese children than in the controls. Simultaneous administration of Gal plus GHRH significantly increased the GH response to GHRH in all the obese subjects, so that their mean peak GH levels and AUC after Gal plus GHRH were similar to those of the control children after GHRH. Also, in control children Gal caused a significant augmentation of the GH response to GHRH. Mean peak GH levels and mean AUC after Gal plus GHRH were significantlyhigher in the controls than in the obese children given the same treatment. Our data indicate that obese children have a blunted GH response to Gal, which, however, is able to enhance the GH response to GHRH. This observation strengthens the view that the mechanism of action of Gal involves modulation of endogenous somatostatin (SRIH) release. In addition, similarity between the effects of Gal and pyridostigmine on baseline and GHRH-stimulated GH release in obese children may indicate the existence of a cholinergic link in the action of Gal. Reduced GH responses to a wide variety of stimuli (see Glass et al., 1981 for review), including GHRH (Williams et al., 1984; Kopelman et al., 1985; Pertzelan et al., 1986; Loche et al., 1987; Rosskamp et al., 1987) is a characteristic feature of obese subjects. Correspondence: Dr Sandro Loche, Cattedra di Endocrinologia Pediatnca, Ospedale Microcitemico, via Jenner, 09100 Cagliari, Italy.
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Although the cause of this reduced GH secretion is not clear, a number of findings indicate that an increased release of endogenous somatostatin (SRIH) may be at least in part responsible for these phenomena. Obese children tend to have elevated somatomedin C/IGF1 (Loche et al., 1987, 1988; Rosskamp et al., 1987; Minuto et al., 1988) and FFA (Opie & Walfish, 1963) levels, both of which can inhibit GH secretion by increasing endogenous SRIH release (Berelowitz et al., 1981; Imaki et al., 1985). Furthermore, administration of cholinergic agonist drugs which, reportedly (Richardson et at., 1980; Locatelli et al., 1986;Torsello et al., 1988), inhibit endogenous SRIH release, restore GH responsivenessto GHRH both in obese adults (Ghigo et al., 1989)and in children (Loche et al., 1989a). Galanin (Gal) is a 29-aminoacid peptide which was first isolated from porcine intestine (Tatemoto et al., 1983)and then found in high concentrations in the mammalian central nervous system (Rokaeus et al., 1984; Skofitsch & Jacobowitz, 1985).Gal administration stimulates growth hormone (GH) secretion both in animals (Murakami et al., 1987; Ottlecz et al., 1986; Cella et al., 1988) and man (Bauer et al., 1986; Loche et al., 1989b). Studies on its mechanism of action in humans have shown that the stimulatory effect of Gal on GH secretion probably results from the inhibition of hypothalamic SRIH release (Davis et af., 1987; Chatterjee et af., 1987, 1988; Loche et al., 1990). In this study, we have evaluated the effect of Gal on baseline and GHRH-stimulated GH secretion in a group of obese children.
MATERIALS AND METHODS Five obese prepubertal children (three males and two females) aged 8.8-10.0 years, with excess body weight ranging from 40 to 77% for their stature, were studied. Seven normal prepubertal children (six males and one female aged 7.7-12.8 years) served as controls. They were referred to our Department for their short stature, and were ultimately found to have constitutional growth delay and/or familial short stature (Loche et al., 1990).All had a stature below the 3rd percentile for age, body weight within L- 10% of their ideal weight, and a GH response to stimulation > 14 mU/1(mU/l x 0.5 = ng/l). None had taken long-term medication prior to the study. The existence of other endocrine abnormalities was excluded in all obese children by means of careful clinical and laboratory investigations. In particular, thyroid function (assessed by means of serum T3, T4 and TSH RIAs), adrenal function (assessed by serum cortisol determinations at time 0800 and 1600 h), and skull X-ray, were normal. The studies were carried out under institutionally approved protocols and informed consent was obtained from the children or from their legal guardians. All children were tested on three occasions with: (1) GHRH (1-29) at the dose of 1 pg/ kg i.v.; (2) Gal (synthetic porcine, Inalco, Milan) infused at the dose of 15 pg/kg/h for 1 h, as previously described (Loche et al., 1989b); (3) Gal plus GHRH; GHRH was administered as above at the start of Gal infusion (time 0). Blood samples were drawn from an indwelling catheter inserted in an antecubital vein at times - 60, - 30,0, 15,30, 60,90 and 120 min. The experiments were carried out in random order with an interval of 3-5 days. All experiments started between 0800 and 0900 h after the children fasted overnight.
Galanin and GH
189
GH was measured by double antibody RIA using reagents provided by CEA-IRE Sorin (Italy). The sensitivity of the assay was 0.4 mU/1 with an intra and inter-assay coefficient of variation of 4.5 and 7.9%,respectively. All values are expressed as peak GH levels or area under the curve (AUC) calculated by trapezoidal integration. Statistical analysis of the results was carried out by means of analysis of variance for repeated measures. Paired t-test was used to compare GH peak and AUC responses to GHRH and Gal plus GHRH. All values are given as the mean 5 SEM.
RESULTS Gal administration was well tolerated and apart from a bitter taste in the mouth did not induce noticeable side-effects either alone or in combination with GHRH. Peak GH values after GHRH were 15.2f3.2 and 77.8 f21.6 mU/1 (P
THE EFFECT OF GALANIN ON BASELINE AND GHRH-INDUCED GROWTH HORMONE SECRETION IN OBESE CHILDREN S. LOCHE, S. PINTUS, S. G . CELLA, M. BOGHEN, S. VANNELLI, L. BENSO, E. E. MULLER, R. CORDA A N D C. PINTOR Department of Pediatrics, University of Cagliari; Department of Pharmacology, University of Milan; Pierrel Medical Department, Milan; and 2nd Department of Pediatrics, University of Turin, Italy (Received 31 October 1989; returned for revision I I December 1989;fmaIIy revised 5 February 1990; accepted 14 February 1990)
SUMMARY
We have evaluated the effect of the administration of galanin (Gal), a newly identified hypothalamic peptide, on baseline and GHRH-induced GH rise in five obese children and in seven controls. The GH response to GHRH (hpGRF(1-29), 1 pg/kg i.v.), and to Gal (15 pg/kg/h for 1 h), evaluated both as the maximum GH peak and as integrated area under the curve (AUC), was significantly lower in the obese children than in the controls. Simultaneous administration of Gal plus GHRH significantly increased the GH response to GHRH in all the obese subjects, so that their mean peak GH levels and AUC after Gal plus GHRH were similar to those of the control children after GHRH. Also, in control children Gal caused a significant augmentation of the GH response to GHRH. Mean peak GH levels and mean AUC after Gal plus GHRH were significantlyhigher in the controls than in the obese children given the same treatment. Our data indicate that obese children have a blunted GH response to Gal, which, however, is able to enhance the GH response to GHRH. This observation strengthens the view that the mechanism of action of Gal involves modulation of endogenous somatostatin (SRIH) release. In addition, similarity between the effects of Gal and pyridostigmine on baseline and GHRH-stimulated GH release in obese children may indicate the existence of a cholinergic link in the action of Gal. Reduced GH responses to a wide variety of stimuli (see Glass et al., 1981 for review), including GHRH (Williams et al., 1984; Kopelman et al., 1985; Pertzelan et al., 1986; Loche et al., 1987; Rosskamp et al., 1987) is a characteristic feature of obese subjects. Correspondence: Dr Sandro Loche, Cattedra di Endocrinologia Pediatnca, Ospedale Microcitemico, via Jenner, 09100 Cagliari, Italy.
187
188
S. Loche et al.
Although the cause of this reduced GH secretion is not clear, a number of findings indicate that an increased release of endogenous somatostatin (SRIH) may be at least in part responsible for these phenomena. Obese children tend to have elevated somatomedin C/IGF1 (Loche et al., 1987, 1988; Rosskamp et al., 1987; Minuto et al., 1988) and FFA (Opie & Walfish, 1963) levels, both of which can inhibit GH secretion by increasing endogenous SRIH release (Berelowitz et al., 1981; Imaki et al., 1985). Furthermore, administration of cholinergic agonist drugs which, reportedly (Richardson et at., 1980; Locatelli et al., 1986;Torsello et al., 1988), inhibit endogenous SRIH release, restore GH responsivenessto GHRH both in obese adults (Ghigo et al., 1989)and in children (Loche et al., 1989a). Galanin (Gal) is a 29-aminoacid peptide which was first isolated from porcine intestine (Tatemoto et al., 1983)and then found in high concentrations in the mammalian central nervous system (Rokaeus et al., 1984; Skofitsch & Jacobowitz, 1985).Gal administration stimulates growth hormone (GH) secretion both in animals (Murakami et al., 1987; Ottlecz et al., 1986; Cella et al., 1988) and man (Bauer et al., 1986; Loche et al., 1989b). Studies on its mechanism of action in humans have shown that the stimulatory effect of Gal on GH secretion probably results from the inhibition of hypothalamic SRIH release (Davis et af., 1987; Chatterjee et af., 1987, 1988; Loche et al., 1990). In this study, we have evaluated the effect of Gal on baseline and GHRH-stimulated GH secretion in a group of obese children.
MATERIALS AND METHODS Five obese prepubertal children (three males and two females) aged 8.8-10.0 years, with excess body weight ranging from 40 to 77% for their stature, were studied. Seven normal prepubertal children (six males and one female aged 7.7-12.8 years) served as controls. They were referred to our Department for their short stature, and were ultimately found to have constitutional growth delay and/or familial short stature (Loche et al., 1990).All had a stature below the 3rd percentile for age, body weight within L- 10% of their ideal weight, and a GH response to stimulation > 14 mU/1(mU/l x 0.5 = ng/l). None had taken long-term medication prior to the study. The existence of other endocrine abnormalities was excluded in all obese children by means of careful clinical and laboratory investigations. In particular, thyroid function (assessed by means of serum T3, T4 and TSH RIAs), adrenal function (assessed by serum cortisol determinations at time 0800 and 1600 h), and skull X-ray, were normal. The studies were carried out under institutionally approved protocols and informed consent was obtained from the children or from their legal guardians. All children were tested on three occasions with: (1) GHRH (1-29) at the dose of 1 pg/ kg i.v.; (2) Gal (synthetic porcine, Inalco, Milan) infused at the dose of 15 pg/kg/h for 1 h, as previously described (Loche et al., 1989b); (3) Gal plus GHRH; GHRH was administered as above at the start of Gal infusion (time 0). Blood samples were drawn from an indwelling catheter inserted in an antecubital vein at times - 60, - 30,0, 15,30, 60,90 and 120 min. The experiments were carried out in random order with an interval of 3-5 days. All experiments started between 0800 and 0900 h after the children fasted overnight.
Galanin and GH
189
GH was measured by double antibody RIA using reagents provided by CEA-IRE Sorin (Italy). The sensitivity of the assay was 0.4 mU/1 with an intra and inter-assay coefficient of variation of 4.5 and 7.9%,respectively. All values are expressed as peak GH levels or area under the curve (AUC) calculated by trapezoidal integration. Statistical analysis of the results was carried out by means of analysis of variance for repeated measures. Paired t-test was used to compare GH peak and AUC responses to GHRH and Gal plus GHRH. All values are given as the mean 5 SEM.
RESULTS Gal administration was well tolerated and apart from a bitter taste in the mouth did not induce noticeable side-effects either alone or in combination with GHRH. Peak GH values after GHRH were 15.2f3.2 and 77.8 f21.6 mU/1 (P
