Influence of Somatostatin on Splanchnic Glucose Metabolism in Postabsorptive and 60-Hour Fasted Humans JOHN WAHREN, SUAD EFENDI(, ROLF LUFT, LARS HAGENFELDT, OLA BJORKMAN, and PHILIP FELIG From the Department of Clinical Physiology, Serafimer Hospital, Stockholm, Sweden, the Departments of Endocrinology and Clinical Chemistry, Karolinska Hospital, Stockholm, Sweden, and the Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06510
A B S T R A C T Cyclic somatostatin was administered intravenously (10 ,ug/min for 60 min) to 10 healthy overnight fasted (postabsorptive) subjects and to 5 healthy 60-h fasted subjects. In both groups, arterial insulin and glucagon fell 50%o and splanchnic release of these hormones was inhibited. In the overnight fasted subjects splanchnic glucose output fell 70%, splanchnic uptake of lactate and pyruvate was unchanged, alanine uptake fell by 25%, and glycerol uptake rose more than twofold in parallel with an increase in arterial glycerol. In the 60-h fasted group splanchnic glucose output was less than 40%o of that observed in the overnight fasted subjects. Somatostatin led to a further decrease (-70%) in glucose production. Splanchnic uptake of lactate and pyruvate fell by 30-40%o, amino acid uptake was unchanged, while uptake of glycerol rose fivefold. Total uptake of glucose precursors thus exceeded the simultaneous glucose output by more than 200%o. Splanchnic uptake of FFA rose fourfold during somatostatin while output of beta-hydroxybutyrate increased by 75%. Estimated hepatic blood flow fell 25-35% and returned to base line as soon as the somatostatin infusion ended. It is concluded that (a) somatostatin-induced hypoglucagonemia results in inhibition of splanchnic
glucose output in glycogen-depleted, 60-h fasted subjects as well as in postabsorptive subjects, indicating an effect of glucagon on hepatic gluconeogenesis as well as glycogenolysis; (b) the glucagonsensitive step(s) in gluconeogenesis affected by somatostatin involves primarily intra-hepatic disposal rather than net hepatic uptake of glucose precursors; (c) splanchnic uptake of fatty acids and ketone output are increased in the face of combined insulin and glucagon deficiency; and (d) diminished splanchnic blood flow may contribute to some of the effects of somatostatin on splanchnic metabolism.
INTRODUCTION Somatostatin, a tetradecapeptide, originally isolated from the hypothalamus (1) and also subsequently identified in the D cells of the islets of Langerhans (2), has been demonstrated to inhibit the secretion of growth hormone, insulin, and glucagon in both in vivo and in vitro systems (1, 3-11). Administration of somatostatin is accompanied by a fall in blood glucose in man and animals (8, 12, 13), the nature of which is incompletely understood. Studies with isotopically labeled glucose in baboons (4) and isotopically labeled glucose plus hepatic vein catheterization in dogs (14) have suggested that the lowering of blood glucose levels during somatostatin infusion is primarily Dr. Felig is the recipient of a Research Career Devleopment a consequence of diminished glucose production Award (AM 70219) from the National Institutes of Health. rather than of increased peripheral utilization. Since Reprints may be obtained from Dr. Felig, Department of no information is available on the influence of somatoInternal Medicine, Yale University School of Medicine, statin on hepatic glucose metabolism in man, the New Haven, Conn. 06510. present study was undertaken to examine in healthy, Receivedfor publication 9 August 1976 and in revisedform 11 October 1976. postabsorptive subjects the effects of this hormone The Journal of Clinical Investigation Volume 59 February 1977*299 -307 299
gon lack of the processes involved in hepatic uptake and intrahepatic disposal of gluconeogenic substrates. lOOn Gkcago
METHODS
80!ao--
.60-
Q
20-
501 Insulin
0
40VI',
30I
10-
I
y
-10
0
I
-7I---I
10 20 30 40 50 60 10
20 30min
Post hnf.-m. Basalm Smstatin kfusion 0) and hepatic venous (HV) FIGURE 1 Arterial (A) (O (S 0) concentrations of glucagon and insulin in the basal state, during and after somatostatin infusion (10 ug/min) in postabsorptive subjects. Mean values±SE are indicated.
Two groups of subjects were studied, one in the overnight (12-14 h) fasted state (postabsorptive subjects) and the other after 60-64 h of fasting. The former group was made up of 10 healthy, nonobese, male subjects 23-42 yr of age. Their mean body weight was 72 kg (range 67-80 kg). The latter group consisted of five healthy, nonobese, female subjects, who fasted for 60-64 hours before the study. Their age was 24-37 yr and their mean body weight was 61 kg (53-69 kg). The subjects in both groups were all within 10%/ of ideal body weight (Metropolitan Life Insurance Tables). All subjects were informed of the nature, purpose, and possible risks involved in the study before giving their consent to participate. Procedure. The subjects were studied in the morning after 12-14 h overnight fast. Catheters were inserted percutaneously into a peripheral vein, a brachial artery and into a right-sided hepatic vein under fluoroscopic control. Blood samples for determination of substrate and hormone concentrations were drawn from the arterial and hepatic venous catheters in the basal state as well as during and after the intravenous infusion of sterile, pyrogen-free cyclic somatostatin (10 ,ug/min) (Supplied by A. B. Kabi, Stockholm, Sweden, and by Wyeth Laboratories, Radnor, Pa.). The infusion was administered for 60 min and blood sampling continued for 30 min after the end of the somatostatin infusion. Hepatic blood flow was estimated with the continuous infusion technique (17) and indocyanine green dye (18). In six subjects, the study was repeated on another occasion, at which time saline instead of somatostatin was infused intravenously; catheterization and blood sampling procedures were identical, except that no post-infusion samples were drawn after saline infusion. In the second group of subjects, studied after 60-64 h of fasting, the catheterization procedure, blood sampling, and somatostatin administration were the same as described
on splanchnic glucose output and uptake of glucose precursors. In the postabsorptive, overnight-fasted individual approximately 75% of hepatic glucose output is derived from hepatic glycogenolysis, while the remainder reflects de novo glucose synthesis by above. Analytical methods. Glucose was analyzed in whole hepatic gluconeogenesis (15, 16). Thus an effect of blood by the glucose oxidase reaction (19). Lactate (20), somatostatin on splanchnic glucose output in over- pyruvate (21), glycerol (22), and 3-hydroxy-butyrate (23) night fasted subjects may reflect an alteration of he- were all determined enzymatically in whole blood. Indipatic glycogenolysis or gluconeogenesis or both. vidual acidic and neutral amino acids were measured in by the automated ion-exchange chromatographic Furthermore, an effect on gluconeogenesis could plasma Plasma glucagon (25) and insulin were determethod (24). involve alterations in the uptake and (or) intra- mined by radioimmunoassay, with talc to separate bound hepatic disposal of glucose precursors. To examine and free insulin (26). Plasma free fatty acids were measured more selectively the influence of somatostatin on by gas chromatography, with heptadecanoic acid as an standard (27). Blood urea concentration was deterhepatic gluconeogenesis, healthy subjects who had internal using a colorimetric method (28). fasted for 60 h were studied. In this situation glu- mined Data in the text, tables, and figures are given as mean cose production from the liver is primarily dependent +±SE. Standard statistical methods (29) were employed, on gluconeogenesis, inasmuch as the hepatic with the paired t test when applicable. glycogen stores are virtually completely exhausted (16). Thus, any effect of somatostatin on hepatic RESULTS glucose output in the 6S-h fasted state should rePostabsorptive subjects. Fig. 1 shows the concenflect a change in hepatic gluconeogenesis. Furthermore, by measuring net splanchnic exchange of trations of glucagon and insulin in arterial and hepatic glucose precursors in these subjects information venous plasma. A consistently greater concentration can be obtained on the relative sensitivity to gluca- (30-55%) of both hormones was observed in samples J. Wahren, S. Efendic, R. Luft, L. Hagenfeldt, 0. Bjorkman, and P. Felig 300
2.OC Splic Glkoe Output
-61.0E 0.5-
6 lo 20 30 40 50 60 lo 20 48a4-Somatostati or Sae hf.--P--tm hnf.
-15
30min
FIGURE 2 Arterial glucose concentration and splanchnic glucose output in the basal state and during infusion of 0) at 10 ug/min or infusion of saline somatostatin (00) in postabsorptive subjects. Mean values+SE are (O indicated.
from the hepatic vein as compared to arterial samples (P < 0.02-0.01). Somatostatin infusion was accompanied by a prompt fall in arterial as well as hepatic venous glucagon concentrations. A new, relatively stable level was established at approximately 509o of the initial arterial glucagon concentration. An
hepatic venous-arterial concentration gradient for glucagon was not detectable during the infusion. Similarly, the arterial insulin level fell by 40-50%o during somatostatin infusion. A new level was reached and arterial and hepatic venous insulin concentrations became similar. In contrast, a rapid rise in hormone concentrations was observed immediately after the end of the somatostatin infusion, the hepatic venous concentrations rising to significantly higher levels than the arterial (Fig. 1). At 30 min after the end of the somatostatin infusion, both the glucagon (P < 0.05) and the insulin (P
A B S T R A C T Cyclic somatostatin was administered intravenously (10 ,ug/min for 60 min) to 10 healthy overnight fasted (postabsorptive) subjects and to 5 healthy 60-h fasted subjects. In both groups, arterial insulin and glucagon fell 50%o and splanchnic release of these hormones was inhibited. In the overnight fasted subjects splanchnic glucose output fell 70%, splanchnic uptake of lactate and pyruvate was unchanged, alanine uptake fell by 25%, and glycerol uptake rose more than twofold in parallel with an increase in arterial glycerol. In the 60-h fasted group splanchnic glucose output was less than 40%o of that observed in the overnight fasted subjects. Somatostatin led to a further decrease (-70%) in glucose production. Splanchnic uptake of lactate and pyruvate fell by 30-40%o, amino acid uptake was unchanged, while uptake of glycerol rose fivefold. Total uptake of glucose precursors thus exceeded the simultaneous glucose output by more than 200%o. Splanchnic uptake of FFA rose fourfold during somatostatin while output of beta-hydroxybutyrate increased by 75%. Estimated hepatic blood flow fell 25-35% and returned to base line as soon as the somatostatin infusion ended. It is concluded that (a) somatostatin-induced hypoglucagonemia results in inhibition of splanchnic
glucose output in glycogen-depleted, 60-h fasted subjects as well as in postabsorptive subjects, indicating an effect of glucagon on hepatic gluconeogenesis as well as glycogenolysis; (b) the glucagonsensitive step(s) in gluconeogenesis affected by somatostatin involves primarily intra-hepatic disposal rather than net hepatic uptake of glucose precursors; (c) splanchnic uptake of fatty acids and ketone output are increased in the face of combined insulin and glucagon deficiency; and (d) diminished splanchnic blood flow may contribute to some of the effects of somatostatin on splanchnic metabolism.
INTRODUCTION Somatostatin, a tetradecapeptide, originally isolated from the hypothalamus (1) and also subsequently identified in the D cells of the islets of Langerhans (2), has been demonstrated to inhibit the secretion of growth hormone, insulin, and glucagon in both in vivo and in vitro systems (1, 3-11). Administration of somatostatin is accompanied by a fall in blood glucose in man and animals (8, 12, 13), the nature of which is incompletely understood. Studies with isotopically labeled glucose in baboons (4) and isotopically labeled glucose plus hepatic vein catheterization in dogs (14) have suggested that the lowering of blood glucose levels during somatostatin infusion is primarily Dr. Felig is the recipient of a Research Career Devleopment a consequence of diminished glucose production Award (AM 70219) from the National Institutes of Health. rather than of increased peripheral utilization. Since Reprints may be obtained from Dr. Felig, Department of no information is available on the influence of somatoInternal Medicine, Yale University School of Medicine, statin on hepatic glucose metabolism in man, the New Haven, Conn. 06510. present study was undertaken to examine in healthy, Receivedfor publication 9 August 1976 and in revisedform 11 October 1976. postabsorptive subjects the effects of this hormone The Journal of Clinical Investigation Volume 59 February 1977*299 -307 299
gon lack of the processes involved in hepatic uptake and intrahepatic disposal of gluconeogenic substrates. lOOn Gkcago
METHODS
80!ao--
.60-
Q
20-
501 Insulin
0
40VI',
30I
10-
I
y
-10
0
I
-7I---I
10 20 30 40 50 60 10
20 30min
Post hnf.-m. Basalm Smstatin kfusion 0) and hepatic venous (HV) FIGURE 1 Arterial (A) (O (S 0) concentrations of glucagon and insulin in the basal state, during and after somatostatin infusion (10 ug/min) in postabsorptive subjects. Mean values±SE are indicated.
Two groups of subjects were studied, one in the overnight (12-14 h) fasted state (postabsorptive subjects) and the other after 60-64 h of fasting. The former group was made up of 10 healthy, nonobese, male subjects 23-42 yr of age. Their mean body weight was 72 kg (range 67-80 kg). The latter group consisted of five healthy, nonobese, female subjects, who fasted for 60-64 hours before the study. Their age was 24-37 yr and their mean body weight was 61 kg (53-69 kg). The subjects in both groups were all within 10%/ of ideal body weight (Metropolitan Life Insurance Tables). All subjects were informed of the nature, purpose, and possible risks involved in the study before giving their consent to participate. Procedure. The subjects were studied in the morning after 12-14 h overnight fast. Catheters were inserted percutaneously into a peripheral vein, a brachial artery and into a right-sided hepatic vein under fluoroscopic control. Blood samples for determination of substrate and hormone concentrations were drawn from the arterial and hepatic venous catheters in the basal state as well as during and after the intravenous infusion of sterile, pyrogen-free cyclic somatostatin (10 ,ug/min) (Supplied by A. B. Kabi, Stockholm, Sweden, and by Wyeth Laboratories, Radnor, Pa.). The infusion was administered for 60 min and blood sampling continued for 30 min after the end of the somatostatin infusion. Hepatic blood flow was estimated with the continuous infusion technique (17) and indocyanine green dye (18). In six subjects, the study was repeated on another occasion, at which time saline instead of somatostatin was infused intravenously; catheterization and blood sampling procedures were identical, except that no post-infusion samples were drawn after saline infusion. In the second group of subjects, studied after 60-64 h of fasting, the catheterization procedure, blood sampling, and somatostatin administration were the same as described
on splanchnic glucose output and uptake of glucose precursors. In the postabsorptive, overnight-fasted individual approximately 75% of hepatic glucose output is derived from hepatic glycogenolysis, while the remainder reflects de novo glucose synthesis by above. Analytical methods. Glucose was analyzed in whole hepatic gluconeogenesis (15, 16). Thus an effect of blood by the glucose oxidase reaction (19). Lactate (20), somatostatin on splanchnic glucose output in over- pyruvate (21), glycerol (22), and 3-hydroxy-butyrate (23) night fasted subjects may reflect an alteration of he- were all determined enzymatically in whole blood. Indipatic glycogenolysis or gluconeogenesis or both. vidual acidic and neutral amino acids were measured in by the automated ion-exchange chromatographic Furthermore, an effect on gluconeogenesis could plasma Plasma glucagon (25) and insulin were determethod (24). involve alterations in the uptake and (or) intra- mined by radioimmunoassay, with talc to separate bound hepatic disposal of glucose precursors. To examine and free insulin (26). Plasma free fatty acids were measured more selectively the influence of somatostatin on by gas chromatography, with heptadecanoic acid as an standard (27). Blood urea concentration was deterhepatic gluconeogenesis, healthy subjects who had internal using a colorimetric method (28). fasted for 60 h were studied. In this situation glu- mined Data in the text, tables, and figures are given as mean cose production from the liver is primarily dependent +±SE. Standard statistical methods (29) were employed, on gluconeogenesis, inasmuch as the hepatic with the paired t test when applicable. glycogen stores are virtually completely exhausted (16). Thus, any effect of somatostatin on hepatic RESULTS glucose output in the 6S-h fasted state should rePostabsorptive subjects. Fig. 1 shows the concenflect a change in hepatic gluconeogenesis. Furthermore, by measuring net splanchnic exchange of trations of glucagon and insulin in arterial and hepatic glucose precursors in these subjects information venous plasma. A consistently greater concentration can be obtained on the relative sensitivity to gluca- (30-55%) of both hormones was observed in samples J. Wahren, S. Efendic, R. Luft, L. Hagenfeldt, 0. Bjorkman, and P. Felig 300
2.OC Splic Glkoe Output
-61.0E 0.5-
6 lo 20 30 40 50 60 lo 20 48a4-Somatostati or Sae hf.--P--tm hnf.
-15
30min
FIGURE 2 Arterial glucose concentration and splanchnic glucose output in the basal state and during infusion of 0) at 10 ug/min or infusion of saline somatostatin (00) in postabsorptive subjects. Mean values+SE are (O indicated.
from the hepatic vein as compared to arterial samples (P < 0.02-0.01). Somatostatin infusion was accompanied by a prompt fall in arterial as well as hepatic venous glucagon concentrations. A new, relatively stable level was established at approximately 509o of the initial arterial glucagon concentration. An
hepatic venous-arterial concentration gradient for glucagon was not detectable during the infusion. Similarly, the arterial insulin level fell by 40-50%o during somatostatin infusion. A new level was reached and arterial and hepatic venous insulin concentrations became similar. In contrast, a rapid rise in hormone concentrations was observed immediately after the end of the somatostatin infusion, the hepatic venous concentrations rising to significantly higher levels than the arterial (Fig. 1). At 30 min after the end of the somatostatin infusion, both the glucagon (P < 0.05) and the insulin (P
