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Glucagon suppression by somatostatin reduces or abolishes hyperglycemia in dogs made insulin-deficient by somatostatin, alloxan, or total pancreatectomy. This suggests that the development of severe diabetic hyperglycemia requires the presence of glucagon, whether secreted by pancreatic or newly identified gastrointestinal A cells, as well as a lack of insulin. Glucagon suppression could improve therapeutic glucoregulation in diabetes.

To determine the effect of an increase in insulin levels within the range occurring under physiologic conditions on the protein- and acid-induced release of splanchnic somatostatin, insulin was infused in dogs for 1 h following the intragastric instillation of a neutral protein load (20% liver extract at pH 7), a weak stimulus of somatostatin-like immunoreactivity (SLI), and after an intragastric HCl, a strong stimulus of SLI release, instilled 30 min later. Insulin levels between 50 and 60 microunits/ml significantly reduced the rise in peripheral venous SLI levels elicited by the acid load from a mean integrated incremental value of 1705 +/- 182 pg/ml in controls to 840 +/- 312 in the insulin-infused group (P less than 0.05). Prevention of the insulin-induced hypoglycemia and the secondary rise in glucagon, a known stimulus of pancreatic somatostatin secretion, by means of a concomitant infusion of glucose, did not modify the reduction in acid-induced increase in plasma SLI concentration associated with hyperinsulinemia. Insulin-glucose infusion significantly lowered the SLI in the pancreaticoduodenal vein, and in the gastroepiploic vein draining the antrum (P less than 0.02; P less than 0.05), but not in the short gastric veins draining the fundus of the stomach in response to the acid load. It is concluded that physiologic elevation of insulin levels causes significantly reduced response of SLI to an intragastric acid load in dogs. This reduction is explained by a diminished increment of SLI in the venous effluent of the pancreas and the antrum.

The effects of antisomatostatin serum upon the levels of growth hormone, glucagon-like immunoreactivity (GLI), glucagon, insulin and post-prandial triglyceride levels were examined in a group of 5 dogs before and after a fat-rich meal. Within 1 min after the injection of sheep antisomatostatin, plasma growth hormone and GLI levels increased significantly above baseline levels before the meal and remained elevated for 45 to 60 min after the meal, whereas the administration of nonimmune sheep serum to the same dogs did not cause significant changes in either hormone. Plasma insulin, glucagon and triglyceride levels after antisomatostatin serum were not significantly different from the controls. These findings suggest that endogenous somatostatin influences the secretion of growth hormone and GLI via a pathway readily accessible to intravenously injected antibodies, probably via the circulation, whereas any influence that somatostatin may have upon the secretion of insulin and glucagon must take place via a pathway inaccessible to intravenously administered antisomatostatin serum, i.e. within the islets themselves.

Chronic clamping of plasma glucose levels at greater than or equal to 250 mg/dl in four partially depancreatized but previously nondiabetic dogs was followed within 2 wk by persistent hyperglycemia and glycosuria of less than or equal to 500 g/day, ketonuria, and weight loss. Three of the four dogs required daily insulin injections to control these catabolic manifestations. There was no evidence of spontaneous improvement of the severe diabetic state during the 39-69 days of observation after discontinuation of intravenous glucose infusion. Impairment of intravenous glucose tolerance, loss of the insulin response to glucose and arginine, fasting hyperglucagonemia, exaggerated glucagon responsiveness to arginine, and a significant reduction in sensitivity to insulin were characteristic of all diabetic dogs. Morphometric analysis of the endocrine pancreas revealed a profound reduction in the number and size of identifiable islets of the hyperglycemic dogs compared with islets from their own pancreases resected months earlier and with those from pancreatic remnants of eight subtotally depancreatized control dogs that had not been subjected to chronic hyperglycemic clamping. The reduction in number and size of islets of the hyperglycemic dogs was largely the consequence of depletion of insulin-containing cells and was similar to that of dogs with long-standing alloxan-induced diabetes. In the eight control dogs, clinical evidence of diabetes did not develop during a follow-up period of 193-296 days. In this group, there was no evidence of diminution of intravenous glucose tolerance, of the insulin response to glucose or arginine, or of insulin sensitivity as determined by an acute hyperinsulinemic hyperglycemic clamp. The number and size of islets and number of beta-cells in pancreatic remnants from these dogs did not differ morphometrically from those of the pancreatic segment that had been resected. We conclude that in subtotally depancreatized but nondiabetic dogs, maintenance of constant hyperglycemia of greater than or equal to 250 mg/dl by means of intravenous glucose infusion causes a severe, persistent, and often insulin-requiring diabetic state that does not occur in the absence of the hyperglycemia.

The synthesis by solid-phase methodology of two glycosylated analogs of somatostatin [Glc-Asn 5 ]-SS and [NAcGlc-Asn 5 ]-SS is described. These two analogs have been biologically tested on the secretion of pituitary growth hormone, pancreatic glucagon and insulin. The results show that glycosylation of somatostatin on the Asn 5 residue decreases by a hundred fold the inhibition activity on GH release when tested in vitro . In vivo , since the activity is similar to somatostatin the carbohydrates are probably removed by some enzymatic reaction and thus liberate the full activity of somatostatin.

The present study was designed to determine the role of the adrenergic nerves upon basal and postprandial gastric and pancreatic SLI release. In 19 chemically sympathectomized dogs peripheral venous plasma SLI levels in the basal and postprandial state were significantly below those of 30 controls for the first 135 min after the ingestion of a fat-protein meal. To determine the origin of this reduction, the SLI release from fundus, antrum and pancreas was studied in anesthetized dogs during the gastric phase of a meal at either pH 7 or pH 2. In response to a liver meal at pH 7 fundic, antral and pancreatic vein SLI levels were below the control and the rise in inferior vena cava SLI was abolished. In response to a liver meat at pH 2, the rise in antral and pancreatic vein SLI as clearly reduced in the sympathectomized dogs, while the decrease in fundic SLI was not influenced. The data demonstrate that adrenergic innervation plays a role in basal and postprandial SLI release from the stomach and pancreas.

To determine the hormonal status of somatostatin in man, plasma levels of approximately 1600-dalton somatostatin-like immunoreactivity (SLI) were measured before and after a mixed meal. Plasma was subjected to gel filtration and the fractions coeluting with somatostatin were concentrated ninefold before radioimmunoassay. In this system the recovery of synthetic somatostatin added to plasma averaged 71 +/- 4.6% (mean +/- SE, N = 5). Synthetic somatostatin infused into normal volunteers gave a dose-related increase in the measured SLI value. Fasting SLI in 13 normal volunteers was 8.0 +/- 0.7 pg/ml (mean +/- SE) and rose to 18.6 +/- 1.5 pg/ml and 20.3 +/- 2.0 pg/ml at 60 and 120 min, respectively, after the meal (P less than 0.001). In seven type I diabetics, the fasting level was 11.5 +/- 1.6 pg/ml and the 60- and 120-min postprandial levels were 21.4 +/- 2.5 and 22.3 +/- 2.9 pg/ml, respectively. The meal-induced rise in approximately 1600 M.W. SLI approximated that produced by infusing somatostatin at 2 microgram/h, a rate that significantly suppressed glucagon levels. These results are therefore consistent with a hormonal role for somatostatin in man.

The validity of measurements of somatostatin-like immunoreactivity (SLI) in canine plasma has been examined. The radioimmunoassay employed had a minimal sensitivity of 50 pg/ml and a discriminatory sensitivity of 15 pg/ml above this. The coefficient of variation within and between assays was 6% and 18%, respectively. There was no cross-reaction with any of 9 other peptide hormones tested. Significant incubation damage by canine plasma to the [125I]-tyrosine1-somatostatin tracer was effectively prevented by Trasylol and EDTA, and recovery of synthetic somatostatin added to canine plasma and incubated for 3 h at 20°C was 96%. Subcutaneous injections of somatostatin were followed by a prompt rise in plasma SLI that was significantly correlated with decrease in plasma glucagon levels. Serial dilutions of plasma specimens containing high levels of either endogenous SLI or injected synthetic somatostatin gave proportional readings and their slopes paralleled those of synthetic somatostatin in plasma-free buffer. Ninety-five percent of endogenous plasma SLI was removed by passage of plasma specimens through a column of immobilized somatostatin antibodies. Both endogenous SLI in plasma and synthetic somatostatin added to plasma were eluted in the void volume of Biogel P-10 columns, but following isolation by affinity chromatography the molecular size of both was approx. 1600, suggesting that both endogenous SLI and synthetic somatostatin circulate in plasma bound to larger molecules. It is concluded that this radioimmunoassay permits valid measurements of endogenous SLI in canine plasma.

We investigated the possible existence of a negative short-loop feedback of circulating insulin on the parent beta cell in 10 lean Caucasians, 10 obese Caucasians, and 10 obese Pima Indians. Plasma insulin levels were raised acutely by 100 microunits per milliliter for 90 minutes, and plasma glucose was maintained by the "clamp" technique. C-peptide levels were suppressed in all groups to approximately 50 per cent of basal values. However, the obese groups had absolute C-peptide levels much higher than those of the lean group. During the hour after infusion, the rate and magnitude of C-peptide recovery in the obese groups were higher than in the lean group. Thus, negative short-loop insulin-beta-cell feedback was operative in both the lean and obese states. Despite this suppression, the insulin-secretion rate in obese subjects was still greater than that in non-obese subjects. Inadequate feedback suppression may account in part for the prevailing hyperinsulinemia of the obese.

To examine the mechanism of the recently reported effect of an acidified intragastric test meal on insulin release and glucose homeostasis, a liver extract test meal at either pH 2 or pH 7 was instilled into the stomach of normal dogs and dogs with a chemical sympathectomy or indomethacin-induced prostaglandin deficiency, all of which had a bisected pylorus and gastric fistula. In the normal dogs the instillation of the liver meal at pH 2 elicited a significant rise in plasma glucose, glucagon and insulin levels, while in response to the meal at pH 7 only glucagon rose significantly. This was not altered in chemically sympathectomized dogs, nor during the infusion of indomethacin. In all experiments gastrin or gastric glucagon release in response to the meal at pH 2 was either lower than or similar to the response to the meal at pH 7. These data suggest that the influence of the stomach upon islet cell function and glucose homeostasis does not depend on either adrenergic innervation or the presence of prostaglandins, but rather is mediated by a yet undetermined mechanism.

Infusion of prostaglandin E 2 (1 ug/kg/min) in six normal dogs elicited a greater than two-fold rise in pancreaticoduodenal vein somatostatin-like immunoreactivity. Insulin and glucagon also rose. The results raise the possibility that the function of the canine pancreatic D-cell is under prostaglandinergic influence.

Recent studies have demonstrated that an acidified liver meal stimulates insulin release and raises plasma glucose levels. To examine the mechanism of these changes, a liver extract test meal at either pH7 or at pH2 was instilled into the stomach of dogs with a bisected pylorus and a gastric fistula during the infusion of either cimetidine, a specific H2-receptor antagonist, or a saline control. In response to the meal at pH2 insulin, glucagon and glucose levels rose significantly and were not significantly changed by the infusion of cimetidine. In response to the liver meal at pH7 a late rise in plasma glucagon levels was observed while plasma insulin and glucose did not change significantly; however, during the infusion of cimetidine a significant rise in plasma insulin and glucose levels occurred. The present data suggest that H2-receptors participate in an inhibitory mechanism with respect to the insulin and glucose response during the gastric phase of a neutral meal, but they do not seem to be involved in the rise in insulin and glucose observed in response to an acidified gastric meal.

To elucidate the relation of noninsulin-dependent (type II) diabetes mellitus to plasma levels of gastrin, pepsinogen I, and pepsinogen II, gastric acid secretion, and gastric emptying, we studied diabetic and nondiabetic obese Pima Indian subjects. Fasting and postprandial plasma gastrin concentrations were significantly higher (P less than 0.02) in diabetic than in nondiabetic subjects, but gastric acid outputs basally, after an acaloric liquid meal, and in response to betazole were similar in the two groups. Plasma pepsinogen I and pepsinogen II levels were also similar in both groups. A significant negative relation (r = -0.84; P less than 0.01) was found between basal gastrin levels and gastric acid production in nondiabetic Indians, but not in diabetic Pimas. The fractional gastric emptying rate of an acaloric liquid meal was significantly decreased in diabetic Pimas (P less than 0.01); and at least one test showing abnormal vagal function, as estimated by the Valsalva maneuver, heart rate changes between deep expiration and inspiration, and postural hypotension, was found in every diabetic subject. These findings suggest that hypergastrinemia in type II diabetes is not related to hypochlorhydria, but, instead, results from autonomic dysfunction with slow gastric emptying.

Synthetic bombesin, perfused in the isolated canine pancreas at a rate of 340-380 ng/min for 10 min, elicited a 4-fold rise in insulin to a peak at 2 min; a rapid decline followed discontinuation of bombesin. Glucagon rose by 50% to a peak at 6 min, but remained elevated after discontinuation of the bombesin. Somato-statin-like immunoreactivity was not significantly affected by perfusion with bombesin.

Somatostatin-like immunoreactivity (SLI) was measured by RIA in the plasma of normal and severely alloxan diabetic dogs in the fasting state and after the administration of nutrients. The iv infusion of glucose for 6 h was associated with a small but significant decline in plasma SLI (162 ± 10 to 146 ± 9 pg/ml; P < 0.01). In nine alloxan diabetic dogs, the baseline SLI levels averaged 212 ± 16 pg/ml, significantly higher than normal (P < 0.005), and there was little or no change during glucose infusion. Intragastric glucose elicited only a small transient rise in SLI in normal dogs, while in the diabetic dogs, a significant change in SLI was not observed. Intragastric administration of casein hydrolysate to nine normal dogs was associated with a rise in plasma SLI from < 0.02). After a liver meal, SLI rose in normal dogs from 134 ± 7 to 190 ± 15 pg/ml within 30 min (P < 0.001) and in the diabetic dogs, it rose from 240 ± 20 to a 30-min level of 244 ± 33 pg/ml (P < 0.005). In normal dogs, a fat-protein mea...

The Berson Memorial Lecture was established to perpetuate the memory of a great scientist, Dr. Solomon Berson (Figure 1), who died tragically at age 53, just 5 years before Dr. Rosalyn Yalow received the Nobel Prize in Physiology or Medicine for their development of the radioimmunoassay. I am deeply honored to have been selected to be the first Berson Memorial Lecturer, but for me the award has a special significance that transcends the honor itself. This is because, in my eyes, Berson was more than the legendary figure whose brilliance as a scientist, clinician, mathematician, and classical musician won him the admiration and affection of his colleagues. To me, he was a special kind of friend, one who set the course of my research career.

Recent studies have suggested that gastric factors other than gastrin may be released in response to gastric test meals and stimulate islet cell function. The present study was designed to examine this further. In anesthetised, laparotomized dogs with a bisected pylorus and a gastric fistula, a liver meal at pH 2 or pH 7 was instilled intragastrically. Although gastrin levels were lower with the acidified meal, inferior vena cava, insulin, glucagon and plasma glucose levels were significantly higher than after a meal at pH 7. These differences were not changed by truncal vagotomy. The differences in insulin or plasma glucose levels were not altered by infusion of atropine, although the difference in glucagon levels was reduced considerably. The present data suggest that factors other than gastrin and unrelated to the vagus or to atropine sensitive pathways are able to influence islet cell function and possibly glucose homeostasis.

The effects of the instillation of glucose, fat, casein hydrolysate, and HCl into the gastrointestinal tract upon plasma levels of somatostatin-like immunoreactivity (SLI) in the venous effluent of the pancreas, fundus and antrum of the stomach, and in the inferior vena cava (IVC) were determined in normal laparotomized dogs. Fasting SLI levels in the effluent plasma from these sites were significantly greater than IVC levels. The intragastric administration of glucose elicited a prompt and significant rise in SLI levels in pancreatic, fundic and antral venous plasma, and in IVC plasma; intraduodenal glucose elicited smaller increments. After intragastric fat, a smaller, more gradual increase in the pancreatic and fundic effluents was observed, whereas the rise in antral SLI was minute, and IVC SLI did not rise significantly. Intraduodenal fat elicited a prompt increase in the pancreatic and antral vein SLI levels, and a small but significant increase in fundic and IVC plasma which suggests faster release of enteric factors that influence SLI secretion in the pancreas and antrum. Intragastric casein hydrolysate elicited a prompt increase in SLI in both the pancreatic and fundic veins, the latter being marked, but the antral SLI response was small; IVC SLI rose significantly within 15 min. Intragastric HCl provoked a prompt and marked rise in pancreaticoduodenal and antral vein SLI but no increase in fundic vein SLI; IVC SLI levels rose significantly within 20 min. Intraduodenal HCl elicited an even more prompt and marked pancreatic SLI response, and SLI rose significantly in both the fundic and antral venous effluents; IVC SLI also rose more promptly. In dogs with a gastric fistula that prevented intraduodenal entry of HCl, intragastric HCl elicited only a very small and transient rise in pancreaticoduodenal vein SLI, markedly stimulated the antral SLI response, but completely suppressed fundic venous SLI levels. The results indicate that all three nutrients stimulate SLI release from the pancreas and stomach. The greater SLI response to intragastric, as opposed to intraduodenal, glucose suggests that unidentified local factors are of importance. The responses to the intraduodenal instillation of HCl and fat suggest a role of enteric hormones in the release of SLI from the pancreas and fundus and antrum of the stomach. Additionally, there is evidence of direct effects of HCl upon gastric SLI release.

Glucagon release from the gastric fundus and pancreas were compared in normal dogs by measuring glucagon in plasma from a major gastroepiploic vein, the superior pancreaticoduodenal vein, and the inferior vena cava. In 32 dogs in the basal state, gastric vein glucagon averaged 97 +/- 40 pg/ml, not significantly different from the 93 +/- 41 pg/ml level in the vena cava. Pancreaticoduodenal vein glucagon averaged 250 +/- 32 pg/ml (P less than 0.001). Intravenous arginine infused in four dogs caused a rise in mean gastric vein glucagon to 210 +/- 33 pg/ml within 3 min, and glucagon remained between 53 and 98 pg/ml above the vena caval level thereafter. In the gastric vein, the rise in glucagon was significantly greater than in the vena cava at 3, 5, and 10 min (P less than 0.05), but was far less than in the pancreaticoduodenal vein where glucagon rose to 1,295 +/- 379 pg/ml at 1.5 min. Evidence of modest gastric glucagon release was observed after the intragastric instillation of arginine, but not during insulin or phloridzin-induced hypoglycemia. It was concluded that in normal dogs under the circumstances studied, the gastric fundus is not a major source of circulating glucagon.

To determine if gastric A-cells are a major source of the glucagonemia of insulindeprived depancreatized dogs and to examine their secretory behavior, immunoreactive glucagon (IRG) was measured simultaneously in plasma from the inferior vena cava (VC) and from a gastric vein (GV) draining the fundus. Basal GV IRG averaged 205 ± 35 pg/ml, significantly above the VC level of 71 ± 30 (P < 0.001) and rose to 1417 ± 498 1.5 minutes after the start of an arginine infusion, exceeding VC IRG at all points (P < 0.01). Measurement of IRG in gastric, jejunal, and ileal veins and vena cava revealed an IRG gradient only across the stomach. Measurement of glucagon-like immunoreactivity (GLI) revealed no gradient across the stomach, jejunum, or ileum, thus excluding cross-reaction with GLI as the cause of the GV hyperglucagonemia. Intragastric arginine elicited a near doubling of GV IRG within 1.5 minutes and this persisted for at least 120 minutes, ranging from 142 to 623 pg/ml above the VC level. Infusion of insulin a...

Plasma glucose, immunoreactive glucagon (IRG), and insulin were measured in hypophysectomized dogs receiving cortisol and thyroid replacement therapy. 4 wk after hypophysectomy mean fasting plasma glucose levels had declined from 90+/-2 mg/100 ml to 64+/-2; fasting and arginine-stimulated insulin and IRG levels were, respectively, approximately 50% lower and unchanged. 12 wk or more after hypophysectomy, despite lower plasma glucose levels, fasting and arginine-stimulated IRG levels were significantly below control dogs. Hypophysectomized and shamhypophysectomized dogs were subjected to total pancreatectomy. Postoperatively, in the sham-hypophysectomized, depancreatized dogs fasting glucose levels ranged from 300-500 mg/100 ml on 8-10 U/day of insulin; IRG levels averaged 215+/-29 pg/ml. The hypophysectomized, depancreatized dogs required 0-4 U/day and fasting glucose levels under 100 mg/100 ml were not uncommon, even without insulin; fasting IRG levels averaged 63+/-4 pg/ml (P0.001). During arginine infusion in sham-hypophysectomized, depancreatized dogs, IRG levels rose from 215+/-60 pg/ml to a peak of 404+/-112 pg/ml; in hypophysectomized, depancreatized dogs, the base line IRG averaged 44+/-8 and the peak 110+/-25 pg/ml (P0.05). IRG levels in the venous effluent of the gastric fundus, the major source of nonpancreatic glucagon, reached a peak of 4,898+/-959 pg/ml in the sham-hypophysectomized, depancreatized group during arginine infusion and only 219+/-128 pg/ml in the hypophysectomized, depancreatized group. In three hypophysectomized, depancreatized dogs, a replacement infusion with glucagon for 10 h promptly increased hyperglycemia by 80-180 mg/100 ml and worsened glycosuria, evidence of a hepatic response to glucagon replacement. It is concluded that hypophysectomy somehow decreased both the hypersecretion of gastric IRG and the severe hyperglycemia that otherwise follows pancreatectomy. The hypophysectomized, depancreatized animal, therefore, has combined insulin and glucagon deficiency, and the latter may contribute to reduced severity of its hyperglycemia.

The islets of Langerhans contain at least four major cell types—the A, A2, or α cell; the B or β cell; the D or A1 cell; and the F cell—containing, respectively, glucagon, insulin, somatostatin, and pancreatic polypeptide. In every species thus far examined, these four cell types bear a constant topographical relationship to one another, although the particular cellular arrangements may differ from species to species. In man and in the rat, the A cells are situated in the outer rim of the islet and make up approximately 25% of the total islet cell population (Fujita et al, 1976; Orci et aL, 1976b). The D cells are situated immediately under this outer A-cell rim and make up approximately 10% of the endocrine cells of the endocrine pancreas. The B cells form the central mass of the islets, accounting for at least 65% in the rat. F cells replace A cells in islets situated close to the duodenum (Orci, 1976a); these islets are particularly rich in polypeptide-containing cells and poor in glucagon-containing cells.

In response to a single intravenous injection of bovine growth hormone (GH, 100 micrograms/kg) the non-steady-state turnover of glucose, as well as portal levels of insulin (IRI), glucagon (IRG), somatostatin (SRIF), and glucose were determined in normal conscious dogs. Using the two-compartment model validated to calculate rapid turnover changes and tracer infusion methods, the rate of hepatic output of glucose [Ra(t)] was found to be increased, reaching a maximum of 224 mg/min, 7.4 times the basal rate, 4 min after injection of GH. Ra(t) returned to its basal level 35 min later in a damped oscillatory manner. Hormone determinations were carried out in portal venous blood drawn every 2 min for 2 h from an indwelling catheter. IRG peaked 2 min after GH injection and levels of IRI, SRIF, and glucose peaked between 4 and 8 min. Hormone concentrations returned to normal, i.e., were oscillating around base-line levels, about 30 min after GH. These experiments demonstrate for the first time in vivo that a pulse of GH causes transient changes of glucose turnover and measurable alterations of the hormonal homeostasis in the splanchnic area.

Diabetes mellitus, steatorrhea, cholelithiasis and a tumor distorting the duodenum prompted a work-up for somatostatinoma in a 52-year-old man. The responses of pancreatic B-cells but not of A-cells to nutrient stimuli were inhibited, and growth-hormone release was suppressed, suggesting somatostatin resistance in some target tissues. Plasma somatostatin-like immunoreactivity ranged from 9000 to 13,000 pg per milliliter (normal: 88+/-8, mean +/- S.E.M.) and was distributed in four molecular forms, including free somatostatin. The primary tumor contained 5 microgram of somatostatin-like immunoreactivity per milligram of wet tissue, distributed in three of the molecular forms noted in plasma. Plasma calcitonin was also elevated (4650 pg per milliliter; normal: less than 120). Immunocytochemical studies showed that cells of the primary tumor contained somatostatin and calcitonin but no other peptide hormones. Only somatostatin was present in the metastases. Somatostatin was localized electron microscopically in all secretory granules, irrespective of size and shape, whereas calcitonin was present only within a single subpopulation of small granules in the same cells.

The location of the somatostatin-containing D-cells of the pancreatic islets between the A- and B-cells suggests that their function might be to inhibit insulin and/or glucagon secretion by these neighboring cells. To determine if insulin and/or glucagon, in concentrations that might be present in the extracellular space surrounding the D-cells, stimulate immunoreactive somatostatin (IRS) release, we perfused 10 microng of glucagon or 10 milliunits of insulin per ml in 11 isolated dog pancreases, for 40 min in seven experiments and for 100 min in four experiments. In eight of the nine experiments in which glucagon was perfused, a prompt and significant rise in mean IRS release, ranging from 71 to 128% above the control level, was observed. In the eight experiments in which insulin was perfused. IRS did not increase during the first 40 min; in the two 100-min insulin experiments, it did rise during the final 50 min, however. To determine the effect of an A- and B-cell secretogogue on IRS release, we perfused 20 mM arginine for 60 min in six experiments. In all, IRS rose within 3 min and reached a level 71-465% above the control, remaining significantly elevated throughout the perfusion, while glucagon and insulin rose to peak levels at 2 min and then declined somewhat despite continuing arginine perfusion. The results indicate that perfusion of the normal dog pancreas with high doses of glucagon or arginine is accompanied by a prompt increase in IRS release and are compatible with a local feedback circuit involving A- and D-cells. Insulin appears not to augment IRS release, at least not promptly, but IRS stimulated by local endogenous glucagon could inhibit the B-cell response to locally secreted glucagon and thereby influence the composition of the insulin/glucagon secretion mixture.

The present study was designed to identify the physicochemical, immunologic, and biologic properties of the immunoreactive glucagon (IRG) moieties of canine gastric fundus and to compare them with those of the canine pancreas. Acid-alcohol extracts of the gastric fundus and pancreas of dogs were subjected to Bio-Gel P-10 chromatography, The elution profiles of extracts of both organs revealed IRG peaks in the Mr = 2,000 3,500, and 9,000 zones; in the gastric extracts, a void volume peak was also present. On the basis of Sephadex G-150 rechromatography and sucrose density gradient ultracentrifugation the latter IRG was estimated to have a Mr = 65,000. Incubation of fundic IRG65,000 in 8 M urea failed to alter its elution position. Its pI was 6.4, while fundic IRG3,500 had a pI of 6.15 and pancreatic glucagon 6.25.Fundic IRG9,000 had a pI of 4.5 and pancreatic IRG9,000 4.65. Dilution curves of these three fundic and two pancreatic IRGs were parallel to crystalline beef-pork glucagon. The glycogenolytic activity of fundic IRG3,500 and IRG65,000, measured in the isolated rat liver system, was not different from that of immunoequivalent amounts of dog pancreatic glucagon or crystalline beef-pork glucagon. Both fundic and pancreatic IRG9,000 were devoid of glycogenolytic activity and lacker adenylate cyclase stimulating activity and 125I-glucagon displacing activity when tested on partially purified rat liver membranes. Fundic IRG65,000, however, stimulated adenylate cyclase and displaced 125I-glucagon to the same degree as immunoequivalent amounts of pancreatic glucagon. Fundic IRG3,500 was more active than pancreatic glucagon in stimulating adenylate cyclase activity. This was not clearly attributable to differences in binding to liver cell membranes.

Exogenous glucagon is known to increase hepatic lysosomes, but the relationships between endogenous glucagon and insulin levels and hepatic lysosomes have not been examined. To determine if the hormones of the pancreatic islets influence the development of these organelles glycogenosomes, dense bodies, and autophagosomes were morphometrically quantitated in normal rats, in rats with mild streptozotocin diabetes with normal hormone levels, and in rats with severe streptozotocin diabetes with hyperglucagonemia, hypo-insulinemia, and clinical evidence of uncontrolled diabetes and ketoacidosis. In the latter volume density of lysosomes averaged 222.8x10(-4) (SEM +/-19.8x10(-4)), significantly above the control value of 75x10(-4) (SEM +/-7.0x10(-4)) (P

The current controversy concerning the role of glucagon in the pathogenesis of diabetes is reviewed. The traditional "unihormonal abnormality concept," namely, that all of the metabolic derangements of diabetes are the direct consequence of deficient insulin secretion or activity, and the newer so-called bihormonal abnormality hypothesis, proposing that the fullblown diabetic syndrome requires, in addition to the insulin abnormality, a relative glucagon excess, are scrutinized. The relationship of insulin deficiency to the A-cell malfunction of diabetes, the conflicting evidence concerning the essential role of glucagon in mediating the marked overproduction of glucose and ketones in severe insulin deficiency and the contribution of glucagon to the endogenous hyperglycemia of diabetics without insulin deficiency are examined. Finally, the possibility that therapeutic suppression of diabetic hyperglucagonemia may make possible better control of hyperglycemia than is presently attainable by conventional therapeutic methods is considered. It is concluded that (1) although insulin lowers glucagon levels, restoration to normal of the A-cell dysfunction of diabetes requires that plasma insulin levels vary appropriately with glycemic change; (2) that glucagon mediates the severe endogenous hyperglycemia and hyperketonemia observed in the absence of insulin; (3) that in diabetics in whom insulin is present but relatively fixed an increase in glucagon causes hyperglycemia and glycosuria; and (4) that glucagon suppression could be a potentially useful adjunct to conventional antihyperglycemic treatment of diabetics.

Alpha adrenergic blockade with phentolamine (10 microM) reduces the glucagon response to severe glucopenia (from 150 to 25 mg/dl) to 22% of the control values in the isolated perfused rat pancreas. Propranolol (10 microM) had no significant effect. Neither alpha nor beta adrenergic blockade reduced the magnitude of glucopenic suppression of insulin secretion, but phentolamine increased insulin levels before and during glucopenia. The pattern of somatostatin secretion in these experiments resembled that of insulin. Depletion of norepinephrine from sympathetic nerve endings by pretreatment with 6-hydroxydopamine lowered the pancreatic norepinephrine content to less than 20% of control values and reduced the glucagon response to glucopenia to 69% of the controls. Combined alpha and beta adrenergic blockade during less severe glucopenia (from 120 to 60 mg/dl) reduced the glucagon response to 21% of controls. However, slight glucopenia (from 100 to 80 mg/dl), which elicited only 11% increase in glucagon in the control experiments, was not altered significantly by combined alpha and beta adrenergic blockade. Morphologic studies of adrenergic nerve terminals labeled with [3H]norepinephrine revealed associations with alpha cells. It is concluded that in the isolated rat pancreas adrenergic mediation accounts for most of the glucagon but not insulin response to glucopenia. It is controlled within the pancreas itself, possibly through a direct enhancement by glucopenia of norepinephrine release from nerve endings.

The purpose of these studies was to measure circulating gastrin and somatostatin concentrations during sham feeding in humans and to evaluate the effect of two doses of intravenous atropine on circulating concentrations of these peptides. Gastric acid and bicarbonate secretion and pulse rate were also measured. Sham feeding increased plasma gastrin concentrations by approximately 15 pg/ml but had no effect on plasma somatostatin-like immunoreactivity (SLI). A small dose of atropine (5 micrograms/kg) augmented plasma gastrin concentrations during sham feeding significantly (P less than 0.01), but did not affect plasma SLI. Atropine also significantly inhibited gastric acid secretion and gastric bicarbonate secretion (by 62% and 52%, respectively), but pulse rate was not affected. A larger dose of atropine (15 micrograms/kg intravenously) suppressed plasma gastrin concentrations significantly compared to the smaller 5 micrograms/kg atropine dose (P less than 0.02), so that plasma gastrin concentrations when 15 micrograms/kg atropine was given were not significantly different from those during the control study. 15 micrograms/kg atropine reduced gastric acid and bicarbonate secretion by 81% and 66%, respectively, and also increased pulse rate by 15 min-1. These studies indicate that small doses of atropine enhance vagally mediated gastrin release in humans, probably by blocking a cholinergic inhibitory pathway for gastrin release. Although the nature of this cholinergic inhibitory mechanism is unclear, we found no evidence to incriminate somatostatin. Our finding that the larger dose of atropine reduced serum gastrin concentrations compared with the smaller dose suggests that certain vagal-cholinergic pathways may facilitate gastrin release.

Studies were designed (a) to determine whether somatostatin is released into the circulation after meals in sufficient amounts to regulate gastric or pancreatic islet function in humans and (b) to investigate the possible role of somatostatin in the pathogenesis of duodenal ulcer disease. Mean plasma somatostatin-like immunoreactivity (SLI) increased from 6.2 +/- 1.5 pg/ml to a peak level of 13.8 +/- 1.3 pg/ml in eight healthy subjects after a 1,440-cal steak meal (P less than 0.005). When somatostatin-14 was infused intravenously, basal and food-stimulated gastric acid secretion and also basal and food-simulated plasma insulin and glucagon concentrations were reduced significantly at mean plasma SLI concentrations within the range seen after a meal. Thus, the amount of somatostatin reaching the systemic circulation after a steak meal was sufficient to inhibit gastric acid secretion and islet cell function. On the other hand, basal and food-stimulated plasma gastrin concentrations were reduced by intravenous somatostatin only at plasma SLI concentrations that were several-fold greater than post-prandial SLI concentrations. Although duodenal ulcer patients had significantly higher basal, food-stimulated, and peak pentagastrin-stimulated gastric acid secretion rates than healthy controls, duodenal ulcer patients and controls had nearly identical basal and food-stimulated SLI concentrations. Moreover, food-stimulated gastric acid secretion and gastrin release were inhibited by intravenous somatostatin to the same extent in ulcer patients and controls. These studies suggest that duodenal ulcer patients release normal amounts of somatostatin into the circulation and that target cells controlling acid secretion and gastrin release are normally sensitive to somatostatin in these patients.

Fasting serum glucagon, insulin and glucose levels were determined in 25 patients with acute myocardial infarction 1 day after their admission to the hospital and, in most instances, once again at a later date. Two control groups were used, one with coronary insufficiency but without myocardial infarction (10 patients) and the other without clinically recognizable coronary artery disease (12 patients). Serum glucagon levels were significantly higher in the patients with acute myocardial infarction on admission (121.6 ± 15.3 pg/ml) than in the other two groups and highest in patients with acute myocardial infarction and cardiogenic shock (239.3 ± 31 pg/ml, p

The ability of varying levels of circulating insulin to suppress α- and Β-cell secretion was assessed by plasma glucagon and C-peptide measurement in 6 obese and 6 nonobese subjects maintained in a euglycemic state, with an insulin concentration elevated by 10, 20, or 100 μU/ml above basal levels by a primed-continuous infusion of insulin. The 10-μU/ml increase did not suppress C-peptide levels significantly in either group. However, incremental increases in plasma insulin of approximately 20 and 100 μU/ml above basal suppressed plasma C-peptide by 0.27 ± 0.14 and 0.53 ± 0.07 pmol/ml, respectively, in the obese subjects (14% and 31% of the basal values of 2.20 ± 0.18 and 2.19 ± 0.26 pmol/ml, respectively) and by 0.16 ± 0.06 and 0.17 ± 0.06 pmol/ml in the nonobese subjects (20% and 25% the basal values of 0.74 ± 0.11 and 0.78 ± 0.11 pmol/ml, respectively). Plasma glucagon levels were suppressed to a similar degree in each group in a dose-related manner during both the 20-μU/ ml and 100-μU/ml clamps. We were unable to identify an increment of insulin that suppressed C-peptide and/ or glucagon in one group but not in another. These data demonstrate inhibition of α- and Β-cell secretion by insulin within its physiologic range in both non-obese and obese man, and exclude insulin resistance of α- and β-cells in obese individuals. However, despite their much higher insulin levels before and during the insulin infusions, obese subjects had C-peptide levels that, at all times, were 3–3.5-fold higher than those of the nonobese subjects. This is consistent with a greater number and/or a higher secretory activity of β-cells in the obese subjects.

To determine if the abnormal A-cell function of human diabetes can be corrected by insulin therapy, 10 patients with juvenile-type and 10 with adult-onset types of diabetes were aggressively treated with insulin for up to 10 days. Glucose, immunoreactive glucagon (IRG), and, where possible, insulin were measured in plasma specimens obtained at two-hour intervals for periods of up to 10 days. These patients were compared with nine nondiabetics who were studied similarly. During a two-day “uncontrolled” period, marked hyperglycemie, glycosurie, and elevated IRG concentrations were present in both groups of diabetic patients. “Improved control” was achieved in the juvenile-type diabetic group with an average insulin dose of 115 ± 24 U. per day. Such therapy significantly reduced the mean plasma glucose (p < 0.001) and IRG (p < 0.05) concentrations when compared with the “uncontrolled” period, but both remained above (p < 0.05) the values seen in the nondiabetk subjects. “Improved control” was achieved in the maturity-onset group of patients with an average insulin dose of 160 ± 24 U. per day. This dose was associated with a mean plasma-insulin value of 106 ± 26 μU. per milliliter, significantly greater (p < 0.05) than that of the nondiabetk: group. Mean plasma glucose (p < 0.001) and IRG (p < 0.02) concentrations were reduced significantly as compared with the “uncontrolled” period; the mean IRG level was the same as that of the nondiabetics, but the mean plasma glucose levels remained significantly greater (p < 0.001) than in the nondiabetics. The results indicate that aggressive administration of insulin by conventional means does significantly reduce the average IRG level in juvenile-type and adult-type diabetics. However, despite the large doses of insulin and unphysiologically high concentrations of circulating insulin in the juvenile-diabetic group, IRG remained significantly above that of the nondiabetics. In the adult-onset group, although it was reduced to normal, the IRG level can be viewed as above normal relative to the persistent hyperglycemie and hyperinsulinemia.

We studied the relation between the control of blood glucose and the width of skeletal-muscle capillary basement membrane in 23 insulin-dependent (Type I) diabetic patients. After initial measurement of levels of glycosylated hemoglobin and width of skeletal-muscle capillary basement membrane, the patients were divided into two groups: an experimental group of 13 patients who were treated with continuous subcutaneous insulin infusion, and a control group of 10 patients who continued to receive conventional treatment--usually two injections of insulin daily. After two years, the experimental group had a significant decrease in glycosylated hemoglobin levels as compared with base-line values (mean +/- S.E.M., 7.6 +/- 0.4 vs 10.2 +/- 0.7 per cent; P less than 0.001), reflecting improved control of blood glucose, and a significant reduction in the width of skeletal-muscle capillary basement membrane (1293 +/- 68 vs. 1717 +/- 182 A; P less than 0.05). The control group of patients had no significant change in their levels of glycosylated hemoglobin or in the width of their skeletal-muscle capillary basement membranes. If changes in the capillaries in skeletal muscle parallel those in the capillaries in retinal or renal tissue, then meticulous control of blood glucose may be beneficial over time in preventing the microvascular complications of diabetes.

By means of an exquisitely sensitive and highly specific radioimmunoassay, glucagon has been measured in the plasma of dogs and man for the first time. Its identification in the effluent plasma of the pancreas and the demonstration of alterations in its secretion induced by changes in blood glucose concentration support the view that it is a true hormone with a major role in blood glucose regulation. Glucagon secretion has been shown to rise during all forms of glucose need; this rise is suppressed by glucose refeeding. This favors the concept of glucagon as a hormone of glucose need, the function of which is to maximize hepatic glucose production when food is not available, thereby serving to maintain the flow of glucose to the brain. The current status of efforts to identify a disorder of glucagon secretion in man is reviewed briefly.

The prevalence of hyperglucagonemia was studied in twenty-six consecutive patients admitted to Dallas hospitals in diabetic ketoacidosis. Plasma glucagon averaged 390 pg/ml, ranging from 120 to 1,290 pg/ml, significantly greater than the fasting level of 118 pg/ml in diabetic subjects without ketoacidosis. Absolute hyperglucagonemia, i.e., levels over 240 pg/ml, was present in sixteen; all had "relative hyperglucagonemia." Glucagon levels declined after four hours of therapy and were normal at discharge. The plasma glucagon level was significantly correlated with the blood glucose level, respiratory rate and hours of insulin therapy required to correct the ketonemia. Patients with absolute hyperglucagonemia required significantly more insulin than patients without absolute hyperglucagonemia. The results indicate that glucagon excess is present in most patients hospitalized with diabetic ketoacidosis and are compatible with the view that glucagon, an insulin-opposing hormone, may increase the severity of the disease and its insulin requirements.

Hyperaminoacidemia is a powerful stimulus of pancreatic glucagon secretion. These studies were designed to elucidate the role of aminogenic hyperglucagonemia in glucoregulation. Conscious dogs with previously implanted indwelling venous catheters were employed. The results support the view that a role of glucagon is to limit blood glucose decline during hyperaminoacidemia.First, a significant negative correlation between the area of glucagon increment during the 1st 20 min of a 10 amino acid infusion and the maximum fall in glucose concentration was observed. Second, when endogenous glucagon secretion was suppressed by means of a continuous glucose infusion, hyperaminoacidemia induced a maximal glucose decline which averaged 35 mg/100 ml, differing significantly from mean maximal fall of 3 mg/100 ml, which normally occurs in the presence of endogenous hyperglucagonemia. Third, when, during hyperglycemic suppression of endogenous glucagon secretion, 50 mmug of exogenous glucagon/min was infused via the mesenteric vein with the amino acids, the fall in glucose was reduced to an average of 5 mg/100 ml. Similarly when pancreozymin, administered during the combined infusion of glucose and amino acids, overcame glucose suppression of endogenous glucagon secretion, plasma glucose did not fall. Similar results were obtained when aminogenic hyperglucagonemia was prevented by other means. Hyperlipacidemia, induced by infusing a triglyceride emulsion and giving heparin injections, also suppressed aminogenic hyperglucagonemia in two of four experiments; in these two dogs glucose fell 15 and 11 mg/100 ml. In a final group of experiments, the canine pancreas was resected except for the uncinate process, which is virtually devoid of alpha-cells. In two dogs, in which this procedure resulted in zero portal venous glucagon levels, the administration of amino acids and/or pancreozymin resulted in a glucose decline of 14 and 16 mg/100 ml, despite the reduced beta-cell population resulting from the subtotal pancreotectomy. It thus appears that the secretion of pancreatic glucagon during hyperaminoacidemia in association with insulin secretion, serves to limit the decline of glucose concentration.

It has been suggested that glucagon-like immunoreactivity (GLI) of gastrointestinal tissues might, like pancreatic glucagon, have calcium-lowering activity. Studies were designed, therefore, to determine if calcium absorption was associated with GLI release from the gut. The intraduodenal administration of 4.5 mmoles of calcium chloride per kg of body weight to conscious dogs was associated with a prompt rise in plasma GLI from a base line of 2.2 ng/ml (SEM ±0.2) to a peak of 4.3 ng/ml (SEM ±0.3) at 45 and 60 min, in association with a rise of plasma calcium from 8.6 to 10.4 mg/100 ml. Neither pancreatic glucagon, insulin, nor glucose changed. Smaller calcium loads had progressively diminishing effects on GLI release. Calcium lactate also appeared to stimulate effectively GLI release. Both magnesium chloride and sodium chloride given intraduodenally were associated with a significant though modest increase in GLI. To determine if stimulation of GLI release by substances other than calcium would lower serum calcium, glucose was administered intraduodenally. Despite a marked increase in GLI, plasma calcium fell only 9%, a decline which could be entirely accounted for by hemodilution. Although the physiologic significance of this demonstration that the absorption of calcium salts is associated with GLI release is open to serious question, the findings are not incompatible with the concept that glucagon-like polypeptides are released from the gut during the absorption of certain salts, possibly to alert appropriate homeostatic regulators so as to avoid major changes in electrolyte concentration after the ingestion of large salt loads.

The effect of 20 L-amino acids upon pancreatic glucagon secretion has been studied in conscious dogs. Each amino acid was administered intravenously over a 15 min period in a dose of 1 mmole/kg of body weight to a group of four or five dogs. Pancreatic glucagon and insulin were measured by radioimmunoassay. 17 of the 20 amino acids caused a substantial increase in plasma glucagon. Asparagine had the most glucagon-stimulating activity (GSA), followed by glycine, phenylalanine, serine, aspartate, cysteine, tryptophan, alanine, glutamate, threonine, glutamine, arginine, ornithine, proline, methionine, lysine, and histidine. Only valine, leucine, and isoleucine failed to stimulate glucagon secretion, and isoleucine may have reduced it. No relationship between glucagon-stimulating activity and insulin-stimulating activity was observed. The amino acids which enter the gluconeogenic pathway as pyruvate and, which are believed to provide most of the amino acid-derived glucose, had a significantly greater GSA than the amino acids which enter as succinyl CoA or as alpha-ketoglutarate. However, pyruvate itself did not stimulate glucagon secretion. The R-chain structure of the amino acid did not appear to be related to its GSA, except that the aliphatic branched chain amino acids, valine, leucine, and isoleucine, were devoid of GSA.

The glucagon immunoreactivity present in canine pancreatic extracts can be separated by gel filtration into two fractions; one fraction, comprising over 90% of the immunoreactivity, is similar in molecular size to the glucagon-131I marker, while the other appears to be at least twice as large. Incubation of this large glucagon immunoreactivity (LGI) in solutions such as 1 m acetic acid, 8 m urea, 0.1 m mercaptoethanol, or 6 m guanidine hydrochloride, which favor the dissociation of noncovalent protein complexes, fails to change its molecular size as determined by gel filtration, suggesting that LGI is not glucagon noncovalently bound either to itself or to another protein. However, tryptic hydrolysis of LGI results in the disappearance of most of the immunoreactivity and in a reduction in the molecular size of the remaining immunoreactivity to approximately that of glucagon-131I. Neither LGI nor its tryptic product, both of which resemble glucagon immunologically, has glycogenolytic activity in the perfused rat liver. It is possible that LGI includes the immunoreactive sequence of glucagon or of an immunologically similar peptide.

The role of pancreatic glucagon in starvation has been difficult to assess in humans because of the nonspecificity of antisera heretofore available for glucagon radioimmunoassay. The development of a relatively specific antispnim for pacreation glucagon has now made possible valid measurements of pancreatic glueagun in human plasma and the effect of total starvation on plasma glucagon was, therefore, re-examined. Ten healthy male volunteers abstained from food for seventy-two hours or longer. During this period the mean level of glucose declined from 86 to 70 mg./100 ml., insulin declined from 10 to 3 μ./ml., while glucagon rose progressively from a mean prestarvation level of 126 μμg./ml. to 157, 189, and 178 μμg./ml. at the end of one, two, and three days' starvation, respectively. The responsiveness of the alpha cells to arginine stimulation was tested at the end of the starvation period by means of a forty-minute infusion of arginine at a rate of 11.5 mg./kg./min. Every one of the five subjects tested exhibited a prompt rise in glucagon secretion which reached a peak of 516 μμg./ml. in thirty minutes, significantly greater than the glucagon response of fed controls. Mean insulin concentration during the arginine infusion rose only 6.8 μU./ml. in contrast to a 29 μU./ml. rise in fed subjects. The biologic effect of the modest rise (about 50 per cent) in glucagon concentration would be exaggerated by the concomitant decline in insulin concentration. The magnitude and promptness of the gjucagon response to arginine suggests that the pancreas contains abundant glucagon after three days of total starvation.

The effect of intensive physical exercise upon plasma levels of pancreatic glucagon was investigated in dogs and in man. In 7 dogs, treadmill exercise until collapse was invariably associated with a rise in plasma glucagon, which at the time of collapse averaged 426 pg/ml (sem ± 71), more than 4 times the baseline average of 111 pg/ml (sem ± 26) (p < 0.005). Glucose rose in parallel from 88 mg/100 ml prior to exercise (sem ± 2) to a peak of 105 mg/100 ml (sem ± 4) at collapse (p < 0.01). Hypoglycemia did not occur in any dog. Insulin remained unchanged but rose briefly soon after collapse. In 4 human volunteers exercised to exhaustion on a stationary bicycle glucagon rose from 68 pg/ml (sem ± 17) to 116 pg/ml (sem ± 14) 10 min after the exhaustion point (p < 0.02), and again glucose rose in parallel from a pre-exercise value of 93 mg/100 ml (sem ± 3) to 124 mg/100 ml (sem ± 8) during recovery. Insulin also rose during recovery. When dogs were exercised to collapse during a 15 mg/kg/min intravenou...

The extremely high levels of glucagon recently observed in dogs with severe alloxan-induced diabetes decline promptly and precipitously to normal as soon as exogenous insulin is infused. This suggests that the normal response of the pancreatic alpha cell to hyperglycemia requires the presence of circulating insulin. To determine if the relative hyperglucagonemia of human diabetics responds similarly to insulin repletion, the plasma glucagon response of ten adult-type diabetic patients to a large, predominantly carbohydrate meal was determined with and without the simultaneous forty-five-minute intravenous infusion of glucagonfree insulin (0.12 to 0.2 U./kg.). The glucagon response to the carbohydrate meal during prompt and supernormal hyperinsulinemia resulting from the infusion did not differ from that of the control meal, i.e. normal suppression of glucagon by hyperglycemia was not restored by the abundance of circulating insulin. To determine if still higher plasma levels of insulin would overcome the hyposuppressibility of the diabetic alpha cell to hyperglycemia, 0.6 U. per kilogram per hour of insulin was infused at a constant rate for two hours together with 0.6 gm. per kilogram per hour of glucose to prevent hypoglycemia. Insulin levels of more than 1,200 μ,U. per milliliter were thus attained. Under these conditions, plasma glucagon declined from a mean preinfusion level of 97 pg./ml. (SEM ± 11) to a nadir of 75 pg./ml. (SEM ± 10) ninety minutes later. This slow, modest, statistically significant (p < 0.01) decline differed strikingly from the response of eight nondiabetic patients given intravenous glucose alone; in these subjects, at a comparable level of hyperglycemia, glucagon declined from a mean fasting level of 90 pg./ml. (SEM ± 8) to 57 pg./ml. (SEM ± 8) within thirty minutes, despite an insulin rise to only 46 μU./ml. It was concluded that in human diabetics the acute restoration of plasma insulin, even to supernormal levels, does not promptly restore to normal the alpha cell responsiveness to hyperglycemia. Simple insulin lack may not, therefore, adequately explain the alpha cell abnormality in human diabetes.

Ce travail decrit la presence de specialisations des membranes plasmatiques entre les cellules endocrines des ilots de Langerhans chez le rat. Ces specialisations sont revelees par le cryodecapage («freeze-etching») et apparaissent sous la forme de nexus («gap-junctions») ou de jonctions serrees («tight-junctions»). Elles representent probablement la base structurale d'un couplage ionique et metabolique entre les cellules endocrines.

Highly purified secretin, infused endoportally in five conscious mongrel dogs at a rate of 10 clinical units per min for 20 min, caused a prompt and statistically significant reduction in the pancreaticoduodenal vein level of pancreatic glucagon from a control average of 1130 pg/ml (SEM±312) to a nadir of 492 pg/ml (SEM±194) 15 min later (P < 0.01). During modest hyperglycemia of about 130 mg/100 ml, induced by glucose infusion, the infusion of secretin at the same rate elicited even more dramatic suppression of pancreaticoduodenal glucagon levels to virtually unmeasurable concentrations. At a lower rate of infusion (5 U priming injection followed by 1 U/min for 20 min) significant suppression of glucagon secretion during hyperglycemia was also observed. Stimulation of endogenous secretin release by the intraduodenal administration of 14 mEq of HCl in 10 dogs during intravenous glucose infusion was followed by a decline in pancreaticoduodenal vein glucagon from 130 pg/ml (SEM±34) to a nadir of 99 pg/ml (SEM±32) 5 min later (P < 0.05). The infusion of secretin at a rate of 10 U/min in alloxan-diabetic dogs was associated with a significant decline in peripheral venous plasma glucagon, from a mean preinfusion level of 272 pg/ml (SEM±39) to a nadir of 128 pg/ml (SEM±22) (P < 0.01). It was concluded that exogenous secretin in the doses employed in this study is a potent suppressor of glucagon secretion, particularly during hyperglycemia. HCl-stimulated endogenous secretin also suppresses glucagon secretion. The ability of secretin to augment the glucagon-suppressing effect of ingested glucose qualifies it uniquely for a physiologic role as a modifier of the islet cell response to ingested glucose. The fact that it lowers the hyperglucagonemia of alloxan-diabetic dogs suggests that its glucagon-suppressing activity may not be insulin dependent.