Peptide and protein carboxyl-terminal labeling through carboxypeptidase Y-catalyzed transpeptidation

A survey of carboxypeptidase Y-catalyzed carboxyl-terminal modification of short peptides in the presence of various amino acids revealed that transpeptidation occurred in significant yield only with peptides containing a proline at the penultimate or antepenultimate position. For these peptides, transpeptidation was shown to occur specifically at the carboxyl side of the proline, thus suggesting a determining role of this residue for transpeptidation. Two model peptides, YPFP-GPI and YPFVEPI, were studied in detail. Initial yields of transpeptidation in the presence of various nucleophiles were compared. Among natural amino acids, the highest yield was obtained with methionine, followed by other amino acids bearing hydrophobic side chains. In order to transpose the method of transpeptidation to a protein, a variant of Escherichia coli methionyl-tRNA synthetase bearing the carboxyl-terminal Glu-Pro-Met sequence was genetically created. Under the conditions optimized for the transpeptidation of YPF-VEPI with methionine, this protein could be labeled specifically at its carboxyl-terminal end. Moreover, the parameters of the labeling reaction were in agreement with those observed in the transpeptidation of the model peptide.

Glucagon in women with polycystic ovary syndrome (PCO): relationship to abnormalities of insulin and androgens

To investigate the glucagon status of women with polycystic ovary syndrome (PCO) and to relate this to serum concentrations of insulin, androgens and SHBG, 44 women with PCO and 23 control subjects underwent a 75-g oral glucose tolerance test. Although obese (body mass index greater than 30 kg/m2) women with PCO had higher concentrations of glucose and insulin than overweight (BMI 25-30 kg/m2) and non-obese (BMI less than 25 kg/m2) women with PCO and control subjects, fasting and summed values of glucagon in response to oral glucose were similar in all groups. The fasting and summed concentrations of glucagon were inversely related to those of testosterone and androstenedione in obese women with PCO, but no other relationships were demonstrated between hormone values and those of glucagon in the other groups. We conclude that glucagon is not implicated in peripheral insulin resistance in women with PCO.

Effect of gastrin-releasing peptide on the secretion of mouse islet hormones in vitro

Collagenase-isolated mouse islets were incubated with gastrin-releasing peptide (GRP). At 5.6 mmol glucose/l. 10 nmol GRP/l increased the release of insulin (by 50%) and glucagon (by twofold), decreased the release of pancreatic polypeptide (by 35%), but did not significantly affect the release of somatostatin. At 16.7 mmol glucose/l, 10 nmol GRP/l increased glucagon release (by fivefold) and decreased pancreatic polypeptide release (by 46%), without significantly altering insulin and somatostatin release. GRP (200 nmol/l) did not affect insulin release by perifused mouse islets at 2.8 mmol glucose/l, but increased both first and second phase insulin release after a square wave increase in the glucose concentration to 11.1 mmol/l. At 5.6 mmol glucose/l, GRP (100 pmol/1-100 nmol/l) increased (by 50-70%) insulin release by the RINm5F clonal cell line. GRP did not affect glucose oxidation or the cyclic adenosine monophosphate content of RINm5F cells. However, the intracellular free Ca2+ concentration of RINm5F cells was rapidly and transiently increased by GRP (maximum increase of 64% about 10 s after exposure to 1 mumol GRP/l). The rise of intracellular free Ca2+ was approximately halved in the absence of extracellular Ca2+. The results suggest that GRP may contribute to the normal regulation of the endocrine pancreas. The insulin-releasing effect of GRP is mediated via increased cytosolic free Ca2+, derived both from an increased net influx of extracellular Ca2+ and from mobilization of intracellular Ca2+ stores.

Food deprivation alters liver glycogen metabolism and endocrine responses to hemorrhage

Liver glycogen content, blood glucose, insulin, glucagon, and epinephrine were determined during 1 h hemorrhagic hypotension at 60 mmHg and 23 h thereafter in fed and two groups of 24-h food-deprived rats receiving either no infusion or 30% glucose intravenously during hemorrhage. Liver glycogen content was reduced by greater than 90% after 24-h food deprivation. Fed and food-deprived rats given glucose developed similar and substantial elevations of blood glucose during hemorrhage, whereas changes in blood glucose were modest in food-deprived rats given no infusion. In fed rats, liver glycogen was reduced by 60% during the 1-h bleed, but within 2 h after hemorrhage repletion of liver glycogen content commenced. By 6 h, approximately 75% of the glycogen lost during hemorrhage had been restored, and 23 h after hemorrhage liver glycogen content was six times greater compared with nonbled controls. Although glycogen levels increased after hemorrhage in food-deprived animals, the increase was negligible compared with that found in fed rats. Infusion of glucose during hemorrhage or adrenergic blockade after hemorrhage did not alter glycogen repletion in food-deprived rats. Posthemorrhage fed animals had high levels of insulin, glucagon, and epinephrine during hemorrhage, whereas insulin levels remained low in food-deprived rats despite exogenously induced hyperglycemia. It is concluded that rapid and substantial glycogen repletion can occur even immediately poststress. The conditions seem to be related to the nutritional state at the time of the insult.

Reduced insulinotropic effects of glucagonlike peptide I-(7-36)-amide and gastric inhibitory polypeptide in isolated perfused diabetic rat pancreas

The pathophysiological role of incretin in diabetes mellitus has not been established. We therefore examined the effects of glucagonlike peptide I-(7-36)-amide (truncated GLP-I) and gastric inhibitory polypeptide (GIP) on insulin and glucagon release from isolated perfused pancreases of diabetic rats (12-14 wk of age, mean +/- SE fasting plasma glucose 8.9 +/- 0.6 mM, n = 25) after an injection of 90 mg/kg streptozocin on the 2nd day after birth and compared the results with those of nondiabetic control rats. In diabetic rats, the infusion of 1 nM GLP-I or GIP in perfusates with varying glucose concentrations (2.8, 5.6, 8.3, 11.1, or 22.2 mM) caused a nearly equal degree of insulin stimulation from a similar basal insulin level. Meanwhile, basal and GLP-I- or GIP-stimulated insulin release increased in correlation with the ambient glucose concentration in nondiabetic rats. The degree of stimulation of insulin release at glucose concentrations of 5.6 mM in diabetic rats was approximately 33% that of nondiabetic rats. The stimulation potency was the same between GLP-I and GIP. The insulin treatment for diabetic rats (5 U/kg NPH insulin at 0900 and 2100 for 6 days) brought only a slight improvement in the glucose dependency of GLP-I-stimulated insulin release. The effects of GLP-I and GIP on glucagon release were completely opposite. GLP-I suppressed release; GIP stimulated it. In diabetic rats, the degree of suppression by GLP-I and stimulation by GIP were almost the same with similar basal glucagon levels in the perfusate with varying glucose concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental and tissue-specific regulation of proglucagon gene expression

The pattern of glucagon gene expression and the posttranslational processing of proglucagon was studied in the fetal and neonatal rat. Pancreatic immunoreactive glucagon (IRG) and glucagon-like immunoreactivity (GLI) were low in both fetal pancreas and intestine, respectively. Immediately after birth, pancreatic IRG rose markedly and reached a peak concentration at postnatal day 7, followed by a gradual return to its adult level. Intestinal GLI was low until postnatal day 7 and rose steadily thereafter to adult levels. The levels of GLI in the hypothalamus were much lower than in intestine, yet the developmental accumulation of hypothalamic GLI resembled the pattern observed in intestine. In contrast, the levels of GLI and IRG in the brain stem were higher in the fetus and neonate, and decreased to adult levels. Proglucagon mRNA transcripts, uniform in size, were detected in RNA isolated from fetal or adult brainstem, pancreas, and intestine. However, fetal proglucagon mRNA transcripts were larger than adult proglucagon mRNA transcripts in pancreas and intestine, but not brainstem. The results of RNAse mapping studies, including analysis of both the 5'- and 3'-ends of the mRNA transcripts, demonstrated that the larger fetal mRNA transcripts could be accounted for by an increase in the length of the polyadenylate tail in the fetal tissues. These observations demonstrate that the developing rat exhibits tissue-specific differences in both proglucagon gene expression and the pattern of posttranslational processing of the prohormone.

Altered glucagon- and catecholamine hormone-sensitive adenylyl cyclase responsiveness in rat liver membranes induced by manipulation of dietary fatty acid intake

Glucagon-stimulated adenylyl cyclase activity has been shown to change in liver membranes manipulated to alter either their fatty acid composition or fluidity. We examined whether membrane alterations induced by dietary manipulation affected receptor function. Glucagon- and beta-adrenergic-stimulated receptor-adenylyl cyclase systems were examined in liver membranes of rats fed diets containing 10% corn oil, 10% coconut oil (essential FFA deficient), or 8.5% coconut oil with 1.5% corn oil (essential FFA repleat). Basal and maximal nonreceptor-mediated adenylyl cyclase activity (stimulated by NaF, guanylylimidodiphosphate, and forskolin) was the same in membranes of each of the dietary groups, suggesting that Gs-protein and the catalytic unit activity per se were unaltered by the manipulations. Glucagon-stimulated adenylyl cyclase activity increased with increasing unsaturation of dietary fatty acids; activity in coconut oil-fed rats was 527 +/- 30 (mean +/- SEM) pmol/mg.10 min, that in coconut/corn oil-fed rats was 752 +/- 74 pmol/mg.10 min, and that in corn oil-fed rats was 981 +/- 94 pmol cAMP/mg.10 min. [125I]Monoiodoglucagon binding did not increase in parallel to the adenylyl cyclase alterations; coconut oil-fed animals (614 fmol/mg) differed from the other groups (450 and 430 fmol/mg). Isoproterenol (beta-adrenergic)-stimulated adenylyl cyclase activity was also highest in the corn oil-fed animals, but was similar in the other dietary groups, with no difference in other characteristics of [125I]iodopindolol binding between the groups. The results demonstrate that alterations in the glucagon-stimulated adenylyl cyclase response are different from those in the beta-adrenergic adenylyl cyclase response. Further, they suggest that although direct activations of the catalytic unit or its interaction with the guanine nucleotide-sensitive protein are apparently not affected, hormone receptor-mediated adenylyl cyclase activity may be altered by these dietary manipulations.

Inhibitory effect of rat amylin on the insulin responses to glucose and arginine in the perfused rat pancreas

Amylin, a 37-amino acid polypeptide, is the main component of amyloid deposits in the islets of Langerhans, and has been identified in the B-cell secretory granules. We have investigated the effect of rat amylin on the insulin and glucagon release by the isolated, perfused rat pancreas. Amylin infusion at 750 nM, markedly reduced unstimulated insulin release (ca. 50%, P less than 0.025), whereas it did not modify glucagon output. At the same concentration, amylin also blocked the insulin response to 9 mM glucose (ca. 80%, P less than 0.025) without affecting the suppressor effect of glucose on glucagon release. The inhibitory effect of amylin on glucose-induced insulin secretion was confirmed by lowering the amylin concentration (500 nM) and increasing the glucose stimulus (11 mM); again, no effect of amylin on glucagon release was observed. Finally, amylin, at 500 nM, reduced the insulin response to 3.5 mM arginine (ca. 40%, P less than 0.025) without modifying the secretion of glucagon elicited by this amino acid. It can be concluded that, in the rat pancreas, the inhibitory effect of homologous amylin on unstimulated insulin secretion, as well as on the insulin responses to metabolic substrates (glucose and arginine), favours the concept of this novel peptide as a potential diabetogenic agent.

Metabolic clearance rates of oxyntomodulin and glucagon in the rat: contribution of the kidney

The half-life (t1/2) and metabolic clearance rate (MCR) of exogenous natural porcine oxyntomodulin (porcine OXM) and the synthetic analog of rat oxyntomodulin, [Nle27]-OXM (rat OXM), were compared with that of glucagon in control, sham-operated and acutely nephrectomized rats using the primed-continuous infusion technique. The half-disappearance times for porcine OXM (8.2 +/- 0.5 min) and rat OXM (6.4 +/- 0.5 min) were 3-fold slower than that of glucagon (1.9 +/- 0.1 min). Acute bilateral nephrectomy significantly prolonged the half-disappearance time of rat OXM (8.2 +/- 0.7 min) and glucagon (3.6 +/- 0.4 min) compared with that of sham-operated animals (6.5 +/- 0.8 min and 2.5 +/- 0.2 min, respectively). The mean MCRs were similar for porcine and rat OXM (11.3 +/- 0.7 and 11.9 +/- 0.5 ml.kg-1.min-1) but were 3 times lower than that measured with glucagon (36 +/- 5 ml.kg-1.min-1). Bilateral nephrectomy reduced the MCR of OXM and glucagon by 38% and 34%, respectively. No significant increase in C-terminal glucagon immunoreactivity was noticed during infusion of either porcine or rat OXM, measured directly in plasma, with a specific C-terminal glucagon antiserum or after HPLC. In the course of the glucagon infusion, blood glucose was increased 2-fold, while the same dose of porcine OXM or of rat OXM induced only a small increase over the values in phosphate buffer-infused rats. 10 times higher doses of rat OXM were necessary to obtain a similar hyperglycemic effect. These results indicate that: (1) the metabolism of OXM is 3-fold slower than that of glucagon, (2) renal clearance contributed close to 35% of the overall metabolic plasma extraction for OXM and glucagon and (3) OXM, although effective at a higher dose, when compared with glucagon, displays a hyperglycemic effect probably through the glucagon receptors.

Modulation of arginine-induced insulin and glucagon secretion by the hepatic vagus nerve in the rat: effects of celiac vagotomy and administration of atropine

We hypothesized the existence of vagal arginine sensors in the liver which modulate arginine-induced pancreatic hormone secretion. The present study was carried out to examine the efferent pathways and receptor mechanisms from arginine sensors using selective vagotomies and autonomic drugs on the secretion of insulin and glucagon after ip injection of L-arginine (1 g/kg BW) in rats in an unanesthetized and unrestrained state. Hepatic vagotomy (sectioning of the hepatic branch of the vagus nerve) enhanced both plasma insulin and glucagon concentrations after ip arginine more than those in sham-vagotomized (control) rats. The effect of hepatic vagotomy was blocked by adding celiac vagotomy (sectioning of the celiac branches of the vagus nerve) or by previous administration of atropine methyl nitrate (10 mg/kg BW), but not by phentolamine (1 mg/kg BW) or propranolol (2 mg/kg BW). Celiac vagotomy alone did not affect the plasma insulin concentration; however, it reduced the plasma glucagon concentration after ip arginine compared to that in sham-vagotomized rats. Administration of atropine alone did not affect plasma insulin or glucagon concentrations after ip arginine. These results suggest that celiac branches of the vagus nerve act as efferent pathways to the pancreas through a muscarinic receptor mechanism in the hepatic arginine sensor-mediated pancreatic neuroendocrine system. The physiological role of these hepatic sensors may be to prevent arginine-induced exaggerated pancreatic hormone secretion and maintain blood glucose homeostasis.

Secretion and degradation of glucagon by HIT cells

HIT cells have been widely used to study synthesis and secretion of insulin. It has been assumed that this cell line secretes no other islet hormones. To ascertain whether HIT cells synthesize, secrete, and degrade glucagon, we examined cell extracts for this peptide and compared secretion and degradation of glucagon and insulin during stimulation of the cells by arginine. Glucagon levels in acid extracts of HIT cells were found to be 0.72 +/- 0.15 pmol/mg protein. Both glucagon and insulin were maximally stimulated in a glucagon/insulin molar ratio of 0.029 by arginine concentrations of 25-50 nM, and the concentration of arginine that provided half-maximum responses for both hormones was approximately 3 mM. Diminution of arginine-induced glucagon secretion was caused by somatostatin, a physiological inhibitor of pancreatic islet alpha-cell function. HPLC was used to authenticate the glucagon levels stimulated by arginine for 60 min and measured by RIA. Thirty-six percent of immunoreactive glucagon was found in the fractions representing authentic glucagon, whereas the remaining 64% eluted earlier. Experiments examining the fate of radiolabeled glucagon exposed to HIT cells revealed time-dependent degradation of the radioisotope to earlier eluting forms, which accounted for approximately 50% of the radioactivity by 60 min and was complete by 18 h, indicating that the early peak detected by RIA represented a metabolite of glucagon. Radioisotopic insulin was degraded more slowly with an apparent half-life of approximately 36 h. We conclude that HIT cells are not only able to synthesize, secrete, and degrade insulin, but also much smaller amounts of glucagon.

Dexamethasone pretreatment of rat insulinoma cells decreases binding of glucagon-like peptide-1(7-36)amide

The effect of dexamethasone on binding of glucagon-like peptide-1(7-36)amide (GLP-1(7-36)amide) to rat insulinoma-derived cells (RINm5F) was investigated. Preincubation of RINm5F cells with dexamethasone (100 nmol/l) for 24 h resulted in a decrease of GLP-1(7-36)amide binding to 55.0 +/- 8.16% (mean +/- S.E.M.), incubation for 48 h to 39.1 +/- 1.76%, and for 72 h to 15.5 +/- 4.35% of maximal binding. The GLP-1(7-36)amide-induced stimulation of cyclic AMP (cAMP) production was significantly decreased to 61.03 +/- 7.4% of maximum production in cells pretreated with dexamethasone (100 nmol/l) for 48 h. The decreased binding was due to a reduction of the receptor number while the receptor affinity remained unchanged. These inhibitory effects on binding and cAMP formation induced by dexamethasone were completely abolished when the antiglucocorticoid RU 38486 (100 nmol/l) was added during preincubation with dexamethasone. RU 38486 alone had no effects. Our data suggest that the biological action of GLP-1(7-36)amide at the B-cell may be modified by glucocorticoids.

Effect of functional adrenalectomy on glucagon secretion and circulating catecholamines during insulin hypoglycemia in the dog

The present study was carried out to determine whether an increase in the pancreatic immunoreactive glucagon (IRG) secretion during the acute phase of insulin-induced hypoglycemia depends on circulating catecholamines of adrenal origin. Hypoglycemia was induced by a bolus insulin injection (0.15 IU/kg, i.v.) in dogs anesthetized with sodium pentobarbital (35 mg/kg, i.v.). Plasma aortic epinephrine (E) and norepinephrine (NE) concentrations increased significantly 30 min after the injection of insulin. At this time point, a functional adrenalectomy (diversion of bilateral adrenal venous blood from the systemic circulation) was performed for 5 min. The increased aortic E and NE concentrations significantly decreased reaching, within 5 min, a level below the corresponding preinjection control value. The basal output of pancreatic IRG (6.58 +/- 1.12 ng/min, n = 6) significantly increased (24.93 +/- 2.77 ng/min, p less than 0.05, n = 6) 30 min after insulin injection. During the functional adrenalectomy, the increased pancreatic IRG output diminished rapidly, within 5 min, to approximately 50% (11.73 +/- 3.19 ng/min, p less than 0.05, n = 6) of the value observed 30 min after insulin administration. In the other group of dogs receiving sham adrenalectomy, the increased aortic E and NE concentrations and pancreatic IRG output following insulin injection remained elevated above the levels observed immediately before the sham adrenalectomy. The net decrease in IRG output during the adrenalectomy was significant (p less than 0.05) compared with the corresponding net IRG output observed in the sham group.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoreactivities for chromogranin A and B, and secretogranin II in the guinea-pig endocrine pancreas

The chromogranins are acidic proteins present in various endocrine cells and organs. They consist of chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). In the pancreas, these proteins or their breakdown products are possibly involved in the regulation of pancreatic hormone secretion. The guinea-pig endocrine pancreas was now investigated immunohistochemically for the presence of the chromogranins in five endocrine cell types. CgA is a regular constituent of insulin (B-), pancreatic polypeptide (PP-) and enterochromaffin (EC-) cells. In addition, a minority of somatostatin (D-) cells were immunoreactive for CgA. CgB immunoreactivities were very faint and exclusively observed in B-cells. SgII was found in B- and PP-cells; a faint immunostaining for SgII was also seen in a few glucagon (A-) cells. Typically, the densities of CgA or SgII immunoreactivities varied among the members of a given cell population, e.g. among individual B- or PP-cells. The present findings about the heterogeneities of immunoreactivities for the chromogranins are in line with findings obtained in pancreatic endocrine cells of other species. The true reasons for these heterogeneities are enigmatic. It seems probable, however, that the corresponding immunoreactivities depend on the intracellular processing of the chromogranins which in turn might be related to the metabolic state of endocrine cells. This has to be examined in future by experimental investigations.

[Glucagon receptor binding and its effect on the cAMP level in isolated rat and chicken hepatocytes]

The binding sites to glucagon with KD 10(-9) M in rat and chicken isolated hepatocytes and with KD 10(-7) M in chicken hepatocytes only where revealed. The first, but not the second binding sites where decreased in their affinity by the adding of GTP nonhydrolyzing analogue Gpp(NH). Glucagon activated the cAMP accumulation in rat and chicken hepatocytes in dose-depended manner. The dose-response curve being plateau after maximum in rats and decreased in chicken. Glucagon inserted an inhibiting effect when occupying chicken-specific sites of binding with KD 10(-7) M. The nature of these binding sites and mechanism of glucagon inhibiting effect on the cAMP accumulation are discussed.

Hepatotoxicity induced by diethylnitrosamine causes no significant disturbances of systemic glucose homeostasis in rats

In rats, a moderately hepatotoxic single dose of diethylnitrosamine (DEN) 100 mg/kg causing depletion of liver glycogen, elevation of aspartate aminotransferase and decreased liver uptake of 3-O-methylglucose, resulted in substantial changes in insulin and glucagon balance. Two days after DEN, insulin binding to liver membranes and insulin removal by the liver were sharply reduced whereas its binding to muscle and adipocyte membranes remained unaltered. Serum insulin (random and after an overnight fast) remained normal. Intravenous (I.V.) insulin (10 U/kg) caused the usual degree of hypoglycemia that, however, lasted longer than in the control animals. Removal of glucagon by liver was also depressed in spite of its normal binding to hepatocytes, and peripheral serum glucagon was increased three-fold. I.V. glucagon (40 micrograms/kg) resulted in a blunted response of plasma glucose. I.V. glucose tolerance test (1 g/kg) remained normal in spite of the insulin increase to a level twice as high as in the controls, and in spite of nonsuppressed glucagon. These changes were still present after 1-3 months, but disappeared by 6 months. The results demonstrate remarkable ability of homeostatic mechanisms to preserve normal plasma glucose and glucose tolerance in spite of dramatic changes in insulin and glucagon.

Chronic hyperinsulinemia decreases insulin action but not insulin sensitivity

Hyperinsulinemia and insulin resistance are commonly seen in obese and non-insulin-dependent diabetes mellitus (NIDDM) patients, suggesting a causal link exists between hyperinsulinemia and insulin resistance. In a previous study, we demonstrated that chronic (28 days) intraportal hyperinsulinemia (50% increase in basal insulin levels) resulted in a decrease in insulin action as assessed by a one-step euglycemic hyperinsulinemic clamp. Since only one dose of insulin was used during the clamp, it was not possible to determine if the decrease in insulin action was due to a change in insulin sensitivity and/or maximal insulin responsiveness. In the present study, insulin resistance was induced as before, but insulin action was assessed in overnight fasted conscious dogs using a four-step euglycemic hyperinsulinemic clamp (1, 2, 10, and 15 mU/kg/min). Insulin responsiveness was assessed before the induction of chronic hyperinsulinemia (day 0), and after 28 days of hyperinsulinemia (day 28). Transhepatic glucose balance and whole-body glucose utilization were measured to allow assessment of both the hepatic and peripheral effects of insulin. Chronic hyperinsulinemia increased basal insulin levels from 13 +/- 2 to 21 +/- 4 microU/mL. After 4 weeks of chronic hyperinsulinemia, maximal insulin-stimulated glucose utilization was decreased 23% +/- 4% (P less than .05) and insulin sensitivity (ED50) was not significantly altered. During the four-step clamp, the liver was a major site of glucose utilization. The liver was responsible for 13% of the total glucose disposal rate on day 0 (2.9 mg/kg/min) at the highest insulin infusion rate (15 mU/kg/min; 2,000 microU/mL).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of oxytocin on in vivo release of insulin and glucagon studied by microdialysis in the rat pancreas and autoradiographic evidence for [3H]oxytocin binding sites within the islets of Langerhans

In the present investigation it was studied whether oxytocin administered directly in the pancreas of the rat stimulates the release of insulin and glucagon. In order to study such effects in vivo, a new experimental model applying the microdialysis technique was developed. To test the validity of the method, glucose or arginine were infused i.v. and it was shown that perfusate concentrations of insulin and glucagon increased significantly to 344 and 292% of basal overflow, respectively. Administration of oxytocin via the dialysis probe into the splenic portion of the pancreas resulted in significant elevations of insulin and glucagon concentrations to 210 (P less than 0.05) and 528% (P less than 0.01), respectively. The present study also includes a combined autoradiographic and immunohistochemical investigation of binding sites for oxytocin in the rat pancreas. A high density of [3H]oxytocin binding was present in the periphery of the islets of Langerhans, corresponding to the localization of the glucagon-producing alpha-cells. Both oxytocin and arginine(A)-vasopressin displaced [3H]oxytocin. The IC50 values were 10 and 180 nM, respectively. In conclusion, the oxytocin-induced release of insulin and glucagon as previously demonstrated in a number of species, may be due to a stimulation exerted by the peptide directly within the pancreas.

Pancreatic function in the essential fatty acid deficient rat

The influence of essential fatty acid (EFA) deficiency on pancreatic endocrine and exocrine function was studied in 120-day-old rats. The plasma insulin response was determined after in vivo administration of glucose and arginine. The plasma glucagon response was assessed after infusion of arginine. Islet peptides were examined by immunocytochemistry. The exocrine function of pancreas was studied by amylase secretion in isolated pancreatic acinar cells after stimulation with the cholinergic agonist carbacholine chloride. The EFA-deficient (EFAD) rats showed higher basal plasma insulin concentrations and lower basal glucose levels than control rats (P less than .01 and P less than .01, respectively). The plasma insulin response to glucose was potentiated in the EFAD rats (P less than .001). Both insulin and glucagon responses to arginine were normal. The isolated pancreatic acinar cells showed a low basal amylase secretion, but a normal response to carbacholine chloride. There were no overt morphological changes seen in the pancreas and the immunocytochemical staining pattern of insulin, glucagon, somatostatin, and pancreatic polypeptide cells did not differ from controls. The results of the study show that the secretory function of the endocrine and exocrine pancreas is operational in EFA deficiency. The EFA deficiency was accompanied by a basal hyperinsulinemia and hypoglycemia and an exaggerated insulin response to glucose, the pathophysiology of which has to be further studied.

Inhibition of insulin and somatostatin secretion and stimulation of glucagon release by homologous galanin in perfused rat pancreas

Results of studies on the effects of exogenous galanin on islet cell secretion are controversial. Until recently, only pig galanin has been available, and structural dissimilarities among the galanin molecules of different species might have contributed to discrepancies among the study results. Thus, we investigated the influence of synthetic rat galanin (50 nM) on unstimulated insulin, glucagon, and somatostatin release and on the responses of these hormones to arginine (10 mM), glucose (16.6 mM), and vasoactive intestinal polypeptide (VIP; 1 nM) in a homologous animal model, the perfused rat pancreas. In addition, the effect of an equimolar concentration of pig galanin on arginine-induced islet cell secretion was examined. Infusion of rat galanin reduced unstimulated insulin release (approximately 60%, P less than 0.01) and the insulin responses to arginine (approximately 30%, P less than 0.025), glucose (100%, P less than 0.01), and VIP (approximately 80%, P less than 0.025). Galanin also inhibited unstimulated somatostatin secretion (approximately 15%, P less than 0.05) and virtually abolished the somatostatin output evoked by arginine, glucose, and VIP. Conversely, rat galanin increased unstimulated glucagon output (approximately 20%, P less than 0.05), potentiated the glucagon response to arginine (approximately 50%, P less than 0.05) and VIP (approximately 90%, P less than 0.05), and counteracted the suppressor effect of glucose on alpha-cell secretion. Pig galanin inhibited the insulin output elicited by arginine (approximately 45%, P less than 0.05) but did not affect the somatostatin and glucagon responses to the aminogenic stimulus. In conclusion, the opposite effects of galanin on insulin and glucagon secretion favor the concept of galanin as a diabetogenic agent. Galanin also behaves as a potent inhibitor of somatostatin release. Finally, the importance of using homologous galanin to study the biological activity of this peptide must be emphasized.

Effects of porcine diazepam-binding inhibitor on insulin and glucagon secretion in vitro from the rat endocrine pancreas

Porcine diazepam-binding inhibitor (pDBI) is a novel peptide that has been isolated from the small bowel of the pig, and that occurs also in the islet D-cells. We have studied its effects on hormone release in vitro from the endocrine pancreas of the rat. In isolated islets, pDBI (10(-9)-10(-6)M) did not affect basal insulin release at 3.3 mM glucose, whereas stimulated release at 8.3 mM glucose was dose-dependently suppressed by 32-69% (P less than 0.01). Furthermore, insulin secretion stimulated by either 16.7 mM glucose or 1 mM IBMX (3-isobutyl-1-methylxanthine) or 1 micrograms/ml glibenclamide was suppressed by pDBI at 10(-8) M (by 28-30%, P less than 0.05) and 10(-7) M (by 43-47%, P less than 0.01). In contrast, islet insulin secretion induced by 20 mM arginine was unaffected by these concentrations of pDBI. In the perfused rat pancreas, pDBI (10(-8) M) enhanced by 30% (P less than 0.05) the first phase (0-5 min) of arginine-stimulated insulin release, whereas the second phase (5-20 min) was unchanged. Moreover, pDBI suppressed by 28% (P less than 0.05) the second phase of arginine-induced glucagon release. Arginine-induced somatostatin release was not significantly affected by the peptide. Since pDBI immunoreactivity has been localized also to islet D-cells, the present results suggest that pDBI may act as a local modulator of islet hormone release.

Somatostatin analogue and tissue cultures in the study of a human malignant glucagonoma

A patient with metastasizing glucagonoma producing multiple molecular forms of glucagon is reported. The patient responded to symptomatic treatment with a somatostatin analogue (SMS 201-995). Glucagonoma tumour cells were studied in two tissue culture systems: intraocular transplants of immunosuppressed rats and long-term cell cultures. In both systems, several region-specific glucagon antisera gave a positive immunoreaction with tumour cells indicating synthesis of multiple molecular species. Intraocular tumour transplants released glucagon into the chamber fluid. In animals with unilateral transplants, glucagon was also detected in the contralateral eye chamber, indicating passage from the transplants via unknown mechanisms. Treatment of tumour cells during culture with SMS 201-995 inhibited rapidly the spontaneous release of glucagon without evident cytotoxic effects. The inhibitory effect decreased with time.

Insulin and glucagon secretion in swimming mice: effects of autonomic receptor antagonism

To study the regulation of islet hormone secretion in exercise-stress, we developed a swimming mouse model. Mice swam for 2, 6, or 10 minutes whereafter blood was sampled for analysis of plasma levels of insulin, glucagon, and glucose. Plasma insulin levels, which were not different from resting controls after 2 or 6 minutes of swimming, were slightly lower after 10 minutes of swimming (P less than .05). Plasma glucagon levels were increased after 2, 6, and 10 minutes of swimming (P less than .001), and plasma glucose levels were lower after 6 and 10 minutes of swimming (P less than .05). Glucose (5.6 mmol/kg)-stimulated insulin secretion was inhibited by 52% +/- 9% by the swimming (P less than .001). The mechanisms behind this inhibition of glucose-stimulated insulin secretion and the increase in basal plasma glucagon levels induced during 2 minutes of swimming were investigated by the use of autonomic receptor antagonists, administered intraperitoneally 20 minutes before the swimming period. The ganglionic antagonist hexamethonium (56 mumols/kg) prevented the swimming-induced inhibition of glucose-stimulated insulin secretion, indicating involvement of nerves in the inhibition. Also the nonselective alpha-adrenoceptor antagonist phentolamine (6.0 mumols/kg) and the alpha 2-adrenoceptor antagonist yohimbine (3.6 mumols/kg) prevented the inhibition of glucose-stimulated insulin secretion induced by swimming, whereas the beta-adrenoceptor antagonist L-propranolol (9.6 mumols/kg) had no effect. The swimming-induced increase in plasma glucagon levels was partially inhibited by hexamethonium by (58% +/- 24%, P less than .05). Phentolamine and yohimbine totally prevented the increase in plasma glucagon levels, whereas L-propranolol had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Pancreatic glucagon secretion during a short period of hemorrhage in anesthetized dogs

Glucagon has been implicated in the hormonal metabolic response to hemorrhage. However, evidence for this has been obtained largely from observations of circulating plasma glucagon concentration. A clear increase in the pancreatic glucagon secretion remains to be demonstrated. Plasma concentrations of pancreatic immunoreactive glucagon (IRG) and insulin (IRI) were determined in portal venous and aortic blood, and plasma glucose in aortic blood. Dogs were bled (approximately 15 mL/kg) until aortic systolic blood pressure dropped to approximately 50% (70.5 +/- 8.1 mmHg, n = 7) (1 mmHg = 133.32 Pa) of its control value (135 +/- 7.1 mmHg, n = 7), and the hemorrhagic hypotension was maintained for 10 min. The net portal venous IRG delivery rate rose significantly and continued to increase during the hemorrhagic hypotension despite a significant fall in the portal venous blood flow. Aortic IRG increased significantly along with the increase in portal venous IRG delivery rate (r = 0.838, n = 42, p less than 0.01). The portal venous delivery rate of IRI decreased significantly in response to hemorrhage. The aortic IRG/IRI concentration ratio increased significantly during the hemorrhage-induced hypotension. Aortic glucose concentration increased significantly 5 min after hemorrhage and continued to rise until the end of the hemorrhagic hypotension. The present study demonstrates that the secretion of pancreatic glucagon actually increases during the early phase of hemorrhage. The results also indicate that the increase in aortic IRG during the hemorrhagic hypotension is due to the increased pancreatic glucagon secretion. It is suggested that the pancreatic glucagon may be involved in the early hyperglycemic response to hemorrhage.