Effect of pancreastatin on pancreatic endocrine function in the conscious rat

We have studied the effects of pancreastatin on insulin and glucagon secretions in vivo in the conscious rat. Rats were prepared with a gastric fistula and with both external jugular veins cannulated. We found that an i.v. infusion of pancreastatin (1 and 10 nmol/kg/h) inhibited the plasma insulin response and increased the plasma glucose response to the intragastric infusion of glucose in a dose-dependent manner. Furthermore, the infusion of pancreastatin increased the plasma glucagon response to the i.v. infusion of arginine in a dose-dependent manner, and it inhibited the plasma insulin response. However, such an infusion of pancreastatin had no effect on the basal plasma glucose level, nor did it have any effect on plasma insulin and glucagon concentrations. Thus, it is suggested that in the rat, the newly discovered pancreastatin is a regulator of islet cell function.     

A comparative study of several serotonin receptor antagonists on basal and stimulus induced release of insulin and glucagon in the intact rat.

Several commonly used serotonin receptor antagonists were studied for their ability to influence basal plasma insulin and glucagon (using 30K antibody) levels as well as the response of these hormones to a glucose or arginine challenge administered systematically to overnight fasted rats. Cyproheptadine, in contrast to other antagonists employed, induced large increases of insulin, glucagon and glucose, although this hyperinsulinemia was of a smaller magnitude when compared with hormone levels observed during an equivalent hyperglycemia resulting from glucose administration. The pancreatic response to a glucose load (increased insulin and decreased glucagon release) and an arginine load (increased insulin and glucagon release) were prevented by cyproheptadine pretreatment. Basal insulin levels were bot consistently altered by methysergide or cinanserin and were slightly elevated by metergoline. Basal glucagon levels were unaffected by these drugs. These three agents potentiated the insulinotropic effect of an arginine load whereas only metergoline exerted a similar effect on the response to glucose loading. Glucagon release in response to these stimuli was not significantly altered by drug pretreatment.     

Glucagon secretion in chronic pancreatitis.

Plasma insulin, pancreatic glucagon and immunoreactive glucagon-like polypeptide of intestinal origin (enteroglucagon) have been measured in 10 patients with chronic pancreatitis and 5 normal subjects. Basal levels and changes following oral glucose (50 g) and an intravenous infusion of arginine (25 g in 30 min) have been studied. In patients with chronic pancreatitis the plasma insulin response to oral glucose and intravenous arginine was reduced. Basal pancreatic glucagon was increased in the patients and increased further with oral glucose. During an arginine infusion the pancreatic glucagon showed a brisk early increase greater than that seen in the normal subjects. Basal enteroglucagon levels were significantly increased in chronic pancreatitis but response to orla glucose and arginine infusion were little different from those seen in the normal subjects.     

Somatostatin response to glucose before and after prolonged fasting in lean and obese non-diabetic subjects

Insulin, glucagon, and somatostatin concentrations were measured in 7 lean and 7 obese non-diabetic subjects over 7 days of fasting. In addition each subject was given a 75 g oral glucose tolerance test after fasts of 12 h and 7 days. In lean subjects complete food deprivation induced a significant decrease in the circulating levels of both insulin and somatostatin, while glucagon nearly doubled by 48 h and then remained constant for the duration of starvation. Refeeding with oral glucose suppressed the increased plasma glucagon, but insulin and somatostatin responses were enhanced in comparison with the prefast values, as assessed by the integrated areas of change. In obese subjects peripheral insulin and somatostatin levels were significantly lowered, but plasma glucagon level was unchanged at the end of the starvation period. In the same group glucose-induced insulin and somatostatin release were greater than in the fed state. Suppression of plasma glucagon by glucose appeared less complete in obese than in lean subjects. It is concluded that prolonged starvation enhances D-cell responsiveness to glucose in lean and obese subjects.     

Urinary and plasma cyclic AMP levels during short term starvation in obese man: response to glucagon stimulation.

Glucagon is known to elevate the intracellular concentration of cyclic AMP in the hepatocyte. The increase in intracellular cyclic AMP is reflected by an increase in the plasma concentration of the nucleotide. Intravenous glucagon stimulation was performed on six obese non-diabetic human subjects before and after a three day fast. All patients responded to starvation by a lowering of plasma immunoreactive insulin and blood glucose. Whereas the plasma immunoreactive glucagon concentration increased over the three day period, the plasma and urinary cyclic AMP did not significantly change. Intravenous glucagon promoted qualitatively similar increases in the blood glucose and plasma concentrations of insulin and cyclic AMP before and after three days starvation.     

Relationships between glucose, insulin and glucagon during fasting in late gestation in the rat

Plasma glucose, insulin and glucagon were measured in pregnant and age-matched virgin rats in the fed state and after fasting 6, 48 or 120 hours during day 16–21 of gestation. The fed state in pregnancy was characterized by a metabolic setting favoring anabolism. The lower plasma glucose in the fed pregnant rats was associated with higher insulin, slightly lower glucagon and higher insulin/glucose and insulin/glucagon ratios than in virgin rats. During fasting, glucose fell to sustained hypoglycemic levels in the pregnant animals whereas glucose declined but did not achieve hypoglycemia at any point in the virgins. Despite the hypoglycemia, greater levels of plasma insulin persisted in the pregnant throughout the 120 hours of fasting and insulin/glucagon ratios did not differ significantly from the euglycemic virgins. Thus, “accelerated starvation” in pregnancy cannot be ascribed to relative glucagon excess. Rather, the preservation of normal insulin/glucagon ratios despite prevailing hypoglycemia, may provide a mechanism during fasting in pregnancy for restraining maternal protein catabolism in the face of the added fuel demands of the conceptus.     

Modulation of A and B cell functions by tolbutamide and arginine in the pancreas of thiamine-deficient rats

The effects of administration of glucose orally and tolbutamide or arginine intravenously on insulin and glucagon secretion and blood glucose level were studied in normal and thiamine-deficient rats. In thiamine deficiency, insulin secretion and glucose tolerance were impaired during glucose ingestion. Tolbutamide decreased the blood glucose level in both control and thiamine-deficient rats but its stimulatory effect on insulin secretion was minimal in thiamine-deficient rats unlike the control animals. Arginine did not alter substantially the blood glucose or insulin in thiamine-deficient rats, whereas it increased the insulin level in control rats. The fasting plasma glucagon level was high in thiamine deficiency. Tolbutamide increased the plasma glucagon in control rats, but did so only marginally in thiamine-deficient rats. Arginine also increased the glucagon secretion throughout the period of study in control rats. In thiamine-deficient rats the glucagon secretion was pronounced only after 20 min of arginine administration. These results suggest that an unimpaired glucose metabolism is a prerequisite to induce proper insulin secretion. Only proper insulin secretion can check the glucagon secretion rather than the increased glucose level. Hypoglycemia can induce glucagon secretion independent of the insulin level.     

Role of SCN in Daily Rhythms of Plasma Glucose,FFA, Insulin and Glucagon

The daily changes in plasma glucose, FFA, insulin and glucagon concentrations in rats under 12 hr-12 hr light-dark conditions, and the role of the suprachiasmatic nucleus (SCN) of the hypothalamus in these changes were examined. In sham-operated rats, the four parameters showed significant daily rhythms. However, after bilateral lesions of the SCN, daily rhythms could not be detected in these parameters under the present experimental conditions. Furthermore, after the SCN lesions the plasma glucose concentration remained at the minimum level of that in sham-operated rats, while the plasma insulin and glucagon concentrations reduced to approximately the mean level and about half the minimum level of sham-operated rats, respectively, and the FFA concentration lowered to somewhat below the minimum level. Gradual increase in the plasma insulin concentration at the end of the light period was observed in intact rats even after starvation for 24 hr. These findings suggest that the SCN is essential for generation of the daily changes in the plasma glucose, FFA, insulin and glucagon concentrations and also that it plays critical roles in regulation of the secretion of pancreatic hormones. The gradual increase in the plasma insulin level observed at the end of the light period is discussed in connection with initiation of spontaneous feeding behaviour.     

Role of SCN in daily rhythms of plasma glucose, FFA, insulin and glucagon

The daily changes in plasma glucose, FFA, insulin and glucagon concentrations in rats under 12 hr-12 hr light-dark conditions, and the role of the suprachiasmatic nucleus (SCN) of the hypothalamus in these changes were examined. In sham-operated rats, the four parameters showed significant daily rhythms. However, after bilateral lesions of the SCN, daily rhythms could not be detected in these parameters under the present experimental conditions. Furthermore, after the SCN lesions the plasma glucose concentration remained at the minimum level of that in sham-operated rats, while the plasma insulin and glucagon concentrations reduced to approximately the mean level and about half the minimum level of sham-operated rats, respectively, and the FFA concentration lowered to somewhat below the minimum level. Gradual increase in the plasma insulin concentration at the end of the light period was observed in intact rats even after starvation for 24 hr. These findings suggest that the SCN is essential for generation of the daily changes in the plasma glucose, FFA, insulin and glucagon concentrations and also that it plays critical roles in regulation of the secretion of pancreatic hormones. The gradual increase in the plasma insulin level observed at the end of the light period is discussed in connection with initiation of spontaneous feeding behaviour.     

Effects of amino-acids on pancreatic hormones and gut glucagon-like immunoreactivity in the goose

In the goose, alanine and arginine, intravenously or orally administered, act in the same way on pancreatic hormones; they both stimulate insulin and glucagon secretions. Conversely, whereas alanine treatment has no effect on plasma gut GLI, oral arginine stimulates gut GLI secretion. Since stimulation of gut GLI secretion does not occur with i.v. arginine, it may be assumed that this secretion depends on the intestinal transit of arginine and, as already described (Sitbon and Mialhe 1979), of glucose. The results, compared with studies on a similar species (duck) and on mammals, point out that i.v. infusion of alanine stimulates IRI and GLI secretions in the goose and not in the duck. In the same way, arginine i.v. infusion, contrarily to the observation made in the duck, is without effect on gut GLI secretion in the goose. Furthermore, insulin seems to be able to inhibit the alpha cell response to arginine infusion, as in mammals, whereas this is not the case in ducks.     

Superactive somatostatin analog decreases plasma glucose and glucagon levels in diabetic rats

The action of the new analog of somatostatin, D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160), on plasma glucagon and glucose levels was evaluated in streptozotocin-diabetic rats. The effect of this analog on the insulin-induced hypoglycemia in diabetic rats was also investigated in order to evaluate the risk of exacerbating hypoglycemia. Administration of analog RC-160, in a dose of 25 micrograms/kg b. wt. SC, inhibited plasma glucagon secretion and decreased plasma glucose levels. This effect also occurred when plasma glucagon and glucose levels were first elevated by arginine infusion, 1000 mg/kg/hr for 30 min. Subcutaneous injection of regular insulin, 15 U/kg b. wt., produced hypoglycemia with a progressive increase in glucagon levels. Analog RC-160 completely suppressed the hypoglycemia-induced glucagon release for up to 150 min after injection of the analog or insulin. A greater decrease in the plasma glucose level was observed in the group treated with insulin and the analog than in the group injected only with insulin. These results indicate that somatostatin analog RC-160 can produce a marked and prolonged inhibition of glucagon release and a decrease in the plasma glucose level in diabetic rats. This analog may be useful as an adjunct to insulin in the treatment of diabetic patients, although caution should be exercised, to prevent hypoglycemia when using somatostatin analogs together with insulin.     

Insulin and glucagon secretion in rats: effects of calcitonin gene-related peptide

Immunoreactive calcitonin gene-related peptide (CGRP) has been shown to occur in intrapancreatic nerves and islet somatostatin cells in the rat. Therefore, we investigated the effects of CGRP on insulin and glucagon secretion in the rat. CGRP was infused i.v. at one of 3 dose levels (4.3, 17 or 68 pmol/min). Infusion of CGRP alone was found to elevate basal plasma levels of both insulin and glucagon. In contrast, CGRP impaired the plasma insulin responses to both glucose (7 mg/min; P less than 0.001) and arginine (8.5 mg/min; P less than 0.001), and inhibited the arginine-induced increase in plasma glucagon concentrations (P less than 0.001). Since CGRP and somatostatin are colocalized within the D-cells, we also infused CGRP and somatostatin together at equimolar dose levels (17 pmol/min), with glucose (7 mg/min). By that, the increase in plasma insulin concentrations decreased more rapidly than during infusion of either peptide alone. Since alpha 2-adrenoceptor activation is known to inhibit glucose-stimulated insulin secretion, we also infused CGRP together with the specific alpha 2-adrenoceptor antagonist yohimbine (37 nmol/min). In that way, the plasma insulin-lowering effect of CGRP was prevented. We have shown in the rat: (1) that CGRP stimulates basal insulin and glucagon secretion; (2) that CGRP inhibits stimulated insulin and glucagon secretion; (3) that CGRP and somatostatin more rapidly induce a potent inhibitory action on glucose-stimulated insulin secretion when given together; and (4) that the alpha 2-adrenoceptor antagonist, yohimbine, counteracts the inhibitory action of CGRP on glucose-stimulated insulin secretion. We suggest that CGRP is of importance for the regulation of insulin and glucagon secretion in the rat. The mechanisms behind the islet effects of CGRP can not be established by the present results, though they apparently require intact alpha 2-adrenoceptors.     

Hormonal responses to intravenous glucose and arginine in patients with pancreatitis

19 subjects with an acute episode of pancreatitis, and 5 patients with chronic pancreatitis received intravenous glucose tolerance tests with measurement of glucose, insulin and glucagon. Patients recovering from acute pancreatitis demonstrated defects in their ability to dispose of a glucose load. 10 patients had overt glucose intolerance; of these, 4 were insulin-deficient, 3 had a loss of an acute insulin response to glucose, and 3 had marked hyperglucagonemia with normal to increased insulin levels. These abnormalities were seen in response both to intravenous glucose and intravenous arginine. Therefore, according to this study, at least three factors are clearly implicated in the production of glucose intolerance after an acute episode of pancreatitis: hypoinsulinemia, delayed insulin secretory response and hyperglucagonemia.     

An anti-insulin serum, but not a glucagon antagonist, alters glycemia in fed chickens.

Attempts at altering plasma glucose and, as a consequence, food intake were performed in fed broiler chickens by single i.v. injection of des-His1(Glu9) glucagon amide (a glucagon antagonist) or a non-stimulating anti-insulin serum. Plasma glucose level was not altered by des-His1(Glu9) glucagon amide but was rapidly and largely increased (for at least 2 h) by the injection of the insulin-immune serum. Hour and cumulative food intake were unaltered up to 10 h post injection. These results strongly suggest that in fed chickens, plasma glucose is mainly, if not exclusively, controlled by plasma insulin, and that the transient and heavy hyperglycemia evoked by inhibiting insulin action does not alter food intake.     

Insulin and glucagon family peptides in relation to activities of hepatic hexokinase and other enzymes in fed and starved Atlantic salmon (Salmo salar) and cod (Gadus morhua).

1. Plasma levels of insulin, glucagon, and glucagon-like peptide (Glp) were all reduced by starvation of salmon and cod. In the salmon the drop in Glp was larger than in insulin and glucagon. 2. After starvation the activity of hexokinase (EC 2.7.1.1) was increased in salmon liver, but decreased in cod liver. The salmon hepatic hexokinase activity was inversely correlated with the Glp/insulin ratio. 3. Activities of hepatic glycogen phosphorylase (EC 2.4.1.1) and phosphofructokinase (EC 2.7.1.11) were increased in starved as compared to fed salmon. In cod, starvation resulted in decreased or unchanged activity of phosphorylase. This discrepancy may be related to different degrees of environmental and handling stress. 4. Intraperitoneal injection of human insulin in salmon gave increased hepatic phosphorylase and hexokinase activities and reduced plasma levels of glucagon, Glp and endogenous fish insulin at sampling after 30 hr. 5. No differences in hepatic hexokinase activities or plasma hormone levels were observed between cod fed low and high carbohydrate diets. Apparently, regulation of glucose phosphorylation by dietary carbohydrate does not occur.     

Long-term administration of PACAP receptor antagonist, PACAP(6-27), impairs glucose tolerance and insulin sensitivity in obese diabetic ob/ob mice

Pituitary adenylate cyclase-activating peptide (PACAP) is a ubiquitous peptide of the glucagon superfamily that is involved in glucose homeostasis and regulation of insulin secretion. This study employed the PACAP receptor antagonist, PACAP(6-27) to evaluate the role of endogenous PACAP in genetic obesity-related diabetes and related metabolic abnormalities using ob/ob mice. Acute in vivo antagonistic potency of PACAP(6-27) was confirmed in ob/ob mice by blockade of the insulin-releasing action but not hyperglycaemia. In longer-term studies, ob/ob mice were given once daily injections of PACAP(6-27) or vehicle for 14 days. Feeding activity, body weight, basal plasma glucose and plasma insulin concentrations were not significantly affected by chronic PACAP(6-27) treatment. However, PACAP(6-27) treatment impaired glucose tolerance, insulin sensitivity and the glycaemic response to feeding. Plasma glucagon and lipids were unchanged. These observations indicate a role of endogenous PACAP for normal glucose homeostasis, but indicate a minor involvement in the regulation of insulin secretion in ob/ob mice.     

Increase by somatostatin of the arginine induced rise in blood glucose in untreated insulin requiring diabetics.

We have demonstrated previously that cyclic somatostatin (GH-RIH) exerts a diabetogenic action in healthy subjects. To further examine the impact of this phenomenon studies of blood glucose (BG), immunoreactive insulin (IRI), glucagon (IRG) and growth hormone (GH) were performed in insulin requiring diabetics (n = 6) receiving i.v. arginine (0.5 g/kg) both in the absence and presence of i.v. GH-RIH (500 microgram/h). The infusion of GH-RIH-resulted in a persistent diminution in plasma IRI, IRG and GH. BG fell during i.v. GH-RIH during the initial 30 min and was below control values up to 45 min after initiation of i.v. arginine, but subsequently exceeded control levels (p less than 0.05 - less than 0.025). The excess rise in BG occurred in spite of suppression by somatostatin of the ariginine induced release of IRG, IRI and GH. A fall in BG was seen following cessation of i.v. GH-RIH and during a rebound of insulin release with glucagon levels remaining in the basal range. These findings indicate a diabetogenic action of somatostatin also in insulin requiring diabetics as long as some residual capacity for insulin release is retained.     

Carbohydrate intolerance in gonadal dysgenesis: evidence for insulin resistance and hyperglucagonemia

To determine the pathogenesis of carbohydrate intolerance associated with gonadal dysgenesis, plasma glucose, insulin, glucagon, and growth hormone responses to oral glucose and intravenous tolbutamide, arginine and insulin were evaluated in 21 nonobese patients, 7-19 years old. Glucose intolerance was present in 9 of 21 nonobese patients (42.8%). Insulin levels, the area under the insulin curve after oral glucose and intravenous tolbutamide and the insulin to glucose ratio were significantly greater in patients than in controls (p less than 0.005). The decrease in plasma glucose following intravenous tolbutamide was significantly less in patients than in controls (p less than 0.05) despite insulin levels which were greater than in controls (p less than 0.05). After intravenous insulin, plasma glucose fell significantly less in patients than in controls (p less than 0.01). Plasma glucagon levels and the area under the glucagon curve after oral glucose and arginine infusion were significantly greater in patients than in controls (p less than 0.005 and p less than 0.01, respectively). The increase in glucagon after insulin-induced hypoglycemia was significantly less in patients than in controls (p less than 0.025). Fasting and stimulated growth hormone levels and the mean 24-hour growth hormone concentration were similar in patients and controls. These results indicate that glucose intolerance occurs frequently in gonadal dysgenesis and is associated with normal or increased insulin secretory responses. These abnormalities are probably due to insulin resistance and hyperglucagonemia. The decrease in insulin action does not appear to result from excessive growth hormone secretion or treatment with anabolic steroids or estrogen-progesterone medications.     

Factors influencing insulin and glucagon secretion in lean and genetically obese mice.

The control of insulin and glucagon secretion from isolated pancreatic islets of lean and genetically obese mice has been compared. The enlarged islets of obese mouse pancreas and islets of obese mouse pancreas and islets of obese mice maintained on a restricted diet manifested a greater response to glucose stimulation of insulin secretion than the lean mice islets. The glucagon content of the islets, the secretion of glucagon in a medium containing 150 mg% glucose and the stimulation of glucagon secretion by arginine did not differ significantly in the two groups. Adrenaline stimulated glucagon secretion in vitro from obese mice but not from lean mice. Antinsulin serum injections into obese mice increased the plasma glucagon levels about twofold and had no effect on glucagon levels in lean mice, although the level of hyperglycaemia was the same in both groups. It is suggested that the suppression of glucagon release by glucose requires a higher concentration of insulin in the obese mouse pancreas than in lean mice.     

Secretion of glucagon and insulin in hypophysectomized rats: effect of tolbutamide.

Normal and hypophysectomized (hypox) rats, fed ad libitum, received intraperitoneal injections of tolbutamide (75 mg/kg/day) or of saline for 6 weeks. 24 h after the last injection, blood samples were taken for glucose, insulin and glucagon determinations. In normal rats, tolbutamide treatment did not alter serum glucose, insulin and glucagon, although it suppressed the secretion of insulin and glucagon by the pancreatic islets. In hypox rats, tolbutamide decreased serum glucose and insulin, elevated serum glucagon and stimulated the secretion of glucagon, but not that of insulin by the pancreatic islets. In addition, tolbutamide treatment increased the glucagon response to arginine in normal, but not in hypox rats. The serum glucose response to arginine was decreased by tolbutamide treatment and by hypophysectomy and, thus, appeared independent of the glucagon rise or preexisting glucagon level. We conclude that tolbutamide treatment decreased the secretion of glucagon and insulin in normal rats and stimulated that of glucagon in hypox rats, perhaps because of the low levels of insulin in the serum and in the pancreas of the latter. Our results are compatible with the hypothesis that the pancreatic action of tolbutamide is influenced by the pituitary.