Genetic obesity and dietary sucrose decrease hepatic glucagon and insulin receptors in LA/N-corpulent rats

A catabolic and hypolipemic effect of glucagon has been described in normal animals. We therefore studied the role of glucagon in genetically obese, hyperlipemic rats. Twelve genetically obese hyperlipemic LA/N-cp/cp (corpulent) rats and 12 lean littermates were fed either 54% starch or 54% sucrose for 12 weeks. Plasma glucagon and insulin levels and glucagon and insulin binding to liver membranes were measured. Comparing all corpulent and lean animals regardless of diet, a significant (P less than 0.0001) phenotypical effect (cp/cp greater than lean) was observed in plasma insulin levels (464 +/- 54 vs 70.3 +/- 7.6 muu/ml, mean +/- SEM). Insulin binding (2.68 vs 16.1%/50 micrograms protein) and glucagon binding (25.6 vs 47.3%/50 micrograms protein) were both significantly lower (P less than 0.0001) in corpulent rats as compared to their lean littermates. Sucrose feeding had marginal effect on plasma insulin or insulin binding. It, however, decreased glucagon binding in corpulent rats but not in their controls. A significant negative correlation was observed between plasma insulin and insulin binding, while a positive correlation was seen for plasma glucagon and glucagon binding. A significant negative correlation was observed between plasma glucagon and lipogenic enzymes (glucose-6-phosphate dehydrogenase and malic enzyme) in liver and between glucagon binding and these enzymes. We propose that in these genetically obese rats, in addition to hyperinsulinemia, impaired glucagon activity as manifested by decreased glucagon binding to target cells may be an important contributor to the hyperlipemia and obesity. A further decrease in glucagon binding in rats fed sucrose indicates that sucrose, per se, may be an additional contributory factor.     

Effect of dietary carbohydrates on insulin and glucagon receptors in a new model of noninsulin-dependent diabetes-SHR/N-corpulent rat

A new congenic strain of rat, the SHR/N-corpulent, provides a good model for noninsulin-dependent diabetes and was used in the present study. Corpulent rats as compared to their lean littermates are obese, hyperlipidemic, and severely hyperinsulinemic, and show an age-dependent loss of glucose tolerance. Mild fasting hyperglycemia is seen only in corpulent rats fed sucrose. Since dietary sucrose is more lipogenic than starch and since insulin and glucagon are involved in lipid and carbohydrate metabolism, we studied the effect of the type of dietary carbohydrate on insulin and glucagon levels and their receptors in lean and corpulent SHR/N rats. A significant phenotypic effect was observed (corpulent greater than lean) on plasma levels of triglyceride, cholesterol, and insulin. Dietary sucrose increased these parameters in corpulent rats but not in lean rats. Insulin and glucagon binding to liver plasma membranes was lower in corpulent rats than in lean; decreases were due to fewer receptors without a significant change in affinity. Thus, in corpulent rats, in addition to hyperinsulinemia, fewer glucagon receptors and their failure to be regulated by plasma glucagon levels appear to contribute to the hyperlipidemia. Furthermore, the hyperglycemia observed in sucrose-fed corpulent rats may be due to extreme resistance to insulin despite lower plasma glucagon and fewer glucagon receptors.     

Role of endocrine pancreas in temperature acclimation

Role of endocrine pancreas in temperature acclimation in rats was investigated. Plasma glucagon level increased and insulin level decreased in cold-acclimated rats (CA). The reverse was observed in heat-acclimated rats (HA). In the pancreas there were no changes in glucagon and insulin in CA, but a decrease in glucagon and an increase in insulin were found in HA. Plasma insulin/glucagon molar ratio (I/G) declined in CA and rose in HA. Pancreatic I/G rose in HA. Acute cold exposure elevated plasma glucagon, but did not affect plasma insulin. Pancreatic glucagon, insulin and I/G were not influenced by acute cold exposure, while plasma I/G decreased. Plasma I/G was inversely correlated with both blood free fatty acids and glucose levels. These results suggest that endocrine pancreas is closely associated with metabolic acclimation to cold and heat through its regulation of the metabolic direction to catabolic phase in cold acclimation and to anabolic phase in heat acclimation.     

Increased glucagon receptors in chronically hypersomatotrophic and hyperglucagonemic rats

The effect of increased levels of growth hormone on glucagon binding by isolated hepatocytes and on the cellular cyclic AMP response to glucagon was evaluated in rats bearing growth hormone-secreting tumor (Mt-T-W15) and in rats treated with rat growth hormone. An increased binding, due to an increased number of receptors, was observed in both groups of animals. Glucagon binding did not correlate with plasma glucagon levels, suggesting a failure of down regulation, possibly due to an effect of growth hormone and insulin on the number of receptors. Tumor-bearing and growth hormone-treated rats had larger hepatocytes so that, when hormone binding was expressed in terms of square micrometer of membrane surface, it appeared decreased. When the tumor was removed the increase in the number of glucagon receptors per cell persisted, even though the average cell size returned toward normal. It is suggested that this retention of the receptors may have been the result of continuing hyperinsulinism. Basal cAMP levels were elevated in hepatocytes of tumor-bearing and growth hormone-treated animals, possibly due to cell hypertrophy. On the other hand, the maximum cAMP response to glucagon was not altered by the experimental procedures. A negative effect of insulin on cAMP accumulation may explain this apparent paradox. Indeed, hepatocytes isolated from rats following tumor removal, but with continuing hyperinsulinemia, had a lower maximum cAMP response, even though the glucagon binding per cell or per unit of cell surface was increased.     

Comparison of effects of decapitation and anesthesia on metabolic and hormonal parameters in Sprague-Dawley rats.

The modes of euthanasia by either anesthesia or by decapitation were compared by assessing several metabolic and hormonal parameters from plasma and hormone receptors from liver plasma membranes. Two different anesthetics were used. Compared to decapitation, euthanasia by anesthesia significantly increased plasma glucose and triglyceride levels but not plasma cholesterol. Plasma insulin was also significantly increased by anesthetics. No significant differences were observed in plasma glucagon levels or insulin and glucagon receptors from liver plasma membranes between rats euthanized by decapitation and anesthesia. Glucagon receptors were however, affected by dietary carbohydrates. It is concluded that in studies involving measurements of metabolic and hormonal parameters, the use of anesthesia is to be avoided for euthanasia and that decapitation should be the method of choice.     

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.     

Hormonal effects on fatty acid binding and physical properties of rat liver plasma membranes

Summary The fluorescent fatty acids,trans-parimaric andcis-parinaric acid, were used as analogs of saturated and unsaturated fatty acids in order to evaluate binding of fatty acids to liver plasma membranes isolated from normal fed rats. Insulin (10^–8 to 10^–6 m) decreasedtrans-parinaric acid binding 7 to 26% whilecis-parinaric acid binding was unaffected. Glucagon (10^–6 m) increasedtrans-parinaric acid binding 44%. The fluorescence polarization oftrans-parinarate,cis-parinarate and 1,6-diphenyl-1,3,5-hexatriene was used to investigate effects of triiodothyronine, insulin and glucagon on the structure of liver plasma membranes from normal fed rats or from rats treated with triiodothyronine or propylthiouracil. The fluorescence polarization oftrans-parinarate,cis-parinarate, and 1,6-diphenyl-1,3,5-hexatriene was 0.300±0.004, 0.251±0.003, and 0.302±0.003, respectively, in liver plasma membranes from control rats and 0.316±0.003, 0.276±0.003 and 0.316±0.003, respectively, in liver plasma membranes from hyperthyroid rats (p<0.025,n=5). Propylthiouracil treatment did not significantly alter the fluorescence polarization of these probe molecules in the liver plasma membranes. Thus, liver plasma membranes from hyperthyroid animals appear to be more rigid than those of control animals. The effects of triiodothyronine, insulin and glucagon addedin vitro to isolated liver plasma membrane preparations were also evaluated as follows: insulin (10^–10 m) and triiodothyronine (10^–10 m) increased fluorescence polarization oftrans-parinaric acid,cis-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene in liver plasma membranes while glucagon (10^–10 m) had no effects. These hormonal effects on probe fluorescence polarization in liver plasma membranes were abolished by pretreatment of the rats for 7 days with triiodothyronine. Administration of triiodothyronine (10^–10 m)in vitro increased the fluorescence polarization of trans-parinaric acid in liver plasma membranes from propylthiouracil-treated rats. Thus, hyperthyroidism appeared to abolish thein vitro increase in polarization of probe molecules in the liver plasma membranes. Temperature dependencies in Arrhenius plots of absorption-corrected fluorescence and fluorescence polarization oftrans-parinaric acid,cis-parinaric acid and 1,6-diphenyl-1,3,5-hexatriene were noted near 25°C in liver plasma membranes from triiodothyronine-treated rats and near 18°C in liver plasma membranes from propylthiouracil-treated rats. In summary, hormones such as triiodothyronine, insulin and glucagon may at least in part exert their biological effects on metabolism by altering the structure of the liver plasma membranes.     

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.     

Alpha-melanocyte stimulating hormone increases plasma levels of glucagon and insulin in rabbits

Intravenous injections of 25 and 2.5 micrograms alpha-melanocyte stimulating hormone (alpha-MSH) increased plasma levels of glucagon, insulin and free fatty acids in fasted and fed rabbits. 45 micrograms beta-melanocyte stimulating hormone (beta-MSH) had similar effects, whereas 22 micrograms gamma-2-melanocyte stimulating hormone (gamma-MSH) was inactive. The alpha-MSH-induced increases in the plasma levels of glucagon, insulin and free fatty acids were not inhibited by alpha- or beta-adrenergic blocking drugs. The alpha-MSH-induced increases in the plasma levels of insulin were, however, augmented by phentolamine (an alpha-adrenergic receptor blocking drug). The plasma levels of glucose were increased by 25 micrograms alpha-MSH in fed rabbits, only, and were decreased by alpha-MSH during alpha-receptor blockade. The acute in vivo effects of alpha-MSH and beta-MSH on the plasma levels of glucagon, insulin and free fatty acids were rather similar to those previously reported for corticotropin (ACTH). It is possible that the 4-10 ACTH sequence, present in alpha-MSH, beta-MSH and ACTH, but not in gamma-MSH, is a message sequence for the observed effects. However, ORG 2766, a 4-9 ACTH analogue, was inactive. The mechanism by which alpha-MSH increased the plasma levels of glucagon and insulin in rabbits remains to be determined. It is possible, that the effects were mediated by both a central nervous action and a direct action on the endocrine pancreas.     

Effects of acute sodium salicylate on the abnormal counterregulatory glucagon and epinephrine responses to insulin hypoglycemia in diabetic rats

Effects of acute sodium salicylate infusion on glucagon and epinephrine responses to insulin hypoglycemia were studied in streptozotocin diabetic and age-matched control rats. Sodium salicylate (50 mg/kg/h) was infused intravenously alone for 90 minutes and then with insulin in short-term (10-15 days post-streptozotocin) and long-term (80-100 days post-streptozotocin) diabetic as well as age-matched control rats to produce hypoglycemia. Sodium salicylate decreased basal plasma glucose in control and diabetic rats but increased basal plasma glucagon levels only in control rats. The infusion of sodium salicylate during insulin-hypoglycemia in control and short-term diabetic rats caused a significant increase in glucagon secretion. Long-term diabetic rats have impaired glucagon and epinephrine secretory responses to insulin-hypoglycemia. This defect was normalized by acute sodium salicylate infusion during insulin-hypoglycemia. However, indomethacin (5 mg/kg i.p.; twice at 18 hr intervals) improved, but failed to completely normalize the abnormal glucagon and epinephrine secretory responses to insulin-hypoglycemia in long-term diabetic rats. These results suggest that endogenous prostaglandins may play a partial role in the impairment of glucagon and epinephrine secretion in response to insulin-hypoglycemia in long-term diabetic rats.     

Effects of hypersecretion of growth hormone and prolactin on plasma levels of glucagon and insulin in GH3-cell-tumor-bearing rats, and the influence of bromocriptine treatment

Plasma levels of prolactin, growth hormone, glucagon insulin and glucose were measured in non-treated control rats, bromocriptine-treated control rats and GH3-cell-tumor-bearing rats with and without bromocriptine treatment. Bromocriptine treatment increased plasma levels of glucagon, insulin and glucose in control rats. Tumor-bearing rats had increased body weight and increased plasma levels of prolactin, growth hormone, glucagon, insulin and glucose. Bromocriptine treatment reduced body weight and decreased the plasma levels of prolactin, glucagon and insulin, as compared to non-treated tumor-bearing rats. The drug had no effect on plasma levels of growth hormone and glucose. These results indicate that, in GH3-cell-tumor-bearing rats, prolactin, glucagon and insulin are more sensitive to the action of bromocriptine than growth hormone.     

Effect of calorie restriction on skeletal muscle and liver insulin binding in growing rat

The effect of specific calorie deprivation was studied in meal-fed growing rats. It resulted in a 50% decrease in growth rate. Blood glucose and most non-essential blood free amino acid levels were depressed. Postprandial plasma insulin was decreased. With insulin ranging from 0.01 to 100 nM, insulin binding to crude Triton X-100 solubilized membranes from liver was higher in calorie restricted rats when compared with control rats. Wheat germ agglutinin (WGA) purified receptor preparations also exhibited higher insulin binding in liver from experimental group but the significance (P less than 0.05) was only visible with low insulin levels; both basal and insulin-stimulated tyrosine-kinase activity were left unchanged. In contrast, whatever the skeletal muscle insulin receptor preparation (enriched plasma membranes, crude Triton X-100 solubilized or wheat-germ agglutinin purified extracts) insulin binding was similar in control and calorie-restricted rats.     

Studies on the mechanism of action of acetazolamide in the prophylaxis of hyperkalemic periodic paralysis.

Levels of glycogen and cyclic 3′, 5′-adenosine monophosphate (cAMP) were determined in livers of rats treated with 10, 25, 50 or 100 mg/kg of acetazolamide (Diamox). When compared with livers of untreated rats, there were significant decreases in liver glycogen content and significant increases in cAMP levels at all doses of the drug. When liver slices were incubated in the presence of 10^?5 to 10^?3 molar acetazolamide, no difference was found between treated and untreated slices.Plasma insulin and blood glucose levels were also determined and it was found that although plasma insulin levels were significantly increased at all four doses of acetazolamide, blood glucose remained unchanged.These data suggest that acetazolamide induces glycogenolysis through an indirect mechanism dependent upon the release of some endogenous factor, e.g., glucagon or epinephrine, which, in turn, increases levels of cAMP. However, because insulin levels are increased, the increased glycogenolysis does not elevate blood glucose. Thus, it is suggested that acetazolamide stabilizes blood glucose levels while stimulating insulin secretion to potentiate the movement of potassium across muscle membranes and thereby correct the defect which causes attacks of hyperkalemic periodic paralysis.     

Effect of tetrahydrocurcumin on insulin receptor status in type 2 diabetic rats: studies on insulin binding to erythrocytes

Curcumin is the most active component of turmeric. It is believed that curcumin is a potent antioxidant and anti-inflammatory agent. Tetrahydrocurcumin (THC) is one of the major metabolites of curcumin, and exhibits many of the same physiological and pharmacological activities as curcumin and, in some systems, may exert greater antioxidant activity than curcumin. Using circulating erythrocytes as the cellular mode, the insulin-binding effect of THC and curcumin was investigated. Streptozotocin (STZ)-nicotinamide-induced male Wistar rats were used as the experimental models. THC (80 mg/kg body weight) was administered orally for 45 days. The effect of THC on blood glucose, plasma insulin and insulin binding to its receptor on the cell membrane of erythrocytes were studied. Mean specific binding of insulin was significantly lowered in diabetic rats with a decrease in plasma insulin. This was due to a significant decrease in mean insulin receptors. Erythrocytes from diabetic rats showed a decreased ability for insulin-receptor binding when compared with THC-treated diabetic rats. Scatchard analysis demonstrated that the decrease in insulin binding was accounted for by a decrease in insulin receptor sites per cell, with erythrocytes of diabetic rats having less insulin receptor sites per cell than THC-treated rats. High affinity (K d1), low affinity (K d2) and kinetic analyses revealed an increase in the average receptor affinity of erythrocytes from THC-treated rats compared with those of diabetic rats. These results suggest that acute alteration of the insulin receptor on the membranes of erythrocytes occurred in diabetic rats. Treatment with THC significantly improved specific insulin binding to the receptors, with receptor numbers and affinity binding reaching near-normal levels. Our study suggests the mechanism by which THC increases the number of total cellular insulin binding sites resulting in a significant increase in plasma insulin. The effect of THC is more prominent than that of curcumin.     

Oxytocin increases extrapancreatic glucagon secretion and glucose production in pancreatectomized dogs

Infusion of oxytocin into normal dogs increases plasma levels of insulin and glucagon and glucose production and uptake. To determine whether infused oxytocin also increases glucagon secretion from extrapancreatic sites, pancreatectomized dogs, off insulin for 18 hr, were infused with oxytocin and plasma glucagon, and glucose production and uptake were measured using the [6-3H]glucose primer-infusion technique. The diabetic dogs, in the control period, had elevated plasma glucose and glucagon levels, an increased rate of glucose production, and a relative decrease in glucose uptake (decreased clearance). Infusion of oxytocin (500 microU/kg/min) caused a rise in plasma glucagon and glucose levels, increased glucose production, and further decreased glucose clearance. It is concluded that oxytocin can stimulate secretion of extrapancreatic glucagon, which contributes to the increased glucose production.     

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.     

Decreased binding of insulin to its receptors in rats with hormone induced insulin resistance

Insulin and glucagon receptor binding was studied in purified liver membranes from rats made insulin resistant by implantation of an MtT pituitary tumor which secretes growth hormone, prolactin, and ACTH. Insulin binding to its receptors was decreased and correlated with the degree of insulin resistance. In contrast, binding of glucagon to its receptors was unchanged.     

Effects of bacterial endotoxin on protecting copper-deficient rats from hyperoxia

The administration of very low doses of bacterial endotoxin protects rats during exposure to hyperoxia and is associated with the induction of lung antioxidant enzyme activities. Copper-deficient rats have increased susceptibility to O2 toxicity, which may be related to their decreased lung superoxide dismutase activity (SOD) or decreased plasma ceruloplasmin concentrations. To determine whether endotoxin can protect against hyperoxia in this susceptible model, we exposed copper-deficient and control rats to a fractional inspiratory concentration of O2 greater than 0.95 for 96 h after pretreatment with 500 micrograms/kg of bacterial endotoxin or phosphate-buffered saline (PBS). Mortality in the copper-deficient and control rats given PBS and exposed to O2 for 96 h was 100%. Copper-deficient rats died significantly earlier during the exposure than controls. No mortality occurred in either group treated with endotoxin and hyperoxia despite the decreased activity of copper-dependent enzymes in the copper-deficient rats. Copper-deficient rats treated with endotoxin and exposed to hyperoxia did increase lung Cu-Zn-SOD activity, but activity remained below levels found in air-exposed controls. Mn-SOD activity was found to be induced above air-exposed controls in the copper-deficient rats treated with endotoxin and exposed to hyperoxia. Hyperoxic exposure resulted in a marked increase in plasma ceruloplasmin concentrations in the control rats, but no increases in ceruloplasmin occurred in the copper-deficient animals. Endotoxin protects copper-deficient rats from hyperoxia despite their decreased lung Cu-Zn-SOD activity, and decreased plasma ceruloplasmin.     

The relationship between glucagon receptors and metabolic profile in two strains of rats: Wistar-Furth and Sprague-Dawley

We studied glucagon and insulin binding to isolated hepatocyte receptors in Wistar-Furth (WF) and Sprague-Dawley (SD) rats, using 125I-labeled hormones. Hepatocytes from WF rats bound more glucagon than hepatocytes from SD rats. There were no differences in insulin binding. These observations prompted us to investigate other strain differences. Fasting and nonfasting serum glucose, glucagon, insulin, and growth hormone were measured. WF animals had a lower fasting glucose and higher fasting glucagon than SD animals, while SD rats had higher nonfasting insulin levels and a higher hepatic glycogen content. Total hepatic glucose production in response to glucagon (10(-8) M) was greater in WF than in SD rats, while glucagon-stimulated gluconeogenesis from alanine was the same in the two groups of animals. We concluded that the decreased glucagon binding does not play a significant role in the maintenance of serum glucose or in the gluconeogenetic response glucagon, and that neither these responses nor the serum glucagon levels appears to be correlated with the number of glucagon receptors. We conclude further that different animal strains of the same species may differ in their biologic responses.     

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.