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Total immunoreactive glucagon (IRG) and immunoreactive glucagon of A cell origin (IRGa) were measured in the serum of normal, sham-operated and depancreatized rats, after the administration of three glucagon antagonists: insulin (5--200 mU/rat/h), somatostatin (SRIF; 100 microgram/kg/h) and antiglucagon serum (AGS, enough to bind three times the calculated total amount of circulating IRG). Since no differences were noted between the responses of normal and sham-operated animals, the values were pooled and used as controls. Pancreatectomy caused a significant increase in serum glucose, IRGa and total IRG and a significant decrease in serum insulin. AGS and SRIF significantly decreased serum glucose in control, but not in depancreatized rats, even though SRIF caused a significant decrease of IRGa in all animals. SRIF significantly decreased plasma insulin in control rats, but did not modify total IRG secretion in either groups. In control rats the minimum effective hypoglycaemic dose of insulin (5 mU/rat/h) may have decreased serum IRGa, but not total IRG. At higher doses (20 mU/rat/h) insulin stimulated glucagon secretion. In depancreatized animals, higher doses of insulin (200 mU/rat/h) were needed to lower serum glucose. On the other hand, a dose of 100 muU/rat/h was sufficient to lower the serum IRG. We conclude that although hyperglucagonaemia may contribute to the hyperglycaemia of the untreated depancreatized rats, the excessive secretion of glucagon is secondary to insulin insufficiency and that, at least in this animal model, the hypoglycaemic action of insulin is only minimally dependent upon its ability to suppress glucagon secretion.

Glucose, insulin (IRI), pancreatic (IRG) and total (GLI) immunoreactive glucagon were measured in the serum of normal hamsters and of hamsters with an insulin- and glucagon-secreting, transplantable insuloma. The tumor-bearing animals were hypoglycemic, hyperinsulinemic and hyperglucagonemic. The pancreatic islets of tumor-bearing animals secreted less glucagon and insulin in response to arginine or to changes in the glucose concentration of the medium, than did the islets of control hamsters. In addition, the introduction of glucose into the gastro-intestinal tract, which caused a significant rise in the serum GLI concentration of normal hamsters, failed to do so in the tumor-bearing animals. The results suggest that the high levels of serum glucagon and insulin induced by the tumor, suppressed IRI, IRG and GLI secretion in these animals.

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.

Some of the metabolites of arachidonic acid formed in the lipoxygenase and cyclooxygenase pathways stimulate insulin release. We studied the relative importance of each of these pathways in the modulation of glucose-induced insulin release by using inhibitors of arachidonate metabolism. Perfusion of the isolated rat pancreas with two chemically different inhibitors of cyclooxygenase, flurbiprofen and sodium salicylate, markedly inhibited prostaglandin E2 release, but had little effect on glucose-induced insulin release or on potentiation of insulin release caused by prior exposure to glucose. On the other hand, nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, not only inhibited both phases of glucose-induced insulin release but also abolished the potentiation effect. These effects of NDGA prevailed, when it was administered together with flurbiprofen, which caused profound inhibition of prostaglandin E2 release. We conclude that 1) lipoxygenase pathways play a dominant role in glucose-stimulated insulin release, and 2) endogenous lipoxygenase metabolites influence the potentiating effect of glucose on the release of insulin in response to a subsequent stimulation.

To assess the effect of the endocrine environment and, more specifically, of growth hormone and insulin on glucagon receptors, we studied 125I-glucagon binding to liver membranes in five groups of rats: (1) controls, (2) streptozocin (STZ)-treated, (3) tumor-bearing (growth hormone-producing, Mt-T-W15), (4) STZ-treated tumor-bearing, and (5) hypophysectomized rats. Glucagon binding was decreased in tumor-bearing, hypophysectomized, and STZ-treated rats. Basal and glucagon-stimulated cAMP levels were determined in isolated hepatocytes. The basal cAMP levels were increased in STZ-treated, tumor-bearing, STZ-treated tumor-bearing, and hypophysectomized animals. All groups responded and produced more cAMP in response to glucagon stimulation, although the maximal response was greater in STZ-treated, tumor-bearing STZ-treated, and hypophysectomized groups than in the controls. Our data confirm that hyperglucagonemia downregulates the hepatic glucagon receptors and suggest that insulin and growth hormone may play a stimulatory role in their regulation. The results also suggest that the downregulation of glucagon receptors is not directly correlated to the basal or glucagon-stimulated cAMP levels.

Enhancement of arachidonic acid metabolism results in increased insulin secretion. To determine which pathways of arachidonic acid metabolism were involved in this stimulation, we studied the effects of various inhibitors of arachidonate metabolism on arginine-induced insulin and glucagon secretion in the isolated, perfused rat pancreas. The release of PGE2 from the pancreas was monitored to document the efficacy of the inhibitory drugs. p-Bromophenacyl bromide, a phospholipase A2 inhibitor, diminished PGE2 release and significantly inhibited both the early and late phases of insulin and glucagon release in response to arginine. Flurbiprofen, a specific cyclooxygenase inhibitor, decreased the early phase of insulin release and inhibited both phases of arginine-stimulated glucagon secretion; these decreases were concurrent with a large inhibition of PGE2 release. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, at a dose of 10(-5) M did not affect PGE2 release, inhibited the early phase of insulin release, and did not modify glucagon secretion. The combination of flurbiprofen and nordihydroguaiaretic acid, although the most potent in inhibiting PGE2, lowered only the early phase of insulin and had no effect on glucagon secretion. We conclude that: (1) endogenous cyclooxygenase-derived metabolites of arachidonic acid promote insulin and glucagon release, (2) endogenous lipoxygenase products preferentially stimulate insulin release, and (3) phospholipase A2 activity has an intrinsic modulatory effect on insulin and glucagon secretion.

The ability of dispersed islet cells in a perifusion system to secret glucagon and insulin in response to physiologic stimuli was investigated. Normal hamster islets were isolated by collagenase digestion and the cells dispersed by sequential digestion with collagenase and trypsin. Following a 50-min period of equilibrium in buffer with high glucose concentrations (5.0 mg/ml), glucagon secretion was stimulated by glucopenia and subsequently, inhibited by increasing the concentration of glucose. The responsiveness to glucose inhibition was significantly less in dispersed islet cells than in intact islets. However, the dispersed islet cells showed significantly greater response to arginine. Glucagon secretion by dispersed islet cells was stimulated to tolbutamide and epinephrine but somatostatin had no effect. Dispersed islet cell preparations did not augment insulin secretion in response to glucose but did secrete more insulin in response to arginine. Intact islets secreted insulin in response to glucose but not arginine. We conclude that A cells in cell suspension do not need direct contact or an intact intra-islet environment in order to respond to glucose, arginine, epinephrine, or tolbutamide but the extent of response may be influenced by paracrine effects. However, paracrine relationships may be important in determining the response of B cells to secretagogues.

The release of glucagon from pancreatic and extrapancreatic sources was studied in normal rats and in rats carrying transplants of a MtT-W-15 tumor which secretes large quantities of growth hormone and prolactin. The tumor-bearing rats had high serum levels of A cell immunoreactive glucagon (IRGa), total immunoreactive glucagon (IRGT) and immunoreactive insulin (IRI) and an increased total glucagon and insulin content of the pancreas. Pancreatic islets isolated from tumor-bearing rats secreted more glucagon under basal conditions but did not respond significantly to low glucose stimulation. However, they contained more insulin per islet and secreted more insulin under basal and stimulated conditions. The serum IRGa response to arginine infusion in vivo was lower in the tumor-bearing than in the normal rats. The introduction of a 5% glucose solution into the small intestine caused similar increases in the level of serum IRGT in the two groups of rats. Thus, the tumor increased the total pancreatic glucagon content and basal secretion, blunted the A cell response to stimulation, but did not significantly alter the secretion of glucagon by the intestine. We attribute these responses to tumor-induced hypersomatotropinism although we cannot rule out an effect of the large amounts of circulating prolactin.

Much current neuropharmacological research describes drug site of action and effect in terms of rotational behavior in rats. Such studies at the National Institutes of Health led to the development of required instrumentation capabilities. The method developed for quantifying rotational behavior to the exclusion of other locomotor activity is presented. Such full turns counts can be output as mechanical counter inputs, computer inputs, user-selected time interval subtotals, summary totals, or a voltage proportional to cumulative count which provides turning-rate data when recorded on strip-chart. The latter two options are described herein.

Directional response biasing as a function of the recency of an interpolated act was examined on a lever device in a within-S design. The temporal occurrence of an interpolated act was systematically varied (5, 30, or 55 sec. after the criterion act) for three retention intervals (15, 40, and 65 sec.), and the location of the interpolated movement was held constant ± 40 deg. from the criterion position. Analysis of constant errors showed significant positive directional biasing for interpolated acts greater than criterion positions. Further analyses at the 40-and 65-sec. retention intervals supported a recency interpretation. As the retention interval increased, the positive constant error was maintained for interpolated acts with the same post-biasing interval, whereas constant error became increasingly negative as the post-biasing interval increased. Examination of variable error revealed a slight increase over time and no significant differences between directional conditions. The recency findings were discussed in terms of the view that reproduction of a criterion act is dependent on the relative decay states between the interpolated and criterion traces.