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[125I]Insulin binding has been studied in two patients with extreme insulin resistance using cultured B-lymphocytes transformed with Epstein-Barr virus. A cell line from a female infant with leprechaunism had insulin binding which was decreased 90% below the lower limit of normal. Lymphocytes from a young woman with type A extreme insulin resistance (associated with acanthosis nigricans and virilization) had insulin binding which was 80% depressed. In both cases, the defect in binding resulted from a decrease in the number of receptors per cell. The remaining receptors had normal properties, including a normal affinity for insulin and a normal specificity for insulin analogs. Insulin binding in cultured lymphocytes from these two insulin-resistant patients was also inhibited normally by antibodies to the insulin receptor. Immunological assays using anti-receptor antibodies confirmed the conclusion that the number of receptors was decreased. Affinity labeling of the leprechaun insulin receptor with [125I]insulin demonstrated the existence of an alpha-subunit with apparently normal molecular weight (130,000 daltons). However, the number of receptor molecules per cell appeared reduced.

[125I]Insulin binding has been studied with cultured cells from an insulin-resistant patient with the Rabson-Mendenhall syndrome. Previously, this patient has been demonstrated to have decreased insulin binding to circulating blood cells. Similarly, [125I]insulin binding to cultured lymphocytes and cultured fibroblasts was markedly decreased. Whereas the decrease in [125I]insulin binding to cultured lymphocytes appeared to result from a decrease in receptor number in cultured lymphocytes, there appeared to be a reduction in the affinity of [125I]insulin binding to cultured fibroblasts. This discrepancy between the observations with the two cell types is a general phenomenon which has been described in patients with a variety of syndromes of extreme insulin resistance. It is possible that the interpretation of the studies with the fibroblasts is complicated by the confounding influence of receptors for insulin-like growth factors on the surface of those cells. If the number of insulin receptors is sufficiently reduced on fibroblasts from the patient with extreme insulin resistance, then the low level of residual [125I]insulin binding may involve primarily receptors for insulin-like growth factors, which bind insulin with relatively low affinity.

Hypoglycemia is known to stimulate human pancreatic polypeptide (hPP) secretion. To explore further the relationship between glucose availability and hPP release, we have examined the effect of tissue glucopenia induced by 2-deoxy-D-glucose (2-DG) on hPP plasma levels in normal subjects. As this glucose analogue activates the autonomic nervous system, we have also studied the influence of prior atropinization upon the hPP response to 2-DG. Moreover, we have tested the effects of iv epinephrine and norepinephrine on plasma hPP concentrations. Circulating glucagon was also measured. After the iv infusion of 2-DG (50 mg/kg), plasma hPP increased steeply from a fasting value of 104 +/- 24 pg/ml (SEM) to a peak of 2175 +/- 639 pg/ml at 45 min (P less than 0.01) and remained significantly elevated throughout the test. In contrast, prior injection of atropine (1 mg iv) lowered basal hPP levels and reduced conspicuously the hPP response to 2-DG. Epinephrine administration (6 micrograms/min for 60 min) did not significantly modify plasma hPP concentrations. However, 2 h after epinephrine withdrawal, circulating hPP showed a brisk elevation coinciding with the decline of glycemia to subbaseline values. During norepinephrine infusion (6 micrograms/min for 60 min), only a minor and transient increase of plasma hPP was found. Plasma glucagon rose significantly after 2-DG infusion, but this response was virtually absent in the atropine experiment. Whereas the well known glucagon tropic activity of epinephrine was evidenced, norepinephrine failed to exert an obvious effect on glucagonemia. Our data demonstrate that 2-DG induces a powerful stimulation of hPP secretion in normal subjects and suggest that this action is mediated in part, if not entirely, by the parasympathetic nervous system. On the other hand, a major role of the sympathoadrenal system in response of hPP to 2-DG or to hypoglycemia does not seem probable. Finally, the hyperglucagonemic effect of 2-DG seems also to be dependent on cholinergic transmission.

To study the possible implication of endogenous serotonin in the control of glucagon secretion in man, normal volunteers were subjected to alpha-cell stimulation before and after oral treatment with serotonin antagonists (cyproheptadine and methysergide) and with an inhibitor of serotonin synthesis (para-chlorophenylalanine, PCPA). After administration of cyproheptadine (16 mg daily, for two days) the glucagon responses to arginine (N=12) and to insulin-induced hypoglycemia (N=9) were more marked than in the control experiments (differences between maximal elevations: +165 pg/ml, P less than 0.0001, and +197 pg/ml, P less than 0.02, respectively). After methysergide treatment (9 mg daily, for two days), a potentiation of arginine-provoked glucagon secretion was also observed (+260 pg/ml, P less than 0.002; N=7). Similarly, after PCPA administration (2 g daily, for four days) the alpha-cell responsiveness to both aminogenic (N=12) and hypoglycemic (N=7) stimuli was enhanced (+108 pg/ml, P less than 0.05, and +164 pg/ml, P less than 0.05, respectively). Since glucagon secretion is potentiated by treatment with drugs which either antagonize serotonin action or inhibit its synthesis, the suggestion can be made that endogenous serotonin modulates alpha-cell function in man by acting as an inhibitor.

This work was undertaken to investigate the effect of somatostatin on intestinal glucagon-like immunoreactivity (GLI) secretion in man. In normal subjects GLI release is slightly stimulated by oral glucose while this sugar evokes a much greater GLI response in gastrectomized patients. Therefore, our study was performed in a group of such patients (N = 6). As expected, in the control experiments glucose ingestion elicited a clear-cut elevation of GLI plasma levels as measured with two antisera, 78J and R-8 (maximal peaks: 340% and 150% above basal values, respectively). Somatostatin infusion did not modify fasting GLI concentrations but completely abolished GLI response to glucose. Termination of the infusion was followed by a rebound of circulating GLI. The well-known suppressor effect of somatostatin on glucagon and insulin secretion was also detected. Finally, during somatostatin infusion the initial elevation of blood sugar after oral glucose, in the absence of insulin response, appeared considerably delayed. Our data demonstrate that somatostatin behaves as a potent inhibitory agent of GLI secretion in man. A retarding effect of somatostatin on glucose absorption is also compatible with our results.

In this work we have evaluated the effects of blood sugar changes on human pancreatic polypeptide (hPP) secretion in young, healthy subjects. Mean fasting hPP level was 74 +/- 5 (SEM) pg/ml (n = 53). Insulin-induced as well as tolbutamide-induced hypoglycemia clearly provoked hPP secretion (peaks: 1201 +/- 370 pg/ml, P = 0.03, and 520 +/- 112 pg/ml, P = 0.005, respectively). In contrast, the induction of hyperglycemia by intravenous glucose infusion (0.6 g/min) elicited a significant depression of circulating hPP (37-49% of basal values); discontinuing the infusion resulted in an increase of hPP concentrations (peak: 519 +/- 141 pg/ml, P = 0.018), which coincided with the decline of blood sugar to sub-baseline levels. Glucose as an intravenous bolus (0.33 g/kg) also induced a fall in plasma hPP. Glucose ingestion (1.75 g/kg) was followed by a small and short lived elevation of hPP (154 +/- 34 pg/ml at 15 min, P = 0.04) and by a marked rise during the late hypoglycemic phase of the test (538 +/- 168 pg/ml at 120 min, P = 0.028). Finally, after intravenous arginine, a delayed increase of hPP values was observed, occurring subsequently to the plasma glucose drop. The foregoing data indicate that experimental fluctuations in glycemia inversely affect hPP secretion. Nevertheless, this relationship does not necessarily mean that hPP should be directly implicated in glucose homeostasis.