A B S T R A C T The effects of insulin on the renal handling of sodium, potassium, calcium, and phosphate were studied in man while maintaining the blood glucose concentration at the fasting level by negative feedback servocontrol of a variable glucose infusion. In studies on six water-loaded normal subjects in a steady state of water diuresis, insulin was administered i.v. to raise the plasma insulin concentration to between 98 and 193 PU/ml and infused at a constant rate of 2 mU/kg body weight per min over a total period of 120 min. The blood glucose concentration was not significantly altered, and there was no change in the filtered load of glucose; glomerular filtration rate (CIN) and renal plasma flow (CPAH) were unchanged. Urinary sodium excretion (UNaV) decreased from 401±46 (SEM) to 213+18 iteq/min during insulin administration, the change becoming significant (P < 0.02) within the 30-60-min collection period. Free water clearance (CH2o) increased from 10.6±0.6 to 13±0.5 ml/min (P <0.025); osmolar clearance decreased and urine flow was unchanged. There was no change in plasma aldosterone concentration, which was low throughout the studies, and a slight reduction was observed in plasma glucagon concentration. Urinary potassium (UKV) and phosphate (Ui.V) excretion were also both decreased during insulin administration; UKV decreased from 66±9 to 21±1 Meq/min (P < 0.005), and UrV decreased from 504±93 to 230 ±43 Ag/min (P <0.01). The change in UKV was associated with a significant reduction in plasma potassium concentration. There was also a statistically significant but small reduction in plasma phosphate concentration which was not considered sufficient alone to account for the large reduction in UPV. Urinary calcium excretion (UCaV) increased from 126±24 to 200±17 ug/min (P < 0.01).These studies demonstrate a reduction in UNaV associated with insulin administration that occurs in the absence of changes in the filtered load of glucose, glomerular filtration rate, renal blood flow, and plasma aldosterone concentration. The effect of insulin on CH2o suggests that insulin's effect on sodium excretion is due to enhancement of sodium reabsorption in the diluting segment of the distal nephron.

A B S T R A C T The effect of 20 L-amlino acids upon pancreatic glucagon secretion has been studied in conscious dogs. Each amino acid was administered intravenously over a 15 min period in a dose of 1 mmole/kg of body weight to a group of four or five dogs. Pancreatic glucagon and insulin were measured by radioimnmunoassay.17 of the 20 amino acids caused a substantial increase in plasma glucagon. Asparagine had the most glucagonstimulating activity (GSA), followed by glycine, phenyl-

A B S T R A C r Suppression of pancreatic glucagon secretion by hyperglycemia is a characteristic of normal alpha cell function. However, in diabetic subjects, plasma glucagon is normal or high despite hyperglycemia. It seemed possible that the presence of glucose or its metabolites within the alpha cell might be essential for suppression of glucagon secretion, and that in diabetes an intracellular deficiency of glucose secondary to insulin lack might be responsible for the nonsuppressibility.The present study was designed to determine the effect upon glucagon secretion of blockade of glucose metabolism and of experimental insulin deficiency.Blockade of glucose metabolism was induced in dogs by administration of 2-deoxyglucose or mannoheptulose. A striking rise in glucagon was observed despite accompanying hyperglycemia and hyperinsulinemia, which, in the case of mannoheptulose, was induced by infusing crystalline insulin.To determine if insulin lack also causes paradoxical hyperglucagonemia, dogs were made severely diabetic by alloxan. Fasting glucagon levels ranged from 3 to 22 times normal despite severe hyperglycemia, and were quickly restored to normal by infusing insulin. Diabetes induced in rats by anti-insulin serum was also associated with significant elevation in plasma glucagon. However, diazoxide-induced insulin lack did not increase glucagon in dogs.It is concluded that normal suppression of glucagon secretion by hyperglycemia does not occur when glucose metabolism is blocked or when severe insulin deficiency is produced. It is suggested that normal glucose metabolism within the alpha cell may be an insulin-requiring process without which hyperglycemic suppression of glucagon release cannot occur.

Glucagon suppression by somatostatin reduces or abolishes hyperglycemia in dogs made insulin-deficient by somatostatin, alloxan, or total pancreatectomy. This suggests that the development of severe diabetic hyperglycemia requires the presence of glucagon, whether secreted by pancreatic or newly identified gastrointestinal A cells, as well as a lack of insulin. Glucagon suppression could improve therapeutic glucoregulation in diabetes.

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