Squirrel and rhesus monkeys were given oral glucose (4 gm./kg.), intravenous glucose (0.4 gm./kg.), intravenous glucose and tolbutamide (0.4 gm./kg. glucose and 50 mg./kg. tolbutamide), or intravenous tolbutamide (15 and 50 mg./kg.). There was delayed disposal of the relatively large doses of orally administered glucose in squirrel monkeys, contrasted with rhesus monkeys. Differences in glucose metabolism between the two species were less apparent during the other tests. Concentrations of plasma -insulin were significantly lower in squirrel than in rhesus monkeys during all of the stimulatory tests, except during the infusion of the lower dose of tolbutamide, when levels in both were relatively low. In contrast, pancreatic islet morphology and concentrations of pancreatic insulin did not differ significantly between the two groups, suggesting that differences in plasma insulin concentrations during stimulatory tests might have been the result of differences in insulin secretory rates. In our group of squirrel monkeys, we could not recognize two populations with respect to any of the parameters studied.

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