Somatostatin-like immunoreactivity (SLI) was measured by RIA in the plasma of normal and severely alloxan diabetic dogs in the fasting state and after the administration of nutrients. The iv infusion of glucose for 6 h was associated with a small but significant decline in plasma SLI (162 ± 10 to 146 ± 9 pg/ml; P < 0.01). In nine alloxan diabetic dogs, the baseline SLI levels averaged 212 ± 16 pg/ml, significantly higher than normal (P < 0.005), and there was little or no change during glucose infusion. Intragastric glucose elicited only a small transient rise in SLI in normal dogs, while in the diabetic dogs, a significant change in SLI was not observed. Intragastric administration of casein hydrolysate to nine normal dogs was associated with a rise in plasma SLI from < 0.02). After a liver meal, SLI rose in normal dogs from 134 ± 7 to 190 ± 15 pg/ml within 30 min (P < 0.001) and in the diabetic dogs, it rose from 240 ± 20 to a 30-min level of 244 ± 33 pg/ml (P < 0.005). In normal dogs, a fat-protein meal elicited a rise from 160 ± 10 to a peak of 228 ± 21 pg/ml (P < 0.001), and SLI levels remained elevated for 6 h, while in the diabetics, the SLI rose from 230 ± 17 to 295 ± 28 pg/ml during the first 60 min but subsequently reached a peak of 64 pg/ml above the baseline. The mean incremental SLI during the first hour after the fat-protein meal was 254 ±41 pg/ml in the normal dogs and only 118 ± 22 pg/ml in the diabetic dogs (P < 0.05). In the normal dogs, iv glucose lowered the SLI response to the fat-protein meal, but in the diabetic dogs, an increase in the SLI rise was oserved. In the nondiabetic dogs, insulin infusion did not influence the basal SLI levels or meal-induced changes in SLI, whereas in the alloxan diabetic dogs, the postprandial increments of SLI were abolished by insulin after 180 min. It is concluded that in nondiabetic dogs 1) peripheral venous SLI levels decline during glucose infusion; 2) after the ingestion of low fat and high fat protein meals, SLI levels increase, but this is reduced by iv glucose; and 3) iv insulin does not influence the postprandial SLI response of nondiabetic dogs. In alloxan-diabetic dogs, 1) fasting SLI levels are significantly above normal; 2) after low and high fat protein meals, the rise in SLI is delayed but ultimately exceeds normal and is further increased by iv glucose; and 3) insulin lowers the postprandial SLI response in diabetic animals.
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