Fluctuations in basal levels and effects of altered nutrition on plasma somatostatin.

Abstract

Rapid oscillations in basal plasma levels of insulin, C-peptide, glucagon, and glucose in rhesus monkeys have been reported previously. We now report large minute-to-minute fluctuations in plasma somatostatinlike immunoreactivity (SLI) in undisturbed, chair-adapted, and chronically cannulated male rhesus monkeys. Plasma samples were drawn from eight monkeys at 1- to 2-min intervals for 30-40 min following an overnight fast. Large fluctuations in SLI levels with periods of 4.4-9.4 min/cycle and possibly secondary periods of 14-18 min/cycle with average amplitudes of +/- 23% relative to the respective mean SLI levels were observed both within a single experiment and across monkeys under basal conditions. No consistent relationship was found between SLI fluctuations and that of insulin or glucagon. When portal and central blood samples were drawn precisely simultaneously no consistent portal-central gradient was found. Patterns of fluctuations in central and portal SLI levels were not correlated. Overfeeding significantly increased insulin levels but did not alter SLI levels. After 5 days of food deprivation basal SLI levels were unchanged. These data indicate the need to exercise care in the interpretation of single samples in the measurement of plasma SLI levels. Somatostatin secreted into the blood under basal, unstimulated conditions appears to be unrelated to nutritional balance.