Plasma somatostatin turnover rate and hormonal responses to feeding in chronically cold-exposed sheep

Abstract

Ten crossbred wether lambs (44.9 ± 1.0 kg) were housed for 9 wk in either a thermoneutral (TN) (20 °C) or cold (CC) (0 °C) environment and fed a pelleted barley:soybean meal diet (19.6% crude protein) at 28.8 g d−1 kg−1. Environmental temperature significantly altered mean concentrations of free fatty acid (TN 0.32 mM, CC 0.43 mM; P < 0.02, SEM = 0.01), insulin (TN 2.06 ng mL−1, CC 0.68 ng mL−1; P < 0.03, SEM = 0.10), and glucagon (TN 0.27 ng mL−1 CC 0.20 ng mL−1; P < 0.05, SEM = 0.01) but had no effect on glucose, somatostatin, or growth hormone. Glucose (P < 0.001) and insulin (P < 0.001) concentrations increased, whereas free fatty acid (P < 0.001) and growth hormone (P < 0.001) concentrations decreased after feeding. Somatostatin concentrations did not change postprandially. Following an injection of somatostatin-14 (1.13 ± 0.08 μg kg−1 BW), plasma-free fatty acid concentrations increased (P < 0.001) within 2 min and remained elevated for 30–75 min. Somatostatin-14 injection caused a transient (5–7 min) decrease in plasma insulin in both environments and glucagon in the TN environment. Somatostatin had a longer half-life, slower turnover rate, and reduced metabolic clearance and secretion rate (P < 0.05) in the cold environment, but the reduced secretion rate resulted in no change in basal concentrations of somatostatin. Key words: Cold, feeding, somatostatin, sheep, metabolic clearance rate