Circulating leptin response to feeding and exogenous infusion of insulin in sheep exposed to thermoneutral and cold environments

Leptin has been shown to regulate feed intake and energy expenditure. Insulin stimulates leptin secretion in rodents, but its action on leptin secretion is still obscure in ruminants. If insulin stimulates leptin secretion in ruminants, circulating leptin concentrations may change during exposure to cold, because of fluctuating insulin secretion and action in the cold environment. The present experiment was designed to determine whether feeding or exogenous administration of insulin affects circulating leptin levels in sheep exposed to thermoneutral and cold environments. Suffolk rams that were shorn and fed a diet once daily were subjected to a thermoneutral (20 degrees C) or cold (0 degrees C) environment for at least 1 week. Overall mean concentrations of plasma leptin in the feeding experiment were lower (P