Episodic growth hormone secretion in sheep in relation to time of feeding, spontaneous meals and short term fasting.

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Abstract
Blood samples were taken every 20 min (for at least 28 h) from 5 castrate male and 2 anestrus female ad lib fed sheep. Analysis for plasma growth hormone (GH) showed that 2 of the males, on 2 occasions, had regular, although individually specific, patterns of GH secretion (peaks 3.5-5 h). The other animals all had irregular patterns of GH release. Throughout the experiments, meal sizes and frequency were recorded. Of 80 spontaneous meals of at least 50 g, 57 (71%) occurred in the hour after GH peaks, which accounted for 50% of the total time. On 20 of 24 occasions GH levels started falling before expected feeding time when fresh food was offered and animals normally consumed large meals. The removal of the food from 3 of the males for 10 h during an experiment prompted an increase both in the size and frequency of the GH peaks. After re-feeding, GH levels immediately fell and remained low for 1-2 h. Results show an association between GH secretion and meal feeding in sheep, and GH secretion quickly responds to fasting. As GH levels fell before or in the early stages of meals, a neural reflex may be involved in the inhibition of GH before a meal.