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

Abstract

SUMMARY1. Blood samples were taken every 20 min (for at least 28 hr) from five castrate male and two anoestrus female ad libitum fed sheep. Analysis for plasma growth hormone (GH) showed that two of the males, on two occasions, had regular, although individually specific, patterns of GH secretion (peaks 35-5 hr). The other animals all had irregular patterns of GH release.2. Throughout the experiments, meal sizes and frequency were recorded and it was found that out of eighty spontaneous meals of at least 50 g, 57 (71 %) occurred in the hour after GH peaks, which accounted for 50 % of the total time. Furthermore, on twenty out of twenty-four occasions GH levels were found to be falling before the 'expected' feeding time when fresh food was offered and the animals normally consumed a large meal. The removal of the food from three of the males for 10 hr 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 hr. 3. We believe that these results show an association between GH secretion and meal feeding in sheep, and that GH secretion quickly responds to fasting. As GH levels fell before, or in the early stages of meals, this indicates a neural reflex in the inhibition of GH before a meal.

Intracerebroventricular infusion of leptin elevates the secretion of luteinising hormone without affecting food intake in long-term food-restricted sheep, but increases growth hormone irrespective of bodyweight

“…On the other hand, we have previously reported a lack of effect of leptin on plasma GH levels in normally fed ovariectomized ewes using a range of doses (1 µg/h-20 µg/h) or a variable time-span (3 days-1 week) (Henry et al 1999, I J Clarke, unpublished results). The effect of leptin in increasing GH secretion is not consistent with the supposed role of leptin as an 'adipostat' but corresponds to the reduction in food intake seen in the ad lib group, since plasma GH levels are generally increased with fasting (Driver & Forbes 1981). On the other hand, leptin increased GH levels in ad lib and food-restricted animals alike, thus dissociating the effects of leptin per se and reduced food intake.…”

Effects of short-term feed restriction on milk yield and composition, and hormone and metabolite profiles in mid-lactation Sarda dairy sheep with different body condition score

“…Growth hormone concentration ( Figure 10) was higher in L-BCS (2.71±1.72; mean±SD) than in H-BCS (1.89±1.00) ewes. Throughout sampling, average GH showed a peak at 52 h. An increase in GH due to food deprivation or undernutrition had been previously observed in different species (Atinmo et al, 1978;Driver and Forbes, 1981;McGuire et al, 1995), including lactating ewes. Even if the interaction between BCS and sampling was not significant, the GH pattern showed a marked peak only in L-BCS ewes.…”

Postprandial changes in plasma GH and insulin concentrations, and responses to stimulation with GH-releasing hormone (GHRH) and GHRP-6 in calves around weaning

“…Feeding commonly reduces plasma GH levels, as shown in sheep (Bassett 1974a,b, Driver & Forbes 1981, Trenkle 1989, Thomas et al 1991, Matsunaga et al 1998, calves (Moseley et al 1988) and humans (Merimee & Fineberg 1974, Ishizuka et al 1983, Jaffe et al 1998, although it seemed to increase with feeding in lambs (Driver & Forbes 1981), steers Open symbols indicate a significant difference from the prefeeding level. *P<0·05.…”