Inhibition of GH Releasing Factor (GRF)-lnduced GH Secretion by Intraruminal Infusion of Volatile Fatty Acids (VFA) in Sheep.

Abstract

Abstract. A VFA mixture solution containing acetate, propionate and butyrate (the molar ratio of acetate, propionate and n-butyrate = 61.7:24.3:14.0) was infused into the rumen at various rates (53.5, 107 and 214 ,umol kg-i mini) over 6 h to examine the effects on basal and growth hormone-releasing factor (GRF, 0.25 µg kg-i)-induced increase in secretion of GH, insulin, glucagon and somatostatin (SRIF) in five castrated male sheep. Intraruminal infusion of the VFA mixture into the 18-h-fasted animals at the rates of 53.5, 107 and 214 j mol kg-i min-1 finally raised the total intraruminal VFA concentration from 91.4 to 100.2 (P>0.05), 175.9 (P<0.05) and 234.5 (P<0.05) mmol 1-1, respectively. A preliminary experiment showed that an infusion rate of 107 jimol kg-i min-1 mimics the postprandial increase in ruminal VFA. The basal plasma GH concentrations (2 to 4 h after the start of VFA infusion) and the area under the profiles for GH release in response to the intravenous GRF injection, which was done 4 h after the start of VFA infusion, were significantly decreased by the VFA infusion rates of 107 and 214 µmol kg-1 min-1. Furthermore, the VFA infusion noticeably increased basal plasma concentrations of insulin, but it scarcely changed the basal levels of glucagon, SRIF and glucose. From these results we conclude that an increase in the ruminal VFA concentration, even within the physiological range, would suppress GH secretion from the ovine anterior pituitary, and that the postprandial rise in the ruminal VFA concentration may be one of the factors normally suppressing GH secretion in sheep. Although large quantities of volatile fatty acids (VFA) are produced from dietary carbohydrates by microbial fermentation in the rumen, to meet a large proportion of the requirements for energy and cause an increase in the secretion of metabolic hormones such as insulin and glucagon [1,7], little attention has been paid to GH secretion following feeding in ruminants.The results that have been published are conflicting [1,[8][9][10]. In our previous study [11], intravenous infusion of propionate or butyrate at rates of 3,10 and 30 pmol kg-i min-1,

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

“…The dose of GHRH (Peptide Research Institute, Osaka, Japan) was determined from our previous report (Matsunaga et al 1997), whereas the dose of GHRP-6 (Peptide Research Institute) employed was 10 times greater than that of GHRH, because the potency of GHRP for GH-releasing activity has been found to be 10-fold less than that of GHRH (Ohata et al 1997). The morning feed was given at 1000 h, but the afternoon feed was given after the final sample had been taken.…”

Autonomic regulation of plasma insulin, glucagon and growth hormone responses to feeding in sheep fed a diet supplemented with calcium propionate

“…In the present experiment, postprandial changes in plasma GH concentrations were not significant for the saline infusion experiment with the Prop diet, whereas for the propranolol and hexamethonium infusions plasma GH concentrations decreased (P < 0.05) after the initiation of feeding. Similarly, plasma GH concentrations were reduced by both feeding and intraruminal propionate administration (Bassett 1974;Trenkle 1989;Matsunaga et al 1997). Therefore, it may be difficult to show the effects of propranolol and hexamethonium infusions on GH release in this type of experiment.…”

“…Therefore, it may be difficult to show the effects of propranolol and hexamethonium infusions on GH release in this type of experiment. The response would be better assessed when GH release is accelerated by stimulants such as GH-releasing factor or aspartic acid (Trenkle 1989;Kuhara et al 1991;Matsunaga et al 1997).…”

“…La libération de l'insuline se fait par l'entremise de l'activation du système nerveux parasympathique, encore que dans nos travaux les réponses n'étaient pas significatives, alors que la libération du glucagon passe par l'activation, à la fois du système nerveux parasympathique (SNP) et par les (-récepteurs adrénergiques du système nerveux sympathique (SNS). Ces observations n'apportent aucun appui à l'hypothèse d'une éventuelle intervention du système nerveux autonome dans la régulation de la libération de GH.Mots clés: Système nerveux autonome, insuline, glucagon, hormone de croissance, propionate, moutonIn ruminants, volatile fatty acids (VFA) produced in the rumen may alter the release of insulin, glucagon and growth hormone (GH) (De Jong 1982;Istasse et al 1987;Matsunaga et al 1997). Propionate is the second most abundant VFA after acetate in the rumen and blood.…”

“…In ruminants, volatile fatty acids (VFA) produced in the rumen may alter the release of insulin, glucagon and growth hormone (GH) (De Jong 1982;Istasse et al 1987;Matsunaga et al 1997). Propionate is the second most abundant VFA after acetate in the rumen and blood.…”