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Abstract. The effect of intravenous infusion of acetate, propionate and butyrate (0, 3, 10, 30 µmol kg-' min-1 over 40 min) on the secretion of growth hormone (GH), insulin and glucagon in response to growth hormone-releasing factor (GRF) injection (0.25 µg/kg, 10 min after the onset of acid infusion) was determined in six sheep. The intravenous injection of GRF caused a marked increase in plasma GH at every dose of each acid. The GH response to GRF was unaffected by an intravenous infusion of acetate. The basal plasma levels of insulin, glucagon and glucose were unchanged by acetate infusion. The infusion of propionate markedly suppressed the GH response to GRF in a dose-dependent manner. Propionate produced increases in plasma insulin, glucagon and glucose concentrations. Butyrate infusion also caused a significant attenuation of GRF-induced GH secretion. Butyrate infusion stimulated the secretion of both insulin and glucagon and caused hyperglycemia. After cessation of the infusion of propionate or butyrate plasma GH tended to increase again. Plasma somatostatin concentrations, which were measured only for the highest dose of butyrate, were unchanged during acid infusion, but increased on discontinuing the infusion. It is concluded that propionate and butyrate suppress GH secretion, while stimulating the secretion of insulin and glucagon in sheep.Key words: Growth hormone, Volatile fatty acids, Growth hormone-releasing factor, Sheep.( the rumen is metabolized in the rumen epithelium to produce ketone bodies and the remainder is oxidized in the liver [3]. Thus a basic role of VFA in ruminants is to meet a large proportion of their energy needs.In addition to the importance of VFA as an energy source for the animal, some attention has been paid to the effects of VFA on the secretion of metabolic hormones such as insulin and glucagon. Manns and Boda [4] first reported that butyrate and propionate injected intravenously enhanced insulin secretion in sheep. These observations have been confirmed by other workers [5]. Infusions of butyrate or propionate into the portal vein of sheep at rates producing portal plasma concentrations within the range observed after feeding caused increased insulin secretion, suggesting a

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,

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