CONTROL OF PITUITARY HORMONE SECRETION BY RUMINAL VFA IN THE RUMINANT.

饲喂（苜蓿干草袋，体重的2%）立即引起基础生长激素（GH）浓度的显著和持续降低，但提高了基础催乳素（PRL）浓度。GRF或TRH引起GH或PRL分泌的剂量依赖性升高。喂养显著降低了grf诱导的GH分泌，但trh诱导的PRL分泌没有变化。将VFA混合物（乙酸：丙酸：丁酸摩尔比=75:19:6,pH4.5）输注到瘤胃中，其输注速率（100mumol/kg/min）很好地模拟了餐后瘤胃VFA总浓度的变化，导致基础和grf诱导的GH分泌显著减少，但PRL分泌没有变化。由此得出结论：1)饲粮减少生长激素的分泌，这可能是由餐后瘤胃VFA浓度升高引起的；2)然而，瘤胃VFA的增加不影响绵羊PRL分泌。这些结果也表明来自瘤胃的信号，虽然详细的途径尚未确定，但具体控制构成垂体前叶的单个分泌细胞。

Feeding (lucerne hay cuges, 2% of body weight) promptly caused a significant and sustained reduction of basal growth hormone (GH) concentrations, but it raised the basal prolactin (PRL) concentrations. GRF or TRH caused a dose-dependent rise in GH or PRL secretion. Feeding significantly reduced GRF-induced GH secretion, but it caused no changes in TRH-induced PRL secretion. The VFA mixture infusion (the molar ratio of acetate : propionate : butyrate=75 : 19 : 6, pH4.5) into the rumen, the infusion rate (100mumol/kg/min) of which well mimiced the postprandial change in the total ruminal VFA concentrations, caused a significant decrease in basal and GRF-induced GH secretion, but no changes in PRL secretion. From these results it is concluded that 1) feeding reduces the secretion of GH,which should be caused by a postprandial rise in ruminal VFA cncentrations ; 2) however, an increase in ruminal VFA never affects the PRL secretion in sheep. These results also suggest that the signals from the rumen, altough the detailed pathways are not difined yet, specifically control the individual secretory cells composing the anterior pituitary.