McShane T M, Petersen S L, McCrone S, Keisler D H
Department of Animal Science, University of Missouri, Columbia 65211.
Biol Reprod. 1993 Oct;49(4):831-9. doi: 10.1095/biolreprod49.4.831.
Chronic food restriction decreases secretion of LH as a result of inhibitory influences on secretion of LHRH. We have previously reported that neuropeptide-Y (NPY) may directly or indirectly mediate this inhibitory effect on LHRH secretion. In the study reported here, we tested the hypothesis that long-term food restriction suppresses tonic release of LH as a result of 1) an increase in biosynthetic activity of NPY neurons in the arcuate nucleus of the hypothalamus, 2) an increase in activity of neurons that secrete beta-endorphin, and 3) a decrease in biosynthesis of LHRH. To test predictions of the hypothesis, we compared levels of mRNA encoding NPY, proopiomelanocortin (POMC; the precursor peptide of beta-endorphin), and LHRH, as well as tonic secretion of LH in food-restricted and well-nourished ewe lambs. Ten ewe lambs were ovariectomized at 18 wk of age and randomly assigned to receive either 100% nutritional requirements (FED; n = 5), or 30% requirements (R; n = 5) between 18 and 25 wk of age. At 25 wk of age, blood samples were taken every 10 min for 6 h and assayed for LH. The tonic release of LH in R lambs was less than that of FED lambs. Hypothalami were collected 4 days after blood sampling and sectioned at 12 microns for use in in situ hybridization. Radiolabeled molecular probes specific for mRNAs encoding NPY, POMC, or LHRH were hybridized to hypothalamic tissue sections. Levels of NPY mRNA were 88% greater in R vs. FED lambs (p < 0.01), whereas levels of POMC mRNA were 52% lower in R vs. FED lambs (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
长期食物限制由于对促性腺激素释放激素（LHRH）分泌的抑制作用而降低促黄体生成素（LH）的分泌。我们之前报道过神经肽Y（NPY）可能直接或间接介导这种对LHRH分泌的抑制作用。在本文报道的研究中，我们检验了这样一个假设，即长期食物限制会抑制LH的持续性释放，其原因是：1）下丘脑弓状核中NPY神经元的生物合成活性增加；2）分泌β-内啡肽的神经元活性增加；3）LHRH的生物合成减少。为了检验该假设的预测结果，我们比较了食物限制组和营养良好的母羊羔羊中编码NPY、阿黑皮素原（POMC；β-内啡肽的前体肽）和LHRH的mRNA水平，以及LH的持续性分泌。10只母羊羔羊在18周龄时进行卵巢切除，并随机分配在18至25周龄期间接受100%的营养需求（FED组；n = 5）或30%的需求（R组；n = 5）。在25周龄时，每10分钟采集一次血样，共采集6小时，并检测LH。R组羔羊中LH的持续性释放低于FED组羔羊。在采血4天后收集下丘脑，并切成12微米厚的切片用于原位杂交。将编码NPY、POMC或LHRH的mRNA的放射性标记分子探针与下丘脑组织切片杂交。与FED组羔羊相比，R组羔羊中NPY mRNA水平高88%（p < 0.01），而POMC mRNA水平低52%（p < 0.01）。（摘要截断于250字）
