Metabolic Control of Reproductive system by the brain

哺乳动物的生殖功能在禁食或营养不良的情况下受到抑制。本研究旨在探讨在上述条件下促性腺激素分泌的神经内分泌机制。胰腺葡萄糖激酶(GK)被认为是胰腺β细胞葡萄糖敏感单位的重要元件。我们用GK免疫组织化学和共聚焦显微镜观察了GK样免疫反应在大鼠脑内的解剖分布。我们在整个脑室系统的室管膜细胞、内皮细胞和许多5-羟色胺能神经元中发现了很强的GK样免疫反应。Gk阳性的室管膜细胞纤毛上有葡萄糖转运体(GLUT)2样免疫反应。在5-羟色胺能神经元中，GK样免疫反应见于胞浆及其突起。目前的结果提出了这样一种可能性，即这些GK样免疫阳性细胞构成了大脑中巨大的葡萄糖感知机制的一部分。此外，还研究了在糖尿病条件下，在补充或不补充胰岛素的情况下，脉冲性黄体生成素(LH)分泌的变化。未补充胰岛素的糖尿病羔羊的促黄体生成素分泌受到抑制。另一方面，长期补充胰岛素的糖尿病羔羊的促黄体生成素分泌是持续的。这一发现支持这样一种观点，即胰岛素和/或胰岛素依赖的葡萄糖可获得性变化调节了黄体生成素脉冲生成系统。

The reproductive functions are suppressed under fasting or malnutritional condition in mammals. The present study was performed to determine the neuroendocrinological mechanism by which the secretion of gonadtropins are regulated under above-mentioned condition.Pancreatic glucokinase (GK) is considered an important element of glucose sensing unit in pancreatic β-cells. We employed GK immunohistochemistry and confocal microscopy to examine the anatomical distribution of GK-like immunoreactivities in the rat brain. We found strong GK-like immunoreactivities in the ependymocytes, endothelial cells and many serotonergic neurons throughout the ventricular system. The Gk-positive ependymocytes were found to have glucose transporter (GLUT) 2-like immunoreactivities on the cilia. In serotonergic neurons, GK-like immunoreactivity was found in the cytoplasm and their processes. The present results raise the possibility that these GK-like immunopositive cells comprise a part of a vast glucose-sensing mechanism in the brain.The changes in pulsatile luteinizing hormone (LH) secretion under diabetic conditions, with or without insulin supplementation, was also investigated. LH secretion was suppressed in diabetic lambs without insulin supplementation. On the other hand, LH secretion was sustained in diabetic lambs with chronical insulin supplementation. The finding supports the contention that insulin and/or insulin-dependent changes in glucose availability modulate LH pulse generating system.