Katakami H, Downs T R, Frohman L A
Department of Medicine, University of Cincinnati College of Medicine, Ohio 45267.
Endocrinology. 1988 Aug;123(2):1103-9. doi: 10.1210/endo-123-2-1103.
Possible inhibitory effects of somatostatin (SRIF) on GRF were studied by assessing spontaneous GH secretion and GRF content and release in adult male rats depleted of hypothalamic SRIF by anterolateral hypothalamic deafferentation (AHD) or electrolytic lesions in the medial preoptic area (MPO). Plasma GH levels were measured 7 days postoperatively every 20 min in conscious animals with indwelling iv cannulae. Median eminence SRIF was markedly reduced 8 days postoperatively in both AHD and MPO rats, as determined by immunohistochemistry and RIA (P less than 0.01). Although GRF immunoreactivity in the median eminence of AHD and MPO animals appeared well preserved immunocytochemically, hypothalamic GRF content by RIA was significantly decreased at 8 days (P less than 0.01). Spontaneous GH secretion was pulsatile in sham-operated animals. In contrast, basal GH levels in AHD and MPO animals were markedly elevated (P less than 0.01), and secretory pulses were absent. Intravenous injection of specific anti-GRF serum into MPO animals decreased the elevated plasma GH levels (P less than 0.01), indicating increased hypothalamic GRF secretion. GRF release from hypothalamic median eminence-arcuate nucleus complexes in vitro was significantly greater in AHD and MPO animals than in control animals 4 and 8 days postoperatively in response to 30 mM K+ (P less than 0.01), but not under basal conditions. These results suggest that hypothalamic medial preoptic area somatostatinergic neurons play a tonic inhibitory role in the regulation of GRF release and that GH hypersecretion observed after MPO and AHD is attributable to changes in both SRIF and GRF.
通过评估下丘脑前外侧去传入（AHD）或视前内侧区（MPO）电解损伤所致成年雄性大鼠下丘脑生长抑素（SRIF）缺失后的自发性生长激素（GH）分泌、生长激素释放因子（GRF）含量及释放，研究了SRIF对GRF可能的抑制作用。术后7天，对留置静脉插管的清醒动物每隔20分钟测量一次血浆GH水平。免疫组化和放射免疫分析（RIA）结果显示，术后8天AHD和MPO大鼠的正中隆起SRIF均显著降低（P<0.01）。虽然AHD和MPO动物正中隆起的GRF免疫反应性在免疫细胞化学上显示保存良好，但RIA检测显示术后8天下丘脑GRF含量显著降低（P<0.01）。假手术动物的自发性GH分泌呈脉冲式。相比之下，AHD和MPO动物的基础GH水平显著升高（P<0.01），且无分泌脉冲。给MPO动物静脉注射特异性抗GRF血清可降低升高的血浆GH水平（P<0.01），表明下丘脑GRF分泌增加。术后4天和8天，AHD和MPO动物下丘脑正中隆起-弓状核复合体在体外对30 mM K+刺激的GRF释放显著高于对照动物（P<0.01），但在基础条件下则不然。这些结果表明，下丘脑视前内侧区生长抑素能神经元在GRF释放调节中起紧张性抑制作用，且MPO和AHD后观察到的GH分泌过多归因于SRIF和GRF的变化。
