Abstract

Control injections of saline ip or into the third ventricle (2 fil) failed to modify concentrations of GH or TSH in plasma of conscious, free-moving, ovariectomized (OVX) or OVX, estrogen- and progesteronetreated (OEP) rats. Intraventricular injection of y-aminobutyric acid (GABA) in doses ranging from 0.1–8 fimol induced a rapid elevation in plasma GH within 10 min of injection which was dose related and the elevation persisted for the 60-min duration of the study in both OVX and OEP rats. This effect was completely blocked by the GABA antagonist, bicuculline, which by itself had no effect on plasma GH in doses of 1 or 2 /imol ip. By contrast, GABA administration lowered plasma TSH, which became apparent within 10 min in OVX rats and persisted for the duration of the experiment and appeared to be dose related at the initial sampling time of 10 min. The inhibitory effect of GABA was lessprominent in OEP rats. Bicuculline, which by itself had no effect on plasma TSH, completely blocked the inhibtory effect...

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