Abstract
Ovariectomized adult rats were cannulated via the left carotid artery. Three days later they were heparinized and connected via the cannula to a peristaltic pump for continuous withdrawal of blood. Concentrations of LH in 60 μl samples of whole blood collected at approximately 5 min intervals were determined by radioimmunoassay. Untreated rats, ovariectomized at least one month earlier, exhibited considerable fluctuation in plasma LH concentrations over a 6 hr period. Treatment of such rats with subcutaneous injections of estradiol valerate and progesterone at the time of cannulation resulted in a reduction and stabilization of plasma LH levels when measured 3 days later. A rapid increase in plasma LH levels invariably occurred following the injection of neutralized crude acidic extracts of rat hypothalamic tissue into the aorta of steroid-treated castrates but did not occur following the injection of similarly prepared extracts of cerebral tissue. LH contamination of the hypothalamic extracts, determined...
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