Abstract
Summary
The present experiments indicate that urethane is a satisfactory anesthetic agent for electrophysiological studies on hypothalamic ovulatory mechanisms, provided that it is administered early in the morning of proestrus. However, if treatment is delayed until 11/2 hr prior to the beginning of the critical period, this drug will block ovulation.
Further studies demonstrated that progesterone would advance ovulation by 24 hr in 5-day cyclic rats when administered either subcutaneously or intravenously. The minimal intravenous dose for this effect was 50 μg in propylene glycol. In contrast, a dosage of 20-α-hydroxypregn-4-en-3-one, sixteenfold greater than the minimal effective dose of progesterone, failed to advance ovulation. Treatment of urethanized rats with progesterone did not depress hypothalamic ovulatory mechanisms. In these animals, intravenous administration of the steroid was more effective in advancing ovulation than was subcutaneous treatment.
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