Effect of Norethynodrel on the Ovarian Response of the Immature Rat to Gonadotrophic Stimulation

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Abstract
Treatment of intact immature rats with heavy doses of a purified preparation of norethynodrel (containing ca. 0.17% of ethinyl estradiol-3-methyl ether) did not inhibit, and may have marginally enhanced, ovarian sensitivity to exogenous gonadotrophic stimulation (PMS and CG). The ovarian response observed after combined treatment with norethynodrel and gonadotrophins was slightly greater than that following gonadotrophins alone, possibly as the result of the residual estrogen content of the preparation. Injected by itself, norethynodrel was sufficiently estrogenic to induce precocious opening of the vagina, vaginal cornification and uterine growth. Several factors are discussed that may have influenced these findings and, without affecting their validity, complicated their interpretation. It is concluded that employment of hypophysectomized instead of immature intact animals would have eliminated only one of these factors.