Effect of intramuscular norethisterone enanthate on compensatory ovarian hypertrophy in the rat.

Norethisterone enanthate (N.E.) administered in repeated intramuscular doses was found to bring about by and large a dose-related inhibition of compensatory ovarian hypertrophy (COH) which follows after the surgical removal of one ovary in adult rats. The relative inhibition in the responsiveness of the remaining ovary to compensatory gonadotrophic stimulation leading to the COH was of the order of 14.2, 19.0, 26.3, 25.0 and 42.0% with 0.25, 0.50, 1.0, 2.0 and 4.0 mg doses of N.E., respectively. The ED50 was calculated to be of the order of 7.0 mg. There was no effect of the treatment on the weight of the pituitary at any dose, whatsoever. However, the treatment was found to induce a significant increase in the weight of the uterus and the adrenals at higher doses (2.0 and 4.0 mg). The possibility of delineating the antigonadotrophic activity of activity of 'N.E.' from its contraceptive potential, vis-a-vis the dose employed, is discussed.