Pituitary Hormone Antagonism. ∗

It is known that certain hypophyseal extracts will inhibit the increase in the size of the ovaries of immature rats, which occurs when gonad stimulating extracts are administered. In a previous note (Leonard 1 ), it was stated that the growth hormone of the pituitary was not the inhibiting substance and it was suggested that a sex stimulating fraction or something associated with it, was the antagonistic agent. In further attempts to identify the inhibiting substance with known extracts of the pituitary, several gonad stimulating fractions and a thyroid stimulating fraction were used. The results obtained are reported here.

Antuitrin S† was injected subcutaneously into immature female rats of similar age and weight, in doses which produced ovaries weighing approximately 30 mg., in 5 days. Similar rats were treated for the same period with the same amount of Antuitrin S plus intraperitoneal injections of the several pituitary extracts to be tested for their inhibiting power. These were as follows: follicle-stimulating hormone (F.S.H.) and luteinizing hormone (L.H.) prepared from sheep pituitary (Fevold, et al. 2 ), luteinizing hormone from horse pituitary, unfractionated pregnant mare serum, follicle stimulating urine (F.S.U.) prepared by alcoholic precipitation, and thyroid stimulator from the Schering Corporation.‡ These preparations were all tested and found to be active.

It is quite expedient that the fraction to be tested for inhibition be given intraperitoneally rather than subcutaneously or otherwise the presence of the inhibiting substance may not be detected (Leonard 2 ).

The results of the experiments are summarized in Table I. It is readily seen that the luteinizing fraction prepared from sheep pituitary was the only one to give a complete and definite inhibition of ovarian growth. The follicle stimulating substances from pituitary or urinary sources failed; the pregnant mare serum, the thyroid stimulator and the luteinizing hormone from horse pituitary also failed.