Interstitial Cell Stimulation and Luteinization Under the Influence of Male and Female Hypophyses *

There have been numerous reports6' 7, 8, 12, 14, 15 that luteinization and interstitial cell development are both controlled by the luteinizing hormone (LH), but Evans and co-workers4' 5 have long maintained that the interstitial cells are controlled by an interstitial cell stimulating hormone (ICSH) fraction which is distinct from the LH fraction. Evans' theory more nearly explains the maintenance of interstitial cells and the absence of luteinization observed in experiments on parabiosis2 13 31 and sexual differences of the hypophyses.26 However, recently the investigators" 8, 16, 23, 30 who have been doing the most work with the chemistry of the gonadotropic hormones are agreed that ICSH and LH are identical and that the formerly divergent results arose from differences in the strains of rats used as test animals.9 17 It, therefore, became necessary to re-analyze the failure of luteinization under conditions which will maintain interstitial cells. This apparent discrepancy as it exists in experiments on parabiosis has been explained'0 as due to a difference in the threshold of the two tissues to ICSH in combination with FSH. It is the purpose of the present paper to show that interstitial cells are maintained under the influence of male hypophyses and of masculinized hypophyses of constant estrous females26 where the circulating LH is very low.