INHIBITION BY SEX STEROIDS AND THYROID SUBSTANCE OF LIGHT-INDUCED GONADAL DEVELOPMENT IN THE PASSERINE BIRD, ZOSTEROPS PALPEBROSA JAPONICA

Abstract

Estradiol and testosterone propionate inhibited the growth of the gonads and oviducts of the birds, Zosterops palpebrosa japonica. maintained on an increased daily light ration. Estradiol was more effective than testosterone propionate in this action. The inhibition seems to be due to the suppression of gonadotropin release from the anterior hypophysis, since the simultaneous administration of the gonadotropin from pregnant mare''s serum attenuated the inhibitory effects of the sex steroids on the gonads. The thyroid substance also inhibited the development of the ovaries and oviducts of the birds exposed to a lengthened daily illumination, but not the growth of the testes. The inhibition of the ovarian activities by the thyroid substance seems to be more ascribable to changes in metabolism caused by the extract, rather than to the inhibition of gonadotropin output from the anterior hypophysis. Failure in the growth of the oviducts shows inability of the ovaries to secrete estrogen.