Effects of gonadal hormones on calcium-binding protein in chick duodenum.

The effect of the sex steroid hormones (estrogen, progesterone, and testosterone) and vitamin D₃, alone or in various combinations, on duodenal calcium-binding protein (CaBP) and wet weight was investigated in 7.5- to 10-wk-old female chicks. Chicks were either vitamin D-deficient or vitamin D-replete. Hormones were injected for 1, 2, 3, 4, or 8 days. The design in which injections were made for 8 days proved best for testing the effects of the gonadal hormones. Whereas neither diethylstilbestrol (DES, a synthetic estrogen), progesterone, nor testosterone, alone or in combination, could directly increase CaBP, DES did enhance the vitamin D-stimulated increase in CaBP in rachitic chicks. DES also significantly increased the CaBP levels in vitamin D-replete chicks, working, presumably, through endogenous vitamin D₃. Moreover, in 8-day treatments, DES increased duodenal weight. In contrast, testosterone did not augment the action of vitamin D in either vitamin D-replete or -deficient chicks. Although progesterone did not enhance the action of vitamin D in rachitic chicks, when administered for 8 days to vitamin D-replete chicks, it significantly increased CaBP levels, although to a much smaller extent than did DES. In vitamin D-replete chicks, concomitant administration of progesterone or testosterone inhibited the DES-induced increase in CABP levels. Hence the gonadal hormones appear capable of modulating the action of vitamin D in the regulation of CaBP concentration in the duodenum.