![]() The addition of a hundred-fold excess of non-radioactive estradiol to the incubation medium reduced the 3H-estradiol in the nuclear fraction by 76%, while a hundredfold excess of aldosterone had no effect on nuclear content of estradiol. After rat kidney slices were incubated at 37° C for 45 min with 10 -9 M 3H-estradiol prior to preparation of subcellular fractions, a considerable amount of estradiol (1.5 × 10 -13 moles per mg of protein) was extracted from the purified nuclear fraction. A tenfold excess of non-radioactive estradiol reduced estradiol binding by 67% the same amount of estriol reduced binding by 45%, while a series of nonestrogenic steroids had no significant effect on binding. These estradiol receptor sites have an apparent K association of 6.1 × 10 10 liters/mole and a maximal binding capacity of 5.4 × 10 -14 moles per mg of cytosol protein. We here report the presence of renal estradiol receptor molecules in the cytosol fraction of rat kidney homogenates incubated at 4° C for 3.5 hr with 1 to 4 × 10 -9 M 3H-estradiol-17β. Such estrogendependent retention of sodium independent of mineralocorticoid secretion suggests the possibility of a direct effect of estrogens on the renal tubule. A 35% decrease in urinary excretion of sodium was produced when 17β-estradiol was administered to adrenalectomized male rats in doses of 40 µg/day. Estradiol renal receptor molecules and estradiol-dependent antinatriuresis.
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