Vasopressin responses and receptors in the mesenteric vasculature of estrogen-treated rats.

The effect of treatment with estrogens on the biological activity of arginine8 vasopressin (AVP) in the in vitro perfused mesenteric vascular bed and on the binding characteristics of [3H]AVP on membranes prepared from the same vascular bed was studied. Female rats treated with estradiol (400 micrograms/24 h sc), compared with ovariectomized rats, had an increase in the maximum response to AVP (from 128 +/- 3 to 153 +/- 3 mmHg) in the perfused preparation and an increase in the density of AVP binding sites (from 402 to 732 fmol/mg protein) in the membrane preparation. In male rats, the injection of estradiol increased the maximum response to AVP (from 109 +/- 4 to 137 +/- 3 mmHg) and the density of AVP binding sites (from 289 to 519 fmol/mg protein). The effective concentration producing 50% of maximum response of AVP in the perfused preparation was higher in male than in female rats, while the Kd in the binding experiments was similar in the four experimental groups. Our results show that estrogens upregulate the number of AVP binding sites, leading to an increase in the pressor response to AVP in the rat mesenteric vascular bed.