Growth inhibition and the regulation of cyclic AMP by the triphenylethylene anti-estrogen tamoxifen in the quail oviduct.

The aim of the present study was to investigate the regulation of cAMP by tamoxifen in quail oviduct. A single injection of tamoxifen to immature female quails induced a transient activation of adenylate cyclase. Enzyme activity began to increase 3 h after the injection, peaked at 6 h and then dropped to control level at 12 h. The same time-response curves were observed following the injection of estradiol benzoate or estradiol benzoate + tamoxifen. Moreover, adenylcyclase exhibited the same sensitivity to exogenous activators (guanylylimidodiphosphate and forskolin) in the different treated groups. Phosphodiesterase activity was left unchanged during the prereplicative period and cAMP concentration was significantly increased at 6 h (+ 44.3%). Then, cAMP concentration continued to increase (+ 73.8% at 24 h) while cAMP phosphodiesterase and adenylcyclase activities remained at control levels. Injected concurrently with estradiol benzoate, tamoxifen completely inhibited the growth promoting effect of estradiol. Tamoxifen also inhibited the activation of adenylcyclase and cAMP phosphodiesterase induced by the hormone alone during the proliferative phase of the tissue. Moreover, the combined treatment led to a sustained elevation of cAMP in the oviduct, whereas estradiol benzoate alone decreased the level of cAMP. These results and those of our previous studies showing a significant correlation between the growth inhibitory potency of triphenylethylene derivatives in vivo and their efficiency to inhibit calmodulin-dependent cAMP phosphodiesterase in vitro, strongly suggest that the differential regulation of cAMP levels by estradiol and tamoxifen is essential for the growth promoting or growth inhibiting activities of these molecules.

Effect of estrogen on adenosine 3'5',cyclic monophosphate in quail oviduct: possible involvement in estradiol-activated growth.

Previous studies have shown that estradiol indirectly stimulated the proliferation of oviduct epithelial cells in the quail. The present study was undertaken to investigate the effects of estradiol and other steroid hormones on the cAMP concentration. The ability of forskolin, a specific activator of the catalytic subunit of adenylate cyclase, to induce oviduct cell proliferation and specific protein synthesis (progesterone receptor) in the absence of estrogen was also tested. Administration of estradiol benzoate (EB) to immature female quails produced a transient surge in oviduct cAMP concentration. After EB injection, cAMP concentration increased by 36.7% after 6 h and returned to control values after 12 h. This rise in oviduct cAMP concentration preceded the beginning of DNA synthesis. The same effect was observed even in the absence of increased plasma estradiol, when the hormone was perfused through the hepatic portal vein. Estriol, estrone, and testosterone failed to elevate cAMP concentrations. After repeated EB injections, the oviduct cAMP concentration declined below the control value (-66% after 72 h). A similar drop in the cAMP concentration was observed in developing quails during the proliferative phase of the luminal epithelial and glandular cells. Administration of forskolin to immature female quail pretreated with EB rapidly increased the oviduct cAMP concentration, induced a burst of DNA synthesis, and shortened the prereplicative period. In addition, forskolin administration did not increase the progesterone receptor concentration. These results demonstrate that cAMP is involved in the mechanism by which estradiol indirectly stimulates oviduct epithelial cell proliferation in the quail. The events that may take place during the prereplicative period and the antiproliferative effect of progesterone through a sustained increase in the cAMP concentration in the oviduct are discussed.

Cyclic nucleotide phosphodiesterase activity in the quail oviduct: hormonal regulation and involvement in estrogen-induced growth.

A previous study has shown that cAMP was involved in estrogen-activated growth in the quail oviduct. The present study was undertaken to investigate the hormonal regulation of 3',5'-cyclic nucleotide phosphodiesterase activity in the oviduct. Tamoxifen, an antiestrogen compound, and 3-isobutyl-1-methylxanthine, an inhibitor of phosphodiesterase, were also used to determine the relationship between estradiol-induced cell proliferation and cAMP phosphodiesterase activity. Cyclic nucleotide phosphodiesterase was almost completely restricted to the cytosolic fraction (108,000 X g supernatant) of the quail oviduct homogenate. By affinity chromatography on immobilized calmodulin, we separated and partially characterized three different forms of the enzyme. They differed in their cyclic nucleotide specificities, kinetics, and sensitivity to calmodulin. In vivo, estradiol benzoate (EB) modulated crude cytosolic phosphodiesterase activity. cAMP and cyclic-GMP hydrolyzing activities increased between 12 and 48 h after a single injection of EB and then declined to return to control value by 96 h. Estrone, 17 alpha-estradiol, progesterone, and testosterone were ineffective, while estriol slightly increased cyclic-GMP hydrolyzing activity. When administered with EB, tamoxifen drastically increased oviduct cAMP concentration while it completely inhibited oviduct growth and the activation of cAMP phosphodiesterase induced by EB alone. Moreover, 3-isobutyl-1-methylxanthine produced a dose-dependent inhibition of oviduct cell proliferation when given with EB. These results demonstrate that the activation of cAMP phosphodiesterase after an injection of EB and the subsequent decrease in oviduct cAMP concentration are necessary for the epithelial cells to achieve their proliferative cycle.