The effects of in vivo treatment with estrogen and progesterone on isoproterenol-induced uterine relaxation and beta(2)-adrenoceptor (beta(2)AR) mRNA production in non-pregnant rat myometrium were investigated. Whether homologous myometrial desensitization of beta(2)AR function was dependent on or modulated by the two steroids was also examined. Estrogen treatment alone or in combination with progesterone reduced maximal relaxation (E(max)) of isolated uterine strips subsequently challenged with isoproterenol whereas progesterone alone had no effect on this parameter. The reduction was accompanied by an enhanced beta(2)AR mRNA concentration. The concentration of isoproterenol giving half-maximal relaxing response (EC(50)) increased following estrogen treatment and this effect was curbed by progesterone. Isoproterenol had no effect on beta(2)AR transcription irrespective of the steroid regimes employed. E(max) of isolated uterine strips was reduced following prolonged in vivo treatment with isoproterenol but the effect was found only when estrogen alone was administered concomitantly. Finally, in vivo treatment with isoproterenol increased EC(50) of uterine strips subsequently stimulated with isoproterenol in vitro. This effect was independent of steroid treatment. We conclude that homologous desensitization of beta(2)AR function in non-pregnant rat myometrium in terms of sensitivity (EC(50)) is independent of sex steroids but in terms of maximal response (E(max)) occurs only in the presence of estrogen. We speculate whether progesterone withdrawal in connection with the well-known estrogen dominance at rat parturition may strengthen the desensitization induced by beta(2)AR activation and thus contribute to the transformation of the uterus from a quiescent to a highly contractile organ.

This article has been cited by other articles:

				E. K. Sissom, C. D. Reinhardt, J. P. Hutcheson, W. T. Nichols, D. A. Yates, R. S. Swingle, and B. J. Johnson Response to ractopamine-HCl in heifers is altered by implant strategy across days on feed J Anim Sci, September 1, 2007; 85(9): 2125 - 2132. [Abstract] [Full Text] [PDF]

				R. Gaspar, E. Ducza, A. Mihalyi, A. Marki, Z. Kolarovszki-Sipiczki, E. Paldy, S. Benyhe, A. Borsodi, I. Foldesi, and G. Falkay Pregnancy-induced decrease in the relaxant effect of terbutaline in the late-pregnant rat myometrium: role of G-protein activation and progesterone Reproduction, July 1, 2005; 130(1): 113 - 122. [Abstract] [Full Text] [PDF]

				K. W. L. Kam, J. S. Qi, M. Chen, and T. M. Wong Estrogen Reduces Cardiac Injury and Expression of {beta}1-Adrenoceptor upon Ischemic Insult in the Rat Heart J. Pharmacol. Exp. Ther., April 1, 2004; 309(1): 8 - 15. [Abstract] [Full Text]

				B. Chanrachakul, B. Matharoo-Ball, A. Turner, G. Robinson, F. Broughton-Pipkin, S. Arulkumaran, and R. N. Khan Reduced Expression of Immunoreactive {beta}2-Adrenergic Receptor Protein in Human Myometrium with Labor J. Clin. Endocrinol. Metab., October 1, 2003; 88(10): 4997 - 5001. [Abstract] [Full Text] [PDF]