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Am J Physiol Endocrinol Metab 255: E272-E279, 1988;
0193-1849/88 $5.00
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AJP - Endocrinology and Metabolism, Vol 255, Issue 3 E272-E279, Copyright © 1988 by American Physiological Society

ARTICLES

[3H]rauwolscine binding to myometrial alpha 2-adrenoceptors in pregnant guinea pig

S. J. Arkinstall and C. T. Jones
Laboratory of Developmental Physiology, Nuffield Institute for Medical Research, University of Oxford, United Kingdom.

Uterine sympathetic nerves can exert an excitatory influence in late pregnancy and during parturition. Neuronal norepinephrine release is increased at these times and a diminished alpha 2-adrenoceptor-mediated prejunctional inhibition could account for this. To assess whether an altered receptor population may contribute, [3H]rauwolscine was used to measure alpha 2-adrenoceptors in myometrial membranes at time intervals throughout pregnancy. High affinity [3H]rauwolscine binding [Kd = 11.4 +/- 1.5 nM (n = 42)] yielded linear Scatchard plots that in nonpregnant myometrium indicated a maximum binding density (Bmax) of 217 +/- 42.4 fmol/mg protein. alpha 2-Adrenoceptor density was increased twofold at midpregnancy (31 days) and thereafter fell sharply by up to 90% toward term (67 +/- 2 days). When uterine growth is accounted for and data are expressed in terms of total myometrial population (uncorrected for plasma membrane recovery), alpha 2-adrenoceptor number was eightfold (midpregnancy) and fourfold (term) greater than the nonpregnant value of 804 +/- 322.4 fmol/uterus. alpha 2-Adrenoceptors were also found to bind dopamine with high affinity [Ki = 3.66 +/- 0.45 microM (n = 3)]. These observations could indicate a pregnancy-related change in uterine sympathetic autoinhibitory capacity and, since alpha 2-adrenoceptors appear also to be located postjunctionally, explain in part reports of altered myometrial responsiveness to norepinephrine infusion and also the uterotonic actions of dopamine.


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P. I. Adolfsson, I. Haug, G. Berg, and S. P.S. Svensson
Changes in {beta}2-adrenoceptor expression and in adenylyl cyclase and phosphodiesterase activity in human uterine leiomyomas
Mol. Hum. Reprod., September 1, 2000; 6(9): 835 - 842.
[Abstract] [Full Text] [PDF]


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