EFFECTS OF ESTRADIOL ON NOREPINEPHRINE-INDUCED CONTRACTION, ALPHA-ADRENOCEPTOR NUMBER AND NOREPINEPHRINE CONTENT IN THE FEMALE RABBIT URETHRA

  • 1 January 1984
    • journal article
    • research article
    • Vol. 229  (2) , 557-563
Abstract
Estrogen treatment increases the reactivity to catecholamines of various tissues. Estrogen treatment caused an increased sensitivity to norepinephrine (NE) of the isolated female rabbit urethra. There was a 3-fold shift to the left of the concentration-response curve for longitudinal tension in perfused urethras and for tension in urethral ring preparations. Possible mechanisms for this increase in sensitivity were investigated by studying radioligand binding to the .alpha.-adrenoceptors and by measuring the NE content of the urethras. Using [3H]dihydro-.alpha.-ergocryptine as a marker for .alpha.-adrenoceptors, a more than 2-fold increase in the receptor number was found after estrogen treatment. This may be attributable to a selective increase in the number of .alpha.-2 adrenoceptors. No significant change was found in the affinity of [3H]dihydro-.alpha.-ergocryptine to the receptor. The total NE content in the urethra was not changed by estrogen treatment. If calculated per mg wet wt, the NE content was reduced to half in estrogen treated animals. Evidently in the rabbit urethra the estrogen-induced increased sensitivity to the contractant effects of NE, at least in part, is attributable to an increase in the number of postjunctional .alpha.-2 adrenoceptors.