We have described previously that oxytocin (OXT) increases the density of a2-adrenoceptors within the hypothalamus and amygdala in male and also ovariectomized rats. Since estrogens increase OXT release and binding to OXT receptors, and since estrogens also influence a2-adrenoceptors, the aim of this work was to investigate the role of estrogens on the oxytocin-a2-adrenoceptors interactions within the nucleus of the solitary tract (NTS), hypothalamus and amygdala.

Ovariectomized rats, implanted subcutaneously with pellets containing 0.01 mg of 17 b-estradiol or placebo, received injections of OXT (1 mg/kg) or saline during 10 consecutive days. Quantitative receptor autoradiography was performed for characterization of high affinity a2-adrenoceptors agonist binding using [3H] UK 14.304. The treatment with 17 b-estradiol significantly increased the affinity and the density of the a2-adrenoceptors agonist binding values compared with placebo treatment in NTS, hypothalamus and amygdala (two-way ANOVA: p<0.01 for 17 b-estradiol effect).

Oxytocin increases significantly the density of the a2-adrenoceptors agonist binding compared with saline animals in hypothalamus and amygdala (two-way ANOVA: p<0.01 for OXT treatment). However, two-way ANOVA statistical analysis did not show a significant interaction between the 17 b-estradiol and Oxytocin treatment.

These results demonstrated the effect of 17 b-estradiol in the binding characteristics of the a2-adrenoceptors in all the areas analysed and that the OXT-mediated effects in a2-adrenoceptors is not dependent on 17 b-estradiol. These results may be of relevance for a2-adrenoceptors mediated actions in the central nervous system. This work has been supported by MEC BFU2005-02241 and J. Andalucia SEJ 1323.