The enhanced responsiveness of hypophyseal DA receptors in female rats induced by repeated reserpine treatment is not due to decreased oestrogen secretion.
In a previous study we have demonstrated that repeated reserpine treatment markedly enhances the intrinsic activity of the partial dopamine (DA) agonist (-)-3-PPP (preclamol) on pituitary DA receptors in female rats. This effect was attributed to the DA-depleting action of reserpine. However, since reserpine may also decrease oestrogen secretion, and since this hormone is known to affect dopaminergic transmission, experiments with ovariectomized, oestrogen-replaced female rats were undertaken. Ovariectomized rats were administered a depot preparation of oestradiol valerate in a dose that, according to literature data, yields physiological or slightly supraphysiological plasma concentrations of oestrogen. In spite of this treatment, repeated reserpine administration was found to substantially increase the intrinsic activity of (-)-3-PPP, as well as that of the partial DA agonist TDHL (terguride), on female pituitary DA receptors. It was concluded that repeated reserpine treatment increases pituitary DA receptor responsiveness in female rats by depleting DA, rather than by decreasing oestrogen secretion.
Carlsson
M
M
Department of Pharmacology, University of Göteborg, Sweden.
Eriksson
E
E
D000818:Animals; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D008090:Lisuride / Q000031:analogs & derivatives; D010052:Ovariectomy; D010880:Piperidines / Q000494:pharmacology; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000187:drug effects / Q000378:metabolism*; D012110:Reserpine / Q000494:pharmacology*
D004967:Estrogens; D010880:Piperidines; D011954:Receptors, Dopamine; C006208:dironyl; D004958:Estradiol; D012110:Reserpine; C026539:preclamol; D008090:Lisuride