A developmental study of adenohypophyseal dopaminergic receptors and of haloperidol-induced prolactin release in rats

Abstract

The ontogenesis of adenohypophyseal dopamine receptors, assessed by haloperidol-displaceable [3H]didydroergocryptine (DHE) binding of 1-, 12-, 20-, 28-day-old female rats was studied in correlation with the prolactin releasing effect of haloperidol (1 mg/kg), a dopaminergic antagonist. A specific dopaminergic receptor could be quantified at the time of birth (Bmax = 2.5 +/- 0.5 fmol/mg; Kd = 1.5 +/- 0.2 microM), anterior pituitary receptor density (fmol bound/mg) increased non-significantly henceforth and a slight ontogenic increase of Kd values was also observed. Haloperidol failed to increase prolactin in newborn female rats; at 4 days, a significant increase was evidenced, and from then onwards the response rose markedly with age. As sex differences in the dopaminergic modulation of prolactin release have been documented, the hyperprolactinemic effect of haloperidol in correlation with [3H]DHE binding in anterior pituitary of 28-day-old female and male rats was studied. Though the prolactinemic increment achieved by haloperidol was significantly higher in female than in male rats, [3H]DHE binding was not statistically different between sexes. These data indicate: (a) a specific binding site for [3H]DHE in anterior pituitary of female rats is present from the first postnatal days. From then onwards, a gradual but slight increment in both, Bmax and Kd for the dopaminergic agonist is observed until puberty; (b) at 28 days, no clear difference in Bmax and Kd is present in [3H]DHE binding between male and female rats; (c) by contrast, haloperidol shows a prolactin releasing effect that increases markedly with age in the female.(ABSTRACT TRUNCATED AT 250 WORDS)