INCREASED DETECTION OF PROLACTIN BINDING OF RAT VENTRAL PROSTATE AFTER TREATMENT WITH DEXTRAN COATED CHARCOAL: EVIDENCE FOR A DIRECT DIHYDROTESTOSTERONE-PROLACTIN INTERACTION

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Abstract
The initial objective of this study was to determine the effect of pretreatment of membrane fractions with dextran coated charcoal (DCC) on specific prolactin (PRL) binding of rat prostate. Preincubation of 15,000 χ g and 100,000 × g pellets of adult male rat ventral prostate with DCC consistently increased PRL binding. DCC pretreatment failed to increase PRL binding in prostatic membranes from immature male rats (24–25 days old) and from adult male rats castrated 3 days previously. Prostatic PRL binding of immature rats was two-fold greater than that of intact adult rats,while orchidectomy reduced prostatic PRL binding by 40–50%. Scatchard analysis indicated that the increase in PRL binding of intact adult prostate membranes produced by DCC was due to an increase in the number of PRL receptor sites. The postpubertal decrease in prostatic PRL binding and effect of DCC in intact adult prostate suggested that substances of testicular origin inhibited PRL binding of prostatic membranes. Consequently, membranes from immature rat prostate and from adult animals were coincubated with selected sex steroid hormones to determine whether these compounds inhibited PRL binding activity. Dihydrotestosterone (DHT) at concentrations from 10 ng/ml to 10 μg/ml produced a dose-dependent decrease in PRL binding (13% to 24%),whereas testosterone and estradiol produced little or no inhibitory effect. The specific in vitro effect of DHT suggests that androgen might exert localized inhibition of prostatic PRL binding in addition to the well documented positive androgen-PRL interaction. This local inhibitory effect may be in part responsible for the postpubertal decrease in prostatic PRL binding. These studies also indicate that DCC pretreatment may be useful in removing endogenous substances which interfere with prolactin binding assay.

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