Abstract: 464

PROLACTIN ACTIONS IN THE RAM TESTIS: TEST OF THE PRIMING HYPOTHESIS.

GA Lincoln¹ , J Brooks^{1 *}, HN Jabbour^{1 *}
MRC Reproductive Biology Unit, 37 Chalmers Street, Edinburgh, UK ¹

The aim was to establish whether prolactin (PRL) plays a priming role in the testis under long days (non-mating season) and facilitates gonadal reactivation induced by short days. Adult Soay rams (n=5/group) kept under long days (16L:8D) received 1) vehicle treatment (C); 2) bromocriptine for 10 wk (1 mg sc x 2 daily) (B); 3) bromocriptine (as above) + oPRL (5 mg sc x 2 daily) for 10 wk (B+P). After treatment stopped photoperiod was switched to short days (8L:16D) to reactivate the reproductive axis. Blood samples were collected twice weekly to measure circulating concentrations of PRL and FSH, and testicular diameter and sex skin coloration were measured to provide an on-line index of gonadal activity. On one occasion (wk 10), serial blood samples were collected to study pulsatile LH/testosterone secretion, and a testicular biopsy was collected to assess spermatogenic activity (bromo-deoxyuridine method) and expression of PRL receptor (PRLR; RNase protection assay and immunocytochemistry). The treatments produced marked differences between groups in the blood plasma concentrations of PRL for 10 wk (mean PRL: 74.5±8.1, 5.9±1.0 and 119.4±6.2 ng/ml, C, B, B+P respectively, P<0.001). There were no significant differences between groups in pulsatile LH/T secretion, testicular diameter, spermatogenic activity or testicular PRLR expression; in all groups PRLR expression was localised to germ and Leydig cells. There were no differences between groups in timing and magnitude of the gonadotropin/gonadal response to short days. The rigorous experiment thus failed to support the priming hypothesis.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.