Prolactin actions in the sheep testis: A test of the priming hypothesis

This study investigated whether prolactin (PRL) plays a priming role in the testis during the nonmating season and thereby facilitates gonadal reactiv ation. Sexually inactive Soay rams under long days were treated as follows: 1) group C (control) received vehicle, 2) group B received bromocriptine t o suppress PRL secretion, 3) group B + PRL received bromocriptine + ovine P RL to reinstate physiological levels of PRL (n = 5/group). Treatments were for 10 wk. The photoperiod was then switched to short days to reactivate th e reproductive axis. Testis diameter and sex skin coloration were recorded, and routine blood samples were collected to measure concentrations of FSH, inhibin A, and testosterone (T). At the end of the treatments, blood sampl es were collected every 10 min for 10 h to monitor LH pulses and the T-resp onse to exogenous LH, and a testis biopsy was collected to assess spermatog enic activity (bromodeoxyuridine [BrDU] method) and expression of PRL recep tor (reverse transcription-polymerase chain reaction and immunocytochemistr y). There were no significant differences between groups in spermatogenesis (BrDU index) or steroidogenesis (T-response), and no difference in the tim e taken to achieve full testicular redevelopment under short days. Testis d iameter and inhibin A were marginally increased in group B + PRL. Overall, this thorough experiment provides minimal support for the priming hypothesi s.