Journal article

Prolactin cycles in sheep under constant photoperiod: Evidence that photorefractoriness develops within the pituitary gland independently of the prolactin output signal

GA Lincoln, H Andersson, IJ Clarke

BIOLOGY OF REPRODUCTION | OXFORD UNIV PRESS INC | Published : 2003

Abstract

The present study investigated photorefractoriness in the prolactin (PRL) axis in hypothalamopituitary-disconnected (HPD) sheep exposed to prolonged long days. In experiment 1, HPD Soay rams transferred from short (8L:16D) to long (16L:8D) days for 48 wk to induce a cycle of activation, decline (photorefractoriness), and reactivation in PRL secretion were treated chronically with bromocriptine (dopamine-receptor agonist) or vehicle from the onset of photorefractoriness. Bromocriptine (0.01-0.04 mg kg-1 day-1; 12-24 wk of long days) blocked PRL release and caused a rebound response after the treatment, but it had no effect on the long-term PRL cycle (posttreatment PRL minimum, mean +/- SEM, 3..

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University of Melbourne Researchers