The effect of thyrotropin releasing hormone (TRH) administered intramuscularly (im) on serum levels of prolactin (Prl) in ovariectomized (ovx) adult turkeys before and following the onset of photostimulation, before and during daily administration (im) of progesterone (P; 0.1, 0.4, or 1.0 mg/kg), estradiol benzoate (EB; 0.01, 0.1, or 0.2 mg/kg), or their combination (1.0 mg/kg EB + 0.1 mg/kg P) were studied. Ovariectomy reduced Prl levels in the serum of photostimulated turkeys, and blunted the Prl response to TRH administration. Progesterone treatment had no effect on basal serum Prl levels but the Prl response to TRH was higher in P-treated turkeys than in non-treated ovx turkeys. Basal serum Prl levels were higher (P < 0.05) in the EB-treated ovx turkeys than in the untreated birds. The Prl response to TRH in ovx EB-treated turkeys was greatly increased (P < 0.05). Progesterone treatment of EB-primed ovx turkey did not alter the basal levels of serum Prl or the Prl response to TRH administration. These results suggest that ovarian steroids may be responsible for the increased Prl secretion in the female turkey associated with laying.
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