Photostimulated prolactin release in the turkey hen: Effect of ovariectomy and environmental temperature

Ambient temperature modulates prolactin (PRL) secretion in birds. It is not known whether this modulation directly affects the PRL controlling mechanism(s) or whether it indirectly influences them through the onset of sexual maturity and/or the onset of incubation behavior. These experiments were designed to investigate the effect of elevated (32°) and reduced (10°) ambient temperatures on PRL secretion. Somatically mature, ovariectomized female turkeys were used to avoid the confounding effects of reproductive stage, nesting, and egg stimuli on PRL secretion. Hens were ovariectomized 5 weeks before, on the day of, or 10 days after the inception of photostimulation. Temperature treatments included chronic exposure (5 weeks) to 32 or 10° and acute exposure (i.e., temperature was reversed from 32 to 10° or from 10 to 32° on or after the day of photostimulation). Chronic exposure to either 32 or 10° had no effect on the rise in serum PRL that followed photostimulation in both sham-operated controls and ovariectomized hens. Acute exposure to 10 or 32° altered the photoperiodically stimulated rise in plasma PRL. Birds switched from 10 to 32° showed a significantly greater PRL increase than birds shifted from 32 to 10°. Ovariectomy enhanced the PRL response to the gonadal stimulating photoperiod. The effect was most pronounced in hens photostimulated prior to ovariectomy. These findings suggest that ambient temperature and/or ovariectomy have a modulating effect on the PRL response to long days.