Twenty-four-hour resting prolactin levels in male rats: the effect of septal lesions and order of sacrifice.

Diurnal variation in resting prolactin levels was studied in male rats that were normal, sham-operated, or lesioned in the septal nuclei. Separate groups of rats were sampled by decapitation every 3 or 4 hours in two separate studies during a 24 h period consisting of 12 h light and 12 h dark. Male rats did not exhibit a significant diurnal variation in resting prolactin levels. A septal lesion had no effect on resting prolactin levels. Prolactin levels were found to be highly responsive to environmental disturbances and were subject to the effects of sequential sacrificing procedures. The possibility was raised that prolactin exhibits a diurnal variation in sensitivity to stress which varies as a function of circulating levels of corticosterone.