Changes in pituitary prolactin levels of female hamsters as a function of age, photoperiod, and pinealectomy.

Exposure of intact female hamsters to light:dark cycles of 1 h light alternating with 23 h darkness (LD 1:23) led to involution of the reproductive organs, a drop in prolactin levels within the anterior pituitary gland, and hypertrophy of the intrascapular brown fat. All of these changes were prevented if the animals were pinealectomized. Pituitary prolactin levels in control hamsters maintained in LD 14:10 cycles also decreased during the 8 week experimental period. Pituitaries of hansters killed at the end of the experiment contained about four-fifths less prolactin than those necropsied at the beginning of the study.