Influence of short photoperiods on reproductive organs and estrous cycles of normal and pinealectomized female Djungarian hamsters, Phodopus sungorus.

This study was designed to analyze morphological changes in the reproductive organs and endocrine changes in the serum and pituitaries of female Djungarian hamsters during regression, the period of involution and early spontaneous recrudescence in response to short photoperiods. In addition, the involvement of the pineal gland on the inhibitory response to short photoperiods was investigated. In the first study, 63 adult female hamsters were divided into five groups, which were either pinealectomized at the time of transfer or 11 wk after transfer into short photoperiods, or exposed to different light regimens. The estrous cycles of these hamsters were recorded by vaginal smears for a period of 34 wk. In a second study, 156 adult female hamsters were divided into 14 groups and maintained under the influence of long or short photoperiods for 0-33 wk. The animals were killed by decapitation at 3-wk intervals and analyzed for changes in body weight and morphology of the vagina, ovary, and uterus. A loss of cyclic activity and complete involution of uterus and vagina were observed between Week 9 and Week 27 after transfer into short photoperiods. During this time period, no corpora lutea were observed in the ovaries. Under the influence of short photoperiods, the numbers of medium and antral follicles declined continuously until Week 15, and afterwards gradually recovered to maximal numbers in Week 27. This biphasic response to short photoperiods was not observed in the number of small follicles. These morphological changes were accompanied by changes in serum and pituitary FSH concentrations. Pinealectomy prevented the loss of estrous cyclicity after transfer into short photoperiods.(ABSTRACT TRUNCATED AT 250 WORDS)