Endocrine Abstracts

Gerbil (Meriones unguiculatus) a non traditional laboratory model with reproductive state influenced by photoperiod, was used to analyze those photoperiodic mechanisms involving reproductive regulation. The 14:10 photoperiod has been widely used for reproductive research since 1950 (Everett). As is well known gerbils locomotor activity cycle has been reported to be crepuscular and reproductive cycle presents two annual peaks. As for the estrous cycle (EC), it has been analyzed mainly under a12hr:12hr light (L)dark(D) photoperiod, and reported as mostly irregular. In this research, female gerbils were exposed to 8:16, 12:12, 14:10 and 16:8 LD conditions. The EC were monitored by cytology via vaginal smears every four hours (ZT) for 3 consecutive cycles, where ZT2 was the first (ZT0 was the light onset). Under the 14:10 photoperiod, the EC was the most stable. Cycles lengthen in between to five and four days and stable phase duration. When the other photoperiods were analyzed the EC showed not only less stability (3–9 days) but also variability in the phase duration, i.e. diestrus increased its duration under 8:16 and12:12 LD, meanwhile at 16:8 photoperiod diestrus and estrus, showed a significant increase when compared with 14:10 LD. In a period of 15 days an average of 2 cycles on 16:8, 12:12 and 8:16 and 3 EC for 14:10 were presented. Proestrus and metaestrus did not show a significative variance under any condition. A shift in the time of the day when estrus phase become settled was reported; vaginal smear showed predominantly cornified cells under 12:12 and 14:10 LD at ZT6; for 6:8 LD ZT2, and under 8:16 photoperiod a shift to the dark phase was found starting at ZT22. As cytological examination of vaginal smears is a good indicator for endocrine condition of the female, the estradiol and progesterone level are being analyzed by ELISA.