Similarities in the regulatory patterns of pregnant and cycling rats

The patterns of food intake, water intake and body weight of the female rat during the estrous cycle and pregnancy were determined. During the 4-day estrous cycle, intake and body weight were reduced on the day of ovulation. In contrast, animals with 5-day estrous cycles reduced intake and body weight for 2 days, the day prior to ovulation as well as on the day of ovulation. Intake of pregnant rats around the time of birth was compared to that of cycling females and similarities were observed. The peripartum pattern of food intake was systematically related to the length of the gestation period. Rats that littered 22 days after mating showed depressed food intake only on the day of birth. Those with 23-day gestation periods decreased food intake both on the day of birth and on the following day. The similarities in the intake patterns during 4- and 5-day estrous cycle to that of the peripartum segment of 22- and 23-day pregnancies suggest that there may be common neuroendocrine factors controlling these behaviors during the two reproductive periods.