EFFECT OF ACUTE FOOD-DEPRIVATION ON LACTATIONAL INFERTILITY IN RATS IS REDUCED BY LEPTIN ADMINISTRATION

The goals of these experiments were to determine whether lactational a nestrus would be prolonged by a 48-h fast at days 13 and 14 postpartum (pp) and, if so, to determine whether this effect could be reversed b y treatment with the Ob protein leptin. We found that food deprivation on days 13 and 14 pp prolonged lactational infertility by 7 days and that the nutritional experience of both the dam and her litter contrib uted to this effect. Leptin administration (2.5 mg.kg(-1).day(-1)) dur ing food deprivation was sufficient to reduce the length of lactationa l infertility compared with vehicle-treated food-deprived rats (P < 0. 05). Similar leptin treatment in ad libitum-fed animals reduced food i ntake (P < 0.05) and litter growth (P < 0.05) but had no statistically significant effect on maternal weight gain or length of lactational i nfertility. Food-deprived lactating animals had lower circulating lept in levels than ad libitum-fed lactating animals on day 15 pp (P < 0.05 ), as determined by RIA. Levels in nonlactating rats were higher than in either lactating group (P < 0.05).