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 anestrus 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 by 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 contributed to this effect. Leptin administration (2.5 mg ⋅ kg-1 ⋅ day-1) during food deprivation was sufficient to reduce the length of lactational infertility compared with vehicle-treated food-deprived rats ( P < 0.05). Similar leptin treatment in ad libitum-fed animals reduced food intake ( P < 0.05) and litter growth ( P < 0.05) but had no statistically significant effect on maternal weight gain or length of lactational infertility. Food-deprived lactating animals had lower circulating leptin 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).