Fourteen days of leptin treatment to ob/ob mice increases uterine and ovarian weights in females, while leptin increases seminal vesicle and testes weights in males compared to saline-treated, pair-fed ob/ob controls, despite considerable body weight loss in all groups. The stimulatory effect on the reproductive organs appears to have functional significance, as leptin-treated male and female ob/ob mice are able to mate successfully with their wild-type counterparts. These studies (among others) show that the weight loss experienced by pair-fed ob/ob animals does not restore fertility, implying that obesity alone is not the cause of infertility to ob/ob mice and strengthening the case that leptin is directly responsible for these changes in reproductive capacity. flovent inhaler
Circulating leptin levels decrease with fasting in rodents and humans, indicating that leptin levels can also reflect acute changes in metabolic status. Could this decrease in leptin levels be responsible for the attenuation of gonadotropin secretion during fasting? In an experiment designed to mimic the fall of leptin levels during fasting, leptin antiserum was administered into the lateral ventricle of rats, which caused a decrease in LH pulsatility and a cessation of estrous cyclicity. We attempted to answer this question more directly in the rhesus macaque. Peripubertal male macaques were fasted for two days while being given i.v. infusions of either leptin or vehicle. During the second day of fasting, 3 out of 4 leptin-treated monkeys had LH pulses, whereas 0 out of 4 saline-treated monkeys had LH pulses (Fig. 1). Leptin-treated animals had higher mean plasma LH and FSH levels than controls, demonstrating the ability of leptin to counteract the effects of fasting on gonadotropin secretion. Similar results on LH secretion have been found by others in mice and rats. After 48 h of fasting in adult female rats, reduced LH pulse frequency is restored to the level of fed animals by i.p. injections of leptin. However, reinstatement of gonadotropin secretion during periods of fasting does not mean an animal is competent to reproduce. Wade et al. found that leptin facilitates lordosis in fed hamsters, but apparently leptin cannot overcome the suppression of sexual behavior in food-deprived female hamsters.
FIG. 1. Plasma LH levels during fasting in two male monkeys. Animals were fasted for two days during which time they received either leptin or saline i.v. infusions. Each animal received both treatments (leptin and saline) on separate occasions. During the evening of the second day of fasting, saline-treated monkeys showed suppression of LH pulses, whereas leptin-treated animals showed clear evidence of LH pulsatility.