Food restriction neither improves nor exacerbates reproduction in obese female Zucker rats.

Obese female Zucker rats have several reproductive abnormalities, including delayed puberty, abnormal estrous cyclicity, and behavioral hyporesponsiveness to ovarian steroid hormones. To ascertain whether excessive body weight per se causes these reproductive abnormalities, obese Zucker female rats were fed ad lib or were food restricted to match their body weights to those of lean counterparts. Food restriction neither accelerated vaginal opening nor normalized estrous cyclicity in obese female rats. Following ovariectomy, an injection of estradiol benzoate (EB, 15 microg/kg, s.c.) induced extremely low sexual receptivity in all rats, and proceptive behaviors were never observed. After treatment with EB plus progesterone (P, 2 mg/kg, s.c.), lean rats were very receptive (lordosis quotient, LQ = 94 +/- 2%) and proceptive (PRO = 12.5 +/- 2 events/min) while both ad lib-fed and food-restricted obese rats were only marginally receptive and proceptive (LQ= 19 +/- 9%, PRO = 1.8 +/- 0.7 events/min; LQ = 31 +/- 15%, PRO = 4.7 +/- 3 events/min, respectively). A higher progesterone dose (20 mg/kg) elicited vigorous sexual receptivity (LQ = 88-99%) and proceptivity (PRO = 16.5-20.4 events/min) in all EB-treated rats. Adiposity was significantly lower in food-restricted obese rats as compared to ad lib-fed obese rats (36.5 +/- 1.7% vs. 69.4 +/- 2.7%), but greater than that observed in lean rats (24.4 +/- 1.1%). These data suggest that excessive body weight per se does not underlie reproductive abnormalities in obese Zucker rats, but do not rule out the possibility that excessive adiposity may contribute to their infertility.