Sex hormones and the selective estrogen receptor modulator tamoxifen modulate weekly body weights and food intakes in adolescent and adult rats

This study documented the effect of changes in male and female sex hormones and the selective estrogen receptor modulator (SERM) tamoxifen on weight g ain and food consumption of rats from puberty to adulthood, and assessed wh ether age at onset of treatment affected outcome. In Study 1, male and fema le WKY rats were either neutered or sham-operated before puberty, and a sub group of neutered females underwent estrogen replacement (ERT) at the age o f puberty. In Study 2, subgroups of neutered females received either ERT or tamoxifen beginning well into the postpuberty period. Weekly body weight a nd food consumption were assessed, and food consumption was normalized to m etabolic weight (body weight(0.67)). Neutering reduced the rate of weight g ain in males (P < 0.05), but significantly increased it in females (P < 0.0 001). ERT immediately reduced weight gain and prevented any further increas e, resulting in weights below that of sham-operated females (P < 0.05). Tam oxifen prevented further weight gain and returned profiles to that of sham- operated females. Food consumption, normalized to metabolic weight, was sim ilar in females and males, and both sexes showed a decrease through maturat ion to adulthood. Neutering decreased food consumption below that of sham-o perated animals in both males and females (P < 0.05), and ERT returned it t o sham levels. Despite the fact that tamoxifen had an effect on body weight similar to that of ERT, females receiving tamoxifen treatment consumed les s food than both sham-operated and ERT females (P < 0.05). Weight gain is m odulated by sex hormones in male and female rats, with both estrogen and ta moxifen exerting immediate effects in females, irrespective of the age at w hich treatment is initiated. Differences in food consumption do not appear to account for the effects of hormones and tamoxifen on body weight, sugges ting that they exert a direct effect on overall body metabolism.