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Nutrient Requirements

Body Weight and Food Intake Profiles Are Modulated by Sex Hormones and Tamoxifen in Chronically Hypertensive Rats¹

W. Jack Wallen^*,**, Michael P. Belanger and Carin Wittnich^*,,**2

Departments of ^* Physiology and Surgery, and ^** The Cardiovascular Sciences Collaborative Program, University of Toronto, Toronto, Canada M5S 1A8

²To whom correspondence should be addressed. E-mail: c.wittnich{at}utoronto.ca.

Sex hormones and the selective estrogen receptor modulator tamoxifen affect food consumption and body weight in normotensive rats. This study investigated the effects of hormone manipulation and tamoxifen on weight gain and food intake in the presence of chronic systemic hypertension. Male and female spontaneously hypertensive rats (SHR) were either neutered or sham operated before puberty, and subgroups of neutered females received either estrogen replacement therapy (ERT) or tamoxifen at the age of 12 wk. Weekly body weight and food consumption were assessed, and food consumption was normalized to metabolic weight (g body^2/3). Neutering reduced weight gain in males (P = 0.0001), but increased it in females (P < 0.0001). Both ERT and tamoxifen treatment prevented this increase in weight, with body weight dropping to levels of sham-operated rats for ERT, whereas rats given tamoxifen maintained greater body weights than sham-operated rats (P < 0.0001). This contrasts with previous work in normotensive females in which sham-operated and tamoxifen-treated females did not differ. Neutering reduced normalized food consumption relative to sham-operated rats in both males and females (P < 0.05). Although ERT returned it to normalized intakes of sham-operated rats, tamoxifen reduced normalized food consumption relative to that of both sham-operated and ERT groups. In hypertensive rats, body weight is modulated by sex hormones in both males and females, but in opposite directions. Both estrogen and tamoxifen exert immediate effects in females. Interestingly, the effect of tamoxifen on body weight appears to be greater in hypertensive than in normotensive rats.

KEY WORDS: • spontaneously hypertensive rats • gender • 17ß-estradiol • selective estrogen receptor modulator

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