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Division of Clinical Pharmacology and Metabolic Research, Department of Medicine, University of Vermont, Burlington, Vermont 05405
Prior studies
suggest that estradiol and progesterone regulate body composition in
growing female rats. Because these studies did not consider the
confounding effect of changes in food intake, it remains unclear
whether ovarian hormones regulate body composition independently of
their effects on food intake. We utilized a pair-feeding paradigm to
examine the effects of these hormones on body composition. In addition,
skeletal muscle protein fractional synthesis rate and adipose tissue
lipoprotein lipase activity were measured to examine pathways of
substrate deposition into fat and fat-free tissue. Female
Sprague-Dawley rats [pubertal: 7-8 wk old; 190 ± 0.5 (SE)
g] were separated into four groups: 1) sham-operated (S;
n = 8), 2) ovariectomized plus placebo (OVX;
n = 8), 3) ovariectomized plus estradiol
(OVX+E; n = 8), and 4) ovariectomized plus
progesterone (OVX+P; n = 8). All ovariectomized groups
were pair-fed to the S group. Body composition was measured using total
body electrical conductivity. The relative increase in fat-free mass
was greater (P < 0.01) in the OVX group (31 ± 2%) than in the S (17 ± 2%), OVX+E (18 ± 2%), and OVX+P
(22 ± 2%) groups. The fractional synthetic rates of
gastrocnemius muscle protein paralleled changes in fat-free mass: OVX
had a higher (P < 0.05) synthesis rate (21 ± 3%/day) than S (12 ± 2%/day), OVX+E (11 ± 2%/day), and
OVX+P (8 ± 1%/day) groups. Body fat increased in the S group
(31 ± 7%; P < 0.01), whereas the OVX groups
lost fat (OVX: 
10 ± 7%; OVX+E: 15 ± 7%; OVX+P:
13 ± 7%). No differences in lipoprotein lipase were found. Our
results suggest that estradiol and progesterone may regulate the growth
of fat and fat-free tissues in female rats. Moreover, ovarian hormones
may influence skeletal muscle growth through their effects on skeletal
muscle protein synthesis.
skeletal muscle; adipose tissue; flooding dose
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