Oestradiol and somatomedin-C influence body weight patterns in premenarchial rhesus monkeys housed outdoors

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Abstract
The influence of gonadal status on the pattern of changes in body weight was examined in three groups of outdoor-housed premenarchial rhesus monkeys (Macaca mulatta) from 1 to 2 years of age. Gonadally intact (n=8) and ovariectomized oestradiol-treated females (n=5) gained significantly more weight than ovariectomized untreated females (n=5). The overall larger weight gains for the intact and ovariectomized oestradiol-treated groups were associated with significantly higher fasting levels of serum insulin. All subjects exhibited two periods of significant weight gain from 12 to 16 months of age between May and September and from 21 to 24 months of age between February and May. Serum GH and somatomedin-C levels were also raised during these periods of accelerated growth. Although the pattern of serum GH was similar among groups, serum somatomedin-C levels were significantly higher in both intact and ovariectomized oestradiol-treated subjects from 21 to 24 months of age, suggesting physiological levels of oestradiol may facilitate somatomedin-C production during periods of increased GH secretion. Thus, absolute changes in body weight in outdoor-housed premenarchial rhesus monkeys are influenced by gonadal status, possibly mediated through increases in serum insulin. Furthermore, dynamic changes in body weight occur during prepubertal development, with the largest increments associated with increased somatomedin-C levels at specific ages synchronized with natural changes in the environment. J. Endocr. (1984) 102, 311–317