Puberty in the Chimpanzee: Somatomedin-C and Its Relationship to Somatic Growth and Steroid Hormone Concentrations*

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Abstract
A relationship between sex steroids and the somatomedins (Sms) is well known, but poorly defined. In some primates, including man, there are pubertal increases in Sms, concurrent with increased growth and sex steroid production. In the current studies, indices of somatic growth [body wt, crown-rump length (CRL) and testis size (testicular volume index)] and circulating concentrations of testosterone (T), estradiol (E2), dehydroepiandroserone sulfate (DHEA-S), cortisol, and Sm-C were determined (n = 208) in 86 male and female chimpanzees during a 1 yr period. Whether plasma Sm-C concentrations correlate with serum levels of estrogen and androgens were determined. In male animals between 6 and 8 yr of age, there was a marked increase in testicular size, concurrent with an increase in serum T and preceding slightly an increase in the rate of body wt gain. There were no detectable increases in serum E2 or the CRL slope. In females between 6 and 8 yr of age, serum T increased, concurrent with an increase in the rate of body wt gain much smaller than that in male animals. Serum E2 increased only after 10 yr of age, and no increased linear growth (CRL) was found. In both sexes, increases in serum DHEA-S were found by 4-6 yr of age, in contrast to cortisol concentrations, which were high and remained unchanged from birth to 12 yr of age, except for lower values in the very youngest and very oldest female animals. An increase in Sm-C occurred in both sexes by 4-6 yr of age, with higher values in female than in male animals 0-2, 4-6 and 6-8 yr of age, and when all ages were considered together. In both sexes, plasma Sm-C concentrations correlated with serum T (r = 0.60 and P < 0.001; r = 0.68 and P < 0.001; females and males, respectively), although when both sexes were analyzed together, the correlation was not as good (r = 0.36; P < 0.001). Sm-C concentrations correlated with serum DHEA-S when the 2 sexes were analyzed separately (r = 0.44 and P < 0.001; r = 0.54 and P < 0.001; females and males, respectively), or together (r = 0.49; P < 0.001). Sm-C correlated poorly with serum E2 levels in females (r = 0.20; P < 0.05) and did not correlate with E2 in males. Apparently, in the chimpanzee, Sm-C concentrations increase at the time of puberty and are related to increases in gonadal and adrenal androgen production. Although illustrating some differences between the chimpanzee and man, this study does demonstrate close similarities between the chimpanzee and man, in terms of both somatic growth and Sm-C and androgen concentrations.