The baboon as a model for puberty: growth, testis size, plasma testosterone, and somatomedin-C

Abstract

Physical and hormonal changes of human puberty have been described extensively, yet a nonhuman primate model for pubertal events is lacking. This study is a cross-section analysis of pubertal growth, testis size, and plasma concentration of testosterone (T) and somatomedin-C (SM-C) in the male baboon (Paplo sp.). Baboons (n = 84) with known dates of birth (3 - 272 weeks of age) and 10 adults (> 10 years) were examined by the same investigators for body weight (BWt), crown-rump length (CRL), and testis size. A plasma sample was drawn for determination of T by RIA. A separate group of 26 male baboons, ages 3 weeks to adult, were studied cross-sectionally for SM-C. As in the human, testis size increased only slightly before puberty. By 3 to 3.5 years, there was a marked increase in testis size coincident with or slightly preceding increases in BWt, CRL, and plasma T. Testis size continued to increase slightly after 5 years to adult size. By 3 to 4 years, there was a significant increase in SM-C which declined in adults (0 - 3 yr, M ± SE = 1.00 ± 0.14, n = 12; 3 - 4 yr, 8.46 ± 0.57, n = 10; > 6 yr, 3.90 ± 0.21, n = 4). Regression analyses of BWt, CRL, and testis size vs. age revealed significant changes in slope beginning at about 3 years. In conclusion, these data define the age of puberty and describe pubertal changes in somatic growth and testicular development in the baboon and suggest that this species may be an appropriate nonhuman primate model for human pubertal growth and development. (SM-C tracer supplied by J. Van Wyk.)