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Male Sexual Development in the Monkey. I. Cross-Sectional Analysis of Pulsatile Hypothalamic-Pituitary-Testicular Function^*

Neonatal and Pediatric Medicine Branch and Biometry Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20205

Address requests for reprints to: Barry B. Bercu, M.D., Building 10, Room 8 C429, Neonatal and Pediatric Medicine Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20205.

Pulsatile secretion of serum gonadotropins and testosterone was studied in 46 monkeys of varying ages from 9 days of age through adult life. Although some of the hormonal analysis was longitudinal in nature, most comparisons were cross-sectional. On the basis of pulsatile secretory patterns, hCG and GnRH stimulation, skeletal age, testicular volume, and histology, we have arbitrarily defined four developmental age groups: postnatal (<7 months), prepubertal or juvenile (7–27 months), pubertal (28–59 months), and adult (60 months). In accomplishing the pulsatile studies, blood was withdrawn at 15-min intervals over 24 h without anesthesia using a mobile vest and tether assembly to support an indwelling cannula. GnRH and hCG challenge tests were done on one or more occasions on all animals. Plasma samples were analyzed for concentrations of FSH, LH, testosterone, dihydrotestosterone and ⁴-androstenedione by established RIAs and an in vitro bioassay for LH.

During the frequent sampling period of 24-h duration for all except postnatal animals, testosterone pulses of large amplitude (up to 8-fold) occurred in postnatal, pubertal, and adult animals. Pulsatile gonadotropin secretion was seen at all ages; however, the highest pulses (up to 15-fold) occurred in prepubertal animals even though this was an infrequent occurrence. Time series analysis techniques were applied for objective statistical characterization of cycttc patterns. Basic rhythms corresponding to 50- to 90-min frequency cycles in gonadotropin secretion were identified. Substantive differences between LH concentrations by bioassay and RIA were seen infrequently. Our findings illustrate that: 1) circulating gonadotropin and testosterone pulses change in amplitude but not necessarily frequency during pubertal development, and 2) primate models are a useful paradym for the longitudinal study of human male sexual development. We conclude that where direct human investigation may be limited, much can be learned by study of these primate surrogates. (J Clin Endocrinol Metab 56: 1214,1983)

^* Parts of this manuscript were presented at the Society for the Study of Reproduction, Corvallis, Oregon, 1981; Lawson Wilkins Pediatric Endocrine Society and the European Pediatric Endocrine Society, Geneva, Switzerland, 1981; Second International Conference on The Control of the Onset of Puberty II, Stressa, Italy, 1981; American Society of Andrology, Hilton Head, South Carolina, 1982; Society for Pediatric Research, Washington, DC, 1982; and the 64th Annual Meeting of The Endocrine Society, San Francisco, California, 1982.

Received June 28, 1982.

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