Age-Related Changes in Diurnal Rhythms and Levels of Gonadotropins, Testosterone, and Inhibin B in Male Rhesus Monkeys (Macaca mulatta)

• Published in: Biology of reproduction Vol. 79; no. 1; pp. 93 - 99
• Main Authors: Schlatt, Stefan, Pohl, Clifford R, Ehmcke, Jens, Ramaswamy, Suresh
• Format: Journal Article
• Language: English
• Published: Madison, WI Society for the Study of Reproduction, Inc 01-07-2008; Society for the Study of Reproduction
• Subjects: Age Factors; Aging - blood; Animals; Biological and medical sciences; Circadian Rhythm - physiology; Fundamental and applied biological sciences. Psychology; Gonadotropins - blood; Hormone metabolism and regulation; Inhibins - blood; Macaca mulatta; Male; Mammalian male genital system; Pulsatile Flow; Testosterone - blood; Vertebrates: reproduction; Androgen; Inhibin; Monkey; gonadotropins; Macaca mulatta; Gonadotropin; Circadian rhythm; Hypothalamohypophysogonadal axis; testis; Testicle; Male genital system; Testosterone; Vertebrata; Mammalia; Adenohypophyseal hormone; Primates; Simioidea; Luteinizing hormone; Testicular hormone; aging; Sex steroid hormone; Age
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod.107.066126

Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns. In elderly men, the diurnal rhythm of testosterone is blunted and inhibin levels fall. Here we explore whether aging exerts similar effects in the rhesus monkey. We collected blood samples from groups of young (6-9 yr) and old (12-16 yr) male rhesus monkeys at 20-min intervals for a period of 24 h under remote sampling via a venous catheter. We determined moment-to-moment changes in plasma levels of testosterone, FSH, and LH by RIA, and of inhibin B by ELISA. We found significant diurnal patterns of testosterone in both groups. The circadian rhythm in testosterone was enhanced in older monkeys. Testosterone levels and pulse frequencies dropped significantly below those of young monkeys during midday hours. Diminished pulse frequency of LH appeared to be responsible for the midday testosterone decrease in old monkeys, while LH and testosterone pulse frequency did not change in young monkeys at corresponding time points. Old monkeys showed extended periods of LH-pulse quiescence in the morning and midday hours. Inhibin B and FSH levels were generally lower in old monkeys compared with the young group, but neither inhibin B nor FSH showed circadian rhythms. We conclude from these data that old rhesus monkeys have a more prominent circadian rhythm of LH and testosterone resulting from an extended midday period of quiescence in the hypothalamus-pituitary-gonadal axis.