Ultradian luteinizing hormone and testosterone rhythms in the adult male monkey, Macaca fascicularis.

Abstract

Using the RIA for measuring serum testosterone (T) levels and the mouse interstitial cell bioassay for measuring monkey LH, we studied the secretory dynamics of these hormones in the adult male monkey. Eight sexually mature monkeys of the species Macaca fascicularis were sedated and blood was sampled under various protocols over 24 h. All experiments were conducted between February and June. A pronounced diurnal rhythm in the serum concentration of T was revealed by measurements from individual means summed over 4-h morning and evening intervals (0700–1100 and 1900–2300 h) in eight animals. The mean evening T levels (12.2 ± 0.8 ng/ml) were significantly greater than the morning values (9.1 ± 0.8 ng/ml; P < 0.02). Measurements at 20-min intervals over the 4-h periods revealed discrete pulses of T and LH secretion occurring during the morning (0700–1100 h) and evening (1900–2300 h). Analysis of T pulse frequencies and amplitudes between morning and evening showed a significantly higher frequency of pulses occurring in the evening (1.5 ± 0.27 pulses/4 h) than in the morning (0.25 ± 0.27/4 h); pulse amplitudes were not different between morning and evening samples. Samplings at 20-min intervals over 24 h showed a similar pattern. A clear relationship was found between episodic LH and T secretion during both day and nighttime sampling intervals; each individual pulse of T began within 20 min after discrete 3- to 10-fold increases in the serum LH concentration. These data show that in the male monkey, the apparent diurnal rhythm of serum T level is due to a diurnal modulation of the frequency of a pronounced ultradian rhythm in the secretion of this hormone; furthermore, these data document a nearly one to one relationship between pulsatile T andLH secretion, and suggest that the central nervous systempituitary axis operates on a diurnal schedule to modulate the frequency of pulsatile LH secretion in this species.