Alteration of Circadian Period Length Does Not Influence the Ovarian Cycle Length in Common Marmosets, Callithrix j. jacchus (Primates)

Abstract

To investigate the coupling between the circadian system and the regulation of the ovarian cycle in nonhuman primates, the effect of Zeitgeber-induced alterations of the circadian period (23 vs 26 h) on the ovarian cycle length was studied in the long-cycling polyestrous common marmoset, Callithrix j. jucchus. For that purpose, six female marmosets were isolated for ∼4 months each under artificial lighting regimens of 23 h [light-dark (LD) 11.5:11.5] and of 26 h (LD 13:13; 300:0.03 Ix). Samples of “morning urine” were collected in each circadian period and analyzed by radioimmunoassay for their estrone (E₁) and estradiol-17β (E₂) concentrations. Clear ovarian cyclic variations of the creatinine-related urinary E₁ and E₂ concentrations were ascertained in each individual, with the E₂ concentrations being 5-10 times higher than the E₁ concentrations. In a total of 48 recorded ovarian cycles, the cycle length varied between 16 and 39 days and was 28.3 ± 4.1 days on average. As measured in circadian periods, the marmosets' ovarian cycle was significantly longer (p > 0.05) under entrainment to LD 11.5:11.5 than under entrainment to LD 13:13. When measured in objective days, however. no difference in cycle length was demonstrated. Hence, in Cullilhrix. the mechanisms regulating the ovarian cycle length do not seem to be closely coupled to the circadian system, but rather corroborate the more classic hypothesis pre- suming that in polyestrous mammals different (at most weakly coupled) timing mechanisms or oscillator systems are responsible for the regulation of the circa- dian and the ovarian cycles.

Key Words:

• Circadian rhythm-Entrainment range
• Ovarian cycle
• Urinary estrogens
• Cullilhrix
• Primates