Seasonal effects on ovarian folliculogenesis in rhesus monkeys

• Published in: Biology of reproduction Vol. 33; no. 3; pp. 653 - 659
• Main Authors: HUTZ, R. J, DIERSCHKE, D. J, WOLF, R. C
• Format: Journal Article
• Language: English
• Published: Madison, WI Society for the Study of Reproduction 01-10-1985
• Subjects: Animals; Biological and medical sciences; Estrus; Female; Follicle Stimulating Hormone - blood; Follicular Phase; Fundamental and applied biological sciences. Psychology; Luteal Phase; Luteinizing Hormone - blood; Macaca mulatta; Mammalian female genital system; Morphology. Physiology; Ovarian Follicle - physiology; Ovulation; Progesterone - blood; Seasons; Vertebrates: reproduction; Ovary; Vertebrata; Circannual rhythm; Mammalia; Seasonal variation; Female genital system; Monkey; Primates; Ovarian follicle
• ISSN: 0006-3363; 1529-7268
• DOI: 10.1095/biolreprod33.3.653

Reproductive performance is reportedly reduced in some rhesus monkeys during the summer months, even when environmental conditions
are controlled. The mechanism(s) underlying this phenomenon remain unknown. We noted that the pattern of folliculogenesis
appeared to be altered in rhesus monkeys that continued to exhibit ovulatory menstrual cycles during the "nonbreeding" season.
This study was designed to investigate the effect of season on development of the dominant follicle (DF) and upon levels of
serum gonadotropins and sex steroids in animals maintained in a controlled environment. Forty-four menstrual cycles were evaluated
from October, 1982 to October, 1983. Animals were housed individually in controlled light (12L:12D) and temperature (22-25
degrees C). A DF was identified by laparoscopy on Day 6 of the cycle in only 45% of cycles during the months of May through
September, compared with 87.5% the remainder of the year. No effect of season was detected on either the length of the menstrual
cycle or luteal phase, mean follicular diameter, or the percentage of ovulatory cycles. During the follicular phase, amounts
of follicle-stimulating hormone (FSH) in peripheral sera were depressed, whereas those of luteinizing hormone (LH) were consistently
elevated. Amounts of circulating estradiol were similar between groups. However, serum concentrations of progesterone were
markedly reduced in the summer. Development of the DF appeared to be delayed in the early follicular phase during the summer
months in those rhesus monkeys that had ovulatory menstrual cycles. This delay was accompanied by an alteration in the FSH
to LH ratio. Although most cycles were ovulatory, altered follicular development resulted in deficient luteal function.