Effects of ovarian tissue reduction on the menstrual cycle: persistent normalcy after near-total oophorectomy

These experiments were designed to evaluate whether removal of approximately 95% visible ovarian tissue would interrupt the short- or long-term regulation of cyclic ovarian function. On cycle Days 2 4 (onset of menses = Day 1), the entire left ovary and approximately 90% of the right ovary were removed from three cycling cynomolgus monkeys. After approximately 95% ovariectomy, there was an acute elevation of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which lasted 11 +/- 2 days. A midcycle-like gonadotropin surge occurred 20 +/- 3 days following approximately 95% ovariectomy; the next menses occurred 19 +/- 1 days later. Follicular phase patterns of estradiol preceded the midcycle gonadotropin surge, and luteal phase progesterone levels indicated subsequent ovulation. Two of three monkeys resumed normal menstrual cyclicity in the following cycle with follicular phase, luteal phase, and menstrual cycle lengths similar to pretreatment levels. Histological examination of the ovarian remnant removed on Day 21 of the next cycle revealed a morphologically normal corpus luteum and many small follicles. A second group of 6 rhesus monkeys also underwent approximately 95% ovariectomy for long-term evaluation of menstrual cyclicity; typical 28-day menstrual cycle patterns were observed in 4 of the 6 monkeys for 5 mo, with 2 of these 3 animals maintaining regular menstrual cycles for 1 yr. In summary, our data suggest that normal ovarian function, i.e. recruitment, selection, and dominance of the ovulatory follicle, ovulation, and subsequent corpus luteum function, is maintained with only approximately 5% of functional ovarian tissue remaining.(ABSTRACT TRUNCATED AT 250 WORDS)