Evaluation of antral follicle growth, selection and luteal structure-function in the macaque ovary during the menstrual cycle by high-resolution ultrasonography

Abstract

Use high-resolution ultrasonography to detect: 1) the dominant follicle (DF), 2) the corpus luteum (CL), and 3) small antral follicles (especially in the absence of a dominant structure), on the ovaries of rhesus monkeys during a natural menstrual cycle. Imaging of ovaries was performed on sedated monkeys using a GE Medical Systems Voluson 730 Expert Doppler ultrasound instrument. Menstruation was monitored, and blood samples were collected daily from day 6 following onset of menses to measure serum levels of estradiol (E) and progesterone. Initially, monkeys were selected for transabdominal scans at discrete stages of the menstrual cycle: late follicular, mid-luteal, and menses (n = 6/stage). Subsequently, monkeys (n = 5) underwent serial scanning at the following stages: day of/before onset of E surge; at early, mid, late, and very late stages of the luteal phase to observe the CL and growth of antral follicles; at early, mid, and late follicular phase to follow the selection, growth and ovulation of the DF. The dominant structure was identified in 5/6 individuals scanned during the late follicular and mid-luteal phases. The CL was visualized by Doppler signature. Additional small antral follicles were observed during the luteal phase and at menses. Average duration of follicular and luteal phases for animals undergoing serial scans was 13 ± 0.6 and 15 ± 0.3 days, respectively. During serial scanning, antral follicles (0.2 − 1 mm diameter) were identified throughout the menstrual cycle on the dominant follicle/CL- bearing and contralateral ovaries. By day 3 of the cycle (and as early as the onset of menses in 2 animals) one follicle was identified as larger than its cohorts, and could be tracked to ovulation. The DF measured 5.1 ± 0.6 mm at mid-cycle. It is possible to observe antral follicles throughout the menstrual cycle of the macaque by transabdominal scanning. The growth of the DF may be prospectively followed, which (based on size differential) appears to be selected by day 3 following menses. The use of Doppler imaging to monitor blood flow greatly improves identification of the CL. Thus, the population dynamics of the antral follicle pool and luteal structure-function can be non-invasively evaluated in spontaneous menstrual cycles, as well as in conditions of ovarian dysfunction or pharmacologic treatment.