Electrical Correlates of Ovulation in the Rhesus Monkey *

It has been generally agreed by most investigators that ovulation in the higher primates occurs in the middle of the menstrual cycle. In humans, the ovulation period is believed to fall on or about 14 days, plus or minus twenty-four hours, before the onset of the succeeding menses. The test for ovulation has been records of mating, with subsequent pregnancy, or the recovery of young ova in elective laparotomy. Many studies have been made on ovulation in the monkey, notable among which are the papers of Hartman,' VanWagenen,16 and Allen.' Hartman reported ovulation in rhesus between the 11th and 14th day of the menstrual cycle. VanWagenen's more recent study repQrted that the 11th and 12th days constituted the critical period. Most of the studies commonly quoted indicate the approximate time of ovulation. Pragmatically, determining with certainty the moment of follicular rupture may not be very important. However, if it were known accurately, the age of the corpus luteum could be ascertained within hours, if not minutes. Burr and Musselman"5 noted a series of interesting potential changes between the index fingers in women, followed through successive menstrual cycles. Sharp rises in potential difference occurred during the period when ovulation in women is believed to be most probable. These facts were subsequently confirmed by Barton.2 Paralleling these studies, Burr, Hill, and Allen8 undertook to determine the validity of potential changes during ovulation in the rabbit. In this mammal, ovulation is believed to occur from 9 to 12 hours after mating. An electrical study of this period revealed a sharp rise in potential difference between vagina and symphysis pubis. This was confirmed at laparotomy shortly after cessation of the voltage changes. In one instance, with the ovary inclosed in a suitable chamber where it could be observed with the microscope, a developing follicle was watched while electrometric determinations were being made. As the follicle increased in size, the potential rose and reached a peak at the instant of rupture. This was followed by a decline in the voltage gradient. Subsequently Reboul, Friedgood, and Davis' confirmed these findings and contributed the fact that various stab wounds of abdominal viscera produced no such changes in electrical properties.