FURTHER EVIDENCE FOR SYNERGISM BETWEEN LH AND FSH IN THE INDUCTION OF OVULATION IN RATS; LACK OF EFFECTS OF PROLACTIN

Summary. Attempts were made to induce premature ovulation on the day of pro-oestrus in the 4-day cyclic rat by lh, fsh and/or prolactin administered a day earlier. Doses of 5 \g=m\glh and 15 \g=m\gfsh, when given alone, induced partial ovulation in a few animals but the combination induced normal ovulation in 93 % of the rats. Ovine prolactin given alone failed to induce ovulation and, when given in combination with lh, fsh or both, did not exert synergistic effects on ovulation. These data provide additional evidence that lh and fsh interact to induce ovulation in the normal oestrous cycle and that the ovulating hormone is composed of at least lh and fsh. Ovulation occurs between 01.00 and 02.00 hours on the day of oestrus in the 4-day cyclic rat (Everett, 1961). Administration of lh on the day before pro-oestrus, i.e. dioestrus, provokes ovulation on the following day, i.e. a full 24 hr before the expected time, in a proportion of rats. Both the incidence and rate of ovulation, however, are lower than in rats blocked with antioestrogen o