CHANGES IN PLASMA FOLLICLE-STIMULATING-HORMONE, LUTEINIZING-HORMONE, ESTROGEN AND PROGESTERONE DURING GROWTH OF OVULATORY FOLLICLES IN THE PIG

This experiment was conducted to determine the changes in secretion of LH, FSH, estrogen and progesterone during follicle maturation. Ovaries were recovered from 11 non-treated (control) gilts, three on day 13, four on day 16, and four on day 19 of the estrous cycle, and from four altrenogest-treated gilts on day 19. Altrenogest, a progesterone agonist, was fed at a dose of 20 mg once daily from days 13 to 18 to block spontaneous follicle maturation. Gilts were bled daily from day 12 until slaughter. For control gilts, the number of follicles/gilt 1-6 mm in diameter decreased (P<.05) from 93.5 on day 13 to 21.5 on day 19, and the number of large (>6 mm) follicles increased (P<.05) from 5.3 to 13.2. Altrenogest treatment blocked loss of small follicles and growth of large follicles between days 13 and 19. Plasma progesterone decreased (P<.001) between days 12 and 16 in both control and altrenogest-treated gilts. Plasma FSH decreased (P<.05) between days 12 and 16 only in control gilts. Plasma LH was not significantly affected by day or altrenogest treatment. Plasma estrogen increased (P<.05) between days 15 and 19 only in control gilts. These results indicate that 1) no increased LH secretion was detected in conjunction with emergence of ovulatory follicles, and 2) atresia of nonovulatory follicles was associated with decreased secretion of FSH. Both atresia and decreasing FSH secretion began before estrogen concentration increased in the systemic circulation. © 1990.