Oviductal Motility Amplitude and Ovarian Steroid Secretion During Egg Transport in the Rabbit

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Abstract
New Zealand White rabbits were used to measure oviductal mortility amplitude in vivo and ovarian vein concentrations of estrone (E1), estradiol (E2), progesterone (P) and 20α-hydroxypregn-4-en-3-one (20α-OH-P) at several times before and after the induction of ovulation with human chorionic gonadotropin (hCG). The experiments were designed to determine the relationship between oviductal motility amplitude and ovarian steroid secretion during the time eggs are being transported through the oviducts. Oviductal motility amplitude of the isthmus decreased slightly at 6 h after hCG, then steadily increased to a peak at 36 h and subsequently declined between 36 and 72 h after hCG. E2, P and 20α-OH-P increased to peak concentrations at 6 h after hCG. At 12 h after hCG E1 and E2 were at the lowest levels observed in these experiments. E1 increased between 12 and 36 h and then declined slowly up to 72 h after hCG. From its nadir at 12 h, E2 increased gradually until 72 h. Both P and 20α-OH-P decreased after their peaks at 6 h. P increased again at 36 h after hCG, but 20α-OH-P remained low from 36 to 72 h. There were no statistically significant correlations between oviductal motility amplitude and any of the ovarian vein steroid concentrations. Thus, changes in ovarian steroid secretion and changes in oviductal motility may be out of phase; preovulatooy steroid surges may induce delayed changes in oviductal motility. It is suggested that preovulatory steroid surges induce an increase in the amplitude of contractions of the oviductal isthmus which effectively impedes passage of eggs through the oviduct. The postovulatory increase in progesterone secretion may decrease oviductal motility amplitude thereby allowing the eggs to move through the isthmus into the uterus.