Coitus induced changes in oviductal motility & effect of progesterone

Motility of different oviductal segments of conscious rabbits was recorded through permanently implanted sensors using the technique of impedance plethysmography. The implants were around the oviductal wall and therefore did not obstruct its lumen. Pre-ovulatory ampullary motility was always less than the isthmic motility. Coitus induced ovulation produced a characteristic oviductal motility pattern consisting of (i) initial relaxation of both isthmus and ampulla (4-12 h) followed by (ii) increased isthmic motility in the face of a continually relaxed ampulla (36-48 h), and finally phase (iii) leading to restitution of both ampullary and isthmic motility to the base-line at 72-96 h. Estimation of ova positions indicated the presence of fertilized eggs in the ampulla and ampullo-isthmic junction at 48 h and the ova could come to the end of the isthmic segment only at 72 h or after. Increased isthmic motility thus served to counter the transportation of ova and their retention in the ampulla. Rabbits in which oviducts were not taken out for ova positioning achieved normal pregnancy. Administration of progesterone (im, 2.5 mg) produced complete relaxation of both isthmus and ampulla, did not produce increased isthmic contractility on coitus, accelerated the ovum transport rate and inhibited pregnancy, again emphasising the ova retentive role of oviductal motility.