Ovarian follicular fluid, progesterone and Ca2+ ion influences on sperm release from the Fallopian tube reservoir

As a means of determining whether ovarian follicular fluid reaches the func tional sperm reservoir in the caudal isthmus of the Fallopian tube shortly after ovulation, 0.01-0.02 mi aliquots of whole or steroid-free follicular fluid were introduced into the distal extremity of the isthmus within 1 hr before ovulation. Eggs were recovered during a second intervention 4 hr 45 mind hr 10 min after treatment and examined by phase-contrast microscopy fo r the normality of fertilisation. In a separate experiment, 0.01-0.02 mi al iquots of 10 mu M calcium ionophore solution were introduced into the same site in comparable animals. Sixty-nine fertilised eggs were recovered from 12 fallopian tubes treated with whole follicular fluid, of which 24 (34.8%) were polyspermic. The 12 contralateral control tubes (PBS-treated) yielded 47 fertilised eggs, of which only one (2.1%) was polyspermic (P < 0.001). Steroid-free aliquots of the same follicular fluid introduced bilaterally i nto eight fallopian tubes (4 animals) resulted in recovery of 59 fertilised eggs, of which only one (1.7%) was polyspermic. Treatment with ionophore s olution yielded a 41.6% incidence of polyspermy (10 of 24 eggs from four tu bes) compared with 3.8% polyspermy (1 egg) from the control tubes (P < 0.01 ). Dispermy was the principal form of polyspermy. The numbers of accessory spermatozoa on/in the zona pellucida were increased by the experimental tre atment. Follicular fluid passing down the fallopian tube ampulla at ovulati on was therefore considered not to be the physiological stimulus for an ini tial, tightly-controlled release of spermatozoa from epithelial binding in the caudal isthmus. Indeed, because such sperm activation commences shortly before ovulation, a locally transmitted ovarian programming with relativel y high concentrations of follicular hormones remains the favoured model. Al though pre-ovulatory progesterone is considered to be the coordinating ster oid of increasing influence in these pre-fertilisation events, its effects are proposed to be modulated in the endosalpinx by mobilisation of Ca2+ ion s into a discrete population of bound spermatozoa. Results of the steroid-f ree follicular fluid and calcium ionophore treatments stand in support. (C) 1999 Wiley-Liss, Inc.