Ovulation induction and gamete transport in the female tract of the musk shrew, Suncus murinus.

Abstract

The musk shrew Suncus murinus was studied with regard to induction of ovulation, the genesis and role of the vaginal copulation plug, and the behaviour of gametes and embryos within the Fallopian tube. Ovulation occurred about 15 h after ejaculation, which required a mean of 5.2 (range 2-10) intromittent thrusts. Since ovulation occurred also after five thrusts without ejaculation, and after ejaculation without plug formation or sperm deposition, the primary stimulus for this seemed to be the thrust of the penis, the glans of which was covered by a dense field of spines. Neither vasectomized nor prostatectomized males formed a plug at ejaculation, and in the latter case the mean number of spermatozoa reaching the isthmus of the Fallopian tube, the number at the ampullary fertilization site and the rate of fertilisation were lower than in females mated to normal males. Thus both the vesicular gland on the vas deferens and the prostate are essential for formation of the copulation plug, which appears to enhance sperm transport within the female tract. At ejaculation, < or = 10(6) spermatozoa were incarcerated by the plug in the anterior vagina for 6-7 h, by which time a maximal population of several hundred had become established in posterior crypts of the isthmus of the Fallopian tube as small groups of free languidly moving spermatozoa. It remains to be established whether oviductal crypts in this and other shrews have a storage function for spermatozoa or sequester spermatozoa and so regulate the number that reach the fertilization site. Very few spermatozoa reached the ampulla of Suncus. Generally, only one or two spermatozoa had reached the ampulla by 4-5 h, and often less than ten had done so by 5-13 h after ovulation. As a probable correlate, few eggs were penetrated during the first 5 h, with a frequent delay of 10-13 h before most eggs were fertilized. Thereafter, unfertilized eggs were transported through the oviduct at the same rate as developing embryos, which entered the uterus about 85 h after ovulation at the 32-cell stage. There were highly significant differences between the larger KAT/SK strains and smaller OK strain with regard to Fallopian tube length (mean 6.9 mm versus 9.7 mm), as well as the rates of hCG-induced ovulation (5.6 versus 3.25) and of unilateral ovulation (6% versus 50%).