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

• Published in: Journal of reproduction & fertility Vol. 110; no. 1; pp. 115 - 125
• Main Authors: Bedford, J M, Mori, T, Oda, S
• Format: Journal Article
• Language: English
• Published: England Society for Reproduction and Fertility 01-05-1997
• Subjects: Animals; Copulation; Fallopian Tubes - anatomy & histology; Female; Fertilization - physiology; Male; Ovulation - physiology; Penis - anatomy & histology; Shrews - physiology; Species Specificity; Sperm Transport - physiology; Time Factors; Uterus - anatomy & histology; Vagina - anatomy & histology
• ISSN: 1470-1626; 0022-4251; 1741-7899
• DOI: 10.1530/jrf.0.1100115

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, ≤ 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%).