Two methods of artificial insemination and removal of copulatory plugs were used to investigate the role of the plug in the guinea pig. In addition, the effectiveness of the copulatory plug in blocking the passage of spermatozoa from the second mating was tested in albino females, where coat color was used as a genetic marker. Thirteen female guinea pigs that were either in proestrus, estrus, or metestrus, and inseminated with freshly collected copulatory plugs containing living spermatozoa, did not conceive. In a group of six females from which the copulatory plus was immediately removed, five conceived. Of nine estrous females artificially inseminated, five conceived. In five albino females, copulatory plugs from albino males completely blocked spermatozoa deposited by colored males, and 20 offspring, all albino were born. In a second group of four albino females where the plugs of albino males were removed prior to copulation with colored males, resulting litters were sired by either male or a combination of both males.
Single spermatozoa and spermatozoa in rouleaux were found throughout the genital tract of 21 female guinea pigs killed 15 minutes to 24 hours after copulation. Three females killed three to five minutes postcopulation had single spermatozoa and spermatozoa in rouleaux in the vagina, cervix, and uterus but not in the oviduct, The number of rouleaux and the number of spermatozoa in individual rouleaux decreased after copulation in all parts of the female genital tract with time while a corresponding increase in single spermatozoa was evident. The rate of rouleaux dissociation was faster in uteri than in oviducts. Only single spermatozoa were found near ova in the oviducts. The uterotubal junction appeared to act as a barrier to multitudes of spermatozoa passing from the uterus to the oviducts. However, some single spermatozoa and some rouleaux passed this barrier. Unusually large rouleaux were observed up to 12 hours after copulation in the pockets of the uterotubal junction. Single spermatozoa and few rouleaux of two spermatozoa in the uteri of females killed 8 to 24 hours postcopulation were phagocytised. No phagocytosis of spermatozoa was observed at any time in the oviduct.
The effects of cyproterone acetate (CA) on fertility of spermatozoa and rouleau formation were investigated in male guinea pigs. Twelve of 15 matings during CA treatment resulted in pregnancy even when rouleaux were absent in ejaculates, indicating that the rouleau condition is not necessary for the fertilizing ability of guinea pig spermatozoa. Examination of epididymides and vasa deferentia revealed that rouleaux diminished progressively with treatment time and were absent in the excurrent ducts of all males during the eighth and ninth weeks of treatment. Following a latent period after treatment, rouleaux were first noted in a specific epididymal region and were present throughout the distal excurrent ducts and ejaculates by 6 wk posttreatment. This sequence of rouleau loss and reappearance in the excurrent ducts suggests that rouleau formation is dependent on a regional epididymal influence that requires androgens. Spermatogenesis was not arrested; however, seminal vesicle and body weights were reduced in treated males.
The morphology and fertility of spermatozoa from vasa deferentia of guinea pigs were observed following hemicastration or castration for approximately 40 days. The morphology of these aged sperm was studied from living and fixed preparations. Fertilizing ability was assayed by artificial insemination of estrous females and subsequent counting of embryos. Spermatozoa underwent morphological changes including dissociation of rouleaux, curving of tails, and loss of acrosomes; physio!ogical changes included a decline in the number of sperm with progressive motility and increased numbers of immotile spermatozoa with time after the operations. The fertilizing capacity of spermatozoa was maintained for approximately 30 days in both groups. However, sperm from one of the hemicastrated males resulted in conception 36 days postoperation. The data suggest that the loss of motility and decline in fertilizing ability were the result of spermatozoan senescence rather than testicular androgen deficiency.
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