The present study was carried out to determine the detailed histological and cytological features of the excurrent ducts of the male reproductive system in the rhesus monkey. The excurrent ducts show a regional difference in their histological features. The use of some of these features as histological markers and their possible functional significance are discussed.

The epithelial cells in the different components of the excurrent duct system possess cytological features which suggest their involvement in absorption and the secretion of different products into the lumen.

Ultrastructural studies on the spermatozoa in different regions of the epididymis of the rhesus monkey have shown that the process of sperm maturation is associated with the caudad migration of the cytoplastmic droplet, a reduction in the volume of the cytoplasmic droplet, and an obvious wrinkling of the plasma membrane surrounding the head of the spermatozoa. These changes are completed by the time the spermatozoa reach the distal-middle segment of the epididymis. The present studies also indicate that spermatozoa are incorporated into the intraepithelial cells in the epidymis. This finding suggests that spermiophagy is a normal occurrence in the epidymis of rhesus monkey.

The ultrastructural features of the principal cell in the epididymal epithelium of the monkey epididymis are suggestive of the cell carrying out a dual function of absorption and secretion. Both these functions occur on the luminal surface of the cell as well as on the lateral and basal aspects of the cell which face the intercellular spaces. Transmision Electron Microscopic studies of epididymal tissues following their impregnation with lanthanum nitrate indicated that the intercellular spaces are effectively sealed-off from the luminal space by the apically situated tight junctions between adjoining principal cells. The intercellular spaces are contiguous with the perivascular spaces of the subepithelial blood capillaries. It is suggested that the absorptive and secretory functions occuring on the apical surface of cells may be related to the creation of an appropriate intraluminal milieu for the maturation of spermatozoa while the occurrence of these functions in the intercellular spaces may represent an exchange of substances between the principal cells and the subepithelial capillaries.

The importance of developing of drugs which could be taken post-coitally or used once-a-month in the case of a delay in the onset of the menses is well recognized. The availability of such technology would limit exposure to fertility regulating agents to such occasions where there is coital exposure or possibility of pregnancy.

Methods of post-coital contraception used so far include IUD’s inserted post-coitally, estrogens, and combinations of estrogens and gestagens. These are reserved primarily for emergency situations to protect women from unwanted pregnancy resulting from rape or unprotected coitus. Levonorgestrel has shown satisfactory results in terms of contraceptive efficacy and is being further evaluated clinically. A number of problems inherent in the development of post-coital contraception are discussed.

Menstrual regulation could be achieved by a number of approaches: (a) block progesterone receptors and interfere with the preparation of the endometrium for implantation; (b) luteolysis leading to decreased progesterone levels and interruption of implantation; and (c) termination of early pregnancy by prostaglandins. A number of progesterone antagonists have been evaluated. One of the compounds, RU38486 is being evaluated clinically for termination of very early pregnancy.

Deglycosylated derivatives of human chorionic gonadotropin have been shown to antagonize the action of human chorionic gonadotropin and interfere with established pregnancy in rats. Appropriate methods of delivery, immunogenicity and alternate methods for production of human chorionic gonadotropin need to be considered before evaluation of the derivatives for clinical use.

In vitro and invivo models need to be developed for evaluation of the teratogenicity and embryotoxicity of post-coital and menses inducing agents.

There are a number of gaps in the knowledge of the processes regulating implantation which should be investigated in rodents and in different non-human primate species.

Estrogens secreted by the ovary during the pre/periimplantation period and/or by the blastocyst and acting locally on the endometrium are involved in the initiation of implantation. Estrogens induce a cascade of metabolic changes in the uterus and blastocyst prior to and soon after the attachment and implantation of the blastocysts. Antiestrogens either administered intraluminally into the uterus prior to implantation or washing free blastocysts with antiestrogens prior to transfer to uteri of progesterone treated hamsters leads to failure of implantation. A number of antiestrogens which inhibit fertility in the rats do not interfere with implantation in the hamster and monkey when administered post-coitally. However, Zuclomiphene administered during days 5–11 of the menstrual cycle inhibits implantation in the rhesus monkey. Antiestrogens are being evaluated in other non-human primates to confirm the above results and to determine the time in the menstrual cycle susceptible to modification and inhibition of implantation. Tamoxifen administered from days 18–30 of the cycle to mated bonnet monkeys inhibited implantation despite maintenance of high levels of circulating progesterone. Neutralization of the vitamin carrier proteins (by active immunization against these proteins) interferes with established pregnancy in the rat and perhaps in the bonnet monkey. Whether antiestrogens can reduce the levels of vitamin carrier proteins to a level which is not adequate for maintenance of early pregnancy is not clear. Compounds which show antiestrogenic and antiprogestational properties may have advantages in inhibiting implantation or disruption of early pregnancy. Critical experiments need to be carried out in non-human primates to delineate the effectiveness of antiestrogens, with particular emphasis on time, dose, duration and route of administration in inhibition of implantation. Centchroman, an antiestrogen with antiprogestational properties, has been found to provide pregnancy protection with minimal side effects. However, several concerns relating to safety in toxicological studies in monkeys and a dose which would provide acceptable rate of contraceptive efficacy without major effects on the menstrual cycle need to be clarified before considering the potential of centchroman as a possible oral contraceptive administered either post-coitally or once a week. Inhibition of implantation by administration of tamoxifen opens up new possibilities of use of antiestrogens for fertility regulation.