STUDIES ON THE ROLE OF PROLACTIN IN THE CONTROL OF EPIDIDYMAL STRUCTURE AND FUNCTION IN MALE ALBINO RATS

Abstract

The intention of this study was to investigate if prolactin had an influence on the epididymis, a region of the male reproductive tract concerned with the functional development of the sperm. The epididymis helps sperm acquire the characteristics of motility and fertilizing ability. This is made possible by the special milieu in which the sperm are bathed while being nurtured within the duct. The composition of this milieu is further dependent on the secretory and absorptive nature of the epididymal epithelium. The nature of the epididymal epithelium is in turn dependent on several factors, both hormonal and non-hormonal. Thus, it seems that one big cascade of events is involved, that finally culminates in the production of functionally developed sperm. The crux of the problem was to first select an appropriate parameter to assess the functional status of the epididymis and then identify the various factors that influence it. The next step was to investigate if prolactin had a role to play. Sialic acid was one of the parameters that was chosen. Although there is yet no clear appreciation of the significance of sialic acid for sperm function, there is evidence to suggest that the epididymis synthesizes this compound. Experiments involving sham-operated, duct ligated and orchidectomised animals clearly showed that the sialic acid derived from testis could significantly contribute to the levels in the epididymis. Nevertheless, the presence of sialic acid in epididymis even after efferent duct ligation and the higher levels of this compound in cauda than in the caput made it amply clear that the epididymis is capable of synthesizing sialic acid. Moreover, these studies also showed that factors derived from testicular fluid including androgens controlled sialic acid level in the epididymis. A simple way to see if prolactin is involved is to inject prolactin in animals from an exogenous source (as practised by other investigators) and then look for the impact on the epididymis. But then, it was inferred from the preceeding experiment that several factors of testicular origin affect sialic acid level in the epididymis. For this reason, prolactin treatment in intact rats was not preferred. The choice now was to use efferent . duct ligated or orchidectomised animals for prolactin treatment because all components of testicular origin could be kept away. Accordingly, when prolactin was administered at various doses, the epididymis of orchidectomised and not the duct ligated animals responded to prolactin treatment. The following explanations could be offered. Efferent duct ligation prevents the testicular fluid and spermatozoa from reaching the epididymis but maintains the availability of androgens through general circulation. Orchidectomy, on the otherhand, involves the removal of the primary source of androgens together with all testicular factors known to influence epididymal function. Since the androgens continue to reach the epididymis in duct ligated animals and the epididymis is predominantly an androgen dependent organ, it has been proposed that the action of prolactin is perhaps masked by the much greater effects of androgens in the tissue. In view of these results it was clear that orchidectomised animals would be the most appropriate model to study the effect of prolactin in the epididymis. Prolactin treatment to orchidectomised rats increased the sialic acid levels in a dose dependent manner. It had been suggested that prolactin directly influences the epididymal sialic acid, perhaps at the level of synthesis. The experiment when repeated with bromocryptine treatment (an ergot alkaloid that reduces circulating levels of prolactin) to orchidectomised rats confirmed that prolactin was involved. It was also clarified that prolactin does not interfere with the assay of sialic acid. The activity of two representative glycosidases was used as yet another parameter to monitor the effoct of prolactin on the epididymis. In this case, the response although positive, was not exactly dose related, implicating that different parameters need not necessarily respond alike to tho samo treatment. It has 11 been suggested that the activity of glycosidases measured may represent the net result of an interaction between steroid (androgen) and protein (prolactin) hormone action at each dose of prolactin treatment. In order to see how long the injected prolactin remains in circulation, the circadian pattern of serum prolactin bioactivity in orchidectomised animals given various doses of prolactin injection was determined. It appeared that the half life of injected prolactin was small, perhaps less than 15 min. In addition, a rebounding phenomenon was observed. In the first two Chapters prolactin was shown to influence biochemical parameters like the sialic acid and the activity of glycosidases in the epididymis. However, the impact of prolactin on the structure of the epididymal epithelium particularly the principal cells, was not known. For this purpose, both light and electron microscopic studies were performed. From the light microscopic studies it was clear that prolactin had a positive effect on the epididymal epithelium but had no influence on the muscular layer. Electron microscopic studies revealed that prolactin profoundly influenced the ultrastructure of the principal cell. Orchidectomy induced atrophic changes and prolactin treatment to these animals brought about rejuvenation. Thus, prolactin was shown to have a trophic action in the epididymis.