INFLUENCE OF PROLACTIN ON THE EPIDIDYMAL LIPID PROFILES OF MALE ALBINO RATS

Abstract

Over the past few decades there has been an accumula tion of reports concerning fertility disorders in man with disturbed levels of serum prolactin. One such fertility dis order is defective sperm maturation which is associated with the epididymis. The epididymis is unique, in the sense, it facilitates sperm maturation at its proximal end and stores them in a quiescent yet viable form at the distal region. Thus, the epididymis by virtue of performing two contrast ing functions has puzzled many an andrologist. In addition, the identification of binding sites for prolactin in the epididymis has drawn the attention of many investigators at the present time. Thus, an attempt has been ma-de to in vestigate the role of prolactin in the epididymis. As a means of achieving this objective, experiments have been designed so that other factors that influence epididymal function are delineated and the precise action of prolactin are exposed. The approach has.been to perform the experiments on castrated animals so that the interfer ence from spermatozoa, testicular fluid and androgens could be minimized. Further, prolactin from an exogenous source is injected at different doses (50,100,150 and 200/ig of 0- PRL/100 g body weight, daily, subcutaneously for 7 days) to simulate clinical conditions where reproductive dis orders have been observed. Incidentally, hyperprolactinemia -il ls also associated with low levels of androgens and this also fits in very well with the experimental design. One group of animals has also been treated with bromocryptine !an ergot alkaloid, which significantly reduces the levels of circulating prolactin at a dose of 0.3 mg/100 g body weight, for a similar period of 7 days) to see the response of the epididymis when serum prolactin levels are low. The response of the male reproductive tract to prolactin was initially monitored in terms of changes in weight of these tissues. It was now felt necessary to establish how long the exogenously administered prolactin remained in circulation. Hence, a time course study was done and the serum levels of prolactin monitored at intervals of 15 min, 30 min, 2h, 6h and 24 h after the last of the series of 7 injections. Since interest was in the biological activity of the hetero logous prolactin present in samples, this hormone was mea sured by the 'local micro' pigeon crop sac bioassay. From the results, it is clear that the exogenously administered prolactin has a short half life and is not detectable at 15 min. The action of prolactin on the functional status of the epididymis also needed to be known. In this connection, it was thought that measurement of glycerophosphocholine (GPC) could throw more light, since it has been used as an -iiiindex for this purpose by other investigators in the past. Kany compounds are known to interfere with the determina tion of GPC. Thus, in order to make an accurate analysis, GPC was isolated and purified by a rapid procedure using Amberlite CG 400 'semi micro' columns and then quantified. Since the function of the epididymis change-along its course, the analysis was done in segments that could form gross points of reference (caput, corpus and cauda). Prolactin was found to generally increase GPC levels in all segments of the epididymis but to a varying degree. Of the three re gions, the action of prolactin on GPC levels of the caput seems to be more pronounced. The composition of epididymal fluid of which GPC forms a part is crucial for sperm matu ration and storage. Therefore, it is suggested that any change in the level of this compound is bound to have the repercussions on this process. Lipids are important molecules that have multiple func tions in the epididymis. The acyl glycerols provide fatty acid side chains, the metabolism of which results in the release of energy much needed by sperm during their tranit through the epididymis. Phospholipids are also known to be important sources of oxidizable substrate, in addi tion to their role in maintaining the stability and permea bility characteristics of membranes. Like other macromolecules, the epididymal lipid composition is under the influf hormones, predominantly androgens. A number of other s ence oj -ivhormones as well have been implicated, but the action of prolactin remains to be elucidated. In the present study total lipids were extracted in chloroform: methanol ( 2: 1 V/V) and quantified by gravi metric methods. The individual lipid subclasses from these extracts were separated using thin layer chromatographic techniques and quantified spectrophotometrically. Recent reviews on this subject have suggested that measurement of the pool size of individual lipid classes ( as done in the p-esent study) rather than estimation of the enzymes invol ved in lipid metabolism truly reflect the situation in vivo. Prolactin increased total lipids which could be attri buted to the general rise in total glyceride glycerol, to tal cholesterol and total phospholipids. A reduction in the level of diacylglycerol was observed with a concomitant rise in triacylglycerols, indicating a tendency for lipid storage. Prolactin also ensured the conversion of choles terol from the free to the esterified form. Among the phos pholipids, phosphatidyl serine, sphingomyelin and phospha tide acid were reduced while phosphatidyl inositol, phos phatidyl choline and phosphatidyl ethanolamine showed a rise. The results enumerated above are prominent in the 100 ,Mg O-PRL treated group which seems to be the dose at which maximum changes are effected in the androgen starved condition. Thus, it could be deduced that prolactin treat- vtnent leads to an accumulation of triacylglycerol, phospha tidyl inositol, phosphatidyl ethanolamine and phosphatidyl choline. Based on these results, it has been inferred that prolactin selectively favours metabolism through specific pathways. The implications of these results are discussed.