[The effects of parotin components on testosterone biosynthesis in rats]

During our studies on the active moiety of parotin, we succeeded in purifying MP-parotin (MW = 130000) and parotin-subunit (MW = 45000) from crude parotin. Furthermore, AA-1 (MW = 9100) was isolated after the tryptic cleavage of the parotin-subunit. AA-1 was the smallest unit ever obtained which had serum Ca-decreasing activity and circulating leucocyte-increasing activity together with the nature of specific localization in bone. Therefore, AA-1 was considered to contain the essential residues for parotin activity in its structure. Since crude parotin was also known to show andromimetic action, these parotin components reduced in size were assayed in this regard. A daily injection of MP-parotin (500 micrograms/kg), parotin-subunit (20 micrograms/kg) or AA-1 (20 micrograms/kg) was administered subcutaneously for two weeks to male rats weighing 200 approximately 220 g. The dynamics of the testicular biosynthesis of testosterone from 3H-pregnenolone and 14C-progesterone via delta 4, delta 5-pathway and the transition of delta 5 to delta 4-steroids were measured. MP-parotin and the parotin-subunit stimulated the pathway of pregnenolone----17-hydroxypregnenolone----dehydroepiandrosterone---- androstenedione----testosterone and resulted in the elevation of serum testosterone levels. Cyclic AMP levels in the testicular homogenate and the motility of epididymal sperm were also increased by the treatment. On the other hand, AA-1 showed no effect on these parameters. It was concluded that andromimetic activity, which is involved in MP-parotin or parotin subunit was independent of parotin activity on the bone tissue.