Effect of cyclic AMP, imidazole and triiodothyronine on the rate of RNA synthesis by ejaculated ram spermatozoa

Abstract

The effects of cyclic AMP (cAMP) and of triiodothyronine (T 3) on the enhancement of sperm motility and metabolism are well documented, and the present study was undertaken to investigate the mechanisms underlying these effects in terms of their influence on sperm RNA synthesis in vitro. Washed ram sperm were diluted to 1 40 (v/v) with incubation buffer that contained 100 μg/ml penicillin-G and 400 mg% glucose, followed by incubation at 37°C for a period of 4 h. Washed ram spermatozoa incubated with graded doses of cAMP (10 −8, 10 −6 and 10 −4 M) showed significant enhancements of the rate of 3H-uridine incorporation into RNA, with maximal effect occurring at 10 −8 M. The presence of 3.75, 7.50 or 15.00 μM T 3 also stimulated the rate of RNA synthesis by the washed ram sperm, with maximal effect occurring at 7.50 μM. On the contrary, imidazole (a compound known to stimulate phosphodiesterase activity and consequently to decrease the intracellular cAMP levels in many tissues) was found to cause consistent inhibition of spermatozoal RNA synthesis. The inhibition was 47, 90 and 92% of control for 10, 50 and 100 mM imidazole, respectively. The results obtained indicate that cAMP may act either as a first or a second messenger in the mature sperm. The data also indicate that T 3 (possibly mediated by cAMP) may act on the ram sperm by the induction of enzymes, which are required for the well-known effects of this hormone in enhancing the sperm metabolic activity.