Serotonin or its agonist 5-methoxytryptamine can stimulate hamster sperm acrosome reactions in a more direct manner than catecholamines.

Serotonin (50 microM) or its agonist 5-methoxytryptamine (5 microM) stimulated the acrosome reactions of golden hamster sperm within 15 min after addition to sperm capacitated in vitro for 4.5 h. The stimulation was inhibited by the serotonin receptor antagonists quipazine or cyproheptadine. Epinephrine (70 microM), norepinephrine (50 microM), and dopamine (25 microM) were unable to stimulate acrosome reactions even at 30 min under the same conditions, even though previous studies had demonstrated stimulation by these catecholamines at the same concentrations when present from the start of the capacitation time course. Epinephrine (5 microM) also was unable to stimulate at 30 min. These results demonstrate that serotonin and its agonist have a more direct effect on the hamster sperm acrosome reaction than other biogenic amines and that the effect is receptor-mediated.