Further Evidence Suggesting the Hormonal Stimulation of Hamster Sperm Acrosome Reactions by Catecholamines in vitro

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Abstract
Catecholamines can stimulate activation (motility characteristic of capacitation) and the acrosome reaction in hamster sperm in vitro. Both .alpha.- and .beta.-adrenergic mechanisms are evidently involved in this stimulation. Further evidence to support or modify the conclusion that catecholamines can stimulate these events in hamster sperm in vitro through hormonal mechanisms is provided. The (-)-isomers of epinephrine, norepinephrine and the .beta.-adrenergic agonist isoproterenol (all at 50 .mu.M) significantly stimulated greater numbers of acrosome reactions than did the (+)-isomers. Sperm incubated with the (+)-isomers gave significantly greater numbers of acrosome reactions than did the control sperm incubated in the absence of the (-)- and (+)-isomers. Evidently (-)-isomers stimulated acrosome reactions through interaction with adrenergic receptors. In all cases the (-)- and (+)-isomers stimulated activation to the same extent over control levels. Physiological levels (0.5 nM) of (-)-epinephrine significantly stimulated acrosome reactions, but only in the presence of the chelator D-penicillamine (20 .mu.M). The latter alone also increased acrosome reactions compared to the control, but to a significantly lower level than when in the presence of (-)-epinephrine (0.5 nM). (+)-Epinephrine (0.5 nM) did not increase acrosome reactions over the control level, either in the presence or absence of D-pencillamine. (-)-Epinephrine or D-penicillamine alone or (+)-epinephrine (0.5 nM) plus D-pencillamine stimulated activation to the same extent over control levels. The .beta.-adrenergic antagonist oxprenolol (2.5 nM) inhibited the stimulation of acrosome reactions by (-)-epinephrine plus D-penicillamine to the level obtained with D-penicillamine alone. Oxprenolol did not inhibit activation. The results of experiments with 3 other chelators, chromotropic acid, catechol-3,5-disulfonic acid and EDTA, were identical to those obtained with D-penicillamine. Evidently (-)-isomers of catecholamines do stimulate acrosome reactions primarily by interaction with adrenergic receptors. The (+)-isomers appear to stimulate primarily through nonhormonal mechanisms.

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