The effect of catecholamines and their antagonists on the fertilization of cumulus-free mouse ova in vitro at a suboptimal spermatozoal density

A suboptimal sperm concentration was used to assess the capacity of catecholamines to stimulate the fertilization of cumulus free F₁,(C57BL × CBA) mouse ova in vitro. At a concentration of 50 μM, (L) epinephrine significantly increased the proportion of ova fertilized at 2 × l0⁵ spermatozoa/ml. However, when (D, L) propranolol at an equimolar concentration was tested for inhibition of the (L) epinephrine effect, fertilization was inhibited in both the test and control dishes. At l0μM, propanolol by itself or in the presence of 50μM (L) epinephrine significantly increased the number of ova fertilized at 2 × l0⁵ sperm/ml. Norepinephrine (50 μM) and phentolamine (50 μM), either alone or together, were also slightly stimulatory. Some data are presented to suggest that propranolol may act in a nonadrenergic manner to precipitate the acrosome reaction and that the stimulatory effect is maximised when it is added to spermatozoa at the same time as ova addition. It was suggested that propranolol may act to trigger calcium influx by a nonspecific alteration in membrane function for example in (Ca + Mg) ATPase activity. It was concluded that spermatozoa at suboptimal densities are capable of achieving fertilization and that sperm concentration dependency in fertilization in vitro may be a reflection of the proportion of spermatozoa achieving capacitation.