On Mechanisms of Head-to-Head Association in Bovine Spermatozoa

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Abstract
Several different agents cause head-to-head association in mammalian spermatozoa. At least two types of mechanisms may be discerned: 1) One depends on removal of substance(s), provisionally called antagglutin, from the surface of spermatozoa where it is bound to specific sites. The time dependence of association in seminal plasma under the influence of atmospheric oxygen was studied. Sperm associated by oxidation appeared to be dissociated by fumaramide, just as were sperm associated by washing. Association caused by removal of antagglutin may be reversed by addition of antagglutin or substances with varied basic structures, most of them containing enone structure (a carbonyl group conjugated with a C-C double bond). This dissociating effect of progesterone and testosterone was blocked by mersalyl, which also dissociated washed spermatozoa although lacking enone structure. Substances studied with respect to the dependence of their effects on the Ca2+ concentration, all showed the same pattern: they induced dissociation of sperm washed at 2 x 10-6 M Ca2+, association of similarly pretreated sperm upon simultaneous increase of the Ca2+ concentration to 2 x 10-5 M, and dissociation of sperm washed with Tyrode solution (Ca2+ concentration, 1.8 x 10-3 M). The mechanism of this association seems to depend on instability of the cell membrane in connection with rebinding of Ca2+ previously washed out. 2) Another type of association induced by ATP, ADP, and catecholamines is thought to depend on formation of cAMP which also elicits this effect. This type was not influenced by mersalyl, except when induced by adrenaline, which it stimulated. Imidazole (2 x 10-5 M), which dissociates sperm associated by washing, stimulated association induced by exogenous cAMP. Neither of these two actions can depend on stimulation by phosphodiesterase.