Effect of adrenergic neurotransmitters upon the ejaculatory process in the stallion.

Successful empirical treatment of 17 out of 24 stallions, which had failed to ejaculate after normal penile erection, intromission and friction, by chemical blockage of beta-receptors and additional stimulation of alpha-receptors led us to investigate stallions with normal ejaculatory patterns. In an initial experiment one adult half-bred stallion was injected with 4.88 mg noradrenaline hydrochloride (treatment A), 10 mg bunitrolol (treatment B = beta-receptor blockage) and a combination of treatment A and B. Investigations of the same stallion on dated occasions without treatment served as controls. The test criteria were heart rate during copulation by telemetric measurement, volume of ejaculates and sperm concentration per ml and per ejaculate. In a second experiment, 2 stallions were treated after a modified test schedule. In addition to the criteria used in the first experiment seminal citric acid, ergothioneine, and glycerophosphocholine were measured. Administration of the beta-blocker alone or in combination with alpha-receptor stimulation resulted in (a) significant lowering of the maximal heart rate, (b) significant increase of sperm count per ejaculate and (c) significant rise of glycerophosphocholine.