Induction of Acrosome Reactions in Stallion Sperm by Equine Zona Pellucida, Porcine Zona Pellucida, and Progesterone1

Abstract

Progesterone and zona pellucida glycoproteins are capable of inducing acrosome reactions in capacitated sperm from humans, pigs, and horses. The goal of the present study was to determine whether capacitated stallion sperm could be induced to undergo the acrosome reaction by homologous (equine) zona pellucida, and heterologous (porcine) zona pellucida and to compare these results with progesterone-induced acrosome reactions. The greater availability of porcine zonae compared to equine zonae would allow this material to be used during clinical evaluation of stallion sperm function and specifically to test the ability of stallion sperm to become capac-itated in vitro. Motile sperm from 5 stallions were capacitated by incubation for 5 h at 39°C in TEST/Tyrode's albumin-lactate-pyruvate (TALP) medium. Sperm suspensions were then treated by the addition of one of the following: 1) solvent control, 2) 3.18 |iM progesterone, 3) 150 ng/ml heat-solubilized porcine zona pellucida (pZP), or 4) intact equine zona pellucida. Acrosomal status in viable sperm was evaluated by epifluorescence microscopy. Percentages of acrosome reactions in viable sperm were 8 ± 1 (control), 23 ± 2 (progesterone), 22 ± 3 (pZP), and 27 ± 3 (equine zona-bound sperm). These data suggest that equine sperm are equally able to acrosome-react in response to several physiological stimuli. The potential exists for the use of pZP or progesterone as clinical probes for equine sperm function and to investigate the physiology of sperm-egg interaction in the horse.