Abstract. This study investigated whether a cyclic adenosine 3',5'-monophosphate (cAMP) analogue, cBiMPS, could induce hyperactivated motility in frozen-thawed Japanese Black bull spermatozoa and compared the ability of spermatozoa to undergo hyperactivation between fertile and subfertile bulls. Frozen-thawed spermatozoa from 3 fertile and 2 subfertile bulls were washed, suspended in BO-Hepes medium and incubated in the presence of 0.1 mM cBiMPS for up to 4 h. At 1-h intervals, the spermatozoa were examined for hyperactivated motility. The proportions of spermatozoa showing a circular swimming pattern with asymmetrical flagellar beating and those showing whiplash beating of flagella to the total number of motile spermatozoa were expressed as C% and W%, respectively. The motile spermatozoa % was barely affected by treatment with cBiMPS or the fertility status of the sperm donor, although it gradually decreased in all sperm samples during the 4-h incubation. In the fertile bulls, the C% was 0% at 0 h of incubation but rapidly increased during the 1-h incubation with cBiMPS. It then decreased slightly towards 4 h concomitantly with a gradual increase in W% towards 4 h. In the subfertile bulls, however, the cBiMPS-induced increase of C% was delayed for 1-3 h, although the incubation time-related changes in mean W% were similar between the fertile and subfertile bulls. In the vehicle controls for cBiMPS, the C% and W% were 0% throughout incubation for all the samples examined. The results suggest that hyperactivation of the flagellum can be induced by the cAMP analogue, cBiMPS, in frozen-thawed Japanese Black bull spermatozoa and that induction of hyperactivation may serve as a useful tool for detection of functional abnormality of spermatozoa from subfertile Japanese Black bulls. Key words: Bull, Cyclic adenosine 3',5'-monophosphate (cAMP), Hyperactivation, Spermatozoa, Subfertility (J. Reprod. Dev. 56: [36][37][38][39][40] 2010) ammalian spermatozoa must acquire fertilizing ability prior to penetration of the oocyte, and this is generally called capacitation [1]. This change includes two kinds of processes: priming for the occurrence of the acrosome reaction, which is capacitation of the sperm head, and hyperactivated motility of the flagellum (hyperactivation). Capacitation, hyperactivation and the acrosome reaction are essential prerequisites for mammalian spermatozoa to fertilize eggs. Impairment of any of these functions might cause fertilization failure leading to possible infertility or subfertility. Such cases have also been reported in humans [2,3].Recent studies have revealed that in boar spermatozoa, hyperactivated motility is induced by cyclic adenosine 3',5'-monophosphate (cAMP), protein kinase A (PKA)-dependent tyrosine kinase and activation of phospholipase Cγ-protein kinase C signalling via SYK activation [4][5][6]. In bull spermatozoa, however, hyperactivated motility and capacitation may be regulated by different pathways [7], although Ca 2+ may be essential for both functions [8,9]. It has been...
