Urocortin (UCN), a newly identified corticotrophinreleasing-factor (CRF) related peptide, has been demonstrated to play important roles in female reproductive system. However, few studies were reported about its effects on male reproduction. This study aimed to investigate the expression profile of UCN and CRF receptors (CRFR) in mouse testis and functions of UCN in male reproduction. Expression of UCN and CRFR mRNA was detected by RT-PCR. Localization of UCN peptide was determined by

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... ochemistry and double-immunostaining. We found that both UCN mRNA and peptide were obviously expressed in mature spermatozoa, whereas CRFR1 and CRFR2 were expressed respectively in spermatocytes and spermatogonia. Doubleimmunostaining results showed that UCN expression decreased with acrosome reaction (AR) proceeding. UCN significantly inhibited AR initiated by progesterone with chlortetracycline staining and Key Words Urocortin (UCN) • Corticotrophin-releasing factor (CRF) • Sperm motility • Acrosome reaction (AR) • T-type calcium channel decreased spermatozoa motility concentrationdependently. Pre-incubation of spermatozoa with astressin, a CRFR antagonist, did not affect these inhibitions. In addition, flow cytometry showed that UCN concentration-dependently decreased intracellular Ca 2+ [Ca 2+ ] i in spermatozoa. In summary, UCN located in mouse spermatozoa and exerted inhibitory effects on male reproductive functions including motility and AR. UCN's inhibition on [Ca 2+ ] i via T-type calcium channels might be responsible for these effects.