In the present study, the expression of pituitary adenylate cyclase-activating polypeptide (PACAP) mRNA was investigated in rat testis and epididymis during postnatal development and experimental cryptorchidism using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. The results revealed that i) in the testis, PACAP mRNA expression was first detected on day 20 after birth and gradually increased from day 20 to reach a maximum level on day 60, mainly in the spermatocytes and round spermatids; ii) in the epididymis, PACAP mRNA was first detected on day 10 after birth and remained at higher levels from day 40; iii) the levels of PACAP mRNA in the testis and epididymis markedly decreased in a time-dependent manner from 1 week after cryptorchid surgery until they had almost disappeared at 4 weeks. These results suggested that the pattern of PACAP mRNA expression is developmentally dependent in both the testis and epididymis, and the expression of PACAP mRNA is regulated by the local temperature within the testis. In conclusion, the pattern of expression of PACAP in the testis and epididymis suggests a possible role of PACAP in spermatogenesis and sperm maturation.

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