Pituitary adenylate cyclase-activating polypeptide (PACAP): effects on blood flow in the testis and caput epididymidis of the rat.
Pituitary adenylate cyclase-activating polypeptide (PACAP) is synthesized in developing germ cells in the testis and may act as a paracrine modulator of spermatogenesis and/or participate in tubule-interstitial interactions. Despite the abundance of PACAP in the organ, its role in testicular function has not yet been studied in vivo. Using laser Doppler flowmetry, the effects of PACAP on blood flow in the testis and caput epididymidis were studied on anesthetized adult rats. When given intratesticularly as 5- and 50-ng doses, PACAP increased blood flow by 55+/-21% (mean +/- SEM, P < 0.05) and by 68+/-11% at 5 mm from the injection site, respectively. Whereas 5 ng PACAP did not influence blood flow 15 mm from the site of injection, flow was reduced (-7+/-3; P < 0.05) at this site following treatment with 50 ng. Injection of 50 ng PACAP into the caput epididymidis increased epididymal blood flow by 18+/-4% (P < 0.05) at 1 mm from the injection site. None of the treatments above significantly affected the mean arterial blood pressure. Using immunohistochemistry, PACAP was observed in elongated spermatids and in the acrosomes of round spermatids in some, but not all, seminiferous tubules. Also, distinct PACAP immunoreactivity was seen in epithelial cells, particularly in clear cells, of the caput epididymidis. In conclusion, PACAP can induce vasodilatation in both testicular and epididymal microvessels and may be involved in regulating blood flow in these organs. Whereas the vasodilatory effect of PACAP is strong in the testis, the epididymal response appears to be more moderate.