Comparison of the effects of prostaglandins E2 and I2 on testicular nociceptor activities studied in vitro

Summary Effects of exogenous prostaglandin (PG) E₂ and PGI₂ on testicular polymodal receptor activities were compared in in vitro recordings of single- or multi-fiber discharges from canine testis-spermatic nerve preparations. PGI₂ up to 1.4×10^–6 mol/l (cumulative method) or 1.0×10^–5 mol/l (non-cumulative method) excited only weakly some of the receptors, and similar observations were made with PGE2. Both PGs applied cumulatively or non-cumulatively at concentrations above 1.4×10^–8 mol/l augmented the response to bradykinin (9.4×10^–8 mol/l) in more than half of the cases tested. The augmenting effect of PGE₂ lasted longer than that of PGI₂ both with the cumulative and the non-cumulative method. The degree of augmentation tended to increase dependent on concentration, but some cases showed no further increase or rather a decrease in augmentation by PGs at a ten times higher concentration, especially when PGs were applied cumulatively. A second challenge by PG after a short interval (2 min) did not induce augmentation. These phenomena were considered to be tachyphylaxis to PGs. Cross-tachyphylaxis to PGE₂ and PGI₂ was also observed. There was not much difference in excitatory and augmenting potencies between these two PGs, but there was a clear difference in the concentrations of the PGs necessary to induce excitation of polymodal receptors and to facilitate their response to bradykinin. Send offprint requests to T. Kumazawa at the above address