Effects of prostaglandins and other putative chemical intermediaries on the activity of canine testicular polymodal receptors studied in vitro

Abstract

An in vitro testis-superior spermatic nerve preparation was used to evaluate the effects of chemical agents applied in the bathing solution. Both directly evoked discharges and responses to algesic solutions [bradykinin (BK) 9 X 10(-8) M, hypertonic saline 616 mM and high K+ solution 60 mM] of polymodal receptors were studied. Prostaglandin (PG)-E2 (1.4 X 10(-6)-1.4 X 10(-5) M) and serotonin (5-HT) (1.1 X 10(-6) to 1.4 X 10(-4) M) had only a weak excitatory effect. However, test responses to algesic substances were regularly greatly increased by PG-E2, -I2 and 5-HT. Concentrations of PG-E2 of 1.4 X 10(-8) M or greater augmented BK responses; higher concentrations and/or longer applications were needed to enhance responses to algesic salt solutions. Effective concentrations for the PGs and 5-HT were near those reported for inflamed tissues and exudate. Aspirin (ASA) (5.5 X 10(-4) M or greater, for more than 4 min) suppressed the responses to BK but not those evoked by hypertonic saline. The ASA effect on the BK response was largely restored by an addition of PG-E2. Substance P also had a weak excitatory effect on some polymodal receptors, but no significant enhancement of the response to BK was noted. These results further support a role of polymodal receptors in transmitting nociceptive information, of inflammatory origin.