PHARMACOLOGICAL CHARACTERIZATION OF THE VANILLOID RECEPTOR IN THE RATISOLATED VAS-DEFERENS

The present study set out to further characterize the vanilloid recept or in the rat isolated vas deferens. In this preparation, both capsaic in and resiniferatoxin (RTX) evoked a concentration-dependent inhibiti on in the amplitude of electrically-evoked contractions with pEC50 val ues of 7.62 +/- 0.03 and 12.2 +/- 0.21 respectively. Responses to caps aicin were fast in onset and faded rapidly over a 30-min exposure peri od, whereas those to RTX were slow in onset and well maintained, an ob servation believed to reflect pharmacokinetic differences in the rate of penetration to the vanilloid receptor. Responses to both agonists s howed mutual cross-desensitization and were antagonized by both the va nilloid-receptor antagonist capsazepine and the ion-channel blocker ru thenium red. The capsaicin analogue, olvanil failed to either mimic or antagonize capsaicin-evoked responses in the rat isolated vas deferen s, an effect at variance with previous observations in other tissues. The reason for these differences is unclear, but the possibility of mu ltiple classes of receptor cannot at this stage be ruled out.