CAPSAICIN-SENSITIVE NERVES IN THE JEJUNUM OF NIPPOSTRONGYLUS-BRASILIENSIS-SENSITIZED RATS PARTICIPATE IN A CARDIOVASCULAR DEPRESSOR REFLEX

Superfusion of capsaicin onto the serosal surface of jejunum of Nippos trongylus brasiliensis-sensitized rats induces a short-lasting (I - 3 min), dose-dependent (2 to 20 mug) decrease in blood pressure which ra nges from -5.3+/-1.4% to -22.6+/-2.2%. The hypotension evoked by capsa icin was more marked in sensitized rats than in unsensitized animals, which responded only to the highest dose (20 mg) of capsaicin tested. The hypotensive effects of capsaicin were not affected by intravenous injections of mepyramine (10 mg/kg), a histamine receptor antagonist, or by the cycloxygenase inhibitor indomethacin (10 mg/kg). However, an intravenous injection of a platelet-activating factor (PAF) antagonis t, BN 52021 (20 mg/kg), or an intraperitoneal injection of guanethidin e (8 mg/kg) 18 h prior to experimentation, to functionally impair the sympathetic nerves, abolished the capsaicin-induced drop in blood pres sure. Treatment of neonatal rats with capsaicin reduced by 75% the hyp otensive effects of capsaicin, whereas the capsaicin antagonist, ruthe nium red, reduced non-significantly the hypotensive action of capsaici n. It is concluded that the activation of jejunal sensory nerves in N. brasiliensis-sensitized rats by capsaicin induced a reflex hypotensio n that is dependent upon PAF release from mast cells and functional sy mpathetic nerves. In addition, the afferent function of the sensory ne rves are not totally blocked by ruthenium red as capsaicin elicits the reflex hypotension in the presence of this blocker of sensory nerve e fferent function.