SKIN STIMULATION WITH COLD-WATER INHIBITS CAPSAICIN-INDUCED COUGH ANDDECREASES SUBSTANCE P-LIKE IMMUNOREACTIVITY IN GUINEA-PIG LUNGS

The effect of repeated skin stimulation with cold water on substance P -like immunoreactivity (SP-IR) in the lung and on capsaicin induced co ughing was studied in awake guinea pigs. The coughing number was deter mined by observing the changes in air flow and abdominal pressure caus ed by a strong cough. Inhalation of capsaicin (10 mu M) for 1 min incr eased significantly the coughing number as compared to inhalation of t he vehicle. SP-IR in the lung decreased significantly in the guinea pi gs treated with capsaicin (10 mu M) for 1 min as compared to placebo. In guinea pigs that were exposed to repeated cold water skin stimulati on for 14 consecutive days, both lung SP-IR and coughing number induce d by inhalation of capsaicin (10 mu M) for 1 min decreased significant ly as compared to the control. Pretreatment with phosphoramidon (2.5 m g/kg, i.v.) increased the coughing number induced by capsaicin in cont rol guinea pigs but not in guinea pigs that were stimulated with cold water. These findings show that capsaicin-induced cough is inhibited i n guinea pigs subjected to repeated cold water skin stimulation and th is decrease is associated with a reduction in the SP contained in sens ory nerves of the lungs.