Effect of capsaicin pretreatment on capsaicin-induced catecholamine secretion from the adrenal medulla in rats.

The effect of capsaicin pretreatment on adrenal catecholamine secretion induced by intravenously administered capsaicin was investigated in alpha-chloralose and urethane anesthetized rats. In neonatal vehicle pretreated rats, capsaicin (200 micrograms/kg, iv) caused a rapid and significant increase in adrenal epinephrine secretion, but neonatal capsaicin pretreatment (50 mg/kg, sc, on the 2nd day of life) significantly reduced both the basal and capsaicin-induced epinephrine secretion from the adrenal medulla. Adult capsaicin pretreatment (6 increasing doses/6 days, total 310 mg/kg, sc) also reduced both the basal and capsaicin-stimulated adrenal epinephrine secretion, though it was less effective compared with the neonatal capsaicin pretreatment. These results suggest the participation of capsaicin-sensitive neurons in capsaicin-induced catecholamine secretion from the adrenal medulla.