title: Naloxone reversal of 5-hydroxytryptamine tachyphylaxis in humans.
abstract: The dorsal hand vein, a suitable substrate for testing the effects of spasmogenic amines in vivo, exhibits a rapid tachyphylaxis to 5-hydroxytryptamine (5-HT)-induced vasoconstriction in healthy subjects. In the tachyphylactic vein, naloxone promptly restores and sometimes potentiates the sensitivity to 5-HT. The local opioid system could be excited by the 5-HT-induced release of noradrenaline (NA) into the neuromuscular junction, thereby participating in the 5-HT tachyphylaxis. Naloxone, antagonizing this mechanism, restores the 5-HT spasm. Therefore, the 5-HT tachyphylaxis could be due to an increased opioid modulation and not (or perhaps partially) to a depletion of the NA in the sympathergic neuron.
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009270:Naloxone / Q000494:pharmacology*; D012701:Serotonin / Q000494:pharmacology*; D013618:Tachyphylaxis
chemical_list: D012701:Serotonin; D009270:Naloxone