Role of adrenal steroids on electroacupuncture analgesia and on antagonising potency of naloxone

Electroacupuncture (EA), a form of transcutaneous electrical stimulation, produces opiate-like antinociception and catalepsy in rats. This effect of EA cannot be produced in hypophysectomised rats, whereas adrenalectomised rats show increased sensitivity. In intact rats, adrenocorticotrophic hormone and dexamethasone have been found to be effective to sensitise the animals to the analgesic effect of EA. Deoxycorticosterone, on the contrary, attenuates this effect. Spironolactone is also effective to potentiate EA response, which is accompanied with severe respiratory depression. Drugs that are known to affect adrenal aldosterone secretion also modulate the effect of EA. Naloxone administration, 15 min prior to the initiation of EA stimulation, potentiates the effect of EA, whereas it counteracts the effect of EA if administered after initiation of EA stimulation. Moreover, this counteracting ability of naloxone increases with the increase in time interval between initiation of stimulation and naloxone challenge. Pretreatment with drugs that impair adrenal mineralocorticoid response to physiological stimuli inhibits the counteracting effect of naloxone. On the contrary, mineralocorticoid supplemented rats show greater sensitivity to naloxone counteraction.