Brief (7-14 days) social deprivation stress has been found to increase blood pressure in Wistar rats, an effect dependent on activation of opioid function. The role of central opioids in this and other responses to stress has been repeatedly determined, but the possible involvement of modifications of peripheral opioid mechanisms is poorly understood. To further increase this knowledge, we have examined the opioid sensitivity of tail arteries taken from social deprived Wistar rats by studying the effect of beta-endorphin and DADLE "in vitro". Both opioids inhibited the electrically-induced constriction of the preparations in a dose-dependent manner, but these actions were significantly attenuated after 7-14 days of social deprivation. When the rats were isolated for 30-35 days, the hypertensive response was still present but the arteries from group-housed and isolated animals no longer showed differential sensitivity to opioids. This difference with respect to 7-14 days of isolation could be related to age-dependent changes of opioid function, which were observed among group-housed animals. The results suggest that social deprivation stress induces an adaptation of the tail arteries to the opioid effects on contractility. It is suggested that this endogenous adaptation could be contributing to the hypertensive response observed after social deprivation.