The effect of alpha(1)- and beta-adrenergic blockade on daily rhythms of urinary adrenalin (ADR) and cortisol (CORT) under basal conditions were evaluated. Voles acclimated to a 12:12 h light/dark cycle at 26+/-2 degrees C received a single dose of either propranolol (PROP; 4.5 mg/kg) or prazosin (PRAZ; 1 mg/kg) 1 h before lights off. Urine samples were collected for 24 h at 4 h intervals. PROP evokes a significant increase in mean urinary ADR; although CORT was unaffected by PROP, PRAZ administration significantly decreased both urinary ADR and CORT during the scotophase as compared with control voles. Cosinor analysis indicated a significant 24 h rhythm in urinary ADR, but not in CORT secretion. ADR mesor and amplitude were increased and acrophase was significantly delayed by 5 h in PROP-treated voles; PRAZ elicited opposite effects. Unexpectedly, these changes in the 24 h ADR rhythm persisted 4-weeks after PROP-treatment. The 24 h rhythm components of urinary CORT were marginally altered 4-weeks post-PROP, but only the acrophase showed a significant change. Collectively, the results indicate that sympathetic activity has a redundant compensatory mechanism defending against physiological changes induced by beta-blockade. The simultaneous decrease in adrenal hormones induced by PRAZ suggests that alpha(1)-adrenoceptors may contribute to the mechanism of integrated stress responses.