OBJECTIVE Our purpose was to study the effect of oophorectomy on the passive and active mechanical characteristics of rabbit small cerebral and small coronary arteries. METHODS Ring preparations of small cerebral and small coronary arteries from rabbits that had undergone oophorectomy and sham operation were mounted on myographs 6 weeks after operation. Experiments were performed as follows. (1) concentration-response relations for vasopressin (10(-11) to 10(-7) mol/L), U46619 (10(-10) to 10(-6) mol/L), 5-hydroxytryptamine (10(-7) to 10(-5) mol/L), and endothelin (10(-13) to 10(-7) mol/L); (2) relaxing effects of acetylcholine (10(-8) to 10(-4) mol/L); (3) length-tension relations after addition of high potassium (124 mmol/L), vasopressin (10(-7) mol/L), and a mixture composed of potassium (124 mmol/L), vasopressin (10(-7) mol/L), and prostaglandin F 2 alpha (10(-5) mol/L); (4) calculation of vessel morphologic features and determination of hydroxyproline as a measure of collagen content. RESULTS Oophorectomy did not influence basal tone, relaxant effects of acetylcholine, vessel morphologic features, elastic characteristics, or hydroxyproline content of the vessels. However, in cerebral arteries at a normalized lumen diameter, oophorectomy induced a marked increase in the force development after stimulation with agonists but not after depolarization with high potassium. The reason for this was a leftward shift in the active length-tension curves (vasopressin activation). In coronary arteries none of these changes were seen after oophorectomy. CONCLUSIONS These data demonstrate that withdrawal of ovarian hormones changes the position of the active length-tension curve for pharmacomechanical but not electromechanical coupling of small cerebral arteries without interference with the elastic characteristics of these vessels.