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. STUDY DESIGN: 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(2α) (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. CONCLUSION: 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.