Downregulation by estrogen of nitric oxide synthase activity in the femalerabbit lower urinary tract

Objectives. Because female urinary tract tissues are considered to be targe ts for estrogen, and because nitric oxide (NO) is known to participate in t he nerve-induced relaxation in the lower urinary tract, the effect of estro gen on nitric oxide synthase (NOS) in the upper and lower urinary tracts wa s examined. Methods. Ovariectomized rabbits were treated with polyestradiol phosphate, and NOS in both cytosolic and particulate fractions from kidney, urinary pe lvis, ureter, urinary bladder, trigonum, and urethra was characterized. NOS activity was measured by the formation of [C-14]-L-citrulline from [C-14]- L-arginine. Results. NOS was considerably higher in cytosolic than in particulate fract ions from all urinary tracts, and activity in both fractions was highly cal cium dependent. NOS activity was much lower (fourfold to eightfold) in the kidney and pelvis than in the ureter. Estrogen treatment caused no change i n NOS in either fraction from upper urinary tract tissues. In the lower uri nary tract, NOS was slightly higher in the bladder and trigonum than in the urethra, and activities were comparable to NOS in the ureter. In contrast to the upper urinary tract, estrogen treatment led to a significant reducti on of cytosolic NOS in the bladder, trigonum, and urethra. Estrogen, howeve r, caused no significant change in the particulate NOS. Conclusions. Downregulation by estrogen in cytosolic NOS in the tissue of t he lower urinary tract is consistent with the presence of estrogen receptor s and suggests a physiologic significance. (C) 1999, Elsevier Science Inc. All rights reserved.