Characterization of nitric oxide synthase activity in sheep urinary tract: functional implications

Area of Science:

• Urology
• Physiology
• Biochemistry

Background:

• Nitric oxide (NO) plays a crucial role in regulating urinary tract function.
• Understanding the distribution and activity of nitric oxide synthase (NOS) is essential for elucidating NO-mediated physiological processes in the urinary system.

Purpose of the Study:

• To investigate the presence and characteristics of NOS activity in the sheep urethra, detrusor, and ureter.
• To correlate NOS activity with functional NO-mediated responses to electrical field stimulation (EFS).

Main Methods:

• Assayed NOS activity by measuring the conversion of L-arginine to L-citrulline in tissue homogenates.
• Utilized thin layer chromatography to confirm endogenous citrulline production.
• Evaluated the effects of Ca(2+)-calmodulin, NOS inhibitors (L-NOARG, L-NAME, L-NMMA, 7-NI), and superoxide dismutase on NOS activity.
• Measured NO-mediated relaxations induced by EFS in isolated urinary tract tissues.

Main Results:

• NOS enzymatic activity was detected in the cytosolic fraction of sheep urethra, detrusor, and ureter, with the highest activity in the urethra.
• NOS activity was dependent on Ca(2+)-calmodulin and required NADPH and tetrahydrobiopterin (BH4).
• Electrical field stimulation induced significant NO-mediated relaxations in the urethra, which were inhibited by NOS inhibitors, while detrusor and ureter showed minimal responses.

Conclusions:

• The study demonstrates the presence of constitutive NOS activity in the sheep urinary tract, particularly in the urethral muscle.
• This urethral NOS activity likely mediates NO-dependent relaxation during micturition.
• The role of NOS in regulating detrusor and ureteral motor function appears to be limited.