Effect of adrenergic agents on urethral pressure and urethral compliance measurements in dog proximal urethra.

The effects of adrenergic drugs on urethral compliance and urethral closure pressure at the proximal urethra of dogs were investigated using a new probe. The probe, with a balloon at the tip, was equipped with two generating and two detecting electrodes. The probe was inserted into the proximal urethra, and saline was then infused at a constant rate into the balloon with an infusion pump. The pressure and cross-sectional area of the urethra were recorded and a correlation curve of these parameters was drawn. The regression (of the form y = ax + b) was determined from the curve. Urethral compliance and closure pressures were obtained from the values of "a" and "-b/a" respectively, and the maximum cross-sectional area was measured when no further distension of the urethra was obtained. Urethral compliance decreased after the administration of phenylephrine, but increased after the administration of prazosin and labetalol. The urethral closure pressure decreased after the administration of dopamine and haloperidol. There was no change in either urethral compliance or closure pressure after the administration of clonidine, yohimbine, isoproterenol, or propranolol. The results indicate that adrenergic drugs work on urethral compliance, and that the alpha-adrenergic receptor of the proximal urethra is of the alpha-1 type. The changes in the urethral pressure after dopamine administration seems to be a response mediated by dopamine receptors.