Effect of muscle length on adrenergic stimulation of canine detrusor

The effect of muscle length on adrenergic stimulation of canine detrusor was studied in an vitro muscle bath. The commonly reported response of muscle relaxation with norepinephrine stimulation was seen in muscle strips at or near the resting length. When the muscle strips were stretched, however, an alpha receptor mediated contraction was noted. Length, rather than norepinephrine dose or tension, was the predominant factor determining whether a given strip would respond in an alpha or beta fashion. Sympathetic stimulation may enhance accommodation (beta effect) during bladder filling at low muscle length and potentiate bladder emptying (alpha effect) at increased muscle length.