Modulation of the release of [3H]norepinephrine from the base and body of the rat urinary bladder by endogenous adrenergic and cholinergic mechanisms.

Modulation of [3H]NE release was studied in rat urinary bladder strips prelabeled with [3H]NE. [3H]NE uptake occurred in strips from the bladder base and body, but was very prominent in the base where the noradrenergic innervation is most dense. Electrical field stimulation markedly increased [3H]NE outflow from the superfused tissue. The quantity of [3H]NE release was approximately equal during three consecutive periods of stimulation. Activation of presynaptic muscarinic receptors by 1.0 microM oxotremorine reduced [3H]NE release to 46% of the control. Atropine (1 microM) blocked the effect of oxotremorine and increased the release to 147% of predrug control levels. Activation of presynaptic alpha-2 adrenoceptors by 1 microM clonidine reduced [3H]NE release to 55% of control. Yohimbine blocked the action of clonidine and increased the release to 148% of control. The release of [3H]NE from the bladder base and body was increased by both 1 microM atropine (to 167% and 174% of control, respectively) and 1 microM yohimbine (to 286% and 425% of control, respectively). Atropine and yohimbine administered in combination had similar facilitatory effects as when administered alone. We conclude that the release of [3H]NE from adrenergic nerve endings in electrically stimulated bladder strips is modulated via endogenous transmitters acting on both muscarinic and alpha-2 adrenergic presynaptic receptors and that the latter provide the most prominent control.