Endorphins and the central inhibition of urinary bladder motility.

The involvement of endogenous opioid mechanisms in the central neurogenic control of urinary bladder function has been examined in anesthetized rats. Intracerebroventricular (ICV) microinjections of beta-endorphin (0.5-2.0 micrograms) produced powerful inhibition of rhythmic bladder contractions initiated by central reflex activity. The peptide fragments gamma-endorphin and alpha-endorphin (4-16 micrograms), formed by the processing of beta-endorphin by membrane homogenates of brain, were less active than the parent compound. The inhibitory effects of beta-endorphin was reversed by ICV naloxone (1-2 micrograms) but higher doses were required to reverse gamma- or alpha-endorphin effects. ICV naloxone administered alone increased intravesicular pressure and bladder contraction frequency. These observations support the hypothesis that the endorphins have a physiological role in the central regulation of urinary bladder activity.