Opiate agonists increase tone of the vesical sphincter which may make urination difficult. These effects, in conjunction with the central effect of the drugs on release of vasopressin, may produce oliguria; however, results of one study suggest that decreased urine output may occur without any apparent release of vasopressin and may be attributed to decreased rate of glomerular filtration and solute excretion. Some clinicians have attributed decreased urine output to decreased renal plasma flow or increased reabsorption.Large doses of opiate agonists may cause bronchoconstriction, but this effect is rarely seen with therapeutic doses. |