Estrogen-induced alterations in the autonomic responses of the rabbit urinary bladder

The effect of estrogen administration on the autonomic innervation of the rabbit urinary bladder was studied. Immature female white rabbits were injected twice daily with estrogen (150 microgram/kg) for 4 consecutive days. Control animals received injections of vehicle. The response of bladder strips to the following agonists were determined for control and estrogen-treated animals: methoxamine (alpha adrenergic); isoproterenol (beta adrenergic); bethanechol (muscarinic cholinergic); ATP (purinergic); and potassium chloride (nonreceptor mediated). Additionally, the adrenergic and cholinergic receptor densities were determined by standard radioligand binding techniques. Estrogen induced a marked increase in the response to alpha adrenergic, muscarinic cholinergic and purinergic agonists in the bladder body and midbladder. No significant alterations were noted in the bladder base. In addition, no alterations were noted for isoproterenol or potassium chloride. The receptor densities paralleled closely the physiological responses. Estrogen induced a significant increase in alpha adrenergic and muscarinic receptors in the bladder body and midsection, whereas no change was noted in the receptor density of the bladder base. Estrogen did not alter the beta receptor density. These findings indicate that the urinary bladder responds as a target organ for estrogen-induced alterations in autonomic innervation.