Effects of pregnancy on adrenergic function in the rabbit urinary bladder

Pregnancy induces morphological as well as functional changes in the urinary tract. Urinary frequency, incontinence, and an increase in residual urine are common clinical findings during gestation. Previous studies from this laboratory have shown a decreased cholinergic response and cholinergic receptor density in the urinary bladders of pregnant rabbits. In the present study, the adrenergic functions of the bladders of pregnant and virgin New Zealand White rabbits were compared using isolated muscle strips. Dose‐response curves showed that the contractile responses to epinephrine (alpha and beta agonist) and methoxamine (alpha agonist) were significantly reduced in tissues from the base and the mid‐segment, but not the body of the pregnant rabbit bladders. No significant difference was observed in the degree of isoproterenol (beta agonist) induced relaxations between the two groups. Thus, the results demonstrated a decreased alpha responsiveness in the midsegment and base of the pregnant bladders. Physiologically, a decrease in alpha tone at the bladder base would be advantageous for bladder emptying as the resultant relaxation at the bladder outlet theoretically would alleviate the effect of decreased bladder body contractility as well as any mechanical stress imposed on the urethra by the enlarging uterus.