Acute Contractile Effects of Epidermal Growth Factor on Bladder Smooth Muscles: An In Vivoand In VitroStudy in Rats

Chronic treatment with epidermal growth factor (EGF) stimulates growth of all wall layers of the urinary tract in pigs and rats. Herein, we investigated the acute effects of EGF on detrusor smooth muscle activity. For in vivoexamination, awake rats received EGF (75 μg/kg) intravenously and detrusor smooth muscle activity was monitored cystometrically. The EGF bolus caused no alteration in diuresis but a doubling of the micturition frequency, a 25% increase in micturition pressures, and increased irregular baseline contractile activity. For in vitroexamination detrusor smooth muscle strips were exposed to EGF (1 μg/ml). EGF caused contraction and increase in the spontaneous activity. In conclusion, EGF increases rat detrusor smooth muscle contractile activity in vivoand in vitro.The finding suggests that a direct effect of EGF on bladder smooth muscles is part of the genesis to the growth of the detrusor smooth muscle observed after chronic EGF treatment.