Urinary bladder and urethral responses to pelvic and hypogastric nerve stimulation and their relation to vasoactive intestinal polypeptide in the anaesthetized dog.

The effects on the urinary bladder and urethra of pelvic and hypogastric nerve stimulation and their relation to vasoactive intestinal polypeptides (VIP) were investigated in the anaesthetized dog. Both pelvic and hypogastric nerve stimulation elicited a twofold increase in urinary bladder blood flow and a clear-cut increase in bladder venous effluent VIP concentration. Hypogastric nerve stimulation induced an initial, partly alpha-adrenergic and partly non-adrenergic, non-cholinergic, contraction of the urinary bladder followed by a relaxation. The urethra response was a maintained alpha-adrenergic contraction. Pelvic nerve stimulation elicited a bladder contraction with an initial non-cholinergic peak, whereafter the bladder pressure was maintained at a lower level, an effect which was mainly cholinergic in origin. The urethral response was an initial non-adrenergic, non-cholinergic contraction followed by a maintained cholinergic contractile response. Afferent pelvic nerve stimulation led to an efferent activity that seemed to be a combination of activity in pelvic and hypogastric pathways to the urinary bladder and the urethra. VIP (10 nmol) injected i.v. induced a relaxation of the urinary bladder and the urethra, together with a fall in systemic blood pressure. However, despite high plasma concentrations, no vasodilation was elicited in the urinary bladder. Thus, the main target for the VIP release during pelvic and hypogastric nerve stimulation is probably not the bladder vasculature, but instead perhaps the bladder smooth muscle proper.