Adrenergic and histaminergic neural interactions in dog paws

The mechanisms underlying the vascular responses of superficial fibular nerve stimulation (SFNS) have not been defined. Right hindpaws of anesthetized heparinized dogs were vascularly and neurally isolated, enclosed in a volume recorder, and perfused with controlled pressure. Vascular volume (VV) (131I-labeled albumin) and rate of tissue volume changes (VT) (plethysmography) were determined. SFNS increased blood flow resistance, reduced capillary filtration coefficient (CFC) and permeability-surface area product (PS) of 86Rb, increased VV, and reduced 131I-albumin recovery. VT increased at the rate of 3.35 +/- 0.45 ml/min. SFNS during terbutaline increased resistance, CFC, PS, and VV were unchanged, 131I-albumin recovery was complete, and VT increased at one-fourth the control rate. Phentolamine and yohimbine blocked all responses to SFNS. Prazosin with SFNS attenuated hemodynamic changes and VT increased to two-thirds of control, decreased VV, albumin, and Rb recovery but not PS and CFC. SFNS during pyrilamine maleate reduced VT increase to two-thirds of control rate and blocked decreases in PS and CFC. Metiamide did not change the SFNS responses, except to reduce vascular volume and VT. The combined histamine H1 and H2 blockers reduced VT increase to one-third of control and attenuated albumin loss, prevented histamine dilation, attenuated vasopressin and norepinephrine but not angiotensin constriction. SFNS stimulation increased precapillary resistance by alpha 1- and alpha 2-receptors and venous resistance by alpha 2-receptors and increased permeability by histamine release from endothelium.