Frequency-dependent control of nutritional and nonnutritional circuits in the dog paw.

The neural control of blood flow and volume distribution between parallel nutritional and nonnutritional circuits has been investigated in 13 vascularly and neurally isolated dog hindpaws. The superficial and deep fibular nerves and the tibial nerve were cut and individually stimulated at frequencies of 0.1, 1, 5, 10 and 15 Hz. Increasing stimulation rates to each nerve progressively increased blood flow resistance. Vascular volume changes were determined by indicator dilution and tissue volume changes by plethysmography. The permeability surface area product of 86Rb (PS) and the capillary filtration coefficient (CFC) were determined. Superficial fibular nerve and deep fibular nerve stimulations caused progressively increased nonnutritional circuit constriction with increasing stimulation frequencies resulting in blood flow redistribution to the nutritional circuit as evidenced by increasing PS and CFC values. Tibial nerve stimulation at 0.1 Hz caused nonnutritional circuit constriction and blood flow redistribution to the nutritional circuit (PS and CFC increased). As the stimulation frequency was increased, there was progressive increase of the nutritional circuit constriction and altered blood flow distribution; i.e., CFC and PS decreased with increasing frequency of stimulation, presumably due to predominantly arterial segment resistance increase.