Sympathetic stimulation and intestinal capillary fluid exchange.

Sympathetic nerve stimulation is generally considered not to alter intestinal capillary pressure or filtration rate because of appropriate adjustments in the pre-to-postcapillary resistance ratio. To directly assess this possibility, we measured lymph flow, capillary pressure, capillary filtration coefficient, and the transcapillary oncotic pressure gradient in the cat small intestine. Measurements were taken under control conditions and during the steady-state phase of periarterial nerve stimulation, i.e., following completion of the escape phase. Venous outflow pressure was held constant (0 mmHg) during the entire experiment. Nerve stimulation resulted in a significant reduction of lymph flow (by 65%), capillary filtration coefficient (by 75%), and capillary pressure (by 15%). Interstitial fluid pressure, calculated from the measured parameters in the Starling equation, was also reduced (from -0.74 to -2.53 mmHg) by nerve stimulation. The results of this study indicate that intestinal capillary pressure and capillary filtration rate are not "autoregulated" during sympathetic nerve stimulation. Capillary derecruitment appears to be largely responsible for the dramatic reduction in filtration rate associated with adrenergic stimulation.