Gerald Pollack has shown that water at contact surfaces will organize into a "gel-phase", analogous to ice but without the hydrogen protons that bond the lattice sheets vertically (Pollack, 2013). This "gel" is negatively charged, and the excluded protons tend to gather adjacent to it. His model explains surface tension, and is well documented, experimentally proven, with simple experiments that can be reproduced at minimal effort and minimal cost.
This gel-phase of water means that cations like hydronium exists in abundance at the outside surface of the capillary endothelium. Since blood is negatively charged, it will tend to attract these cations. Inflow of hydronium at the proximal end of the capillary, causes circulation with filtration out at the distal end. This mechanism is similar to osmosis.
The pre-capillary sphincters provide volume for inflow at the proximal end.
In this electromotive theory of capillary exchange, mixing between the blood and the interstitial fluid is a result of the circulation into the proximal end and out of the distal end.
It would be expected that the precapillary sphincters contract with increased need for tissue perfusion. Epinephrine has been shown to contract these sphincters in mesenteric tissue (Dietrich, 1984) and skeletal muscle (Szwed, 1975). Increased perfusion in the intestine should then increase nutrient absorption, and that might have some support by empirical data, epinephrine has been shown to increase glucose uptake from the intestine by 500% (Grayson, 1983).
Synapses
Pollack, G. (2013). The Fourth Phase Of Water. Seattle, WA. Ebner & Sons.
Dietrich H.H., Weigelt H. (1984) Effect of Adrenaline on Capillary Diameter in the Frog Mesentery. In: Lübbers D.W., Acker H., Leniger-Follert E., Goldstrick T.K. (eds) Oxygen Transport to Tissue-V. Advances in Experimental Medicine and Biology, vol 169. Springer, Boston, MA
Szwed, J. J., & Friedman, J. J. (1975). Comparative effects of norepinephrine, epinephrine, angiotensin on pre- and postcapillary resistance vessels in dog skeletal muscle. Microvascular Research, 9(2), 206–221. https://doi.org/10.1016/0026-2862(75)90081-3
Grayson, J., & Oyebola, D. D. (1983). The effect of catecholamines on intestinal glucose and oxygen uptake in the dog. The Journal of Physiology, 343(1), 311–322. https://doi.org/10.1113/jphysiol.1983.sp014894