The effects of isoprenaline and bradykinin on capillary filtration in the cat small intestine.

1 Lymph flow, and both lymph and plasma protein concentrations were measured in isolated, blood-perfused loops of cat ileum. 2 Permeability-surface ares (PS) products and the osmotic reflection coefficient (sigma) of the intestinal capillaries were calculated. 3 Isoprenaline (one dose) or bradykinin (two different doses) was infused into the superior mesenteric artery. 4 Isoprenaline (blood concentration about 50 ng/ml) did not affect PS or sigma. 5 Bradykinin (about 36 ng/ml) increased PS but as a sigma was unaltered, this was primarily due to an increased capillary surface area. 6 Bradykinin (about 680 ng/ml) increased PS and as sigma was reduced, there was an increased capillary permeability. 7 Reasons for the lack of effect of isoprenaline at concentrations which increase capillary filtration coefficient are discussed. 8 These data show that this technique separates drug effects on capillary surface area from effects on capillary permeability.