EFFECTS OF ISOPRENALINE AND BRADYKININ ON CAPILLARY FILTRATION IN THE CAT SMALL-INTESTINE

Lymph flow, and both lymph and plasma protein concentrations were measured in isolated, blood‐perfused loops of cat ileum. Permeability‐surface area (PS) products and the osmotic reflection coefficient (σ) of the intestinal capillaries were calculated. Isoprenaline (one dose) or bradykinin (two different doses) was infused into the superior mesenteric artery. Isoprenaline (blood concentration about 50 ng/ml) did not affect PS or σ. Bradykinin (about 36 ng/ml) increased PS but as σ was unaltered, this was primarily due to an increased capillary surface area. Bradykinin (about 680 ng/ml) increased PS and as σ was reduced, there was an increased capillary permeability. Reasons for the lack of effect of isoprenaline at concentrations which increase capillary filtration coefficient are discussed. These data show that this technique separates drug effects on capillary surface area from effects on capillary permeability. 1979 British Pharmacological Society