Kinins

The role of bradykinin in endotoxic shock of intestinal origin

A relationship was looked for between blood levels of bradykinin and endotoxaemia produced by superior mesenteric artery occlusion in the rabbit. The levels of bradykinin were unrelated to and unaltered by the degree of endotoxaemia observed in the systemic and portal circulations. These findings suggest that bradykinin is not responsible for the release of endotoxin from the gut, or the circulatory collapse which follows.

Lowering of kininogen in rat blood by adrenaline and its inhibition by sympatholytic agents, heparin and aspirin

1 (-)-Adrenaline lowered the kininogen content and transitorily elevated the fibrinolytic activity of plasma following intravenous injection into the rat. Its effect on kininogen increased when administered by intravenous infusion.2 Although less effective, (-)-noradrenaline had a similar action to adrenaline; (+/-)-isoprenaline was inactive and failed to inhibit the effect of adrenaline.3 The effect of adrenaline on kininogen could be reproduced in vitro by incubation of whole blood, but not cell-free plasma, with the catecholamine for 5 min at 37 degrees C.4 Propranolol or phenoxybenzamine, as well as heparin or acetylsalicylic acid (aspirin), blocked the reduction of rat blood kininogen by adrenaline in vivo and in vitro.

Endothelial contraction induced by histamine-type mediators: an electron microscopic study

Previous work has shown that endogenous chemical mediators, of which histamine is the prototype, increase the permeability of blood vessels by causing gaps to appear between endothelial cells. In the present paper, morphologic and statistical evidence is presented, to suggest that endothelial cells contract under the influence of mediators, and that this contraction causes the formation of intercellular gaps. Histamine, serotonin, and bradykinin were injected subcutaneously into the scrotum of the rat, and the vessels of the underlying cremaster muscle were examined by electron microscopy. To eliminate the vascular collapse induced by routine fixation, in one series of animals (including controls) the root of the cremaster was constricted for 2-4 min prior to sacrifice, and the tissues were fixed under conditions of mild venous congestion. Electron micrographs were taken of 599 nuclei from the endothelium of small blood vessels representing the various experimental situations. Nuclear deformations were classified into four types of increasing tightness (notches, foldsl closing folds, and pinches. In the latter the apposed surfaces of the nuclear membrane are in contact). It was found that: (1) venous congestion tends to straighten the nuclei in al groups; (2) mediators cause a highly significant increase in the number of pinches (P < 0.001), also if the vessels are distended by venous congestion; (3) fixation without venous congestion causes vascular collapse. The degree of endothelial recoil, as measured by nuclear pinches, is very different from that caused by mediators (P < 0.001). (4) Pinched nuclei are more frequent in leaking vessels, and in cells adjacent to gaps (P < 0.001); (5) mediators also induce, in the endothelium, cytoplasmic changes suggestive of contraction, and similar to those of contracted smooth muscle; (6) there is no evidence of pericyte contraction under the conditions tested. Occasional pericytes appeared to receive fine nerve endings. Various hypotheses to explain nuclear pinching are discussed; the only satisfactory explanation is that which requires endothelial contraction.