Microcirculatory aspects of atherogenesis, thrombogenesis, and antiatherosclerotics

Meso-Inositol Hexanicotinate Induced Protection against Experimental Anoxia and Oedema

It is shown that Meso-Inositol Hexanicotinate (MIHN; Hexopal) inhibits experimentally induced oedema of the paw in rats and that mice exposed to hypoxic atmospheres (4% oxygen) show significant increase in survival time if pre-dosed with MIHN.

The protection against oedema and hypoxia conferred by MIHN in experimental animals may well be related to the mode of action of the substance in man, and particularly could explain the usefulness of MIHN in the treatment of cerebral and peripheral atherosclerosis.

Angiotensin and bradykinin interactions with phospholipids

Reversible interactions were demonstrated between some phospholipids and some polypeptides related to angiotensin and bradykinin. The extent of the interaction was dependent on the structures of the lipid and peptide. The naturally occurring compounds that interacted most avidly were cardiolipin and (des-Asp1)-angiotensins. The apparent dissociation constant of this complex in chloroform was 10(-5) M. The complex contained more than one cardiolipin molecule/molecule of peptide. Kinins interacted most strongly with lecithin. The phospholipids altered the chromatographic behavior of radioiodinated derivatives of the polypeptides, and solubilized radioactive and unlabeled polypeptides in chloroform. In aqueous media, cardiolipin suspensions preferentially bound (des-Asp1)-angiotensin II, and inhibited its binding by antibody. The interactions were sensitive to pH and cations in the aqueous phase, and were reversed by some reagents added to the organic phase. These interactions have direct implications for binding reactions of peptides in vitro, and may bear upon the actions of the hormones in vivo.

The effect of sulfinpyrazone on morphological changes in the coronary vasculature induced by prolonged unpredictable stress in the rat

It was confirmed that prolonged unpredictable stress in the rat induces morphological change in the coronary microcirculation. These changes include dilation in venules, deposits staining positive with PAS in the venules due to platelet aggregation and a breakdown of the endothelial lining in arterioles. Sulfinpyrazone is reported to prevent platelet agglutination, and shows effectiveness in the clinic in preventing re-infarction following infarction. Accordingly rats were exposed to the stress regimen for 50 days, and groups were treated with sulfinpyrazone, either prophylactically (receive drug for 50 days) or therapeutically (receive drug Day 30 to Day 50). The morphology of the hearts of treated animals were compared with those of placebo treated controls. It was demonstrated that therapeutic sulfinpyrazone did not prevent (p less than 0.01), but reduced the incidence of morphological change in the coronary microcirculation. Prophylactic sulfinpyrazone had a distinct protective effect (p less than 0.001). It was demonstrated that the plasma corticosterone levels in both drug groups did not fall to the level found in control groups. The results are discussed in terms of a glucocorticoid-sulfinpyrazone interaction preventing prostaglandin release which will prevent platelet aggregation. It is possible that the interaction relates to maintaining the integrity of the microcirculatory endothelial cells, thus preventing the local release of inflammatory substances.

Changes in the coronary vascular system following prolonged exposure to stress

Hearts of stressed rats showed marked changes in the coronary vasculature. It was suggested that such morphological changes could be explained on the basis of an increased coronary vascular permeability. Endogenous inflammatory substances could induce swelling of the endothelial cells and cause separation of the neighbouring cells from one another, thus allowing the passage of lipid molecules through the endothelial lining. In order to gain supportive evidence for the above hypotheses an electron microscope study was undertaken. The presence of junctional gaps in the endothelial lining of the coronary vascular system was observed following prolonged stress, as well as platelet aggregation. The use of lipid staining of frozen sections indicated the presence of large lipid deposits in the arteriole walls, corresponding to vacuoles seen previously. It would appear therefore, that prolonged exposure to stress may result in pathological changes in the myocardium associated with changes in the vascular endothelial permeability, and platelet aggregation. Pathological changes induced in this way, however, should be inhibitd by high glucocorticoid levels and should not be manifested until adaptation of the steroid response to stress has occurred. Measurement of plasma glucocorticoid levels over the period of prolonged stress shows a good correlation between the adaptation of the steroid response and the onset of a progressive degeneration of the coronary vascular system.

Morphological changes induced in rats following prolonged exposure to stress

Prolonged exposure of male C. S. F. rats to irregular signalled footshick from which they could escape for up to 71 days produced profound morphological changes. Retardation in growth, adrenal hypertrophy associated with an increase in the zona fasiculata a-nd zona reticularis, and changes in the microcirculation of the heart were observed. There was a significant degree of congestion and dilatation of the microcirculation which was most marked in large venules, collecting venules and veins. An increase in PAS +ve material marginated in the venous endothelium was observed also, together with a suggested increase in mast cells and presence of vacuoles in the intima-media of the coronary arterioles. No pathological changes were observed in the renal cortex and medulla or the gastric lining. The changes in the microcirculation of the heart are discussed in terms of an oedematous reaction and a histamine type leakage of the endothelial lining.