Ischemic carotid endothelium. Scanning electron microscopical studies

The normal luminal surface and the effect of ischemia on the endothelium of the common carotid arteries of rhesus monkeys were examined by scanning electron microscopy. Clamps were placed proximally and distally on the right common carotid arteries, totally occluding the vessels for periods ranging from five minutes to four hours. The clamps were then removed and fixation carried out by intravascular perfusion. The contralateral sham-operated carotids, as well as those from unoperated animals were used as control specimens. The most obvious effect of ischemia was the appearance of conical, crater-like defects in the cytoplasm of endothelial cells. Such "craters" were observed following as little as 15 minutes of ischemia, were much less frequent in sham-operated vessels, and were not seen in the unoperated control specimens.

Cyclic 3',5'-AMP phosphodiesterase of rabbit aorta

Cyclic AMP and cyclic GMP phosphodiesterase activities (3' : 5'-cyclic AMP 5'-nucleotidohydrolase, EC 3.1.4.17) were demonstrated in the isolated intima, media, and adventitia of rabbit aorta. The activity for cyclic AMP hydrolysis in the intima was 2.7-fold higher than that for cyclic GMP hydrolysis. The activity for cyclic AMP hydrolysis in the media was approximately equal to that for cyclic GMP hydrolysis, but in the adventitia, cyclic GMP hydrolytic activity was 2.1-fold higher than cyclic AMP hydrolytic activity. Distribution of the activator of the phosphodiesterase was studied in the three layers. Each layer contained the activator. The activator was predominantly localized in the smooth muscle layer (the media). The effect of the activator and Ca2+ on the media cyclic AMP and cyclic GMP phosphodiesterase was also briefly studied. The activity of the cyclic GMP phosphodiesterase was stimulated by micromolar concentration of Ca2+ in the presence of the activator. However, the activity of the cyclic AMP phosphodiesterase was not significantly stimulated by Ca2+ up to 100 muM in the presence of the activator. Above 90% of cyclic nucleotide phosphodiesterase activity in the whole aorta was found to be derived from the media. A major portion (60-70%) of the media enzyme was found in 105 000 times g supernatant. Cyclic AMP phosphodiesterase in the supernatant was partially purified through Sepharose 6B column chromatography and partially separated from cyclic GMP phosphodiesterase. Using a partially purified preparation from the 105 000 times g supernatant the main kinetic parameters were specified as follows: 1) The pH optimum was found to be about 9.0 using Tris-maleate buffer. The maximum stimulation of the enzyme by Mg2+ was achieved at 4mM of MgC12. 2) High concentration of cyclic GMP (0.1 mM) inhibited noncompetitively the enzyme activity, and the activity was not stimulated at any tested concentration of cyclic GMP. 3) Activity-substrate concentration relationship revealed a high affinity (Km equals 1.0 muM) and low affinity (Km equals 45 muM) for cyclic AMP. The homogenate and 105 000 times g supernatant of the media also showed non-linear kinetics similar to the Sepharose 6B preparation and their apparent Km values for cyclic AMP hydrolysis were 1.2 muM and 36-40 muM and an enzyme extracted by sonication from 105 000 times g precipitate also exhibited non-linear kinetics (Km equals 5.1 muM and 70 muM). 4) Papaverine exhibited much stronger inhibition on the aorta cyclic AMP phosphodiesterase (50% inhibition of the intima enzyme, I5 o at 0.62 muM, I5 o of the media at 0.62 muM and I5 o of the adventitia at 1.0 muM) than on the brain (I5 o at 8.5 muM) and serum (I5 o at 20 muM) cyclic AMP phosphodiesterase, while theophylline inhibited these enzymes similarly. However, cyclic GMP phosphodiesterases in all tissues examined were inhibited similarly, not only by theophylline but also by papaverine.

Immunofluorescent demonstration of plasma protein entry into arterial wall by cholesterol, epinephrine, norepinephrine and angiotensin II

Thepresence of IgG and beta-lipoprotein in thoracic and abdominal aortas of 33 rhesus monkeys under various conditions was observed by immunofluorescence and interference filter technique. In untreated and placebo control monkeys, a definite fluorescence due to IgG was seen in highly limited areas of the subendothelial space and the innermost layers and a weak but positive fluorescence due to beta-lipoprotein was sometimes show in highly limited spots of the subendothelial space, but not the medial layers. In challenged animals with cholesterol (1 g/kg p.o.) or epinephrine (1 mug/kg i.v.) or norepinephrine (10 mug/kg i.v.) or angiotensin II (1 mug/kg i.v.) or cholesterol (1 g/kg p.o.) plus epinephrine (1 mug/kg i.v.), definite fluorescence showing the entry of beta-lipoprotein and IgG from the vessel lumen into the subendothelial space and then into the medial layers of the arterial wall was clearly shown by serial sacrificing of animals after each challenge. The passage of beta-lipoprotein through the internal elastic lamina into the medial layer, was characteristically delayed as compared with that of IgG. In pretreated animals with pyridinolcarbamate (PDC) (10 mg/kg p.o.), EG467 (1 mg/kg p.o.) and Premarin (5 mg/kg i.v.), the acute entry of those plasma proteins was significantly inhibited.

Hyperreactive arterial endothelial cells in atherogenesis and cyclic AMP phosphodiesterase inhibitor in prevention and treatment of atherosclerotic disorders

The hyperreactive arterial endothelial cells have been introduced in this paper. They are characterized by their ability to transport particles too large for the small holes of the internal elastic lamina locating underneath the endothelial cells, such as carbon particles with the similar size of LDL, floating beta-lipoprotein, Lp(a) and especially of VLDL, into the subendothelial space from the blood stream by their abnormally strong contracting and phagocytosis-like activity. Large particles such as carbon particles with a size of 200 to 700 angstrom are too large to penetrate further through holes of the internal elastic lamina from the subendothelial space to muscular layers of the arterial wall, resulting in stagnating for a long time in the subendothelial space, thus showing the atherogenic property of the hyperreactive arterial endothelial cells. Such endothelial cells appear spotty and streaky in the localized endothelial lining of predominantly susceptible parts to atherosclerosis in susceptible animal species such as rabbit, chicken, and rhesus monkey especially densely in their atheromatous lesions, but do not generally appear in non-susceptible animals to atherosclerosis like rate and dog. They are extremely few in infant rabbit, but increase by age.They appear in hypertensive rat, showing a characteristic distribution even in small groups of arteriessuch as the circle of Willis. Cyclic AMP, and especially dibutyryl cyclic AMP, exhibited an inhibitory effect on the hyperreactivity of those cells. Cyclic AMP phosphodiesterase inhibitors, EG467 and eg626, exhibited a powerful inhibitory effect on the contracting and phagocytosis-like activity of those cells, as in the case of pyridinolcarbamate, which enhances enzymes to produce ATP and inhibits slightly cyclic AMP phosphodiesterase, although its inhibitory effect on cyclic AMP phosphodiesterase is weaker than that of EF467 and EG626. The usefulness of the inhibitors on cyclic AMP phospodiesterase of arterial endothelial cells and platelets and on that of brain, such as EG467 AND EG626, has been suggested in the treatment of atherosclerotic disorders, especially of cerebral atherosclerosis. Some of the hitherto desperate mental disability of the aged seem to be a promising target for treatment with cyclic AMP phosphodiesterase inhibitors.