Hyperglycemia has been shown to diminish Na+-K+ ATPase activity in rabbit aorta. To examine the basis for this effect, aortic rings were incubated for 3 h in Krebs-Henseleit solution containing 5.5 or 44 mM glucose, and Na+-K+ ATPase activity was then quantified on the basis of ouabain-sensitive (OS) 'Rb-uptake. Incubation with 44 mM glucose medium caused a 60% decrease in Na+-K+ ATPase activity in rings with intact endothelium (from 0.22±0.01 to 0.091±0.006 nmol/min per mg dry wt; P < 0.01). Similar decreases (45%; P < 0.01) in Na+-K+ ATPase activity were seen when rings incubated with 5.5 mM glucose were exposed to NG-monomethyl L-arginine (300 1M), an inhibitor of endothelium-derived nitric oxide (EDNO) synthesis or when the endothelium was removed (43% decrease). The decrease in Na+-K+ ATPase activity induced by hyperglycemia was totally reversed upon adding to the medium either L-arginine, a precursor of EDNO biosynthesis or sodium nitroprusside, which bypasses endothelium and directly activates the soluble guanylate cyclase in vascular smooth muscle. A decrease in Na+-K+ ATPase activity (42%; P < 0.05), only seen in the presence of endothelium, was also observed in aortas taken directly from alloxan-induced diabetic rabbits. These studies suggest that the decrease in vascular Na+-K+ ATPase activity induced by hyperglycemia is related, at least in part, to a decrease in the basal release of EDNO. They also suggest that alterations in basal EDNO release and possibly Na+-K+ ATPase activity contribute to the impairment in vascular relaxation caused by hyperglycemia and diabetes. (J. Clin. Invest. 1992. 90:727-732.)

An endothelium-derived factor with the properties of nitric oxide (NO) has been implicated in the regulation of Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity in vascular smooth muscle. To examine this phenomenon further and to explore its modulation by guanosine 3',5'-cyclic monophosphate (cGMP), studies were carried out in the isolated rabbit aorta. Incubation of endothelium-denuded rings with NO (1 microM) or sodium nitroprusside (SNP, 10 microM) caused a time-dependent increase in ouabain-sensitive (OS) 86Rb uptake with the maximal stimulation (approximately 170%) seen after 20 min. In contrast, increases in cGMP concentration caused by NO and SNP (40- and 20-fold increases, respectively) were transient, with peak values observed after 2 min and significantly lower values by 10 min. The ability of NO or SNP to increase OS Rb uptake in endothelium-denuded rings was not mimicked by incubation with 8-bromo- or dibutyryl-cGMP or increases in cGMP caused by treatment with the phosphodiesterase inhibitor isobutylmethylxanthine. Depletion of intracellular cGMP levels by the guanylate cyclase inhibitor LY83583 also did not alter OS Rb uptake. SNP-stimulated OS Rb uptake was not inhibited by LY83583 in endothelium-denuded rings; however, it was completely prevented by the Na(+)-H+ exchange inhibitors amiloride and ethylisopropylamiloride. The results suggest that NO stimulates Na(+)-K(+)-ATPase activity in rabbit aorta by a mechanism independent of its ability to increase the intracellular cGMP concentration. They also suggest that NO may stimulate Na(+)-K(+)-ATPase activity secondary to increases in Na(+)-H+ exchange.

An endothelium-derived factor with the properties of nitric oxide (NO) has recently been implicated in the regulation of basal Na(+)-K(+)-adenosinetriphosphatase (ATPase) activity in vascular smooth muscle. To determine whether this factor also plays a role in the stimulation of ouabain-sensitive (OS) 86Rb uptake by specific agonists, studies were carried out using rabbit aortic rings. In endothelium-intact rings incubated for 3 h with Krebs-Henseleit solution containing 5.5 mM glucose, endothelin (ET) caused a concentration-dependent increase in OS 86Rb uptake (maximal increase = 205%, with 100 nM ET). Incubation with phenylephrine (Phe; 0.1 and 1 microM) or phorbol 12,13-dibutyrate (PDBu; 0.1 microM), under the same conditions, increased OS 86Rb uptake by 128, 144, and 140%, respectively. Removal of endothelium before incubation decreased the ability of ET to stimulate OS 86Rb uptake by 38-45%, but it did not diminish the stimulation of OS 86Rb uptake by Phe or PDBu. An increase in the concentration of glucose from 5.5 to 44 mM diminished ET-stimulated OS 86Rb uptake by 50% in endothelium-intact rings but had no effect on Phe- or PDBu-induced increases in OS 86Rb uptake. Addition of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA; 0.3 mM) to the medium decreased ET-stimulated OS 86Rb uptake by 40%. Guanosine 3',5'-cyclic monophophate (cGMP) formation in endothelium-intact rings was also increased (65%) by ET but not by Phe or PDBu. The increase in cGMP by ET was totally inhibited by L-NMMA or endothelium denudation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aschoff [1906] first drew attention to the high content of cholesterol in atheromatous aortas. Since that time many quantitative micro-analyses have been performed on the lipids of whole aortas showing varying degrees of atheroma. Schoenheimer [1926; 1928] concluded that the total extractable lipid of the aorta increased with the age of the individual and the severity of atherosclerosis. Furthermore, in the early stages the relative amounts of phospholipid and cholesteryl esters increased with iticreasing total extractable lipid. A stage was reached, however, at which the percentage of phospholipid and cholesteryl ester in the total lipid became constant. He explained these results on the basis of infiltration and deposition of a lipid mixture elaborated elsewhere. These and other early investigations have been reviewed by Wells [1933]. Later studies [Meeker & Jobling, 1934; Zeek, 1936] have dealt with the changing ratios between total cholesterol, free cholesterol and phospholipids in isolated plaques classified according to the degree of atheroma. The results of these more extensive analytical investigations were at variance with those of Schoenheimer. They indicated that the values of the ratio free cholesterol/bound cholesterol in early plaques were lower than those for normal intimal tissues, while in the advanced lesions they were normal or above normal. Total cholesterol, cholesteryl esters, fatty acids and lecithin were found to increase with the progress of atheroma. Weinhouse & Hirsch [1940] and Page [1941] determined free cholesterol, cholesteryl esters and phospholipids (neutral fat by difference) in the lipid mixtures of normal human plasma and atheromatous plaques, and drew attention to the quantitative similarity in the compositions of these lipids. Comparatively little work has been done on the isolation or identification of the individual constituents of the various fractions of the lipid from atheromatous aortas. Schoenheimer [1928] isolated free cholesterol, the cholesteryl esters of oleic, palmitic and stearic acids, and a galactoside, by fractional crystallization of the acetone, light petroleum (l.p.) and alcoholic extracts of the adventitia-free atheromatous aortas. He also found indications of the presence of 'oxycholesterol' and fatty acids having more than one double bond, but these were not identified. He failed to find glycerides in the mixture. Schoenheimer, von Behring & Hummel [1930] investigated the saturated sterol content of the lipids from various animal sources. Of the many tissues examined, atheromatous aortas yielded unsaponifiable lipid having the highest values for saturated sterol content (5.1-5.3 % of the total sterol). The suggestion was made that such saturated sterols might have been formed by intermediary hydrogenation of cholesterol. However, it is worthy of note that Gardner & Gainsborough [1934] found Schoenheimer's method for separating saturated from unsaturated sterols unsatisfactory from a quantitative point of view. They were not successful in obtaining the sa...

Investigation of the hydrolysis of phosphatidylcholines (lecithins) in hot aqueous alcohol under the influence of mercuric chloride has shown that glycerylphosphorylcholine is formed and that neither racemization nor migration of the phosphorylcholine moiety occurs. 'I'he fatty acids are split off much more rapidly than is choline and as a consequence appreciable amounts of glycerylphosphorylcholine are formed. On the basis of these observations a procedrlrc was devised for the hydrolysis of crride lecithin and the isolation of glyccrylphosphorylcholine in a yield of 69y0. The product was identified as I,-aglycerylphosphorylcholine by analysis of its cadmium chloride complex, and comparison of its optical rotation with that of the synthetic compound of known configuration. Recovery of the diester froin this complex was accomplished through removal of the inorganic salt by ion-exchange resins and the free L-a-glycerylphosphorylcholine was crystallized from 99y0 ethanol. 1