Erythrocyte membrane sialic acids in primary and secondary hypertension in man and rat

Sialic acids of erythrocyte membranes (erythrocyte 'ghosts') and blood plasma were studied in patients with essential or chronic renal hypertension, and in spontaneously hypertensive rats (SHR). The total content of sialic acids in erythrocyte membranes (determined by thiobarbituric-acid assay) was around 100 mumol/g protein in both the hypertensive patients and controls, there being no difference between the three groups. Similarly total sialic-acid content of plasma did not differ between the hypertensive patients and controls, being around 2 mmol/l. Although total membrane sialic acid was unchanged, the sialic-acid content of glycolipids extracted from erythrocyte membranes was 17% greater (P less than 0.001) in patients with essential hypertension than in renal hypertensive patients and controls (22.1 +/- 0.5 mumol/g protein v. 18.2 +/- 0.8 and 18.9 +/- 0.8, respectively). Sialic acid in plasma glycolipid did not differ between the patient groups. The animal study revealed no differences between total--or glycolipid--sialic-acid content in plasma and erythrocyte membrane in SHR and normotensive rats. The finding of an increase in the sialic-acid content of erythrocyte membrane glycolipid in essential hypertension is in agreement with recent studies demonstrating structural abnormalities in hydrophobic regions of erythrocyte membrane, and is considered a manifestation of membrane glycolipid alteration in primary hypertension.