Elevated serum activity of N-acetyl-beta-glucosaminidase in essential hypertension: diagnostic value and reversal to normal values after antihypertensive therapy

Abstract

Previous studies have shown that urinary N-acetyl-beta-glucosaminidase (NAG) is elevated in patients with hypertension, even without renal disease. To elucidate the value of measuring NAG, both in urine and serum of hypertensive patients, we measured NAG activity in the serum, plasma, and 24-hour urine by the fluorimetric method in 84 patients with uncomplicated essential hypertension before and after 6 months of effective treatment. NAG activities of these hypertensive patients were compared with those of 102 healthy normotensive subjects and 97 patients with various renal diseases and controlled hypertension. Serum NAG activity was clearly greater in patients with essential hypertension (427 +/- 124 U/mL) than in normotensive subjects (380 +/- 109 U/mL) or patients with renal disorders (393 +/- 115 U/mL) (P less than or equal to 0.004). The greater was the diastolic pressure in the hypertensive group, the greater was serum NAG activity (r = +0.30, P = 0.004). Hypertensive patients with high serum NAG activity were further characterized by a more exaggerated increase in systolic pressure (34 +/- 16 v 25 +/- 15 mm Hg, P = 0.051) and total peripheral resistance (19% +/- 18% v 12% +/- 13%, P = 0.042) in response to the cold pressor test and by a greater increase in systolic pressure (56 +/- 15 v 45 +/- 13 mm Hg, P = 0.009) and diastolic pressure (11 +/- 7 v 6 +/- 9, P = 0.043) in response to bicycle exercise testing than the group with low serum NAG activity. In contrast, urinary NAG activity tended to be only slightly higher in patients with essential hypertension than in the normotensive control group (33 +/- 31 v 23 +/- 29 U/mg creatinine [cr], P = 0.062), whereas patients with renal diseases had clearly increased urinary NAG activity (87 +/- 105 U/mg cr) (P less than 0.001). Following effective antihypertensive therapy, serum NAG activity decreased in patients with essential hypertension to values of normotensive control subjects (from 427 +/- 124 U/mL to 386 +/- 106 U/mL, P less than 0.01). A significant decrease in serum NAG activity was observed in patients with both initially high as well as low pretreatment serum NAG activities (P less than 0.001 and P less than 0.02, respectively). Urinary NAG activity overall was unchanged by antihypertensive treatment. We conclude that in patients with mild essential hypertension, serum NAG activity was already elevated (whereas urinary NAG activity was not) and was normalized by effective antihypertensive treatment.(ABSTRACT TRUNCATED AT 400 WORDS)