SERUM BETA-GLUCURONIDASE, GLUCOSE TOLERANCE, AND ATHEROSCLEROTIC DISEASE

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

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)

A simple automated colorimetric method for determination of N-acetyl- beta-D-glucosaminidase

An automated method for the determination of N-acetyl-beta-D-glucosaminidase in serum or plasma using p-nitrophenol (pNP) N-acetyl-beta-D-glucosamine as substrate and a Pye Unicam AURA system is described. Normal samples had activities of 853 +/- 146 (SD) nmol pNP liberated/ml/h, with intra-assay coefficient of variation 1.2% and inter-assay coefficient of variation 1.6%. Inhibition of enzyme activity by heparin in plasma samples can be reversed by the addition of calcium chloride to the buffer.

Increased plasma activities of N-acetyl-beta-D-glucosaminidase isoenzymes in human diabetes mellitus

Plasma N-acetyl-beta-D-glucosaminidase activities are raised in maturity-onset insulin-dependent diabetic patients. Continuous gradient DEAE-cellulose column chromatography and assay of heat-stable enzyme activity both show that the activities of all isoenzymes are equally increased rather than a previously described increase of specific isoenzymes. Plasma enzyme activities are similarly increased in patients with and without diabetic retinopathy, and correlate with simultaneous plasma glucose concentrations.

Serum and urine N-acetyl-beta-D-glucosaminidase in diabetics on diagnosis and subsequent treatment, and stable insulin dependent diabetics

N-Acetyl-beta-D-glucosaminidase (NAG) activity has been measured in the serum and urine of diabetics. Results have shown significantly higher levels of serum NAG in newly diagnosed diabetics (945 +/- 372 units/ml) compared to non-diabetic controll (668 +/- 225, p less than 0.005) and the levels were reduced by treatment (778 +/- 218, p less than 0.05). Changes occurred in the same direction when urinary NAG was measured falling from a mean of 572 +/- 298 units/mg urinary creatinine, on diagnosis to 291 +/- 176 after treatment (p less than 0.005), as compared with 177 +/- 86 in non-diabetic controls. Established insulin-treated diabetics had a urinary NAG activity of 461 +/- 440 and a serum NAG activity of 790 +/- 245. No correlation was found between urine NAG activity and urine glucose (r = 0.315), or serum NAG and serum glucose (r = 0.273). An assessment of this enzyme is made in relation to early microangiopathy.