title: Decreased erythrocyte activity of methemoglobin and glutathione reductases may explain age-related high blood pressure.
abstract: OBJECTIVE
  Erythrocytes may play an important role in regulating blood pressure as storage sites for nitric oxide (NO). The objective of this work was to determine whether factors related to variations in erythrocyte metabolism associated with NO bioavailability, such as the activity of two enzymes--methemoglobin reductase (MHbR) and glutathione reductase (GSHR)--may help explain age-related increased blood pressure.
  
  
  METHODS
  The sample consisted of 468 individuals of both sexes, 237 hypertensive (HT) and 231 normotensive (NT), aged between 18 and 98 years (48.81 +/- 19.46). The activity of MHbR (micromol.g Hb-1.min-1) and of GSHR (micromol.g Hb-1.min-1) was determined in erythrocytes by spectrophotometry. The statistical methods used were the Mann-Whitney test, Spearman's correlation coefficient and binary logistic regression.
  
  
  RESULTS
  In this population, age was a risk factor for hypertension (OR=1.055, 95% CI = 1.045-1.065, p < 0.001). There was a significant difference in erythrocyte activity of these enzymes between normotensive and hypertensive subjects, with lower values in hypertensives: MHbR-NT = 16.97 (3.82-34.63), HT = 16.26 (3.26-37.10), p = 0.012; and GSHR-NT=57.60 (21.59-96.58), HT = 39.26 (23.07-90.27), p < 0.001. Enzyme activity was inversely correlated with age (MHbR: r = -0.193, p < 0.001; GSHR: r = -0.757, p < 0.001). MHbR correlated directly with GSHR only in hypertensive patients (r = 0.343, p = 0.034), which was not observed in normotensives.
  
  
  CONCLUSIONS
  Age was a risk factor for hypertension. The erythrocyte activity of glutathione and metahemoglobin reductases, essential for redox balance and nitric oxide bioavailability in erythrocytes, may contribute only partially to the increased prevalence of age-related hypertension, and other factors should be taken into consideration, such as nutrition and antihypertensive medication.
authors.affiliation: Laboratório de Genética, Centro de Metabolismo e Endocrinologia, Faculdade de Medicina da Universidade de Lisboa, Lisboa, Portugal.
authors.forename: Alda Pereira
authors.initials: AP
authors.lastname: Da Silva
authors.forename: Cláudia
authors.initials: C
authors.lastname: Marinho
authors.forename: Ma Conceição
authors.initials: MC
authors.lastname: Gonçalves
authors.forename: Cristina
authors.initials: C
authors.lastname: Monteiro
authors.forename: Ma José
authors.initials: MJ
authors.lastname: Laires
authors.forename: Luiz Menezes
authors.initials: LM
authors.lastname: Falcão
authors.forename: José Braz
authors.initials: JB
authors.lastname: Nogueira
authors.forename: Manuel
authors.initials: M
authors.lastname: Bich
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D042966:Cytochrome-B(5) Reductase / Q000378:metabolism*; D004912:Erythrocytes / Q000201:enzymology*; D005260:Female; D005980:Glutathione Reductase / Q000378:metabolism*; D006801:Humans; D006973:Hypertension / Q000201:enzymology* / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D042966:Cytochrome-B(5) Reductase; D005980:Glutathione Reductase