title: Deficiency of renal dopaminergic-dependent natriuretic response to acute sodium load in black salt-sensitive subjects in contrast to salt-resistant subjects.
abstract: OBJECTIVE
  To evaluate the involvement of the renal dopaminergic system in the natriuretic responses to acute saline load in salt-resistant (SR) and salt-sensitive (SS) black normotensive (NT) and hypertensive (HT) subjects.
  
  
  METHODS
  We studied the relationship between the urinary excretion of dopa, dopamine (DA) and its metabolite DOPAC and the natriuretic responses to acute volume expansion (2 l NaCl 0.9% over 2 h) in 20 black NT subjects (12 SR and 8 SS) and 19 black HT subjects (10 SS and 9 SR). Subjects received a low salt (LS) diet (40 mmol sodium/day) for 1 week and a high salt (HS) diet (300 mmol sodium/day) for 1 week; the sequence of the dietary regimens was randomized. Comparisons were made between the results before the saline infusion (baseline) and the results 2 h after the infusion.
  
  
  RESULTS
  In all the groups saline infusion induced significant increases in urinary volume (ml/4 h) of two- to three-fold and in urinary sodium excretion (mmol/4 h) of three- to ten-fold; these increases were significantly greater during the HS diet than during the LS diet. Saline infusion significantly increased the mean arterial pressure (MAP) by 5 mmHg in HT-SS subjects and by 4-5 mmHg in NT-SS subjects, but the MAP did not changed in the NT-SR and HT-SR groups. Under the LS diet, saline infusion changed the DA excretion (in nmol/4 h) by -49+/-89 in HT-SS subjects, by 17+/-52 in NT-SS subjects, by 235+/-72 in HT-SR subjects and by 220+/-86 in NT-SR subjects (P < 0.05 between SR and SS subjects). The saline infusion-induced changes in DA excretion correlated significantly with the increases in urinary sodium excretion (r = 0.71, P < 0.01) in the NT-SR and HT-SR subjects under the LS diet, but not in the SR groups on the HS diet nor in the SS groups (HT and NT) on either diet. Saline infusion significantly reduced the DA/dopa ratio in SS (NT and HT) but not SR (NT and HT) subjects, whereas the DA/DOPAC (dihydroxyphenylacetic acid) ratios were similar in all the groups.
  
  
  CONCLUSIONS
  The urinary dopaminergic system may participate in the natriuretic responses to acute sodium load only in SR subjects (NT and HT) and only under LS diets, but not in SS subjects (NT and HT). This strongly suggests that black NT- and HT-SS subjects have an underlying impairment in the activity of the renal dopaminergic system which may be associated with a reduced decarboxylation of dopa into DA.
authors.affiliation: Faculdade Medicina Universidade Eduardo Mondlane, Maputo, Mozambique.
authors.forename: A
authors.initials: A
authors.lastname: Damasceno
authors.forename: A
authors.initials: A
authors.lastname: Santos
authors.forename: P
authors.initials: P
authors.lastname: Serrão
authors.forename: P
authors.initials: P
authors.lastname: Caupers
authors.forename: P
authors.initials: P
authors.lastname: Soares-da-Silva
authors.forename: J
authors.initials: J
authors.lastname: Polónia
mesh_terms: D000328:Adult; D044383:Black People; D004295:Dihydroxyphenylalanine / Q000037:antagonists & inhibitors; D004298:Dopamine / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004351:Drug Resistance; D005260:Female; D006801:Humans; D006973:Hypertension / Q000208:ethnology / Q000503:physiopathology* / Q000652:urine; D007668:Kidney / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D009318:Natriuresis / Q000187:drug effects / Q000502:physiology*; D012016:Reference Values; D012964:Sodium / Q000652:urine; D012965:Sodium Chloride / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D018492:Dopamine Antagonists; D012965:Sodium Chloride; D004295:Dihydroxyphenylalanine; D012964:Sodium; D004298:Dopamine