title: Inhibition of neutral endopeptidase causes vasoconstriction of human resistance vessels in vivo.
abstract: BACKGROUND
  Neutral endopeptidase (NEP) degrades vasoactive peptides, including the natriuretic peptides, angiotensin II, and endothelin-1. Systemic inhibition of NEP does not consistently lower blood pressure, even though it increases natriuretic peptide concentrations and causes natriuresis and diuresis. We therefore investigated the direct effects of local inhibition of NEP on forearm resistance vessel tone.
  
  
  RESULTS
  Four separate studies were performed, each with 90-minute drug infusions. In the first study, 10 healthy subjects received a brachial artery infusion of the NEP inhibitor candoxatrilat (125 nmol/min), which caused a slowly progressive forearm vasoconstriction (12+/-2%; P=0.001). In a second two-phase study, 6 healthy subjects received, 4 hours after enalapril (20 mg) or placebo, an intra-arterial infusion of the NEP inhibitor thiorphan (30 nmol/min). Thiorphan caused similar degrees of local forearm vasoconstriction (P=0.6) after pretreatment with both placebo (13+/-1%, P=0.006) and enalapril (17+/-6%, P=0.05). In a third three-phase study, 8 healthy subjects received intra-arterial thiorphan (30 nmol/min), the endothelin ETA antagonist BQ-123 (100 nmol/min), and both combined. Thiorphan caused local forearm vasoconstriction (13+/-1%, P=0.0001); BQ-123 caused local vasodilatation (33+/-3%, P=0.0001). Combined thiorphan and BQ-123 caused vasodilatation (32+/-1%, P=0.0001) similar to BQ-123 alone (P=0.98). In a fourth study, 6 hypertensive patients (blood pressure >160/100 mm Hg) received intra-arterial thiorphan (30 nmol/min). Thiorphan caused a slowly progressive forearm vasoconstriction (10+/-2%, P=0.0001).
  
  
  CONCLUSIONS
  Inhibition of local NEP causes vasoconstriction in forearm resistance vessels of both healthy volunteers and patients with hypertension. The lack of effect of ACE inhibition on the vasoconstriction produced by thiorphan and its absence during concomitant ETA receptor blockade suggest that it is mediated by endothelin-1 and not angiotensin II. These findings may help to explain the failure of systemic NEP inhibition to lower blood pressure.
authors.affiliation: Clinical Pharmacology Unit and Research Centre, University of Edinburgh, Western General Hospital, UK.
authors.forename: C J
authors.initials: CJ
authors.lastname: Ferro
authors.forename: J C
authors.initials: JC
authors.lastname: Spratt
authors.forename: W G
authors.initials: WG
authors.lastname: Haynes
authors.forename: D J
authors.initials: DJ
authors.lastname: Webb
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000097:blood; D000804:Angiotensin II / Q000378:metabolism; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000008:administration & dosage; D009320:Atrial Natriuretic Factor / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D003331:Coronary Vessels / Q000187:drug effects* / Q000201:enzymology; D018592:Cross-Over Studies; D003509:Cyclohexanecarboxylic Acids / Q000008:administration & dosage; D004656:Enalapril / Q000008:administration & dosage; D019332:Endothelin-1 / Q000378:metabolism; D006801:Humans; D006973:Hypertension / Q000188:drug therapy / Q000503:physiopathology; D007269:Injections, Intra-Arterial; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000201:enzymology; D015260:Neprilysin / Q000037:antagonists & inhibitors*; D010456:Peptides, Cyclic / Q000008:administration & dosage; D011480:Protease Inhibitors / Q000008:administration & dosage; D012083:Renin / Q000097:blood; D016037:Single-Blind Method; D015244:Thiorphan / Q000008:administration & dosage; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D000806:Angiotensin-Converting Enzyme Inhibitors; D003509:Cyclohexanecarboxylic Acids; D019332:Endothelin-1; D010456:Peptides, Cyclic; D011480:Protease Inhibitors; D000804:Angiotensin II; D000450:Aldosterone; D004656:Enalapril; C060942:candoxatrilat; D009320:Atrial Natriuretic Factor; D015244:Thiorphan; D012083:Renin; D015260:Neprilysin; C072247:cyclo(Trp-Asp-Pro-Val-Leu)