Fiona Johnston

Endothelium-derived hyperpolarizing factor: Identification and mechanisms of action in human subcutaneous resistance arteries

BackgroundBoth a vascular endothelial cytochrome P450 (CYP450) product of arachidonic acid metabolism and the potassium ion (K+) have been identified as endothelium-derived hyperpolarizing factors (EDHFs) in animal vascular tissues. We studied the relative importance of EDHF, nitric oxide (NO), and prostacyclin (PGI2) as vasodilators in human subcutaneous arteries. We also examined the mechanisms underlying the vasodilator action of EDHF to elucidate its identity. Methods and ResultsSubcutaneous resistance arteries were obtained from 41 healthy volunteers. The contribution of EDHF to the vasodilation induced by acetylcholine was assessed by inhibiting production of NO, PGI2, and membrane hyperpolarization. The mechanisms underlying the relaxation evoked by K+ and EDHF were elucidated. EDHF was found to account for ≈80% of acetylcholine-mediated vasorelaxation. Its action was insensitive to the combination of barium and ouabain, whereas barium and ouabain reversed K+-mediated vasorelaxation. EDHF-mediated vasorelaxation, however, was sensitive to the phospholipase A2 inhibitor oleyloxyethyl phosphorylcholine and the CYP450 inhibitor ketoconazole. ConclusionsEDHF is the major contributor to endothelium-dependent vasorelaxation in human subcutaneous resistance arteries. A product of phospholipase A2/CYP450-dependent metabolism of arachidonic acid and not K+ is the likely identity of EDHF in human subcutaneous resistance arteries.

Is the Pregnancy Hormone Relaxin Also a Vasodilator Peptide Secreted by the Heart

Background—It has been shown recently that the pregnancy and parturition hormone, relaxin, is secreted by the heart. This study examined the effects of relaxin in small human resistance arteries from the systemic and pulmonary circulations. Methods and Results—Arteries were obtained from gluteal biopsies and resected lung tissue and studied with the use of wire myography. Cumulative concentration relaxation curves were constructed in systemic arteries with substance P, epoprostenol, atrial natriuretic peptide, and relaxin (concentration range 10−13 -10−7M). The maximal responses were 88(±5)%, 67(±10)%, 52(±16)% and 66(±16)%, respectively. Endothelium removal virtually abolished the action of relaxin. Relaxin had no vasodilator effect in pulmonary arteries. Conclusions—Relaxin is a powerful dilator of systemic resistance arteries secreted by the heart that may contribute to cardiovascular regulation.

Signalling mechanisms underlying the myogenic response in human subcutaneous resistance arteries.

OBJECTIVE In this study we have examined for the first time the signal transduction mechanisms involved in the generation of pressure-dependent myogenic tone in human small resistance arteries from the subcutaneous vascular bed. METHODS Myogenic responses and the subcellular mechanisms involved in the generation of this response were studied on a pressure myograph. RESULTS AND CONCLUSION Human subcutaneous resistance arteries constricted 14.1+/-1.1% in response to an increases in intraluminal pressure from 40 to 80 mmHg and a further 3.5+/-1.7% in response to the 80-120-mmHg pressure step. Ca(2+) depletion or nifedipine abolished this response, whereas BAY K 8644 increased this response to 20.6+/-2.1% (P<0.05, response vs. control). The phospholipase C inhibitor U-73122 reduced the myogenic response to 2.5+/-1.0% at 80 mmHg (P<0.01, response vs. control) and abolished it at 120 mmHg. Diacylglycerol lipase inhibition with RHC-80267 abolished all myogenic responses to pressure. The protein kinase C (PKC) activator phorbol 12,13-dibutyrate increased the maximal myogenic response to 20.9+/-1.8% (P<0.05, response vs. control), whereas the PKC inhibitor calphostin C abolished myogenic responses. These data show that the generation of pressure-dependent myogenic tone in human subcutaneous arteries is dependent on Ca(2+) influx via voltage operated Ca(2+) channels (VOCCs) and a concomitant requirement for the activation of phospholipase C (PLC), diacylglycerol, and PKC.

Endothelial function is preserved in pregnant women with well‐controlled type 1 diabetes

Objective Pregnant women with diabetes mellitus have a higher incidence of adverse pregnancy outcomes. Vascular, and in particular, endothelial function may be significantly modified in diabetes resulting in impaired endothelium‐dependent relaxation. This study aims to investigate endothelium‐dependent relaxation in pregnant women with pre‐existing type 1 diabetes mellitus.

Effect of adrenomedullin on the production of endothelin-1 and on its vasoconstrictor action in resistance arteries: evidence for a receptor-specific functional interaction in patients with heart failure.

Endothelin-1 (ET-1) and adrenomedullin (ADM) are both produced in the arterial wall, but have opposing biological actions. Evidence from experimental animals suggests a functional interaction between ET-1 and ADM. We have tested this in humans. Small resistance arteries were obtained from gluteal biopsies taken from patients with chronic heart failure (CHF) due to coronary heart disease (CHD), or with CHD and preserved ventricular function. The contractile responses to big ET-1 and to ET-1 in both sets of vessels were studied in the absence (control) and presence of ADM at 20 pmol/l (low ADM) or 200 pmol/l (high ADM), using wire myography. ADM did not affect the conversion of big ET-1 into ET-1 in vessels from patients with either CHD or CHF. Low ADM did not alter the contractile response to ET-1 in vessels from patients with CHF. Low ADM was not tested in vessels from patients with CHD, but high ADM did not affect this response in arteries from these patients. High ADM did, however, significantly reduce the vasoconstrictor effect of ET-1 in vessels from patients with CHF. The maximum response, as a percentage of the response to high potassium, was 199% (S.E.M. 25%) in the control experiments (n=14), 205% (27%) in the low-ADM (n=7) studies and 150% (17%) in the high-ADM (n=6) experiments (P<0.001). Furthermore, the Hill coefficient increased from 0.57+/-0.05 in the absence of ADM to 1.16+/-0.15 in the high-ADM experiments, indicating that ADM at 200 pmol/l specifically antagonized one receptor type in vessels from patients with CHF. We conclude that there is a one-site receptor interaction between ADM and ET-1 that is specific for vessels from patients with CHF. This functional interaction between ADM and ET-1 in resistance arteries may be of pathophysiological importance in CHF.

The dual endothelin converting enzyme/neutral endopeptidase inhibitor SLV-306 (daglutril), inhibits systemic conversion of big endothelin-1 in humans.

AIMS Inhibition of neutral endopeptidases (NEP) results in a beneficial increase in plasma concentrations of natriuretic peptides such as ANP. However NEP inhibitors were ineffective anti-hypertensives, probably because NEP also degrades vasoconstrictor peptides, including endothelin-1 (ET-1). Dual NEP and endothelin converting enzyme (ECE) inhibition may be more useful. The aim of the study was to determine whether SLV-306 (daglutril), a combined ECE/NEP inhibitor, reduced the systemic conversion of big ET-1 to the mature peptide. Secondly, to determine whether plasma ANP levels were increased. MAIN METHODS Following oral administration of three increasing doses of SLV-306 (to reach an average target concentration of 75, 300, 1200 ng ml(-1) of the active metabolite KC-12615), in a randomised, double blinded regime, big ET-1 was infused into thirteen healthy male volunteers. Big ET-1 was administered at a rate of 8 and 12 pmol kg(-1)min(-1) (20 min each). Plasma samples were collected pre, during and post big ET-1 infusion. ET-1, C-terminal fragment (CTF), big ET-1, and atrial natriuretic peptide (ANP) were measured. KEY FINDINGS At the two highest concentrations tested, SLV-306 dose dependently attenuated the rise in blood pressure after big ET-1 infusion. There was a significant increase in circulating big ET-1 levels, compared with placebo, indicating that SLV-306 was inhibiting an increasing proportion of endogenous ECE activity. Plasma ANP concentrations also significantly increased, consistent with systemic NEP inhibition. SIGNIFICANCE SLV-306 leads to inhibition of both NEP and ECE in humans. Simultaneous augmentation of ANP and inhibition of ET-1 production is of potential therapeutic benefit in cardiovascular disease.

Effect of Neutral Endopeptidase Inhibition on the Actions of Adrenomedullin and Endothelin-1 in Resistance Arteries From Patients With Chronic Heart Failure

Adrenomedullin and endothelin are novel peptides that are produced in the blood vessel wall and have contrasting biologic actions. Both may play a pathophysiological role in atherosclerosis and chronic heart failure. It has also been suggested that both peptides may be metabolized by neutral endopeptidase and that pharmacological manipulation of this enzyme may be of therapeutic interest. We investigated the effect of thiorphan, a neutral endopeptidase inhibitor, on the vasodilator response to adrenomedullin and the vasoconstrictor response to endothelin in small resistance arteries taken from patients with heart failure caused by coronary heart disease. Small resistance arteries were dissected from gluteal biopsy samples and studied with wire myography. Thiorphan did not affect the vasodilator response to adrenomedullin in arteries preconstricted with norepinephrine. Maximal responses were 66% (SD 11%) and 72% (8%) in the absence and presence of thiorphan, respectively (n=8). The vasoconstrictor response to endothelin was also unaffected. The maximum vasoconstrictor responses in the absence and presence of thiorphan were 152% (11%) and 132% (12%), respectively (n=8). The values of corresponding −log concentrations of agonist required to effect a 50% response (pD2) were 8.52 (0.11) and 8.64 (0.15), respectively. We showed that the inhibition of neutral endopeptidase does not augment the vasodilator and vasoconstrictor activities of adrenomedullin and endothelin, respectively, in small resistance arteries from patients with chronic heart failure. This suggests that neutral endopeptidase inhibition, as a therapeutic strategy, will enhance neither the potentially desirable vascular actions of adrenomedullin nor the potentially unfavorable vascular effects of endothelin-1 in human cardiovascular disease states.