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Biomedical subjects

W G Haynes

Publications and source records attributed to W G Haynes.

At least 73 records · Page 4Linked to original sources
PubMed1995

Forearm vasoconstriction to endothelin-1 is mediated by ETA and ETB receptors in vivo in humans.

The role of endothelin (ET)-B (ETB) receptors in mediating vasoconstriction in humans is unclear. As yet, in vitro data have been contradictory, and there have been no in vivo studies in resistance vessels. We investigated the function of ETB receptors in vivo in human forearm resistance vessels using ET-1 as a nonselective agonist at ETA and ETB receptors and ET-3 and sarafotoxin S6c as ETB receptor agonists. Brachial artery infusion of ET-1 and ET-3 caused slow-onset, dose-dependent forearm vasoconstriction. Although ET-3 caused significantly less forearm vasoconstriction than ET-1 at low doses, vasoconstriction to the two isopeptides was similar at the highest dose (60 pmol/min). ET-3 caused initial transient forearm vasodilatation at this dose, whereas ET-1 showed only a nonsignificant trend toward causing early vasodilatation. Intra-arterial sarafotoxin S6c caused a progressive reduction in forearm blood flow, although less than that to ET-1. Therefore, ETB receptor agonists contract human resistance vessels in vivo. The effects of ET-3 and sarafotoxin S6c, compared with ET-1, suggest that both ETA and ETB receptors mediate vasoconstriction. Antagonists at both ETA and ETB receptors, or inhibitors of the generation of ET-1, may be necessary to completely prevent vasoconstriction to endogenously generated ET-1.

Adult↗
PubMed1994

Contribution of endogenous generation of endothelin-1 to basal vascular tone.

Endothelin-1 is an endothelium-derived vasoconstrictor peptide, possibly involved in the pathophysiology of cardiovascular disease. We examined the contribution of endogenously generated endothelin-1 to maintenance of peripheral vascular tone in healthy subjects by local intraarterial administration of an inhibitor of endothelin converting enzyme, phosphoramidon, and of a selective endothelin receptor A antagonist, BQ-123. Brachial artery infusion of local doses of proendothelin-1, the precursor to endothelin-1, caused a slow-onset dose-dependent forearm vasoconstriction which was abolished by co-infusion of phosphoramidon. Phosphoramidon did not affect responses to endothelin-1. Phosphoramidon caused slow-onset vasodilatation when infused alone, with blood flow increasing by 37% at 90 min (p = 0.03). Vasoconstriction to endothelin-1 was abolished by co-infusion of BQ-123 (p = 0.006), with forearm blood flow tending to increase. Infusion of BQ-123 alone caused progressive vasodilatation, with blood flow increasing by 64% after 60 min (p = 0.007). These results show that endogenous production of endothelin-1 contributes to the maintenance of vascular tone. Endothelin converting enzyme inhibitors and receptor antagonists may have therapeutic potential as vasodilators.

Adult↗
PubMed1994

Plasma endothelin following cardiac arrest: differences between survivors and non-survivors.

Cardiac arrest is associated with major metabolic disturbances, including severe hypoxia and large increases in circulating catecholamines, both of which are known to stimulate generation of the potent endothelium-derived vasoconstrictor peptide endothelin-1. We have, therefore, examined plasma immunoreactive endothelin concentrations following cardiac arrest. Blood was sampled at 10-min intervals from a central venous catheter inserted at onset of resuscitation in 38 patients (13 female; mean age, 67 years) presenting with cardiac arrest to the Accident and Emergency Department at the Royal Infirmary of Edinburgh. Plasma immunoreactive endothelin concentrations (mean +/- S.D.) in patients following cardiac arrest (5.4 +/- 2.3 pg/ml) were no different from those in healthy subjects (5.1 +/- 1.2 pg/ml). There was no significant difference between endothelin concentrations at presentation in survivors and non-survivors of cardiac arrest. However, non-survivors had a significant fall in endothelin concentrations with time from onset of resuscitation from 5.4 +/- 2.2 pg/ml to 3.5 +/- 1.8 pg/ml (P = 0.002), while survivors had a non-significant increase in concentrations. On multiple regression analysis there was a significant association between higher plasma endothelin concentration and survival (r = 0.37; P = 0.009). The failure of plasma endothelin to increase after cardiac arrest is unexpected. Although the fall in plasma endothelin with time in non-survivors may reflect the adverse physiological milieu that occurs during cardiac arrest, it is also possible that low endothelin concentrations contribute to the poor prognosis in this condition.

Aged↗
PubMed1994

Raised plasma endothelin in unstable angina and non-Q wave myocardial infarction: relation to cardiovascular outcome.

BACKGROUND: Among patients with independent evidence of coronary disease and recent onset unstable angina or non-Q wave myocardial infarction the incidence of subsequent cardiovascular events is high. Markers predictive of adverse cardiac outcome in unstable angina and non-Q wave myocardial infarction need to be defined more accurately. Endothelin-1 is a potent endothelium derived vasoconstrictor peptide that may play a part in the pathophysiology of acute myocardial ischaemia. AIM AND STUDY DESIGN: In a study that specifically identified high risk patients a group of 16 consecutive patients with either unstable angina at rest or non-Q wave myocardial infarction were prospectively investigated to establish whether these conditions are associated with high plasma immunoreactive endothelin and whether endothelin concentration at presentation is related to cardiovascular events within the next 12 weeks. Controls consisted of a group of 40 healthy subjects. RESULTS: Patients had significantly higher mean (SD) plasma endothelin at presentation than did healthy controls (7.4 (1.1) v 5.0 (1.2) pg/ml, P < 0.0001). At nine weeks plasma endothelin was still significantly higher in those patients who had subsequent cardiovascular events, (n = 9, acute myocardial infarction or refractory angina with electrocardiographic changes and revascularisation procedures, 8.5 (2.6) pg/ml, P < 0.005 v controls) whereas its concentration returned to normal in those patients who had a favourable outcome (n = 7, 5.9 (0.7) pg/ml). Compared with those patients who had an uneventful course, patients with subsequent events had significantly higher plasma endothelin, both at presentation and at nine weeks (P < 0.05 on both occasions). IMPLICATIONS: Endothelin may contribute to the pathophysiology of acute coronary syndromes and may relate to subsequent cardiovascular outcome.

Adolescent↗
PubMed1994

Direct and sympathetically mediated venoconstriction in essential hypertension. Enhanced responses to endothelin-1.

Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide. Although circulating concentrations are not increased in essential hypertension, enhanced sensitivity to endothelin-1 has been observed in animal models of hypertension. We investigated dorsal hand vein responses to local infusion of endothelin-1 and norepinephrine in 12 patients with essential hypertension who had never received treatment and in 12 age and sex matched normotensive control subjects. The maximal venoconstriction and the geometric mean of the dose of norepinephrine that caused 50% of maximal venoconstriction were similar in hypertensive (mean +/- SE; 80 +/- 4%; 31 +/- 8 pmol/min) and normotensive subjects (87 +/- 5%, 22 +/- 9 pmol/min). In contrast, mean venoconstriction to endothelin-1 was significantly greater in hypertensive (49 +/- 5%) than in normotensive subjects (27 +/- 2%; P = 0.004). Sympathetically mediated venoconstriction elicited by deep breath was substantially potentiated by endothelin-1 in hypertensive (67 +/- 7% at 90 min) but not normotensive subjects (11 +/- 3% at 90 min; P = 0.001). Venoconstriction to endothelin-1 correlated positively with mean arterial pressure in the hypertensive subjects (r = 0.82; p = 0.001) but negatively in the normotensive subjects (r = -0.58; p = 0.047). Endothelin-1 may contribute to the reduction of venous compliance occurring in the early stages of essential hypertension and to the altered systemic hemodynamics in this condition.

Adult↗
PubMed1993

Endothelium-dependent modulation of responses to endothelin-I in human veins.

1. We have investigated whether local vascular production of nitric oxide or prostacyclin regulates venoconstriction induced by the endothelium-derived peptide, endothelin-1, in vivo in man. 2. Six healthy subjects received local dorsal hand vein infusion of endothelin-1 for 60 min alone or, on two separate occasions, co-infused with the donator of nitric oxide, glyceryl trinitrate, or the vasodilator prostaglandin, prostacyclin. In further studies, endothelin-1 was co-infused with an inhibitor of nitric oxide production, NG-monomethyl-L-arginine, or after oral administration of the irreversible inhibitor of prostaglandin production, acetylsalicylic acid (aspirin). 3. At a low dose (5 pmol/min), endothelin-1 alone caused slowly developing and long-lasting venoconstriction (maximal constriction: 66 +/- 4%). Although glyceryl trinitrate partially prevented endothelin-1-induced venoconstriction (maximum: 33 +/- 5%), inhibition of nitric oxide production did not affect endothelin-1-induced venoconstriction (maximum: 55 +/- 4%). 4. Prostacyclin was more effective at blocking the venoconstriction in response to endothelin-1 than glyceryl trinitrate (maximum: 12 +/- 3%), and there was substantial potentiation of endothelin-1-induced venoconstriction after pretreatment with aspirin (maximum: 90 +/- 3%). 5. Despite the capacity of nitric oxide to attenuate responses to endothelin-1, NG-monomethyl-L-arginine did not potentiate endothelin-1-induced venoconstriction, suggesting little or no stimulated production of nitric oxide in human veins. However, the potentiation of responses to endothelin-1 by aspirin indicates that endothelial production of prostacyclin attenuates responses to endothelin-1 in human veins in vivo.

Adult↗
PubMed1993

Inhibition of nitric oxide synthesis increases blood pressure in healthy humans.

OBJECTIVE: To examine whether endogenous production of the endothelium-derived vasodilator nitric oxide influences blood pressure in healthy humans. METHODS: After preliminary pilot dose-ranging studies, 3 mg/kg NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthase, and saline placebo were infused intravenously over 5 min to eight healthy subjects in a two-phase, randomized, single-blind crossover study. Blood pressure and cardiac and renal function were measured. RESULTS: Compared with placebo, L-NMMA increased mean arterial pressure by 10%, decreased heart rate by 19%, decreased cardiac index by 25% and increased calculated total peripheral resistance by 46%. Effects were maximal 10-15 min after starting L-NMMA infusion. Urinary sodium and fractional sodium excretions were increased by L-NMMA, but creatinine clearance was unchanged. CONCLUSIONS: Basal generation of nitric oxide influences total peripheral resistance and blood pressure in healthy humans. The natriuresis induced by L-NMMA may be related to the increase in blood pressure, or arise from inhibition of the intrarenal actions of nitric oxide. Any decrease in nitric oxide generation, as has been postulated to occur in essential hypertension, could have substantial effects on blood pressure and tissue blood flow.

Adult↗
PubMed1993

Modulators of calcium and potassium channels: their effects on endothelin-1 binding to cardiac membranes.

Endothelin-1 (ET-1) causes long-lasting vasoconstriction associated with a prolonged elevation of intracellular free Ca2+. Because this may be mediated through an effect on membrane ion channels, we investigated the effects of the dihydropyridine calcium channel antagonist nifedipine; two structurally distinct K+ channel openers, pinacidil and levcromakalim; and the inactive stereoisomer of levcromakalim (D-cromakalim), as well as ET-1 and ET-3, on binding of 125I-labeled endothelin-1 to rat cardiac membranes. Specific binding of 125I-ET-1 was inhibited in a concentration-dependent manner by unlabeled ET-1 (IC50 = 1.56 +/- 0.78 nM; slope = -0.49 +/- 0.10) and ET-3 (IC50 = 314 +/- 54 nM; slope = -0.34 +/- 0.11). Nifedipine, in concentrations < or = 10(-5) M, did not affect 125I-ET-1 binding. However, levcromakalim significantly inhibited 125I-ET-1 binding (maximum binding 49 4/- 9%; p = 0.04), whereas the inactive isomer, D-cromakalim, had no effect. Pinacidil also inhibited 125I-ET-1 binding, although to a lesser extent than levcromakalim (maximum binding 63 +/- 7%). These findings provide evidence for a stereospecific interaction between K(+)-channel openers and ET-1 binding in rat cardiac membranes. Because the slope of the logistic fit was substantially less than unity, and the effects of pinacidil and levcromakalim were incomplete, there may be two or more receptors for ET-1 in rat heart, only one of which is sensitive to K(+)-channel openers.

Animals↗
PubMed1993

Endothelin-1 and aggregation of human platelets in vitro.

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide produced by endothelial cells. We investigated whether ET-1, like other potent endothelium-derived vasoactive agents, interacts directly with human platelets in vitro. Platelet-rich plasma was obtained from healthy male volunteers and incubated with ET-1 (1 microM) or vehicle (sodium chloride 154 mM) for 10 min at 37 degrees C. Platelet aggregation was measured by the Born method, using light transmittance through the plasma sample as an index of activation. Although a significant increase in light transmittance was observed when plasma was incubated with ET-1 compared with vehicle, (3.8 +/- 0.4% versus 2.7 +/- 0.2%; n = 24; p = 0.038), this effect was small and is unlikely to be of biologic significance. To investigate the possibility that ET-1-stimulated platelet nitric oxide (NO) synthesis might be masking a direct aggregatory effect of ET-1, in a second study in six subjects NG-monomethyl-L-arginine (L-NMMA, 10 and 100 microM), an inhibitor of NO synthase, was preincubated with the plasma before the addition of ET-1 (1 nM and 1 microM). No significant difference was observed whether samples were incubated with L-NMMA alone or with L-NMMA and ET-1. The results of this study suggest that ET-1 does not have a major direct effect as a platelet aggregating agent.

Adult↗
PubMed1993

Venoconstriction to endothelin-1 in humans is attenuated by local generation of prostacyclin but not nitric oxide.

Endothelin-1 (ET-1) is known to be a potent and long-lasting constrictor of arteries and veins. We investigated whether local endothelial production of nitric oxide (NO) or prostacyclin modulates venoconstriction induced by the endothelium-derived peptide ET-1 in vivo in humans. Six healthy volunteers each received local dorsal hand vein infusion of ET-1 (5 pmol/min) for 60 min in five separate studies: once given alone; on three occasions co-infused with either the NO donor glyceryl trinitrate (GTN), the vasodilator prostaglandin, prostacyclin, or the inhibitor of nitric oxide synthase (NOS) NG-monomethyl-arginine (L-NMMA); and once given 30 min after oral administration of the irreversible inhibitor of cyclooxygenase, acetylsalicylic acid (aspirin). ET-1 alone caused slowly developing and long-lasting venoconstriction (maximal constriction 66 +/- 4%). Although GTN partially prevented ET-1-induced constriction (maximum 33 +/- 5%, p = 0.004 versus ET-1), inhibition of NOS did not affect ET-1-induced venoconstriction (maximum 55 +/- 4%). Prostacyclin was more effective at blocking the venoconstriction to ET-1 than GTN (maximum 12 +/- 3%, p = 0.0001) and there was substantial potentiation of ET-1-induced venoconstriction after pretreatment with aspirin (maximum 90 +/- 3%, p = 0.001). Despite the capacity of NO to attenuate responses to ET-1, L-NMMA did not potentiate ET-1-induced venoconstriction, suggesting little or no stimulated production of NO by ET-1 in human hand veins. However, substantial potentiation of ET-1-induced venoconstriction by aspirin indicates that endothelial production of prostacyclin modulates responses to ET-1 in human veins in vivo.

Adult↗
PubMed1993

Screening for human immunodeficiency virus: a survey of British clinical pharmacology units.

1. A survey of screening practices used to detect infection with the human immunodeficiency virus (HIV), covering the 12 months from June 1990 to May 1991, was carried out in 74 clinical pharmacology units performing phase I and II studies. Forty-five units were identified from the Technomark commercial register, and 29 units were identified from the clinical academic membership of the British Pharmacological Society. 2. An overall response rate of 92% was obtained: 41 replies from commercial units; 27 replies from academic units. Seventeen commercial units and 26 academic units reported involvement with healthy volunteer studies; these were the 43 questionnaires analysed. 3. The majority of clinical pharmacology units did not believe that it was necessary to perform HIV screening by HIV antibody testing. Six commercial units (35%) and three academic units (12%) did perform HIV antibody testing in healthy volunteers. 4. Reasons frequently given for testing were protection of clinical and laboratory staff, and the advantages to the volunteer of prophylaxis and treatment at an early stage of HIV infection. Reasons for not testing included the perceived low risk of a positive test, a lack of benefit from treatment, and the adverse implications in relation to health insurance. Advice from an Ethics Review Committee was not generally a reason for testing. 5. In future, screening patterns may change, depending on prevalence of HIV positivity in the community, the benefits of diagnosis and treatment, and the perceived or real disadvantages of having an HIV antibody test. For the present, we believe that indirect methods, such as an HIV risks questionnaire, are more appropriate than direct antibody testing.

Adolescent↗
PubMed1993

Venoconstriction to endothelin-1 in humans: role of calcium and potassium channels.

Recent studies in vitro have suggested that there may be an interaction between endothelin-1 and ATP-sensitive K+ channels in vascular smooth muscle. Here we have investigated whether agents acting on membrane Ca2+ and K+ channels modulate endothelin-1-induced venoconstriction in vivo in human subjects. In a series of studies, six healthy subjects received, on separate occasions, local infusions into dorsal hand veins of endothelin-1 coinfused with 1) the ATP-sensitive K+ channel opener, cromakalim; 2) the dihydropyridine Ca2+ antagonist, nicardipine; 3) a control vasodilator, hydralazine; and 4) saline placebo. Endothelin-1 caused local venoconstriction with a maximum reduction in vein size of 66 +/- 4% at 60 min (P = 0.0001 vs. basal). Cromakalim prevented endothelin-1-induced venoconstriction (9 +/- 10% maximum constriction; P = 0.68 vs. basal). By contrast, nicardipine, in a dose sufficient to block depolarization-induced constriction caused by K+ infusion, had only a partial effect on endothelin-1-induced venoconstriction (35 +/- 8% maximum constriction; P = 0.001 vs. basal; P = 0.02 vs. endothelin-1), whereas a 10-fold higher dose of nicardipine had no additional effect and hydralazine had no effect. In further studies, cromakalim, but not nicardipine, reversed endothelin-1-induced venoconstriction. Cromakalim did not prevent constriction induced by norepinephrine. Although calcium entry through dihydropyridine-sensitive Ca2+ channels may account in part for the vasoconstrictor action of endothelin-1 in humans, the abolition of endothelin-1 responses by a K+ channel opener suggests additional mechanisms of action for endothelin-1.

Adult↗