Microvascular correlates of blood pressure, plasma glucose, and insulin resistance in health.

OBJECTIVES: The associations between hypertension, insulin resistance and glucose intolerance are poorly understood. Altered microvascular structure and function could contribute by increasing peripheral vascular resistance and decreasing tissue delivery of glucose. We addressed this hypothesis in a sample of healthy men. METHODS: We studied 105 healthy young men aged 23-33 years. Insulin resistance was calculated using the Homeostasis Model Assessment (HOMA). Video capillaroscopy was used on the dorsum of the finger to measure skin capillary density, and in nailfold capillaries to measure capillary blood velocity. Skin vasodilatation was measured with laser Doppler fluximetry on the forearm following heating and iontophoresis of acetylcholine. RESULTS: Higher systolic blood pressure was associated with insulin resistance (r=0.31, P<0.005), lower dermal capillary density (r= -0.25, P<0.05), and impaired maximum dermal blood flow after heating (r= -0.26, P<0.01), but not with capillary blood velocity (r=0.07) or dilator responses to acetylcholine (r=0.09). Insulin resistance did not correlate with indices of microvascular structure or function (all r<+/-0.15). However, higher fasting plasma glucose was associated with lower capillary density (r= -0.27, P<0.01), and increased capillary blood velocity (r=0.30, P<0.05). CONCLUSIONS: The association between hypertension and insulin resistance is unlikely to be explained by altered microvascular structure and function. However, changes in the microvasculature are found in subjects with early and subtle elevations in blood pressure or fasting plasma glucose in advance of their crossing conventional thresholds for the diagnosis of hypertension or diabetes mellitus.

Activation of the endothelin system in insulin resistance.

Endothelin-1, released from the vascular endothelium after cleavage from big endothelin-1, is a potent paracrine vasoconstrictor peptide. Small studies suggest that circulating levels of endothelin-1 are elevated in subjects with cardiovascular risk factors. Big endothelin-1 levels may better reflect endothelin-1 generation. We examined relationships between plasma endothelin-1, plasma big endothelin-1, and predisposition to hypertension or other cardiovascular risk factors associated with insulin resistance in a large group of healthy young men. We recruited 96 healthy men aged 24-33 years from a cohort of 864 young men and women in whom predisposition to hypertension had been defined on the basis of their own blood pressure and the blood pressures of their parents. They attended after an overnight fast for measurement of blood pressure, anthropometry, and plasma lipids, insulin, glucose, endothelin-1 and big endothelin-1. Plasma endothelin-1 and big endothelin-1 levels did not correlate with blood pressure (r=0.09, -0.002 respectively) and were not influenced by parental blood pressure. Higher plasma endothelin-1 levels were associated with higher body mass index (r=0.29, p<0.005), and higher plasma insulin (r=0.21, p<0.05). Higher plasma big endothelin-1 levels were associated with insulin resistance, as assessed by the Homeostasis Model of Assessment resistance index (r=0.30, p<0.005). Endothelin-1 levels are not related to blood pressure, but are higher in healthy young men with insulin resistance and obesity.

Beta(2)-adrenoceptor polymorphism determines vascular reactivity in humans.

Altered beta-adrenergic regulation has been reported in individuals with hypertension. The variability in vascular responsiveness to beta-agonists, such as isoproterenol, observed in humans may be explained partially by beta(2)-adrenoceptor polymorphism. Individuals with the Gln27 form of the receptor may show reduced vascular reactivity because of downregulation expression of the receptor in the vasculature. We screened 127 normotensive white subjects, 37 of whom were homozygous for these alleles. Thirty-two subjects (17 Gln27 and 15 Glu27) agreed to receive brachial artery infusions of isoproterenol at doses of 1 to 300 ng. min(-1); forearm blood flow was measured by using venous occlusion plethysmography. Of these subjects, 25 (12 Glu27 and 13 Gln27) received local doses of isoproterenol (0.3 to 30.0 ng. min(-1)) via a dorsal hand vein preconstricted with norepinephrine. Compared with subjects homozygous for the Glu27 allele, subjects with the Gln27 substitution had lower baseline blood flow and, in response to isoproterenol, had a significantly attenuated increase in forearm blood flow. This pattern was more marked in veins. We also studied the relationship between the position 16 polymorphism and vascular reactivity. Homozygotes for Arg16 had significantly lower basal blood flow and attenuated increases in forearm blood flow compared with the Gly16 homozygotes. This was significant in veins but not in arteries. Thus, beta(2)-adrenoceptor genotype determines vascular responses to isoproterenol in forearm resistance vessels and in capacitance vessels. Further studies are necessary to establish whether beta(2)-adrenoceptor polymorphisms are important in the genesis of hypertension.

Nurses' and doctors' attitudes towards suicidal behaviour in young people.

This paper presents an exploratory study performed to identify the attitudes towards suicidal behaviour in young people, amongst nurses (and nursing lecturers), and doctors working in in-patient medical and mental health care settings. The Suicide Opinion Questionnaire (SOQ) was administered to 59 participants. Responses were scored using eight clinical scales, and tested by using a Kruskal-Wallis one way analysis of variance. An Independent Sample t-test was used to analyse gender differences. Qualitative interviews were conducted in a sample of respondents. SOQ findings revealed no overall significant differences in the relevant groups of nurses and doctors, with the exception of gender and the clinical scale relating to a 'Cry for Help'. The focused interviews generated five categories relating to suicidal behaviour and young people. Nurses and doctors working in these areas possess a range of influential perceptions of suicidal behaviour and need to be considered in the contexts of care and treatment of young people.

Platelet aggregation in young men with contrasting predisposition to high blood pressure.

In essential hypertension, abnormal platelet function may induce vasospasm and predispose to thrombotic vascular occlusion. We studied in vitro aggregability in platelets from young men with contrasting predisposition to hypertension, defined by their own blood pressure and blood pressures of their parents. Among offspring of parents with low blood pressure, higher blood pressure was associated with impaired aggregation in response to epinephrine (2 x 10(-8) to 5 x 10(-6) mol/L), which was unaffected by endothelin-1 (10(-9) mol/L). By contrast, among offspring of parents with high blood pressure, higher blood pressure was associated with normal aggregation to epinephrine and potentiation of the primary phase of aggregation by endothelin-1. We conclude that enhanced platelet sensitivity to endothelin-1 appears to be a feature of the familial predisposition to hypertension, rather than a nonspecific consequence of high blood pressure.

Impairment of forearm vasodilatation to acetylcholine in hypercholesterolemia is reversed by aspirin.

OBJECTIVE: Impaired cholinergic vasodilatation in the forearm in hypertension and hypercholesterolemia has been attributed to impaired nitric oxide bioavailability. However, inhibition of cyclooxygenase reverses the impaired cholinergic dilatation in hypertensive animals and patients. The aim of this study was to examine the effect of aspirin on cholinergic vasodilatation in hypercholesterolemic patients. METHODS: We examined responses to brachial artery infusion of acetylcholine and the endothelium-independent vasodilator sodium nitroprusside in the presence or absence of aspirin in 10 hypercholesterolemic patients (7 men/3 women; aged 38-63 yr; systolic blood pressure 133 +/- 5 mmHg; diastolic blood pressure 80 +/- 3) compared with 10 matched controls (7 men/3 women; aged 38-63 yr; systolic blood pressure 126 +/- 2; diastolic blood pressure 77 +/- 2). RESULTS: In hypercholesterolemic patients, forearm vasodilatation was impaired in response to acetylcholine (112 +/- 20 vs. 346 +/- 30% increase in blood flow in controls, at the highest dose [15 micrograms min-1]; P < 0.0001) but not in response to sodium nitroprusside. With the addition of aspirin, baseline forearm blood flow was unaltered. However, forearm vasodilatation to acetylcholine was partially restored in hypercholesterolemics (from 112 +/- 20 to 193 +/- 30%; P < 0.001) though not affected in controls. Vasodilator responses to sodium nitroprusside were unaffected by aspirin in either group. CONCLUSIONS: In hypercholesterolemia, an altered balance between vasoconstrictor and dilator prostanoids, favouring constrictors, may contribute to endothelial dysfunction either directly or through an effect on nitric oxide synthesis. Restoration of this imbalance may be a component of the therapeutic benefit of aspirin in cardiovascular disease.

Studies with iontophoretic administration of drugs to human dermal vessels in vivo: cholinergic vasodilatation is mediated by dilator prostanoids rather than nitric oxide.

AIMS: Impaired function of the vascular endothelium has been well documented in hypertension and hypercholesterolaemia. However, the 'gold standard' method for assessing endothelial function, using intra-arterial drug infusion, is invasive and has only been applied in the forearm and coronary circulations in vivo. The aim of the present study was to establish the non-invasive technique of transdermal drug iontophoresis to assess endothelial function in human dermal vessels in vivo. METHODS: In healthy male volunteers, we delivered acetylcholine (ACh) and sodium nitroprusside (SNP) to dermal vessels of the forearm using iontophoresis, and measured vasodilatation using laser Doppler fluximetry. Drugs were diluted in a methylcellulose gel vehicle which did not induce vasodilatation. To assess the contribution of nitric oxide and vasoactive prostanoids to cholinergic dilatation, the procedure was repeated during brachial artery infusion of the nitric oxide synthase inhibitor, L-N(G)-monomethyl-arginine (L-NMMA) and after intravenous administration of the cyclooxygenase inhibitor, aspirin. As a control for the vasoconstrictor effect of L-NMMA, which was measured by venous occlusion plethysmography, iontophoresis was repeated during brachial artery infusion of noradrenaline. RESULTS: Flux increased in response to iontophoresis of ACh (from 45 +/- 9 to 499 +/- 80 units; P < 0.0001) and SNP (from 32 +/- 11 to 607 +/- 82 units; P < 0.0001). Brachial artery infusions of L-NMMA or noradrenaline caused reductions in forearm blood flow (by 43 +/- 2% and 44 +/- 2%, respectively) but did not inhibit vasodilatation in response to iontophoresis of ACh or SNP. In contrast, aspirin inhibited the response to iontophoresis of ACh (from 473 +/- 81 to 222 +/- 43 units; P < 0.0001) but did not affect the response to SNP (from 348 +/- 59 to 355 +/- 58). CONCLUSIONS: We conclude that in healthy subjects, in contrast to the forearm circulation, dermal vasodilatation in response to iontophoresis of ACh is mediated predominately by a dilator prostanoid rather than by nitric oxide generation. Furthermore, the non-invasive technique of iontophoresis could complement existing invasive tests of endothelial function in future clinical studies.

Contribution of parental blood pressures to association between low birth weight and adult high blood pressure: cross sectional study.

OBJECTIVE: To examine the possibility that low birth weight is a feature of the inherited predisposition to high blood pressure. DESIGN: Cross sectional study. SETTING: Primary care medical centre in Edinburgh. SUBJECTS: One offspring of 452 families (231 men and 221 women aged 16-26 years) in whom blood pressure, weight, and height were measured in 1986 and whose parents had blood pressure measured in 1979. Birth weights were obtained from case records (270 offspring) or by questionnaires sent to the mothers (182 offspring). MAIN OUTCOME MEASURES: Birth weight and adult systolic blood pressure in offspring in relation to parental blood pressure. RESULTS: If parental blood pressures were not considered, a 1 kg decrease in birth weight was associated with a 2.24 mm Hg increase in systolic blood pressure of offspring (P = 0.06) after correction for current weight and sex. However, parental blood pressures correlated positively with blood pressure of offspring, and higher maternal blood pressure was associated with lower birth weight (-3.03 g/mm Hg, P < 0.01). After correction for parental blood pressures, a 1 kg decrease in birth weight was associated with only a 1.71 mm Hg increase in the systolic blood pressure of the offspring (P = 0.15). CONCLUSIONS: Low birth weight is a feature of the inherited predisposition to hypertension, perhaps because it is associated with higher maternal blood pressure during pregnancy. Parental blood pressure may be an important confounding factor in the relation between low birth weight and subsequent hypertension.

Increased glucocorticoid activity in men with cardiovascular risk factors.

The association between hypertension and insulin resistance might be explained by increased activity of the principal glucocorticoid, cortisol. Recent data show that the intensity of dermal vasoconstriction after topical application of glucocorticoids is increased in patients with essential hypertension. In this report, we examine whether increased glucocorticoid sensitivity or secretion is associated with insulin resistance and is a cause or consequence of hypertension. We studied 32 men (aged 47 to 56 years) from a cross-sectional study and 105 men (aged 23 to 33 years) in whom predisposition to high blood pressure has been defined by their own blood pressure and the blood pressures of their parents. In both populations, increased dermal glucocorticoid sensitivity was associated with relative hypertension, insulin resistance, and hyperglycemia. In young men with higher blood pressure whose parents also had high blood pressure, enhanced glucocorticoid sensitivity was accompanied by enhanced secretion of cortisol, enhanced ligand-binding affinities for dexamethasone in leukocytes, and impaired conversion of cortisol to inactive metabolites (cortisone and 5beta-dihydrocortisol). Increased tissue sensitivity to cortisol, amplified by enhanced secretion of cortisol, is a feature of the familial predisposition to high blood pressure rather than a secondary effect of high blood pressure. It may be mediated by an abnormal glucocorticoid receptor, and it may contribute to the association between hypertension and insulin resistance.

Seasonal variation in glucocorticoid activity in healthy men.

Many endocrine systems are subject to seasonal variation. However, studies of the hypothalamic-pituitary-adrenal axis in man have been limited to patients with psychiatric illness with conflicting results. We studied 105 healthy men, age 24-33 yr, during a 15-month period that included two winters. We measured cortisol and its metabolites by gas chromatography/mass spectrometry in plasma and urine and the intensity of dermal blanching after overnight topical application of beclomethasone dipropionate. There were no differences between subjects studied during the two winter periods, but marked differences between subjects studied in winter and summer. In winter, 0900-h plasma cortisol concentrations were higher (73 +/- 10 ng/mL, n = 41 vs. 35 +/- 4, n = 25 in summer; P < 0.01), total cortisol metabolite excretion was lower (678 +/- 67 micrograms/mmol creatinine vs. 900 +/- 98; P < 0.05), the ratio of metabolites of cortisol to those of cortisone was higher (3.0 +/- 0.2 vs. 2.1 +/- 0.1; P < 0.01), and dermal glucocorticoid sensitivity was higher (7.2 +/- 0.4 arbitrary units vs. 5.6 +/- 0.5; P < 0.02). Although blood pressure and fasting insulin/glucose relationships were not measurably different between seasons, these correlated with dermal vasoconstriction and cortisol metabolite excretion rate. We conclude that plasma cortisol and tissue sensitivity to glucocorticoids are higher in winter, but cortisol production rate is reduced. This could be explained by a reduction in cortisol clearance rate: urinary free cortisol/cortisone ratios were not different but A-ring-reduced metabolites of cortisol were higher in winter, suggesting that conversion of cortisone to cortisol by hepatic 11 beta-hydroxysteroid dehydrogenase 1 is enhanced. It is an intriguing possibility that increased glucocorticoid activity contributes to the increased prevalence of disease during the winter.

Haemodynamic effects of adrenomedullin in human resistance and capacitance vessels.

AIMS: The haemodynamic effects of adrenomedullin and calcitonin gene-related peptide (CGRP) were studied in resistance and capacitance vessels of healthy volunteers. METHODS: Adrenomedullin and CGRP were infused into the brachial artery of eight healthy subjects on two separate occasions at doses between 0.3-30 pmol min(-1). Forearm blood flow was measured using venous occlusion plethysmography. Venodilatation to adrenomedullin and CGRP was assessed in a further eight subjects by infusing the peptides at doses between 0.3-10 pmol min(-1) into a dorsal hand vein preconstricted with noradrenaline. Venodilator responses were measured as percentage reduction in noradrenaline preconstriction. RESULTS: Adrenomedullin and CGRP at a dose of 30 pmol min(-1), produced an increase in forearm blood flow of 288 +/- 42% and 252 +/- 30% respectively (mean +/- s.e. mean, P<0.001). At doses between 3 and 10 pmol min(-1) adrenomedullin was significantly more potent than CGRP. The vasodilatation to both peptides was of similar duration with a biological half-life of approximately 18 min. Adrenomedullin reversed constriction in dorsal hand veins by 84 +/- 2% (P<0.001) at a dose of 10 pmol min(-1). CGRP produced a similar effect reversing constriction by 72 +/- 12% at the same dose (P<0.01). In veins, adrenomedullin was also more potent than CGRP at doses between 0.3 and 3 pmol min(-1). CONCLUSIONS: The lowest dose of adrenomedullin producing significant arteriolar dilatation was calculated to produce plasma levels similar to those found in heart failure. These findings suggest that in pathophysiological conditions such as heart failure circulating levels of adrenomedullin may be within a range capable of influencing vascular resistance directly.

Impaired microvascular dilatation and capillary rarefaction in young adults with a predisposition to high blood pressure.

Increased vascular resistance in essential hypertension occurs mainly in microvessels with luminal diameters < 100 microm. It is not known whether abnormalities in these vessels are a cause or consequence of high blood pressure (BP). We studied 105 men (aged 23-33 yr) in whom predisposition to high blood pressure has been characterized by both their own BP and those of their parents. Factors that are secondary to high BP correlate with offspring BP irrespective of parental BP, but factors that are components of the familial predisposition to high BP are more closely associated with higher BP in offspring whose parents also have high BP. Offspring with high BP whose parents also have high BP had impaired dermal vasodilatation in the forearm following ischemia and heating (289+/-27 [n = 25] versus 529+/-40 [n = 26], 476+/-38 [n = 30], and 539+/-41 flux units [n = 24] in other groups; P < 0.0001) and fewer capillaries on the dorsum of the finger (23+/-0.8 capillaries/0.25 mm2 versus 26+/-0.8 in all other groups; P < 0.003). Except for BP, other hemodynamic indices (including cardiac output and forearm vascular resistance) were not different. The dermal vessels of men who express a familial predisposition to high BP exhibit increased minimum resistance and capillary rarefaction. Defective angiogenesis may be an etiological component in the inheritance of high BP.

A comparison of techniques to assess skin blanching following the topical application of glucocorticoids.

Glucocorticoid-induced dermal blanching provides a useful research tool to study steroid potency and sensitivity. Conventional measurement of the intensity of blanching relies on subjective assessment by a trained observer using a visual score. Several objective techniques have recently been reported to detect skin blanching, but their sensitivity has not been compared previously with subjective visual recordings. In this report we aimed to establish whether objective methods offer sufficient sensitivity to be employed in epidemiological studies of glucocorticoid responsiveness. In healthy subjects we applied beclomethasone dipropionate at three concentrations (1, 10 and 100 micrograms/ml) under an occluded dressing overnight. The following morning we measured blanching using a visual score, laser Doppler velocimetry with the MBF 3D monitor (Moor Instruments Ltd, U.K.) and a perfusion imager (Lisca, Sweden), and reflectance spectrophotometry with the Dia-Stron 'erythemameter'. Using the visual score, blanching was detected at all concentrations of steroid. Neither laser Doppler instrument detected vasoconstriction at any concentration. By contrast, the reflectance spectrophotometer successfully recorded blanching at 10 and 100 micrograms/ml, but not at 1 microgram/ml. We conclude that laser Doppler instruments, including the novel scanning perfusion imager, do not detect glucocorticoid-induced skin blanching, perhaps because it reflects venular rather than arteriolar vasoconstriction. By contrast, the Dia-Stron reflectance spectrophotometer has sufficient sensitivity to be used as an alternative to visual assessment in epidemiological studies of human glucocorticoid-induced dermal blanching.

Local inhibition of nitric oxide generation in man reduces blood flow in finger pulp but not in hand dorsum skin.

1. Nitric oxide generation is important in the regulation of resistance vessel tone. Until now, however, there has been no evidence of such a role for basal generation of nitric oxide in the skin microcirculation of humans. 2. To investigate this, L-NG-monomethylarginine (L-NMMA), a competitive inhibitor of nitric oxide synthase, was administered at 1, 2 and 4 mumol min-1 (each for 10 min), via the brachial artery, in six healthy male subjects. 3. At each dose, using laser Doppler fluximetry, red blood cell flux was measured as an index of blood flow in the pulp of the thumb, an area rich in arteriovenous anastomoses, and on the dorsal surface of the hand, where arteriovenous anastomoses are rare. Finger nailfold capillary blood velocity was monitored at each dose using videomicroscopy. Forearm blood flow was measured by venous occlusion plethysmography, before, and 8 min after, completing infusion of L-NMMA. All data were obtained from both the infused and control arms. 4. L-NMMA reduced blood flow in the infused forearm by 37% (P = 0.005). In contrast, dorsum red cell flux, capillary blood velocity, and skin temperature were unchanged. There was, however, a significant reduction in thumb red cell flux (ANOVA, P = 0.0001), reaching a maximum reduction of 33% with 4 mumol min-1 L-NMMA. There were no effects apparent in the opposite arm. 5. These results suggest that endogenous nitric oxide production may be more important in regulating microvascular skin blood flow in regions rich in arteriovenous anastomoses than in areas containing mainly nutritive vessels.

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.

Calcium leakage as a cause of the high resting tension in vascular smooth muscle from the spontaneously hypertensive rat.

Aortic strips from spontaneously hypertensive (SH) rats relax in calcium-free physiological medium and contract to approximately 60% of maximum when calcium is again restored to the medium. In vivid contrast, the resting tension of aortic strips from normal rats is unaffected by manipulation of the calcium concentration of the bathing medium. These findings, as well as the reduced sensitivity of aortic strips from SH rats to norepinephrine and the observation that aortic strips from SH rats relax at a faster rate in calcium-free medium in comparison with aortic strips from normal rats, are consistent with the hypothesis that vascular smooth muscle membranes from SH rats leak calcium at a rate that is only partially compensated by the calcium pump.

Norepinephrine release from nerve terminals within the rabbit superior cervical ganglion.

Norepinephrine-3H (NE-3H) and its metabolic normetanephrine-3H were released from the superfused rabbit SCG incubated in tyrosine-3H in response to preganglionic stimulation. Neither dopamine-3H nor its metabolite, 3-methoxy-tyrosine could be detected in the superfusate from "control" or "nerve stimulated" tissues. Nerve stimulated NE-3H release a) was calcium dependent, b) had a stimulus threshold similar to that of C fibers, c) was not blocked by either 50 micromolar curare or 100 micromolar atropine, d) was abolished by chronic decentralization and e) was elicited by stimulation of both the cervical sympathetic and internal carotid nerves. These results suggest that there is a here-to-for undescribed, noradrenergic pathway which originates elsewhere in the sympathetic chain but terminates in the superior cervical ganglion.

Some physiological and pharmalogical characteristics of the stimulus induced release of norepinephrine from the rabbit superior cervical ganglion.

The cervical sympathetic nerve stimulated release of norepinephrine (NE) from the rabbit superior cervical ganglion (SCG) was characterized. The quantity of NE released per impulse declined with increasing stimulation frequency over the range of 3/sec to 15/sec. Nerve stimulated NE release was potentiated by 1 micromolar desmethylimipramine and 25 micromolar phenoxylbenzamine and inhibited by 1 micromolar bretylium, 25 micromolar methoxamine and 1 micromolar prostaglandin E1. These results suggest that nerve stimulated NE release in the rabbit SCG occurs from sympathetic fibers which are subject to the same neurosecretory control mechanisms as sympathetic fibers elsewhere in the autonomic nervous system.