Plasma and platelet free catecholamine concentrations in patients with familial hypercholesterolaemia

Heart rate variability in hypothyroid patients: A systematic review and meta-analysis

Introduction

Hypothyroidism may be associated with changes in the autonomic regulation of the cardiovascular system, which may have clinical implications.

Objective

To conduct a systematic review and meta-analysis on the impact of hypothyroidism on HRV.

Materials and methods

PubMed, Cochrane, Embase and Google Scholar were searched until 20 August 2021 for articles reporting HRV parameters in untreated hypothyroidism and healthy controls. Random-effects meta-analysis were stratified by degree of hypothyroidism for each HRV parameters: RR intervals (or normal to normal-NN intervals), SDNN (standard deviation of RR intervals), RMSSD (square root of the mean difference of successive RR intervals), pNN50 (percentage of RR intervals with >50ms variation), total power (TP), LFnu (low-frequency normalized unit), HFnu (high-frequency), VLF (very low frequency), and LF/HF ratio.

Results

We included 17 studies with 11438 patients: 1163 hypothyroid patients and 10275 healthy controls. There was a decrease in SDNN (effect size = -1.27, 95% CI -1.72 to -0.83), RMSSD (-1.66, -2.32 to -1.00), pNN50 (-1.41, -1.98 to -0.84), TP (-1.55, -2.1 to -1.00), HFnu (-1.21, -1.78 to -0.63) with an increase in LFnu (1.14, 0.63 to 1.66) and LF/HF ratio (1.26, 0.71 to 1.81) (p <0.001). HRV alteration increased with severity of hypothyroidism.

Conclusions

Hypothyroidism is associated with a decreased HRV, that may be explained by molecular mechanisms involving catecholamines and by the effect of TSH on HRV. The increased sympathetic and decreased parasympathetic activity may have clinical implications.

Reduced contribution of endothelin to the regulation of systemic and pulmonary vascular tone in severe familial hypercholesterolaemia

Vascular dysfunction has been associated with familial hypercholesterolaemia (FH), a severe form of hyperlipidaemia. We recently demonstrated that swine with FH exhibit reduced exercise-induced systemic, but not pulmonary, vasodilatation involving reduced nitric oxide (NO) bioavailability. Since NO normally limits endothelin (ET) action, we examined the hypothesis that reduced systemic vasodilatation during exercise in FH swine results from increased ET-mediated vasoconstriction. Systemic and pulmonary vascular responses to exercise were examined in chronically instrumented normal and FH swine in the absence and presence of the ETA/B receptor antagonist tezosentan. Intrinsic reactivity to ET was further assessed in skeletal muscle arterioles. FH swine exhibited ∼9-fold elevation in total plasma cholesterol versus normal swine. Similar to our recent findings, systemic, not pulmonary, vasodilatation during exercise was reduced in FH swine. Blockade of ET receptors caused marked systemic vasodilatation at rest and during exercise in normal swine that was significantly reduced in FH swine. The reduced role of ET in FH swine in vivo was not the result of decreased arteriolar ET responsiveness, as responsiveness was increased in isolated arterioles. Smooth muscle ET receptor protein content was unaltered by FH. However, circulating plasma ET levels were reduced in FH swine. ET receptor antagonism caused pulmonary vasodilatation at rest and during exercise in normal, but not FH, swine. Therefore, contrary to our hypothesis, FH swine exhibit a generalised reduction in the role of ET in regulating vascular tone in vivo probably resulting from reduced ET production. This may represent a unique vascular consequence of severe familial hypercholesterolaemia.

Association of sympathovagal imbalance with cardiovascular risks in overt hypothyroidism

Background:

Cardiovascular morbidities have been reported in hypothyroidism.

Aims:

The objective of this study is to investigate the link of sympathovagal imbalance (SVI) to cardiovascular risks (CVRs) and the plausible mechanisms of CVR in hypothyroidism.

Materials and Methods:

Age-matched 104 females (50 controls, 54 hypothyroids) were recruited and their body mass index (BMI), cardiovascular parameters, autonomic function tests by spectral analysis of heart rate variability (HRV), heart rate response to standing, deep breathing and blood pressure response to isometric handgrip were studied. Thyroid profile, lipid profile, immunological and inflammatory markers were estimated and their association with low-frequency to the high-frequency ratio (LF-HF) of HRV, the marker of SVI was assessed by multivariate regression.

Results:

Increased diastolic pressure, decreased HRV, increased LF-HF, dyslipidemia and increased high-sensitive C-reactive protein (hsCRP) were observed in hypothyroid patients and all these parameters had significant correlation with LF-HF. BMI had no significant association with LF-HF. Atherogenic index (β 1.144, P = 0.001) and hsCRP (b 0.578, P = 0.009) had independent contribution to LF-HF. LF-HF could significantly predict hypertension status (odds ratio 2.05, confidence interval 1.110-5.352, P = 0.008) in hypothyroid subjects.

Conclusions:

SVI due to sympathetic activation and vagal withdrawal occurs in hypothyroidism. Dyslipidemia and low-grade inflammation, but not obesity contribute to SVI and SVI contributes to cardiovascular risks.

Nocturnal pulse wave attenuation is associated with office blood pressure in a population based cohort

OBJECTIVE AND BACKGROUND

Pulse wave amplitude (PWA) derived from the digital vascular bed has been used in sleep studies. The nocturnal attenuation of PWA has been shown to reflect sympathetic activation during sleep. We assessed the relationship between nocturnal PWA attenuation and office blood pressure (BP).

METHODS

Eighty-one subjects (46 men; age 60+/-7 years; body mass index [BMI] 28.2+/-4.3 kg/m(2); apnea hypopnea index [AHI], 25.4+/-22.6 events/h; systolic BP 137+/-15 mm Hg; diastolic BP 79+/-7 mm Hg) recruited from a population based cohort underwent simultaneous ambulatory polysomnography (PSG) and peripheral arterial tonometry (PAT) recording. Episodic attenuations of PWA derived from the pulse waveform of the PAT signal were identified and characterized. Generalized least squares regression models were used to identify the associations between median PWA attenuation (PWA.att), office BP and sleep-related disordered breathing.

RESULTS

We found that the association between PWA.att and office BP was independent of gender, age, BMI, antihypertensive medication, number of attenuation episodes, AHI, oxygen desaturation 4% index (ODI4) and arousal index. Each 10% increase in PWA.att was associated with increases of 5.0 mm Hg systolic BP (P=0.02) and 3.0 mm Hg diastolic BP (P=0.005). We also found independent relationships between systolic/diastolic BP and BMI (P=0.0006/0.001), AHI (P=0.03/0.1) and ODI4 (P=0.03/0.03).

CONCLUSIONS

The degree of PWA attenuation during the night is associated with office BP independent of sleep-disordered breathing. Continuous assessment of PWA during sleep may provide novel insights into cardiovascular physiology and morbidity.

Antioxidative action of aspirin on endothelial function in hypercholesterolaemic rats

The role of aspirin on vascular endothelial changes during hypercholesterolaemia prior to development of actual atherosclerotic lesions is not known. Therefore, in the present study, we tested the hypothesis that aspirin by its antioxidant action improves endothelial function in a rat model of hypercholesterolaemia. Hypercholesterolaemia was induced in Wistar rats by feeding a 1% cholesterol-rich diet for 10 weeks. Lipid profile, lipid peroxidation and reduced glutathione were estimated in serum. Endothelial function and beta(2)-adrenoceptor activity was tested by studying the dose-response relationship of acetylcholine and isoproterenol, respectively, on isolated aortic tissues in an organ bath setup. Hypercholesterolaemic rats showed a significant increase in total cholesterol, low-density lipoprotein cholesterol (LDL-C) and very low-density lipoprotein cholesterol (VLDL-C), and a significant fall in high-density lipoprotein cholesterol (HDL-C) compared to the control rats. Isolated aortic tissues from hypercholesterolaemic rats showed endothelial dysfunction and decreased sensitivity to beta(2)-adrenoceptor. Treatment with aspirin was associated with a fall in total cholesterol, LDL-C and VLDL-C, and a significant rise in serum HDL-C. Aspirin treatment also restored endothelial function and beta(2)-adrenoceptor activity. Hypercholesterolaemic rats showed free radical generation, evident by increase in serum lipid peroxidation and reduction in serum reduced glutathione content compared to the control rats. Aspirin treatment was associated with reduction in free radical stress evident by decreased lipid peroxidation and significantly prevented reduction in glutathione content compared to hypercholesterolaemic controls. Aspirin improves endothelial function and beta(2)-adrenoceptor activity during experimentally induced hypercholesterolaemia in rats, possibly due to an antioxidant effect.

CCK4-induced panic in healthy subjects II: neurochemical correlates

Cholecystokinin tetrapeptide (CCK4) induces symptoms similar to those of panic attack. The present study investigated the effects of CCK4 administration on catecholaminergic system. In this double blind, randomised, crossover experiment, 16 healthy subjects received injections of either 25 microg of CCK4 or placebo on two separate occasions. Platelet and plasma catecholamine concentrations were assessed before the administration and compared to post-injection values. The results clearly show that both plasma and platelet concentrations of catecholamines are significantly affected by CCK4. Plasma norepinephrine (NE) and epinephrine (EPI) raised significantly above baseline in the immediate post-CCK4 period, while in plasma dopamine (DA), the significant increases were delayed. In the platelets, significant post-CCK4 increases of NE and EPI concentrations were observed with a delay of several minutes. In summary, we have demonstrated that, in healthy subjects, CCK4 increases peripheral concentrations of catecholamines in both plasma and platelets, with the most consistent changes occurring in platelet NE and plasma EPI concentrations.

Platelet alpha 2-adrenergic receptors in hypercholesterolemia: relationship between binding studies and epinephrine-induced platelet aggregation

BACKGROUND

Platelets isolated from patients with hypercholesterolemia are more sensitive in vitro to various aggregating agents, including epinephrine, than those isolated from normocholesterolemic subjects. Increased platelet reactivity is one mechanism that may explain the enhanced risk of thromboembolism in hypercholesterolemia. This study assessed whether platelet hyperreactivity to epinephrine in hypercholesterolemia is associated with higher alpha 2-adrenergic receptor density or affinity for epinephrine.

METHODS

Platelet aggregation and binding studies, with use of [3H]yohimbine as ligand, were performed on platelets isolated from 30 patients with type IIa hypercholesterolemia and 23 control subjects.

RESULTS

Platelet aggregation in response to epinephrine was significantly higher in patients with hypercholesterolemia than in control subjects. A statistically significantly higher alpha 2-adrenergic receptor density was observed in a subgroup of 13 patients with hypercholesterolemia than in 13 sex- and age-matched control subjects (280 +/- 61 and 230 +/- 49 fmol/mg protein respectively; p < 0.03), but no difference was observed in receptor affinity for the ligand. In these subgroups plasma total and levels of low-density lipoprotein (LDL) cholesterol were inversely correlated with platelet aggregation but directly correlated with platelet receptor density.

CONCLUSION

Platelet alpha 2-adrenergic receptor density is increased in hypercholesterolemia and directly correlates with plasma total and levels of LDL cholesterol, providing at least a partial explanation for the enhanced platelet response to epinephrine that is observed in hypercholesterolemia.

Reduced platelet serotonin content and release in familial hypercholesterolaemia

Plasma and platelet serotonin (5-HT) concentrations, and resting and collagen-induced 5-HT release in platelet-rich plasma were studied in normal and familial hypercholesterolaemic (FH) subjects. Platelet 5-HT concentrations were significantly reduced (-37%, P < 0.01) in FH patients whilst mean plasma concentrations, although increased, were not significantly different from those in normal subjects. Platelet 5-HT correlated negatively with plasma cholesterol when the data for normal subjects and FH, patients were combined (r = -0.48, P = 0.005). It also correlated negatively with low-density lipoprotein (LDL) (FH data, r = -0.59, P = 0.03; normal and FH data, r = -0.49, P = 0.004) but positively with high-density lipoprotein (HDL) (FH r = 0.79, P = 0.001; normal and FH, r = 0.37, P = 0.03). Collagen (5-160 micrograms/ml) stimulated platelet 5-HT release occurred in a concentration-dependent manner. In FH patients stimulated 5-HT release was reduced (10 micrograms/ml collagen, -40%, P < 0.05) and accompanied by increased collagen EC50 values (P < 0.02). Resting 5-HT release was increased substantially in FH patients but not significantly. Our data provide evidence for a relationship between circulating cholesterol and platelet serotonergic mechanisms. It is proposed that abnormalities relating to platelet-plasma 5-HT dynamics, perhaps due to enhanced platelet activity or decreased platelet uptake, may contribute to the cardiovascular complications in FH.

Evidence for separate serotonin and catecholamine compartments in human platelets

Serotonin (5-HT) and the catecholamines (CA), noradrenaline (NA) and adrenaline (Ad), are platelet dense-granule constituents which influence platelet activity and vessel tone. Platelets accumulate 5-HT via an active process whilst CA uptake occurs mainly by passive diffusion. The platelet contents and collagen-stimulated efflux of 5-HT, NA and Ad were examined in normal individuals to establish whether relationships exist between these monoamines. Regression analysis revealed that platelet 5-HT was not related to platelet NA or Ad levels. Platelet NA, however, correlated positively with Ad (r = 0.61, P < 0.01). Collagen-induced release of all three monoamines occurred in a dose-dependent manner. The collagen EC50 values for 5-HT and CA release, however, differed and were greater for 5-HT release: 9.6 +/- 0.8 vs. 3.8 +/- 0.2 microgram/ml collagen, 5-HT vs. NA, P < 0.001; 9.6 +/- 0.8 vs. 3.9 +/- 0.5 microgram/ml, 5-HT vs Ad, P < 0.001. These data may reflect differences regarding the triggering mechanisms for 5-HT and CA release and provide evidence for separate compartments of intra-platelet 5-HT and CA and possibly distinct populations of 5-HT and CA containing dense granules and/or platelets.

Cholesterol-fed rabbits: study of the response of the vas deferens to adrenergic and non-adrenergic stimulus and to a kappa-opioid agonist

The aim of the present study was to analyse the contractility of the isolated vas deferens from hypercholesterolaemic rabbits; for this purpose we evaluated the contractile response induced by noradrenaline and by electrical stimulation. A significant increase in the amplitude of adrenergic and non-adrenergic responses was observed in vas deferens from hypercholesterolaemic rabbits. These data suggest an increase in the contractility of the smooth muscle in these animals.

Platelet transmembrane signalling responses to collagen in familial hypercholesterolaemia

Washed platelets from patients with familial hypercholesterolaemia (FH) were found to be more reactive towards collagen than those from control subjects. The dose required to achieve half maximum aggregation was found to be 0.6 ml-1 for FH patients whilst that for control subjects was 1.25 micrograms ml-1. In both types of platelet, intracellular Ca2+ levels, as monitored by the Ca(2+)-dependent photoprotein, aequorin, rose on stimulation with collagen and then fell to basal levels, probably due to resequestration by the reticular system. This effect was not due to exhaustion of the supply of aequorin since sustained Ca2+ influx induced by the ionophore, A23187, gave a stable signal that did not return to baseline. Similarly, inositol 1,4,5, trisphosphate levels increased in the cytosol after stimulation and then fell to unstimulated values. When stimulated with collagen, platelets from FH patients showed a greater extent of cytoplasmic calcium mobilization (P < 0.05) when compared to controls, coupled with a greater extent of inositol phospholipid hydrolysis (P < 0.05). At doses of collagen sufficient to give either 100% or 50% aggregation, platelets from patients or control subjects showed the same amplitude of ATP release at either dose suggesting that the trigger for vesicle release is more sensitive in FH.

Platelet function in patients with hypercholesterolaemia

Platelets and plasma lipoproteins, particularly low density lipoprotein, have important roles in atherogenesis. Evidence from several sources suggests that important interactions occur between these individual components of the atherogeneic process. Here we review work from our own laboratory on platelet function in normal individuals and patients heterozygous for familial hypercholesterolaemia (FH). Data is presented on the role of platelet noradrenaline and also on altered cellular signalling in platelets from FH individuals who have plasma low density lipoprotein concentrations which are approximately double those seen in normal subjects.

Decreased sensitivity to adenosine in platelets from patients with familial hypercholesterolaemia--a change reversed by cholestyramine treatment

Platelet-rich plasma was obtained from patients with untreated heterozygous familial hypercholesterolaemia (FH), from FH patients treated with cholestyramine and from control subjects. Responsiveness of platelets to the aggregation inhibitors adenosine, its analogue N-ethylcarboxamidoadenosine (NECA) and prostaglandin I2 was decreased in FH. Patients on cholestyramine therapy showed normal responsiveness to adenosine and NECA. There were only minor changes in the binding of [3H]NECA to high-affinity binding sites on platelet membranes from untreated FH or cholestyramine-treated FH patients. The initial rate of cyclic AMP formation in response to a high concentration of NECA was severely decreased in platelets from FH patients. By contrast, the rate of cyclic AMP formation in response to forskolin or a high concentration of prostaglandin I2 was unchanged. These data point to a defect in the coupling of the platelet A2 adenosine receptor to adenylyl cyclase in untreated FH patients.