Genetic variation in alpha2-adrenoreceptors and heart rate recovery after exercise

Heart rate recovery in normal and obese males with and without parental history of cardiovascular disease

Background:

Parental history of cardiovascular disease (CVD) and obesity is associated with delayed parasympathetic nervous system reactivation after exercise. Heart rate recovery (HRRe) after a minute of exercise is inversely related to cardiovascular events.

Aim:

To determine the effect of body mass index (BMI) and parental CVD history on HRRe in apparently healthy young Indian males.

Method:

The present cross-sectional experimental study involved 100 males, aged18–25 years. Subjects were divided into two equal groups based on the parental CVD history—(i) Parental CVD history present, and (ii) Parental CVD history absent. Each of these groups were further divided into two equal sub groups based on BMI—(a) BMI <23kg/m², and (b) BMI ≥25 kg/m². Participants exercised on the treadmill at variable speeds and grades to achieve their target HR (THR). THR was calculated by adding 60–90% HR-reserve (HRR) in their basal HR (BHR). HRR was calculated by subtracting maximal HR (MHR) from BHR. MHR was estimated by the formula: 208–0.7 × age. The HRRe was calculated by subtracting the immediate postexercise HR with the HR after a minute of rest postexercise. ANOVA with post-hoc Tukey was applied and a P value ≤0.05 was considered as statistically significant.

Results:

HRRe value was significantly lesser in subjects having a positive parental history of CVD than the subjects with no parental history of CVD, irrespective of BMI. Also, HRRe was inversely related to BMI.

Conclusion:

Not only obesity but also a family history of CVD impacts the recovery of HR after vigorous-intensity exercise.

Genetics and the heart rate response to exercise

The acute heart rate response to exercise, i.e., heart rate increase during and heart rate recovery after exercise, has often been associated with all-cause and cardiovascular mortality. The long-term response of heart rate to exercise results in favourable changes in chronotropic function, including decreased resting and submaximal heart rate as well as increased heart rate recovery. Both the acute and long-term heart rate response to exercise have been shown to be heritable. Advances in genetic analysis enable researchers to investigate this hereditary component to gain insights in possible molecular mechanisms underlying interindividual differences in the heart rate response to exercise. In this review, we comprehensively searched candidate gene, linkage, and genome-wide association studies that investigated the heart rate response to exercise. A total of ten genes were associated with the acute heart rate response to exercise in candidate gene studies. Only one gene (CHRM2), related to heart rate recovery, was replicated in recent genome-wide association studies (GWASs). Additional 17 candidate causal genes were identified for heart rate increase and 26 for heart rate recovery in these GWASs. Nine of these genes were associated with both acute increase and recovery of the heart rate during exercise. These genes can be broadly categorized into four categories: (1) development of the nervous system (CCDC141, PAX2, SOX5, and CAV2); (2) prolongation of neuronal life span (SYT10); (3) cardiac development (RNF220 and MCTP2); (4) cardiac rhythm (SCN10A and RGS6). Additional 10 genes were linked to long-term modification of the heart rate response to exercise, nine with heart rate increase and one with heart rate recovery. Follow-up will be essential to get functional insights in how candidate causal genes affect the heart rate response to exercise. Future work will be required to translate these findings to preventive and therapeutic applications.

Human Placenta Expresses α2-Adrenergic Receptors and May Be Implicated in Pathogenesis of Preeclampsia and Fetal Growth Restriction

α₂-Adrenergic receptors (α₂ARs) are G-protein-coupled receptors involved in catecholamine signaling by extracellular regulated protein kinase 1 and 2 (ERK1/2) pathways. We examined placental expression and function of α₂AR subtypes in women with severe preeclampsia (sPE) with and without intrauterine growth restriction (IUGR). Placental biopsies were analyzed from 52 women with i) sPE (n = 8); ii) sPE + IUGR (n = 9); iii) idiopathic IUGR (n = 8); iv) idiopathic preterm birth (n = 16); and v) healthy term controls (n = 11). Expression of α₂AR subtypes (α_2A, α_2B, α_2C) and phospho-ERK1/2 (receptor activation marker) was investigated by immunohistochemistry and/or quantitative real-time RT-PCR. The effects of α_2CAR knockdown on syncytialization (syncytin-1 and -2) and β-human chorionic gonadotropin secretion were examined in BeWo cells stimulated with forskolin. The effects of α₂AR agonist UK 14,304 and specific α_2CAR antagonist were tested, using a trophoblast migration assay. All three α₂ARs were expressed and functionally active in human placenta with site-specific localization. Highest α_2BAR and α_2CAR mRNA expression was identified in sPE + IUGR. α_2CAR knockdown increased expression of syncytin-1 and -2 but decreased secretion of β-human chorionic gonadotropin. UK 14,304 impaired trophoblast migration. The observed α₂AR expression pattern suggests different function for each subtype. α_2CAR modulates trophoblast syncytialization and migration and may carry pathogenic role in sPE + IUGR.

Need for Systematic Efforts to Modify Health-Related Behaviors After Acute Myocardial Infarction in Korea

BACKGROUND

Modification of health-related behaviors may improve clinical outcomes after acute myocardial infarction (AMI), but the need for systematic efforts to modify such behaviors and the estimated effect have not been investigated, especially in Asian populations. The aim of the study was to investigate changes in smoking and physical activity after AMI and their associations with death and recurrent revascularization. Methods and Results: Using the Korean National Insurance Health Service database, we included 13,452 patients with AMI in 2011, who were stable until 1.5 years on average after onset. Patients were grouped according to their smoking status and physical activity before and after AMI. After AMI, 44.6% of smokers continued smoking and only 11.0% of inactive patients increased their physical activity to a sufficient level. The 'smoker/smoker' group and 'non-smoker/smoker' group showed higher mortality (hazard ratio (HR): 1.566, 95% confidence interval (CI): 1.192-2.035; HR: 1.785, 95% CI: 1.061-2.815, respectively). On the other hand, the 'active/active' group and 'inactive/active' group showed less mortality (HR: 0.625, 95% CI: 0.460-0.832; HR: 0.681, 95% CI: 0.438-1.009, respectively) and the 'inactive/active' group showed less recurrent revascularization (HR: 0.761, 95% CI: 0.599-0.952).

CONCLUSIONS

Smoking cessation and maintaining sufficient physical activity after AMI remain challenging for many Korean patients, and are associated with higher rates of mortality and recurrent revascularization. Systematic nationwide efforts such as cardiac rehabilitation (CR) to change health-related behaviors after AMI are required in Korea.

Sexual dimorphism in heart rate recovery from peak exercise

PURPOSE

There is lack of consensus on whether sex, per se, affects heart rate recovery (HRR). To discriminate between the role of sex and that of cardiovascular fitness on HRR, we compared two groups of male and female participants matched for age and peak oxygen uptake (VO_2peak) percentile.

METHODS

Forty healthy individuals with above-average cardiovascular fitness (VO_2peak >50th percentile), aged 18-27 years (23 men; 17 women), performed maximal cycle-ergometer tests with cardiorespiratory measurements. HRR was obtained at 1 and 2 min of passive recovery. Multiple linear regression analysis was used to determine whether the relationship between VO_2peak and HRR differed between sexes.

RESULTS

Men attained greater peak values for VO₂ and work rate (p < 0.05). Both groups of participants exhibited similar heart rate response to peak exercise and no sex differences were observed in VO_2peak percentile or ventilatory threshold. HRR at 1 and 2 min of passive recovery was similar between sexes. In multiple linear models, VO_2peak explained 11.2% of the variance in HRR_1min both in men and women (p < 0.05). Most importantly, sex, VO_2peak, and their interaction were all significant predictors of HRR_2min (explained variance 29.2%) (p < 0.05).

CONCLUSIONS

This study shows that, for a given VO_2peak percentile (>50th percentile), there is no sexual dimorphism in HRR obtained at 1 or 2 min of recovery. It also demonstrates that, in persons with similar VO_2peak values, HRR obtained at 2 min of peak exercise cessation is affected by sex.

Age-related effects of dexmedetomidine on myocardial contraction and coronary circulation in isolated guinea pig hearts

Dexmedetomidine is a selective α2 adrenergic agonist. Although dexmedetomidine is widely used for sedation and analgesia, it frequently produces hypotension and bradycardia. The present study aimed to evaluate the effects of dexmedetomidine on cardiac function and coronary circulation using Langendorff-perfused guinea pig hearts. Coronary perfusion pressure (CPP) and left ventricular pressure (LVP) were continuously monitored, and electric field stimulation (EFS) was applied to stimulate sympathetic nerve terminals. Dexmedetomidine almost completely inhibited the EFS-induced increase in LVP at all ages. The effect of dexmedetomidine on coronary artery resistance varied according to postnatal age, i.e., dexmedetomidine had little effect on CPP in young hearts (<4 weeks) but increased CPP by 10 mmHg at 4-8 weeks and by 15 mmHg at >8 weeks. The increase in CPP in adult hearts was inhibited by imiloxan, an α2B antagonist, and prazosin, an α1 antagonist. The results suggest that dexmedetomidine acts on α2 adrenergic receptors at sympathetic nerve terminals to suppress the release of norepinephrine. In addition, the findings suggest that dexmedetomidine directly affects α1 adrenoceptors and/or α2B adrenoceptors on coronary smooth muscles to increase CPP. The age-related changes in α adrenoceptor subtypes may be linked to the cardiodepressant effects of dexmedetomidine.