Cardiac and Plasma Catecholamine Responses to Exercise in Patients with Type 2 Diabetes: Prognostic Implications for Cardiac-Cerebrovascular Events

Type 2 diabetes and reduced exercise tolerance: a review of the literature through an integrated physiology approach

The association between type 2 diabetes mellitus (T2DM) and heart failure (HF) is well established. Early in the course of the diabetic disease, some degree of impaired exercise capacity (a powerful marker of health status with prognostic value) can be frequently highlighted in otherwise asymptomatic T2DM subjects. However, the literature is quite heterogeneous, and the underlying pathophysiologic mechanisms are far from clear. Imaging-cardiopulmonary exercise testing (CPET) is a non-invasive, provocative test providing a multi-variable assessment of pulmonary, cardiovascular, muscular, and cellular oxidative systems during exercise, capable of offering unique integrated pathophysiological information. With this review we aimed at defying the cardiorespiratory alterations revealed through imaging-CPET that appear specific of T2DM subjects without overt cardiovascular or pulmonary disease. In synthesis, there is compelling evidence indicating a reduction of peak workload, peak oxygen assumption, oxygen pulse, as well as ventilatory efficiency. On the contrary, evidence remains inconclusive about reduced peripheral oxygen extraction, impaired heart rate adjustment, and lower anaerobic threshold, compared to non-diabetic subjects. Based on the multiparametric evaluation provided by imaging-CPET, a dissection and a hierarchy of the underlying mechanisms can be obtained. Here we propose four possible integrated pathophysiological mechanisms, namely myocardiogenic, myogenic, vasculogenic and neurogenic. While each hypothesis alone can potentially explain the majority of the CPET alterations observed, seemingly different combinations exist in any given subject. Finally, a discussion on the effects -and on the physiological mechanisms-of physical activity and exercise training on oxygen uptake in T2DM subjects is also offered. The understanding of the early alterations in the cardiopulmonary response that are specific of T2DM would allow the early identification of those at a higher risk of developing HF and possibly help to understand the pathophysiological link between T2DM and HF.

Difference of catecholamine responses to exercise in men with trisomy 21, with or without chronotropic incompetence

OBJECTIVE

Our purpose was to analyse if catecholamine responses to exercise would be different in Down syndrome (DS) with or without chronotropic incompetence.

RESEARCH DESIGN AND METHODS

Twenty five men with DS (mean age 22.2 ± 3.2) and twenty six controls (CONT, mean age 22.5 ± 1.4) participated in the study, and are divided into 3 groups: CONT, DS with chronotropic incompetence (DS+) and DS without chronotropic incompetence (DS-). During two treadmill incremental tests, blood samples were collected for the determination of hormonal and metabolic variables.

RESULTS

Ten out of 25 DS had chronotropic incompetence whereas no CONT. At rest, compared to CONT, despite similar physical activity, DS with chronotropic incompetence had significantly higher subcutaneous fat mass (p<0.001), lower epinephrine concentration (p<0.01), and higher leptin (p<0.01) and insulin concentrations (p<0.05). At peak exercise, all DS had lower heart rate, oxygen uptake and blood lactate concentrations than controls (p<0.001). During a 'Submaximal incremental test', DS with chronotropic incompetence had lower HR and lactate values (p<0.001) compared to CONT and DS without chronotropic incompetence (p<0.01). They also had blunted epinephrine and impaired norepinephrine responses to exercise compared to DS without chronotropic incompetence and CONT (p<0.01 and p<0.05 respectively).

CONCLUSIONS

Our results indicate that catecholamine adaptations to exercise are not adequate in DS+ and are associated with exercise intolerance. Thus, this endocrine profile at rest and during exercise may limit endurance performance of DS.

Sympathetic overdrive and cardiovascular risk in the metabolic syndrome

Sympathetic neural factors are involved in energy balance as well as in blood pressure control. This represents the background for the hypothesis that an adrenergic overdrive may be implicated in the development and/or progression of the metabolic syndrome. Indirect and direct markers of sympathetic drive have confirmed this hypothesis, by showing the occurrence of an adrenergic activation both at the cardiac and peripheral vascular level. It is likely that this sympathetic dysfunction is triggered by reflex mechanisms (arterial baroreceptor impairment), metabolic factors (insulin resistance), and humoral agents (angiotensin II, leptin). The adrenergic overdrive exerts a number of adverse effects on the cardiovascular system, by favoring the genesis of cardiac hypertrophy, vascular hypertrophy, arterial remodeling and endothelial dysfunction and thereby aggravating the already elevated cardiovascular risk profile of the patient. This carries obvious clinical and therapeutic implications, including the suggestion that sympathetic inhibition should be included among the goals of both pharmacological and non-pharmacological interventions employed in the treatment of the metabolic syndrome.

Protective role ofPanax ginseng extract standardized with ginsenoside Rg3 against acrylamide-induced neurotoxicity in rats

Acrylamide (ACR) is an industrial neurotoxic chemical that has been recently found in carbohydrate-rich foods cooked at high temperatures. ACR was designated as a probable human carcinogen by IARC (1994) and USEPA (1988). Panax ginseng extract has efficacies such as anticancer, antihypertension, antidiabetes and antinociception. The objective of the current study is to evaluate the protective effects of Panax ginseng extract against ACR-induced toxicity in rats. Sixty adult Sprague Dawley female rats were divided into six groups included a control group, a group treated orally with ACR (50 mg kg(-1) body weight; b.w.) for 11 days, a group treated orally with Panax ginseng extract (20 mg kg(-1) b.w.) for 11 days and groups treated orally with Panax ginseng for 11 days before, during or after 11 days of ACR treatment. The results indicated that treatment with ACR alone resulted in a significant increase in lipid peroxidation level and LDH activity in brain homogenate as well as in serum CK activity, whereas it caused a significant decrease in SOD activity and a small but statistically insignificant decrease in Na(+)K(+)-ATPase activity in brain homogenate. Serum serotonin, corticosterone, T3, T4, TSH, estradiol, progesterone and plasma adrenaline were significantly decreased in ACR-treated rats. Treatment with Panax ginseng before, during or after ACR treatment reduced or partially antagonized the effects induced by ACR towards the normal values of controls. It could be concluded that Panax ginseng extract exhibited a protective action against ACR toxicity and it is worth noting that treatment with Panax ginseng extract before or at the same time as ACR treatment was more effective than when administered after ACR treatment.

Benefit and risk of exercise on myocardial function in diabetes

Regular physical activity promotes cardiorespiratory fitness and has been considered a cornerstone for non-pharmacological treatment of more than 17 million Americans with diabetes mellitus. Physical exercise has been shown to positively affect certain cardiovascular risk factors such as insulin resistance, glucose metabolism, blood pressure and body fat composition, which are closely associated with diabetes and heart disease. With the increasingly sedentary life style in our society, routine daily exercise of moderate intensity is highly recommended to reduce cardiovascular risk, the leading cause of death in diabetic patients. Exercise produces many beneficial effects to the heart function such as reduced incidence of coronary heart disease, attenuated severity of diabetic cardiomyopathy, improved cardiac performance, cardiac reserve and autonomic regulation. Nevertheless, many diabetic patients do not appear to gain much benefit from exercise or may even be at risk of performing physical exercise. This review summarizes the benefit and risk of exercise on diabetic heart function, with a special emphasis on myocardial and autonomic function.

Exercise induces excessive normetanephrine responses in hypertensive diabetic patients

BACKGROUND

Exaggerated sympathoadrenal function has been accused of contributing to hypertension in type-2 diabetes. Recently, plasma unconjugated (free) metanephrines were reported to be stable markers of catecholamine hypersecretion. Thus, we aimed to examine whether unconjugated metanephrines are reliable markers of stress response induced by standardized cycling exercise and to identify differences in such stress responses between hypertensive and/or diabetic patients.

DESIGN

Type-2 diabetic patients with (DM/H; n= 8, 50 +/- 7 years, HbA1c: 7.7 +/- 0.6%) or without hypertension (DM/N; n = 6, 48 +/- 10 years, 7.5 +/- 1.8%) and nondiabetic hypertensive patients (H; n = 8, 56 +/- 4 years) were studied during incremental cycling exercise (15 min) to 75% of individual VO(2)max and during recovery (60 min). Plasma catecholamines and unconjugated metanephrines were measured by high-performance liquid chromatography with electrochemical detection. Hormone responses were quantified from the areas under the concentration-time curves and compared with those of age-, sex- and BMI-matched healthy volunteers (CON, n= 22).

RESULTS

Blood pressure responses of DM/H and H, but not DM/N, were greater than those of CON (P < 0.01), whereas heart rates increased similarly in all groups. Unconjugated normetanephrine responses were only increased (P = 0.04) in DM/H (2156 vs. 1133 pg mL(-1) min(-1) but not in DM/N (1528 vs. 1300 pg mL(-1) min(-1) and H (1960 vs. 1425 pg mL(-1) min(-1) when compared with respective CON. Unconjugated metanephrines did not change from baseline, whereas catecholamine responses were comparable in all groups.

CONCLUSIONS

The excessive response of plasma unconjugated normetanephrine to cycling may serve as a marker of exaggerated sympathoadrenal function in hypertensive type-2 diabetic patients.

Use of heart rate reserve and rating of perceived exertion to prescribe exercise intensity in diabetic autonomic neuropathy

OBJECTIVE

Individuals with diabetic autonomic neuropathy (DAN) exhibit an increased resting heart rate but depressed maximal heart rate. Thus, the purpose of this study was to examine the validity of using either percent of heart rate reserve (HRR) or a rating of perceived exertion (RPE) scale to prescribe exercise intensity in diabetic individuals both with and without DAN.

RESEARCH DESIGN AND METHODS

The subjects consisted of 23 individuals with type 2 diabetes, ages 45-75 years, with (DAN; n = 13) or without (No DAN; n = 10) clinical signs of DAN, as assessed by heart rate variability using the expiration-to-inspiration ratio of the R-R interval. Peak aerobic capacity was determined using a graded protocol on a cycle ergometer, with RPE, heart rate, and VO(2) values recorded at each stage.

RESULTS

The subjects were similar with the exception of depressed autonomic function in DAN subjects. Peak respiratory exchange ratio values were significantly higher (P < 0.05) in the DAN group (1.08 +/- 0.02 vs. 1.02 +/- 0.01 in No DAN subjects), although DAN subjects exhibited a significantly lower (P < 0.05) peak exercise heart rate. A similarly highly linear relationship between %HRR and percent VO(2) reserve (VO(2)R) existed for both groups (r = 0.98). A similar slightly weaker relationship (r = 0.94) was found between RPE and %VO(2)R.

CONCLUSIONS

In conclusion, in diabetic individuals, %HRR provides an accurate prediction of %VO(2)R and can be used to prescribe and monitor exercise intensity, regardless of the presence of DAN. The RPE scale is also a valid, albeit slightly less accurate, method to monitor exercise intensity in diabetic individuals.