The Effects of Weight Loss on Neuroadrenergic Function

Baker Heart Research Institute120 enrolled

Overview

Elevated subconscious nervous system activity is a characteristic of the obese state and contributes importantly to the risk of heart disease and diabetes. This project will compare sympathetic nervous system activity and function in a group of obese persons with differing levels of sugar tolerance (normal, impaired and type 2 diabetic). Inter-relationships with insulin action, blood pressure, heart and kidney function will be determined before and after a 4-month weight loss and 3-month weight loss maintenance program. It is hypothesized that the transition from normal sugar tolerance to impaired sugar tolerance to type 2 diabetes will be accompanied by escalating sympathetic nervous system dysfunction. Furthermore, that weight loss will favorably improve sympathetic function, with greatest benefits occurring in those subjects who are insulin resistant with high blood insulin concentration.

The twin epidemics of obesity and diabetes represent a major public health problem worldwide. There is a growing body of evidence to suggest that autonomic dysfunction, comprising elevated sympathetic nervous system (SNS) activity and blunted sympathetic neural responsiveness plays a role in both the pathogenesis and target organ complications of obesity and diabetes. The proposed project will undertake a detailed comparative analysis of neuroadrenergic function along the diabetes continuum, its inter-relationship with insulin sensitivity and secretion, and target organ function, and the benefits of active weight loss and weight loss maintenance within different strata of metabolic risk.

Study Type

INTERVENTIONAL

Allocation

NON_RANDOMIZED

Purpose

TREATMENT

Masking

NONE

Enrollment

120

Conditions

Eligibility

Sex: ALLMin age: 45 YearsMax age: 65 Years

Medical Language ↔ Plain English

Inclusion Criteria: Men and postmenopausal women (n=120), untreated, weight-stable, non-smoking, aged 45-65 years, BMI 27-45 kg/m2, will be recruited. Glucose tolerance status will be determined by a 75-g oral glucose tolerance test (OGTT), using WHO criteria (53): normal glucose tolerance, fasting plasma glucose \< 7.0 mmol/L and 2-h plasma glucose \< 7.8 mmol/L; IGT, fasting plasma glucose \< 7.0 mmol/L and 2-h plasma glucose \> 7.8 and \< 11.1 mmol/L; T2D, fasting plasma glucose \> 7.0 mmol/L or 2-h plasma glucose \> 11.1 mmol/L. Hyper-insulinemia will be defined as an insulin area under the curve during OGTT \> 8000 mU/L ∙ min-1 and hypo-insulinemia as \< 8000 mU/L ∙ min-1. Exclusion Criteria: Prior history of cardiovascular disease (previous myocardial infarction, angina, stroke, heart failure, secondary hypertension), renal (serum creatinine \>0.12 mmol/L or estimated GFR \<60 ml/min/1.73 m2) or hepatic disease or diseases which may affect measured parameters (e.g. thyroid disease); severe hypertension; a history of surgical weight loss; CPAP therapy; and \>4 alcoholic drinks/day. T2D individuals with moderate hyperglycemia (HbA1c \>9%) will be excluded so that hypoglycaemic pharmacotherapy may be instituted (54). Participants will be sought through newspaper advertising and poster displays in primary health care centres (General Practices). Newly diagnosed T2D subjects

Outcomes

Primary Outcomes

Change in whole-body norepinephrine kinetics

The study will examine the dynamic processes of norepinephrine spillover into and removal from the central plasma compartment using the isotope dilution technique.Measurements will be made at baseline, after 4 months active weight loss, and again after 3 months weight loss maintenance. The weight loss maintenance phase will permit differentiation of the effects of active weight loss (incorporating both negative energy balance and weight loss per se) and stable lower body weight on sympathetic neural parameters.

Time frame: 4 months and 7 months

Secondary Outcomes

Change in muscle sympathetic nerve activity

Muscle sympathetic nerve firing will be quantified by the technique of mirconeurography at baseline and after 4 months active weight loss and 3 months weight loss maintenance. The weight loss maintenance phase will permit differentiation of the effects of active weight loss (incorporating both negative energy balance and weight loss per se) and stable lower body weight on sympathetic nerve firing and pattern.