AGE-RELATED AND GENDER-RELATED CHANGES IN ENDOTHELIN AND CATECHOLAMINE RELEASE, AND IN AUTONOMIC BALANCE IN RESPONSE TO HEAD-UP TILT

1. There is an increase in circulating levels of vasoconstrictive horm ones and an alternation in baroreceptor responsiveness with aging. The role of changes in endothelium-dependent and -independent vasoconstri ctive hormones in relation to age and gender, with simultaneous assess ment of autonomic balance in response to head-up tilt, has been incomp letely studied. 2. Sixteen young [25 +/- 3 years (mean +/- SEM)] and 1 6 older normal volunteers (68 +/- 7 years) underwent a 30 min head-up tilt test at 60 degrees. Haemodynamics were measured every 5 min and b lood samples for neurohormone measurement were drawn at baseline, 5, 1 0, 15 and 30 min into the test. Heart rate variability was analysed in 5 mill segments at the baseline, and during the test. The younger sub jects exhibited a greater increase in heart rate and diastolic blood p ressure, despite lower absolute levels of noradrenaline (norepinephrin e) and endothelin-1. Analysis of heart rate variability yielded a decr ease in both high-and low-frequency bands in the aged; power at low-fr equency decreased only in the young subjects. The age-related differen ces in blood pressure and noradrenaline levels were markedly attenuate d in the female subjects. In addition, endothelin-1 levels and power s pectral measurements at low frequency were the lowest in younger femal es throughout the tilt. 3. Despite attenuated cardiovascular response to tilt, both systemic adrenergic 'drive' and endothelin-1 levels incr ease in parallel with aging. Thus, endothelium-dependent and -independ ent vasoconstrictive hormone levels increase with age in the resting s tate and in response to neurohumoral stimulation in humans.