Orthostatic intolerance (01) is a common disorder associated with orthostatic symptoms. There is often high circulating catecholamines and exaggerated heart rate increase on standing. Involvement of the sympathetic nervous system in OI is ill-defined, with no studies of adrenoreceptor (AR) function in the presence of Ol patients with high catecholamine levels. Objective: To assess cardiovascular AR sensitivity in OI with normal or high catecholamine levels. Methods: We studied 12 patients and 10 controls . Non-invasive beat-to-beat BP and HR were measured at baseline and after boluses of saline and graded doses of isoproterenol (ISO), phenylephrine (PHE), tyramine (TYR), propranolol (Prop), and atropine (Atrp). Results: We established a dose-response curve to estimate the drug dose which caused an increase in SBP by 25 mm Hg (PHE+25 and TYR+25), a decrease in SBP by 25 mm Hg (NTP.25 and ISO.25) or an increase in HR by 25 bpm (ISO-25). The results are presented in the following jable. Drug ISO,2J ISO.2S PHE. TYR,25 NTP. Prop-HR Atrp-HR Dose in: ug Hg ug mg Hg/fcg 0.2mg/kg 2 mg AR β1-AR β2-AR α1-AR α-AR none β-AR M-(Ach) OI 0.5 ±.06 1 051.1 115 ±10 2.9 ±.35 1.05 ±.05 -17 ±2 bpm 41 ±4 bpm Control .95±.12 85±.1 225 ±15 2 ±2 1 2 .2 -11 ±2 bpm 39 ±4 bpm P value -006 ns -002 -0055 ns 015 ns Copcliicion: Patients with OI have an increased cardiac sensitivity to β1-AR and vascular sensitivity to α1-AR agonists. Furthermore, they have resistance to the NE-releasing effect of tyramine despite an increase in α-AR sensitivity. These findings are suggestive of partial autonomie denervation of the cardiovascular system.
|Journal||Journal of Investigative Medicine|
|Publication status||Published - 1996|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)