title: Decreased sensitivity to alpha-adrenergic stimulation in hypothyroid patients.
abstract: Nine hypothyroid patients had blood pressure and pulse rate responses to the alpha-adrenergic agonist phenylephrine measured before [T4 index, 45.045 +/- 9.009 nmol/L (mean +/- SEM); TSH, 57.1 +/- 23.6 mU/L] and after 4 +/- 0.5 months of thyroid replacement therapy (T4 index, 141.570 +/- 29.601 nmol/L; TSH, 2.6 +/- 1.0 mU/L). Hypothyroid patients had a smaller blood pressure increment and heart rate decrement at both 66.7 and 100 micrograms/min infusion rates of phenylephrine. Furthermore, the slope of the dose-response curves for systolic (2.06 +/- 0.22 vs. 1.32 +/- 0.19; P less than 0.01) and diastolic (1.04 +/- 0.18 vs. 0.62 +/- 0.08; P less than 0.01) blood pressures were significantly greater after thyroid replacement therapy. Pulse rate changes remained proportional to blood pressure changes in hypothyroid patients, so there was no change in baroreflex sensitivity. Plasma norepinephrine levels were higher before than after thyroid replacement (2.41 +/- 0.28 vs. 1.82 +/- 0.29 nmol/L, respectively; P less than 0.01). Thus, hypothyroid patients have diminished pressor sensitivity to an alpha-adrenergic agonist and increased plasma levels of the alpha-adrenergic neutrotransmitter norepinephrine.
authors.affiliation: Divisions of Cardiology, University of California Medical Center, San Diego 92103.
authors.forename: R
authors.initials: R
authors.lastname: Polikar
authors.forename: B
authors.initials: B
authors.lastname: Kennedy
authors.forename: M
authors.initials: M
authors.lastname: Ziegler
authors.forename: J
authors.initials: J
authors.lastname: Smith
authors.forename: P
authors.initials: P
authors.lastname: Nicod
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000097:blood; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007037:Hypothyroidism / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood; D010656:Phenylephrine / Q000494:pharmacology*; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000378:metabolism
chemical_list: D014284:Triiodothyronine; D010656:Phenylephrine; D013974:Thyroxine; D009638:Norepinephrine; D004837:Epinephrine