Acute effects of triiodothyronine on endothelial function in human subjects.
BACKGROUND
Thyroid hormone regulates several cardiovascular functions, and low T(3) levels are frequently associated with cardiovascular diseases. Whether T(3) exerts any acute and direct effect on endothelial function in humans is unknown.


OBJECTIVE
Our objective was to clarify whether acute changes in serum T3 concentration affect endothelial function.


METHODS
Ten healthy subjects (age, 24 +/- 1 yr) participated in a double-blind, placebo-controlled trial at a university hospital.


METHODS
T3 (or placebo) was infused for 7 h into the brachial artery to raise local T3 to levels observed in moderate hyperthyroidism. Vascular reactivity was tested by intraarterial infusion of vasoactive agents.


METHODS
We assessed changes in forearm blood flow (FBF) measured by plethysmography.


RESULTS
FBF response to the endothelium-dependent vasodilator acetylcholine was enhanced by T3 (P = 0.002 for the interaction between T3 and acetylcholine). The slopes of the dose-response curves were 0.41 +/- 0.06 and 0.23 +/- 0.04 ml/dl x min/microg in the T3 and placebo study, respectively (P = 0.03). T3 infusion had no effect on the FBF response to sodium nitroprusside. T3 potentiated the vasoconstrictor response to norepinephrine (P = 0.006 for the interaction). Also, the slopes of the dose-response curves were affected by T3 (1.95 +/- 0.77 and 3.83 +/- 0.35 ml/dl x min/mg in the placebo and T3 study, respectively; P < 0.05). The increase in basal FBF induced by T3 was inhibited by NG-monomethyl-L-arginine.


CONCLUSIONS
T3 exerts direct and acute effects on the resistance vessels by enhancing endothelial function and norepinephrine-induced vasoconstriction. The data may help clarify the vascular impact of the low T3 syndrome and point to potential therapeutic strategies.
Napoli
Raffaele
R
Department of Internal Medicine and Cardiovascular Sciences, Via Pansini, 80131 Napoli, Italy. napoli@unina.it
Guardasole
Vincenzo
V
Angelini
Valentina
V
Zarra
Emanuela
E
Terracciano
Daniela
D
D'Anna
Carolina
C
Matarazzo
Margherita
M
Oliviero
Ugo
U
Macchia
Vincenzo
V
Saccà
Luigi
L
D000328:Adult; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000502:physiology; D005260:Female; D005542:Forearm / Q000098:blood supply; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D014284:Triiodothyronine / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects
D014284:Triiodothyronine; D009638:Norepinephrine