Changes in autonomic modulation to the heart and intracellular catecholamines. A longitudinal study in differentiated thyroid carcinoma during short-term hypothyroidism and thyroid hormone replacement.
BACKGROUND
The effects of thyroid deprivation on the autonomic modulation to the heart remain controversial.


METHODS
In this study in patients followed for thyroid carcinoma, we investigated (1) heart rate variability parameters and the baroreflex gain and (2) intracellular catecholamine levels in circulating lymphocytes during short-term hypothyroidism (phase 1) and after reinstitution of TSH-suppressive thyroid hormone replacement (phase 2).


RESULTS
The RR interval value (p < 0.01) and systolic blood pressure (p < 0.05) were higher in phase 1 than in phase 2. The low-frequency/high-frequency (LF/HF) ratio was significantly lower in the hypothyroid state (p < 0.05), with a higher HF component (p < 0.05). After adjusting for mean RR interval in the regression model, the difference between the power of RR interval oscillations calculated in the two states was greater for the LF band (p = 0.005) and it was borderline significant for the HF band (p = 0.052). The baroreflex gain alpha(LF) index was similar in the two phases. The stimulus-induced cellular production of norepinephrine and epinephrine in peripheral blood mononuclear cells was significantly higher in phase 2.


CONCLUSIONS
The neurally-mediated influences on the sinus node and the study of intracellular catecholamine production suggest a reduced sympathoexcitation in hypothyroidism compared with the treatment phase. The early increase in blood pressure observed after thyroid hormone withdrawal is not due to impaired sensitivity of the baroreflex arc.
Guasti
L
L
Department of Clinical Medicine, University of Insubria, Varese, Italy. luigina.guasti@uninsubria.it
Marino
F
F
Cosentino
M
M
Cimpanelli
M
M
Piantanida
E
E
Mainardi
L T
LT
Vanoli
P
P
De Palma
D
D
Bombelli
R
R
Ferrari
M
M
Crespi
C
C
Simoni
C
C
Klersy
C
C
Gaudio
G
G
Maroni
L
L
Grandi
A M
AM
Tanda
M
M
Bartalena
L
L
Cerutti
S
S
Lecchini
S
S
Venco
A
A
D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002291:Carcinoma, Papillary / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D002395:Catecholamines / Q000652:urine*; D002478:Cells, Cultured; D004298:Dopamine / Q000652:urine; D004837:Epinephrine / Q000652:urine; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy* / Q000503:physiopathology*; D008214:Lymphocytes / Q000166:cytology / Q000378:metabolism; D009638:Norepinephrine / Q000652:urine; D011877:Radionuclide Imaging; D012849:Sinoatrial Node / Q000187:drug effects / Q000502:physiology; D013963:Thyroid Hormones / Q000097:blood / Q000627:therapeutic use*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy / Q000601:surgery; D013965:Thyroidectomy; D051598:Whole Body Imaging
D002395:Catecholamines; D013963:Thyroid Hormones; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine