PLASMA-CATECHOLAMINES AFTER THYROTROPIN-RELEASING-HORMONE ADMINISTRATION IN HYPOTHYROID PATIENTS BEFORE AND DURING THERAPY

In order to investigate sympathoadrenal activity in hypothyroidism we studied the cardiovascular and catecholamine responses to thyrotropin- releasing hormone (TRH) infusion in nine hypothyroid patients before a nd during adequate therapy and in seven healthy subjects. We evaluated mean arterial pressure, heart rate, plasma epinephrine and norepineph rine levels after TRH administration (200 mu g iv) in the three groups . Mean arterial pressure, heart rate and plasma epinephrine levels wer e not different in the three groups and did not change after TRH admin istration. Hypothyroid subjects showed increased plasma norepinephrine levels (1.48 +/- 0.15 nmol/l), which were reduced after euthyroidism was reached (0.84 +/- 0.11 nmol/l) (p < 0.01). An exaggerated response of norepinephrine to TRH was observed in hypothyroid patients before therapy (incremental peak (IP) = 0.59 +/- 0.13 nmol/l) but not in hypo thyroid patients during therapy (IP = 0.19 +/- 0.02 nmol/l p < 0.02) o r in the control group (TP = 0.15 +/- 0.04 nmol/l; p < 0.05). This stu dy indicated that TRH administration is able to influence the sympathe tic activity during hypothyroidism in humans.