Prolonged Dopamine Administration and Thyroid Hormone Economy in Normal and Critically 111 Subject*

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Abstract
A 48 h dopamine (DA) infusion (5-7.5 .mu.g/kg per min) given to 6 healthy euthyroid males resulted in a suppression of thyroidal iodine release and serum TSH [thyrotropin] by 44 .+-. 3% (P < 0.01), serum T3 [triiodothyronine] by 9 .+-. 2% (P < 0.01) and serum T4 [thyroxine] by 5 .+-. 1% (P < 0.05) below baseline levels, without a significant change in serum r reverse T3 levels. In critically ill patients receiving DA (2-21 .mu.g/kg per min) for treatment of shock, serum TSH values and T4 production rates were decreased 60 and 56%, respectively, below the respective levels observed in non-DA-treated patients (P < 0.01). Serial serum samples collected before and during DA therapy revealed a decrease of 52% in TSH (P < 0.005) and 30% in T4 (P < 0.05). The finding of a normal serum TSH value during DA therapy in a critically ill patient with primary hypothyroidism emphasized the inhibitory potential of DA on TSH secretion. The prolonged administration of pharmacological doses of DA significantly reduced serum TSH levels and thyroid hormone secretion in normal and critically ill patients, most likely by a direct inhibition of pituitary TSH with a secondary effect on thyroid gland secretion. DA therapy probably prolongs and aggravates the low T4 state in critical illness.

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