ELEVATED PLASMA ADRENOMEDULLIN LEVEL IN HYPERTHYROIDISM

Adrenomedullin is a recently discovered peptide that was first purifie d from phaeochromocytoma tissue and has marked vasodilatory activity, causing hypotension. In thyrotoxicosis, various haemodynamic changes a re observed, including an increase in cardiac output and heart rate wi th a concomitant decrease in peripheral vascular resistance. To evalua te the mechanism underlying these haemodynamic changes in thyrotoxicos is, we measured the plasma adrenomedullin concentration in thyrotoxic patients with Graves' disease. The plasma concentration of adrenomedul lin was elevated in hyperthyroid patients (14.7 +/- 5.7 pmol L(-1)) co mpared with euthyroid control subjects (5.6 +/- 1.3 pmol L(-1)) (P < 0 .001). The correlation between the plasma adrenomedullin concentration and serum free thyroid hormone levels was marginally significant. The mean blood pressure was relatively low in the face of an elevated pla sma adrenomedullin level. Adrenomedullin may therefore be responsible for the vasodilatation observed in thyrotoxicosis.