ELEVATION OF CIRCULATING PROADRENOMEDULLIN-N TERMINAL 20-PEPTIDE IN THYROTOXICOSIS

BACKGROUND AND OBJECTIVE Adrenomedullin (AM) is a recently discovered peptide which has potent vasodilatory activity, We have found that the plasma adrenomedullin level is elevated in hyperthyroidism, suggestin g a potential role of AM in the decrease of vascular resistance in thy rotoxicosis, Proadrenomedullin, a precursor of adrenomedullin, yields another peptide termed proadrenomedullin-N terminal 20-peptide (PAMP). PAMP also has potent vasodilatory activity. Although the regulation o f secretion of AM and PAMP is not fully understood and the mechanism b y which the plasma AM level is elevated in hyperthyroidism remains unk nown, it is of interest to determine the plasma concentration of PAMP in thyrotoxicosis, DESIGN AND PATIENTS We measured the plasma concentr ation of immunoreactive AM and PAMP in newly recruited untreated thyro toxic Graves' patients using specific antibodies to each peptide, RESU LTS Not only AM, but also the plasma concentration of PAMP in thyrotox ic patients was significantly (P < 0.01) elevated (4.7 +/- 0.9 pmol/l) , compared to that in control subjects (2.6 +/- 0.8 pmol/l), The corre lation was marginally significant between the plasma AM concentration and serum free thyroid hormone levels. The plasma PAMP level tended to be more elevated when thyrotoxicosis was severe but the correlation w as not statistically significant. Correlation was not demonstrated bet ween the AM and PAMP levels in thyrotoxic patients. CONCLUSIONS Elevat ion of the plasma adrenomedullin and proadrenomedullin-N terminal 20-p eptide levels raises the possibility of involvement of these vasodilat ory peptides in the haemodynamic changes in thyrotoxicosis.