EVIDENCE FOR CIRCULATING VASOPRESSIN-LIKE PEPTIDES IN A CASE OF POLYURIA

Plasma immunoreactive vasopressin (iAVP) was studied by RIA in a patie nt suffering from polyuria during chronic treatment with lithium. The combined use of two antisera specific for different regions of the AVP molecule allowed us to detect circulating forms which are modified in the acyclic tripeptide portion.In this lithium-treated patient, iAVP was abnormally low with respect to plasma osmolality. However, MVP inc reased during hypertonic saline infusion, probably through an osmosens itive mechanism. A remarkable finding was that contrary to the observa tions made in healthy subjects and in another patient with diabetes in sipidus, iAVP measured with the antiserum specific for the acyclic por tion of the AVP molecule was below the values measured with the antise rum specific for the hexapeptide ring. This unusual immunoreactivity p rofile suggests that the plasma of this polyuric lithium-treated patie nt contains vasopressin-like peptides which differ from arginine vasop ressin in the structure of the C-terminal tripeptide tail.