Endocrine Abstracts

Background: Copeptin, the C-terminal part of the arginine vasopressin (AVP) precursor, is a 39-amino acid peptide stoichiometrically secreted with AVP in 1:1 ratio from the posterior pituitary. In contrast to AVP, copeptin remains stable ex vivo for several days in serum or plasma. Here, we investigated the use of the copeptin assay in the diagnostic workup of patients with suspected anterior pituitary dysfunction.

Patients and methods: We measured cortisol, GH, ACTH and copeptin during glucagon stimulation test (GST) in 56 subjects divided into healthy controls (Group 1, n=21), subjects with history of pituitary disease (usually pituitary adenomas), but without evidence of pituitary dysfunction (Group 2, n=22), and those with overt hypopituitarism (Group 3, n=13). Blood samples were taken at 0, 60, 90, 120, 150 and 180 min after i.m. injection of 1–1.5 mg of glucagon.

Results: There were no significant age or BMI differences between groups 1, 2 and 3. Copeptin concentrations at 150 and 180 minutes of GST (in comparison to initial values) were significantly higher in both Group 1 and Group 2 (P<0.01), but remained unchanged in Group 3 (P=NS). In contrast to cortisol, there was a trend towards higher copeptin concentrations in Group 1 vs Group 2 (31.25±12.01 vs 12.59±3.94 pmol/l (mean±S.E.M.), P=0.06 and 21.08±6.65 vs 12.59±3.94 pmol/l, P<0.05, P=0.055, at 150′ and 180′ of GST respectively). Differences between all subgroups became significant when comparisons were made for area under the curve for copeptin concentrations during multiple measurements. In Group 1 there was a correlation between serum copeptin concentrations and ACTH and cortisol (but not GH) at 150′ and 180′ of GST.

Conclusions: Our data demonstrate that copeptin is released following glucagon stimulation. This raises a possibility that measurements of serum copeptin concentrations might be potentially useful in assessment of anterior pituitary function.