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Apelin levels high in patients with nephrogenic diabetes insipidus
An increased or decreased ratio of apelin to copeptin reflects a disturbed osmotic and body fluid homeostasis in patients with central or nephrogenic diabetes insipidus, study data show.
However, a normal water homeostasis is found with a normal ratio of plasma apelin to copeptin in primary polydipsia, the researchers wrote.
Sandrine Andrea Urwyler, MD, of the University Hospital in Switzerland, and colleagues evaluated 31 patients with polyuria-polydipsia syndrome and 113 healthy controls to evaluate plasma apelin levels and ratios of plasma apelin to copeptin using copeptin as a surrogate marker for arginine-vasopressin.
Among the polyuria-polydipsia syndrome group, 15 had complete central diabetes insipidus, seven had complete nephrogenic diabetes insipidus and 19 had primary polydipsia.
Compared with controls, patients with complete nephrogenic diabetes insipidus had higher apelin levels (P = .01), whereas those with complete central diabetes insipidus (P = .02) and those with primary polydipsia (P = .0001) had lower apelin levels.
Median copeptin levels were highest in patients with nephrogenic diabetes insipidus (56.7 pmol/L), followed by controls (4.1 pmol/L), patients with primary polydipsia (3.9 pmol/L) and those with complete central diabetes insipidus (1.9 pmol/L).
Patients with primary polydipsia and controls had a similar ratio of plasma apelin to copeptin. Compared with controls, the ratio of plasma apelin to copeptin was lower in patients with complete central diabetes insipidus (P = .02) and in those with complete nephrogenic diabetes insipidus (P < .001).
“We show that apelin levels are highest in patients with nephrogenic [diabetes insipidus] and lower in patients with [primary polydipsia] or complete central [diabetes insipidus] compared to healthy subjects,” the researchers wrote. “In contrast to healthy volunteers, where an inverse action of [arginine-vasopressin]/copeptin and apelin is known, this study shows that in patients with central and nephrogenic [diabetes insipidus] [arginine-vasopressin]/copeptin and apelin decrease or increase, respectively, in parallel with each other.” – by Amber Cox
Disclosure: The researchers report no relevant financial disclosures.