Oral Levodopa Stimulates Copeptin Secretion in Children and Adolescents with Intact Posterior Pituitary Function

Copeptin stimulation tests can be used in the differential diagnosis of polyuria-polydipsia syndrome. Current stimulation methods rely on intravenous or subcutaneous administration. Oral stimulus can further simplify the diagnostic approach. The levodopa stimulation test is widely used in the evaluation of growth hormone deficiency, and the dopamine pathway was reported to be associated with arginine vasopressin secretion. This study aims to investigate the effect of oral levodopa on copeptin secretion.

This study was a prospective observational single-center cohort study. Patients <18 years old with short stature and no symptoms of polyuria or polydipsia undergoing the levodopa stimulation test for suspected growth hormone deficiency were recruited from May 2023 to Nov 2023. Copeptin and growth hormone were measured at 0, 30, 60, 90, and 120 min during the levodopa test. The insulin tolerance test with copeptin and growth hormone measured at the same time points was conducted in part of patients.

Forty-four participants were included in the final analysis. In the levodopa stimulation test, the median (interquartile range) copeptin concentration increased from 5.20 (3.51, 8.25) pmol/L to a maximum of 19.36 (8.97, 108.08) pmol/L (P < .001), 3.94 (1.41, 13.88) times that of the baseline (P < .001). Compared with the insulin tolerance test, peak copeptin in the levodopa test was significantly higher (34.61 [13.67, 98.96] vs 8.88 [7.14, 15.42] pmol/L, P = .009). Higher copeptin was associated with a larger dose of levodopa.

Oral levodopa could be used to stimulate copeptin.