Endocrine Abstracts

Introduction: Copeptin can be used as a tool to directly assess serum antidiuretic hormone (ADH) level. A certain pool of ADH are synthesized in hypothalamus, together with corticoliberin (CRH). Then they are released into the pituitary portal circulation, where through the V1bR receptor ADH stimulates adrenocorticotropic cells and ACTH secretion, followed by cortisol and catecholamines production. The stimulus for ADH secretion is, among others, stress. In turn, presynaptic stimulation of the α 2 receptor inhibits the secretion of noradrenaline. On the other hand, stimulation of the alpha2-receptor is widely used in the diagnosis of growth hormone deficiency (GHD) in children. Clonidine, by stimulation of the presynaptic alpha2-adrenergic receptor, in addition to inhibiting the release of noradrenaline, stimulates the secretion of somatoliberin (GHRH) from the hypothalamus, which in turn stimulates the synthesis of GH. Because other possible ADH effects on the pituitary have not been recognized so far, we decided to evaluate the effect of stimulating alpha2-adrenergic receptors after clonidine administration on copeptin, as well as to assess the differences in response to the above mentioned stimulation in groups of children with normal and decreased GH secretion (ISS and GHD groups).

Material and Methods: The serum concentrations of copeptin, GH, cortisol and ACTH at individual time points (0’, 30’, 60’, 90’ and 120’) during the 2-h stimulation test for GH secretion after oral clonidine administration at a dose of 0.15 mg/m² were assessed. The test was carried out for diagnostic purposes in 49 children (mean age± s.d.: 9.55 ± 3.48 yrs) with short stature (height < − 2.0 s.d.). In 29 children ISS and in 20 GHD were diagnosed.

Results: We did not find any differences between copeptin concentration in groups of GHD and ISS children. In both groups (GHD and ISS children), a significant reduction in copeptin secretion after clonidine administration was observed: mean pg/ml ± s.e.m.: 0’–460.5 ± 103.7; 30’–369.0 ± 74.4; 60’–353.1 ± 75.7; 90’–339.0 ± 63.1; 120’–376.1 ± 73.0. ACTH and cortisol levels also decreased with consecutive withdrawals during the stimulation test for GH secretion.

Conclusions: Short-term adrenergic stimulation of alpha2-receptors (after oral clonidine administration) seems to influence (reduce) copeptin secretion in children with short stature in both the ISS and GHD groups.