Orally administered prednisolone decreases plasma arginine vasopressin and serum copeptin concentrations in healthy dogs.

Abstract

BACKGROUND: The pathophysiology of polyuria and polydipsia secondary to exogenous glucocorticoid excess is incompletely understood. OBJECTIVE: Investigate plasma AVP (pAVP) and serum CoP (sCoP) concentrations in healthy dogs before, during, and after abrupt discontinuation of a long-term course of orally administered prednisolone. ANIMALS: Eight healthy neutered young adult research Beagles. METHODS: In our prospective longitudinal study, Beagles were treated with a placebo PO q24h for 15&#x2009;days (baseline), followed by a 35-day course of prednisolone (2.35-2.75&#x2009;mg/kg PO q24h) and then abrupt discontinuation of prednisolone. Serial pAVP and sCoP concentrations, urine specific gravity (USG) and calculated plasma osmolality (pOsm) were determined during placebo and prednisolone administration, and up to 4&#x2009;weeks after prednisolone discontinuation. Paired plasma samples for pAVP measurement were obtained in EDTA tubes with (pAVP) and without (pAVP) a proprietary combination of protease, esterase, and dipeptidyl peptidase-IV inhibitors (BD Biosciences P800). RESULTS: Mean pAVPand sCoP concentrations were significantly lower at the end of the prednisolone course (25.8&#x2009;&#xb1;&#x2009;8.1 pg/mL&#xa0;and 166&#x2009;pg/mL, range, 131-223) vs baseline (34.1&#x2009;&#xb1;&#x2009;5.4 pg/mL and 243&#x2009;pg/mL, range, 157-336; P&#x2009;=&#x2009;.02, P&#x2009;=&#x2009;.02, respectively). Correlations between pAVPand sCoP (r&#x2009;=&#x2009;.77, P&#x2009;=&#x2009;.001) and pAVPand USG (r&#x2009;=&#x2009;.61, P&#x2009;=&#x2009;.02) were positive, despite no correlation between pAVPand pOsm, sCoP and pOsm, and sCoP and USG. On paired samples, mean pAVPwas significantly lower (5.0&#x2009;&#xb1;&#x2009;2.5&#x2009;pg/mL) than mean pAVP(34.1&#x2009;&#xb1;&#x2009;5.4&#x2009;pg/mL; P&#x2009;<&#x2009;.0001). CONCLUSIONS AND CLINICAL IMPORTANCE: Orally administered prednisolone led to markedly decreased plasma AVP and serum CoP concentrations despite increased calculated plasma osmolality and stable systolic blood pressure.