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

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 days (baseline), followed by a 35-day course of prednisolone (2.35-2.75 mg/kg PO q24h) and then abrupt discontinuation of prednisolone. Serial pAVP and sCoP concentrations, urine specific gravity (USG) and calculated plasma osmolality (pOsm_calculated) were determined during placebo and prednisolone administration, and up to 4 weeks after prednisolone discontinuation. Paired plasma samples for pAVP measurement were obtained in EDTA tubes with (pAVP_P800) and without (pAVP_EDTA) a proprietary combination of protease, esterase, and dipeptidyl peptidase-IV inhibitors (BD Biosciences P800).

Results

Mean pAVP_P800 and sCoP concentrations were significantly lower at the end of the prednisolone course (25.8 ± 8.1 pg/mL and 166 pg/mL, range, 131-223) vs baseline (34.1 ± 5.4 pg/mL and 243 pg/mL, range, 157-336; P = .02, P = .02, respectively). Correlations between pAVP_P800 and sCoP (r = .77, P = .001) and pAVP_P800 and USG (r = .61, P = .02) were positive, despite no correlation between pAVP_P800 and pOsm_calculated, sCoP and pOsm_calculated, and sCoP and USG. On paired samples, mean pAVP_EDTA was significantly lower (5.0 ± 2.5 pg/mL) than mean pAVP_P800 (34.1 ± 5.4 pg/mL; P < .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.