Corticosterone in drinking water: altered kinetics of a single oral dose of corticosterone and concentrations of plasma sodium, albumin, globulin, and total protein

Abstract

Effects of chronic exposure to corticosterone in drinking water on corticosterone kinetics, blood chemistry, and concentrations of catecholamines in parts of brain were studied in Long-Evans rats. Rats were randomly grouped into 3-2 treatments (n-4), with three treatments of drinking water (tap water, or 2.5% ethanol, or 400 mg/mL of corticosterone in 2.5% ethanol) for 28 days and two treatments of gavage with a single dose of either corn oil or corticosterone 20 mg/kg on day 28. Blood samples were collected at 0, 15, 30, 60, 120, 240, 480, and 720 min after dosing to determine plasma corticosterone concentrations. Blood samples were collected for clinical pathology on day 42. Hippocampus, cerebral cortex, caudate-putamen, and pons were examined to determine concentrations of catecholamines and activities of esterases. Concentrations of plasma corticosterone before gavage of the corticosterone-drinking rats (47.619 ± 1.13 ng/mL) were lower than the water (418.479 ± 1.13 ng/mL) or the ethanol rats (383.719 ± 1.13 ng/mL, P <0.0001). Plasma corticosterone rose to peak concentrations by 15 min after gavage in all three groups of drinking rats. Corticosterone- drinking rats had concentrations of plasma corticosterone that returned to basal levels slower than water- and ethanol-drinking rats. Plasma sodium and chloride concentrations were lower in the corticosterone-drinking rats than the water-drinking rats P <0.01). Plasma albumin, globulin, and total protein were highest in the corticosterone-drinking rats when compared to the other groups of drinking rats P <0.001, P <0.05, and P <0.001, respectively). Corticosterone in drinking water did not affect activities of brain neurotoxic esterase, carboxylesterase, acetylcholinesterase, or concentrations of monoamines and their metabolites. A single oral dose of corticosterone reduced neurotoxic esterase activity in the cerebral cortex P <0.05) and increased norepinephrine concentrations in the hippocampus P <0.05).