Metabolism and residue differences of Enrofloxacin between the brain and peripheral tissues and the resulting brain damages in crucian carp (Carassius auratus var. Pengze)

Abstract

This study aimed to explore the metabolism and residue differences of Enrofloxacin (ENR) at two doses between the brain and peripheral tissues (liver, kidney, and muscle) along with the brain damages caused by ENR in crucian carp (Carassius auratus var. Pengze). The concentrations of ENR in tissues were determined using a validated high‐performance liquid chromatography (HPLC) analysis. Relying on the hematoxylin–eosin (HE) staining method, brain damages caused by the drug were evaluated by the section of pathological tissue. Metabolism and residue results showed that ENR could be detected in the brain throughout the experiment both at median lethal dose (LD50 at 96 h, 1949.84 mg/kg) and safe dose (SD, 194.98 mg/kg), as well as in the three peripheral tissues. The maximum residue at LD50 followed the decreasing order of liver >kidney > brain > muscle. Although the Cmax of ENR at SD in the brain was significantly lower than that in other peripheral tissues (p < .05), it still reached 41.91 μg/g. The T1/2 of ENR in brain tissue at the same dose was both shorter than that in peripheral tissues. At LD50, the amount of ENR residues in brain was lower than that in peripheral tissues on the whole, except that it had been higher than in the muscle for the first 3 h. At SD, the drug residue in brain tissue was lower than that in peripheral tissues from 12 h to 960 h, but it exceeded the muscle and kidney at 1 h and 6 h, respectively. At 960 h, the residual amount of ENR at SD in the brain was 0.09 μg/g, while it was up to 0.15 μg/g following the oral administration at LD50. Demonstrated by the HE staining, there were pathological lesions caused by ENR in the brain at LD50, which were characterized by sparse neural network and increased staining of glial cells. The present results indicated that metabolism and residue of ENR in crucian carp were affected by the tissue type and drug dosage, and the ENR could also bring about histopathological changes in the brain.