Evaluation of the importance of the porta-renal system in parrots (Amazona aestiva)

Abstract

When injected in the thigh muscles of a bird, the local capillaries absorb the drug and the blood flow goes to the external iliac vein that has a porta-renal valve close to the kidney. Controlled by the autonomous nervous system, this valve can be opened or closed by the sympathetic or parasympathetic stimuli respectively. When opened, the blood flow goes to the renal vein then to the vena cava and reaches the systemic circulation. However, when the valve is closed, the blood flow goes to the renal parenchyma where it is mixed with the arterial blood. Thus, the kidney can excrete the drug that was given before it reaches the systemic circulation. The objective of this study was to evaluate the efficacy of ketamine when injected into the thigh or breast muscle of parrots (Amazona aestiva). Six birds were anesthetized with 30 mg/kg ketamine by intramuscular injection in the breast (G I, n =6) or thigh (G2, n =6), using the same parrots in both groups. The following parameters were evaluated: time from administration until recumbency, latency period, duration of anesthesia and recovery period. No significant statistical difference was found between the two groups, but two birds of the G2 group were excluded from statistical analysis because they did not show clinical signs of anesthesia. It was probably caused by a relative underdose; that is, part of the ketamine could have been eliminated by the porta-renal system before reaching the systemic circulation. It is suggested that the intramuscular administration of drugs in the thigh should be avoided when the drugs are excreted "in natura" by the kidneys.