DE GARDE, ELION ITOU ROMARIC, Animal Physiology Laboratory, Faculty of Science and Technology, Marien University Ngouabi, BP69, Brazzaville, Congo. National Institute for Health Sciences Research (Scientific City of Brazzaville (formerly ORSTOM), Route de l’Auberge de Gascogne (chateau d’eau), Congo. Laboratory of Biochemistry and Pharmacology, Faculty of Health Sciences, University Marien Ngouabi, BP 69, Brazzaville, Congo, Congo