Evaluation of toxicity of catfish skin toxin using diffuse reflectance methods

Abstract

Fright induced epidermal secretions from Arabian Gulf catfish (Arius Mine&us, Valenciennes) are lethal when intravenously injected into rabbits at doses in excess of 2 mg of protein mixture per kg body weight [l]. Death is generally noted within 2 min. Sublethal, as well as lethal, doses induce major lesions in lung and liver tissues, as well as alterred levels of liver and plasma enzymes. The toxic responses of rabbits to intravenous injections of the epidermal secretions (skin toxins, ST) can be largely blocked by pretreatment of test animals with indomethacin or hydrocortisone [2]. This had led to a conclusion that the toxic responses result largely from epidermal substances stimulating phospholipase A2 activity in blood cells to yield arachidonic acid, which is metabolized to give toxic levels of prostaglandins [3]. Support for this conclusion was obtained by observations that an increase in prostaglandins was noted in plasma of injected animals [2], and that similarly prostaglandin release was noted following in vitro treatment of arterial tissue sections with the epidermal secretions [4]. Catfish epidermal secretions induced contraction of isolated smooth muscle tissues. The contraction was only partially blocked by indomethacin. This suggested that the secretions contain some neuroactive agents with acetylcholinelike muscarinic activation of cells, which could also play a r61e in toxic responses [4]. We have employed a novel diffuse reflectance spectroscopic method for monitoring responses to toxic substances. This method is capable of following some of the early events of toxicity which are induced by the epidermal secretion. The method demonstrated toxininduced constriction and subsequent dilation of blood vessels, changes in ratios of oxyto deoxyhaemoglobin and the formation of methaemoglobin. Blood flow rates were simultaneously monitored with a laser doppler (LD) flowmeter.