Die Pufferkapazität von Blut und Verdauungssaft von Pieris brassicae und der Einfluss von Anoxie und Bacillus thuringiensis-Endotoxin auf die Permeabilität der Darmwand

Abstract

In larvae of Pieris brassicae (L.) the blood has pH 6·64 and a buffer capacity β = 0·026. Only minor changes in the blood pH occur at different developmental stages. The pH of both the crop and the midgut fluids are approximately 9·34, the buffer capacity of the crop fluid being higher ( β = 0·056) than that of the midgut fluid. Except between pH 6·7 and 7·5 the buffer capacity of the blood is higher than that of the gut fluid. When equal volumes of these two body fluids are mixed, a pH of about 7·6 is reached. But when the gut of a larva is injured with a needle so that the gut contents can freely leak into the blood, the pH rises only to about 7·17. It is therefore postulated that the volume of blood per larva is 2·5 to 3 times that of the gut fluid. Anoxia increases the permeability of the gut wall. This has been demonstrated by the leaking of red kale colour from the gut into the blood. It is suggested that the increased permeability of the gut wall during anaerobiosis may result from the accumulation of acid in the cells of the midget epithelium. As a result of the increased gut permeability the pH of the crop juice decreases rapidly, whereas the blood pH increases only very slightly. Nevertheless, symptoms of general paralysis with dorsal muscle contraction occur, caused by the leaking of a paralytic substance from the gut into the blood. When larvae are fed with sporulated Bacillus thuringiensis Berliner, the gut wall becomes even more permeable. This causes a sharp drop in the pH of the gut fluid to about 7·18, and a rise of the blood pH to about 7·14, i.e. approximately the pH value obtained when the gut has been injured so that blood and gut contents have completely mixed in a larva. Anoxia as well as intoxication and infection with sporulated B. thuringiensis lead to septicaemia, which in turn causes a general decrease of the pH values. Since acid metabolic products accumulate during anaerobiosis, the drop in pH is more pronounced during septicaemia caused by anoxia than after infection with B. thuringiensis, although the latter treatment causes heavier septicaemia.