Activity and metabolic roles of the pentose phosphate cycle in several rattissues

Activity of the pentose-phosphate pathway in several rat tissues was invest igated, developing a new method that gives the activity of each phase (oxid ative and non-oxidative) as well as the whole pathway separately. Our resul ts demonstrate that this method is easy to carry out and that it has not th e problems of indirect determinations of the previous ones. The activities of the oxidative and non-oxidative phases assayed separately gives us new i nformation on the design of the pathway in the different tissues, from whic h several conclusions about the physiological role of this pathway can be d erived. In all cases the activity of the oxidative phase was much higher th an the non-oxidative one, and the global activity of the whole pathway was the same as the activity of the non-oxidative phase. The highest activity w as found in lactating mammary gland and adipose tissue. Lung and liver show ed to have a moderately high activity. Brain, kidney, skeletal muscle, and intestinal mucosa showed to have also a significant activity although less than other tissues. The switch in the mammary gland from the non-lactating state to the lactating one causes a very high increase of activity of 22 ti mes, remaining the same ratio between the activity of the two phases.