The biological activities, particularly the inhibitory action on the lipolysis, of the purified porcine proinsulin (manufactured by Eli Lilly Co.) were studied on the epididymal adipose tissue of a rat in a in vitro experiment with reference to the release of glycerol. The results obtained were as follows.
1) Proinsulin inhibited the lypolytic action of norepinephrine and glucagon.
2) Proinsulin inhibited also the action of theophylline which accelerated lypolysis by inhibiting the phosphodiesterase activity.
3) The inhibitory action on lypolysis of proinsulin was always weaker than that of insulin and, based on the molar concentration, about 100 times as much of proinsulin was necessary in order to obtain the same effect as insulin.
