Correlation between the rhythms of blood insulin levels and the stimulation of spleen lymphocytes by concanavalin-A in mice.

An ultradian rhythm of DNA synthesis and an in-vitro response to Concanavalin-A (Con-A) stimulation has been found in splenocytes of DBA/2 male mice, living under conditions standardized for light-synchronized periodicity. It was characterized by two peaks during the nycthemeral cycle. One of them was very sharp. In spite of a constant mode of synchronization of the animals, there were seasonal variations of the rhythm. Such variations did not, however, affect the position of the sharp peak, which occurred always at the same hour. The rhythm of incorporation of [3H]-thymidine by splenocytes, whether or not stimulated by Con-A, seemed correlated with that of blood insulin levels in mice. The possible effect of the physiological increase in blood insulin during the circadian cycle has been confirmed experimentally. Thus it seems probable that insulin would be one of the internal synchronizers .