Suppression of milk secretion (exocytosis) by concanavalin a in vitro

The observation that concanavalin A can inhibit milk secretion was evaluated in an in vitro system employing minced mammary gland or isolated alveoli from lactating rats. Release of milk constituents (casein, lactose and fat globules) into the medium in the presence and absence of concanavalin A was measured during 1 or 2 h incubations. The effect of concanavalin A on glucose uptake and CO2 production of the minced tissue was also studied. Concanavalin A suppressed release of milk components at a concentration as low as 80 micrograms/ml of medium. Respiration of minced mammary tissue in the presence of concanavalin A (100 micrograms/ml of medium) was essentially the same as that of the control. The data are evidence that concanavalin A acts directly on the mammary cell in suppressing milk secretion and that the effect is not due to cytotoxicity.