Prolactin-stimulated growth of cell cultures established from malignant Nb rat lymphomas

A malignant Nb rat lymphoma which in vivo is stimulated by estrogens has been established in suspension culture. The cultured cells grew readily in Fischer's medium supplemented with fetal calf serum (10%) and 2-mercaptoethanol (10(-4) M). If horse serum was substituted for fetal calf serum, population growth ceased; i.e., cultures became "stationary." Such stationary cultures could be induced to resume active growth by the addition of a pituitary hormone, prolactin (ovine, rat); concentrations as low as 10 pg/ml had a detectable effect. In contrast, other pituitary hormones or estrogens had little or no effect. The evidence in this and an accompanying paper suggests that prolactin (or related substances) has a role in the growth of some cancers of lymphoid origin in rats.