Growth enhancement of prolactin-sensitive mammary tumor by periaqueductal gray stimulation

The weight of prolactin-insensitive and prolactin-sensitive tumors implanted in female rats was measured upon their sacrifice. The group that received periaqueductal gray (PAG) stimulation subsequent to prolactin-sensitive tumor implantation had statistically higher incidence of enhanced tumor growth than non-PAG stimulated control group (P < .001). There was no statistically significant difference seen in the tumor growth in rats implanted with prolactin insensitive tumor, whether or not they had PAG stimulation. These results suggest that enhanced tumor growth with PAG stimulation may be related to prolactin release, previously reported to occur with β-endorphin and opiate administration.