Comparison of efficacy of cysteamine in depleting prolactin immunoreactivity in different hyperprolactinemic animal models

We have examined the effects of cysteamine on its ability to deplete prolactin in various states of hyperprolactinemia. Administration of subtoxic doses of cysteamine (75 and 150 mg/kg,sc) dramatically reduces serum prolactin levels as well as pituitary prolactin content in a dose-dependent manner in estrogen-primed brown Irish ACI female rats. A similar dose-dependent decrease in anterior pituitary prolactin levels was observed in two ectopic prolactin secreting pituitary tumor models (MtTW15 and 7315a). However, a significant reduction in serum prolactin levels was seen in these same tumor bearing animals at only the 150 mg/kg dose of cysteamine. Interestingly, the prolactin content of each of the prolactin secreting tumors, although reduced by cysteamine administration, the effect was neither dose-dependent nor as dramatic as that observed in the anterior pituitary gland proper. These data demonstrate that cysteamine can significantly lower prolactin concentrations in hyperprolactinemia. Further, ectopic prolactin secreting pituitary tissue appears less sensitive to the prolactin-depleting effects of cysteamine. This latter finding may explain, in part, why serum prolactin levels were not as severely reduced in the ectopic tumor bearing female rats as in estrogen-induced hyperprolactinemic animals.