LEUKEMIA INHIBITORY FACTOR EXPRESSION IN CULTURED RAT ANTERIOR-PITUITARY IS REGULATED BY GLUCOCORTICOIDS

Leukaemia inhibitory factor (LIF) is the generally recognized nomenclature for a pleiotropic cytokine that exerts multiple biological effects in different systems. However, its role in the neuroendocrine system is relatively unexplored, with the exception of one report indicating that LIF may act to determine the unique vascular organization of the pituitary gland. In the present study the expression of LIF mRNA has been demonstrated for the first time in the pituitary gland of the rat, in all three pituitary lobes. However, LIF gene expression is restricted to tissues in explant culture where LIF transcripts are readily detectable by Northern Techniques. Similar studies using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique also failed to detect LIF transcripts in fresh tissue from adult animals, These results are consistent with the hypothesis that LIF acts to mediate the response to trauma, a response that may include the induction of neuropeptide expression in the anterior pituitary. In further studies it has also been shown that anterior pituitary LIF mRNA is super-induced in the presence of protein synthesis inhibitors, a response that indicates a role for a labile protein in the attentuation of LIF expression. Both the explantation response, and the response to protein synthesis inhibitory drugs are decreased in the presence of dexamethasone indicating that a glucocorticoid receptor mechanism acts as a general modulatory influence on LIF mRNA levels. These findings are consistent with the presence of multiple regulatory controls on the expression of LIF that serve to restrict its expression to pathological conditions, and indicate that LIF does not participate in normal endocrine physiology.