There is increasing evidence that hormones play an important role in the control of endothelial cell function and growth by regulating the production of vascular endothelial growth factor (VEGF). VEGF regulates vascular permeability and represents the most powerful growth factor for endothelial cells. In the normal anterior pituitary, VEGF has been detected only in folliculostellate (FS) cells. In the present study, the regulation of the release of VEGF from FS-like mouse TtT/GF cells, and from FS cells of rat pituitary monolayer cell cultures was investigated using a specific VEGF ELISA. Basal release of VEGF was demonstrated in cultures of both TtT/GF cells and rat pituitary cells. Interestingly, the VEGF secretion was stimulated by both forms of pituitary adenylate cyclase-activating polypeptide (PACAP-38 and PACAP-27), indicating that this hypothalamic peptide regulates endothelial cell function and growth within the pituitary. VEGF secretion was also stimulated by interleukin-6 (IL-6) whereas basal, IL-6- and PACAP-stimulated secretion was inhibited by the synthetic glucocorticoid dexamethasone. The inhibitory action of dexamethasone was reversed by the glucocorticoid receptor antagonist RU486, suggesting that in FS cells functional glucocorticoid receptors mediate the inhibitory action of glucocorticoids on the VEGF secretion. The endocrine and auto-/paracrine control of VEGF production in pituitary FS cells by PACAP, IL-6 and glucocorticoids may play an important role both in angiogenesis and vascular permeability regulation within the pituitary under physiological and pathophysiological conditions.

Two of the most potent cytokines regulating anterior pituitary cell function are leukemia inhibitory factor (LIF) and interleukin (IL)-6, which belong to the cytokine family using the common gp130 signal transducer. Recently, the expression and action of two other members of this family, IL-11 and ciliary neurotrophic factor (CNTF), on different cell lines has also been demonstrated. We studied the expression of the specific receptor subunits for CNTF in mammotropic, non-functioning and somatotropic tumors and the action of CNTF and IL-11 in the regulation of hormone secretion in these and normal pituitary cells. The mRNA for the alpha chain specific for the CNTF receptor was detected by Northern blot in tumors secreting prolactin (PRL) and GH and in non-functioning tumors. We found that both IL-11 and CNTF exerted a similar stimulatory effect on GH mRNA expression in somatotropic monolayer cell cultures from acromegalic tumors, but these cytokines had no significant influence on GH secretion. CNTF stimulates prolactin secretion in lactotropic monolayer cell cultures from patients with prolactinoma. In monolayer cell cultures from normal rat anterior pituitary, IL-11 and CNTF had no significant effect on the release of either GH or PRL, or on GH mRNA. However, when the cells were cultured in aggregate cultures, in which the three-dimensional structure of the cells is reconstituted, both cytokines, in doses at which they had no effect on monolayer cultures, significantly stimulated both PRL and GH secretion. These data show that IL-11 and CNTF may act as regulatory factors in anterior pituitary cells, in which the three-dimensional structure of the gland is of critical importance.