Functional membrane changes due to tumor induction in rat pituitary cell cultures

Membrane functions in tumorous cells are different from those in healthy cells. The aim of the present study was to investigate the changes in pituitary cell membrane functions and hormone secretion after tumor induction in vivo and in vitro. Prolactinomas were induced in vivo in female Wistar rats with estrone acetate. Normal anterior pituitaries and prolactinomas of female Wistar rats were dissociated enzymatically and mechanically, then cultured on collagen-treated plastic dishes. Some normal anterior pituitary cultures were treated with benz(c)acridines as tumorigenic agents in vitro. Intracellular 3',5'-cyclic-adenosine monophosphate (cAMP) levels were determined by a competitive binding technique, membrane fluidity was assayed by fluorescence anisotropy, and ATP-ase activities were estimated via ATP loss. The results indicated decreased membrane fluidity in tumorous cell cultures. However, in vitro benz(c)acridine treatment exerted more pronounced effects than those observed after in vivo estrone treatment. The ATP-ase activities were highly increased in benz(c)acridine-treated cells and in estrogen-induced prolactinoma cells, more strongly so in the former ones. The intracellular cAMP levels were higher than normal in both of them. The results concerning the ACTH, alpha-MSH, PRL and GH levels of normal and tumorous cell cultures were published in our previous study. Our findings show that the tumorous transformation of pituitary cells can cause significant changes in functional membrane parameters and hormone secretion. Decreased membrane fluidity was accompanied by an increased exocytosis (hormone release) and adenylate cyclase activity in tumorous cells.

Molecular forms of alpha-melanocyte-stimulating hormone in pheochromocytoma tissue

The molecular forms of alpha-melanocyte-stimulating hormone (MSH) in pheochromocytoma tissues have been characterized using reversed-phase HPLC and radioimmunoassay. Six alpha-MSH-related peptides were detected. Three of the six peaks had elution times identical to those of synthetic desacetyl-alpha-MSH, alpha-MSH and diacetyl-alpha-MSH. The remaining three forms of the alpha-MSH-like immunoreactivity suggest a different processing of pro-opiomelanocortin in this tissue than in the intermediate lobe of the pituitary gland. Current results confirm that alpha-MSH are present in human pheochromocytoma and suggest that alpha-MSH has role in the pathophysiology of this tissue.

Surface changes and hormone production in pituitary cells during tumorigenesis

Prolactinomas were induced by chronic estrone acetate treatment in female Wistar rats in vivo. After enzymatic dissociation of the tumor tissue, monolayer cell cultures were obtained. In vitro tumor induction was performed by treatment of normal monolayer anterior pituitary cell cultures with a 1:1 mixture of 7,9-dimethylbenz[c]acridine: 8-methylbenz[c]acridine. For immunohistochemistry, the cell cultures were stained by the peroxidase-antiperoxidase method for standardization; the nonspecific hormone release was induced with 30 mM K+. The prolactin, alpha-melanotropin, and adrenocorticotropin levels in the supernatant were measured by specific, sensitive radioimmunoassays. The results indicated surface differences between the in vivo induced prolactinoma cells and normal pituitary cells: the attachment of the prolactinoma cells required 15% collagen treatment, whereas normal cells required only 3-4% collagen. Tumor cells induced in vitro by methylbenz[c]acridine treatment were able to attach only after ammonia activation of the collagen surface. These findings strongly suggest that the mode of tumor induction can result in differences in membrane fluidity; this phenomenon is possibly connected with the levels of prolactin, adrenocorticotropin and alpha-melanotropin hormone production of these endocrine tumor cells.