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

Membrane functions in tumorous cells are different from those in healthy ce lls. The aim of the present study was to investigate the changes in pituita ry cell membrane functions and hormone secretion after tumor induction in v ivo and in vitro. Prolactinomas were induced in vivo in female Wistar rats with estrone aceta te. Normal anterior pituitaries and prolactinomas of female Wistar rats wer e dissociated enzymatically and mechanically, then cultured on collagen-tre ated plastic dishes. Some normal anterior pituitary cultures were treated w ith benz(c)acridines as tumorigenic agents in vitro. Intracellular 3',5'-cy clic-adenosine monophosphate (cAMP) levels were determined by a competitive binding technique, membrane fluidity was assayed by fluorescence anisotrop y, 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 effec ts than those observed after in vivo estrone treatment. The ATP-ase activit ies were highly increased in benz(c)acridine-treated cells and in estrogen- induced prolactinoma cells, more strongly so in the former ones. The intrac ellular cAMP levels were higher than normal in both of them. The results co ncerning 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 c ause significant changes in functional membrane parameters and hormone secr etion. Decreased membrane fluidity was accompanied by an increased exocytos is (hormone release) and adenylate cyclase activity in tumorous cells.