digitonin and Pituitary-Neoplasms

The selective immunosuppressants cyclosporin A (CsA) and tacrolimus (FK506) are used in the prevention of allogenic transplant rejection and in the therapy of chronic autoimmune inflammatory pathologies. Chronic treatment with CsA leads to secondary functional and trophic alterations of multiple organs and cell systems among which endocrine ones, through insofar uncharacterized mechanisms. With the recent use of FK506 there have been reports of an improved therapeutic efficacy and a reduction of side-effects, as compared to CsA. An intriguing hypothesis is that toxic damage could be due to a systemic CsA activation of arachidonic acid (AA) metabolism, through pathways as yet only partially characterized. The side-effects of both drugs have been poorly studied on cells from tissues other than blood or kidney. We have thus proceeded to study their action on AA release in corticotropic AtT-20/D16-16 cells. The results obtained are as follows: 1) during incubation times > or =12 h, basal AA release is increased by CsA, but not FK506; the acute effect (10 min) of melittin, a PLA2 activator, is significantly potentiated starting from a 30 min pretreatment with CsA but not FK506; manoalide, a PLA2 inhibitor, antagonizes the melittin potentiation of AA release by CsA whereas the inhibition of the melittin stimulus by glucocorticoids is antagonized both by CsA and FK506. 2) during longer (>2 d) incubation times, cell growth is inhibited by CsA but not FK506. These results indicate a role for CsA, not apparent for FK506, in the activation of PLA2 and in the inhibition of cell growth. They also suggest that CsA does not have a direct (i.e. not mediated by the immune system) therapeutic effect in inflammatory processes.

Topics: Animals; Arachidonic Acid; Cell Division; Cell Size; Cell Survival; Cyclosporine; Dexamethasone; Digitonin; Dose-Response Relationship, Drug; Enzyme Activation; Immunosuppressive Agents; Interleukin-1; Melitten; Mice; Phospholipases A; Phospholipases A2; Pituitary Neoplasms; Tacrolimus; Terpenes; Time Factors; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha; Vitamin E

The actions of thapsigargin (Tg), a plant sesquiterpene lactone, on Ca2+ homeostasis were investigated in digitonin-permeabilized GH4C1 rat pituitary cells. Tg (1 microM) caused a rapid and sustained increase in ambient Ca2+ concentration [( Ca2+]) and inhibited the rise in [Ca2+] induced by subsequent addition of TRH (100 nM), inositol 1,4,5-trisphosphate (IP3, 10 microM), or the nonhydrolyzable GTP analogue guanosine 5'-0-(3-thiotriphosphate) (GTP gamma S, 10 microM). However, neither IP3 nor GTP gamma S pretreatment, which themselves release sequestered Ca2+, prevented the Ca2+ accumulation induced by Tg. Pretreatment with heparin (100 micrograms/ml, 10 min), an IP3 receptor antagonist, did not affect Ca2+ accumulation induced by Tg, although it abolished the rise in [Ca2+] induced by IP3. The ability of Tg to increase [Ca2+] was dependent on added ATP. We conclude that, in GH4C1 cells, Tg acts, in part, on TRH-, IP3- and GTP gamma S-sensitive Ca2+ pools; however, Tg also acts on an ATP-dependent pool of intracellular Ca2+ which is not sensitive to TRH, IP3 or GTP gamma S, indicating a complexity of intracellular Ca2+ pools not previously appreciated in these cells.

Topics: Adenosine Triphosphate; Animals; Calcium; Calcium Channels; Cell Line; Cell Membrane Permeability; Digitonin; Guanosine 5'-O-(3-Thiotriphosphate); Heparin; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Kinetics; Pituitary Neoplasms; Rats; Receptors, Cell Surface; Receptors, Cytoplasmic and Nuclear; Terpenes; Thapsigargin; Thyrotropin-Releasing Hormone