adenosine-3--5--cyclic-phosphorothioate and Pheochromocytoma

Adrenomedullin is a potent vasorelaxant/hypotensive peptide recently isolated from human pheochromocytoma. We demonstrate here a novel role of this peptide as an apoptosis survival factor for rat endothelial cells. When rendered quiescent by serum deprivation, a fraction of endothelial cell cultures showed morphological and biochemical features characteristic of apoptosis. Adrenomedullin significantly suppressed apoptosis without inducing cell proliferation. Rat endothelial cells that contained high affinity binding sites for adrenomedullin expressed adrenomedullin gene and released the peptide into culture media. Addition of preimmune rabbit serum prevented apoptosis, whereas rabbit antiadrenomedullin antiserum partially, but significantly, abrogated the protective effect of the preimmune serum, suggesting its autocrine/paracrine role. Although adrenomedullin induced intracellular cAMP formation, other cAMP-elevating agonists, such as prostaglandin I2 and forskolin, did not affect apoptosis. Furthermore, adenosine 3',5'-cyclicmonophosphothioate Rp-isomer, a cAMP antagonist, did not block the cell survival effect of adrenomedullin. Adrenomedullin neither increased intracellular Ca2+ concentrations nor inositol-1,4,5-trisphosphate levels in rat endothelial cells. These results demonstrate that adrenomedullin suppresses serum deprivation-induced apoptosis of rat endothelial cells via cAMP-independent mechanism.

Topics: Adrenal Gland Neoplasms; Adrenomedullin; Animals; Aorta; Apoptosis; Cell Division; Cell Survival; Cells, Cultured; Colforsin; Cyclic AMP; DNA; Endothelium, Vascular; Epoprostenol; Humans; Immune Sera; Kinetics; Male; Membrane Proteins; Peptides; Pheochromocytoma; Rabbits; Rats; Rats, Wistar; Receptors, Adrenomedullin; Receptors, Peptide; Thionucleotides; Vasodilator Agents

Our purpose was to determine the role of protein kinases in the mediation of the stimulatory effects of lead on catecholamine secretion. Pheochromocytoma cells were incubated for 90 minutes with W-7 (calmodulin antagonist), calphostin C (protein kinase C inhibitor), Sp-cAMPS (cAMP agonist), Rp-cAMPS (cAMP antagonist), forskolin (activator of adenylyl cyclase), or lead nitrate. Catecholamines were measured by liquid chromatography. Lead had a stimulatory effect on catecholamine secretion, whereas W-7 was inhibitory. In the presence of both lead and W-7, the response was markedly decreased compared to that seen with lead alone. Calphostin C suppressed the secretion of catecholamines; however, in the presence of lead and calphostin C, the secretion was similar to that seen with lead alone. Compared to control, Sp-cAMPS was stimulatory. Co-incubation of Sp-cAMPS and lead had a slight synergistic effect. Rp-cAMPS decreased catecholamine secretion, but co-incubation of Rp-cAMPS and lead resulted in a slight reduction compared to lead alone. Forskolin markedly increased the secretion of catecholamines, and co-incubation of lead and forskolin resulted in a synergistic increase. In the absence of calcium, lead had no effect. We conclude that lead stimulates catecholamine secretion by acting through the calcium/calmodulin-dependent protein kinase II system and not through the protein kinase C or protein kinase A system, and requires the presence of calcium for its action.

Topics: Adenylyl Cyclases; Animals; Calmodulin; Catecholamines; Colforsin; Cyclic AMP; Enzyme Activation; Enzyme Inhibitors; Lead; Models, Biological; Naphthalenes; Nitrates; Pheochromocytoma; Protein Kinase C; Rats; Sulfonamides; Thionucleotides; Tumor Cells, Cultured

The fate of cyclic AMP (cAMP), dibutyryl-cAMP (Bt2-cAMP), and the (Sp)-isomer of adenosine 3',5'-monophosphorothioate [(Sp)-cAMPS] was studied in the PC12 culture medium by means of HPLC. In the absence of PC12 cells, cAMP and Bt2-cAMP were rapidly degraded by nonspecific esterases and cyclic nucleotide phosphodiesterase both originating from the serum commonly used as a culture medium ingredient, whereas (Sp)-cAMPS was completely stable. Since 5'-AMP, adenosine, inosine, and hypoxanthine appeared in the culture medium after incubation with cAMP or Bt2-cAMP, we have determined their effect on nerve growth factor (NGF)-induced neurite outgrowth. 5'-AMP, adenosine, and inosine were indeed potent agents in producing a potentiating effect on NGF-induced early neurite outgrowth at a concentration of 1 mM. Thus, cAMP metabolites had the capacity to induce an effect that has been described as cAMP-specific. In serum-free culture medium and in the presence of cells, all cyclic nucleotides were taken up by PC12 cells. Uptake was highly correlated with the hydrophobic nature of the compounds, and was accompanied by a simultaneous excretion of metabolites. On incubation with cAMP, NGF had a pronounced effect on the metabolic pattern found in the culture medium. In particular, dephosphorylation of 5'-AMP was specifically enhanced. This effect of NGF on the degradation of cAMP was also apparent when cAMP metabolites were incubated with PC12 cells. Whereas 5'-AMP degradation was greatly increased, NGF had no effect on the metabolism of the other purine compounds.

Topics: Adrenal Gland Neoplasms; Animals; Axons; Blood; Bucladesine; Cell Line; Culture Media; Cyclic AMP; Kinetics; Nerve Growth Factors; Neurons; Pheochromocytoma; Rats; Thionucleotides