Cooperative action of insulin and catecholamines on stimulation of ornithine decarboxylase activity in neonatal rat heart cells.

Stimulation of ornithine decarboxylase (ODC) activity was examined in cultured heart cells from neonatal rats. Fetal bovine serum had a concentration-dependent effect on ODC activity with maximum response obtained at 10% serum. ODC activity peaked 4 h after the addition of serum and returned to initial levels at 8 h. In the absence of serum, non-cytotoxic concentrations of the adrenergic agonists epinephrine, norepinephrine or isoproterenol did not stimulate ODC activity. Co-administration of serum and catecholamines at 10(-5) M induced an ODC response that was significantly greater than that induced by serum alone. A screen of various constituents of serum revealed that insulin, though relatively ineffective alone, acted cooperatively with catecholamines to produce an ODC response equivalent to that induced by 10% serum. Propranolol effectively blocked the cooperative effect of insulin on catecholamine stimulation of ODC activity, and markedly inhibited the stimulation of ODC by 10% serum. Insulin also acted cooperatively with the second-messenger analogue dibutyryl-cAMP. The calcium ionophore A23187 significantly increased ODC activity and this response was potentiated by the presence of insulin. The present findings are concordant with in vivo observations in that beta-adrenergic activation stimulates ODC activity in cultured heart cells, but it also demonstrates that the cooperative action of other factors present in serum, such as insulin, are required.

Comparative toxicity of allylamine and acrolein in cultured myocytes and fibroblasts from neonatal rat heart.

Allylamine is toxic to the cardiovascular system causing aortic, valvular and myocardial lesions. Acute toxicity is believed to involve metabolism of allylamine to highly reactive acrolein. Comparative toxicity of allylamine and acrolein was evaluated in cardiac fibroblasts and myocytes, which were obtained from neonatal rat hearts by a differential plating technique. Allylamine and acrolein were added directly to serum supplemented culture media (M199). Toxicity was assessed by measuring lactate dehydrogenase (LDH) release as an indicator of cell lysis. Spontaneous beating activity of myocytes, and adenosine 5' triphosphate (ATP) levels of myocytes and fibroblasts were also assessed. Cell lysis occurred 4 h after treatment of myocytes with 0.5 mM allylamine, whereas 20 mM allylamine was required to lyse fibroblasts. Acrolein, at a concentration of 0.05 mM, was equally toxic to fibroblasts and myocytes. Semicarbazide, a benzylamine oxidase inhibitor, protected myocytes from allylamine toxicity, but clorgyline, a monoamine oxidase inhibitor, was ineffective. Semicarbazide was ineffective against acrolein toxicity. Beating activity of myocytes was arrested by 0.05 mM acrolein and 0.5 mM allylamine, although 0.05-0.1 mM allylamine reduced beating activity. Myocyte ATP levels were reduced 4 h after exposure to 0.01 mM acrolein. Allylamine at 0.05 mM reduced ATP in myocytes, but 10 mM allylamine was required to reduce ATP in fibroblasts. ATP levels remained normal in myocytes exposed to 1 mM allylamine in the presence of 0.1 mM semicarbazide. The findings support the hypothesis that the toxicity of allylamine in cultured myocytes is dependent on its metabolism to acrolein, and that cytotoxicity may result from interference with energy production.