| Research Abstract |
Monocrotaline pyrrole (MCTP) is a metabolite of the pyrrolizidine alkaloid plant toxin monocrotaline, and is known to cause pulmonary hypertension in experimental animals. We have investigated the effects of MCTP on cellular functions in cultured calf pulmonary artery endothelial cells (CPAE). MCTP decreased the number of cells and induced cellular enlargement in a concentration dependent manner. Acetylcholine (ACh)-induced Ca^<2+> transient was observed both in control and MCTP-treated CPAE, but the amplitudes of the ACh-induced Ca Responses was significantly smaller in MCTP-treated cells. CPAE-layered, pulmonary artery smooth muscle cells-embedded collagen gel showed endothelium-derived relaxation to ACh, when control endothelium was used. However, ACh induced further gel contraction when MCTP-treated CPAE was layered. ATP and ACh-induced intracellular production of nitric oxide (NO), measured by diaminofluorescein-2, was significantly smaller in MCTP-treated cells than control. Expression of eNOS mRNA, examined with RT-PCR, was not affected in MCTP-treated cells. However, protein level of eNOS was markedly suppressed in MCTP-treated cells. Excess concentration of L-arginine (10 mM) restored endothelium-dependent relaxation of the gel. These results indicate that MCTP inhibits NO productivity in CPAE, mainly due to the inhibition of eNOS protein expression and Ca^<2+> mobilization, which would be overcome by excess amount of L-arginine.
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