Chronic l-arginine treatment reduces vascular smooth muscle cell hypertrophy through cell cycle modifications in spontaneously hypertensive rats.

OBJECTIVE: To investigate the effect of long-term l-arginine supplementation on phenotype and proliferative status of vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) as well as the possible changes in nitric oxide (NO) availability.
METHODS: Male SHR, 22 weeks of age, received l-arginine (660 mg/kg per day) in their drinking water for 12 weeks. VSMCs from untreated (C-VSMC) and l-arginine-treated (l-Arg-VSMC) SHR were isolated from the common carotid artery, cultured and used until passage five. Size, protein content, cell proliferation and ploidy were evaluated in carotid VSMCs in culture, as well as the possible association of NO in these changes.
RESULTS: Relative cell size, total protein content per cell, and number of polyploid cells were significantly lower in l-Arg-VSMC compared to C-VSMC. Fetal calf serum stimulation (10% FCS) increased cell number only in l-Arg-VSMC. DNA synthesis, assessed by [H]methylthymidine incorporation after 10% FCS stimulation, was higher in l-Arg-VSMC than in C-VSMC. Cell cycle analysis revealed a significant increase of the number of l-Arg-VSMC at the G1 phase, together with a reduction at the G2 + M phase. In contrast, C-VSMC were arrested at the G2 + M phase of the cell cycle. Nitrite/nitrate levels, as well as intracellular cyclic guanosine monophosphate (cGMP) content, were significantly higher in l-Arg-VSMC. This was accompanied by enhanced inducible nitric oxide synthase (iNOS) expression and activity and a decreased constitutive nitric oxide synthase (cNOS) activity in these cells.
CONCLUSIONS: The results suggest that chronic treatment with l-arginine induces changes in VSMC size, ploidy and cell cycle. These changes are accompanied by iNOS induction and stimulation of the NO-cGMP pathway.