Abstract
The present work tested the hypothesis that short-term (S-T) dietary deficiency of magnesium (Mg) (21 days) in rats would: 1) result in reduction in serum(s) sphingomyelin (SM) and changes in several blood lipids, HDL-cholesterol (HDL-C) and phosphatidylcholine (PC) concomitant with elevations in s cholesterol (chol), s LDL+VLDL and trigycerides (TG), as well as reduction in the PC/cholesterol ratio; 2) lead to oxidative stress, characterized by reductions in glutathione (glut) content in the various chambers of the heart and activation of e-NOS and n-NOS in the atria, ventricles and aortic smooth muscle (ASM); 3) produce early cardiac damage characterized by leakage of creatine kinase (CK) and lactic dehydrogenase (LDH); and 4) demonstrate that these pathophysiological changes are a result of profound reductions in s ionized Mg (Mg
2+
) and activation of the SM-ceramide pathway. In addition, we hypothesized that: 1) exposure of primary cultured vascular smooth muscle cells (VSMCs) to low extracellular Mg
2+
would lead to de novo synthesis of ceramide and activation of NO synthase with reduction in glut, both of which would be attenuated by inhibition of sphingomyelinase (SMase) and serine palmitoyl CoA transferase (SPT); and 2) low levels of Mg
2+
added to the drinking water would either prevent or ameliorate these manifestations. Our data indicate that S-T Mg deficiency resulted in reductions in s Mg
2+
, SM, PC, HDL-C and the PC/chol ratio concomitant with decreases in tissue levels of glut, leakage of cardiac CK and LDH, as well as activation of e-NOS and n-NOS in all chambers of the heart and ASM. The greater the reduction in s Mg
2+
, the greater the effects on all parameters analyzed; very significant correlations to levels of s SM and Mg
2+
were found with all of the serum and tissue biochemical -molecular analytes measured. Our experiments also showed that VSMCs exposed to low Mg
2+
resulted in activation of NO synthase, loss of glut and de novo synthesis of ceramide which were attenuated by inhibitors of SMase and SPT. Low levels of drinking water Mg
2+
(e.g., 15 ppm) were cardio- and vascular protective. We believe these new findings support our concept of an important role for the SM-ceramide pathway in the manifestations of Mg deficiency and atherogenesis.