Enhancement of endotoxin-induced vascular hyporeactivity to phenylephrine in the thoracic aortas of Mg-deficient rats ex vivo

Antihyperlipidemic and antihypertensive effect of a triterpenoid-rich extract from bamboo shavings and vasodilator effect of friedelin on phenylephrine-induced vasoconstriction in thoracic aortas of rats

Triterpenoids, which are widely distributed throughout the plant kingdom, were applied to the development of functional foods as physiological and pharmacological active agents. Some physiological activities of a triterpenoid-rich extract from bamboo shavings (EBS), i.e. antihyperlipidemic and antihypertensive effects, were systematically evaluated in the present study. The results demonstrated that EBS could reduce the serum total cholesterol (TC) and total triglyceride (TG) levels, which are the main factors directly leading to pathological changes in cardiovascular diseases, in hyperlipidemic rats (p < 0.05). Furthermore, EBS could significantly reduce the systolic pressure of spontaneously hypertensive rats (SHR) but its maximum effect time was less than 24 h. Meanwhile, EBS did not influence the heart rate of SHR. On the other hand, the vasodilator effects of friedelin, a main triterpenoid compound separated from EBS, on phenylephrine-induced vasoconstriction in the thoracic aortas of rats were also discussed. The results showed that friedelin probably served a function of vasodilator responses in the thoracic aortas of rats in accordance with the antihypertensive effect of EBS. The results also suggested that EBS might prevent some cardiovascular diseases by its impact on lipid metabolism.

In vitro application of endotoxin to thoracic aortas from magnesium-deficient rats enhances vascular hyporeactivity to phenylephrine

OBJECTIVE

Endotoxin-induced vascular hyporeactivity to phenylephrine (PE) is well described in rat aortas, but has not been investigated in those from magnesium (Mg)-deficient rats in vitro.

METHODS

Segments of thoracic aorta from control and Mg-deficient rats were incubated in culture medium for 6 hours in the presence or absence of bacterial lipopolysaccharide (LPS; 0.001-10 microg/mL). Contractions to PE were measured with or without an inducible nitric oxide synthase (iNOS) inhibitor (1400W; 0.1 and 1 microM), a guanylate cyclase inhibitor (ODQ; 0.1 and 1 microM), or a potassium channel inhibitor (TEA; 1 and 10 mM).

RESULTS

LPS induced hyporeactivity in a concentration-dependent manner under relatively low concentrations (0.001-0.1 microg/mL), however, there was no significant difference at 0.1, 1 and 10 microg/mL. LPS-induced hyporeactivity was not significantly affected by endothelium-denudation. The hyporeactivity was enhanced in thoracic aortas from Mg-deficient rats by LPS (0.01, 0.1 and 1 microg/mL). LPS (1 microg/mL) induced hyporeactivity was reversed with 1400W, ODQ or TEA in both aortas in a concentration-dependent manner, however the degree of reversal was weaker in the Mg-deficient rat aorta than in the control rat one. iNOS mRNA level was increased by LPS (0.1 microg/mL) and the increment was significantly high in Mg-deficient rat thoracic aorta.

CONCLUSIONS

From these results it is clearly demonstrated that LPS-induced vascular hyporeactivity to PE is enhanced in thoracic aorta from Mg-deficient rats, and it is suggested that LPS-induced NO production might contribute to the enhancement via stimulation of NO-cyclic GMP-potassium channel pathway.