Hypotensive response in rats and toxicological mechanisms induced by shuanghuanglian, an herbal extract mixture.

Shuanghuanglian (SHL), an extract mixture isolated from three medicinal herbs, has been used in China as an injection in traditional Chinese medicine to treat viral or bacterial infection. This study examined the hypotensive response in rats induced by SHL and its possible mechanisms. Mean arterial pressure (MAP) and electrocardiograms (ECGs) were studied after intravenous injection of histamine and SHL. Diphenhydramine, an H1 receptor antagonist, the compound 48/80, a promoter of histamine release, and cromolyn, a histamine release inhibitor, were also used to investigate the potential mechanisms of that response. In addition, the histamine level in plasma was measured after administration of SHL and compound 48/80. Both SHL and histamine led to a MAP reduction immediately but did not affect ECGs when initially administered in a similar manner, though this reduction was partially attenuated by diphenhydramine. Pretreatment blocked the rats' reaction to compound 48/80 but not to SHL. The plasma histamine level in rats was also elevated by SHL. SHL can induce severe hypotension through histamine release upon initial administration. In combination with the direct effects of its histaminelike substances on target tissue, SHL likely has the potential to cause an anaphylactoid reaction.