Prostaglandin-related microvascular dilation in pentobarbital- and etomidate-anesthetized rats

Etomidate is characterized by minimal systemic cardiovascular effects, but its effect on the microvasculature has not been assessed. We compared the microvasculature of etomidate-anesthetized animals to that of animals anesthetized with pentobarbital, since its effects on the microvasculature are known. Male Sprague-Dawley rats were anesthetized with etomidate or pentobarbital. The cremaster muscle was prepared for microscopic viewing, leaving the neural and vascular supply intact. Small arterioles were near their maximal diameters in etomidate-anesthetized rats, whereas the pentobarbital group had a large dilator capacity (maximal diameter-basal diameter/basal diameter). The effect on resting arteriolar diameters of endothelium-derived relaxing factor (EDRF) and prostaglandin synthesis inhibitors was tested. Dilator capacity was not affected by the EDRF inhibitor nitro-L-arginine, but it was significantly increased by mefenamic acid and ibuprofen in etomidate-anesthetized animals. To test whether dilator and constrictor mechanisms were normal, serotonin concentration-response curves were obtained in pentobarbital and etomidate-anesthetized animals with and without mefenamate or ibuprofen present. The dilation of small arterioles to serotonin in the etomidate groups with mefenamate or ibuprofen was not significantly different from that of the pentobarbital groups. Serotonin produced a comparable constriction of large arterioles in both anesthetic groups. The topical application of etomidate to the cremaster muscle did not affect arteriolar diameters. Thus, etomidate appears to trigger the release of dilator prostaglandins in striated muscle through a central or indirect mechanism.