Vasomotor responses of rat coronary arteries to isoflurane and halothane depend on preexposure tone and vessel size.
BACKGROUND
The authors previously reported that in rabbits, isoflurane exhibited a heterogeneous vasomotor effect, constricting small resistance coronary arteries and dilating larger conductance arteries. The novelty of isoflurane-induced constriction of small coronary arteries raised the question of whether the finding depended on the unique experimental setup or species used. The purpose of this study was to address these questions. Therefore, a second species was studied, namely rats, as well as a second volatile anesthetic, halothane. In addition, the dependence of the vasomotor effect on the preexisting tone of the vessels was examined.


METHODS
Thirty-six large coronary arteries (262 +/- 23 microns) and 42 small coronary arteries (99 +/- 15 microns) from 31 Wistar rats were isolated. Each vessel was placed in a microvessel chamber and was (1) submaximally preconstricted with the thromboxane analog U46619; (2) submaximally predilated with sodium nitroprusside; or (3) neither preconstricted nor predilated. The vessel was then subjected to increasing concentrations of either isoflurane or halothane, 0-3%. Changes in inner diameter were monitored and recorded with optical density video detection system.


RESULTS
Isoflurane constricted predilated or untreated small coronary arteries, but had no effect on preconstricted small arteries. Isoflurane dilated large coronary arteries, with the preconstricted vessels dilating the most. In contrast, halothane dilated both the small and large coronary arteries to a similar extent. Preconstricted vessels dilated more to halothane than vessels with no added tone.


CONCLUSIONS
Whereas isoflurane has a heterogeneous vasomotor effect in rat coronary arteries, constricting the small vessels and dilating the large ones, halothane dilates both the small and large arteries. The vasoconstriction effect was most evident in vessels with no added tone, whereas the vasodilatory effect was most significant in preconstricted vessels.
Department of Anesthesia and Critical Care, Beth Israel Hospital, Boston, Massachusetts, USA.
K W
KW
Park
H B
HB
Dai
E
E
Lowenstein
F W
FW
Sellke
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000818:Animals; D003331:Coronary Vessels / Q000187:drug effects*; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D011450:Prostaglandin Endoperoxides, Synthetic / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013928:Thromboxane A2 / Q000031:analogs & derivatives / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*; D014666:Vasomotor System / Q000187:drug effects
D011450:Prostaglandin Endoperoxides, Synthetic; D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D009599:Nitroprusside; D013928:Thromboxane A2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D007530:Isoflurane; D006221:Halothane