Clinical and experimental pharmacology & physiology
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Clin. Exp. Pharmacol. Physiol. · Jan 2003
Cardiovascular reflex responses after intrathecal omega-conotoxins or dexmedetomidine in the rabbit.
1. The effects of thoracic intrathecal doses (1 microg/kg) of the alpha2-adrenoceptor agonist dexmedetomidine and omega-conotoxins MVIIA and CVID on vasoconstrictor and heart rate responses to acute central hypovolaemia were studied in seven chronically instrumented rabbits. 2. Gradual inflation of an inferior vena cava cuff to reduce cardiac index (CI) by 8% per minute induced progressive vasoconstriction and an increase in heart rate (phase I). ⋯ Both conotoxins caused progressive failure of vasoconstriction rather than recovery during phase II (P < 0.001). 4. Intrathecal injections of these drugs to control chronic pain may compromise cardiovascular responses to changes in central blood volume. At the single doses studied, there were significant differences between the responses to simulated haemorrhage after MVIIA or dexmedetomidine compared with CVID, with the prolonged effect after MVIIA most likely to be of clinical significance.