Cardiovascular and metabolic responses to two receptor-selective opioid agonists in pregnant sheep

Objective: Our purpose was to assess the effects of an intravenous dose of a highly selective μ-(DALDA) and δ-(DPDPE) opioid peptide to determine which class of peptide has the best clinical potential. Study design: Chronically instrumented pregnant ewes recieved a 0.3 mg/kg intravenous bolus of each peptide with and without opioid receptor blockade by means of a randomized prospective design. Results: Intravenous DALDA produced only mild hypertension and a loss of heart rate variability, whereas DPDPE produced respiratory depression, maternal hypertension, and a fall in heart rate in both mother and fetus. Uterine blood flow, oxygen uptake, and glucose uptake were unchanged with both drugs. The effects of DALDA but not DPDPE were reversed by opioid receptor blockade. Conclusion: The δ-selective agonist had multiple nonopioid adverse effects, whereas the μ-selective agonist was well tolerated by the pregnant ewe, suggesting that μ-selective agonists have better potential for clinical use as an analgesic in pregnancy