delta2 opioid receptor agonist facilitates mean arterial pressure recovery after hemorrhage in conscious rats.

delta opioid receptor agonists exert potent hemodynamic effects under ischemic conditions. This study was designed to assess the cardiovascular effects of Deltorphin-D(variant) (Delt-D(var)), a selective delta(2) opioid receptor agonist, in conscious, freely moving male rats during the posthemorrhage, recompensatory phase of a hemorrhagic trauma. Rats were fitted with femoral arterial and venous catheters for measurements of mean arterial pressure (MAP), heart rate (HR), and intravenous (i.v.) injections of isotonic saline, 1 mg/kg Delt-D(var), or 2 mg/kg Delt-D(var). During hemorrhaging, 30% (approximately 5 mL) of total blood volume was collected from the arterial catheter. MAP-HR was fitted to a logistic equation to determine baroreceptor reflex properties. Hemorrhaged rats progressed through three distinct phases: compensation, decompensation, and recompensation. Saline and 1 mg/kg Delt-D(var) rats treated posthemorrhage had similar MAP and HR after hemorrhage. In contrast, 2 mg/kg Delt-D(var) administered after hemorrhaging led to a faster and more complete recovery of MAP than compared with the other groups. In hemorrhaged rats, the average HR gain (bpm/mmHg) after 2 mg/kg Delt-D(var) treatment was greater and the BP(50) (BP at one-half the HR range) was significantly lower than after saline treatment. The results show that after hemorrhage, during the recompensatory period, stimulation of delta(2) opioid receptors leads to improved MAP, and this recovery may involve a change in baroreflex sensitivity.