Hypertensive state, independent of hypertrophy, exhibits an attenuated decrease in systolic function on cardiac kappa-opioid receptor stimulation

Opioids/opiates are commonly administered to alleviate pain, unload the heart, or decrease breathlessness in patients with advanced heart failure. As such, it is important to evaluate whether the myocardial opioidergic system is altered in cardiac disease. A hamster model of spontaneous hypertension was investigated before the development of hypertension (1 mo of age) and in the hypertensive state (10 mo of age) to evaluate the effect of prolonged hypertension on myocardial opioidergic activity. Plasma beta-endorphin was decreased before the development of hypertension and in the hypertensive state (P < 0.05). There was no change in cardiac beta-endorphin content at either time point. No differences were detected in cardiac or plasma dynorphin A, Met-enkephalin, or Leu-enkephalin, or in cardiac peptide expression of kappa- or delta-opioid receptors. mu-Opioid receptor was not detected in either model. To determine how hypertension affects myocardial opioid signaling, the ex vivo work-performing heart was used to assess the cardiac response to opioid administration in healthy hearts and those subjected to chronic hypertension. Agonists selective for the kappa- and delta-opioid receptors, but not mu-opioid receptors, induced a concentration-dependent decrease in cardiac function. The decrease in left ventricular systolic pressure on administration of the kappa-opioid receptor-selective agonist, U50488H, was attenuated in hearts from hamsters subjected to chronic, untreated hypertension (P < 0.05) compared with control. These results show that peripheral and myocardial opioid expression and signaling are altered in hypertension.