Cardioprotection by kappa-opioid receptor agonist U50488H is mediated by opioidergic regulation but not by calcium current modulation

Kappa Opioid Agonist-Induced Diuresis: Characteristics, Mechanisms, and Beyond

Activation of the kappa opioid receptor (KOR) induces antinociception, anti-pruritic activity, diuresis, sedation, and dysphoria. KOR agonist-induced diuresis is characterized as water diuresis, in which water excretion with urine is increased without altering electrolyte excretion. Both centrally and peripherally acting KOR agonists promote diuresis. KOR antagonists block KOR agonist-evoked diuresis suggesting that the diuretic effect is through activation of the KOR. Studies in different experimental animal species and in humans indicate that KOR agonists decrease antidiuretic hormone (ADH) secretion and release from the hypothalamus and posterior pituitary; decrease response to ADH in kidneys; increase renal sympathetic nerve activity; and increase adrenaline, noradrenaline, and dopamine release from the adrenal medulla. The therapeutic potentials of KOR agonists as water diuretics have been studied in animal models of cerebral edema due to ischemia and intracranial mass, hypertension, and cirrhosis. This chapter reviews characteristics, possible mechanisms, as well as therapeutic potentials of KOR agonist-induced diuresis.

Detection and distribution of opioid peptide receptors in porcine myocardial tissue

There is growing evidence that opioid peptide receptors (OPRs) play an important role in cardiovascular function. Many studies have been conducted in swine, in view of their anatomic and physiologic similarities to humans. Until now, the presence and particularly distribution of OPRs has been unclear. Porcine myocardial tissue was obtained from both the left and right atria and ventricles. Expression of mRNA for μ-, δ- and κ-OPR was determined by reverse transcription PCR. OPR proteins were detected by Western blot, distribution and cellular location were identified using immunohistochemistry. Homogenous expression of mRNA and protein for δ- and κ-OPRs were demonstrated in all porcine myocardial tissue tested, whereas expression of μ-OPR mRNA was not demonstrated in any of the tissues tested. This study demonstrates the expression of δ- and κ-OPRs in porcine myocardial tissue. No differences in distribution of δ- and κ-OPRs were found between the four heart cavities. Modulation of cardiac function by δ- and κ-OPR agonists or antagonists is therefore possible, while μ-OPR-mediated direct cardiac effects appear unlikely, due to nonexpression of the receptor. This study demonstrates that porcine studies can further elucidate the role of OPRs in cardiac (patho-)physiology.