The pressor response to central administration of β‐endorphin results from a centrally mediated increase in noradrenaline release and adrenaline secretion

Abstract

The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) administration of β‐endorphin (0.01, 0.1 and 1.0 nmol kg−1) were examined in conscious rabbits. After i.c.v. β‐endorphin, mean arterial pressure (MAP) increased, heart rate (HR) fell, plasma noradrenaline, adrenaline and glucose increased and there was a rise in Paco2 and fall in Pao2; these effects were reversed by intravenous (i.v.) naloxone (300 nmol kg−1). A combination of prazosin (2 mg kg−1) and yohimbine (1 mg kg−1), given i.v., prevented the rise in MAP induced by i.c.v. β‐endorphin. After i.c. β‐endorphin, MAP, HR and plasma catecholamines were not significantly altered but there was a similar degree of respiratory depression. Clonidine (1.0 μg kg−1, i.c.) reduced MAP and HR; these effects were not blocked by i.v. naloxone (6 μmol kg−1). These results demonstrate that β‐endorphin acts centrally, probably mainly on periventricular μ‐opioid receptors, to increase adrenaline secretion and sympathetic nerve activity leading to α‐adrenoceptor‐mediated vasoconstriction. The respiratory depression is probably mediated by brainstem μ‐receptors. A role for β‐endorphin in the central hypotensive action of α2‐adrenoceptor agonists was opposed by finding that opioid receptor antagonism with naloxone did not block the effects of clonidine.

Cardiovascular complications and related risk factors underlying opium consumption

“…Data on the effect of acute administration of morphine on blood pressure are incongruous. Injection of morphine to rabbits intravenously was observed to trigger the periventricular MOR, leading to increased sympathoadrenal activity, and, therefore, stimulate hypertension (May, Dashwood, Whitehead, & Mathias, ; May, Ham, Heslop, Stone, & Mathias, ; May, Whitehead, & Mathias, ). In line with this finding, administration of agonists for opioid receptor in humans like nalbuphin, fentanyl, or morphine can significantly elevate the serum levels of catecholamine (Hoehe & Duka, ).…”

Achieving Detumescence of Ischemic Priapism with Intra-Cavernosal Injection of entanyl: An Unexpected Outcome of Miscommunication Error

“…Nevertheless, the hemodynamic effects of opioids differ significantly. However, injection of a selective μ-opioid receptor agonist into the hypothalamus of conscious rats was found to decrease the MAP [13]. On the other hand, fentanyl and its potent analog sufentanil do not release histamine, but have probably more effect on vagal tone.…”