Opioid peptides and blood pressure regulation

Found Down Extremity Compartment Syndrome Secondary to Substance Use: An Observational Multicenter Study

With the worsening opioid epidemic in America, more patients are developing found down extremity compartment syndrome (FDECS). The purpose of this study was to describe this patient population, including their presenting symptoms, laboratory test results, and clinical outcomes.

Methods

We performed a 2-center retrospective review of adult patients who developed FDECS secondary to substance use from January 2006 to December 2019. Patients were managed operatively or nonoperatively at the surgeon's discretion. Data on patient demographic characteristics, laboratory values, hospital course, and clinical outcomes were collected from electronic medical records.

Results

In this study, 91 patients were included: 85 patients were managed operatively, and 6 patients were managed nonoperatively. Most patients were male, and the mean patient age (and standard deviation) was 37 ± 11 years. Opioids were the most common substance used. Patients managed operatively underwent a mean of 4 ± 3 surgical procedures, 44% received a skin graft, 25% developed a wound infection, and 11% underwent limb amputation. Patients managed nonoperatively did not undergo a subsequent fasciotomy or amputation. At a mean follow-up of 2.3 years, persistent weakness (66%), pain (78%), persistent sensory deficits (53%), and contractures (18%) were common.

Conclusions

Patients who develop FDECS secondary to substance use have high surgical complication rates and poor clinical outcomes. We found high rates of wound infection, revision surgical procedures, and amputation, often leaving young adults with lifelong disability.

Level of Evidence

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Blockade of central delta-opioid receptors inhibits salt appetite in sodium-depleted rats

Various studies have investigated the role of central opioid peptides in feeding behavior; however, only a few have addressed the participation of opioids in the control of salt appetite. The present study investigated the effect of intracerebroventricular injections of the δ-opioid antagonist, naltrindole (5, 10 and 20 nmol/rat) and the agonist, deltorphin II (2.5, 5, 10 and 20 nmol/rat) on salt intake. Two protocols for inducing salt intake were used: sodium-depletion and the central injection of angiotensin II. In addition, the effect of a central δ-opioid receptor blockade on locomotor activity, on palatable solution intake (0.1% saccharin) and on blood pressure was also studied. The blockade of central δ-opioid receptors inhibits salt intake in sodium-depleted rats, while the pharmacological stimulation of these receptors increases salt intake in sodium-replete animals. Furthermore, the blockade of central δ-opioid receptors inhibits salt intake induced by central angiotensinergic stimulation. These data suggest that during sodium-depletion activation of the δ-opioid receptors regulates salt appetite to correct the sodium imbalance and it is possible that an interaction between opioidergic and angiotensinergic brain system participates in this control. Under normonatremic conditions, δ-opioid receptors may be necessary to modulate sodium intake, a response that could be mediated by angiotensin II. The decrease in salt intake following central δ-opioid receptors blockade does not appear to be due to a general inhibition of locomotor activity, changes in palatability or in blood pressure.

Multiple opioid receptors mediate the hypotensive response induced by central 5-HT(3) receptor stimulation

The aim of the present work was to investigate the role of brain μ, κ and δ opioid receptors in the central serotonergic mechanisms regulating blood pressure in rats. The data obtained show that: (1) pharmacological activation of central 5-HT(3) receptors yields a significant decrease in blood pressure; (2) the blockade of those receptors by a selective antagonist induces an acute hypertensive response; (3) the pharmacological blockade of central opioid receptors by three different opioid antagonists exhibiting variable degrees of selectivity to μ, κ and δ opioid receptors always suppressed the hypotensive response induced by central 5-HT(3) receptor stimulation; (4) the blockade of opioid receptors by the same opioid antagonists that impaired the hypotensive effect of central 5-HT(3) receptor stimulation failed to modify blood pressure in animals not submitted to pharmacological manipulations of central 5-HT(3) receptor function. It is shown that a 5-HT(3) receptor-dependent mechanism seems to be part of the brain serotonergic system that contributes to cardiovascular regulation since the hypertensive response observed after ondansetron administration indicates that central 5-HT(3) receptors exert a tonic inhibitory drive on blood pressure. Furthermore, the data obtained here clearly indicate that the hypotensive response observed after pharmacological stimulation of central 5-HT(3) receptors depends on the functional integrity of brain μ, κ and δ opioid receptors, suggesting that a functional interaction between serotonergic and opiatergic pathways in the brain is part of the complex, multifactorial system that regulates blood pressure in the central nervous system.

mu- and delta-opioid receptor-mediated contractile effects on rat aortic vascular smooth muscle

The actions of opioid receptor agonists and antagonists were studied in isolated rat aortic strips. Morphine (10(-7)-10(-6) M) had no contractile effect on resting strips but when added during the relaxation of the contractions induced by 10(-9) M noradrenaline, it induced a contractile response which was blocked by naloxone. The selective mu-opioid receptor agonist, [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO, 10(-7)-10(-6) M), induced an increase in basal tension which remained after removal of endothelium or in Ca(2+)-free solution, but was inhibited by beta-flunaltrexamine. beta-Flunaltrexamine also inhibited the contractile response induced by DAMGO added during the relaxation of the contractions induced by noradrenaline. The delta-opioid receptor agonist, [D-Pen2,D-Pen5]enkephalin, had no effect on resting tension but potentiated the contractions induced by noradrenaline; these effects were abolished by naltrindol. The selective kappa-opioid receptor agonist, bremazocine, had no effect on resting tension and did not modify the amplitude of the contractions induced by noradrenaline. These results suggest that, at low concentrations, agonists of mu- and delta-opioid receptors may act as modulators of noradrenaline-induced responses, whereas at higher concentrations, mu-opioid receptor stimulation may have a direct contractile effect in isolated rat aorta.

Changes in nociception, arterial blood pressure and heart rate produced by intravenous morphine in the conscious rat

The present study shows that intravenous (i.v.) administration of morphine produces dose-dependent increases in tail flick and hot plate latencies in conscious rats. I.v. morphine also decreased heart rate, but had no significant effects on arterial blood pressure. Transection of the right vagus at the cervical level or pre-treatment with the peripherally acting opioid receptor antagonist naloxone methobromide attenuated the increased tail flick latency produced by either 1.75 or 2.5 mg/kg morphine. In addition, either right vagotomy or naloxone methobromide attenuated the increased hot plate latency produced by 1.75 mg/kg of morphine but not by 2.5 mg/kg of morphine. Following pre-treatment with naloxone methobromide, 1.75 and 2.5 mg/kg of morphine produced a small pressor response 1-3 min after injection. The bradycardia produced by 1.75 mg/kg of morphine was attenuated by naloxone methobromide, but not by right vagotomy. The bradycardia produced by 2.5 mg/kg of morphine was attenuated by either naloxone methobromide or vagotomy. These data obtained in the conscious rat are similar to previous reports using pentobarbital-anesthetized rats except for the following: (i) the dose-response function for inhibition of the tail flick was shifted to the right in conscious rats, (ii) the depressor response to morphine observed in anesthetized rats was attenuated in conscious rats, (iii) following naloxone methobromide, but not unilateral vagotomy, i.v. morphine produced a pressor response in the conscious rat, and (iv) unilateral vagotomy was not as effective in attenuating the antinociception and bradycardia in conscious rats as bilateral vagotomy is in pentobarbital-anesthetized rats.

Chronic kappa-opioid receptor antagonism delays the rise in blood pressure in spontaneously hypertensive rats

A 4-week subcutaneous treatment with the kappa-opioid receptor antagonists, MR 2266 or MR 1452, delayed the age-dependent increase in systolic blood pressure in young spontaneously hypertensive rats (SHR), but not in normotensive rats. The content of beta-endorphin, [Leu5]enkephalin, and catecholamines in various brain tissues was not affected by MR 2266. Specificity of the kappa-opioid receptor antagonism was tested in SHR by injection of the kappa-opioid agonist, MR 2033, and the mu agonist, morphiceptin, after 28 days of MR 1452 or saline and 2 days after the end of treatment. The increase in mean arterial blood pressure (MAP) after MR 2033 did not differ between the two groups at the 28th day of treatment but was higher 2 days later in the previous MR 1452 group, possibly indicating up-regulation of kappa-opioid receptors. Morphiceptin did not alter MAP during or after MR 1452. It is concluded that kappa-opioid receptors may have a tonic influence on the age-dependent increase of blood pressure in SHR but not in normotensive rats.

Influence of chronic opioid delta receptor antagonism on blood pressure development and tissue contents of catecholamines and endogenous opioids in spontaneously hypertensive rats

Opioid delta receptors seem to be involved in blood pressure regulation of spontaneously hypertensive rats (SHR), possibly by an interaction with the sympathetic nervous system. In the present study the effect of four weeks' chronic delta receptor antagonism with ICI 154 129 on development of blood pressure was evaluated in young SHR. Contents of adrenaline and noradrenaline and the opioid peptides beta-endorphin and leucine-enkephalin were measured in brain stem, mid brain, hypothalamus, and adrenal glands. After four weeks' treatment, systolic blood pressure was lower when compared with control SHR. During chronic delta antagonism, concentrations of adrenaline were higher in hypothalamus, mid brain and adrenal glands, contents of noradrenaline were higher in hypothalamus and adrenal glands than in control rats, contents of opioid peptides were not altered with the exception of an increase of beta-endorphin concentration in the hypothalamus. The changes in concentrations of catecholamines following chronic delta antagonism may reflect an alteration of sympathetic activity and could contribute to the retardation of blood pressure development.

Analgesic activity of morphiceptin, beta-casomorphin-4, and deltakephalin in normotensive Wistar-Glaxo and spontaneously hypertensive rats

The effects of intraventricular injection of beta-casomorphin-4, morphiceptin and deltakephalin (DTLET) on hot water tail flick and tail compression responses were investigated in Wistar Albino Glaxo (WAG) and spontaneously hypertensive rats (SHR). The effects of the mu agonist morphiceptin (20 nmol/rat), as assessed by the tail compression test, were significantly greater in SHR rats but did not differ between both strains when measured by tail flick latency. Opioid agonist deltakephalin (2 nmol/rat) in both tests elicited stronger analgesic effects in SHR as compared to WAG and these effects were blocked by naloxone in both tests used. beta-Casomorphin-4 exhibits moderate activity for mu receptors. In the tail flick test peptide (60 nmol/rat) produced an increase in latencies in SHR rats that was significantly greater than was observed in WAG rats. Naloxone pretreatment abolished the analgesic activity of beta-casomorphin-4 solely in the tail compression test in SHR. Analysis of the slopes of the dose-response curves seems to suggest that differences between the activity of these opioid peptides in SHR and WAG rats are based on a difference in the density and affinity of the subpopulation of the opioid receptors in these strains of rats.

Can central neuropeptides be implicated in carotid sinus reflex hypersensitivity?

Carotid sinus reflex hypersensitivity involves profound and intermittent changes in heart rate and blood pressure associated with symptoms of dizziness and syncope. This involves a reflex arc in which the main defect is believed to lie within the central nervous system. The discovery of classical and peptidergic neurotransmitters within the same neurone, and the presence of these peptides within the central nervous system raises the possibility that carotid sinus reflex hypersensitivity may be related to an abnormality of peptide distribution or function.

The effects of intracerebroventricular administration of biologically active peptides in conscious sheep

The present study records the physiological effects of 24-hour intracerebroventricular infusion of a variety of biologically active peptides in conscious sheep. A number of peptides including AVP and TRH produced increases in mean arterial pressure, heart rate and body temperature. There was an overall positive correlation between peptide-induced changes in body temperature and changes in either mean arterial pressure or heart rate. TRH and beta-endorphin had marked effects on behaviour and several peptides reduced food and water intake. Several peptides increased urinary sodium excretion, however, few peptides changes plasma electrolyte concentrations. TRH produced small effects on plasma ACTH and plasma glucose concentrations. The peptides in this study produced physiological changes which were probably mediated by their actions on the central nervous system.

Hypothalamic mu-opioid receptors in cardiovascular control: a review

The endogenous opioid system includes three major families of peptides [22]: dynorphins (derived from pre-proenkephalin B); endorphins (derived from pre-proopiomelanocortin) and enkephalins (derived from pre-proenkephalin A). Multiple species of opioid peptides are derived from these major precursors and many of them possess potent cardiovascular properties. Multiple forms of opioid receptors have been defined in the central nervous system. Although the relationship of these receptors to the multiple actions of the opioid systems is not well understood, some predications can be made: in vitro the dynorphin-related peptides bind preferentially to kappa-opioid receptors; the enkephalins bind preferentially to delta and mu-opioid receptors and while beta-endorphin binds to mu- and delta-, but not to kappa-opioid receptors. While little is known on the role of the opioid system in normal cardiovascular regulation, it has become clear that cardiovascular stress situations substantially modify the activity of the endogenous opioid system. This review focuses on the mu-opioid system in the hypothalamus with special emphasis on its potential role in cardiovascular control of both normal and pathophysiologic states.

Effect of low intravenous doses of TRH, acid-TRH and cyclo(His-Pro) on cerebral and peripheral blood flows

Local cerebral and peripheral blood flow in conscious and anaesthetized rabbits were investigated with the microsphere method, before and after the i.v. administration of 25 or 50 micrograms kg-1 thyrotropin-releasing hormone (TRH). Before the experiment, the cervical sympathetic chain was sectioned on one side in order to evaluate the possible effect of the sympathetic nerves on cranial and extracranial blood flows. Blood flow was also determined in anaesthetized rabbits before and after the administration of the TRH metabolites cyclo(His-Pro) and acid-TRH and after subsequent administration of 50 micrograms kg-1 TRH. TRH caused an increase in mean arterial blood pressure (MAP) of about 1 to 2 kPa whereas cyclo(His-Pro) and acid-TRH had no effect on MAP. In the anaesthetized animal an increase in total cerebral blood flow (CBFtot), from 71 +/- 7 to 107 +/- 12 g min-1 100 g-1 (P less than 0.05) was observed on the sympathetic intact side after 25 micrograms kg-1 TRH and a further increase to 130 +/- 9 g min-1 100g-1 (P less than 0.01) after 50 micrograms kg-1 TRH. A similar effect was observed on the sympathotomized side. An effect on CBF in the conscious animal was not detected. The control CBFtot (104 +/- 8 g min-1 100g-1) was higher in these animals than in the anaesthetized animals (P less than 0.02). Neither cyclo(His-Pro) nor acid-TRH mimicked the effect of TRH on CBF. In several peripheral tissues, e.g. skin, pancreas and gastric mucosa, a reduction in blood flow was noted after the administration of TRH in both anaesthetized and conscious rabbits. It was concluded that TRH can induce cerebral vasodilatation in animals with a depressed CBF, whereas the vasoconstrictor effect of TRH in peripheral organs is not markedly affected by the state of consciousness.

Effects of opiate receptor drugs injected intracerebrally into the normovolemic and hypovolemic monkey

Systemic injection of naloxone (NAL), an opioid-receptor antagonist, significantly elevates systolic blood pressure (SBP) in anesthetized hypovolemic monkeys, providing indirect evidence that endogenous opioids contribute to cardiovascular depression during shock. The purpose of this study was to identify specific centrally located opioid receptor sites that participate in SBP regulation under normovolemic and hypovolemic conditions. In 6 monkeys, bilateral guide cannulae were stereotaxically implanted above areas ranging from the diencephalon to the lower medulla. Microinjections (1 microliter) of D- Ala2-Met-enkephalinamide (DAME) (3.4-27.2 nM) into normovolemic unanesthetized monkeys reduced SBP by 10-65 mm Hg in a dose-related fashion. Subsequent injection of NAL (12.2 nM) attenuated this hypotensive response. Heart rate fell 20-40 bpm with DAME, but not in response to dose. In the anesthetized animal rendered hypotensive (SBP = 45 mm Hg) by hemorrhage. NAL injected into predetermined DAME-sensitive sites failed to increase SBP more than 5 mm Hg. Even consecutive injections into multiple sites elevated SBP only 20 mm Hg. We conclude that the centrally located opioid-sensitive sites tested exert only a mild influence in mediating hemorrhagic hypotension.

Narcotic antagonist-induced hypotension in the spontaneously hypertensive rat

Intravenous naloxone or naltrexone produced transient, dose-related reductions in the mean arterial pressure (MAP) and heart rate (HR) of urethane-anesthetized spontaneously hypertensive rats (SHRs). Yet these same doses of narcotic antagonists reduced HR but not MAP of normotensive Wistar-Kyoto rats (WKYs). Such effects were not observed upon administration to SHRs of increasing doses of methylnaltrexone, which possesses no central activity. (+)-Naloxone, which does not block opiate receptors, reduced HR but not MAP of both SHRs and WKYs. These findings indicate that SHRs and WKYs differ in their MAP and HR responses to narcotic antagonists. The high doses required for effect plus the brevity of the responses suggest that these drug effects are perhaps not mu-opiate receptor-mediated; however, the methylnaltrexone and (+)-naloxone findings clearly implicate a central specificity of action. We conclude that narcotic antagonist-induced changes in MAP and HR in SHRs are possibly specific and central in origin yet not mediated by mu-opiate receptors.

Effects of raised intracranial pressure on regional cerebral blood flow: a comparison of effects of naloxone and TRH on the microcirculation in partial cerebral ischaemia

The effects on regional cerebral blood flow (rCBF) of raised intracranial pressure (ICP) and of naloxone and thyrotropin releasing hormone (TRH) during this condition were studied in anaesthetized rabbits. The ICP was elevated until a central ischaemic response was observed. The regional blood flow was determined with the microsphere technique before and during elevation of the ICP (ICPe) and after drug treatment. Total CBF was reduced by about 70% during ICPe while the uveal blood flow increased slightly and some other peripheral tissue blood flows remained unaffected. The administration of TRH caused an increase in mean arterial blood pressure (MAP) from 11.9 +/- 0.6 to 14.6 +/- 0.7 kPa and a normalization of the rCBF. In some peripheral tissues, e.g. gastric mucosa and spleen, TRH reduced the blood flow by 53% and 76%, respectively. In blood pressure stabilized animals no effect on rCBF was seen after TRH. Naloxone had no consistent effect on MAP or local blood flow. It was concluded that in the range of cerebral perfusion pressure studied there was a passive relationship between cerebral blood flow and perfusion pressure. The lack of effect of naloxone and the marked effect of TRH during cerebral ischaemia are consistent with a mechanism of action of TRH not related to a 'physiological' antagonism of opioids.

The opioid system and central cardiovascular control: analysis of controversies

Opiates, like morphine, were long known to produce changes in blood pressure and cardiac functions. However, the nature of these changes are a subject of continuous controversy. The substantial differences in the opiate effects on the cardiovascular system is also apparent in more recent studies using enkephalins, beta-endorphin and dynorphins. The present review is aimed to indicate the source of the variations in the experimental data and analyze the relative contribution of different experimental factors to the observed effects of opiates and opioid peptides on the cardiovascular system. The major factors which contribute to the nature of the opioid effect on the cardiovascular system are: anesthesia, species, dose, site of action in the brain, respiratory changes and receptor specificity. However, the cardiovascular status per se is an important determinant of the opiates and opioid peptide effects on hemodynamic functions as indicated in states of hypertension and shock. A newly described factor is the plasticity of the opioid receptor system which changes its level and distribution pattern in different physiological and pathophysiological states. This review emphasizes the importance of utilization of highly specific ligands to opiate receptors administered to discrete brain areas in the conscious animal.

Enkephalins in pheochromocytoma: studies in a rat model

Enkephalins, endogenous opioid pentapeptides which are found in high concentration in normal chromaffin tissue, may play a role in blood pressure regulation. We therefore examined the presence and actions of enkephalins in pheochromocytoma in a rat model. Transplantable norepinephrine-rich tumors, which gave rise to significant blood pressure elevations, contained measurable immunoreactive enkephalins as determined by specific radioimmunoassays for leucine-enkephalin and methionine-enkephalin. Enkephalin immunoreactivity paralleled the enkephalin assay standard curves and was not abolished by boiling or by protease inhibitors (EDTA, PMSF). Authenticity of the immunoreactive enkephalins was confirmed by reverse-phase high pressure liquid chromatography. The amount of enkephalin immunoreactivity present initially in these tumors was greatly augmented by the prohormone activators trypsin or trypsin plus carboxypeptidase B, suggesting that most of the immunoreactive enkephalin was present in higher molecular weight precursor form. Enkephalin determinations on human pheochromocytoma and catecholamine measurements in both rat and human pheochromocytoma, demonstrated certain similarities and differences in enkephalin and catecholamine content between rat and human tumors. Total tumor enkephalins correlated (r = 0.91, p less than 0.05) with total tumor catecholamines in rat pheochromocytoma, suggesting co-regulation of synthesis of these 2 chromaffin tissue substances. Physiologic studies, in which intravenous leucine-enkephalin and the opioid antagonist nalaxone were administered to pheochromocytoma-implanted rats and sham-operated controls, failed to uncover an opioid peptide influence upon blood pressure in this animal model of pheochromocytoma.

Autonomic effects of central injections of D-Ala2-Met-enkephalinamide (DAME) in the conscious monkey

The use of naloxone (NAL), an opioid receptor antagonist, has provided indirect evidence that endogenous opioids contribute to cardiovascular depression during shock. To determine if endogenous opioids act centrally to influence cardiovascular function, injections of D-Ala2-Met-enkephalinamide (DAME), a potent Met-enkephalin analog, were made into the 3rd cerebral ventricle (ICV) of 5 conscious cynomulgus monkeys restrained in primate chairs. Systolic blood pressure (SBP) and heart rate (HR) were determined every 10 min during a 30-60 min control period and for up to 5 hr post-injection. Colonic temperature (Tc) was monitored continuously. SBP declined from baseline values with 50 and 100 micrograms (85.2 and 170.4 nM) doses but was significant (p less than 0.001) for only the 100 micrograms dose between 15-125 min post-injection. HR also decreased but did not exhibit any significant variation with time. However, when averaged across time, HR fell significantly (p less than 0.001) from baseline: -9.1 +/- 2.3 and -15.0 +/- 2.1 b/min for 50 and 100 micrograms DAME, respectively. Tc displayed a nonsignificant, delayed (greater than 2 hr) rise in Tc with the 50 micrograms dose, whereas the 100 micrograms dose caused a significant (p less than 0.001) decline in Tc (from 65-125 min post-injection). NAL injected ICV attenuated the effects of DAME but had no effect on SBP, HR or Tc when injected alone. Systemic injection of DAME (300 micrograms) in one monkey produced a transient decline in SBP (26 mmHg within 2 min) which returned to baseline values 4 min post-injection. HR and Tc were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Central cardiovascular actions of D-Ala2-Met5-enkephalinamide in the rat: effects of naloxone and nucleus reticularis gigantocellularis lesion

In pentobarbital-anesthetized rats, intraventricular administration of D-Ala2-Met5-enkephalinamide (D-Ala, 30, 100 or 300 nmol/kg) dose-dependently elicited a reduction in arterial pressure. This D-Ala-promoted hypotension was significantly antagonized by naloxone pretreatment (3 mg/kg, i.c.v.) and attenuated by bilateral focal nucleus reticularis gigantocellularis (NRGC) lesions. At higher doses, D-Ala also produced a delayed hypertension that was not only unaffected by naloxone or NRGC lesions, but was in fact potentiated by such pretreatments. We speculate that D-Ala may produce its cardiovascular effect by activating separate subclasses of opiate receptors, possibly at different neural substrates that include the NRGC.

Angiotensin stimulates beta-endorphin release from anterior pituitary gland cell cultures of rats

The effect of exogenous and locally generated angiotensin II (ANG II) on the release of beta-endorphin (beta-END) from anterior pituitary cell cultures of rats was studied. Angiotensin I (ANG I) and ANG II stimulated the release of beta-END, the ANG I effects being inhibited by addition of the converting enzyme inhibitor captopril. Renin and angiotensinogen had no effect when given separately, but their combination increased beta-END release. Thus ANG II causes the release of beta-END, but the putative pituitary renin system cannot be stimulated by exogenous renin or angiotensinogen; converting enzyme, however, acts locally to produce biologically active ANG II from ANG I.

An increase in opiate receptor-sites is associated with enhanced cardiovascular depressant, but not respiratory depressant action of morphine

Rats were treated for 4 weeks with a constant infusion of 2 mg/kg/h of the opiate antagonist naloxone. This treatment increased mu-, delta- and kappa-binding sites by 60-180% in several brain regions, suggesting effective blockade of the 3 types of opiate sites. The significance of changes in opiate binding sites for opiate receptor mediated physiological responses were examined using cardiovascular and respiratory responses to morphine (assessed after elimination of naloxone) as physiological parameters. Chronically naloxone-treated rats showed no alteration in respiratory responses to morphine, whereas there was a marked supersensitivity to depressor and bradycardic effects and a loss of pressor and tachycardic effects of morphine. These data are the first indication that cardiovascular effects of opiates vary with changes in central opiate receptor levels. Our observations, moreover, show that there are complex relationships between receptor number and receptor-mediated effects of opiates.

Effect of denervation on the leucine-enkephalin content of the adrenal gland of spontaneously hypertensive rats (SHRSP)

Enkephalins are known to inhibit the release of catecholamines from sympathetic nerve endings. Thus a difference in their turnover rate between SHRSP and normotensive rats (WKY) could contribute to the altered sympathetic activity in SHRSP. One week after denervation which inhibits release of leucine-enkephalin (L-ENK), but not synthesis and processing of the L-ENK precursor, L-ENK increased with the same relative extent in both strains of rats, starting from a lower basal concentration in 7 weeks old SHRSP. In adult rats there was no difference between SHRSP and WKY before and after denervation respectively. It is concluded that the lower content of L-ENK in young SHRSP is caused by an increased release.

Regional cerebral, ocular and peripheral vascular effects of naloxone and morphine in unanesthetized rabbits

Effects of morphine and naloxone were investigated on cerebral, ocular and peripheral blood flow in unanesthetized rabbits. Blood flow measurements were performed with the labelled microsphere method. Cervical sympathotomy was performed on one side the day before the flow determination. Naloxone 2 mg/kg b.w. i.v. had no consistent effect on cerebral, ocular or peripheral blood flow or on mean arterial blood pressure. Morphine 2 mg/kg b.w. i.v. caused a rise in PaCO2 of 0.9 kPa and tended to increase cerebral blood flow in all parts investigated. In the hippocampal region, caudate nucleus and collicles the increase in flow was about 30% which is more than expected from the rise in PaCO2. Blood flow in the retina increased while the other parts of the eye showed no consistent changes in blood flow. Morphine reduced the blood flow in the duodenum by 60%. Mean arterial blood pressure did not change after morphine. No effect of the cervical sympathotomy was detected on cerebral or ocular blood flow before or after morphine or naloxone. Thus, we found no evidence for a tonically operating opioid system controlling cerebral, ocular or peripheral blood flow. However, exogenously administrated opiate can influence blood flows in these areas.

Evidence for the presence of enkephalins in the heart

Extracts of guinea pig hearts were subjected to high performance liquid chromatography (HPLC) and the eluted fractions monitored by radioimmunoassays (RIA) for their content of leucine5-enkephalin (Leu-ENK) and methionine5 enkephalin (Met-ENK). Distinct peaks of both Leu-ENK and Met-ENK immunoreactivity were found corresponding to the position of synthetic Leu-ENK and Met-ENK respectively. The ratio of Leu-ENK to Met-ENK content was about 1:4. Chemical sympathectomy with 5-hydroxydopamine (6-OH-DA) produced a dramatic fall in noradrenaline content of the heart by more than 99%, whereas the concentration in Leu-ENK was reduced by only 70%. The Leu-ENK content of the adrenal glands was not affected by this treatment. These observations point to an enkephalinergic innervation of the heart which appears to be mainly of sympathetic origin. The results suggest the participation of enkephalins in cardiac reflex mechanisms.

Differential regulation of beta-endorphin in the anterior pituitary, intermediate lobe, hypothalamus and brain stem

The influence of adrenalectomy (adx), betamethasone (BET) and 11-deoxycorticosterone (DOC) on beta-endorphin-like-immunoactivity (beta-END-LI) in plasma, anterior (AP) and neuro-intermediate lobe (N-IL) of pituitary, hypothalamus (HT) and brain stem (BS) was studied in rats. One day or three weeks after adx animals were injected i.m. for five consecutive days with 0.4mg/kg BET or 3.4mg/kg DOC. Six days after adx beta-END-LI was increased in BS and plasma after four weeks there was an elevation in plasma and AP. BET suppressed beta-END-LI in plasma of both sham-adx and adx animals six days after operation and in the N-IL after six days of adx. DOC led to an increase of beta-END-LI in HT after sham-adx and to a reduction in the N-IL after four weeks of adx. These observations demonstrate that beta-END-LI is regulated differently at its sites of synthesis in the AP, N-IL and HT.

Cardiorespiratory effects of mu and delta opiate agonists following third or fourth ventricular injections

The cardiorespiratory effects of prototype mu (morphine and beta-casomorphine 1-4) and delta (D-Ala2-D-Leu5Enkephalin-DADLE) opioid ligands were compared following microinjection into third and fourth ventricular spaces in conscious and anesthetized rats. The direction of change in arterial pressure produced by ventricular opioid injections varied according to ligand, site of administration, and state of consciousness of the animal. In general, pentobarbital anesthesia blocked or reversed the pressor response to these opiate agonists; depressor responses became magnified following pentobarbital. Qualitatively, the predominant effect of third ventricular DADLE in anesthetized rats was to produce a depression of arterial pressure and pulse pressure, suggesting an involvement of hypothalamic delta opioid receptors in decreasing sympathetic outflow. By contrast, morphine exerted pronounced bradycardic effects following fourth ventricular administration, suggesting an action at mu opioid receptors which influence vagal parasympathetic activity. Both ligands lowered respiratory rates upon fourth ventricular injection, indicating a possible involvement of either opioid receptor subtype in the depression of brainstem respiratory centers. These depressant effects of opioids upon cardiorespiratory function were readily reversed by naloxone. The qualitative similarity between the cardiovascular effects of third ventricular DADLE administration and various forms of circulatory shock may indicate that both phenomena involve delta opioid receptors at hypothalamic sites.