An inhibitory role of beta-endorphin in central cardiovascular regulation

Blood pressure and metabolic factors in relation to chronic pain

Physical pain is a major trigger for changes in many homeostatic systems of the body physiology. Our aim was to study the relationship between blood pressure, metabolism and pain perception in subjects with chronic pain symptoms. This was undertaken in a population-based study in primary health care, including subjects with widespread pain (n = 16), or localized pain (n = 15), and pain-free controls (n = 14). The main outcome measures were office and ambulatory blood pressure, glucose, insulin, lipids, and beta-endorphin. Subjects with widespread pain were more obese and showed higher levels than controls (p < 0.05) of fasting glucose (4.9 vs 4.5 mmol/l), cholesterol (6.9 vs 5.8 mmol/l) and office systolic blood pressure (133 vs 120 mmHg), while the subjects reporting localized pain had values in-between. Ambulatory blood pressure, insulin and beta-endorphin levels did not differ between the groups. In conclusion, subjects with widespread and/or intense chronic pain have higher BMI, more pronounced metabolic disturbances and higher (office) systolic blood pressure, but not ambulatory blood pressure, than subjects without chronic pain. Future epidemiological studies are needed to test whether this is compatible with increased cardiovascular risk.

Plasma levels of beta-endorphin, leucine enkephalin and arginine vasopressin in patients with essential hypertension and the effects of clonidine

In order to investigate the changes of endogenous opiate systems in hypertension and their possible role in the pathogenesis in hypertension, we measured plasma concentrations of beta-endorphin, leucine-enkephalin, neurotension, arginine vasopressin, plasma renin activity and angiotensin II by radioimmunoassay in 60 normal persons and 120 patients with essential hypertension. The results showed that the patient group had lower levels of beta-endorphin and leucine enkephalin (P < 0.001), higher levels of arginine vasopressin, plasma renin activity and angiotensin II (P < 0.01, P < 0.05 and P < 0.05, respectively), and normal level of neurotensin, as compared with those in normal group. Plasma levels of leucine-enkephalin was correlated negatively to the mean artery pressure (r = -0.196, P < 0.05). Plasma level of arginine vasopressin was correlated to the duration of the hypertension (r = 0.216, P < 0.05). After 150 min and 14 days of treatment with clonidine, plasma levels of beta-endorphin, leucine-enkephalin increased significantly (< 0.01) and correlated negatively with the decrease of the mean artery pressure (r = -0.340 and r = -0.436 at 150 min, r = -0.369 and r = -0.441 on the 14th day, respectively, P < 0.01). Plasma renin activity and angiotensin II decreased significantly (P < 0.05 and P < 0.01). Arginine vasopressin and neurotensin did not change significantly. After intravenous administration of opiate antagonist-naloxone, the blood pressure and heart rate increased significantly (P < 0.01). The results suggested that the changes of endogenous opioids may be involved in the pathogenesis of hypertension and in the antihypertensive action of clonidine.

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

1. The effects of intracerebroventricular (i.c.v.) and intracisternal (i.c.) administration of beta-endorphin (0.01, 0.1 and 1.0 nmol kg-1) were examined in conscious rabbits. 2. After i.c.v. beta-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). 3. 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. beta-endorphin. 4. After i.c. beta-endorphin, MAP, HR and plasma catecholamines were not significantly altered but there was a similar degree of respiratory depression. 5. Clonidine (1.0 micrograms kg-1, i.c.) reduced MAP and HR; these effects were not blocked by i.v. naloxone (6 mumol kg-1). 6. These results demonstrate that beta-endorphin acts centrally, probably mainly on periventricular mu-opioid receptors, to increase adrenaline secretion and sympathetic nerve activity leading to alpha-adrenoceptor-mediated vasoconstriction. The respiratory depression is probably mediated by brainstem mu-receptors. 7. A role for beta-endorphin in the central hypotensive action of alpha 2-adrenoceptor agonists was opposed by finding that opioid receptor antagonism with naloxone did not block the effects of clonidine.

Efferents of the opiocortin-containing region of the commissural nucleus tractus solitarius

Efferent projections of the commissural nucleus tractus solitarius (cNTS0 in the region containing opiocortin-immunoreactive (-IR) neurons were identified using Phaseolus vulgaris leucoagglutinin (PHA-L). Efferents were identified in the bed nucleus of the stria terminalis, preoptic area, amygdala, hypothalamus, periaqueductal gray, parabrachial nucleus, locus coeruleus, medullary catecholaminergic groups, and NTS. The PHA-L-IR varicosities in lateral parabrachial nucleus were identified in close association with CRF-IR and enkephalin-IR cells. These data on cNTS projections are consistent with our previous immunocytochemical and lesion studies on opiocortin connectivity and provide anatomical evidence that neurons in the cNTS may influence cardiovascular and sympathetic nervous system function via connectivity with nuclei in the lateral brain stem.

Activation of kappa-opioid receptors in the nucleus ambiguus does not affect cardiovascular function or outcome following acute hemorrhage in the rat

The central cardiovascular response to hemorrhage is believed to be regulated, in part, by specific brain cardioregulatory nuclei, including the nucleus ambiguus (NA) of the hindbrain. Since endogenous opioid peptides and opiate receptors have been localized to this brain region, activation of endogenous opioid systems in the NA may affect the cardiovascular response to acute hemorrhage. The present study examined the effects of intracerebral microinjection of kappa-receptor agonists into the NA prior to acute fixed-volume hemorrhage in awake rats. 15 min prior to fixed volume hemorrhage (7.5 ml/300 g), male Sprague-Dawley rats (n = 59) received a microinjection of either (1) the synthetic kappa-receptor agonist U-50,488H (10 nM) or (2) U-50,488H (100 nM) or (3) the endogenous kappa-receptor agonist dynorphin 1-17 (1 nM) or (4) Des-Tyr dynorphin 2-17, inactive at opiate receptors (1 nM) or (5) equal volume saline. With the exception of the first 10 min post-hemorrhage, where intracerebral injection of both dynorphin 1-17 and dynorphin 2-17 caused a transient suppression of mean arterial blood pressure (P < 0.05 when compared to saline-treated controls), microinjection of the kappa-agonists dynorphin 1-17 or U-50,488H had no effect on blood pressure, heart rate or mortality when compared to control animals. These results suggest that activation of kappa-opiate receptors in the NA does not markedly influence cardiovascular response to acute hemorrhage.

Demonstration by in situ hybridization of the proopiomelanocortin gene in the rat heart

A biotinylated oligonucleotide probe was used to demonstrate the presence in the heart of the portion of the proopiomelanocortin messenger RNA which contains the sequence for beta-endorphin. The probe indicated the presence of beta-endorphin messenger RNA in cardiac tissue and specifically in the cardiac muscle cell. The probe also confirmed the well-documented presence of messenger RNA for beta-endorphin in the anterior and neurointermediate lobes of the pituitary. These findings indicate that in addition to the pituitary, beta-endorphin is produced in situ in the heart.

Adenosine release in morphine-induced hypotension in rats

1. Following intravenous administration of morphine.HCl a reduction in mean arterial blood pressure (MABP) was produced, quaternary morphine analogue was ineffective. 2. Theophylline and 8-phenyltheophylline administration reduced morphine-induced hypotension. 3. A2 adenosine receptor agonist caused an hypotension while A1 adenosine receptor agonist was ineffective. 4. L-NG-Mono-methylarginine administration reduced the hypotensive effect of exogenous A2 agonist while it was ineffective on morphine-induced hypotension. 5. Morphine-induced hypotension was increased by pretreatment with dipyridamole, whereas tetrabenazine abolished it. 6. The present study is consistent with previous reports on the central hypotensive action of morphine and propose a role for adenosine release in morphine-induced hypotension.

Endoproteolytic conversion of beta-endorphin-1-31 to beta-endorphin-1-27 potentiates its central cardioregulatory activity

Brain neurons that express the pro-opiomelanocortin gene secrete multiple forms of beta-endorphin (beta E) which subserve diverse bioregulatory processes. beta E-1-31, for example, is a potent analgetic but beta E-1-27 acts as an opioid antagonist and beta E-1-26, as well as the N-acetyl derivatives of all 3 peptides, lack opioid receptor activity. The present study examines the effects of beta-endorphin processing on its central cardioregulatory potency. Consistent with previous reports, intracisternal beta E-1-31 (1.5 nmol) injection lowered mean arterial pressure (MAP); MAP was reduced by 29.7 +/- 3.9 mm Hg at 60 min and returned toward baseline by 120 min. Unexpectedly, beta E-1-27 displayed a 10-fold greater hypotensive potency than beta E-1-31. At 0.15 nmol, it produced a response equivalent to 1.5 nmol beta E-1-31 while 1.5 nmol beta E-1-27 sustained a maximal reduction in MAP (49.2 +/- 3.9 mm Hg) throughout the 120-min test period. In contrast, beta E-1-26 and N-acetyl-beta E-1-26, -1-27 and -1-31 were inactive at 1.5 nmol. Bradycardia accompanied the depressor response to the higher beta E-1-27 dose but not to beta E-1-31. Naloxone pretreatment completely blocked the depressor effects of both beta E-1-31 and beta E-1-27, and reversed the bradycardia produced by beta E-1-27, suggesting that both peptides act through opioid receptors. beta E-1-27 also stimulated catecholamine release from the perfused adrenal gland but beta E-1-31 was inactive. These findings emphasize the importance of regionally selected post-translational processing in defining the functional specificity of beta E peptides.

Arcuate nucleus projections to brainstem regions which modulate nociception

Anterograde tracing studies were conducted in order to identify efferents from the arcuate nucleus, which contains the hypothalamic opiocortin neuronal pool. Phaseolus vulgaris leucoagglutinin (PHA-L) was stereotaxically iontophoresed into the arcuate nucleus and the terminal fields emanating from the labelled perikarya were identified immunocytochemically. PHA-L-immunoreactive (-ir) fibers were identified in nucleus accumbens, lateral septal nucleus, bed nucleus of the stria terminalis, medial and lateral preoptic areas, anterior hypothalamus, amygdaloid complex, lateral hypothalamus, paraventricular nucleus, zona incerta, dorsal hypothalamus, periventricular gray, medial thalamus and medial habenula. In the brainstem, arcuate terminals were identified in the periaqueductal gray (PAG), dorsal raphe nucleus (DRN), nucleus raphe magnus (NRM), nucleus raphe pallidus, locus coeruleus, parabrachial nucleus, nucleus reticularis gigantocellularis pars alpha, nucleus tractus solitarius and dorsal motor nucleus of the vagus nerve. Dual immunostaining was used to identify the neurochemical content of neurons in arcuate terminal fields in the brainstem. Arcuate fiber terminals established putative contacts with serotonergic neurons in the ventrolateral PAG, DRN and NRM and with noradrenergic neurons in periventricular gray, PAG and locus coeruleus. In the PAG, arcuate fibers terminated in areas with neurons immunoreactive to substance P, neurotensin, enkephalin and cholecystokinin (CCK) and putative contacts were identified with CCK-ir cells. This study provides neuroanatomical evidence that putative opiocortin neurons in the arcuate nucleus influence a descending system which modulates nociception.

High-dose naloxone modifies cardiovascular and neuroendocrine function in ambulant subjects

To determine the role of the opioids in the control of the cardiovascular system in awake ambulatory subjects, eight healthy men were infused with a high dose of naloxone (10 mg bolus plus 7 mg/hr), or saline placebo, for 12 hr. Ambulatory monitoring of blood pressure and heart rate every 10 min indicated no differences between trials for blood pressure (p greater than 0.80), but a significant difference for the maximal heart rate response during stair climbing or 1 km walks (p less than 0.02). Plasma cortisol concentration were increased during the naloxone trials (p less than 0.05), as was total urinary epinephrine and dopamine output (p = 0.005 and less than 0.03, respectively). Plasma FSH and LH concentrations were elevated during naloxone infusion (FSH: p less than 0.02, LH: p less than 0.01), but neither exercise or mental tasks significantly altered their levels (p greater than 0.20). The cardiovascular responses during moderate mental tasks were not affected by naloxone (p greater than 0.05). These results indicate that in the normal ambulatory state the opioid system has a minor role in cardiovascular regulation, as demonstrated by the urinary catecholamines. Its role becomes more evident when considerable stress is imposed.

Modulation of the aortic baroreceptor reflex by neuropeptide Y, neurotensin and vasopressin microinjected into the nucleus tractus solitarii of the rat

Neuropeptide Y (NPY), neurotensin, arginine vasopressin (AVP), angiotensin II (ANG II), atrial natriuretic peptide (ANP) and calcitonin gene-related peptide (CGRP) have been suggested as putative neurotransmitters in the nucleus tractus solitarii (NTS) where baro- and chemoreceptor afferents terminate. To investigate modulation of the aortic baroreceptor reflex by neuropeptides, we microinjected these neuropeptides into the medial area of the rat NTS and examined their effects on the depressor and bradycardic responses to electrical stimulation of the aortic nerve which contains mainly baroreceptor afferent fibers in rats. Male Wistar rats were anesthetized with urethane, paralyzed and artificially ventilated. NPY (3 ng) and neurotensin (0.3 ng) injected into the NTS caused a decrease in blood pressure and/or heart rate, and facilitated the depressor and bradycardic responses to aortic nerve stimulation. AVP (3 ng) produced an increase in blood pressure and heart rate, and inhibited the responses to aortic nerve stimulation, whereas d(CH2)5Tyr(Me)AVP(100 ng), a V1 vasopressin receptor antagonist, did not affect the basal cardiovascular parameters and the baroreflex responses. ANG II (0.3 and 3 ng) caused a decrease in blood pressure and heart rate whereas at 0.3 ng it did not affect the baroreflex responses. ANP (3 ng) and CGRP (3 ng) did not affect the basal blood pressure and heart rate, and the responses to aortic nerve stimulation. These findings indicate that NPY, neurotensin and AVP microinjected into the rats NTS can modify the aortic baroreceptor reflex. Some of these neuropeptides may play a role in modulation of the aortic baroreceptor reflex within the NTS.

Alterations in Na(+)-K(+)-ATPase activity and beta-endorphin content in acute ischemic brain with and without naloxone treatment

The Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase) activity and beta-endorphin immunoreactivity were determined in rat brain at the acute stage of ischemia produced by unilateral occlusion of the middle cerebral artery (MCA). The effect of pretreatment with naloxone on these activities was also evaluated in the same model. After MCA occlusion, Na(+)-K(+)-ATPase activity was promptly reduced in the ischemic hemisphere and remained at a lower level than in the contralateral hemisphere during 90 minutes of ischemia. A single intraperitoneal 0.5-mg injection of naloxone prior to MCA occlusion attenuated the inactivation. On the other hand, beta-endorphin immunoreactivity was significantly increased following ischemia. The increase was marked in the ischemic hemisphere and was also observed in the contralateral hemisphere; this increase was not affected by the administration of naloxone. These results indicate the possibility that naloxone contributes to protecting the brain from ischemia through stabilizing the cellular membrane. The possible mechanism by which naloxone attenuates the inactivation of Na(+)-K(+)-ATPase in the ischemic brain is discussed in view of alterations of the central beta-endorphin system during ischemia.

Intravenous beta-endorphin: behavioral and physiological effects in conscious monkeys

Beta-endorphin (0.7 and 2.8 mg/kg) and morphine (0.15 and 0.60 mg/kg) were administered intravenously to rhesus monkeys responding on an operant schedule. Beta-endorphin injections resulted in dose-dependent effects which included marked, but relatively brief disruptions in behavioral responding, decreases in systolic blood pressure, and more protracted increases in heart rate. Morphine injections were followed by much longer duration decreases in response rates and systolic blood pressure, and an irregular but largely deceleratory heart rate response. On a molar basis, beta-endorphin was approximately twice as potent as morphine. It was concluded that intravenously administered beta-endorphin exerts behavioral and physiological effects in the unanesthetized primate.

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.

Lack of involvement of endogenous mu-receptor opioids in the hypothermic effects of clonidine in normotensive and spontaneously hypertensive rats

The effects of successive injections of the alpha-adrenoceptor agonist clonidine (25, 50 and 100 ug/kg given at hourly intervals) on the body temperature of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats, previously treated for 48 hr with slow release emulsions (subcutaneous) containing either morphine (morphine SR, 100 mg/kg), naloxone (naloxone SR, 80 mg/kg) or no drug (vehicle SR), were examined. The successive injections of clonidine produced dose-dependent falls in body temperature which were quantitatively similar in the vehicle-treated WKY and spontaneously hypertensive rats. The hypothermic effects of clonidine in the morphine-dependent WKY and spontaneously hypertensive rats, and in the naloxone-treated WKY and spontaneously hypertensive rats, were not different to those of the respective vehicle-treated controls. These results suggest that endogenous mu-receptor opioid peptides do not have a major involvement in the hypothermic actions of clonidine, in either normotensive or spontaneously hypertensive rats.

Effect of clonidine on beta-endorphin, ACTH and cortisol secretion in essential hypertension and obesity

The role of alpha 2-adrenoceptor stimulation by clonidine on the secretion of beta-endorphin, ACTH, and cortisol in essential hypertension and obesity was studied in 45 subjects: 15 non-obese hypertensives, 10 obese hypertensives, 11 obese normotensives, and 9 healthy subjects. The circadian rhythm of plasma beta-endorphin, ACTH, and cortisol was determined after placebo and after three days on clonidine 0.45 mg daily. Clonidine lowered the blood pressure and blood ACTH and cortisol levels in all the subjects. A significant decrease in beta-endorphin after clonidine occurred in the healthy subjects. In obese normotensives basal beta-endorphin concentrations were significantly higher than in healthy subjects and did not change after clonidine. In about 50% of non-obese and obese hypertensives a significant increase in beta-endorphin secretion after clonidine was noted (responders). In the subgroup of non-obese hypertensive responders no circadian rhythm of beta-endorphin was observed. The results suggest that adrenergic regulation of beta-endorphin secretion is altered in obesity and in certain patients with essential hypertension.

Naloxone inhibits the centrally-mediated hypotensive actions of BHT-933 (azepexole)

Central administration of BHT 933, a highly selective alpha 2 agonist, to pentobarbital-anesthetized, normotensive dogs resulted in a rapid, significant decrease in blood pressure. The maximal response occurred at 30 min and remained significantly decreased for 60 min. Concomitant with the hypotensive response was a decrease in heart rate. Pretreatment with naloxone 15 min prior to the administration of BHT 933 completely abolished the hypotensive response and significantly inhibited the bradycardia. These results suggest a role for central opioidergic systems in the control of blood pressure which may serve as important sites of antihypertensive drug action. The central regulation of sympathetic tone by catecholaminergic systems plays an important role in the control of cardiovascular function in both normal and pathological states. A high density of catecholaminergic nerve terminals is found in regions of the brainstem involved in cardiovascular control. Stimulation of the alpha receptors in these areas decreases peripheral sympathetic tone and subsequently lowers blood pressure. Recent histochemical evidence has demonstrated the presence of opioid peptides in the nucleus tractus solitarii, nucleus ambiguous and hypothalamus as well as other discrete brain areas associated with cardiovascular control. Activation of the opiate receptors in these brain areas decreases sympathetic tone and blood pressure. Additionally, both catecholaminergic and opioidergic systems have been implicated in the reaction to certain stimuli (i.e., pain, stress) which entail important hemodynamic adaptations. The similarity between the central opiate and catecholaminergic systems suggests a relationship between the two systems in blood pressure control and a potential site of antihypertensive drug action. The purpose of the present study was to determine if an opioidergic component is involved in the hypotensive action of BHT 933 (azepexole). BHT 933 is a relatively new hypotensive agent which is a much more specific alpha 2 agonist than clonidine.

Changes in sympathetic nerve activity during morphine abstinence in the rat

The aim of the study was to examine sympathetic nerve activity, heart rate and blood pressure during naloxone-precipitated withdrawal reactions in morphine-dependent rats. In two groups of rats, one group conscious and the other anaesthetized with chloralose, renal sympathetic nerve activity (rSNA), heart rate (HR) and mean arterial blood pressure (MAP) were recorded before and during naloxone-precipitated abstinence. The conscious rats showed a biphasic pattern in the withdrawal responses. Initially, after small doses of naloxone, rSNA and HR increased and increased somatomotor activity including 'wet-dog' shakes were observed. However, upon further administration of naloxone, rSNA and HR promptly decreased while MAP increased. As rSNA was lowered, the withdrawal behaviour of the rats was markedly diminished and the animals rested calmly in the cages. In contrast, the anaesthetized group reacted with an immediate decrease in rSNA after the lowest dose of naloxone, followed by an increase in MAP and HR after higher doses of naloxone, although rSNA was still decreased. In both groups, rSNA remained below pre-naloxone control levels when the increased MAP was lowered to the pre-naloxone level with sodium nitroprusside, indicating a central origin of the sympathetic inhibition. It is concluded that naloxone elicits a biphasic rSNA response in the conscious, morphine-dependent rat. This includes an initial increase upon low naloxone doses followed by a pronounced inhibition of rSNA after higher doses. In chloralose-anaesthetized rats, rSNA declined already after low doses of naloxone. It is suggested that there might be a tonic, excitatory input on rSNA, mediated by the activation of opiate receptors by high levels of circulating morphine in the addicted animal. Naloxone will therefore decrease the tonic sympathetic nerve activity in these rats.

Effects of naloxone on cardiovascular responses to static exercise and behavior in conscious cats

Conscious cats performing static (isometric) exercise were studied before and after administration of the opiate antagonist naloxone in order to evaluate the possible role of endogenous opiates in regulating cardiovascular responses to static exercise. Intravenous administration (0.4 mg/kg) of naloxone had no effect on resting left ventricular systolic pressure or on heart rate. In addition, similar increases in left ventricular systolic pressure and heart rate occurred during static exercise both before and after naloxone. However, naloxone reduced the number of exercise events the cats would perform per day. We conclude that moderate doses of naloxone do not modulate the cardiovascular responses to moderate static exercise in conscious cats. The results do indicate that endogenous opiates are involved in regulating the number of exercise bouts the cats will perform per day.

Alpha-MSH and other ACTH fragments improve cardiovascular function and survival in experimental hemorrhagic shock

Hypovolemic shock was produced in rats by withdrawing about 50% of the estimated total blood volume. Following mean arterial pressure stabilization in the range of 15-25 mm Hg, with a pulse pressure of 7-12 mm Hg, the rats were given intravenous bolus injections either of ACTH fragments or of saline. The following ACTH fragments or analogs were used: ACTH-(4-10), alpha-MSH, ACTH-(1-16), ACTH-(1-17), ACTH-(1-18), [Nle4,D-Phe7]alpha-MSH, [beta-Ala1,Lys17]ACTH-(1-17)-4-amino-n-butilamide (alsactide). ACTH-(1-24) and human synthetic ACTH-(1-39) were used for comparison. All animals treated with saline died in 22.51 +/- 3.62 min. Treatment with ACTH fragments (160 micrograms/kg i.v.) increased blood pressure and pulse amplitude, the effect starting within a few minutes, gradually increasing, and reaching a maximum in 15-30 min. The blood and pulse pressure increases were sustained, remaining almost stable until the end of the 2 h recording. Two out of nine rats treated with alsactide, which was the least active, died within 2 h after treatment, while all rats treated with the other ACTH fragments or analogs were still surviving at that time. Both on a weight and on a molar basis, the most active was ACTH-(1-24), followed by ACTH-(1-16), by the alpha-MSH analog [Nle4,D-Phe7]ACTH-(1-13), by ACTH-(1-18) and by ACTH-(1-17). The present results show that melanocortins reverse otherwise fatal hypovolemic shock, and suggest a new therapeutic approach for shock treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropin reversal of experimental hemorrhagic shock is antagonized by morphine

ACTH-(1-24) dose-dependently improved cardiovascular function in rats and dogs subjected to experimental hemorrhagic shock, and intravenous dose of 160 and 100/microgram/kg, respectively, completely restoring arterial blood pressure and pulse amplitude. All saline-treated animals died within 30 min of bleeding, while all ACTH-treated animals were still alive at the end of the observation period (2 hr). The injection of ACTH-(1-24) also dramatically improved the respiratory function. Morphine, i.v. injected into rats at the dose of 2.5 mg/kg, antagonised the effect of ACTH-(1-24) to a greater or lesser degree, depending on the dose of peptide employed: at 160/microgram/kg, antagonism was complete, at 320/microgram/kg antagonism was only partial, while at 480/microgram/kg antagonism was almost completely overcome. These data further support the idea that melanocortins are physiological antagonists of opioids, and suggest that melanocortin peptides may prove to be rational and effective drugs in the treatment of hypovolemic shock.

Differential sensitivity of hypothalamic and medullary opiocortin and tyrosine hydroxylase neurons to the neurotoxic effects of monosodium glutamate (MSG)

The distribution of opiocortin- (OP-ir) and tyrosine hydroxylase-immunoreactive (TH-ir) perikarya was examined immunocytochemically in rats treated neonatally with the neurotoxin monosodium glutamate (MSG). While OP-ir and TH-ir perikarya were eliminated in the arcuate nucleus in treated animals, the OP-ir and TH-ir cell groups of the nucleus tractus solitarius and contiguous medullary regions were unaffected. This selective elimination of arcuate neurons permitted us to examine specifically the fiber projections of the medullary OP-ir perikarya in treated animals. This revealed a preferential distribution of delicate fibers originating in NTS, to discrete medullary and pontine areas. In control animals, these same terminal fields appeared to be more densely populated with an additional population of thicker OP-ir fibers, suggesting the possibility of a shared innervation of these brainstem regions by both hypothalamic and medullary OP-ir neurons.

Clonidine normalizes low plasma beta-endorphin concentration and blood pressure in young men with mild essential hypertension

In young men with mild essential hypertension and age-matched normotensive volunteers, plasma concentrations of the endogenous opioid beta-endorphin were determined hourly from 9:00 p.m. to 2:00 a.m. The hypertensive patients' mean plasma beta-endorphin concentration was significantly lower in comparison with normotensive controls. After 14 days of treatment with clonidine, systolic and diastolic blood pressure was significantly reduced in both groups. Plasma beta-endorphin concentration increased in the hypertensive patients, but remained unchanged in the normotensive volunteers. The present findings point to a possible involvement of reduced beta-endorphinergic activity in blood pressure regulation of young men with essential hypertension.

Caerulein and cholecystokinin reverse experimental hemorrhagic shock

Intravenously injected cholecystokinin octapeptide (CCK-8) (5-20/micrograms/kg) and caerulein (1.25-10/micrograms/kg) caused a prompt, dose-dependent and sustained improvement in blood pressure, pulse amplitude and survival in rats subjected to otherwise invariably fatal hemorrhagic shock.

Sodium deprivation increases the antinociceptive activity of morphine

In rats maintained for 50 days on a low-sodium diet and with a compensatory hyperactivity of the renin-angiotensin system, the antinociceptive activity of morphine was significantly longer-lasting than in controls. It is suggested that the renin-angiotensin system modulates opioid system responsivity.

Evidence for a central but not adrenal, opioid mediation in hypertension induced by brief isolation in the rat

Naloxone was found to provoke a hypotensive effect related to the dose on high blood pressure (BP) induced by short-term isolation in young rats. Another opiate antagonist, nalorphine, also reduced the arterial pressure of socially deprived rats. In contrast, naltrexone methylbromide that selectively blocked peripheral opiate receptors did not alter the elevated BP. To investigate whether adrenomedullary opioids were somehow implicated in the development of isolation-induced hypertension, bilaterally adrenalectomized rats were kept under social deprivation for 7 consecutive days. The data obtained indicated that high systolic BP developed in the same manner as in intact rats run in parallel. In conclusion, central opioids appear to be involved in BP elevation due to the stress generated by brief social deprivation in young rats.

Effect of naloxone on cerebral perfusion and cardiac performance during experimental cerebral ischemia

Transient global cerebral ischemia (TGI) was induced in awake rats using the "four-vessel" occlusion model of Pulsinelli and Brierley. Blood pressure, arterial blood gases, cerebral blood flow, and cardiac output were measured during the acute (up to 2 hours) and chronic (2 to 72 hours) postischemic time periods. Coincident with the onset of TGI, cardiac output and caudate blood flow were depressed. The former returned to baseline within 30 minutes after the conclusion of TGI, and the latter progressed to hyperemia at 12 hours (81.8 +/- 4.9 vs 68.6 +/- 3.9 ml/min/100 gm tissue (mean +/- standard error of the mean] and oligemia at 72 hours (45.5 +/- 4.8 ml/min/100 gm tissue) post-TGI in the untreated control rats. Arterial blood gases and blood pressure were unchanged. Naloxone (1mg/kg) given at the time of TGI or as late as 60 minutes post-TGI and every 2 hours thereafter for 24 hours or bilateral cervical vagotomy prevented the depression in cardiac output and blocked the hyperemic-oligemic cerebral blood flow pattern that was predictive of stroke in this rat model. Changes in cardiac output after TGI in this model appear to be mediated by parasympathetic pathways to the heart from the brain stem. Opiate receptor blockade probably blocks endogenous opioid peptide stimulation of these brain-stem circulatory centers, which results in inhibition of parasympathetic activity and improvement in cardiac output. The usefulness of naloxone in the treatment of experimental stroke may be a function of its ability to improve cerebral perfusion in pressure-passive cerebrovascular territories. Variations in cardiac output during experimental stroke may explain the dissimilar responses to naloxone treatment reported by other investigators of experimental stroke.

Endorphins in primate hemorrhagic shock: beneficial action of opiate antagonists

The endogenous opiate beta-endorphin is released concomitantly with adrenocorticotropin from the pituitary during stress. In the present study we investigated the possible involvement of opiate receptors in the cardiovascular depression associated with hypovolemic shock in the nonhuman primate. Changes in circulating levels in beta-endorphin were monitored during hemorrhagic shock in 18 female baboons. Plasma levels of beta-endorphin increased significantly during hemorrhagic shock and were significantly correlated with a decrease in cardiac output (P less than 0.05). Single bolus administration of the opiate receptor antagonist naloxone (2 or 5 mg/kg) produced a transient but significant improvement in cardiac output (P less than 0.05) and mean arterial pressure (P less than 0.05). Hemodynamic improvement was maintained with a constant infusion of naloxone. Opiate receptor blockade with the longer acting antagonist naltrexone (2 or 5 mg/kg) significantly increased mean arterial pressure (MAP; P less than 0.05), and CO (P less than 0.05), and decreased heart rate. Our results suggest that the baboon is an excellent model for the study of hemorrhagic shock and provide further evidence for endogenous opiate involvement in the cardiovascular pathophysiology of hemorrhagic shock.

Ultrastructural evidence for beta-endorphin-like immunoreactivity in the nervous system of the rat duodenum

Using a modified immunoelectron microscopic staining technique the opioid peptide beta-endorphin could be demonstrated within large dense-core vesicles (LDVs) which are localized in presumptive axons and dendrites of the duodenal myenteric plexus of the rat duodenum. Pre-absorption tests with synthetic beta-endorphin (10(-6)M, final concentration) abolished the beta-endorphin immunoreactivity, resulting in only beta-endorphin unstained vesicles. To demonstrate more clearly electron-dense beta-endorphin material within vesicles the ultrathin sections were not counterstained with heavy metal salts. These sections revealed that the beta-endorphin material is localized as 'cores' with a mean diameter of 35-50 nm within LDVs corresponding to cores of LDVs, which are 70-90 nm in mean diameter.

Prolonged disruption of plasma beta-endorphin dynamics following surgery

The purpose of the present study was to examine the effects of surgery on plasma beta-endorphin dynamics. Plasma beta-endorphin levels were measured by liquid chromatography/radioimmunoassay in seven patients undergoing elective surgery. Blood samples were obtained every 4 hr for two 24-hr periods: one beginning 48 hr before surgery and the other beginning 48 hr after surgery. Computer analysis of beta-endorphin levels as a function of clock time demonstrated a true circadian rhythm preoperatively with a mean of 28.0 +/- 5.9 pg/ml. In the postoperative period mean beta-endorphin levels were significantly elevated (85.6 +/- 20.7 pg/ml, P less than 0.005). Surgical procedures caused significant phase shifting in the grouped mean circadian rhythm of plasma beta-endorphin (mean = 2.4 hr). When the data was analyzed individually, plasma circadian rhythms were found to be totally abolished in the three patients with the longest operative times (mean = 3.8 hr) and significantly displaced in time in the remaining four patients. These prolonged alterations in plasma endogenous opioid peptide levels following surgery have not been previously reported, and should be considered in the management of the postsurgical patient.

Beta-endorphin: a common factor in the antihypertensive action of clonidine-type imidazolines in spontaneously hypertensive rats

The hypotensive action of two novel imidazolinic alpha-adrenergic agonists (ICI-106270 and UK-14304) with similar pharmacological properties to clonidine was shown in spontaneously hypertensive (SH) rats. The antihypertensive effect of the clonidine-type agents was prevented by either peripheral administration of the opiate antagonist naloxone or by intracerebroventricular (i.c.v.) injection with a specific antibody against human beta-endorphin (BEN). A dose-response relationship was found for the hypotensive effect of i.c.v. given BEN in SH rats, the low blood pressure being significantly reversed by further treatment with either naloxone or anti-beta h-endorphin. These data confirm and extend the notion of a BEN mediation in the antihypertensive action of clonidine-type alpha-adrenergic agonists in SH rats.

Chronic naloxone increases opiate binding in SHR and WKY rats

We have previously reported that chronic administration of naloxone to SHR and WKY rats results in a significant increase in their systolic blood pressure relative to control animals. In the present study we show that chronic naloxone is also accompanied by a marked increase in the number of brain opiate receptors. Although the relative difference in blood pressure diminishes with increasing maturity, the elevation in brain opiate receptors remains in the treated animals. Mechanisms for these differential effects are discussed.

Effects of naloxone on the cardiovascular responses to muscular contraction in decerebrate cats

The cardiovascular responses to muscular contraction induced by ventral root (L7 and S1) stimulation were studied in unanesthetized decerebrate cats before and after the administration of the opiate antagonist naloxone. Intravenous naloxone (1.0-2.0 mg/kg) did not alter the heart rate or arterial pressure responses to either tetanic or repeated twitch contractions. However, naloxone did increase resting arterial pressure.

Beta-endorphin contributes to the antihypertensive effect of clonidine in a subset of patients with essential hypertension

Naloxone [0.4 mg iv.] increased blood pressure and heart rate of 13 clonidine-treated [0.3 mg per os for 3 days] patients with essential hypertension [reacting group] while it has no such effect in 11 clonidine-treated patients [non-reacting gr.] Clonidine increased plasma beta-endorphin concentration of the reacting patients by 17.53 +/- 1.68 pM/1 and in the non-reacting ones by 5.91 +/- 0.88 pM/1. Significant linear correlation was found between the clonidine-induced increase in plasma beta-endorphin level and the naloxone-induced change in mean blood pressure [r = 0.9572, n:24, p less than 0.001]. In another group of 8 patients clonidine [0.15 mg iv.] decreased mean blood pressure but naloxone, 30 min after the clonidine injection, did not reverse the clonidine hypotension. We suggest that beta-endorphin, released by chr. clonidine therapy, contributes to the anti-hypertensive effect only in the reacting group.

Naloxone inhibition of stress-induced daily torpor

Peromyscus maniculatus, deermice , were induced into daily torpor by restricting food to one-half daily ration. Intraperitoneal injection of naloxone (20 mg/kg) into mice habituated to daily IP injections of saline inhibited or modified the expression of daily torpor. In those individuals demonstrating long duration/deep bouts (greater than 300 min/body temperature 20 degrees C or below) naloxone administration resulted in 1) a significant decrease in the duration of torpor, 2) a significant elevation in minimum body temperatures attained during torpor and 3) a significant delay in the initiation time of torpor. In those individuals demonstrating short duration/shallow bouts (less than 300 min/body temperatures above 20 degrees C), naloxone administration resulted only in a significant delay of initiation time. Upon subsequent return to saline administration, however, these mice displayed a significant increase in the duration and depth of torpor. The results suggest that the endogenous opiates modulate the state of daily torpor.

Co-localization of CRF-ir perikarya and ACTH-ir fibers in rat brain

The distribution of corticotropin-releasing factor immunoreactive (CRF-ir) perikarya and ACTH-ir fibers was examined immunocytochemically, in adjacent sections, in the forebrain and brainstem of the rat. Throughout the nervous system, a remarkable concordance of localization of these neuropeptide systems was noted. Both ACTH-ir fibers and CRF-ir perikarya were conjointly distributed within discrete hypothalamic, limbic and brainstem/autonomic regions previously demonstrated to contain opiate receptors and opiocortin (beta-endorphin, beta-LPH, ACTH) fibers. In view of the demonstrated interactions of CRF with the peripheral (pituitary) opiocortin system, these data suggest the possibility of a similar relationship of CRF and opiocortin systems in the central nervous system as well.

Opiate antagonists reverse the hypoactivity associated with systemic anaphylaxis in mice

Systemic anaphylaxis in the mouse is associated with marked hypoactivity. This effect is reversed by treatment with the opiate antagonists, naloxone (5-10 mg/kg) or naltrexone (1 mg/kg). Administration of naltrexone methyl bromide (1 mg/kg), a selective peripherally acting opiate antagonist, is ineffective in reversing the hypoactivity induced by anaphylaxis. These results suggest a role for central nervous system opiate mechanisms in the hypoactivity induced by anaphylaxis. They support the hypothesis that endogenous opiates contribute to the pathophysiologic consequences of anaphylactic shock.

Increases in heart rate and blood pressure produced by injections of dermorphin into discrete hypothalamic sites

Central cardiovascular sites of action for dermorphin were determined by injecting 40 pmol of the peptide into discrete sites within the hypothalamus of halothane anesthetized rats. Blood pressure and heart rate in 101 rats were 88 +/- 1 mm Hg and 338 +/- 3 beats/min, respectively, prior to 100 nl intrahypothalamic injections of either vehicle or dermorphin. In the caudal anterior hypothalamic nucleus (A5800-5300), dermorphin, but not vehicle, increased blood pressure 8% and heart rate 26%, without changing respiration rate. The peak response was at 32 +/- 5 min, the duration greater than 90 min. Injections of naloxone (30 nmol) into the same anterior hypothalamic site, or 3 mg/kg naloxone administered i.m., completely reversed the cardiovascular actions. Similar increases in heart rate and blood pressure occurred at A6600-6300, the region between medial preoptic and anterior hypothalamic nuclei. Small increases in heart rate, but not blood pressure, resulted from dermorphin injections into the septal area, medial preoptic nucleus, paraventricular hypothalamic nucleus and the lateral ventricle, while injections in the posterior and dorsomedial hypothalamic nuclei were without effect on blood pressure and heart rate. These data provide support for anterior hypothalamic and medial preoptic sites for the cardiovascular actions of the opiate receptor agonist, dermorphin, and indicate greatest effects with this dose (primarily on heart rate) are produced at discrete sites (A6600-6300 and A5800-5300) within these nuclei.

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.

Antianaphylactic effect of naloxone in mice is mediated by increased central sympathetic outflow to sympathetic nerve endings and adrenal medulla

Intravenous naloxone, 1 or 10 mg/kg, protects sensitized mice from lethal anaphylaxis. The protective effect is reversed by pretreatment with the ganglionic blocker, chlorisondamine chloride, peripheral chemical sympathectomy with 6-hydroxydopamine or bilateral adrenal gland denervation. The possible involvement of the sympathetic nervous system in naloxone's antianaphylactic action, suggested by these findings, is discussed.

Immunocytochemical localization of ACTH perikarya in nucleus tractus solitarius: evidence for a second opiocortin neuronal system

Immunocytochemical localization of ACTH-opiocortin perikarya was demonstrated in the medulla of colchicine-treated rat. Neuronal cell bodies and fibers containing ACTH-immunoreactivity were abundant in the caudal region of the nucleus tractus solitarius, specifically within pars commisuralis. Location of these opiocortin neurons within the nucleus tractus solitarius provides additional evidence for a role of these peptides in cardiovascular functions.

Origin of the hypotensive and sympathoinhibitory effect of morphinomimetic agents

In vagotomized dogs, lesions of the lateral reticular nucleus (LRN) region did not change arterial blood pressure and sympathetic nerve activity. The hypertensive and tachycardic responses elicited by section of both carotid sinus nerves and both vagus nerves were not altered. However the sympathoinhibitory component of the baroreflex arc was attenuated. These lesions also abolished the hypotensive and sympathoinhibitory effects of fentanyl (10 micrograms/kg i.v.). In debuffered dogs, bilateral lesions of the LRN regions attenuated the effects of fentanyl (20 micrograms/kg i.v.) on arterial blood pressure and splanchnic discharges. Microinfusion of naloxone into the LRN reduced the effects of fentanyl (10 micrograms/kg) administered intravenously. Microinfusion of [D-Ala2,Met5]enkephalinamide (0.1-1 microgram) into the LRN region produced a dose dependent decrease in arterial blood pressure and sympathetic nerve activity. Lesions of the nucleus ambiguus (NA) region also reduced the effects of fentanyl. In contrast, lesions placed in the ventral median reticular formation or above the NA were ineffective in changing the sympathoinhibitory effect of fentanyl. These results indicate that the lateral reticular formation ventral to the nucleus ambiguus including the lateral reticular nucleus region is involved in the sympathoinhibitory effect of morphinomimetic agents.

Enkephalins induce a centrally mediated rise in blood pressure in rats

The cardiovascular effects of enkephalins after administration directly into the nucleus tractus solitarii (NTS) of urethane anesthetized rats were investigated. Unilateral microinjection of Met-enkephalin and its stable analogue D-Ala2-Met5-enkephalin resulted in a dose-related rise in mean arterial pressure which in the case of the analogue was accompanied by tachycardia. The elevation in blood pressure was anatomically specific and restricted to the intermediate third of the NTS, as verified histologically. These cardiovascular changes were prevented by pretreatment with locally applied naloxone (10 ng). A similar pressor effect was obtained with Leu-enkephalin. Antiserum to Met-enkephalin (1:50 dilution) caused a fall in blood pressure on injection into the NTS, and completely blocked the pressor response and tachycardia induced by D-Ala2-Met5-enkephalin. These results suggest that enkephalins have a pressor role in the central nervous system.

mu Receptors and opioid cardiovascular effects in the NTS of rat

In order to assess the potential role of mu (mu) and delta (delta) opiate receptors in the central regulation of the cardiovascular and respiratory systems, the cardiovascular and respiratory effects of the relatively selective mu-opioid agonist D-Ala2, MePhe4, Gly-ol5 enkephalin (DAGO) and relatively selective delta-agonist D-Ala2-D-Leu5 enkephalin (DADL) were compared following microinjection of these compounds into the nucleus tractus solitarius of pentobarbital-anesthetized rats. Both opioid agonists produced dose dependent increases in systolic and diastolic blood pressure as well as heart rate; but DAGO was nearly ten times more potent in eliciting these changes. Respiratory rate was increased by DADL and by lower doses of DAGO, but was depressed by higher doses of DAGO. Tidal volume was depressed by both peptides. These data support the concept that the cardiovascular pressor responses and tachycardia as well as the respiratory effects of opioids in the rat NTS are mediated by mu receptors.