Immunoreactive Beta-endorphin Research Articles

Neuromodulatory Effect of Endogenous Opioids on the Intensity and Unpleasantness of Breathlessness during Resistive Load Breathing in COPD

Background: Endogenous opioids are naturally occurring peptides released by the brain in response to noxious stimuli. Although these naturally occurring peptides modulate pain, it is unknown whether endogenous opioids affect the perception of breathlessness associated with a specific respiratory challenge. The hypothesis is that intravenous administration of naloxone, used to block opioid signaling and inhibit neural pathways, will increase ratings of breathlessness during resistive load breathing (RLB) in patients with chronic obstructive pulmonary disease (COPD). Methods: Fourteen patients with COPD (age, 64 ± 9 years) inspired through resistances during practice sessions to identify an individualized target load that caused ratings of intensity and/or unpleasantness of breathlessness ≥ 50 mm on a 100 mm visual analog scale. At two intervention visits, serum beta-endorphins were measured, naloxone (10 mg/25 ml) or normal saline (25 ml) was administered intravenously, and patients rated the two dimensions of breathlessness each minute during RLB. Results: Patient ratings of intensity (p = 0.0004) and unpleasantness (p = 0.024) of breathlessness were higher with naloxone compared with normal saline. Eleven patients (79%) reported that it was easier to breathe during RLB with normal saline (p = 0.025). RLB led to significant increases in serum beta-endorphin immunoreactivity and decreases in inspiratory capacity. There were no significant differences in physiological responses between interventions. Conclusions: Endogenous opioids modulate the intensity and the unpleasantness of breathlessness in patients with COPD. Differences in breathlessness ratings between interventions were clinically relevant based on the patients’ global assessment.

The Effect of an Acute Maternal Stress on β-Endorphin and Growth Hormone Releasing Factor in the Rat Fetus

Pregnant rats were injected with saline or L-tyrosine methylester HCl (200 mg/kg) and subjected to an acute forced immobilization stress on day 20 of gestation. At 10, 30, 60, and 120 minutes after the onset of stress, their fetuses were dissected out, and the contents of hypothalamic and pituitary immunoreactive beta-endorphin (IR-beta-EP) and hypothalamic immunoreactive growth hormone-releasing factor (IR-GRF) were determined by specific radioimmunoassays. The maternal stress arose a significant decrease of hypothalamic IR-beta-EP at 30 minutes, while pituitary IR-beta-EP slightly elevated at 30 minutes, then declined at 60 minutes. Hypothalamic IR-GRF showed a gradual increase during the maternal stress. Tyrosine supplementation tended to attenuate stress-induced changes in hypothalamic and pituitary IR-beta-EP, but the response of hypothalamic IR-GRF was less modified by tyrosine. These results showed the functional changes in fetal central beta-EP and GRF under maternal stress in the late gestational life, and suggested that catecholaminergic regulations participate, at least in part, in the fetal neuroendocrine response to maternal stress.

Effect of medial preoptic oestradiol implants on hypothalamic beta-endorphin concentration.

Twenty-four-day-old immature and cyclic female rats in metoestrus were ovariectomized and bilaterally implanted with oestradiol benzoate (OB) and cholesterol at a ratio of 1:360 or with cholesterol alone in the medial preoptic area (MPOA), or, for control, the hypothalamic dorsomedial nucleus. Estimation of beta-endorphin immunoreactivity in the ventromedial-arcuate-median eminence region at 6 and 3 days after implantation, respectively, revealed a significantly higher concentration in rats implanted with OB in the MPOA as compared to those implanted with cholesterol. OB implants placed in the dorsomedial nuclei were ineffective in this regard. The hypothesis is put forward that inhibition of hypothalamic beta-endorphin release as probably resulting from the implantation of OB in the MPOA may be related to desensitization of the negative oestrogen feedback that is induced by similar preoptic oestrogen implantation.

Endogenous opioids modify dyspnoea during treadmill exercise in patients with COPD

Exogenous opioid drugs, such as morphine, relieve breathlessness. The present study hypothesis was that endogenous opioids, released during the stress of exercise, modify dyspnoea in patients with chronic obstructive pulmonary disease. After familiarisation, patients performed an incremental treadmill exercise test followed by constant work on the treadmill for 10 min. At subsequent visits (2 to 3 days apart), patients received two puffs of albuterol, had a catheter placed in an arm vein for removal of blood to measure beta-endorphin immunoreactivity, received normal saline or 10 mg of naloxone intravenously in randomised order, and then performed high-intensity constant work rate exercise on the treadmill. The mean+/-sd age of the 17 patients (eight females and nine males) was 63+/-7 yrs, and post-bronchodilator forced expiratory volume in one second was 50+/-17% predicted. In both conditions, beta-endorphin levels increased three-fold from rest to end-exercise. The regression slope of breathlessness as a function of oxygen consumption (primary outcome), mean ratings of breathlessness throughout exercise and peak ratings of breathlessness were significantly higher with naloxone than normal saline. There were no differences in physiological responses throughout exercise between conditions. In conclusion, endogenous opioids modify dyspnoea during treadmill exercise in patients with chronic obstructive pulmonary disease by apparent alteration of central perception.

Decreased immunoreactive beta-endorphin in mononuclear leucocytes from patients with rheumatic diseases

The neuroendocrine polypeptide hormone beta-endorphin (beta-END), which is released from various tissues including the anterior pituitary gland and cells of the immune system, has recently been implicated as having an immunoregulatory role. We used a radioimmunoassay to measure beta-END levels in circulating mononuclear leucocytes from normal subjects and patients with various rheumatic diseases. Levels of beta-END in leucocytes from patients were lower than in leucocytes from healthy subjects (P less than 0.001). Whereas levels of beta-END in leucocytes from patients with the various rheumatic disorders were not significantly different, an inverse correlation was found between beta-END levels in leucocytes and expression of rheumatoid factor (P less than 0.025) and erythrocyte sedimentation rate (P less than 0.025). This study demonstrates decreased content of beta-END in cells of the immune system related to parameters of inflammatory activity in rheumatic diseases.

Plasma β-endorphin levels in frequent and infrequent tanners before and after ultraviolet and non-ultraviolet stimuli

To the Editor: Ultraviolet (UV) exposure behavior exhibits similarities to other substance-related disorders.1Warthan M.M. Uchida T. Wagner Jr., R.F. UV light tanning as a type of substance-related disorder.Arch Dermatol. 2005; 141: 963-966Crossref PubMed Scopus (128) Google Scholar UV exposure has a direct reinforcing effect on frequent tanners.2Feldman S.R. Liguori A. Kucenic M. Rapp S.R. Fleischer Jr., A.B. Lang W. et al.Ultraviolet exposure is a reinforcing stimulus in frequent indoor tanners.J Am Acad Dermatol. 2004; 51: 45-51Abstract Full Text Full Text PDF PubMed Scopus (118) Google Scholar Cutaneous opioids are induced by UV exposure,3Wintzen M. Yaar M. Burbach J.P. Gilchrest B.A. Proopiomelanocortin gene product regulation in keratinocytes.J Invest Dermatol. 1996; 106: 673-678Crossref PubMed Scopus (128) Google Scholar but whether the reinforcement seen with UV exposure is caused by opioid release is unknown. The potential relationship is complicated, as larger studies have not found an effect of UV on plasma β-endorphin levels.4Wintzen M. Ostijn D.M. Polderman M.C. le Cessie S. Burbach J.P. Vermeer B.J. Total body exposure to ultraviolet radiation does not influence plasma levels of immunoreactive beta-endorphin in man.Photodermatol Photoimmunol Photomed. 2001; 17: 256-260Crossref PubMed Scopus (36) Google Scholar These conflicting results could be caused by differences in UV dose and subject populations, because the tests were not done under conditions in which preference for the UV stimulus was known to occur. To better understand the relationship between cutaneous opioids and the reinforcing effect of UV exposure, we conducted a small double-blind, placebo-controlled, randomized trial and assessed plasma β-endorphin levels in 3 frequent and 3 infrequent adult female tanners, between 25 and 32 years of age and skin types III and IV, before and after non-UV and UV exposures (10 min for frequent tanners and 5-9 min for infrequent tanners based on minimal erythema dose testing). The study was approved by the Institutional Review Board (IRB). Infrequent tanners were defined as individuals who had tanned intermittently in the past (fewer than 8 times per year) but who are not regular tanners. Frequent tanners were defined as tanners who tan more often than is necessary to maintain a tan (8-15 times per month). Commercial indoor tanning beds with Speed 175 and 205 bulbs were used. The bulbs have a UV output of 4% in the UVB range and 96% in the UVA range (estimate dosage of 22.4 j/cm2). Plasma β-endorphin levels were measured on the same day by enzyme-linked immunosorbent assay (MD Biosciences Inc, St Paul, Minn) from blood samples drawn 3 times: before exposure, immediately after non-UV bed, and immediately after UV bed. No discernable trend in plasma β-endorphin levels was observed among the 6 subjects (Fig 1), though the mean plasma β-endorphin level was slightly higher in frequent tanners exposed to UV as compared to baseline. Baseline β-endorphin levels vary and exhibit no distinct pattern of response to UV exposure (at one exposure time in these 6 subjects). The variability in plasma β-endorphin levels complicates attempts to understand the role of endorphins in mediating the preference for UV. Even anxiety about the blood draw could affect endorphin levels. Opioid inhibitor studies may be a better approach to characterize the role of endorphin related effects in mediating physiologic responses to UV.

Reproduction Phase‐Related Expression of β‐Endorphin‐Like Immunoreactivity in the Nucleus Lateralis Tuberis of the Female Indian Major Carp Cirrhinus mrigala: Correlation with the Luteinising Hormone Cells‐Ovary Axis

The present study aimed to determine whether beta-endorphin immunoreactivity (bEP-ir) in the neurones of the nucleus lateralis tuberis (NLT) is linked to the seasonal cycle and shows correlation with the number of luteinising hormone (LH) cells in the pituitary gland and ovaries in the teleost, Cirrhinus mrigala. Although LH cells were moderately immunostained during the resting phase (December to January), the morphological profile suggested increased synthetic and secretory activity during the preparatory (February to April) and prespawning (May to June) phases. However, LH immunoreactivity was greatly reduced (P < 0.001) in the spawning (July to August) phase, suggesting massive discharge of the hormone; this pool was partly replenished in the postspawning (September to November) phase. The ovaries grew rapidly in the preparatory and prespawning phases; maximal size was attained during spawning, when ovulation occurred. Thereafter, the ovaries regressed. The NLT of C. mrigala is divisible into the pars lateralis (NLTl) and medialis (NLTm). During the postspawning and resting phases, bEP-ir was readily detectable in the NLTm as well as NLTl neurones. However, a steady reduction in the immunoreactivity was observed in the NLTm neurones during the preparatory through spawning phases (P < 0.001), suggesting a negative correlation with the LH cells-ovary axis. Thus, the inhibitory influence of beta-endorphin on the gonadotrophin-releasing hormone (GnRH)-LH axis appears to be attenuated during the preparatory through spawning phases. This may be necessary for the rapid stimulation of the axis culminating in spawning. Neurones of the NLTl also showed a gradual reduction in bEP-ir during the preparatory and prespawning phases (P < 0.01) and may therefore play a similar role. However, significant augmentation of the immunoreactivity was noticed in these neurones during the spawning phase (P < 0.001), the physiological significance of which is unknown. Although the present study demonstrated a temporal correlation between the beta-endorphin in the NLT, LH cells and the ovary, we suggest that the peptide in the NLTl and NLTm may show functional duality during the spawning phase.

Hormonal responses to opioid receptor blockade: during rest and exercise in cold and hot environments

Opioid receptors appear to modulate a variety of physiological and metabolic homeostatic responses to stressors such as exercise and thermally extreme environments. To more accurately determine the role of the naloxone (NAL) sensitive opioid receptor system during rest and exercise, subjects were subjected to concomitant environmental thermal stress. Fifteen untrained men rested or performed low intensity (60% VO2peak) or high intensity (80% VO2peak) exercise on a cycle ergometer for 60 min in an environmental chamber during cold (0 degrees C) hot (35 degrees C) air exposure while receiving an infusion of normal saline (SAL) or NAL (0.1 mg kg(-1)). Plasma adrenocorticotropin hormone (ACTH), immunoreactive beta-endorphin (IBE), cortisol and growth hormone were measured at baseline and every 15 min while in the chamber. Time to exhaustion was significantly reduced during high intensity exercise in the heat (P<0.0001). NAL significantly (P=0.0004) reduced the time to exhaustion (38.3+/-2.1 min) during high intensity exercise in the heat compared to SAL (49.4+/-2.1 min). ACTH and IBE increased during hot conditions and cold attenuated this response. Plasma concentrations of IBE, ACTH, and growth hormone increased significantly with NAL during high intensity exercise in the heat compared to SAL. Cold attenuated the response of ACTH, IBE and cortisol to NAL. NAL administration exaggerates plasma hormone concentration during high intensity exercise in the heat, but not cold. These results support a regulatory effect of the opioid receptor system on physiological responses during exercise in thermally stressful environments. Future research should be directed to more clearly defining the effect of environmental temperature on the mechanism of hypothalamic-pituitary-adrenal hormonal release during exercise and hot environmental temperatures.

Effect of the pretreatment with prolactin on the distribution of immunoreactive beta-endorphin through different ovarian compartments in immature, superovulated rats

Beta-endorphin and prolactin (PRL) are natural inhibitors of ovulation via central and peripheral mechanisms, but their possible interactions within the ovary are still unknown. The aims of the present study were to determine the gene expression and the topographic distribution of beta-endorphin, and the possible changes evoked by the pretreatment with PRL on the ovarian beta-endorphin localization in immature, superovulated rats. Prepuberal female Wistar rats weighing 60-70 g were superovulated with 20 IU equine gonadotrophins and, 48 h later, 20 IU human chorionic gonalotropin (hCG). Four hours after the hCG injection, the rats received either 200 microg rat PRL .i.p. (n = 12) or saline vehicle (n = 10). In the following morning the rats were killed and their ovaries were quickly removed. Beta-endorphin localization was assessed by immunohistochemistry and proopiomelanocortin (POMC) mRNA was detected by reverse transcription polymerase chain reaction (RT-PCR). Beta-endorphin was expressed mostly in the corpora lutea and perivascular stroma, but a weak to moderate immunostaining was also present in the theca cells and some granulosa cells of tertiary/antral and preovulatory follicles. The main differences observed in the distribution of ovarian beta-endorphin between the two groups were a more intense immunostaining in the granulosa cells of antral follicles, corpus luteum and stroma of PRL-treated rats. POMC gene transcripts were detected in 2/5 samples from the control group and in 3/7 samples from the PRL-treated group. Thus, the expression of beta-endorphin in tertiary/antral follicles is enhanced by PRL treatment in immature, superovulated rats, providing a putative mechanism by which PRL could inhibit the ovarian response to induced ovulation.

Localization, expression and control of adrenocorticotropic hormone in the nucleus preopticus and pituitary gland of common carp (Cyprinus carpio L.).

Adrenocorticotropic hormone (ACTH) takes a central role in the hypothalamo-pituitary-interrenal axis (HPI axis), which is activated during stress. ACTH is produced by the corticotrope cells of the pituitary pars distalis (PD) and is under control of factors from the nucleus preopticus (NPO). The distribution of ACTH in the hypothalamo-pituitary system in common carp (Cyprinus carpio L.) was assessed by immunohistochemistry. ACTH and beta-endorphin immunoreactivity was observed in the ACTH cells in the PD and in the NPO. Nerve fibers, originating from the NPO and projecting to the pituitary gland, contain beta-endorphin, but not ACTH, and these fibers either control the pituitary pars intermedia (PI) through beta-endorphin or release it to the blood. The release of pituitary ACTH (studied in a superfusion setup) must in vivo be under predominant inhibitory control of dopamine. Release of ACTH is stimulated by corticotropin-releasing hormone, but only when ACTH cells experience dopaminergic inhibition. The expression of the precursor pro-opiomelanocortin in (POMC) NPO, PD and PI was studied in an acute restraint stress paradigm by real-time quantitative polymerase chain reaction (RQ-PCR). POMC gene expression is upregulated in these three key tissues of the hypothalamo-pituitary complex, revealing a hitherto unforeseen complex role for POMC-derived peptides in the regulation of responses to stress.

Pyrogens enhance beta-endorphin release in hypothalamus and trigger fever that can be attenuated by buprenorphine.

At first, we investigated whether both beta-endorphin release level in the hypothalamus and body temperature can be altered after intracerebroventricular (i.c.v.) injection of either lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), or prostaglandin E(2) (PGE(2)) in rats. It was found that in the rat, i.c.v. administration of either LPS (0.5 microg in 10 microl), IL-1beta (10 ng in 10 microl), or PGE(2) (200 ng in 10 microl), in addition to producing fever, upregulated the immunoreactivity of beta-endorphin in the preoptic anterior hypothalamus of rat brain. Secondarily, we assessed whether the fever induced by either LPS, IL-1beta, or PGE(2) can be altered by pretreatment with buprenorphine (an opioid receptor antagonist). The results revealed that i.c.v. administration of buprenorphine (1 - 10 microg in 10 microl) alone had an insignificant effect on the body temperature. However, the fever induced by i.c.v. injection of either LPS, IL-1beta, or PGE(2) was significantly attenuated by pretreatment with i.c.v. injection of buprenorphine 1 h before the pyrogen injection in rats. The results suggest that pyrogens enhance beta-endorphin release in the hypothalamus and trigger fever which can be attenuated by buprenorphine, an opioid receptor antagonist.

Fat-tailed sheep traits as affected by docking.

The literature mostly indicates that docking fat-tailed lambs initially reduces growth but that post-weaning growth and feed conversion efficiency then increase. The amount of fat deposited, the total separable lean meat to fat ratio and the meat quality all increase, while the percentage of bone in the carcase either decreases or does not change in the carcases of the docked lambs. Wool growth and characteristics are, in general, not affected and reproductive traits in ewes and lambs are improved by docking. The rectal temperature, respiration rate and pulse rate are decreased following docking. The concentrations of immunoreactive beta-endorphin and cortisol in the plasma and the incidence of foot stamping and restlessness, as indicators of stress, increase after docking. Other constituents of the blood are not significantly altered following docking or by the methods of docking. Docking of fat-tailed sheep using rubber rings at one day of age can be recommended.

Role of protein kinase C in control of ethanol-modulated beta-endorphin release from hypothalamic neurons in primary cultures.

We have previously shown that short-term exposure to ethanol stimulates immunoreactive beta-endorphin (IR-beta-EP) release from hypothalamic neurons and that chronic ethanol exposure decreases the IR-beta-EP release from these neurons. The role of protein kinase C (PKC) in the ethanol-regulated beta-EP release from hypothalamic neurons has not been established. In this study, by using the primary cultures of hypothalamic neurons, we tested the effects of PKC stimulator phorbol ester 4 beta-phorbol 12-myristate-13-acetate (PMA) and PKC inhibitor chelerythrine chloride on ethanol-induced IR-beta-EP release. Additionally, the effects of ethanol with or without PMA on expression and translocation of various PKC isoenzymes from cytosolic to membrane fraction were determined. PMA treatment increased IR-beta-EP release in a time- and dose-dependent manner. Acute ethanol treatment (3 h) increased, while chronic ethanol treatment (24 h) reduced, the magnitude of PMA-induced IR-beta-EP release. The stimulatory effect of acute ethanol on IR-beta-EP release was reduced by chelerythrine chloride. Determination of the effects of ethanol with or without PMA on seven different PKC isoenzymes (PKC-alpha, -beta I, -beta II, -gamma, -delta, -epsilon, and -zeta) revealed that the expression and translocation of only two PKC isoenzymes, PKC-delta and PKC-epsilon, were stimulated by acute treatment with ethanol. Acute ethanol also increased PMA-stimulated expression of these two isoenzymes. Chronic ethanol treatment reduced both basal and PMA-induced increase of PKC-delta and PKC-epsilon expression and translocation. These data provide evidence for the first time that ethanol-regulated IR-beta-EP secretion is controlled by the PKC system, possibly involving PKC-delta and PKC-epsilon isoenzymes.

Total body exposure to ultraviolet radiation does not influence plasma levels of immunoreactive beta-endorphin in man.

A growing number of reports support evidence of proopiomelanocortin (POMC)-derived peptides in human skin cells, although not consistently. Also the effect of ultraviolet radiation (UVR) on cutaneous and plasma levels of these POMC peptides has not been established unequivocally. We hypothesized that production of beta-endorphin (betaE) may explain the sense of well-being many people experience when sun-bathing. The aim of the present study was to investigate whether exposure of the skin to UVR elevates plasma betaE. Healthy volunteers (n=26) received a single, weighted dose of 15 J/cm2 of UVA. Several times during the hour following irradiation, plasma betaE- immunoreactivity (betaE-IR) was determined by radioimmunoassay. The effect of repeated exposure was assessed in 35 patients treated with UVB, UVA, or UVA-1. Plasma ACTH-IR was monitored in parallel. Overall, plasma levels of betaE-IR and ACTH-IR showed no significant changes during the experiment, indicating that these peptides are not influenced by single or repeated exposures to UVR of different wavelengths. On the basis of these results, the skin does not appear to contribute significantly to the levels of circulating betaE or ACTH. These data offer no support for the hypothesis that exposure to UVR leads to an increased concentration of circulating betaE, which could contribute to the feeling of well-being that often accompanies sun-bathing.

CORRELATION OF β-ENDORPHIN AND PROSTAGLANDIN E2 LEVELS IN PROSTATIC FLUID OF PATIENTS WITH CHRONIC PROSTATITIS WITH DIAGNOSIS AND TREATMENT RESPONSE

The chronic pelvic pain syndrome is a clinically defined symptom complex of unclear etiology. We have noted increased oxidative stress in the prostatic fluid of these patients, implying an active inflammatory response. Immune cells can produce the natural opioid beta-endorphin at the site of injury, which may modulate pain. We measured beta-endorphin and the inflammatory marker prostaglandin E2 in the expressed prostatic secretions of men with prostatitis, and correlated the results with symptoms. Expressed prostatic secretions samples from 70 patients and 8 asymptomatic controls were collected and frozen. beta-Endorphin and prostaglandin E2 were measured by enzyme-linked immunosorbent assay. Results were stratified according to prostatitis category and compared in individuals before and after therapy. In symptomatic patients beta-endorphin and prostaglandin E2 were not significantly different in categories II, IIIa and IIIb expressed prostatic secretions but they were higher than in controls. The mean beta-endorphin level plus or minus standard error of mean in symptomatic patients was significantly higher (23.8 +/- 11 ng./ml. versus 8.7 +/- 4.7, p = 0.0001) and mean prostaglandin E2 was lower (6.01 +/- 2.9 ng./ml. versus 3.01 +/- 2.9, p = 0.001) after successful therapy with antibiotics or antioxidant phytotherapy, Prosta-Q (Farr Laboratories, Santa Clarita, California). We observed a correlation of higher prostaglandin E2 and lower beta-endorphin in symptomatic men with chronic prostatitis. Increased oxidative stress and inflammation may induce prostaglandin E2 production that would inhibit beta-endorphin release. Treatment with therapeutic agents that decrease oxidative stress, such as antibiotics and antioxidant phytotherapy, may function at least partially by increasing beta-endorphin and decreasing prostaglandin E2.

Presence of immunoreactive beta-endorphin in human skin.

The production and its induction by ultraviolet radiation (UVR) of proopiomelanocortin (POMC)-derived peptides by keratinocytes has been reported, albeit not consistently. Recently we demonstrated that only under specific culturing conditions human keratinocytes are capable of producing a beta-endorphin (betaE)-like peptide with the characteristics of beta-lipotropin (betaLPH). Here the presence and UV-induction of betaE-immunoreactivity (betaE-IR) in keratinocytes in human skin in vivo was investigated. betaE-IR was detectable by immunohistochemistry in keratinocytes of the follicular matrix and to some extent in cells of sweat ducts, but was absent from epidermal keratinocytes. Absence of betaE-IR was confirmed by radioimmunoassay of HPLC-fractionated extracts of normal epidermis. Repeated exposure to solar-simulated UVR had no effect. This investigation is the first to demonstrate the presence of betaE-immunoreactive material in the follicular matrix of corporal hairs and in duct cells of sweat glands. The possible meaning of these results is discussed.

Ablation of pituitary pro-opiomelanocortin (POMC) cells produces alterations in hypothalamic POMC mRNA levels and midbrain mu opioid receptor binding in a conditional transgenic mouse model.

The hypothalamic-pituitary-adrenal (HPA) axis is regulated by stress-related excitatory inputs, and various inhibitory and negative-feedback controls by glucocorticoids and opioids, including pro-opiomelanocortin (POMC)-derived peptides. The role of POMC-derived peptides of pituitary origin in the modulation of brain POMC mRNA expression and opioid receptor binding was investigated using a line of transgenic mice that express a fusion gene composed of the pituitary expression-specific promoter region of the POMC gene driving the herpes simplex viral-1 thymidine kinase (TK). Male adult mice were treated with the antiherpes agent ganciclovir that selectively ablates cells expressing TK. Following treatment, POMC mRNA levels, measured by quantitative solution hybridization/RNase protection assays, were decreased by 48% in the pituitary of the TK+/+ mice, reflecting an expected loss of the pituitary corticotrope POMC cells. This treatment also significantly lowered pituitary beta-endorphin immunoreactivity content and plasma concentrations of corticosterone. In contrast, POMC mRNA levels were increased by 79% in the hypothalamus of the TK+/+ mice with pituitary POMC cell ablation. Binding of [(3)H]DAMGO to mu opioid receptors, as measured by quantitative autoradiography, was significantly reduced in several brain regions including the central grey, median raphe and superficial grey layer of the superior colliculus. These regions are innervated by hypothalamic POMC neurones. No significant differences in binding to either kappa or delta opioid receptors were found in the brain regions studied. These results suggest that POMC-derived peptides of pituitary origin may exert a tonic negative-feedback effect on hypothalamic POMC neurones. In turn, the downregulation of central mu opioid receptors in this model may be mediated through a mechanism related to hypothalamic POMC overexpression.

Neonatal monosodium glutamate treatment abolishes both delta opioid receptor-induced and alpha-2 adrenoceptor-mediated gastroprotection in the lower brainstem in rats

Neonatal monosodium glutamate treatment reduced immunoreactive beta-endorphin content in the mediobasal hypothalamus by 50% in adult, male Wistar rats as compared to hypertonic saline-treated littermates; there was also a moderate (approx. 25%) reduction in the rostral part of the nucleus of the solitary tract. In sham-treated adults the intracisternally injected alpha-2 adenoceptor stimulant clonidine (0.47 nmol/rat) and the delta opioid receptor type agonist (D-Ala 2, D-Leu 5)-enkephalin (0.8 nmol/rat) reduced acidified ethanol-induced mucosal lesions in the stomach by 84.1 and 77.5%, respectively, whereas the same doses were completely ineffective in rats treated neonatally by monosodium glutamate. The data taken together with the results of previous studies with the same substances in rats with retroarcuate knifecuts suggest that neuronal damage in the nucleus of the solitary tract region rather than in the arcuate nucleus is responsible for the changes seen in the pharmacological responsiveness.

Peripheral plasma levels of beta-endorphin in alcoholics and highly trained athletes and the relationship to a measure of central opioid tone.

Human beta-endorphin-like immunoactivity was measured in highly trained athletes (n = 10), alcoholics in the early phase of abstinence (n=9) and normal controls (n=15) using the Nichols Allegro immunoradiometric assay. The assay was examined for cross reactivity against related peptides, beta-lipotropin and human N-acetyl beta-endorphin. Venous blood sampling was carried out in the morning at 0900 and 1100 hours in a fasting state. Using two-way analysis of variance there was a significant effect of subject group on beta-endorphin concentration (p=0.029). Post-hoc analysis using the Bonferroni t-test showed that the source of the difference was the alcoholic group having significantly lower beta-endorphin immunoreactivity (p < 0.05). There was no difference between the controls and the athletes. There was a positive correlation between plasma beta-endorphin level at 1100 hours and the subsequent ACTH incremental response to naloxone in the group as a whole (r=0.48, p=0.004). The assay showed 100% cross reactivity with beta-lipotropin and 73% cross reactivity with N-acetyl-beta-endorphin. We conclude that alcoholics have reduced levels of beta-endorphin-like immunoactivity. While beta-endorphin is known not to cross the blood-brain barrier, levels of plasma beta-endorphin-like immunoactivity may indirectly reflect central opioid activity.

Plasma beta-endorphin around parturition and its relationship to cortisol level and resumption of pituitary and ovarian functions in dairy cows.

The objectives were to evaluate the concentrations of beta-endorphin in peripheral circulation around parturition and to investigate their relationship to the concentrations of cortisol and postpartum resumption of pituitary and ovarian functions in dairy cows. Subjects were 21 Holstein-Friesian cows in late pregnancy. Blood samples were collected from these animals from day 270 in pregnancy until the first ovulation after calving. Average immunoreactive (IR) beta-endorphin concentrations in cows with dystocia (n = 8) in periparturient period (from day 270 of pregnancy until 24 h after calving) were slightly higher than those in cows with normal calving (n = 13) in the same period although the difference was not significant. During the periparturient period, the peak level of IR beta-endorphin was seen at the time of rupture in cows with normal calving and it was observed at the time of parturition in cows with dystocia. The trend of IR beta-endorphin secretion appeared to be concomitant with cortisol secretion in the periparturient period but not in postpartum period (from 24 h after calving until the first ovulation). Average IR beta-endorphin concentrations in cows with dystocia in the postpartum period were not significantly different from those in cows with normal calving. There was no significant association between average IR beta-endorphin concentrations in early postpartum period (from 24 h until 7 days after calving) and the responsiveness of luteinising hormone (LH) to exogenous GnRH administered on day 7 postpartum. However, a negative correlation (r = -0.593; n = 21; P = 0.004) was observed between average IR beta-endorphin concentrations and LH concentrations during the period from day 1 until the first ovulation in the 21 cows. In addition, a positive correlation (r = 0.498; n = 21; P = 0.020) was seen between the beta-endorphin concentrations and time to the first ovulation after calving. The results from this study suggest that beta-endorphin may release into peripheral blood differently from cortisol and that it may be involved in regulating LH secretion and thus the resumption of ovarian cyclicity in postpartum dairy cows.