Hormonal and metabolic responses to intracarotid and intrajugular infusion of beta-endorphin in normal dogs

The hormonal and metabolic responses of beta-endorphin infused cephalad into the carotid artery, or via the jugular vein, were examined in 10 normal dogs. The intracarotid administration of beta-endorphin resulted in significant increases in plasma glucagon, adrenocorticotropin, and cortisol levels. Hepatic glucose production increased only transiently and there was no significant change in glucose disappearance or plasma glucose concentrations. Infusion of beta-endorphin in the jugular vein gave rise to significant increases in glucagon and cortisol levels and to a transient increase in plasma epinephrine. Although no significant changes in glucose kinetics could be demonstrated, there was a slight transient decrease in plasma glucose concentrations. In conclusion, both intracarotid and intrajugular infusions of beta-endorphin stimulated glucagon secretion independent of circulating catecholamines, and increased cortisol release, probably through activation of the pituitary-adrenocortical axis.     

Bromocriptine is unable to suppress TRH-stimulated beta-endorphin/beta-lipotropin and cortisol secretion in normal pregnant women after delivery

The course of plasma beta-endorphin/beta-lipotropin, cortisol and prolactin (PRL) levels was followed from 0.5 till 5 h after normal delivery in 13 healthy women. Six subjects who did not want to breast-feed their child received 2.5 mg bromocriptine orally 1 h after delivery. After 3 h the effect of the intravenous administration of 200 micrograms thyrotropin-releasing hormone (TRH) was also measured. Elevated plasma beta-endorphin and cortisol levels decreased after delivery in a (log) linear fashion which was not influenced by bromocriptine. TRH elicited a significant short-lived identical increase in plasma beta-endorphin/beta-lipotropin concentrations in the control and the bromocriptine-treated subjects. TRH similarly delayed the rapid decline in plasma cortisol levels in both groups of women. Basal and TRH-induced PRL levels were rapidly suppressed by bromocriptine. These studies show the presence of a paradoxical increase of beta-endorphin/beta-lipotropin and cortisol levels in response to TRH occurring shortly after delivery in normal women. This response cannot be mediated by the placenta. The absence of an inhibiting effect of bromocriptine on basal and TRH-induced beta-endorphin and cortisol release does not lend support to the hypothesis of the presence of a functionally active intermediate pituitary lobe in man early in puerperium.     

The effect of repetitive haemorrhage on plasma cortisol, beta-endorphin and N-terminal pro-opiomelanocortin in conscious sheep

We measured the effect of repeated haemorrhagic stress, performed on four consecutive days in conscious adult sheep, on the plasma concentrations of cortisol and ACTH-related peptides to determine whether the pituitary-adrenal response was altered by stress repetition. Peptides from the C-terminus of the ACTH pro-hormone was measured by beta-endorphin RIA. Glycopeptides derived from the N-terminus of the ACTH pro-hormone were measured by tau 3-MSH RIA. The immunoreactive tau 3-MSH in sheep plasma was found to have an apparent molecular weight of approximately 10,000 by gel chromatography through Sephadex G-75, which is similar to the size of the major circulating form of pro-tau-MSH found in human and rat plasma. Daily haemorrhage consistently elevated plasma concentrations of cortisol and pro-tau-MSH. There was no significant difference in the daily responses of either cortisol or pro-tau-MSH when considered individually. However, there was a significant change over the four days in the relationship between the cortisol and pro-tau-MSH responses, as judged by analysis of variance of the difference in daily z-scores of cortisol and pro-tau-MSH. This trend indicated a relative increase in the secretion of pro-tau-MSH from the pituitary compared to the cortisol response, and suggested that repeated exposure to stressful stimuli may alter the pituitary-adrenal-axis.     

Assessment of plasma opioid peptides, beta-endorphin and met-enkephalin, at the end of an international nordic ski race

Plasma met-enkephalin, beta-endorphin, cortisol and lactic acid concentrations were measured in seventeen volunteer male subjects at rest and after a long-distance nordic ski race. Immediately after the race, mean plasma met-enkephalin did not show any significant change, but significant rises in beta-endorphin, cortisol and lactic acid were noted in all skiers. The change in beta-endorphin with exercise was significantly related to the change in cortisol (r = 0.68; p less than 0.001) and to the change in plasma lactic acid (r = 0.60; p less than 0.001). Furthermore, the experienced skiers training over 150 km X week-1 of nordic ski had significantly faster skiing times in this event and showed greater beta-endorphin, cortisol and lactic acid levels than the recreational skiers who trained for 20 km X week-1. Our results imply that the changes in plasma beta-endorphin depend on the intensity of exercise. However the significance of higher levels of skiing training or previous nordic ski experience in the release of beta-endorphin is expected and cannot be excluded.     

Secretion of N-terminal pro-opiomelanocortin-derived peptides in response to acute haemorrhagic stress in conscious sheep

To determine whether peptides derived from the N-terminus of the corticotropin/melanotropin/endorphin precursor, pro-opiomelanocortin, are released into blood in response to acute haemorrhagic stress, we examined the effect of haemorrhage on plasma concentrations of immunoreactive gamma 3-melanotropin, beta-endorphin and cortisol. Plasma concentrations of immunoreactive gamma 3-melanotropin (mean +/- SEM) increased within 30 min of haemorrhage from 71.1 +/- 10.4 to 106.8 +/- 6.3 fmol/mL (p less than 0.01) and plasma cortisol increased from 16.2 +/- 3.8 to 85.9 +/- 22.4 pmol/mL (p less than 0.025). The changes in plasma immunoreactive gamma 3-melanotropin and beta-endorphin were positively correlated (p less than 0.025). This study shows that peptides derived from the N-terminus of pro-opiomelanocortin are co-secreted with the C-terminal peptide beta-endorphin during acute haemorrhagic stress in sheep.     

Functioning of the pituitary-adrenal system during the vestibulo-vegetative syndrome and administration of dalargin and nalorphine

Changes in ACTH, cortisol, beta-endorphin have been investigated during vestibulo-vegetative syndrome (VVS) and injections of dalargin (leu-enkephalin analog) and nalorphine (agonist-antagonist of opioid receptors) in 9 volunteers with low level vestibulo-vegetative stability. Cumulative coriolis acceleration test during rotations on a special chair was used for VVS modelling. Dalargin (1-4 mg), nalorphine (5 mg) and placebo (NaCl solution) were injected intravenously 5-15 min before rotation. A significant increase in ACTH, cortisol and beta-endorphin plasma levels has been observed. Mean positive linear correlation (r greater than +0.6) between ACTH and beta-endorphin and ACTH and cortisol was noted immediately after the test only when dalargin was injected. It is suggested that in VVS there develops a hormonal conflict, i. e. an adequate hormonal release is disturbed.     

Response of plasma endorphins, prolactin and catecholamines in women to intense heat in a sauna

Concentrations of immunoreactive beta-endorphin (ir beta-E), corticotropin, cortisol, prolactin and catecholamines in plasma were followed in 11 healthy women during and after exposure to intense heat in a Finnish sauna bath, and compared to those in a similar control situation without exposure to heat. Heat stress significantly increased prolactin and norepinephrine secretion; the percentage increases from the initial plasma concentrations varied from 113 to 1280% (mean 510%) and from 18 to 150% (mean 86%), respectively. The response of the plasma levels of epinephrine, ir beta-E, corticotropin and cortisol to heat exposure was variable. Compared to the control situation, no statistically significant effect of heat exposure on the plasma levels of these hormones was found.     

Stress-induced changes in plasma concentrations of immunoreactive beta-endorphin and cortisol in response to routine surgical procedures in lambs

Following four different surgical procedures in lambs 3-5 weeks old, plasma immunoreactive beta-endorphin (beta-EP) and cortisol were assayed at 15 min and 24 h as determinants of post-operative stress. A threefold increase in mean plasma beta-EP levels occurred 15 min after tail docking, and a maximal eight- to tenfold increase occurred in response to castration and/or mulesing with tail docking. Significant increments in mean plasma cortisol levels followed these surgical procedures with the maximal response 15 min after mulesing plus castration with tail docking. The physiologically active 'free' cortisol in plasma represents about 25% of the cortisol, as measured, and the two are highly correlated. At 24 h, beta-EP levels in all treated groups were similar to controls, although a small elevation in cortisol levels was still present in the lambs subjected to mulesing. Ultrafiltration of plasma extracts showed that peak beta-EP levels contained about 40% immunoreactivity from low molecular weight species (mol. wt less than 10,000). By specific radioimmunoassay and reverse-phase high-performance liquid chromatography this comprised about 75% beta-EP1-31, the most potent analgesic endorphin, 10% beta-EP1-27, and 15% alpha-N-acetyl-beta-EP. Increased beta-EP1-31 levels may modulate post-operative pain in lambs.     

Shuttlebox avoidance in rhesus monkeys: effects on plasma cortisol and beta-endorphin

Groups of monkeys either extensively pretrained to avoid shocks in a shuttlebox or with minimal prior experience were compared for plasma cortisol and beta-endorphin levels immediately following: (1) an exposure to the box with no shock, (2) the box providing repeated inescapable shocks or (3) a re-exposure to the box, again with no shock presentation. Mere exposure to the unfamiliar box elevated plasma cortisol just as much as exposure + shock did when inexperienced monkeys were tested. However, animals with a history of previously successful shock avoidance showed smaller elevations when exposed to the box alone, than they did when inescapable shock was received. Plasma beta-endorphin levels following shuttlebox exposure showed only a sporadic pattern of elevations in either inexperienced or pretrained monkeys. However, levels of beta-endorphin as determined under control conditions in the home cage were lower in pretrained animals, as were plasma levels of cortisol. The results indicate that behavioral factors may effect plasma cortisol and beta-endorphin following both acute and chronic shuttlebox experience.     

Effect of myiasis and acute restraint stress on plasma levels of immunoreactive beta-endorphin, adrenocorticotrophin (ACTH) and cortisol in the sheep

Cutaneous myiasis in sheep arising from the activity of Lucilia cuprina larvae can result in significant physiological changes in susceptible animals. The stress imposed on the pituitary-adrenal axis of the sheep in response to myiasis and acute restraint is the subject of this investigation. Merino wethers were exposed to handling restraint, and blood sampling, during examination for blowfly strike; where necessary, they were treated for cutaneous myiasis. Significant changes in the plasma concentrations of immunoreactive beta-endorphin (beta-EP), ACTH and cortisol were found in sheep with extensive myiasis, as compared with unstruck sheep or those with only localized myiasis. In five susceptible sheep with extensive cutaneous myiasis, mean plasma levels of beta-EP, ACTH and cortisol were 307 +/- 71 pg ml-1, 953 +/- 58 pg ml-1 and 232 +/- 46 nmol l-1 respectively, compared with 818 +/- 89 pg ml-1, 641 +/- 41 pg ml-1 and 107 +/- 17 nmol l-1 in six unstruck sheep handled similarly. Whereas significant increases in plasma ACTH and cortisol can result from pituitary-adrenal responses to acute emotional or surgical stress, and are usually accompanied by a concomitant release of beta-EP from the pituitary, the present findings indicate a marked reduction in beta-EP levels and a significant increase in ACTH and cortisol in sheep following blowfly strike and acute handling restraint. This result suggests that cutaneous myiasis in susceptible sheep can alter the pituitary-adrenal response to acute restraint stress, and this could occur either by an alteration of precursor processing in the pituitary or by the selective release of ACTH.     

Different pituitary beta-endorphin and adrenal cortisol response to ethanol in individuals with high and low risk for future development of alcoholism

The purpose of the present studies was to investigate the activity of the adrenal gland and the pituitary beta-endorphin system in individuals from families with a 3 generation history of alcoholism, High Risk group, or from families without history of alcoholism, Low Risk group. All subjects had a medical examination, a drinking behavior personal interview and the Michigan Alcoholism Screening Test. Individuals with medical problems or excessive drinking were not included in the study. On the day of testing, a blood sample was taken at 9:00 a.m., then the subject drank a placebo drink or an ethanol solution (0.5 g ethanol/kg B.Wt.). Additional blood samples were taken at 15, 45 and 120 minutes post-drink. Results indicated that individuals of the High Risk group had lower basal levels of beta-endorphin like immunoreactivity (beta-EPLIR) than individuals of the Low Risk group. The dose of 0.5 g ethanol/kg B.Wt. induced an increase in the plasma content of beta-EPLIR of the High Risk group, but not of the Low Risk group. In the Low Risk group ethanol did not induce an increase above the 9:00 a.m. levels, however, it attenuated the beta-endorphin decrease overtime, observed following the placebo drink. Analysis of beta-endorphin-like peptides in the plasma of the High Risk group, with Sephadex G-75 chromatography indicated that the major component of the plasma beta-EPLIR was beta-lipotropin. Plasma cortisol levels, following ethanol intake, presented a small increase in the High Risk group but not in the Low Risk group. Both groups presented similar blood alcohol levels. The basal levels of immunoreactive cortisol and beta-endorphin in the plasma of individuals who were alcoholics, but had been abstinent for at least six months prior to testing were similar to the levels of the High Risk group. Thus there are differences both in the basal levels and in the response of the cortisol and the pituitary beta-endorphin system to an acute ethanol challenge between the two groups.     

Effects of ovine corticotropin-releasing factor and vasopressin on plasma beta-endorphin, cortisol and behavior after minor surgery in sheep

The evidence for an analgesic effect arising from increased peripheral concentrations of beta-endorphin (beta-EP) in various animal species is controversial, and has not been fully evaluated in the sheep. To stimulate beta-EP release, ovine corticotropin-releasing factor (oCRF) and arginine vasopressin (AVP) were injected intravenously (iv) into a group of 12 out of 24 sheep, 15 min prior to minor surgery on all sheep. This brought about significant increases (P less than 0.01) in plasma beta-endorphin (beta-EP) and cortisol concentrations, relative to the non-injected control sheep, 15-30 min after injection. Ultrafiltration indicated that less than 30% of the released beta-EP immunoreactivity was present as higher molecular weight forms (mol. wt greater than 10,000) and that the majority (about 75%) of the beta-EP was probably bound to plasma proteins. By 75 min after injection there was no significant difference in plasma beta-EP or cortisol concentrations between the two groups of sheep. Consistent with previous observations the sheep showed a characteristic aversive behavior to the human handler following surgery, lasting several days. This behavior appeared to be unaffected by a pre-operative increase in peripheral plasma beta-EP, and may indicate that this increase in beta-EP was not sufficiently analgesic to block the cognitive response to the operation, or long-lasting enough to prevent the perception of post-operative soreness.     

Plasma beta-endorphin and stress hormones in stress and adaptation

The experiments on white rats have shown that the induction of 4 hour stress produces an acute increase in beta-endorphin level, as well as characteristic changes in ACTH, cortisol, insulin, thyroxin and triiodothyronine concentrations. Different types of adaptation (training with short stress periods or injection of rhodiola rosea extract) promote a moderate increase in the amount of serum immunoreactive beta-endorphin, preventing its subsequent stress-induced elevation. Adaptation is characterized by a decrease or total prevention of hormonal changes peculiar to stress. The role of opioid neuropeptides in enhancing stress tolerance and the effect of adaptation factors are discussed.     

Stress induced changes in testis function

The mechanism through which chronic stress inhibits the hypothalamic-pituitary-testicular axis has been investigated. Chronic restraint stress decreases testosterone secretion, an effect that is associated with a decrease in plasma gonadotropin levels. In chronically stressed rats there was a decrease in hypothalamic luteinizing hormone-releasing hormone (LHRH) content and the response on plasma gonadotropins to LHRH administration was enhanced. Thus the inhibitory effect of chronic stress on plasma LH and FSH levels seems not to be due to a reduction in pituitary responsiveness to LHRH, but rather to a modification in LHRH secretion. It has been suggested that beta-endorphin might interfere with hypothalamic LHRH secretion during stress. Chronic immobilization did not modify hypothalamic beta-endorphin, while an increase in pituitary beta-endorphin secretion was observed. Since we cannot exclude that changes in beta-endorphin secreted by the pituitary or other opioids may play some role in the stress-induced decrease in LHRH secretion, the effect of naltrexone administration on plasma gonadotropin was studied in chronically stressed rats. Naltrexone treatment did not modify the decrease in plasma concentrations of LH or FSH. These findings suggest that the inhibitory effect of restraint on the testicular axis is exerted at hypothalamic level by some mechanism other than opioids.     

Effects of Desacetyl-alpha-MSH on Lipid Mobilization in the Rainbow Trout, Oncorhynchus mykiss

Effects of melanocyte-stimulating hormone (MSH) and beta-endorphin on lipid mobilization were examined in the rainbow trout (Oncorhynchus mykiss). Plasma levels of fatty acid (FA) were measured after intra-arterial administration of alpha-MSH, desacetyl-alpha-MSH, beta-MSH, or beta-endorphin through a cannula in the dorsal aorta. Desacetyl-alpha-MSH at 1 ng/g body weight resulted in an increase in plasma FA levels 1-3 hr after the injection, whereas the other three peptides showed no significant effect at the same dose. There was no significant change in plasma levels of cortisol after administration of any of the peptides. Lipolytic enzyme activity in the liver was significantly increased in a dose-related manner 1 hr after single intra-peritoneal injection of desacetyl-alpha-MSH. The direct effect of desacetyl-alpha-MSH on lipolysis was examined in liver slices incubated in vitro. Lipase activity in the liver slice was stimulated in the medium containing desacetyl-alpha-MSH in a dose-related manner. The results indicate that desacetyl-alpha-MSH is a potent stimulator of lipid mobilization in the rainbow trout.     

ACTH, alpha-MSH, and control of cortisol release: cloning, sequencing, and functional expression of the melanocortin-2 and melanocortin-5 receptor in Cyprinus carpio

Cortisol release from fish head kidney during the acute phase of the stress response is controlled by the adrenocorticotropic hormone (ACTH) from the pituitary pars distalis (PD). Alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin, from the pars intermedia (PI), have been implicated in cortisol release during the chronic phase. The present study addresses the regulation of cortisol release by ACTH and alpha-MSH in common carp (Cyprinus carpio) and includes characterization of their receptors, namely, the melanocortin-2 and melanocortin-5 receptors (MC2R and MC5R). We could not demonstrate corticotropic activity of alpha-MSH, beta-endorphin, and combinations of these. We do show a corticotrope in the PI, but its identity is as yet uncertain. Carp restrained for 1 and 7 days showed elevated plasma cortisol and alpha-MSH levels; cortisol is still elevated but lower at day 7 than day 1 of restraint. Interrenal response capacity is unaffected, as estimated by stimulation with a maximum dose ACTH in a superfusion setup. MC2R and MC5R appear phylogenetically well conserved. MC2R is predominantly expressed in head kidney; a low abundance was found in spleen and kidney. MC5R is expressed in brain, pituitary PD, kidney, and skin. Quantitative PCR analysis of MC2R and MC5R expression in the head kidney of restrained fish reveals MC2R mRNA downregulation after 7 days restraint, in line with lower plasma cortisol levels seen. We discuss regulation of corticosteroid production from a phylogenetic perspective. We propose that increased levels of alpha-MSH exert a positive feedback on hypothalamic corticotropin-releasing hormone release to sustain a mild stress axis activity.     

Changes in free and total plasma cortisol levels in juvenile haddock (Melanogrammus aeglefinus) exposed to long-term handling stress

We measured changes in free and total plasma cortisol levels, plasma glucose, gill hsp70 levels, and growth in haddock (Melanogrammus aeglefinus) subjected to a long-term handling stress (15 s out of water, each day, for 4 weeks), and the effect of this long-term stress on the ability of haddock to respond to an acute stressor. The acute stressor was a single handling stress, and fish were sampled at 1, 6, and 12 h post-stress. During the long-term stress study, free and total plasma cortisol levels increased significantly (10-fold) in the stressed group after the second week. However, the percentage of free cortisol was already significantly elevated by the first week (control 17%, stressed 55%), and remained high during the second week (control 35% and stressed 65%). After 3 and 4 weeks of handling, both free and total cortisol declined in stressed fish to levels that were not significantly different from pre-stress values. Control fish grew significantly more than stressed fish (by 32% and 18%, respectively) over the 4 week study, and condition factor only increased in control fish. Although fish from the control group showed elevated total plasma cortisol levels (to 47 ng mL(-1)) 1 h after the acute stress, and the levels in stressed fish were comparable to those for the control fish, no significant increase in plasma cortisol was measured in the group subjected to the long-term stress. Free plasma cortisol levels did not increase significantly in either group following the acute stress. However, free plasma cortisol levels were significantly higher in long-term stress group, as compared with the control group, at 6 h post-stress. Plasma glucose and gill hsp70 levels were not altered by either the long-term stress or acute stressor. Our data indicate that cortisol (free and total), but not glucose or hsp70, appears to be adequate to assess short- and long-term stress in haddock.     

Plasma cortisol stress response in fingerling rainbow trout, Salmo gairdneri Richardson, to various transport conditions, anaesthesia, and cold shock

Plasma cortisol levels of fingerling rainbow trout were measured as an index of the stress resulting from various procedures used for transport of the fish for stocking. When transported under 'normal' conditions, which included water at the hatchery acclimation temperature (10–11°C), O₂ saturation or supersaturation, and neutral pH, there was a marked increase in plasma cortisol levels within 0.5 h, which was maintained over the next 4 h of transport; there was a significant decrease in plasma cortisol by 8 h of transport. It was found that the plasma cortisol levels at 4 and 8 h were not appreciably altered by transport under partial O₂ desaturation, O₂ saturation, O₂ supersaturation, or 0.5% NaCl, or by anaesthesia with tricaine methanesulfonate (MS 222) prior to capture and transport in MS 222-free water or 0.5% NaCl. A 15 min exposure to an immobilizing dose of buffered or unbuffered MS 222, or 2-phenoxyethanol, caused an increase in plasma cortisol of about 2 h duration, indicating that anaesthetics are themselves stressful. Exposure to chilled water (1° C) caused a large increase in plasma cortisol levels by 4 h after initiation of exposure; plasma cortisol had decreased at 1 day, and by 2 days a constant level was reached which was above the level in fingerling trout under 'normal' hatchery conditions. Trout acclimated to chilled water for 24 h and transported in chilled water had an increase in plasma cortisol during transport. Anaesthesia prior to transport or addition of salt did not reduce the stress of transport as judged by plasma cortisol levels. The results indicate that stress from capture and transport during stocking cannot be avoided using present methods.     

Effect of anaesthetics on the release of beta-endorphin-immunoreactivity in rat plasma

Analgesia and anaesthesia produced by fentanyl, urethane and ether, but not pentobarbital, occurred concomitantly with an increase in the concentration of plasma beta-endorphin like immunoreactivity (BEIR), probably of pituitary origin. This increase was not associated with significant changes in pituitary or brainstem beta-endorphin content. Pretreatment with naloxone caused a reduction in plasma BEIR increase following Hypnorm, ether and urethane; and in the analgesia following Hypnorm and urethane. Pentobarbital, alone or in combination with naloxone, did not increase the concentration of plasma beta-endorphin. These results may indicate participation of endogenous opioids in the mechanism of action of urethane.     

Diurnal rhythms of cortisol,ACTH, and beta-endorphin levels in neonates and adults.

To determine whether a diurnal rhythm exists in neonates admitted to neonatal intensive care units where there is continuous artificial lighting and periodic nursing and medical care, plasma cortisol, adrenocorticotropin (ACTH), and beta-endorphin concentrations were measured in two groups of infants and in adult human volunteers. As expected, a diurnal rhythm was seen in adults. A diurnal rhythm was also found for cortisol and endorphin levels in neonates (3 to 4 days postnatally) with minimal stress and in infants who were clinically severely stressed. There was not a significant difference between the morning and afternoon concentrations of ACTH in these infants, but the afternoon concentrations were lower than the morning''s, as would be expected. We found that a diurnal rhythm does exist in neonates within the first few days of postnatal life and that the continuous lighting and medical and nursing interventions do not interfere with this rhythm.