Adrenalectomy, dexamethasone or stress alters opioid peptides levels in rat anterior pituitary but not intermediate lobe or brain

Nature and control of peptide release from the pars intermedia

Pro-opiocortin, the precursor of ACTH, LPH and gamma-MSH, is biosynthesized in both the cells of the pars intermedia and the corticotrophs of the pars distalis. In the pars distalis its processing does not vary significantly from species to species whereas in the pars intermedia large differences occur. The release of ACTH, beta-LPH and pro-gamma-MSH from the corticotrophs is under common positive control by hypothalamic corticotropin-releasing factor (CRF) and the nature of the peptides remains unchanged when they are secreted. The release of all five pars intermedia peptides that we have measured in vitro appears to be under tonic dopaminergic inhibition. The secreted peptides have also been identified chromatographically. The lack of unequivocal physiological function in the periphery, the diversity of the pars intermedia peptides and this common control mechanism tend to preclude a simple endocrine role for the pars intermedia. The neural effects of MSH and endorphin are well documented and specific neuronal uptake therefore cannot by dismissed. The absence of pars intermedia in the adult human pituitary suggests that such a site of synthesis of these peptides plays a minor role in learning and behaviour in a species (such as Homo sapiens) that has a highly evolved intelligence and may, instead, need to synthesize the peptides only in the brain.

The conditioned enhancement of neutrophil activity is catecholamine dependent

Neutrophil activity was elevated in the conditioned mice for the first time through an established conditioned training process. Catecholamines were proved to be important in the regulation of this conditioned innate immunity. In the study, the camphor odor (as the conditioned stimulus, CS) and poly I: C (as the unconditioned stimulus, US) was used to conditionally elevate the activity of the splenic neutrophils. The mechanism(s) responsible for the conditioned enhancement of neutrophil activity was further investigated using the neurochemical blocking assay and immunohistochemical analysis. Results showed that the neutrophil activity was significantly enhanced through the conditioned training process; both reserpine and 6-hydroxydopamine (6-OHDA) significantly blocked this conditioned innate immunity at the conditioned recall stage. Dexamethasone (Dex), however, showed no effect on the conditioned neutrophil response. Tyrosine hydroxylase (TH)-positive cells significantly increased in the locus coeruleus (LC), hypothalamus, and cortex but not in the spleen of the conditioned animals. These results indicate that during the conditioned recall stage, the brain signals the splenic neutrophils via the sympathetic nervous system (SNS) by releasing the peripheral catecholamines in spleen. The activation of the SNS, on the other hand, is also under the influence of catecholamines released in the LC. The hypothalamic pituitary (HP) axis, on the other hand, plays no role in the regulation of the conditioned neutrophil response.

Effects of naloxone, glycyrrhizic acid, dexamethasone and deoxycorticosterone in repetitive stress

1. The present study examined the effect of naloxone (NAL), glycyrrhizic acid (GCA), deoxycorticosterone (DOC) and dexamethasone (DEX) on daily repeated 2 h chronic restrained stress (RS) on the locomotor activity (LA) of rats tested in the open field arena to elucidate the possible roles of opioids, glucocorticoids and mineralocorticoids in response to stress. 2. Intact and adrenalectomized (ADX) rats were either injected with 0.1 mL of NAL (0.32 microgram/100 g BW), 2.4 mg/kg DOC or 120 micrograms/kg DEX or had 1.0 mg/mL GCA dissolved in their drinking water or normal saline (for the ADX group) dissolved in their drinking water. 3. In intact groups, treatment with NAL completely blocked the stress response and treatment with GCA, DOC and DEX partially prevented the stress response. Adaptation occurred on either days 4, 5, 6 or 7 for intact rats treated with DEX, DOC, GCA or control rats, respectively. All ADX control rats died following the first 2 h RS. Adrenalectomized rats treated with DEX or DOC adapted later compared with intact rats, while rats given either GCA or NAL were unable to block or adapt to chronic RS. 4. These findings demonstrate that the stress response is primarily mediated by endogenous opioids, in that it is blocked by NAL. Both mineralocorticoids and glucocorticoids, which can act centrally to inhibit endorphins, partially blocked the stress response. The effect of GCA in intact rats was similar to that of both DEX and DOC in intact rats. Adrenalectomized rats treated with GCA (despite their lack of endogenous corticosterone) showed a stress response that was significantly different from the other ADX groups, implying that GCA had effects independent of endogenous corticosterone.

Peptide quantification by tandem mass spectrometry

This manuscript reviews the literature on the mass spectrometry (MS) and tandem mass spectrometry (MS/MS) quantification of biologically important peptides that have been extracted from tissues. The most important aspect of this quantification process is the use of MS/MS to link the protonated molecule ion, (M + H)(+) , of the peptide with one or more of its amino acid sequence-determining fragment ions. The actual name of a peptide cannot be used in any study until the amino acid sequence of that peptide has been firmly established. This article reviews the analytical data obtained from the measurement of opioid peptides in human pituitary tissues. For example, the proopiomelanocortin (POMC)-derived beta-endorphin (BE) and the proenkephalin-derived methionine enkephalin (ME) opioid peptides have been quantified. The biogenesis of opioid neuropeptides is briefly reviewed; critical aspects of pituitary neuropeptides are discussed, including their localization and regulation, and their role in tumor formation; other analytical methods used to detect and measure neuropeptides are mentioned, including radioimmunoassay (RIA), radioreceptorassay (RRA), in situ hybridization, mRNA, and cDNA methods; and the MS and MS/MS methods are described. The use of stable isotope-incorporated synthetic peptide internal standards is described. Data are presented on the measurement of BE and ME in control pituitaries and in pituitary tumors (PRL-secreting and nonsecreting tumors). A significant alteration in the POMC peptide BE was found between the control and tumor tissues. That difference suggests that the POMC neuropeptidergic system had been down-regulated in those tumors. © 1997 John Wiley & Sons, Inc.

Mineralocorticoid and glycyrrhizic acid block stress induced hypotension in rats

1. The aim of this study was to investigate the effect of repeated exposure to stress on tail blood pressure (TBP) of normal as well as GCA (glycyrrhizic acid) and steroid treated rats. Male Sprague-Dawley rats (250 g) were exposed to ether vapour to achieve light anaesthesia prior to TBP recording. Rats were injected with either normal saline or naloxone prior to exposure to stress. Tail blood pressure was recorded daily for 2 weeks. 2. We found that ether stress caused a transient drop in TBP in control as well as in dexamethasone (DEX) treated rats. The stress-induced fall in blood pressure was reduced by naloxone in control rats but not in DEX treated rats. However the transient drop in TBP following stress was not seen in either GCA or deoxycorticosterone (DOC) treated rats. 3. We conclude that first, the reduction in TBP was due to the release of endogenous opioids caused by stress. Second, DOC may block the release of such endogenous opioids, preventing the drop in TBP in response to stress, while DEX did not. Third, GCA caused a similar mineralocorticoid effect on reversing stress induced hypotension.

Regulation of prodynorphin gene expression in the hippocampus by glucocorticoids

The regulation of prodynorphin gene expression by glucocorticoids in the hippocampus was examined in rats that were adrenalectomized (ADX) either 7, 30, 60 and 90 days prior to sacrifice. Peptide levels in the hippocampus of ADX rats were determined by radioimmunoassay and immunocytochemistry. Prodynorphin (PDYN) mRNA was measured by Northern blot analysis and in situ hybridization. A time-dependent decrease in dynorphin A(1-8)(DYN) levels in the hippocampus (18% at 7 days; 44% at 30 days; 58% at 60 days) of ADX rats was found, which was accompanied by a comparable decrease in the abundance of PDYN mRNA. An in situ hybridization analysis revealed that both the number of positively hybridized cells and the number of silver grains per cell were decreased in the dentate gyrus after ADX. The administration of dexamethasone after surgery reversed the peptide and mRNA attenuation induced by ADX. ADX had no effect on the expression of proenkephalin mRNA or [Met5]-enkephalin immunoreactivity in the hippocampus. Examination of thionin-counterstained tissue showed that the dentate granule cell layer was intact. The decrement of DYN expression in this system is proposed to have resulted from the removal of glucocorticoid input and not dentate granule cell loss. This study provides the strong evidence for a differential susceptibility of these two opioid peptides in the hippocampus to the removal of glucocorticoids. In addition, these data provide support for a potentially selective, glucocorticoid-permissive component in PDYN gene expression.

Effect of ovariectomy and estrogen replacement on hypothalamic, pituitary and peripheral blood beta-endorphin levels in the rat

This study was initiated to detect possible changes in beta-endorphin (beta-EP) levels of the hypothalamus, anterior pituitary gland, and peripheral blood of rats after ovariectomy and estrogen administration. Attempts were also made to determine the correlation between peripheral and central levels of beta-EP. Twenty-six Sprague-Dawley rats were decapitated. Nine had intact ovaries (Gr. INT), and 17 were ovariectomized 3 weeks before they were killed. Nine of the ovariectomized rats received estradiol benzoate (EB) (Gr. EB) and the other 8 received peanut oil (Gr. OVX) prior to the decapitation. A beta-EP radioimmunoassay was used to analyze homogenates of the hypothalamus and anterior pituitary, and peripheral blood. In the hypothalamus, beta-EP levels were significantly lower in Gr. INT and Gr. EB than in Gr. OVX. In the pituitary gland and peripheral blood, beta-EP levels were significantly higher in Gr. INT than in Gr. OVX. Pituitary beta-EP levels did not vary between Gr. OVX and Gr. EB, although beta-EP levels in peripheral blood were significantly higher in Gr. EB than in Gr. OVX. No significant correlations were noted in beta-EP levels between the hypothalamus, pituitary gland, and peripheral blood in either Gr. INT, Gr. OVX, or Gr. EB. It appears that EB exerts different effects on beta-EP levels in the hypothalamus, anterior pituitary gland, and peripheral blood, and that beta-EP levels in these regions may be independent of one another.

Hypercapnia depresses nociception: endogenous opioids implicated

Hypoventilation produces hypercapnia which can elevate pain thresholds. Hypercapnia is a potent stressor which releases catecholamines and activates the sympathetic nervous system. Some stressors produce analgesia by releasing endogenous opioids. To determine the roles of endogenous opioids and catecholamines in hypercapnic analgesia, we administered CO2 in the inspired gas mixture to conscious rats. CO2 in the range 5-10% elevated tail flick and leg flexion latencies 2- to 3-fold in both intact and spinalised animals. The effects on reflex latencies but not on paCO2 or pHa were blocked by naloxone (2 mg/kg), and were not present in morphine-tolerant animals. The effects were reduced by dexamethasone but were not changed either by adrenalectomy or by systemic guanethidine, propanolol or phentolamine. Hypercapnia delayed the onset of the late phase of behavioural responses to formalin injected into the plantar surface of the hindpaw. We conclude that moderate hypercapnia powerfully depresses flexor withdrawal responses to noxious stimuli, by a mechanism involving release of endogenous opioids but not systemic catecholamines. This effect may account in part for the elevation in pain threshold during hypoventilation.

Morphofunctional study of mammotropic cells following intraventricular administration of met-enkephalin

An ultrastructural and morphometric study was carried out on the adenohypophyseal mammotropic cells of rats treated intraventricularly with an acute dose (150 micrograms) of Met-enkephalin. In the female rats, clear features of cellular hyperactivity appeared after opioid administration. The changes affected the Golgi complex, the rough endoplasmic reticulum, the mature and immature secretory granules and the images of exocytosis. Such changes did not appear when naloxone was administered before the opioid, and naloxone induced an increase in the numerical density of lysosomal dense bodies with lipoid inclusions. In the male animals, administration of an identical dose of Met-enkephalin caused only a few significant changes, similar to those observed in the controls. It is concluded that Met-enkephalin administered intraventricularly causes evident modifications in the mammotropic cells of female rats whereas such changes in the male animals are not significant.

Interaction of stress and ethanol: effect on beta-endorphin and catecholamines

To examine the interaction of ethanol (ET) and stress on beta-endorphin and catecholamine (CA) levels, male rats pretreated with ET (3.0 g/kg, i.p.) or saline were immobilized for 30 min and killed 90 min after the initial injection. Stress resulted in (a) an increase in plasma levels of norepinephrine (NE, 243%), epinephrine (E, 175%), beta-endorphin (220%) and corticosterone (CS, 151%) and a decrease in dopamine (DA, 54%); (b) a decrease in hypothalamic NE (15%) and beta-endorphin (33%) levels and an increase E (23%) and DA (58%) levels; (c) a decrease in pituitary beta-endorphin levels in both the neurointermediate (23%) and anterior (131%) lobes. Treatment with ET resulted in: (a) an increase in plasma NE (81%), E (53%), CS (71%), and beta-endorphin (33%) levels and decrease in DA (54%); (b) a decrease in the hypothalamic NE (12%) levels and an increase DA (27%) and beta-endorphin (46%) levels, and (c) a decrease in beta-endorphin (15.5%) in the intermediate lobe of the pituitary. Treatment with ET of stressed animals had only a small effect: (a) in plasma NE, E, CS, and beta-endorphin levels decreased by 30, 31, 14, and 36%, respectively; (b) in the hypothalamus DA levels decreased by 40% and beta-endorphin increased by 71%; (c) in the pituitary beta-endorphin increased in both the intermediate lobe (25%) and anterior (50%) lobes. Thus when the data of the stressed ET-treated group is compared to that of the nonstressed saline injected group, none of the measures differ significantly. These results confirm our earlier work indicating a significant interaction of ET and stress.

Neuroendocrine and cardiovascular responses to high-dose corticosteroid therapy in canine endotoxin shock

The neuroendocrine and cardiovascular responses to endotoxin administration and the effects of subsequent high-dose corticosteroid therapy have been investigated in dogs. Shock was induced in anaesthetised animals by a large bolus of E. coli endotoxin (5 mg/kg) followed by a continuous infusion (2 mg/kg per hour). One hour after induction of shock, the circulating volume was expanded using a colloidal gelatin solution. Fifteen minutes later, one group of five animals received a bolus of methylprednisolone sodium succinate 30 mg/kg, while a control group of five animals was given an equivalent volume of isotonic saline. The administration of endotoxin produced reductions in mean arterial pressure, cardiac index and left ventricular dp/dtmax, together with increases in systemic and pulmonary vascular resistances. These haemodynamic changes were associated with increases in arterial plasma levels of adrenaline, noradrenaline, cortisol, immunoreactive beta-endorphin and immunoreactive metenkephalin. Cardiovascular improvement followed volume replacement and was associated with reductions in circulating catecholamines. No significant haemodynamic or neuroendocrine changes were demonstrated in the 2 h following steroid therapy.

The effects of immobilization stress on beta-endorphin levels are modulated by testosterone

Immunoreactive beta-endorphin (IR-BE) levels were determined in the anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL) and the hypothalamus of castrated male rats and castrated male rats treated with testosterone proprionate (TP), subsequent to exposure to acute (once for 45 min) or chronic (45 min each day for 15 consecutive days) immobilization stress. Acute stress resulted in a reduction in the concentration of IR-BE in the AP of castrated male rats, which was potentiated by TP. The concentration of IR-BE in the NIL was elevated by acute stress in castrated male rats and was not affected by acute stress in castrated male rats administered TP. Exposure to chronic immobilization stress elevated the concentration of IR-BE in the AP of castrated animals and not animals treated with TP. The concentration of IR-BE in the NIL of castrated animals was not altered by chronic immobilization. Chronic stress did result in a significant rise in the level of IR-BE in the NIL of castrated male rats given TP. Hypothlamic IR-BE levels in castrated male rats were reduced by TP and were not influenced by acute or chronic stress. Chromatographic analysis indicated that acute and chronic stress promoted the accumulation of beta-lipotropin rather than beta-endorphin in the AP. This effect was attenuated by TP. Beta-endorphin was the only form of immunoreactivity detected in the NIL and hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Analgesia in defeated mice: evidence for mediation via central rather than pituitary or adrenal endogenous opioid peptides

Mice subjected to defeat in a social conflict paradigm display an analgesic response that is apparently mediated by endogenous opioids. It is blocked by naloxone and shows full cross-tolerance to and from morphine. The present study investigated the contribution of sources of endogenous opioids outside of the central nervous system, namely the pituitary and adrenal glands. Treatment known to enhance (metyrapone pretreatment), reduce (2% saline in the drinking water) or block (dexamethasone pretreatment) the release of beta-endorphin from the anterior pituitary did not affect the display of analgesia in defeated mice. Similarly, treatments known to enhance (reserpine pretreatment) or block release of enkephalins (removal of the adrenals or hexamethonium pretreatment) from the adrenal medulla also failed to influence defeat-induced analgesia in the expected manner. If anything, adrenalectomy enhanced and reserpine pretreatment suppressed the analgesic response to defeat. The data are discussed in terms of providing evidence that defeat-induced analgesia is mediated primarily by endogenous opioids released and acting within the central nervous system.

Behavioral stress impairs long-term potentiation in rodent hippocampus

A number of hormones secreted from the pituitary-adrenal system during stress affect learning and memory processes. The phenomenon of hippocampal long-term potentiation (LTP) is viewed by many as a putative mechanism of memory storage and has proved a most valuable model for study of neuronal plasticity at the cellular level. The present study was conducted to investigate the possibility that stressful events which occur prior (in vivo) to the preparation of brain slices may influence the electrophysiology of the in vitro hippocampal explant when tested for LTP. Adult male rats (Long-Evans male X Sprague-Dawley female) were pair-housed 1 week prior to testing. One animal in each pair was either placed in a restraining tube for 30 min and received no tail shocks (Restraint) or placed in a restraining tube and received tail shocks (1 microA, 1 s) every minute for 30 min (Restraint + Shock). The other animal in each pair was taken directly from the home cage and received no restraint or tail shock (Control). In vitro hippocampal slices were then prepared immediately from these animals according to standard methods. Our results demonstrate a marked impairment of LTP in hippocampal explants taken from rats exposed to stress. The significance of this result with respect to cellular mechanisms underlying the relationship between stress, cognition, and learning is discussed.

Neurotransmitters and estrogen interact to affect beta-endorphin levels in castrated female rats

The possibility of an interaction between neurotransmitter systems and estrogen in affecting levels of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP), the neurointermediate lobe of the pituitary (NIL) and the hypothalamus was investigated in ovariectomized (OVX) female rats. Chronic administration of the dopamine antagonist, haloperidol (HALO), had no effect on IR-BE levels in the AP. By contrast, the content of IR-BE in the NIL was increased and the content of IR-BE in the hypothalamus was decreased by HALO. Chronic treatment with estradiol benzoate (EB) produced a decrease in IR-BE in all three tissues. The effect of EB on IR-BE levels in the AP and NIL was reversed by administration of HALO, while EB and HALO appeared to act independently on the hypothalamus. Gel chromatography indicated that alterations in IR-BE in the AP corresponded to similar changes in beta-endorphin (BE) and beta-lipotropin (LPH) and that BE alone comprised the immunoreactivity detected in the NIL and hypothalamus regardless of treatment. Chronic treatment with the alpha-adrenergic agonist, clonidine (CLON), increased, whereas treatment with EB decreased, IR-BE levels in the AP, NIL and hypothalamus. EB attenuated the effect of CLON on IR-BE levels in the AP and hypothalamus. Chronic treatment with CLON appeared to promote the formation of BE in the AP, whereas the proportions of BE and LPH were similar in the AP of controls and animals treated with EB or EB and CLON. BE alone was detected in the NIL and hypothalamus of treated and control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Further evidence for beta-endorphin involvement in the long-lasting antagonistic effect of caerulein on amphetamine hyperactivity in rats

The involvement of beta-endorphin (beta-END) in the long-lasting antagonistic effect of caerulein (CLN) on amphetamine (AMP) hyperactivity in rats was investigated. Injection of beta-END antiserum into the lateral ventricle or the nucleus accumbens abolished the CLN effect, whereas the injection of normal rabbit serum had no effect on the susceptibility to AMP for about 2 weeks, as observed in intact rats. Moreover, the CLN effect was blocked by long-term dexamethasone treatment, which inhibits beta-END synthesis. These findings indicate that beta-END in the nucleus accumbens plays an important role in producing the long-lasting effect on CLN, suggesting that dopamine release induced by AMP in the nucleus accumbens is presynaptically inhibited by opiate receptors activated by beta-END.

Dexamethasone differentially alters naltrexone effects on vasopressin and oxytocin release during tail electroshock

The origin of endogenous opioid peptides that inhibit release of vasopressin (VP) and oxytocin (OT) into the bloodstream after tail electroshock was investigated. We hypothesized that endogenous opioid peptides derived from the anterior pituitary reduced secretion of VP and OT during this stimulus. To test this hypothesis, dexamethasone (DEX) was used to preferentially suppress release of endorphins with ACTH from the anterior pituitary. We evaluated the effects of an opiate receptor antagonist, naltrexone, on the rise in plasma [VP] and [OT] after tail electroshock in male Sprague-Dawley rats given DEX either chronically or acutely before the shock. In the chronic study rats were injected SC daily with saline (3.2 ml/kg) or DEX (0.2 mg/kg) for 17 days. In the short term study, rats were injected IP with saline (5 ml/kg) or DEX (0.5 mg/kg) the day before and again 105 min prior to tail electroshock. Thirty min (chronic study) or 90 min (acute study) after saline or DEX was given on the last day, rats were injected SC with saline (1 ml/kg) or naltrexone (1 mg/kg). Fifteen min later, animals received tail electroshock (41 V, 30 sec) and were decapitated 15 sec after shock was completed. Control animals were treated similarly but not shocked. Amounts of VP and OT in plasma and the neurointermediate lobe were quantified by RIA. [VP] and [OT] were elevated in plasma of all rats given tail electroshock. Greater increases (p less than 0.05) in hormone concentrations were measured in plasma of shocked rats treated with DEX.(ABSTRACT TRUNCATED AT 250 WORDS)

Opiate dependence and withdrawal--a new synthesis?

There is a growing body of evidence to suggest that adrenocorticotropin (ACTH) may have a physiological role as an endogenous contra-opioid agonist. In addition to having appreciable affinity for opiate receptors and inducing many behavioural and intracellular effects opposite to those observed following opioid administration, ACTH may interact with endorphins in a mutually antagonistic manner. On the basis of these data a model of opiate dependence is proposed whereby several aspects of the opiate abstinence syndrome may be attributed to the excitatory actions of ACTH acting at opiate receptors. Thus, it may be predicted that opiate antagonist administration during primary abstinence should significantly attenuate many aspects of this behavioural syndrome. The present study was conducted in order to investigate this hypothesis. Results indicated that whilst naloxone (1.5 mg/kg) exerted little influence in non-dependent animals, it significantly attenuated abstinence-exacerbated grooming, body shaking, teeth chattering and sneezing, in addition to completely antagonizing withdrawal hyperalgesia in post-dependent animals. These data are consistent with the proposed existence of an endogenous contra-opioid ligand, the antagonism of which markedly reduces the severity of the morphine withdrawal syndrome.

Autoimmunization against beta-endorphin increases food intakes and body weights of obese rats

Opioid peptides in the brain are postulated to mediate the hunger component of the control of food intake and regulation of body weight and concentrations are increased in the pituitaries of genetically obese rodents. However, systemic increases in opioids have been associated with satiety. Thus a chronic decrease in systemic concentrations of the opioid beta-endorphin induced by autoimmunization was predicted to increase food intake and body weight. Zucker obese (n = 20, 568 +/- 13 g) and lean (n = 20, 299 +/- 16 g) rats were autoimmunized against bovine serum albumin (BSA) or BSA conjugated to beta-endorphin (BSA-BE). Eight weeks after immunization serum from BSA-BE rats bound at least 7 times the circulating concentration of beta-endorphin. Food intakes were greater in BSA-BE obese (31.7 vs. 30.4 g/day, p less than 0.001) and lean rats (21.4 vs. 21.0 g/day, p less than 0.007) during weeks 5-8 and only obese rats, weeks 9-12 (31.8 vs. 30.3 g/day, p less than 0.009). Body weight gains were greater for BSA-BE than BSA obese rats during weeks 1-4 (1.34 vs. 0.92 g/day, p less than 0.05) and 9-12 (0.95 vs. 0.43 g/day, p less than 0.01). At 8 weeks the plasma concentrations of "free" beta-endorphin were decreased 78% (34 vs. 154 pmol/l, p less than 0.001) and "total" ("free" plus antibody-bound) beta-endorphin were increased (427 vs. 101 pmol/l, p less than 0.001). These results suggest that systemic concentrations of beta-endorphin may play an important role in the control of food intake and regulation of energy balance.

Release of immunoreactive beta-endorphin in vitro from pituitaries of young and old male rats

The release of immunoreactive beta-endorphin (IR-BE) in vitro from the anterior pituitary (AP) and the neurointermediate lobe of the pituitary (NIL) from old male rats was significantly greater than from the AP and NIL from young male rats. In addition, the content and concentration of IR-BE in the AP and NIL was significantly greater in old than in young male rats, as was the concentration of IR-BE in the plasma. Chromatographic analysis revealed that in old male rats, the increase in IR-BE contained in and released by the AP and NIL, and found in the plasma, represented an increase in a peptide which coeluted with beta-endorphin rather than beta-lipotropin. These data suggest that both the AP and the NIL contribute to the elevation in plasma levels of IR-BE observed in old male rats, and that the increase in pituitary and plasma IR-BE in old male rats represents an increase in beta-endorphin.

Experimental dissociation of food intake and plasma beta-endorphin following 2-deoxy-D-glucose in rats

The present studies were undertaken to further assess the role of plasma beta-endorphin (beta-EP) in the hyperphagia induced by the glucose antimetabolite, 2-deoxy-D-glucose (2-DG). Plasma concentrations of immunoreactive beta-EP (ir-beta-EP) were measured at the end of the first hour of feeding in all animals treated with 400 mg/kg 2-DG. Previous studies had shown a consistent, positive association between 2-DG hyperphagia and plasma ir-beta-EP concentrations, but the present data revealed dissociations between hyperphagia and plasma ir-beta-EP. Dexamethasone administration blocked the 2-DG-induced rise in plasma ir-beta-EP, but had no effect on the 2-DG hyperphagia measured at 1 hour. Forced drinking of a 2% NaCl solution decreased 2-DG hyperphagia, but not the 2-DG induced rise in plasma ir-beta-EP. Thus, elevations in plasma ir-beta-EP are not necessary for the full expression of 2-DG-induced hyperphagia in dexamethasone-treated rats. Furthermore, decreased feeding responses to 2-DG could coexist with increased levels of plasma ir-beta-EP in NaCl-treated normal rats. Elevations in plasma ir-beta-EP do not appear to be the critical opiate link in 2-DG induced hyperphagia.

Dexamethasone suppresses beta-endorphin in humans

Studies assessing the effect of glucocorticoids on beta-endorphin regulation in man have yielded inconsistent results. As measured by a highly specific beta-endorphin assay procedure, plasma immunoreactive beta-endorphin (irB-EP) in six healthy subjects was significantly suppressed, along with cortisol, after a 2 mg oral dose of dexamethasone (DEX) (pre-DEX mean +/- S.E.M. in pg/ml = 15.3 +/- 2.0, post-DEX = 9.1 +/- 0,5 t = 3.46, p less than 0.01) but not after placebo (pre-placebo = 17.8 +/- 2.9, post-placebo = 17.2 +/- 1.5, t = 0.27). A less specific B-EP assay system, which yielded spurious irB-EP values (102 +/- 2.3 pg/ml) in plasma stripped of B-EP silicic acid, did not detect this DEX-induced change in plasma irB-EP levels (pre-DEX = 119 +/- 9.3, post-DEX = 112 +/- 5.0, t = 0.64; pre-placebo = 118 +/- 6.4, post-placebo = 119 +/- 4.3, t = 0.32). The methodological artifact encountered in this relatively non-specific assay system appears to account for the failure of an earlier study to demonstrate DEX suppression of irB-EP in man.

Response of the rat brain beta-endorphin system to novelty: importance of the fornix connection

In control rats, a step-down inhibitory avoidance training trial using a 0.8 mA footshock, or simple exposure to the training apparatus without footshock, was followed by a decrease of beta-endorphin-like immunoreactivity measured in the hypothalamus and ventral thalamus. The effect of inhibitory avoidance training was also measured in rats submitted to a brain sham operation, to bilateral transection of the dorsal fornix, to anterior or to posterior hypothalamic deafferentation, to adrenal medullectomy, to an adrenal sham operation, to 16 daily ip injections of 0.2 mg/kg dexamethasone, or to 16 daily ip injections of 1 ml/kg saline. The diencephalic beta-endorphin-like immunoreactivity response to training was abolished by fornix transection and was unaffected by all other treatments. This suggests that the response is not mediated by anterior or posterior neural afferents to the hypothalamus, or by a hypersecretion of epinephrine by the adrenal medullae, or of ACTH by the pituitary gland. The response, instead, appears to require the integrity of the pathway that sends projections from the septo-hippocampal system to the hypothalamus. Previous evidence had suggested that the diencephalic beta-endorphin-like immunoreactivity response to training is a result of novelty, and the septo-hippocampal system has been postulated to play a role in the registration of novelty.

Naloxone injections into the periaqueductal grey area and arcuate nucleus block analgesia in defeated mice

In a situation of social conflict, mice that are defeated by an opponent exhibit a marked analgesia. Microinjections of naloxone (1 or 10 micrograms) into the periaqueductal grey area (PAG) or into the region of the arcuate nucleus prior to the defeat prevented the emergence of analgesia. Microinjections of morphine (5 micrograms) into these sites had previously been shown to produce profound analgesia. Mice whose adrenals were removed rapidly developed analgesia when attacked by a stimulus animal. Injection of naloxone into PAG also antagonized defeat-induced analgesia in adrenalectomized mice. These observations indicate that sites and processes in the brain rather than in the periphery are responsible for the development of analgesia in mice that are subjected to social defeat.

Studies of naloxone-induced secretion of beta-endorphin immunoreactivity in dogs

The stimulating effect of naloxone on plasma beta-endorphin immunoreactivity (beta EI) was examined in dogs. Intravenous naloxone at 5, 1, or 0.1 mg/kg caused a significant increase in beta EI while doses of 0.01 or 0.001 mg/kg had no effect. The peak plasma beta EI levels occurred at 25 mins after naloxone. The neurotransmitter and antagonists metergoline, atropine, diphenhydramine and phentolamine all failed to significantly alter basal beta EI secretion; further, they all failed to prevent the increase in beta EI resulting from naloxone administration. Dexamethasone prevented the naloxone-induced rise in beta EI. Our results suggest naloxone's effect on beta EI is not mediated through several neurotransmitter systems known to affect ACTH secretion. Additionally, beta EI secreted in response to naloxone appears to originate mainly from the anterior lobe of the pituitary.

The calcium antagonist nimodipine increases beta-endorphin release from rat hypophysis through an action on adrenal glands. An "in vivo" and "in vitro" study

Intravenous injection of nimodipine (1, 10 and 100 micrograms/Kg) raised plasma ACTH and beta-endorphin (beta-EP) level and reduced pituitary beta-EP content, in the rat. These effects were sharp and short-lasting. Nimodipine (10(-8), 10(-7), 10(-6) M) did not change basal and hypothalamic extract stimulated beta-EP release from pituitary tissue in vitro. Basal release of corticosterone from adrenal glands, superfused in vitro with the calcium antagonist (10(-7) - 10(-6) M), was not modified. However, ACTH-induced release was strongly reduced. Since glucocorticoids feedback regulates biosynthesis and cleavage of pro-opiocortin, nimodipine, which reduces adrenal gland responsiveness to ACTH, might reflexly increase beta-EP release from hypophysis.

Adrenalectomy abolishes the stress-induced increase in pituitary cyclic AMP

We have previously demonstrated that various stressors increase pituitary cyclic AMP in vivo in the rat. In the course of studying the mechanisms mediating this response, we examined the effect of bilateral adrenalectomy on footshock-induced increases in pituitary cyclic AMP. In unoperated rats, intermittent footshock markedly increased pituitary levels of cyclic AMP and plasma levels of corticosterone and prolactin. Adrenalectomy completely abolished the stress-induced increase in pituitary cyclic AMP. The marked increase in plasma prolactin following footshock was not affected by adrenalectomy. Our results indicate that adrenal factors are involved in the stress-induced increase in pituitary cyclic AMP.

Regulation of body temperature and nociception induced by non-noxious stress in rat

The effects of 3 different non-noxious stressors on body temperature (Tb) were investigated in the rat: (1) loose restraint in cylinders, (2) removal of the rats from cylinders, exposure to a novel environment and replacement in cylinders, a stressor called here 'novelty', and (3) gentle holding of the rats by the nape of the neck. Loose restraint and 'novelty' produced hyperthermia. On the contrary, holding induced hypothermia. Hypophysectomy (HX) reduced basal Tb, abolished restraint hyperthermia and reduced both 'novelty' hyperthermia and holding hypothermia. Dexamethasone ( DEXA ) had no effect upon either restraint or novelty hyperthermia but reduced the hypothermia. Naloxone (Nx) produced a slight fall in basal Tb accounting for its reduction of restraint and 'novelty' hyperthermias ; it did not affect holding hypothermia. The inhibitory effects of HX suggest a participation of the pituitary in the hyperthermias ; the neurointermediate lobe would be involved as the hyperthermias were not affected by DEXA , which is known to block the stress-induced release of pituitary secretions from the anterior lobe but not from the neurointermediate lobe. In contrast, substances from the anterior lobe might participate in hypothermia due to holding since it is reduced by HX and DEXA . As to the effects of Nx, endogenous opioids would not be significantly involved in the thermic effects of the stressors used in this study; they might play, if any, only a minor role in the regulation of basal Tb. These results are compared with those previously obtained on nociception using the same non-noxious stressors. It emerges that, depending on the stressor, different types of association between thermoregulation and nociception may occur, i.e. hyperthermia with analgesia, hyperthermia with hyperalgesia and hypothermia with hyperalgesia.

Ethanol dependence and the pituitary adrenal axis in mice. II. Temporal analysis of dependence and withdrawal

The effects of ethanol dependence and withdrawal on pituitary hormone content and corticosterone release were investigated in AKR/J male mice in a vapor chamber. Both chronic ethanol inhalation and ethanol withdrawal were associated with increased adenohypophyseal-adrenocortical activity. Operationally, ethanol exposure was a stressor. Both physical dependence and withdrawal led to increased secretion/synthesis ratios of peptide hormones. The temporal pattern of pituitary ACTH-IR content changes was different from that of beta-endorphin-IR and alpha-MSH-IR. Differences in the pattern of ACTH-IR and alpha-MSH-IR most probably represent lobe-specific differences in the response to chronic ethanol exposure and withdrawal.

Immunological characterization of endorphins, adrenocorticotropin, and melanotropins in frog hypothalamus

To gain more information about the nature and regulation of opiomelanocorticotropic peptides in the frog diencephalon, radioimmunological determinations of alpha- and beta-MSH. ACTH, beta- and gamma-endorphins have been performed in hypothalamic extracts. Sephadex G-50 gel filtration revealed a single peak of alpha-MSH-like immunoreactivity (alpha-MSH-LI) comigrating with synthetic alpha-MSH. Two peaks of ACTH-LI were observed; the major one eluting slightly before human ACTH. Using a porcine beta-endorphin antiserum which exhibited 45% cross-reaction (on a molar basis) with ovine beta-LPH, one major peak of beta-endorphin-LI and two additional components were observed in the elution profile; none of these peaks coeluted with synthetic porcine beta-endorphin. No significant beta-MSH or gamma-endorphin-LI was detected. To investigate a possible role of glucocorticoids on the level of opiomelanocorticotropic peptides in frog hypothalamus, 60 male frogs were treated with dexamethasone (300 micrograms/day) during 8 days. Dexamethasone treatment did not modify the chromatographic distribution and the total amount of alpha-MSH-LI and ACTH-LI in hypothalamic extracts. A slight (15%) increase in beta-endorphin-LI was even observed after 8 days of dexamethasone treatment. From these results it is concluded that three classes of opiomelanocorticotropic peptides are present in the frog hypothalamus in the following order of concentration: beta-endorphin-LI greater than alpha-MSH greater than ACTH. In addition, circulating glucocorticoids which significantly reduce the concentration of opiomelanocorticotropic hormones in the distal lobe of the frog pituitary (S. Jégou, M. C. Tonon, F. Leboulenger, C. Delarue, J. Côté, G. Pelletier, and H. Vaudry (1981a). In "Adv. Physiol. Sci.' E. Stark, G. B. Makara, Zs. Acs, and E. Endröczi, eds., Vol. 13, pp. 129-133. Pergamon, Budapest.) do not modify the amount of these peptides in the hypothalamus.

Prolonged intermittent footshock stress decreases Met and Leu enkephalin levels in brain with concomitant decreases in pain threshold

The influence of a 21 day intermittent footshock regimen upon enkephalin levels in brain and adrenals was examined in the rat. Changes in pain sensitivity as well as analgesic and hyperthermic responsiveness to morphine (7.5 mg/kg) were also monitored. Following the stress regimen, Met and Leu enkephalin levels were decreased by 40 to 50% in brain, but were unchanged in adrenals. Post-stress pain thresholds were markedly decreased in stressed animals while the analgesic properties of morphine were enhanced. Core body temperature of stressed animals was significantly raised, but the hyperthermic response to morphine was unchanged.

Opioid modulation of appetite

The discovery of opiate receptors and endogenous opioid peptides within the central nervous system has resulted in a number of speculations concerning the physiological significance of these peptides. In the present article, we review the evidence suggesting a primary role for some of the opioid peptides as regulators of ingestive behavior. In particular, we elaborate a hypothesis in which we suggest that in some species opioid peptides may play a role as a tonic inducer of ingestive behaviors, held in check by a variety of neuropeptides and monoamines. This review explores in detail the role of the opioid peptides as major mediators of the reward system and as a link between reward and feeding behaviors. Finally, a teleological role for opioid peptides in species preservation, which may explain the discrepancies in the role of the opioid peptides in feeding behavior in different species is proposed. It is suggested that the feeding profile of the animal provides important clues as to whether or not the animal has an opiate-sensitive feeding system. We stress that interactions with ingested nutrients and the milieu interieur provide an important means by which animals modulate the opiate-entrained feeding drives.

Circadian variation of beta-endorphin-like immunoreactivity in neurointermediate pituitary

Immunoreactive beta-endorphin-like activity (-IR) and ACTH-IR were determined in rat pituitary lobes and plasma at 4-hr intervals over a 24-hr period. In addition, we measured beta-endorphin-IR in discrete hypothalamic nuclei, and plasma corticosterone levels at the same time points. Significant and replicable circadian variation was detected only in concentrations of beta-endorphin-IR in neurointermediate pituitary and in plasma corticosterone concentrations.

Relationship between plasma concentrations of immunoreactive beta-endorphin and food intake in rats

Periods of increased food intake in male rats were characterized by significant elevations in the plasma concentrations of immunoreactive beta-endorphin (beta-ep). Administration of 2-deoxy-D-glucose (400 mg/kg) produced rapid and concurrent increases in both food intake and plasma beta-ep. Administration of insulin (10 units/kg) produced large delayed increases in food intake but only modest delayed increases in plasma beta-ep. Spontaneous nocturnal feeding was associated with increased plasma beta-ep. Increases in daytime food intake in rats subjected to 24 hr of food deprivation were also characterized by elevated plasma beta-ep. In all cases examined, those feeding behaviors in male rats which were subject to inhibition by naloxone were characterized by elevated concentration of plasma beta-ep.

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

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

Cold stress in the rat induces parallel changes in plasma and pituitary levels of endorphin and ACTH

Endorphin and ACTH-like materials levels in rat plasma and pituitary were measured by radioimmunoassay under baseline and cold stress conditions. Cold stress significantly increased plasma beta-endorphin and ACTH immunoreactivity. A rise in these two peptides was also found in the neurointermediate lobe of the pituitary, while in the anterior lobe their levels were unaffected. These findings suggest that the rise of beta-endorphin and ACTH content in the neurointermediate lobe occurs as a compensatory biosynthetic mechanism for the peptides released from the adenohypophysis.

Sex-related difference in the rat pituitary [Met5]-enkephalin level--altered by gonadectomy

Ontogenetic study of the rat pituitary [Met5]-enkephalin-like immunoreactivity (ME-LI) revealed that a sex-related difference in the level of this peptide began at 35 days of age. By 70 days of age, the level of male ME-LI was twice that of the female. Castration reduced the ME-LI in male rats and increased the ME-LI in female rats. These results suggest a possible role of sex hormones in regulating the pituitary enkephalin system.

Regulation of pituitary and brain enkephalin systems by estrogen

The roles of estrogen in the regulation of pituitary and brain enkephalin systems were studied. A sex-related difference in the levels of enkephalins was observed in the anterior lobe of rat pituitary. Administration of estradiol to male rats caused a marked reduction in the levels of enkephalins in the anterior lobe. Ovariectomy produced a significant increase in the enkephalin levels of the same region but this increase was completely prevented by replacement with estradiol. These results suggest a physiological role of estrogen in the regulation of pituitary enkephalin systems. Repeated injections of haloperidol elicited effects similar to those of estrogen on the pituitary and brain enkephalin levels; namely, striatal enkephalin levels were increased whereas pituitary enkephalin levels were decreased after long-term treatment with these two compounds. These results raise the possibility that the regulation of estrogen on enkephalin systems may in part be mediated through a dopaminergic mechanism.

Footshock induced analgesia is dependent neither on pituitary nor sympathetic activation

A variety of environmental stimuli have been demonstrated to produce behavioral analgesia. Of these, footshock has been shown to be capable of differentially eliciting opiate or non-opiate analgesia dependent upon the body region shocked; front paw and hind paw shock produce opiate and non-opiate analgesia, respectively. In addition, footshock can be used as a conditioned stimulus to elicit classically conditioned opiate analgesia. A question which arises is whether such plain inhibition is mediated by neural or hormonal pathways. Evidence exists which suggests that endogenous opioids in the pituitary and adrenal medulla may be involved in the production of environmentally induced analgesia. Furthermore, epinephrine administration has previously been shown to produce pronounced pain inhibition. However, the present series of experiments demonstrate that the pituitary-adrenal cortical and sympathetic-adrenal medullary axes are neither necessary nor sufficient for the production of footshock induced analgesia (FSIA). Hypophysectomy failed to attenuate front paw FSIA, hind paw FSIA or classically conditioned analgesia indicating that pituitary beta-endorphin or other pituitary factors are not necessary for the production of analgesia. Adrenal opioids and peripheral catecholamines are also not critical since front paw FSIA was potentiated by adrenalectomy or total sympathetic blockade. Furthermore, pituitary and sympathetic activation are not sufficient for the production of analgesia since low thoracic spinalization allows normal hormonal response to front paw shock yet abolishes shock-induced inhibition of the spinally mediated tail flick reflex. These results provide strong evidence that front paw FSIA, hind paw FSIA and classically conditioned analgesia are mediated by neural, rather than hormonal pathways and provide further parallels between these forms of environmental analgesia, morphine analgesia and brain stimulation produced analgesia.

Opiate vs non-opiate footshock-induced analgesia (FSIA): the body region shocked is a critical factor

Previous work has demonstrated that footshock can elicit either opiate or non-opiate analgesia. The present study has demonstrated that one critical factor determining the involvement of endogenous opioids is the body region shocked. Using 90 s shock, front paw shock produced an opiate analgesia which was significantly antagonized by as little as 0.1 mg/kg systemic naloxone and morphine tolerance. In the latter experiment, a parallel recovery of the analgesic potencies of both front paw shock and morphine was observed following 2 weeks of opiate abstinence. In contrast, hind paw shock produced a non-opiate analgesia which failed to be attenuated by 20 mg/kg systemic naloxone and showed no cross-tolerance to morphine. Since identical shock parameters were used for front paw and hind paw shock in the systemic naloxone experiments, stress per se clearly cannot be the crucial factor determining the involvement of endogenous opioids in footshock-induced analgesia. These results were discussed with respect to clinical treatments of pain which utilize somatosensory stimulation.

The influence of selective adeno- and neurointermedio-hypophysectomy upon plasma and brain levels of beta-endorphin and their response to stress in rats

Selective ablation of the anterior lobe (AL) of the pituitary led to a fall in basal plasma levels of beta-endorphin immunoreactivity (beta-EI) at 3 and 20 weeks post-surgery (p.s.). Further, the stress-evoked rise in circulating levels of beta-EI was abolished. This operation did, however, severely deplete the beta-EI content of the neurointermediate lobe (NIL). Removal of the NIL did not, in contrast, decrease the beta-EI content of the AL but depressed basal plasma levels of beta-EI at 3 weeks p.s. and attenuated, but did not abolish, the increase in these elicited by stress at both 3 and 20 weeks p.s. In rats not possessing a NIL, a secretion of beta-EI into plasma can thus occur. The possibility that NIL pools of beta-EI contribute to circulating levels of beta-EI is discussed. Removal of the AL depressed the beta-EI content of the hypothalamus and periventricular tissue at 3 and 20 weeks p.s. The Met-enkephalin-immunoreactivity (ME-I) content of the hypothalamus was, in contrast, unaffected. These animals still responded to stress at 20 weeks p.s. with a significant fall in hypothalamic levels of beta-EI. Extirpation of the NIL did not, in contrast, change brain levels of either beta-EI or ME-I. The presence of the AL, but not the NIL, is thus essential for the maintenance of usual levels of beta-EI and ME-I in the brain.

Effect of stress and dexamethasone on immunoreactive beta-endorphin levels in rat hypothalamus and pineal

In response to mild stress the levels of immunoreactive beta-endorphin in rat anterior pituitary, hypothalamus and pineal fell within 10 minutes from 210 to 129 pmol/lobe, 1.47 to 0.89 pmol/mg protein and 2.53 to 0.41 pmol/gland, respectively. No alterations were found to take place in beta-endorphin levels in posterior pituitary or plasma. Dexamethasone pretreatment given 18 h prior to stress resulted in significantly greater reduction of beta-endorphin levels in hypothalamus and pineal than stress alone--hypothalamic levels fell to 0.73 pmol/mg protein and pineal to 0.07 pmol/gland. Plasma beta-endorphin levels in dexamethasone pretreated stressed rats were significantly lower than in intact rats (42 fmol/ml vs. 98 fmol/ml). The almost complete disappearance of beta-endorphin from the pineal in response to stress and dexamethasone suggests that pineal does not itself synthesize the hormone but only utilizes and/or stores it. Gel filtration analysis of the beta-endorphin immunoreactivity in tissue extracts and plasma showed that anterior pituitary and plasma contain three immunoreactive components, eluting like beta-endorphin, beta-lipotropin and proopiocortin, whereas only beta-endorphin-like material was detected in posterior pituitary, hypothalamus and pineal.