Beta-endorphin Secretion Research Articles

A paracrine paradigm for in vivo gene therapy in the central nervous system: treatment of chronic pain.

A limitation of current gene therapy efforts aimed at central nervous system disorders concerns distribution of vectors on direct injection into neural tissue. Here we have circumvented this problem by transferring genes to the meninges surrounding the spinal cord, achieving an in vivo gene transfer paradigm for treating chronic pain. The therapeutic vector consisted of a recombinant adenovirus encoding a secreted form of the potent endogenous opioid beta-endorphin. In an inflammation model of persistent pain, administration of the vector into the cerebrospinal fluid (CSF) surrounding the spinal cord transduced meningeal pia mater cells. The resulting increase in beta-endorphin secretion attenuated inflammatory hyperalgesia, yet had no effect on basal nociceptive responses. This demonstration of a gene transfer approach to pain treatment can be generalized to neurodegenerative disorders in which broad spatial distribution of therapeutic effect is critical.

Lactic acid does not directly activate hypothalamic-pituitary corticotroph function.

The role that metabolic products play in regulating the hypothalamic-pituitary-adrenal (HPA) axis during strenuous exercise is speculative. This investigation examined the extent to which lactic acid, a major metabolite of anaerobic exercise, directly affects hypothalamic-pituitary function. Specifically, beta-endorphin secretion was measured from AtT-20 (D-16) mouse corticotroph tumor cells treated either acutely (15 min - 180 min) or chronically (1 day - 3 day) with physiologic levels of lactate (0. 5 x 10-3 M to 5 x 10-2 M) or lactate in combination with the corticotroph releasing factors: corticotroph releasing hormone (CRH), arginine vasopressin (AVP), norepinephrine and/or epinephrine. Findings with AtT-20 cell cultures were shown to be representative of responses in primary cultures of rat anterior pituitary. Lactic acid did not alter the spontaneous release of beta-endorphin by AtT-20 cells under either acute or chronic conditions. While CRH, norepinephrine, and epinephrine evoked significant increases in beta-endorphin release, lactate, in combination with these secretagogues did not alter their effects. Similarly, lactic acid failed to alter basal or stimulated release of beta-endorphin by primary cultures of rat anterior pituitary. The addition of lactate (3 x 103 M) to rat hypothalamic explants did, however, produce a modest but significant reduction in spontaneous CRH release, suggesting that lactate may facilitate the return to basal secretion following exercise. The present findings show that physiologic concentrations of lactate have no effect, either alone or in combination with other pituitary secretagogues, on corticotroph secretion. Whereas a physiologic action for lactate within the hypothalamus is possible, the present findings indicate that lactate is an inhibitor of CRH release. Thus, lactate does not appear to play a direct role in the profound activation of the HPA axis that occurs in response to strenuous exercise.

An insulin-dependent hypoglycaemia induced by electroacupuncture at the Zhongwan (CV12) acupoint in diabetic rats.

Acupuncture at the Zhongwan acupoint has been widely used in traditional Chinese medicine to relieve symptoms of diabetes mellitus. Our study investigated the effect on plasma glucose of electroacupuncture applied at the Zhongwan acupoint in rat diabetic models. Plasma concentrations of insulin, glucagon and beta-endorphin- were also determined using radioimmunoassay. A decrease in plasma glucose was observed in rats after electroacupuncture (15 Hz, 10 mA) for 30 min at the Zhongwan acupoint. This was observed in normal rats and rat models with Type II (non-insulin-dependent) diabetes mellitus. No significant effect on plasma glucose was observed in rat models with Type I (insulin-dependent) diabetes mellitus: neither the streptozotocin (STZ)-induced diabetic rats nor the genetic (BB/W) rats. Further, the hypoglycaemic action of electroacupuncture stimulation disappeared in rats with insulin-resistance induced by an injection of human long-acting insulin repeated daily to cause the loss of tolbutamide-induced hypoglycaemia. An insulin-related action can thus be hypothesised. This hypothesis is supported by an increase in plasma insulin-like immunoreactivity after electroacupuncture stimulation in normal rats. Participation of glucagon was ruled out because there was no change in plasma glucagon-like immunoreactivity resulting from electroacupuncture stimulation. In addition to an increase in plasma beta-endorphin-like immunoreactivity, the plasma glucose lowering action of electroacupuncture stimulation at Zhongwan acupoint was abolished by naloxone in a sufficient dose to block opioid receptors. Thus we suggest that electroacupuncture stimulation at the Zhongwan acupoint induces secretion of endogenous beta-endorphin which reduces plasma glucose concentration in an insulin-dependent manner.

Alterations in brain and pituitary beta-endorphin content in genetically epilepsy-prone rats.

We measured beta-endorphin concentrations in the anterior and neurointermediate lobes of the pituitary gland and in microdissected brain regions of moderate-seizure genetically epilepsy-prone rats (GEPR-3), severe-seizure GEPR-9s and Sprague-Dawley non-epileptic control rats. Plasma concentrations of beta-endorphin and beta-melanocyte-stimulating hormone (alpha-MSH) were also measured as indicators of pituitary POMC-peptide secretion. Concentrations of beta-endorphin in the anterior lobe of GEPR-3s were 53% higher compared to controls and 57% higher compared to GEPR-9s. There were no differences in neurointermediate lobe beta-endorphin concentrations between control and either GEPR strain. Plasma beta-endorphin concentrations were significantly lower in GEPR-9s than controls. Plasma levels of alpha-MSH did not differ between control and GEPRs. In the hypothalamus of GEPR-9s beta-endorphin concentrations in the arcuate nucleus were significantly greater than in GEPR-3s. Concentrations of beta-endorphin in the central amygdala of GEPR-9s were two- to threefold greater than in control or GEPR-3s. Beta-Endorphin concentrations in the central gray of GEPR-3s were 58% lower than control or GEPR-9s. These data suggest that anterior lobe beta-endorphin secretion is reduced in GEPR-9s. Furthermore, brain endorphinergic pathways appear to be differentially altered in GEPR-3s and GEPR-9s. Alterations in pituitary beta-endorphin secretion and brain endorphinergic systems may contribute to seizure susceptibility in GEPRs and to differences in seizure severity between GEPR-3s and GEPR-9s.

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.

PROPOFOL DOES NOT INHIBIT CALCIUM-INDUCED RELEASE OF BETA-ENDORPHIN FROM PERMEABILIZED MOUSE PITUITARY CELLS

S528 INTRODUCTION: Propofol inhibits secretion of beta-endorphin from AtT-20 cells, a mouse pituitary cell line [1]. Cells were permeabilized with digitonin to investigate the biochemical basis of propofol's effects. The calcium concentration in permeabilized cells was fixed at 0 or 10 [micro sign]M, to determine whether propofol acts before or after the rise in calcium associated with secretion of neuropeptides. METHODS: Subconfluent AtT-20 cells grown in 12-well plates (4 wells per condition) were incubated at 37[degree sign]C for 60 minutes in 145 mM NaCl/15 mM HEPES pH 7.4/5.6 mM glucose/5.6 mM KCl/2.2 mM CaCl2,/0.5 mM MgCl2/0.5 mM sodium ascorbate. The cells were then incubated at 37[degree sign]C for 60 minutes in 139 mM potassium glutamate/20 mM PIPES pH 6.6/5 mM EGTA/5 mM MgCl2/5 mM ATP/0.5 mM sodium ascorbate (negative control). Experimental manipulations included addition of CaCl2 to a free concentration of 10 [micro sign]M, 2 [micro sign]M digitonin, and propofol (0 to 100 [micro sign]M). The supernatants were analyzed for beta-endorphin release by ELISA. RESULTS: Raising extracellular calcium to 10 [micro sign]M did not induce secretion from nonpermeabilized cells. beta-endorphin was released from digitonin-permeabilized cells in a calcium-dependent fashion. Propofol (0-100 [micro sign]M) did not inhibit release of beta-endorphin from permeabilized cells. (Figure 1)Figure 1DISCUSSION: Propofol did not inhibit calcium-induced release of beta-endorphin from permeabilized cells, but propofol does inhibit stimulated secretion of beta-endorphin from intact cells. Thus, propofol does not inhibit secretory steps subsequent to the rise in calcium. Instead, propofol inhibits a process required for secretion that occurs at or prior to the rise in calcium. One possible site of action would be entry of calcium into cells via calcium channels.

Physiological effects of hunting red deer (Cervus elaphus).

When red deer (Cervus elaphus) were hunted by humans with hounds the average distance travelled was at least 19 km. This study of 64 hunted red deer provides the first empirical evidence on their state at the time of death. Blood and muscle samples obtained from hunted deer after death were compared with samples from 50 non-hunted red deer that had been cleanly shot with rifles. The effects on deer of long hunts were (i) depletion of carbohydrate resources for powering muscles, (ii) disruption of muscle tissue, and (iii) elevated secretion of beta-endorphin. High concentrations of cortisol, typically associated with extreme physiological and psychological stress, were found. Damage to red blood cells occurred early in the hunts; possible mechanisms are discussed. Taken together, the evidence suggests that red deer are not well-adapted by their evolutionary or individual history to cope with the level of activity imposed on them when hunted with hounds.

Forskolin Delays the Ethanol-Induced Desensitization of Hypothalamic beta-Endorphin Neurons in Primary Cultures

Ethanol and its metabolite acetaldehyde have been shown to stimulate immunoreactive beta-endorphin (IR-beta-EP) secretion from hypothalamic neurons in primary cultures. Also, chronic ethanol and acetal-dehyde have been shown to cause the development of tolerance and desensitization of these neurons. In this study, we determined some of the cellular events leading to desensitization of the function of beta-endorphin (beta-EP) secretory neurons. The fetal hypothalamic cells were treated with various doses of ethanol (25 and 50 mM) or acetaldehyde (6.25, 12.5, and 25 mM) for 6 hr or treated with these drugs at 12 hr intervals for 72 hr. Determination of IR-beta-EP concentrations in the media revealed that ethanol increased IR-beta-EP secretion from these cultures for 12 hr, after this period, the cultured cells did not respond to ethanol. Acetaldehyde stimulated IR-beta-EP secretion from this culture for a period of 48 hr, but the IR-beta-EP secretory response to acetaldehyde reduced gradually with time during the first 48-hr period and reached the basal level at 72 hr. The desensitization of beta-EP neurons 12 hr after treatment with alcohol did not seem to be related to the loss of viable cells, because chronic ethanol exposures did not produce any effect on cell viability. However, reduced IR- beta-EP secretory response to acetaldehyde with time was associated with the time-dependent increase in cell death. Pretreatment of cultures with a cAMP analog, forskolin, increased the activity of functional beta-EP neurons and delayed the ethanol desensitization effects on these neurons. Pretreatment of forskolin did not delay the acetaldehyde desensitization of beta-EP neurons, but protected these cells from acetaldehyde toxicity. These results suggest that (i) chronic treatment with ethanol desensitizes beta-EP-secreting neurons due to reduced cellular functions and (ii) chronic acetaldehyde reduces beta-EP neurotransmission due to cell death. Furthermore, data suggest for the first time that cAMP pretreatments delay the ethanol-induced desensitization of opioid neurons and partly protect against the neurotoxic action of acetaldehyde on opioid neurons.

The 24-hour rhythm of oxytocin and beta-endorphin secretion in human pregnancy.

Animal work suggests that maternal oxytocin secretion is influenced by the secretion of endogenous opioids in pregnancy. Spontaneous labour and pre-labour uterine activity follow a 24-hour rhythm the origin of which has not been explained but may be related to diurnal changes in oxytocin secretion. This study was performed to document the changes over a 24-hour period in maternal oxytocin and beta-endorphin secretion. A 4-hourly blood profile was undertaken for a 24-hour period. Sixteen women with singleton pregnancies of more than 36 weeks gestation and 10 women with pregnancies in the mid trimester were studied. Blood was sampled 4-hourly for 24 hours beginning at 1200 h. Oxytocin was measured in all patients and beta-endorphin-like immunoreactivity was measured in 15 patients. A simple index was defined for comparing night-time levels to daytime levels for both oxytocin and beta-endorphin. In all cases more than 36 weeks gestation the index was positive for oxytocin (night-time levels were higher) and in all cases the index was negative for beta-endorphin (night-time levels were lower). In the mid trimester women all values of the index for oxytocin were positive but in the beta-endorphin group equal numbers demonstrated a positive or a negative index. Reciprocal 24-hour rhythms were demonstrated between oxytocin and beta-endorphin; however, it is not clear whether this relationship is causal.

Stimulatory effects of L-5-hydroxytryptophan on postdexamethasone β-endorphin levels in major depression

Recently it has been shown that acute administration of 200 mg L-5-hydroxytryptophan (L-5-HTP) PO may increase post-dexamethasone (DST) adrenocorticotropic hormone (ACTH) and cortisol levels in major, but not minor, depressed subjects. This study aimed to examine the effects of 200 mg L-5-HTP PO on post-DST beta-endorphin levels in the same depressed subjects. It was found that in major, but not minor, depressed subjects, L-5-HTP significantly increased post-DST beta-endorphin concentrations as compared to placebo. The L-5-HTP-induced post-DST beta-endorphin responses were significantly higher in major than in minor depressed subjects. There was a significant and positive relationship between L-5-HTP-induced post-DST beta-endorphin and ACTH or cortisol responses. There was a significant and positive relationship between L-5-HTP-induced post-DST beta-endorphin values and the Hamilton Depression Rating Scale (HDRS) score. The results show that the acute administration of L-5-HTP may increase the escape of beta-endorphin secretion from suppression by dexamethasone in major, but not minor, depression.

Inhibition of regulated neuropeptide secretion from mouse pituitary cells by propofol.

Neuropeptides modulate neuronal responses to stimuli. Secretion of neuropeptides is a potential site for anesthetic action. This paper examines the hypothesis that propofol alters the secretion of beta-endorphin. Cultures of a mouse pituitary cell line (AtT-20) were exposed to propofol in vitro, then induced to secrete beta-endorphin. Secretion was measured by immunoassay. Propofol caused statistically significant inhibition of secretion. Secretion stimulated by phorbol ester was inhibited by propofol with a calculated 50% inhibitory concentration (IC50) value of 48 microM. The propofol IC50 values for secretion stimulated by other secretagogs were 47 microM (barium), 42 microM (Bay K 8644, a calcium channel agonist), and 28 microM (a cyclic adenosine monophosphate [cAMP] analog). AtT-20 cells recovered their ability to secrete beta-endorphin upon removal of the propofol, which demonstrated that they were not damaged permanently by propofol. The effect was relatively specific to neuropeptide secretion, as AtT-20 cells grew normally for 5 days in the presence of 10 or 80 microM propofol. The finding suggests that propofol inhibited a site in neuropeptide exocytosis common to the three studied pathways of secretion.

Inhibition of Regulated Neuropeptide Secretion from Mouse Pituitary Cells by Propofol

Neuropeptides modulate neuronal responses to stimuli.Secretion of neuropeptides is a potential site for anesthetic action. This paper examines the hypothesis that propofol alters the secretion of beta-endorphin. Cultures of a mouse pituitary cell line (AtT-20) were exposed to propofol in vitro, then induced to secrete beta-endorphin. Secretion was measured by immunoassay. Propofol caused statistically significant inhibition of secretion. Secretion stimulated by phorbol ester was inhibited by propofol with a calculated 50% inhibitory concentration (IC50) value of 48 micro Meter. The propofol IC50 values for secretion stimulated by other secretagogs were 47 micro Meter (barium), 42 micro Meter (Bay K 8644, a calcium channel agonist), and 28 micro Meter (a cyclic adenosine monophosphate [cAMP] analog). AtT-20 cells recovered their ability to secrete beta-endorphin upon removal of the propofol, which demonstrated that they were not damaged permanently by propofol. The effect was relatively specific to neuropeptide secretion, as AtT-20 cells grew normally for 5 days in the presence of 10 or 80 micro Meter propofol. The finding suggests that propofol inhibited a site in neuropeptide exocytosis common to the three studied pathways of secretion. (Anesth Analg 1996;83:611-7)

Effect of monensin on secretory granules and basal beta-endorphin secretion in the melanotroph of the rat pituitary.

The effect of monensin on the Golgi complex, formation of secretory granules and basal beta-endorphin secretion in cultured melanotrophs from the rat pituitary was studied. Earlier studies on the effect of monensin on regulated secretion have generally showed only minor effects on secretory granules. The initial (within 5 min) effect of monensin on the melanotroph was the appearance of large vacuoles at the trans-side of the thiamine pyrophosphatase-positive trans-most Golgi cisternae. This was associated with a dose-dependent inhibition of the condensation of electron-dense secretory products. After 1 h of treatment with 1 microM monensin the Golgi stack was completely vacuolized. At the same time mature secretory granules were enlarged to severalfold their original size, and after 4 h of treatment secretory granules were no longer observed. Despite the marked effects on granule formation and mature secretory granules monensin did not affect the basal release of beta-endorphin-immunoreactive material during continued incubation for up to 4 h, indicating that basal peptide secretion can bypass the monensin block.

Effects of photoperiod and androgen on pituitary function and neuropeptide staining in Siberian hamsters.

Short photoperiods decrease gonadotropin secretion in Siberian hamsters, but it is unknown whether the negative feedback effects of androgens are amplified under such conditions, as is the case in other species. Photoperiod regulates the synthesis and secretion of gonadotropin-releasing hormone (GnRH), beta-endorphin, and arginine vasopressin (AVP), which influence gonadotropin release and sexual behavior but are themselves regulated by gonadal steroid hormones. To determine the role of androgen in these effects of daylength, immunostaining and gonadotropin concentrations were examined after 8 wk of exposure to long or short days (LD or SD). Animals were either left intact, castrated, or castrated with immediate or delayed replacement of testosterone (T). We also investigated effects of age on photoperiodic influences on brain peptides and serum hormone levels. Serum prolactin concentrations were regulated by photoperiod and by gonadal status in LD hamsters. Effects of T on follicle-stimulating hormone secretion were more pronounced in SD hamsters. Older hamsters were generally less responsive to effects of daylength on pituitary function. Photoperiod and gonadal status regulated the number of AVP-immunoreactive (ir) cells in the bed nucleus of the stria terminalis and the medial amygdala. Androgen treatment yielded more AVP-ir neurons in LD than in SD. Photoperiod influenced the number of GnRH-ir cells only in the medial septum of castrated hamsters. Daylength regulated beta-endorphin-ir neurons in intact hamsters, but not in castrates. Only among old hamsters did photoperiod affect the influence of T on beta-endorphin staining in neurons and fibers. Such fiber staining was unaffected by photoperiod in intact and T-treated castrate hamsters, but was reduced in SD castrates. We conclude that daylength modulates the effects of androgen on gonadotropin secretion and influences the effect of T on neuropeptide staining in regionally specific patterns that depend on the age of the animal and its history of prior steroid exposure.

Growth-associated Protein-43 (GAP-43) Facilitates Peptide Hormone Secretion in Mouse Anterior Pituitary AtT-20 Cells

The neuronal growth-associated protein (GAP)-43 (neuromodulin, B-50, F1), which is concentrated in the growth cones of elongating axons during neuronal development and in nerve terminals in restricted regions of the adult nervous system, has been implicated in the release of neurotransmitter. To study the role of GAP-43 in evoked secretion, we transfected mouse anterior pituitary AtT-20 cells with the rat GAP-43 cDNA and derived stably transfected cell lines. Depolarization-mediated beta-endorphin secretion was greatly enhanced in the GAP-43-expressing AtT-20 cells without a significant change in Ca2+ influx; in contrast, expression of GAP-43 did not alter corticotropin-releasing factor-evoked hormone secretion. The transfected cells also displayed a flattened morphology and extended processes when plated on laminin-coated substrates. These results suggest that AtT-20 cells are a useful model system for further investigations on the precise biological function(s) of GAP-43.

Circadian variations in plasma ACTH, cortisol and beta-endorphin levels in normal-weight bulimic women.

In order to establish possible alterations in the secretory patterns of adrenocorticotropic hormone (ACTH), cortisol and/or beta-endorphin in bulimia nervosa, the circadian fluctuations of these hormones were evaluated in blood samples taken at 1-hour intervals over 24 h. Eleven bulimic women with normal body weight and 8 weight- and age-matched normal controls were tested during the follicular phase (days 6-8) of normal menstrual cycles. All women were hospitalized for bulimia or for checkup examinations and were tested 3 days after hospital admission. Both normal and bulimic women showed maximal ACTH, cortisol and beta-endorphin levels at 08.00 h, with minimal ACTH and beta-endorphin levels at midnight and cortisol levels at 02.00 h. The general temporal structure of all hormonal secretions coincided in the two groups. However, whereas all measured ACTH/cortisol levels were quantitatively similar in the two groups, plasma beta-endorphin concentrations were significantly higher in bulimic than in control subjects at all examined time points. The enhancement in the overall 24-hour beta-endorphin secretion suggests the presence of an increased opioid tonus in bulimic women, which might play a role in the pathophysiology of the eating disorder.

Cyclosporin A and FK506 are potent activators of proopiomelanocortin-derived peptide secretion without affecting corticotrope glucocorticoid receptor function.

Unliganded glucocorticoid receptors (GR) are localized in the cytoplasm and are associated with heat shock protein (hsp)90, hsp70, and a member of the immunophilin family, FK506 binding protein 59 (FKBP59). Several members of the cyclophilin and FKBP families have now been shown to associate with unactivated steroid receptors, however the physiological role these immunophilins play in steroid receptor function is questionable. In the present study we have measured GR binding and nuclear translocation of activated receptor in corticotrope cells following treatment with the immunophilin ligands FK506 and cyclospcrin A (CsA). Extensive GR binding studies in AtT20 cells, a mouse corticotrope tumor cell line failed to demonstrate an effect of FK506 or CsA on either the ability of GR to bind ligand, or on nuclear translocation of the liganded receptor at either a saturating or subsaturating dose of dexamethasone (DEX). Consistent with the binding data, functionally, neither CsA nor FK506 altered the glucocorticoid induced decrease in either proopiomelanocortin (POMC) derived peptide secretion or POMC heteronuclear (hn) RNA expression. Despite the fact these drugs did not modulate the actions of glucocorticoids on corticotrope cells, both FK506 and CsA were potent stimulators of basal beta-endorphin secretion (4-6 fold) from rat anterior pituitary cultures and AtT20 cells. In addition, FK506 and CsA potentiated beta-endorphin secretion induced by corticotropin releasing factor (CRF) and phorbol ester, but had no apparent acute (60 min) effect on POMC hnRNA levels. Unlike the acute actions of these immunosuppressant drugs, chronic (24 h) treatment lead to a decrease in cytoplasmic POMC mRNA with no apparent change in the amount of secreted beta-endorphin. Taken together these data suggest that FK506 and CsA do not alter GR activation or function in corticotrope cells, however, they are potent but short lived stimulators of POMC-derived peptide secretion. The observation that CsA and FK506 stimulate POMC-derived peptide secretion, and potentiate both phorbol ester and CRF induced secretion, suggests that these immunosuppressant drugs are acting upon a common point within these intracellular pathways.

Effects of dopamine D1 and D2 receptor agonists and antagonists on basal and ethanol-modulated beta-endorphin secretion from hypothalamic neurons in primary cultures.

In the present study, we determined the effects of dopamine receptor agonists and antagonists on basal and ethanol-modulated beta-endorphin (beta-EP) secretion from hypothalamic neurons in primary cultures. Treatment with various concentrations of dopamine D1 agonist SKF 38393 and D1 antagonist SCH 23390 did not affect basal IR-beta-EP release. However, dopamine D2 receptor agonist LY 141865 reduced basal immunoreactive (IR)-beta-EP release in a concentration dependent manner. D2 receptor antagonist, sulpiride, on the other hand, stimulated basal IR-beta-EP release and blocked LY 141865-induced inhibition of IR-beta-EP release in a concentration dependent manner. When the actions of these DA receptor agents on ethanol-modulated IR-beta-EP release were studied, both D1 and D2 receptor agents failed to affect ethanol-modulated IR-beta-EP release. These data suggest that the endogenous secretion of beta-EP from hypothalamic neurons is under the influence of an inhibitory dopaminergic system involving the D2 receptor. Furthermore, ethanol's effects on beta-EP secretion are not mediated by dopamine.

Glutamate enhances the adenylyl cyclase-cAMP system-induced beta-endorphin secretion and POMC mRNA expression in rat hypothalamic neurons in culture: NMDA receptor-mediated modulation

l-Glutamate, a major excitatory amino acid of the central nervous system, plays important roles as neurotransmitter and neuromodulator in the brain. Increasing evidence suggests that glutamate may also involve in the regulation of the neuroendocrine system at the hypothalamus. Employing long term monolayer hypothalamic cell cultures prepared from neonatal rats, we reported here that whereas glutamate significantly enhanced forskolin-, or N 6,2′-O-dibutyrrladenosine-3′5′-cyclic monophosphate [(Bu) 2cAMP]-stimulated immunoreactive (ir)-β EP release form cultures treated daily for 4 consecutive days, the excitatory amino acid alone produced little effect. This potentiation of glutamate was time-related and dose-dependent with an E max value of the amino acid being approximately 50 μM; at this concentration glutamate augmented ir-β EP secretion about 1.8 times ( P<0.05) that induced by 2 μM forskolin alone. Similar effects were also observed for POMC and mRNA levels in cultures subjected to 6 h of the above treatment regime. This potentiating effect of glutamate appears to be mediated specifically through NMDA receptor as it can be mimicked by NMDA but not by kainic acid or quisqualic acid, and blocked by the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA glutamate receptor antagonist. Interestingly, glutamate was found not to enhance high doses of forskolin (10 μM) or (Bu) 2 cAMP (100 μM) stimulated β EP release and POMC mRNA levels in hypothalamic cell cultures. These novel findings suggests that (i) hypothalamic β EP neurons are subjected to direct glutamatergic modulation, and (ii) the modulating effect of glutamate is mediated, at least in part, through the adenylyl cyclases-cAMP system. Our novel findings have provided a direct evidence supporting the assertion that cortical glutamatergical system may directly involve in the functional modulation of hypothalamic β EP producing neurons.

Diurnal Variation in Luteinizing Hormone-Releasing Hormone and β-Endorphin Release in Pituitary Portal Plasma during the Rat Estrous Cycle1

In this study, we investigated the pattern of both LHRH and beta-endorphin (beta-EP) secretion from the median eminence of cyclic female rats during the estrous cycle by collecting pituitary portal blood for hormone measurements by RIA. On diestrus, proestrus, or estrus (0900 h or 1300 h), rats were hypophysectomized (in order to prevent contamination of portal beta-EP with pituitary beta-EP) and were given a 50-60-min resting period of postsurgical recovery prior to blood sampling. Between 1000 h and 1800 h of the same day, pituitary portal blood samples were collected at 10-min intervals from these animals under Saffan anesthesia. Hormone RIA data revealed that LHRH and beta-EP levels in the portal plasma ranged from 25 to 600 pg/ml and from 0.6 to 4.6 ng/ml, respectively, whereas no discernible amounts of these hormones were detected in the peripheral plasma. Analysis further revealed that secretion of both LHRH and beta-EP showed a diurnal rhythmicity and that both neuropeptides were secreted in a pulsatile manner on each day of the cycle, with most dramatic changes seen in female rats on proestrus. In proestrus rats, portal plasma levels of beta-EP were highest during 1000-1500 h and lower around 1600-1800 h. In contrast, morning and early afternoon values of LHRH were obviously higher in rats on proestrus than in animals on other days of the cycle, and an even greater rise in portal plasma levels of LHRH occurred in late afternoon on proestrus, when beta-EP values were lowest.(ABSTRACT TRUNCATED AT 250 WORDS)