Opioid Secretion Research Articles

Epidural Posterior Insular Stimulation Alleviates Neuropathic Pain Manifestations in Rats With Spared Nerve Injury Through Endogenous Opioid System

ObjectivesNeuropathic pain (NP) is defined as constant disabling pain secondary to a lesion or disease of the somatosensory nervous system. This condition is particularly difficult to treat because it often remains resistant to most treatment strategies. Despite the recent diversification of neurostimulation methods, some patients still suffer from refractory pain syndromes. The central role of the posterior insular cortex (PI) in the modulation of pain signaling and perception has been repeatedly suggested. The objective of this study is to assess whether epidural insular stimulation (IS) could reverse NP behavior. Materials and MethodsA total of 53 adult Sprague-Dawley rats received left-sided spared nerve injury (SNI) or Sham-SNI to induce NP symptoms. Afterward, epidural electrodes were implanted over the right PI. After two weeks of postoperative recovery, three groups of SNI-operated rats each received a different stimulation modality: Sham-IS, low-frequency-IS (LF-IS), or high-frequency-IS (HF-IS). Behavioral and functional tests were conducted before and after IS. They comprised the acetone test, pinprick test, von Frey test, and sciatic functional index. An additional LF-IS group received a dose of opioid antagonist naloxone before IS. Intergroup means were compared through independent-samples t-tests, and pre- and post-IS means in the same group were compared through paired t-tests. ResultsWe found a significant reduction of cold allodynia (p = 0.019), mechanical hyperalgesia (p = 0.040), and functional disability (p = 0.005) after LF-IS but not HF-IS. Mechanical allodynia only showed a tendency to decrease after LF-IS. The observed analgesic effects were reversed by opioid antagonist administration. ConclusionThese results suggest a significant reversal of NP symptoms after LF-IS and offer additional evidence that IS might be beneficial in the treatment of resistant NP syndromes through endogenous opioid secretion. Relying on our novel epidural IS model, further fine tuning of stimulation parameters might be necessary to achieve optimal therapeutic effects.

Opioids in the medial nucleus of the solitary tract are not involved in feeding disorder in activity-based anorexia in rats

<h2>Summary</h2><h3>Background & aims</h3> Activity-based anorexia (ABA) is an abnormal behavior caused by mealtime restriction and excessive running. A previous study revealed that running causes the secretion of opioids in rats, and excessive opioids are known to decrease food intake. Thus, we hypothesized that the suppression of food intake in ABA rats that experienced mealtime restriction and excessive wheel running was due to an increase in opioids caused by running. Our previous study showed that ABA rats consumed more food than the control group after an intraperitoneal injection of naloxone. This result indicates that opioids are involved in the regulation of food intake in ABA rats. Here, we queried the involvement of the medial nucleus of the solitary tract (mNST) of the brain that mediates satiety information from the internal organs in rats' ABA and also examined whether opioids in the mNST were involved in feeding regulation in them. <h3>Methods</h3> Each ABA rat was given a running wheel and received feeding time restriction, followed by microinjection of naloxone or saline into the mNST. Each control rat was subjected to only feeding time restriction and then microinjection of naloxone or saline into the mNST. <h3>Results</h3> The results showed that food intake of the ABA group was not increased by naloxone injection into the mNST. <h3>Conclusions</h3> Our results suggest that the mNST is not involved in the regulation of food intake by opioids. Regulation of food intake by opioids may occur in other parts of the brain, such as the parabrachial nucleus and/or hypothalamus.

Liraglutide Activates Glucagon-Like Peptide 1 Receptor to Attenuate Hyperglycemia through Endogenous Beta-Endorphin in Diabetic Rats.

Liraglutide, an acylated analog of glucagon-like peptide 1 (GLP-1), could improve glycemic control in diabetes. Moreover, endogenous opioid peptides play a role in blood sugar regulation. Since GLP-1 receptors are also expressed in extra-pancreatic tissues, this study investigates the effect of liraglutide on endogenous opioid secretion in type 1-like diabetes. The endogenous opioid level was determined by enzyme-linked immunosorbent assay. The direct effect of liraglutide on endogenous opioid secretion was determined in the isolated adrenal medulla. Acute treatment with liraglutide dose-dependently attenuated hyperglycemia, and increased the plasma opioid neuropeptide, beta-endorphin (BER) levels in diabetic rats. These effects have been blocked by GLP-1 receptor antagonist, naloxone. Additionally, the effects of liraglutide were markedly reduced in adrenalectomized diabetic rats. In the isolated adrenal medulla, liraglutide induced BER secretion and increased the BER mRNA levels. Subcellular effects of liraglutide on the adrenal gland were further identified to mediate through the exchange proteins directly activated by cAMP, mainly using the pharmacological blockade. After repeatedly administering liraglutide, metabolic changes in diabetic rats were investigated, and genes associated with gluconeogenesis in the liver were downregulated. Naloxone pretreatment inhibited these effects of liraglutide, indicating the involvement of endogenous opioids. The present study indicated that liraglutide had an acute effect of reducing hyperglycemia by regulating endogenous opioid BER and modifying the glucose homeostasis.

P7 - Utilization of a microphysiological system to model renal secretion of opioids in humans

P7 - Utilization of a microphysiological system to model renal secretion of opioids in humans

It is not just the drugs that matter: the nocebo effect.

The role of psychological mechanisms in the treatment process cannot be underestimated, the well-known placebo effect unquestionably being a factor in treatment. However, there is also a dark side to the impact of mental processes on health/illness as exemplified by the nocebo effect. This phenomenon includes the emergence or exacerbation of negative symptoms associated with the therapy, but arising as a result of the patient's expectations, rather than being an actual complication of treatment. The exact biological mechanisms of this process are not known, but cholecystokinergic and dopaminergic systems, changes in the HPA axis, and the endogenous secretion of opioids are thought to be involved. The nocebo effect can affect a significant proportion of people undergoing treatment, including cancer patients, leading in some cases to the cessation of potentially effective therapy, because of adverse effects that are not actually part of the biological effect of treatment. In extreme cases, as a result of suggestions and expectations, a paradoxical effect, biologically opposite to the mechanism of the action of the drug, may occur. In addition, the nocebo effect may significantly interfere with the results of clinical trials, being the cause of a significant proportion of complications reported. Knowledge of the phenomenon is thus necessary in order to facilitate its minimalization and thus improve the quality of life of patients and the effectiveness of treatment.

Expression of β-endorphin in peripheral tissues after systemic administration of lipopolysaccharide as a model of endotoxic shock in mice

BackgroundEndogenous β-endorphin is delivered exclusively from the pituitary gland in various stressful conditions and plays an essential role in the nervous system. Recently, a few studies demonstrated peripheral endogenous opioid secretion from immune cells at inflammatory sites. Here, we investigated the expression of β-endorphin, the most powerful endogenous opioid peptide, in peripheral tissues in response to systemic administration of lipopolysaccharide in mice. MethodsMale C57BL/6N mice received intravenously administered lipopolysaccharide to induce an endotoxic shock-like condition. mRNA for proopiomelanocortin, a precursor of β-endorphin, was quantified in peripheral blood cells, liver and spleen. β-endorphin peptide was measured in the liver and spleen. ResultsExpression of proopiomelanocortin mRNA was detected in peripheral tissues after systemic administration of lipopolysaccharide. Lipopolysaccharide also induced β-endorphin expression in the liver and spleen. ConclusionExpression of proopiomelanocortin mRNA and β-endorphin was detected in peripheral tissues after systemic administration of lipopolysaccharide. These results provide new evidence that peripheral endogenous opioids can be produced not only as a result of local inflammation but also by severe systemic stress such as endotoxic shock. Further study is required to clarify the role of peripheral β-endorphin during endotoxic shock.

Diosmin, a Citrus Nutrient, Activates Imidazoline Receptors to Alleviate Blood Glucose and Lipids in Type 1-Like Diabetic Rats.

Diosmin is a nutrient that is widely contained in citrus and that has been indicated to improve glucose metabolism in diabetic disorders. Recently, we demonstrated that diosmin induces β-endorphin to lower hyperglycemia in diabetic rats. However, the mechanisms of diosmin in opioid secretion were unclear. Therefore, we focused on the secretion of opioids from isolated adrenal glands induced by diosmin. The changes in the released β-endorphin-like immunoreactivity (BER) were determined using ELISA. Diosmin increased the BER level in a dose-dependent manner, and this effect was markedly reduced in the absence of calcium ions. Activation of the imidazoline I-2 receptor (I-2R) has been introduced to induce opioid secretion. Interestingly, we observed that diosmin activates CHO cells expressing I-R. Additionally, diosmin-increased BER was inhibited by the blockade of I-2R in isolated adrenal glands. Additionally, an antagonist of I-2R blocked diosmin-induced effects, including the reduction in hyperglycemia and the increase in plasma BER in streptozotocin-induced diabetic rats (STZ-diabetic rats). Repeated treatment of STZ-diabetic rats with diosmin for one week induced changes in hepatic glycogen, lipid levels, and the expression of phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, an antagonist of I-2R blocked the diosmin-induced changes. Additionally, plasma lipids modified by diosmin were also reversed by the blockade of I-2R in STZ-diabetic rats. Taken together, we suggest that diosmin may activate I-2R to enhance the secretion of β-endorphin from adrenal glands and to influence metabolic homeostasis, resulting in alleviation of blood glucose and lipids in STZ-diabetic rats.

Early Repeated Administration of CXCR4 Antagonist AMD3100 Dose-Dependently Improves Neuropathic Pain in Rats After L5 Spinal Nerve Ligation.

AMD3100 is a specific C-X-C chemokine receptor type 4 (CXCR4) antagonist which blocks the interaction between CXCR4 and CXCL12. Multiple lines of evidence suggest that AMD3100 has analgesic effects on many pathological pain states, including peripheral neuropathic pain. However, little is known about the underlying mechanisms. In the current study, we investigated the effect of different doses of AMD3100 on neuropathic pain in rats after L5 spinal nerve ligation. We used naloxone methiodide (NLXM) to further determine whether AMD3100-mediated analgesic effect was opioid-dependent. Behavioral study showed that early repeated administration of AMD3100 (2 and 5mg/kg, i.p.) dose-dependently alleviates peripheral neuropathic pain. Flow cytometry, immunofluorescence and NLXM experiments showed that AMD3100 alleviates neuropathic pain partially by augmenting leukocyte-derived endogenous opioid secretion. Furthermore, we found that pro-inflammatory cytokines were down-regulated by AMD3100 using Enzyme-linked Immunosorbent Assay. Our data indicate that AMD3100 dose-dependently alleviates neuropathic pain partially by augmenting leukocyte-derived endogenous opioid secretion. This finding suggests that AMD3100 may be a viable pharmacotherapeutic strategy for the treatment of neuropathic pain.

Demethylating Drugs as Novel Analgesics for Cancer Pain

In this study, we evaluated the analgesic potential of demethylating drugs on oral cancer pain. Although demethylating drugs could affect expression of many genes, we focused on the mu-opioid receptor (OPRM1) gene pathway, because of its role in pain processing. We determined the antinociceptive effect of OPRM1 re-expression in a mouse oral cancer model. Using a mouse oral cancer model, we determined whether demethylating drugs produced antinociception through re-expression of OPRM1. We then re-expressed OPRM1 with adenoviral transduction and determined if, and by what mechanism, OPRM1 re-expression produced antinociception. To determine the clinical significance of OPRM1 on cancer pain, we quantified OPRM1 methylation in painful cancer tissues and nonpainful contralateral normal tissues of patients with oral cancer, and nonpainful dysplastic tissues of patients with oral dysplasia. We demonstrated that OPRM1 was methylated in cancer tissue, but not normal tissue, of patients with oral cancer, and not in dysplastic tissues from patients with oral dysplasia. Treatment with demethylating drugs resulted in mechanical and thermal antinociception in the mouse cancer model. This behavioral change correlated with OPRM1 re-expression in the cancer and associated neurons. Similarly, adenoviral-mediated OPRM1 re-expression on cancer cells resulted in naloxone-reversible antinociception. OPRM1 re-expression on oral cancer cells in vitro increased β-endorphin secretion from the cancer, and decreased activation of neurons that were treated with cancer supernatant. Our study establishes the regulatory role of methylation in cancer pain. OPRM1 re-expression in cancer cells produces antinociception through cancer-mediated endogenous opioid secretion. Demethylating drugs have an analgesic effect that involves OPRM1.

Immune derived opioidergic inhibition of viscerosensory afferents is decreased in Irritable Bowel Syndrome patients.

Alterations in the neuro-immune axis contribute toward viscerosensory nerve sensitivity and symptoms in Irritable Bowel Syndrome (IBS). Inhibitory factors secreted from immune cells inhibit colo-rectal afferents in health, and loss of this inhibition may lead to hypersensitivity and symptoms. We aimed to determine the immune cell type(s) responsible for opioid secretion in humans and whether this is altered in patients with IBS. The β-endorphin content of specific immune cell lineages in peripheral blood and colonic mucosal biopsies were compared between healthy subjects (HS) and IBS patients. Peripheral blood mononuclear cell (PBMC) supernatants from HS and IBS patients were applied to colo-rectal sensory afferent endings in mice with post-inflammatory chronic visceral hypersensitivity (CVH). β-Endorphin was identified predominantly in monocyte/macrophages relative to T or B cells in human PBMC and colonic lamina propria. Monocyte derived β-endorphin levels and colonic macrophage numbers were lower in IBS patients than healthy subjects. PBMC supernatants from healthy subjects had greater inhibitory effects on colo-rectal afferent mechanosensitivity than those from IBS patients. The inhibitory effects of PBMC supernatants were more prominent in CVH mice compared to healthy mice due to an increase in μ-opioid receptor expression in dorsal root ganglia neurons in CVH mice. Monocyte/macrophages are the predominant immune cell type responsible for β-endorphin secretion in humans. IBS patients have lower monocyte derived β-endorphin levels than healthy subjects, causing less inhibition of colonic afferent endings. Consequently, altered immune function contributes toward visceral hypersensitivity in IBS.

Early Systemic Granulocyte-Colony Stimulating Factor Treatment Attenuates Neuropathic Pain after Peripheral Nerve Injury

Recent studies have shown that opioid treatment can reduce pro-inflammatory cytokine production and counteract various neuropathic pain syndromes. Granulocyte colony-stimulating factor (G-CSF) can promote immune cell differentiation by increasing leukocytes (mainly opioid-containing polymorphonuclear (PMN) cells), suggesting a potential beneficial role in treating chronic pain. This study shows the effectiveness of exogenous G-CSF treatment (200 µg/kg) for alleviating thermal hyperalgesia and mechanical allodynia in rats with chronic constriction injury (CCI), during post-operative days 1–25, compared to that of vehicle treatment. G-CSF also increases the recruitment of opioid-containing PMN cells into the injured nerve. After CCI, single administration of G-CSF on days 0, 1, and 2, but not on day 3, relieved thermal hyperalgesia, which indicated that its effect on neuropathic pain had a therapeutic window of 0–48 h after nerve injury. CCI led to an increase in the levels of interleukin-6 (IL-6) mRNA and tumor necrosis factor-α (TNF-α) protein in the dorsal root ganglia (DRG). These high levels of IL-6 mRNA and TNF-α were suppressed by a single administration of G-CSF 48–144 h and 72–144 h after CCI, respectively. Furthermore, G-CSF administered 72–144 h after CCI suppressed the CCI-induced upregulation of microglial activation in the ipsilateral spinal dorsal horn, which is essential for sensing neuropathic pain. Moreover, the opioid receptor antagonist naloxone methiodide (NLXM) reversed G-CSF-induced antinociception 3 days after CCI, suggesting that G-CSF alleviates hyperalgesia via opioid/opioid receptor interactions. These results suggest that an early single systemic injection of G-CSF alleviates neuropathic pain via activation of PMN cell-derived endogenous opioid secretion to activate opioid receptors in the injured nerve, downregulate IL-6 and TNF-α inflammatory cytokines, and attenuate microglial activation in the spinal dorsal horn. This indicates that G-CSF treatment can suppress early inflammation and prevent the subsequent development of neuropathic pain.

Effect of Interaction Between Testosterone and Morphine on Serum Ghrelin Concentration in Sheep Fed on Different Dietary Energy Levels

BackgroundGhrelin plays an important role in the regulation of food intake and body weight. It also decreases testosterone and opioid secretion.ObjectivesThe goal of the present study was to investigate the effect of testosterone, morphine or simultaneous injection of testosterone and morphine on mean serum ghrelin concentration in sheep.Materials and MethodsTen sheep were divided into two groups (n = 5 in each group), they were fed with either 50 % or 100 % of their dietary energy needs for 10 days. Body weight was measured on the 1st and 10th day of the experiment. Animals in both groups received testosterone (60 μg/kg), morphine (0.15 mg/kg), or a simultaneous infusion of testosterone (60 μg/kg) and morphine (0.15 mg/kg), on the 8th, 9th, or 10th day of the experiment respectively. Blood samples were collected before and 2 hours after the infusions. Ghrelin concentration was determined by RIA (radio immunoassay).ResultsIn the 50 % group, ghrelin concentrations increased significantly on the 8th day of the experiment, compared to the 1st day (P < 0.05). While in the 100 % group, no significant change was observed. In both groups the animals’ body weight did not increase significantly on the 10th day compared to the 1st day. Testosterone significantly increased ghrelin levels after injection compared to before infusion, in both groups (P < 0.05). Morphine increased ghrelin concentration in both groups, but this increase was not statistically significant. Simultaneous injection of testosterone and morphine together, significantly increased ghrelin concentration following injection compared to before infusion, in both groups (P < 0.05).ConclusionsThere is a direct correlation between food restriction, testosterone and ghrelin concentration in ruminants. However, a simultaneous injection of testosterone and morphine did not exert an additive effect on ghrelin secretion.

Opioid receptor imaging in man

The existence of opioid receptors (OR) had long been suspected, but their demonstration in nervous tissue and the discovery of their natural ligands did not come until the 1970’s. By 1985, the study of brain OR was possible in vivo using Positron Emission Tomography (PET), thanks to technical advances in imaging and radiochemistry. Since then, multiple PET studies contributed to clarify the physiology and pathology of human endogenous opioid system in several conditions and pathologies. Thus, activation studies in tonic experimental pain have demonstrated opioid system activation in multiple opioid receptor bearing sites such as the amygdala, the ventrolateral thalamus, the insular cortex and hypothalamus, the anterior cingulate gyrus and the prefrontal cortex. Such activation is negatively correlated with the intensity of pain perception. Activation studies have also demonstrated sex-dependent and COMT (cathecol-O-methyltransferase)-dependent differences in the magnitude and direction of the activation of endogenous opioid systems. Endogenous opioid secretion is very likely to occur as a reaction to acute or chronic nociceptive pain, and PET studies have demonstrated a decrease in the binding of the exogenous ligand in patients suffering pain secondary to chronic inflammatory conditions like rheumatoid arthritis. In neuropathic pain (NP), endogenous reactive opioid secretion is also very likely as a global reaction to pain, but there are differences between central and peripheral causes of NP. Loss or inactivation of OR in the hemisphere containing the causal lesion (contralateral to clinical pain) has been demonstrated in central post-stroke pain, while no such lateralised loss seems to exists in peripheral NP. Difference in OR distribution abnormalities between peripheral and central types of NP might explain in part their differential response to exogenous opioids, which is better in peripheral NP. Motor Cortex Stimulation (MCS) for pain relief appears to induce endogenous opioid secretion in key areas of the endogenous opioid system, thus putatively explaining part of the mechanisms of action of this procedure. All these studies incite to the development of future investigations in order to clarify the role of the opioid system in various disorders of the nervous system, and, in chronic pain syndromes, to study the predictive potential of OR distribution abnormalities in the development of NP and in the clinical response of NP to aggressive therapeutic alternatives, like MCS.

Increase of β-endorphin secretion by agmatine is induced by activation of imidazoline I 2A receptors in adrenal gland of rats

Activation of imidazoline I 2 receptor (I 2R) by agmatine in adrenal gland lowers plasma glucose through increment in β-endorphin release to stimulate the opioid μ-receptor in streptozotocin-induced diabetic rats (STZ rats). However, the subtype of I 2R for agmatine-induced blood glucose lowering effect remains obscure. In the present study, agmatine treatment increased β-endorphin secretion and this effect was blocked by I 2R antagonist (BU224) in the isolated adrenal medulla. We further used amiloride, an established blocker of I 2AR, to identify the subtype of I 2R in adrenal gland. Results showed that agmatine-induced β-endorphin release from adrenal gland was blocked by 0.1 μM amiloride indicating the mediation of I 2AR. It was further confirmed that agmatine-induced plasma glucose decrement and plasma β-endorphin increment in STZ rats were blocked by amiloride. However, amiloride failed to modify the action of guanidine, an agonist of I 2BR, at the sufficient dose to block β-endorphin secretion. Taken together, the increase of plasma β-endorphin by agmatine in STZ rats through activation of imidazoline I 2R was mainly induced by the I 2A subtype located in adrenal gland. Thus, imidazoline I 2A receptor in the adrenal gland might be applied as a new target for induction of opioid secretion.

Endothelin receptor-mediated attenuation of carcinoma-induced nociception is opioid-dependent in mice

Author(s): Quang, Phuong Ngoc | Advisor(s): Damsky, Caroline; Schmidt, Brian L | Abstract: Cancer pain is a frequent and disabling consequence for many patients yet the mechanism of cancer pain remains unknown largely due to its complex etiology. The objective of this thesis work was to investigate the potential of a peptide produced by carcinoma cells, endothelin, as a novel target for cancer pain management. This study provided evidence in support of Hypothesis 1: Oral squamous carcinoma cells produce endogenous opioids in response to changes in endothelin-1 signaling. Effects of endothelin-1 (ET-1) signaling on secretion of opioids by oral squamous cell carcinoma (SCC) were studied in vitro. Oral SCC cell line HSC-3 produces abundant ET-1 that can act in both an autocrine or paracrine manner. In the untreated oral SCC cells, endogenous opioids were detected in both cultured media and cell lysates. When treated with Endothelin-A receptor antagonist, secreted levels of abeta-endorphin and leu-enkephalin were increased; whereas treatment with Endothelin-B receptor agonist increased production of only abeta-endorphin. This apparent regulation of endogenous opioid levels by endothelin receptor drugs in vitro procured evidence suggesting that Hypothesis 2: Endothelin-A receptor antagonist and Endothelin-B receptor agonist attenuate carcinoma-induced nociception in cancer animals through regulation of endogenous opioids. Endothelin-A (ET-AR) antagonism has been demonstrated previously to attenuate carcinoma-mediated hyperalgesia in an orthotopic cancer pain mouse model. In this study, effects of ET-BR agonist in vivo were evaluated and determined to also result in significant increase in paw withdrawal thresholds, indicating attenuation of cancer-induced nociception. When peripheral amu- or adelta-opioid receptor antagonists were administered following ET-AR antagonism, nociceptive attenuation was completely reversed. Attenuation from ET-BR agonism was likewise reversed upon administration of amu-opioid receptor antagonist. Combined results demonstrate that endogenous opioids are the likely mediators responsible for attenuation of carcinoma-induced nociception with either ET-AR antagonist or ET-BR agonist.These novel findings suggest that there exist innate modulation of pain by SCCs involving endogenous opioids that can be exploited through manipulation of endothelin activity in the cancer micro-environment. Regulation of ET-AR or ET-BR signaling may be targets for future innovations for cancer pain management.

Growth hormone secretion and insulin-like growth factor-1 are related to hyperandrogenism in nonobese patients with polycystic ovary syndrome

Women of normal weight with polycystic ovary syndrome (PCOS) and hyperinsulinemia presented high growth hormone (GH) levels in response to the l-dopa test, suggesting that the action of GH and insulin-like growth factor-1 (IGF-1) might be responsible for the elevation in LH and the consequent hyperandrogenic anovulation observed in normal weight women with PCOS. Insulin resistance and obesity are related to a reduction in GH secretion in obese women with PCOS.

Long-term Follow-up of Functional Hypothalamic Amenorrhea and Prognostic Factors

Functional hypothalamic amenorrhea (FHA), caused by deficient output of gonadotropin-releasing hormone, may present with an inadequate luteal phase, anovulation with menstrual irregularity, or actual amenorrhea. The underlying mechanisms remain uncertain but there appear to be numerous neuroendocrine abnormalities in FHA, including hyperfunction of the hypothalamic-pituitary-adrenal axis, leading to increased secretion of corticoids and opioids as well as heightened dopaminergic tone and increased nocturnal melatonin secretion. The investigators followed 93 women with FHA over 7 to 9 years (average, 8.1 years), at which time 65 patients (70.7%) had recovered. The FHA diagnosis was based on amenorrhea for 6 months or longer, the hormonal findings, and a radiologically normal sella turcica. In no case did 5 days of oral medroxyprogesterone acetate induce menstrual bleeding. Patients underwent transabdominal or transvaginal pelvic ultrasonography, which excluded polycystic ovary syndrome. Depending on their wish to conceive, patients received either estrogen replacement therapy or oral contraception. Compared with control women, those with FHA had significantly lower levels of gonadotropins, prolactin, estradiol, and thyrotropin, and higher levels of cortisol. The major historical factors associated with FHA were psychological stress and competitive athletic activity, but these factors did not correlate with the likelihood of recovery. Recovered women had higher baseline body mass indices, but age and the duration of amenorrhea were not factors. The only significant hormonal differences were higher androstenedione and lower cortisol levels in recovered women. Recovery did correlate with an increased body mass index at follow-up, but not with the ultrasonographic appearance of the ovaries (whether multifollicular or not). Recovery rates were 74% in women given hormone replacement therapy, 42% in those receiving oral contraception, and 80% in untreated patients. The respective mean recovery times were 25, 34, and 16.5 months. Twelve recovering women had 14 spontaneous pregnancies during follow-up, all but one of which occurred in the setting of hormone replacement therapy. On multivariate logistic regression analysis, baseline body mass index as well as baseline plasma cortisol and A levels predicted recovery from FHA (Fig. 1). FHA is frequently a result of psychological or physical stress, which, along with an inappropriate diet, may alter energy balance and reduce the body mass index. The disorder is reversible, as was the case in more than two thirds of the present patients. The role of various treatments remains unclear, but a stable or increasing body mass index does seem to be a factor in recovery.

Stimulatory effect of phenylephrine on the secretion of β-endorphin from rat adrenal medulla in vitro

In an attempt to investigate the role of α 1-adrenoceptors in the regulation of opioid secretion from adrenal gland, phenylephrine was employed to investigate the effect on secretion of β-endorphin-like immunoreactivity (BER) from adrenal medulla of rat in vitro. Phenylephrine enhanced the BER from isolated adrenal medulla in a concentration-dependent manner and this action was abolished by the antagonists of α 1-adrenoceptors, prazosin and tamsulosin. Investigations of signal pathway further support that an activation of α 1-adrenoceptors is responsible for the stimulatory effect of phenylephrine on BER secretion from adrenal medulla. In the presence of U73312, the specific inhibitor of phospholipase C (PLC), phenylephrine-induced change of BER was reduced in a concentration-dependent manner but it was not affected by U73343, the negative control of U73312. Moreover, chelerythrine and GF 109203X diminished the action of phenylephrine at concentration sufficient to inhibit protein kinase C (PKC). In conclusion, our results suggest that an activation of α 1-adrenoceptors in adrenal medulla by phenylephrine may enhance the secretion of opioids from adrenal gland of rat via signals of PLC–PKC pathway.

Localized Secretion of ATP and Opioids Revealed through Single Ca2+ Channel Modulation in Bovine Chromaffin Cells

In bovine chromaffin cells, the Ca2+ channels involved in exocytosis are effectively inhibited by ATP and opioids that are coreleased with catecholamines during cell activity. This autocrine loop causes a delay in Ca2+ channel activation that is quickly removed by preceding depolarizations. Changes in Ca2+ channel gating by secreted products thus make it possible to correlate Ca2+ channel activity to secretory events. Here, using cell-attached patch recordings, we found a remarkable correlation between delayed Ca2+ channel openings and neurotransmitter secretion induced by either local or whole-cell Ba2+ stimulation. The action is specific for N- and P/Q-type channels and largely prevented by PTX and mixtures of purinergic and opioid receptor antagonists. Overall, our data provide evidence that exocytosis, viewed through the autocrine inhibition of non-L-type channels, is detectable in membrane patches of ∼1 μm2 distributed over 30%–40% of the total cell surface, while Ca2+ channels and autoreceptors are uniformly distributed over most of the cell membrane.

Neuroanatomical patterns of Fos-like immunoreactivity induced by naltrexone in food-restricted and ad libitum fed rats

Chronic food restriction produces a variety of adaptive changes in physiology and behavior aimed at the preservation of energy homeostasis. The brain opioid system may be involved in the adaptation to food restriction since regional levels of opioid peptides, precursor mRNA, and receptor binding have previously been observed. In the present study, c-Fos immunohistochemistry was used to localize cells that are released from opioid-mediated inhibition by naltrexone under conditions of food restriction and ad libitum feeding. In the majority of hypothalamic and forebrain areas examined, Fos-like immunoreactivity (FLI) was higher in food-restricted rats regardless of injection treatment. This may reflect the persistent stress of underfeeding or the synchronizing effect of afternoon feeding on spontaneous c- fos mRNA expression in food-restricted rats. In two brain regions, bed nucleus of the stria terminalis (BNST) and central amygdala (CEA), naltrexone increased FLI in ad libitum fed rats, exclusively. This result suggests the presence of tonic opioid secretion under basal conditions that is suppressed by food restriction. Interestingly, work in other laboratories indicates that anorectic agents consistently increase FLI in BNST and CEA. In three brain regions – lateral (LH), dorsomedial (DMH) and arcuate hypothalamus (ARC) – naltrexone increased FLI in food-restricted rats, exclusively. This result suggests the presence of opioid secretion that is unique to the state of food restriction. The hypothalamic pattern of FLI is discussed in terms of NPY–opioid interactions that result from the ARC response to changes in circulating insulin, corticosterone and leptin levels during food restriction.