Beta-endorphin inhibits glucose production in the conscious dog

Insulinoma mimic: methadone-induced hypoglycaemia

Methadone use for opioid use disorder and chronic pain has increased since the start of the century with about 4.4 million dispensed prescriptions in 2009. With increased use of methadone, there has been increasing reporting of less commonly reported side effects (ie, hypoglycaemia). Here, we describe a woman in her 70s with history of opioid use disorder on methadone, stage 4 chronic kidney disease and prior hypoglycaemic episodes who initially presented with perforated gastric ulcer requiring surgical repair. Her perioperative course was complicated by profound hyperinsulinaemic hypoglycaemia. Given concern for methadone-induced hypoglycaemia, methadone was discontinued with monitoring of subsequent blood glucose, insulin, C peptide, proinsulin, β-hydroxybutyrate and blood methadone levels. As the serum methadone levels decreased, insulin levels substantially decreased in parallel. After 21 days off methadone, dextrose infusion was discontinued with restoration of euglycaemia. In a patient with hyperinsulinaemic hypoglycaemia and methadone use, it is important to consider discontinuing methadone and re-evaluate fasting glucose levels prior to an extensive and invasive insulinoma workup.

The Clash of Two Epidemics: the Relationship Between Opioids and Glucose Metabolism

PURPOSE OF REVIEW

We are currently in the midst of a global opioid epidemic. Opioids affect many physiological processes, but one side effect that is not often taken into consideration is the opioid-induced alteration in blood glucose levels.

RECENT FINDINGS

This review shows that the vast majority of studies report that opioid stimulation increases blood glucose levels. In addition, plasma levels of the endogenous opioid β-endorphin rise in response to low blood glucose. In contrast, in hyperglycaemic baseline conditions such as in patients with type 2 diabetes mellitus (T2DM), opioid stimulation lowers blood glucose levels. Furthermore, obesity itself alters sensitivity to opioids, changes opioid receptor expression and increases plasma β-endorphin levels. Thus, opioid stimulation can have various side effects on glycaemia that should be taken into consideration upon prescribing opioid-based medication, and more research is needed to unravel the interaction between obesity, glycaemia and opioid use.

Activation of nucleus accumbens μ-opioid receptors enhances the response to a glycaemic challenge

Opioids are known to affect blood glucose levels but their exact role in the physiological control of glucose metabolism remains unclear. Although there are numerous studies investigating the peripheral effects of opioid stimulation, little is known about how central opioids control blood glucose and which brain areas are involved. One brain area possibly involved is the nucleus accumbens because, as well as being a key site for opioid effects on food intake, it has also been implicated in the control of blood glucose levels. Within the nucleus accumbens, μ-opioid receptors are most abundantly expressed. Therefore, in the present study, we investigated the role of μ-opioid receptors in the nucleus accumbens in the control of glucose metabolism. We show that infusion of the μ-opioid receptor agonist [d-Ala2 , N-MePhe4 , Gly-ol]-enkephalin (DAMGO) in the nucleus accumbens by itself does not affect blood glucose levels, but it enhances the glycaemic response after both an insulin tolerance test, as well as a glucose tolerance test. These findings indicate that the nucleus accumbens plays a role in the central effects of opioids on glucose metabolism, and highlight the possibility of nucleus accumbens μ-opioid receptors as a therapeutic target for enhancing the counter-regulatory response.

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.

A Case of Unintentional Methadone Overdose Followed by Hypoglycaemia

Methadone overdose is expected to result in intoxication simulating the other opioids. We report a case of hypoglycaemia following accidental methadone ingestion. A 21-year-old woman presented to a local accident and emergency department 10 hours after ingestion of 800 mg of methadone. She was found to have coma, respiratory suppression, hypotension, prolonged QTc and hypoglycaemia. The hypoglycaemia was reversed by dextrose replacement. The patient required intubation and inotropic support because of cardio-respiratory instability. She eventually recovered without consequence. To date, this is the first reported case of methadone overdose induced hypoglycaemia.

Evaluation of the counter-regulatory responses to hypoglycaemia in patients with type 1 diabetes during opiate receptor blockade with naltrexone

AIMS

Hypoglycaemia is the major limiting factor in achieving optimal glycaemic control in people with type 1 diabetes (T1DM), especially intensively treated patients with impaired glucose counter-regulation during hypoglycaemia. Naloxone, an opiate receptor blocker, has been reported to enhance the acute counter-regulatory response to hypoglycaemia when administered intravenously in humans. The current study was undertaken to investigate the oral formulation of the long-acting opiate antagonist, naltrexone, and determine if it could have a similar effect, and thus might be useful therapeutically in treatment of T1DM patients with a high risk of hypoglycaemia.

MATERIALS AND METHODS

We performed a randomized, placebo-controlled, double-blinded, cross-over study in which 9 intensively treated subjects with T1DM underwent a 2-step euglycaemic-hypoglycaemic-hyperinsulinaemic clamp on 2 separate occasions. At 12 hours and at 1 hour before the clamp study, participants received 100 mg of naltrexone or placebo orally. Counter-regulatory hormonal responses were assessed at baseline and during each step of the hyperinsulinaemic-clamp.

RESULTS

Glucose and insulin levels did not differ significantly between the naltrexone and placebo visits; nor did the glucose infusion rates required to keep glucose levels at target. During hypoglycaemia, naltrexone, in comparison with the placebo group, induced an increase in epinephrine levels ( P  = .05). However, no statistically significant differences in glucagon, cortisol and growth hormone responses were observed.

CONCLUSION

In contrast to the intravenous opiate receptor blocker naloxone, overnight administration of the oral long-acting opiate receptor blocker, naltrexone, at a clinically used dose, had a limited effect on the counter-regulatory response to hypoglycaemia in intensively treated subjects with T1DM.

Opioid μ-receptors as new target for insulin resistance

Type-2 diabetes is one of the fastest growing public health problems worldwide resulting from both environmental and genetic factors. Activation of μ-opioid receptor (MOR) could result in reversal of the impairment of insulin-stimulated glucose disposal in genetically obese Zucker rats via exercise training. This improvement of insulin resistance was associated with an elevation of circulating β-endorphin to ameliorate the post-receptor insulin signaling cascade, including downstream effectors of the phosphatidylinositol 3-kinase (PI3-kinase) signaling pathway. In insulin resistant rats, Loperamide treatment effected on the insulin receptor substrate (IRS)-1/PI3-kinase/Akt signaling cascade and subsequent insulin-stimulated glucose transport trafficking on skeletal muscle, which were all suppressed by MOR antagonism. In addition, induction of insulin resistance by the intake of high fructose is more rapid in MOR knockout mice than in wild-type mice. Improvements in insulin sensitivity through the peripheral MOR activation overcoming defects related to the post-receptor in IRS-1-associated PI3-kinase step have been defined. Opioid receptor activation, especially of the μ-subtype, may provide merits in the amelioration of defective insulin action. Atypical zeta (ζ) isoform of protein kinase C serves as a factor that integrates with peripheral MOR pathway and insulin signals for glucose utilization. The developments call new insights into the chemical compounds and/or herbal products that might enhance opioid peptide secretion and/or stimulate MOR in peripheral insulin-sensitive tissues to serve as potential agents or adjuvants for helping the glucose metabolism. In the present review, we update these topics and discuss the concept of targeting peripheral MOR pathway for the treatment of insulin resistance.

Mediation of Endogenous β-Endorphin in the Plasma Glucose-Lowering Action of Herbal Products Observed in Type 1-Like Diabetic Rats

Recently, there have been advances in the development of new substances effective in managing diabetic disorders. Opioid receptors couple multiple systems to result in various biological effects, although opioids are best known for analgesia. In the present review, we used our recent data to describe the advance in plasma glucose-lowering action of herbal products, especially the mediation of β-endorphin in glucose homeostasis of insulin-deficient diabetes. In type 1-like streptozotocin-induced diabetic rats, we identified many products purified from herbs that show a dose-dependent plasma glucose-lowering action. Increase in β-endorphin secretion from the adrenal gland may activate peripheral opioid μ-receptors (MOR) to enhance the expression of muscle glucose transporters and/or to reduce hepatic gluconeogenesis at the gene level, thereby leading to improved glucose utilization in peripheral tissues for amelioration of severe hyperglycemia. It has also been observed that stimulation of α(1)-adrenoceptors (α(1)-ARs) in the adrenal gland by some herbal products is responsible for the increase in β-endorphin secretion via a phospholipase C-protein kinase dependent pathway. However, an increase in β-endorphin secretion from the adrenal gland by herbal products can function via another receptor. New insights into the mediation of endogenous β-endorphin activation of peripheral MOR by herbal products for regulation of glucose homeostasis without the presence of insulin have been established. Therefore, an increase in β-endorphin secretion and/or direct stimulation of peripheral MOR via an insulin-independent action might serve as the potential target for development of a therapeutic agent or promising adjuvant in intensive plasma glucose control.

Investigations of the mechanism of the reduction of plasma glucose by cold-stress in streptozotocin-induced diabetic rats

Exposure to a cold environment may increase the activity of the sympathetic nervous system inducing an elevation of plasma norepinephrine and may result in hyperglycemia. In the present study, we found that a hypoglycemic effect was produced in streptozotocin-induced diabetic rats after cold-exposure at 4 degrees C for 1 h. In addition to the blockade of this hypoglycemic effect by guanethidine (a ganglion-blocking agent) and prazosin (an alpha1-adrenoceptor antagonist), an increase of plasma norepinephrine was also observed in streptozotocin-induced diabetic rats receiving this cold-stress. Participation of sympathetic hyperactivity can thus be considered. Furthermore, naloxone, in a dose (0.5 mg/kg, i.p.) sufficient to block opioid receptors, reversed this hypoglycemia. Also, an increase of plasma beta-endorphin-like immunoreactivity was observed in streptozotocin-induced diabetic rats receiving this cold-stress. Intravenous injection of beta-endorphin into streptozotocin-induced diabetic rats produced a lowering of plasma glucose. Administration of methoxamine at a dose sufficient to activate the alpha1-adrenoceptors produced hypoglycemia and a similar increase of plasma beta-endorphin-like immunoreactivity in streptozotocin-induced diabetic rats. However, plasma beta-endorphin-like immunoreactivity level was not modified by similar treatment with methoxamine or cold-stress in normoglycemic rats. Therefore, beta-endorphin appears to be responsible for the induction of hypoglycemic effects in streptozotocin-induced diabetic rats after cold exposure which is different to the response in normal rats.

The opiate sufentanil alters the inflammatory, endocrine, and metabolic responses to endotoxin in dogs

Sufentanil is a synthetic mu-opioid receptor agonist frequently used in anesthesia and critically ill patients. To evaluate the effects of sufentanil on the inflammatory, neuroendocrine, and metabolic responses to endotoxin, we studied six dogs during saline infusion (control), during sufentanil infusion (1.5 microg . kg-1 . h-1), after endotoxin injection (1.0 microg/kg iv), and during combined endotoxin and sufentanil administration. The rate of appearance of glucose was determined by infusion of [6,6-2H2]glucose. Sufentanil depressed the endotoxin-induced increase in body temperature (36.9 +/- 0.3 vs. 40.6 +/- 0.5 degrees C, P < 0.05). Sufentanil depressed the tumor necrosis factor (TNF) response to endotoxin by approximately 60% (P < 0.01) but increased the interleukin-6 (IL-6) response by approximately 70% (P < 0.01). Sufentanil per se induced a transient neuroendocrine activation. Sufentanil also increased plasma concentrations of insulin and catecholamines after endotoxin (P < 0.05 vs. endotoxin alone) and increased plasma glucose levels by approximately 36% (from 6.1 +/- 0.1 to 8.3 +/- 0.6 mmol/l, P < 0.05 vs. endotoxin alone). Endotoxin stimulated glucose production transiently by 95% (24.2 +/- 3.2 vs. control 12.4 +/- 1.0 micromol . kg-1 . min-1, P < 0.05). Paradoxically, sufentanil inhibited this endotoxin-induced stimulation of glucose production (P < 0.05 vs. endotoxin alone). In conclusion, sufentanil modulates the response to intravenous endotoxin by dissociating the TNF and IL-6 response, increasing insulin and catecholamine levels, and depressing the increase in glucose production. Therefore, opiates alter inflammatory, endocrine, and metabolic regulation in endotoxemia.

Restoration of stable metabolic conditions during islet suppression in dogs

These studies were undertaken to examine the stability of metabolic conditions during islet suppression with fixed-rate insulin and glucagon replacement. Somatostatin was infused peripherally at 0.8 microgram.min-1.kg-1, insulin was infused intraportally at 200 microU.min-1.kg-1, and glucagon was infused intraportally at 0, 0.6, 1, 2, 5, or 20 ng.min-1.kg-1 in conscious overnight-fasted dogs. [3-3H]glucose was infused for measurement of glucose kinetics. During infusion, plasma insulin was 7.2 +/- 0.4 microU/ml. Plasma glucagon rose linearly with glucagon dose, achieving basal levels at 2 ng.min-1.kg-1 infusion (164 +/- 18 vs. basal = 182 +/- 57 pg/ml). Plasma glucose and hepatic glucose output (HGO) decreased from basal at doses 0, 0.6, and 1 ng.min-1.kg-1, increased from basal at doses 5 and 20 ng.min-1.kg-1, and remained close to basal at dose 2 ng.min-1.kg-1 (92 +/- 20 vs. basal = 99 +/- 3 mg/dl and 2.4 +/- 0.2 vs. basal = 2.7 +/- 0.2 mg.min-1.kg-1 for glucose and HGO, respectively; P greater than 0.47). Glucose clearance and blood lactate were also closely matched to basal at dose 2 ng.min-1.kg-1. Coefficients of variation during 2 ng.min-1.kg-1 glucagon infusion (last hour) were 3.4, 4.6, 4.9, and 4.7% for glucose, HGO, clearance, and lactate, respectively. These findings indicate that fasting metabolic conditions, as inferred from blood glucose, lactate, insulin, and glucagon levels, and the rates of glucose production and uptake can be recreated in toto during fixed-rate islet hormone replacement.

Effects of low- and high-intensity exercise on plasma and cerebrospinal fluid levels of ir-beta-endorphin, ACTH, cortisol, norepinephrine and glucose in the conscious dog

This study was designed to assess effects of exercise on plasma and cerebrospinal fluid (CSF) levels of immunoreactive (ir) beta-endorphin, ACTH, cortisol, norepinephrine, and glucose in the conscious dog. Dogs were exercised on a treadmill at low or high intensity (4.2 miles/h and a 6% or 20% incline) for 90 min, and were allowed to recover for 90 additional min. Neither intensity of exercise changed plasma glucose levels, but dose-related changes in glucose kinetics did occur. CSF glucose declined in both groups. During low intensity exercise, plasma levels of ir-beta-endorphin, ACTH, and cortisol increased with duration of exercise. During high intensity exercise, ACTH, ir-beta-endorphin and cortisol increased faster, and the integrated plasma response of these hormones was greater. Thus, peripheral release of ir-beta-endorphin, ACTH, and cortisol during exercise is dose-related with respect to time and intensity. CSF ir-beta-endorphin and ACTH both increased during low- but not high-intensity exercise. CSF cortisol rose markedly in both exercise groups. During high-intensity exercise there was a 50% increase in CSF norepinephrine, indicating that exercise induces alterations in central noradrenergic turnover. We conclude that exercise is a physiologic regulator of both peripheral and central neuroendocrine systems.

Central effects of beta-endorphins on glucose homeostasis in the conscious dog

The effects of centrally administered beta-endorphins on glucose homeostasis in the conscious dog were studied. Intracerebroventricular administration of beta-endorphin (0.2 mg/h) caused a 70% increase in plasma glucose. The mechanism of the hyperglycemia was twofold: there was an early increase in glucose production and a late inhibition of glucose clearance. These changes are explained by marked increases in plasma epinephrine (30-fold) and norepinephrine (6-fold) that occurred during infusion of beta-endorphin. Central administration of beta-endorphin also resulted in increased levels of adrenocorticotropic hormone and cortisol. In addition there was an increase in plasma insulin but no increase in plasma glucagon. Intravenous administration of beta-endorphin did not alter glucose homeostasis. Intracerebroventricular administration of acetylated beta-endorphin did not perturb glucose kinetics or any of the hormones that changed during infusion of the unacetylated peptide. We conclude that beta-endorphin acts centrally to cause hyperglycemia by stimulating sympathetic outflow and the pituitary-adrenal axis. Acetylation of beta-endorphin abolishes the in vivo activity of the peptide.

Effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid levels of ir-beta-endorphins, ACTH, cortisol, norepinephrine, insulin and glucose in the conscious dog

This study was designed to assess effects of insulin-induced hypoglycemia on plasma and cerebrospinal fluid (CSF) levels of immunoreactive (ir) beta-endorphins, adrenocorticotropin (ACTH), cortisol, norepinephrine, insulin, and glucose in the conscious, overnight fasted dog. Dogs received either an intravenous infusion of saline or insulin (5 mU/kg/min) for 3 h. Infusion of saline alone in conjunction with acute sampling of CSF caused no measurable perturbations of glucose homeostasis. Insulin infusion caused a 60% drop in both plasma and CSF glucose. Plasma levels of ir-beta-endorphins, ACTH and cortisol rose markedly. CSF levels of ir-beta-endorphins and ACTH also increased. While the magnitude of the increase was smaller than that in the plasma, it was greater than would be expected if crossover of the peptides from the plasma were the sole source of the increase. Hypoglycemia also induced elevations in CSF cortisol and insulin. In addition, there was a 45% decrease in CSF norepinephrine in spite of large elevations of norepinephrine in the plasma. We conclude that hypoglycemia is associated with marked changes in central as well as peripheral levels of neuroendocrine factors. The importance of these changes in mediating acute and long-term responses to hypoglycemia remains to be established.

Beta endorphin modulation of the glucoregulatory effects of repeated epinephrine infusion in alloxan-diabetic and normal dogs

When repeated epinephrine infusions are given to normal dogs as a partial stress model, there is exaggerated hyperglycaemia, associated with reduced plasma insulin levels and markedly decreased glucose clearance. In the present study, we have examined the hormonal and metabolic responses to two successive 60-min epinephrine (0.1 microgram . kg-1 . min-1) infusions with or without concomitant infusion of beta endorphin (0.3 microgram . kg-1 . min-1) in 6 alloxan-diabetic dogs. These studies have been compared to similar studies in 5 normal dogs. In the diabetic dogs, plasma glucose rose from 12.3 +/- 2.2 to 16.2 +/- 2.4 mmol/l (p less than 0.001) in response to the first epinephrine infusion and rose further to 18.1 +/- 2.5 mmol/l (p less than 0.001) during the second epinephrine infusion. The increases in plasma glucagon and glucose production were comparable with both infusions, but considerably greater than previously observed in normal dogs. In normal dogs, beta endorphin diminished the insulin response to the first epinephrine infusion (p less than 0.02), and abolished this response to the second (p less than 0.05). In addition beta endorphin also diminished the glucagon response to the second epinephrine infusion (p less than 0.01) and greatly potentiated epinephrine-induced suppression of glucose metabolic clearance during both infusions (p less than 0.001). However, beta endorphin did not appreciably alter the hyperglycaemic response to epinephrine due to a concomitant attenuation of the epinephrine-induced increase in hepatic glucose production. In contrast to normal dogs, beta endorphin did not modulate the effects of either the first or second epinephrine infusion on glucose kinetics in diabetic dogs. Also, beta endorphin failed to inhibit glucagon or insulin secretion in response to epinephrine in the diabetic animals. Since the alloxan-diabetic and normal dogs respond differently to the combined infusion of beta endorphin and epinephrine we conclude that the effects of beta endorphin observed in the normal dogs are dependent upon intact pancreatic endocrine function.

Effect of naloxone on counter insulin hormone secretion in insulin-induced hypoglycemia

To investigate the normal physiologic role of endogenous opiates in glucose homeostasis and as a preliminary study for clarifying the association of endogenous opites with pathophysilogy of NIDDM, we obseved the changes in the secretion of counter-insulin hormones in response to insulin-induced hypoglycemia with or without naloxone.

The results were as follows: Blood glucose was decreased significantly more rapidly with naloxone infusion than after insulin alone, which seems to play a role in the early responses of ACTH and GH. Not only was the more rapid response of ACTH and GH, but also the prolonged secretion of ACTH and Cortisol were observed after administration of insulin and naloxone.

We concluded that endogenous opiates may be involved in the feedback regulation of secretion of ACTH and GH during hypoglycemia either at hypophysis or hypothalamus, and involved in glucose homeostasis via a certain direct mechanism other than regulation of counter hormone secretion.

Beta-endorphin infusion fails to modulate the hormonal and metabolic response to surgery

The effects of an i.v. infusion of synthetic human beta-endorphin on the hormonal, metabolic and cardiovascular responses to surgery were investigated in female patients undergoing pelvic surgery. A beta-endorphin infusion (2 micrograms/kg as a bolus at induction of anaesthesia + 10 micrograms/kg/h for the first hour of surgery) increased plasma beta-endorphin immunoreactivity to values at least 100-fold greater than those seen during surgery in a control group of patients. In spite of this massive increase the only significant findings were a transient augmentation of the expected hyperglycaemic response and increased plasma glucagon values. There were no significant changes in ACTH, GH, insulin and cortisol secretion, in blood concentrations of lactate or glycerol, or in cardiovascular variables. Complete dissociation between plasma and cerebrospinal fluid concentrations of beta-endorphin was found even when plasma values exceeded 10,000 pmol/l in the presence of anaesthesia and surgery. These results show that the increase in circulating beta-endorphin immunoreactivity associated with clinical stress states are unlikely to modulate the associated hormonal, metabolic and cardiovascular changes.

Lack of effect of beta-endorphin on basal or glucagon-stimulated hepatic glucose production in vitro

beta-Endorphin appears to have effects on hepatic glucose production in vivo. In order to determine whether beta-endorphin modulates glucose production directly, the effects of beta-endorphin on isolated rat hepatocytes were investigated. This permitted isolation of the effects of beta-endorphin from hormonal and/or neuronal influences. A significant dose-related stimulatory effect of glucagon (10(-10) to 10(-6) mol/L) on both hepatic glucose production and glycogen phosphorylase a activity was demonstrated. No effect of either physiologic (10(-11) to 10(-9) mol/L) or supraphysiologic (10(-6) mol/L) concentrations of beta-endorphin on these parameters, under basal or glucagon-stimulated conditions, could be detected. These results suggest that reported in vivo effects of beta-endorphin to inhibit hepatic glucose production were either indirect or centrally mediated.

Impaired insulin response to glucose but not to arginine in heroin addicts

Plasma glucose, insulin, glucagon and growth hormone responses to both oral glucose and iv arginine were evaluated in 15 heroin addicts and 15 control subjects matched for age, sex and weight. The heroin users had an exaggerated rise in plasma glucose concentrations following oral sugar, which persisted until the end of the study (102 +/- 5 mg/dl in addicts vs 72 +/- 3 mg/dl in controls at 240 min, p less than 0.01) and significantly lower insulin responses (insulin peak 28 +/- 4 microU/ml in addicts vs 67 +/- 8 microU/ml in controls, p less than 0.01). The inhibitory effect of glucose on glucagon concentrations was less evident in addicts than in controls. The responses of plasma glucose, insulin and glucagon to arginine were not significantly different between addicts and controls, while the growth hormone rise was significantly greater in addicts. These results demonstrate that heroin users have impaired insulin secretion to oral glucose but not to arginine and suggest that: the impaired insulin secretion in heroin addicts is not dependent on beta-cell exhaustion, and a selective inhibition of glucose-induced insulin secretion is operative in these subjects, as it happens in patients with noninsulin-dependent diabetes mellitus.

Effect of opiate-receptor blockade on normoglycemic and hypoglycemic glucoregulation

By use of the opiate antagonist naloxone, we have examined the hormonal and metabolic responses to opiate-receptor blockade under basal conditions and during insulin-induced hypoglycemia in normal dogs. Naloxone treatment had no measurable effect on glucose concentration, turnover, and norepinephrine levels, but stimulated plasma epinephrine, glucagon, and cortisol and inhibited insulin release. Insulin (7 mU X kg-1 X min-1) decreased plasma glucose to 42 +/- 4 mg/dl due to an initial decrease in glucose production and an increase in glucose disappearance. Glucose production then increased, and plasma glucose plateaued. After 50 min of insulin infusion, epinephrine levels increased 26-fold (P less than 0.05), norepinephrine and glucagon 3-fold (P less than 0.02), and cortisol 4-fold (P less than 0.01). Similarly, plasma beta-endorphin and adrenocorticotropin (ACTH) were elevated (6-fold, P less than 0.01, and 16-fold, P less than 0.05, respectively). When naloxone was given during insulin-induced hypoglycemia, there was earlier release of epinephrine, glucagon, beta-endorphin, ACTH, and cortisol as well as a greater release of glucagon (P less than 0.001) and cortisol (P less than 0.0001). This resulted in a greater increase in glucose production (P less than 0.01), thus lessening the insulin-induced hypoglycemic excursion. In conclusion, in the dog, endogenous opiates may play a small role in the regulation of basal insulin and glucagon release and can inhibit the pituitary-adrenal axis under basal conditions and during hypoglycemia. Thus increased glucose production in response to insulin-induced hypoglycemia is consistent with the excessive response of counterregulatory hormones during opiate-receptor blockade.

Endogenous opioid modulation of pancreatic hormone secretion: studies in dogs

The role of endogenous opioid peptides in the modulation of secretion of hormones from the endocrine pancreas was studied in dogs. In response to insulin-induced hypoglycemia, plasma glucagon secretion significantly increased, followed by an increase in plasma somatostatin immunoreactivity. Pretreatment with the opiate antagonist, naloxone, prevented the somatostatin response but had no effect on the augmented glucagon secretion. Neither the degree of hypoglycemia nor recovery from the induced glucose nadir were affected by naloxone. Arginine Hcl administration resulted in prompt increases in immunoreactive glucagon and insulin secretion, as well as a rise in serum glucose. Pretreatment with naloxone failed to affect any of these responses. Our results suggest that endogenous opioid peptides mediate the somatostatin response following hypoglycemia-induced glucagon secretion.

The nature of opioid involvement in the hemodynamic respiratory and humoral responses to exercise

After 30 min rest in the lying position, 12 healthy male volunteers (average age 22 years) received, in a randomized double-blind cross-over protocol, either saline or naloxone (10 mg iv followed by a continuous infusion of 10 mg/hr). Thereafter they rested for a further 30 min in the recumbent position and for 15 min sitting on a bicycle ergometer; they then exercised to exhaustion. At rest plasma levels of adrenocorticotropin (ACTH), cortisol, and aldosterone increased during infusion of naloxone, while body temperature decreased. During exercise the difference in plasma ACTH between naloxone and saline periods was abolished, while the differences in plasma cortisol and aldosterone lost statistical significance. Intra-arterial pressure, heart rate, ventilation, O2 uptake, and CO2 output were continuously monitored throughout the experiment and were not affected by naloxone. This was also the case for several hormonal and biochemical measurements, including those of plasma renin, angiotensin II, norepinephrine, 13,14-dihydro-15-keto-prostaglandin F2 alpha, glucose and lactate, and serum insulin and growth hormone. Exercise performance was not changed by naloxone. In conclusion (1) during exhaustive graded exercise of short duration opioidergic inhibition of the pituitary-adrenocortical axis is probably not sustained, (2) apart from the latter mechanism, the present study does not support the hypothesis that endogenous opioids are involved in various hemodynamic, respiratory, and hormonal responses to this type of exercise.

Endogenous opioids modulate the effect of cholecystokinin on insulin release in dogs

Recently we have demonstrated in dogs and man that endogenous opioids participate in the regulation of pancreatic endocrine function following the ingestion of a meal. Since intestinal hormones such as cholecystokinin (CCK) are also released by the presence of nutrients in the gastrointestinal tract and participate in the postprandial stimulation of pancreatic endocrine function, an interaction between CCK and endogenous opioids seems possible. The present study was designed to examine this further. In a group of 8 conscious dogs the octapeptide of CCK was infused intravenously in its sulfated (CCK-8S) or nonsulfated (CCK-8NS) form and in addition the tetrapeptide of CCK (CCK-4) was given at increasing infusion rates of 50, 200 and 500 pmol/kg . h, respectively. The experiments were performed during a background infusion of saline to assess the effect on basal insulin and during a background infusion of glucose (0.2 g/min) to determine the effects on stimulated insulin release. The effect of endogenous opioids was examined by addition of the opiate-receptor antagonist naloxone. The studies demonstrate that in the basal state CCK-8S has no stimulatory effect on insulin secretion unless naloxone is added indicating that endogenous opioids help to prevent insulin secretion in the absence of elevated glucose levels. During i.v. glucose naloxone reduced the stimulatory effect of CCK-8S at 50 and 200 pmol/kg . h and that of CCK-4 at 50 pmol/kg . h. Infusion of CCK-8S and CCK-4 at 500 pmol/kg . h had no effect on glucose-stimulated insulin levels, however, the addition of naloxone elicited a significant stimulatory effect. These data demonstrate stimulatory as well as inhibitory effects of endogenous opioids depending on the dose of CCK-8 and -4. CCK-8NS reduced glucose-stimulated insulin release already at the lowest dose of 50 pmol/kg . h. This was reversed to a stimulatory effect with the addition of naloxone. These data demonstrate that the interaction between CCK-8 and -4 and endogenous opioids on prestimulated insulin secretion is much more dependent on the dose of CCK - low doses induce stimulatory and high doses inhibitory mechanisms via endogenous opioids. In view of previous in vitro and in vivo studies with exogenously infused opiate-active compounds it might be speculated that increasing doses of CCK elicit a parellel increase in the release of endogenous opioids which might be responsible for some but certainly not all of the effects observed recently for the action of naloxone in the post-prandial state.