Studies on the inhibitory action of opiate compounds in isolated bovine adrenal chromaffin cells: noninvolvement of stereospecific opiate binding sites

Role of the Adrenal Medulla in Hypoglycaemia-Associated Autonomic Failure-A Diabetic Perspective

Hypoglycaemia-associated autonomic failure (HAAF) is characterised by an impairment in adrenal medullary and neurogenic symptom responses following episodes of recurrent hypoglycaemia. Here, we review the status quo of research related to the regulatory mechanisms of the adrenal medulla in its response to single and recurrent hypoglycaemia in both diabetic and non-diabetic subjects with particular focus given to catecholamine synthesis, enzymatic activity, and the impact of adrenal medullary peptides. Short-term post-transcriptional modifications, particularly phosphorylation at specific residues of tyrosine hydroxylase (TH), play a key role in the regulation of catecholamine synthesis. While the effects of recurrent hypoglycaemia on catecholamine synthetic enzymes remain inconsistent, long-term changes in TH protein expression suggest species-specific responses. Adrenomedullary peptides such as neuropeptide Y (NPY), galanin, and proenkephalin exhibit altered gene and protein expression in response to hypoglycaemia, suggesting a potential role in the modulation of catecholamine secretion. Of note is NPY, since its antagonism has been shown to prevent reductions in TH protein expression. This review highlights the need for further investigation into the molecular mechanisms involved in the adrenal medullary response to hypoglycaemia. Despite advancements in our understanding of HAAF in non-diabetic rodents, a reliable diabetic rodent model of HAAF remains a challenge.

Molecular mechanisms of glutamate release by bovine chromaffin cells in primary culture

Previous work indicated that glutamate could be involved in the regulation of catecholamine secretion in bovine chromaffin cells. Thus, the question arises on the source of this putative regulatory glutamate. In this work we have examined the possibility that glutamate could be released from chromaffin cells. Data from this study indicate that chromaffin cells are able to release glutamate when they are stimulated by different depolarising agents such as 60 mM KCl, 1 mM 4-aminopyridine or 50 microM veratridine. The amount of glutamate released by these compounds was 0.32 nmol/10(6) cells (9.24% of cellular glutamate content), 0.275 (7.86%) and 0.158 (4.52%) for KCl, 4-AP and veratridine stimulation, respectively. All these catecholamine-secretagogues induced glutamate secretion by two mechanisms: 1) a Ca(2+)-dependent, probably exocytotic, mechanism and 2) a Ca(2+)-independent mechanism mediated by reversion of the electrogenic glutamate transporter. Analysis of Ca(2+)-dependent and independent releases for different compounds carried out by several experimental approaches, indicate that Ca(2+)-dependent release was the predominant mechanism for release induced by 4-aminopyridine (84% of total release) and high KCl (63%) whilst Ca(2+)-independent release was predominant for veratridine (67%). The Ca(2+)-dependent glutamate release evoked by depolarisation of chromaffin cells with high KCl and 4-AP could be split into both a fast and a slow kinetic component, which might correspond to the release of docked and mobilised chromaffin granules, respectively. On the other hand, depolarisation of cells with veratridine result in glutamate release with only the fast kinetic component. In the case of 60 mM KCl-evoked glutamate release, the fast component exhibited a decay time of <1 s and accounted for 0.63 nmol glu/6x10(6) cells (70% of total exocytotic release), whereas the slow component, which exhibited a decay time of 231 s, accounted for the release of 0.27 nmol glu/6x10(6) cells (30% of total exocytotic release). By contrast in the case of 4-aminopyridine the fast component of exocytosis only represents a 19% of total secretion and the slow a 81% with a decay time of 94 s. These data are very similar to those found in neurones and support the possible intracellular origin of glutamate having a role in the regulation of catecholamine secretion from chromaffin cells. In support of this, we have found that glutamate secretion could be evoked by stimulation of the nicotinic cholinergic receptors.

Uptake of [3H]dopamine in isolated chromaffin cells of the mouse: modulation by intra- and extra-adrenal peptides and other secretagogues

The effects of intra- and extra-adrenal peptides on [3H]dopamine uptake in adrenal chromaffin cells of the mouse were examined in vitro. Dopamine uptake was inhibited by acetylcholine, high potassium, reserpine, imipramine and desmethylimipramine as was in noradrenaline uptake. Among the intra-adrenal peptides, vasoactive intestinal peptide (VIP, 100 pmol/l) and neurotensin inhibited [3H]dopamine uptake by approximately 25%. Somatostatin, enkephalin, and neuropeptide Y did not cause any significant inhibition. An extra-adrenal peptide, bradykinin, inhibited the uptake while angiotensin II showed no significant effect. Intra-adrenal peptides which cause catecholamine secretion inhibit catecholamine uptake probably to extend its effect. Extra-adrenal peptide which causes catecholamine secretion also inhibits catecholamine uptake.

Opioids inhibit dopamine secretion from PC12 rat pheochromocytoma cells in a naloxone-reversible manner

Opioids inhibit the release of catecholamines in the nervous system. Normal adrenal chromaffin cells produce delta opioids and they respond to them by suppressing the release of their catecholamines. Chromaffin cell tumors, the pheochromocytomas, produce mainly kappa opioids. The aim of this work was: (a) to test if pheochromocytomas retain the response of normal chromaffin cell catecholamines to delta opioids and to naloxone (a general opioid antagonist), and (b) to test if kappa opioids exert any specific effect on catecholamine release from these tumors. Since we have previously shown that, in common with human pheochromocytomas, the PC12 rat pheochromocytoma cells express the prodynorphin gene and secret its kappa opioid products, we used these cells to examine the effect of several opioid agonists and of naloxone on basal, nicotine-, and KCl-induced dopamine release. Dopamine is the main PC12 catecholamine. We have found that the specific kappa opioid agonist U-69593 inhibited the release of dopamine in a dose-dependent manner (IC50=0.5 x 10(-8)M). Under basal conditions the mean concentration of dopamine in the culture media was 11.25 +/- 0.57 ng/mg of total cellular protein (n=13). A 30 min exposure to U-69593 at 10(-6) M suppressed basal dopamine release to 58 +/- 2% (n=7) of controls. A 12 hr pre-incubation with U-69593 caused the same degree of suppression. The effect of the synthetic kappa opioid agonist dynorphin A was indistinguishable from that of U-69593. DADLE (a mu and delta synthetic opioid agonist) was significantly less effective in suppressing dopamine release (IC50=10(-7)M). The concentration of dopamine following exposure to 10-6 M of DADLE for 30 min was 74 +/- 5% of the controls (n=4). The mu opioid agonist DAGO was ineffective. The suppressive effect of all opioid agonists was blocked by naloxone suggesting that conventional opioid receptors were involved.

GABAB receptors modulate catecholamine secretion in chromaffin cells by a mechanism involving cyclic AMP formation

1. The function of gamma-aminobutyric acidB (GABAB) receptors in modulation of catecholamine secretion by chromaffin cells and the possible mechanism involved in this action have been examined. 2. The GABAB agonists (-)-baclofen and 3-aminopropylphosphinic acid (3-APPA) were found to induce a dose-dependent increase of basal catecholamine secretion. The EC50s were 151 +/- 35 microM and 225 +/- 58 microM for baclofen and 3-APPA, respectively. This stimulatory effect was specific since it could be blocked by 0.5 mM of the specific GABAB antagonist CGP-35348. 3. In contrast, preincubation of chromaffin cells with the GABAB agonists was found to inhibit, in a dose-dependent manner, the catecholamine secretion evoked by 10 microM nicotine and 200 microM muscimol. 4. The effects of GABAB agonists on both basal and evoked catecholamine secretion were found to be accompanied by parallel changes in intracellular calcium concentration ([Ca2+]i). GABAB agonists produced a dose-dependent increase in [Ca2+]i which was partially blocked by CGP 35348, but they produced a strong inhibition of the [Ca2+]i increase induced by nicotine and muscimol. 5. The GABAB agonists also produced a dose-dependent increase in intracellular cyclic AMP levels, there being a direct correlation between both increase in catecholamine secretion and in intracellular cyclic AMP levels. 6. The pretreatment of chromaffin cells with pertussis toxin doubled the catecholamine secretion and increased by four times the intracellular cyclic AMP levels evoked by GABAB agonists. 7. The possible involvement of adenylate cyclase in the mechanism of GABAA receptor modulation of catecholamine secretion is discussed.

Localisation and pharmacological characterisation of [3H]bremazocine binding in the bovine adrenal medulla

[3H]Bremazocine (5 nM), in the presence of excess unlabelled mu and delta opioid ligands labelled two anatomically distinct populations of binding sites in the bovine adrenal medulla; a high density over the peripheral adrenaline-containing region of the medulla and a lower density over the central noradrenaline-containing region. This non-mu, non-delta opioid binding was specific (diprenorphine sensitive) but did not appear to involve classical kappa (kappa 1), sigma or PCP binding sites being insensitive to high concentrations of dynorphin (1-13), 3-PPP or MK-801. A significant proportion of the binding at both locations was however sensitive to competition by U50,488H or metorphamide. These data provide further evidence to support the existence of multiple opioid binding sites in the bovine adrenal medulla.

Dynorphin A-(1-13)-Tyr14-Leu15-Phe16-Asn17-Gly18-Pro19 : a potent and selective kappa opioid peptide

Dynorphin A-(1-13)-Tyr14-Leu15-Phe16-Asn17-Gly18-Pro19+ ++ (dynorphin Ia: a peptide derived from the structure of adrenal dynorphin I) was synthesized by the solid-phase procedure. The product was purified and compared with dynorphin A-(1-13) and [D-Pro10]dynorphin A-(1-11) for its ability to inhibit the electrically evoked contractions of the guinea pig ileum (GPI) and mouse vas deferens (MVD) and to compete with the binding of [3H]ethylketocyclazocine (kappa ligand), [3H][D-Ala2,MePhe4,Glyol5]enkephalin (mu ligand) and [3H][D-Ser2,Thr6]Leu-enkephalin (delta ligand) to membrane preparations of the guinea pig cerebellum or rat brain. Additionally, the antinociceptive effects of the synthetic peptide were assessed in rat paw-pressure and tail-flick tests. In the GPI, dynorphin Ia possessed a relative potency (IC50 0.5 nM) that was comparable to that of [D-Pro10]dynorphin A-(1-11) (IC50 0.5 nM) or dynorphin A-(1-13) (IC50 0.7 nM). In the delta specific MVD assay, dynorphin Ia displayed a reduced potency (IC50 235 nM) as compared with that of dynorphin A-(1-13) (IC50 20 nM) or [D-Pro10]dynorphin A-(1-11) (IC50 46 nM). The affinity of dynorphin Ia for the kappa site in the guinea pig cerebellum (Ki 0.25 nM) was comparable to those of dynorphin A-(1-13) (Ki 0.11 nM) and [D-Pro10]dynorphin A-(1-11) (Ki 0.10 nM). However, the peptide possessed reduced affinities for the mu (Ki 6.7 nM) and delta (Ki 71 nM) opioid receptors as compared with [D-Pro10]dynorphin A-(1-11) (Ki 1.7 and 1.5 nM) an dynorphin A-(1-13) (Ki 0.5 and 4.4 nM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Opioid inhibition of nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells

The ability of a number of opioid agonists and antagonists to affect nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells has been investigated. High (10 microM) concentrations of the opioid agonist bremazocine produced a significant inhibition of nicotine-induced 45Ca2(+)-uptake throughout the 15 min time course examined. The opioid subtype-selectivity of this inhibition was investigated; mu and delta selective agonists produced only minor effects whereas the kappa selective agonist U50-488H and the endogenous opioid peptides dynorphin(1-13) and metorphamide almost abolished nicotine-induced 45Ca2(+)-uptake. The U50-488H inhibition was significant at 10 nM concentrations with an IC50 of approximately 1 microM. U50-488H inhibition could not be reversed or reduced by the opioid antagonists naxolone, diprenophine or Mr2266. Furthermore, Mr2266 and its optical isomer Mr2267 also produced marked inhibition of 45Ca2(+)-uptake. The inhibition was specific to nicotine-induced 45Ca2(+)-uptake in that a similar level of uptake evoked by potassium depolarization was unaffected by high concentrations of U50-488H. These data indicate that opioid inhibition of nicotine-induced 45Ca2(+)-uptake does not involve classical, stereospecific opioid receptors and suggests the involvement of a pharmacologically distinct opioid recognition site. It is speculated that this may be associated with the nicotine receptor-ionophore complex.

The distribution of opioid binding subtypes in the bovine adrenal medulla

Autoradiography has been used to examine the distribution of opioid binding subtypes in the bovine adrenal gland. Specific opioid binding sites were restricted to the adrenal medulla. Kappa sites, labelled with [3H]bremazocine (in the presence of excess unlabelled mu and delta ligands), were highly concentrated over nerve tracts. These nerve tract associated binding sites were sensitive to competition by the endogenous opioid, dynorphin (1-13). Specific [3H]bremazocine binding sites were also found over the adrenal medullary chromaffin tissue. These binding sites were concentrated over the peripheral, adrenaline-containing region of the medulla and were sensitive to competition by diprenorphine but not dynorphin (1-13). Delta opioid sites, labelled with [3H][D-Ala2,D-Leu5] enkephalin (in the presence of excess unlabelled mu ligand) were selectively localized to the central, noradrenaline-containing region of the adrenal medulla. Mu opioid sites, labelled with [3H][D-Ala2, NMePhe4,Gly-ol5]enkephalin, were low in number and distributed throughout the adrenal medulla. These studies demonstrate that mu, delta and two distinct kappa opioid binding sites are differently distributed within the bovine adrenal medulla and suggest possible new sites of action for the adrenal medullary opioid peptides.

Lack of effect of opioid compounds on angiotensin II responses of bovine adrenal medullary cells

Angiotensin II (10 nM) increased basal adrenaline and noradrenaline secretion from cultured bovine adrenal chromaffin cells by 2.5- to 3-fold and 4- to 6-fold, respectively, and stimulated basal accumulation of inositol phosphates more than 2-fold. Etorphine and diprenorphine in the range 10(-9) to 10(-5) M had no effect on the catecholamine secretion induced by angiotensin II, and, at 10(-8) and 10(-5) M, had no effect on angiotensin II-induced inositol phosphate accumulation. The functions of adrenal medullary opioid receptors remain to be determined.

Secretion from chromaffin cells is controlled by chromogranin A-derived peptides

Chromogranin A (CGA) is the major protein of the secretory granule from chromaffin cells and also is found in a variety of endocrine cells. Although the sequence of this acidic glycoprotein has been elucidated recently, its biological function is unknown. Here we have purified CGA from chromaffin granules; the final preparation contained the 74-kDa native CGA together with two degradation products--three bands near 60 kDa and a single band of 43 kDa. This preparation was found to inhibit (a maximum inhibition of 60% at 1 microM) the nicotine-induced, but not the high K+-evoked, catecholamine secretion from bovine chromaffin cells maintained in primary culture. Spontaneous release was also affected in the nanomolar CGA protein concentration range. The observation that the inhibitory effect is strictly dependent on a preincubation step together with the modification of the CGA protein profile during this preincubation step suggests that the degradation peptide(s) rather than the 74-kDa native CGA--the approximately equal to 60-kDa bands or the 43-kDa singlet band--is actually involved in secretory cell activity. This was demonstrated by using trypsin-generated peptides that were inhibitory without the preincubation period. The finding that unprocessed CGA is not active on chromaffin cell secretion suggests that this molecule is a precursor of a peptide(s) that is able to regulate catecholamine secretion. Thus, the present data suggest that a CGA-derived peptide(s) could exert a feedback control on chromaffin cell secretory activity--a mechanism that might be of importance during stress situations.

Effects of hemorrhage and opiate antagonists on adrenal release of neuropeptides in cats

Concurrent levels of methionine-enkephalin (ME), neuropeptide Y (NPY), peptide YY (PYY), neurotensin (NT), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK) and bombesin (BMB) were measured in adrenal vein (AD), femoral vein (FV) and femoral artery (FA) under baseline conditions and during hypotensive hemorrhage (HTH) in halothane anesthetized cats (Group II, n = 6) and compared to a non-bled control group (Group I, n = 6). Five cats (Group III) received an IV bolus of naltrexone (1 mg/kg) followed by a continuous infusion prior to induction of HTH. A blood volume loss of approximately 40% evoked a selective increase in AD levels of ME, NPY, PYY and NT. No differences in regard to hemodynamics and pattern of neuropeptide levels were observed between Group II and Group III. Administration of naloxone (1 mg/kg, IV) in Group I and Group II at the end of the experiment led to a significant increase in MABP in both groups but did not evoke changes in neuropeptide levels. We conclude that adrenal neuropeptide release during hypotensive hemorrhage is not modulated by actions on opiate receptors in the halothane anesthetized cat.

Inhibitory regulation by co-released peptides of catecholamine secretion by the canine adrenal medulla

1. We have stimulated the peripheral end of the cut left splanchnic nerve in anaesthetized dogs while collecting the venous effluent of the left adrenal gland for catecholamine estimation. 2. With low frequency stimulation the resting output of catecholamines was inhibited but at high frequencies it was augmented. 3. The inhibition of catecholamine output by low frequency stimulation was reversed by opiate antagonists (naloxone and nalmefene) but enhanced by angiotensin converting enzyme inhibitors (captopril and enalapril).

Effects of opioid compounds on basal and muscarinic induced accumulation of inositol phosphates in cultured bovine chromaffin cells

The mammalian adrenal medulla expresses a variety of both opioid peptides and opioid receptors. The function of this adrenal opioid system is, however, largely unknown. We have examined the ability of a number of opioid compounds to influence basal and muscarinic stimulated accumulation of inositol phosphates in cultured bovine chromaffin cells. Muscarine produced a dose-dependent 1.5-fold increase in total inositol phosphates. This response was sensitive to atropine inhibition. The ten opioid compounds examined were chosen because between them they possess selectivity for all of the identified opioid receptor subtypes. However, none of these opioids in the concentration range 10nM-10 microM had any significant effect on either basal or muscarinic induced total inositol phosphate accumulation. We conclude that it is unlikely that opioid peptides released from either the chromaffin cells themselves or the splanchnic nerve can modulate the inositol phosphate second messenger system within the adrenal chromaffin cells.

Prostanoid responses of bovine adrenal medullary cells: lack of effect of opioids

The effects of opioid compounds on catecholamine (CA) secretion and phosphatidylinositol turnover induced by prostaglandins E1 (PGE1) and E2 (PGE2) in cultured bovine adrenal medullary cells have been studied. PGE1 induced CA secretion at 100 nM and above. PGE2 was more potent, inducing CA secretion at 1-10 nM. Both prostaglandins required extracellular calcium to induce CA release. Neither etorphine nor diprenorphine (1 nM-10 microM) affected CA secretion induced by 1 microM PGE1 or 0.1 microM PGE2. PGE1 a small increase in phosphatidylinositol turnover at 10 microM, but had no effect at lower concentrations. PGE2 was effective at 1 and 10 microM. Etorphine and diprenorphine had no effect on phosphatidylinositol turnover induced by PGE1 or PGE2. The results indicate prostaglandins can facilitate CA secretion independently of their effects on phosphatidylinositol metabolism. They also indicate that endogenous adrenal opioid peptides do not act on the opioid binding sites found on adrenal medullary cells to modify their responses to prostaglandins.

Direct and continuous detection of ATP secretion from primary monolayer cultures of bovine adrenal chromaffin cells

A method was developed for direct and continuous detection of secretion of ATP from primary monolayer cultures of bovine adrenal chromaffin cells. ATP, which is costored with catecholamines within adrenal chromaffin cells, was released into the incubation medium, where it reacted with firefly luciferin-luciferase producing light detected by a photomultiplier located directly below the culture well. Acetylcholine, nicotine, the Ca2+ ionophore A23187, BaCl2, and KCl induced release of ATP. Induction of release of ATP by acetylcholine was dose dependent, with a threshold at 10(-7) M and a maximum at 10(-4) M. The dose-response curve for nicotine was bell shaped, with a threshold at 10(-7) M, a maximum at 10(-5) M, and diminished release at higher concentrations, an observation indicative of desensitization. Investigation of the initial rates of ATP secretion revealed that 10(-4) M nicotine actually induced release of ATP at a faster rate than 10(-5) M nicotine. However, the rate of ATP release evoked by 10(-4) M nicotine began to decline by 6 s, a result indicating the onset of receptor desensitization, whereas release induced by 10(-5) M nicotine continued unabated. Induction of release of ATP by acetylcholine or nicotine was biphasic, with a rapid, initial phase of release followed by a plateau at 0.5-1.5 min and a second phase of release beginning at 1.5-2 min, reaching a maximum by 2-3 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of opioid compounds on desensitization of the nicotinic response of isolated bovine adrenal chromaffin cells

Opioid compounds have been assessed for their ability to modify desensitization of nicotine-induced catecholamine secretion from cultured, bovine, adrenal chromaffin cells. Dynorphin-1-13 and metorphamide produced protection against desensitization of the nicotinic response at concentrations between 1 and 20 microM while etorphine and morphine only produced this effect at 100 microM. The opioid antagonists, naloxone and diprenorphine, at 100 microM mimicked the weak ability of the opioid agonists to protect against nicotinic desensitization. All opioid compounds tested were considerably more potent at inhibiting nicotine-induced catecholamine secretion from the cells than at protecting against desensitization of this response. It is concluded that adrenal opioid peptides probably do not act on adrenal opioid binding sites characterised from ligand binding studies to prevent the nicotinic response from desensitizing. They are unlikely, therefore, to be involved in such a mechanism to maintain catecholamine secretion during stress.

Vasoactive intestinal polypeptide stimulates the secretion of catecholamines from the rat adrenal gland

1. Our previous studies have indicated that splanchnic nerves release a substance(s), other than acetylcholine, that induces the secretion of catecholamines from the rat adrenal medulla. To identify the nature of the non-cholinergic substance, the effects of met-enkephalin and vasoactive intestinal polypeptide (VIP) were investigated in the perfused adrenal gland of the rat. 2. The secretion of catecholamines increased from a basal level of 8 ng to a maximum value of 18 ng during perfusion with 100 microM-met-enkephalin. The secretion evoked by 10 micrograms acetylcholine increased from 118 to 143 ng in the presence of 10 microM-met-enkephalin. Higher concentrations of met-enkephalin (100 microM) had no additional effect. Secretion of catecholamines evoked by stimulation of splanchnic nerves (10 Hz for 30 s) was even less (8%) affected by met-enkephalin. 3. 0.3 microM-VIP caused a significant increase in the secretion of catecholamines, and the effect increased with an increase in the concentration of VIP. About 115 ng of catecholamines were secreted during 15 min perfusion with 3 microM-VIP. 4. VIP-evoked secretion was not affected by antagonists of nicotinic and muscarinic receptors, nor by chronic splanchnicotomy. However, removal of calcium ions from, and inclusion of 1 mM-EGTA in, the perfusion medium completely inhibited the secretion evoked by VIP. 5. VIP-evoked secretion was reduced (20-75%) in a concentration-dependent manner by 3-30 microM-naloxone. 6. It is suggested that VIP may be the non-cholinergic excitatory substance present in the splanchnic nerves and released along with acetylcholine during simulation of the nerves to evoke secretion of catecholamine from the rat chromaffin cells.

Inhibition of nicotine-induced secretion from bovine chromaffin cells by the amidated C-terminal sequence of the opioid peptide amidorphin

The nicotine-induced release of catecholamines and opioid peptides from bovine chromaffin cells is inhibited by the amidated opioid peptide amidorphin. The active site of this inhibitory activity is located at the peptide's C-Terminus, which is, in contrast to the N-terminal sequence TYR-GLY-GLY-PHE, not responsible for the opioidergic activity of opioid peptides. The noradrenaline-secretion induced by histamine, a non-cholinergic secretagogue, has not been inhibited by amidorphin.

Effects of opioid peptides and morphine on histamine-induced catecholamine secretion from cultured, bovine adrenal chromaffin cells

The effect of opioid peptides and morphine on histamine-induced catecholamine secretion has been studied in monolayer cultures of dispersed, bovine adrenal chromaffin cells. Histamine-induced a dose-dependent secretion of both adrenaline and noradrenaline with a threshold dose of approximately 5 nM, an EC50 of 150 nM and maximal secretion at 10 microM. Catecholamine secretion induced by 1 microM histamine was completely dependent on extracellular calcium, was inhibited in a dose-dependent manner by mepyramine (1 nM-1 microM), and was unaffected by cimetidine (10 microM) and hexamethonium (0.1 mM). Dynorphin-1-13 (1 nM-20 microM), metorphamide (0.1 nM-10 microM), morphine (1 nM-0.1 mM) and diprenorphine (1 nM-0.1 mM) each had no effect on adrenaline or noradrenaline secretion induced by 1 microM histamine. The characteristics of histamine-induced catecholamine secretion from bovine adrenal chromaffin cells were similar to those reported previously for cat and rat adrenal medulla being calcium-dependent and mediated by H1 histamine-receptors. The results with opioid peptides and morphine suggest that endogenous adrenal opioid peptides do not act on the opioid binding sites found on adrenal medullary chromaffin cells to modify their secretory response to histamine.

Release of catecholamines from superfused bovine adrenal chromaffin cells cultured on microcarrier beads

A procedure is described for the establishment of stable primary cultures of bovine chromaffin cells on microcarrier beads. The cells flatten and send out processes with varicosities over a few days and maintain their catecholamine content for 2 weeks. The beads may be incorporated into a superfusion apparatus with a chamber volume of about 150 microliters, enabling the efficient perfusion of a high density of cells. The response to the introduction of nicotine and high potassium into the perfusing medium is shown to be more rapid and more transient than hitherto described, with each secretagogue producing a different degree of preferential stimulation of noradrenaline-secreting cells.

Metorphamide, a novel endogenous adrenal opioid peptide, inhibits nicotine-induced secretion from bovine adrenal chromaffin cells

Opioid peptides are found in high concentrations in the adrenal medulla. Recently, a novel opioid octapeptide, metorphamide, possessing an amidated C-terminal, was characterized and also found to be present in adrenal tissue. We have studied the ability of this novel peptide to modify nicotine-induced secretion from isolated bovine adrenal chromaffin cells. Exocytosis was monitored by measuring adenosine triphosphate (ATP) release on-line by the luciferin-luciferase bioluminescence method, or by measuring endogenous catecholamine release by high-performance liquid chromatography (HPLC) with electrochemical detection. Metorphamide inhibited 5 microM nicotine-induced ATP release from fresh chromaffin cells by almost 50% at 5 microM. Metorphamide at concentrations less than 1 microM had no effect on 5 microM nicotine-induced adrenaline and noradrenaline release from cultured cells, but at higher concentrations inhibited their release equally, with an IC50 of approximately 10 microM. By contrast, Met5-enkephalin inhibited the release of both catecholamines equally with an IC50 of greater than 1 mM, making metorphamide greater than 100-fold more potent than Met5-enkephalin in this system. Naloxone (10 microM) and diprenorphine (1 microM) failed to antagonise the inhibitory action of metorphamide on nicotine-induced catecholamine release. Metorphamide inhibited the nicotinic response in a non-competitive manner, and failed to affect either adrenaline or noradrenaline release induced by elevated potassium ion concentrations. The results suggest metorphamide acts on naloxone- and diprenorphine-resistant receptors to inhibit chromaffin cell nicotinic secretion and that the novel amidated C-terminal of the peptide is important for this action.

Effects of opioid peptides containing the sequence of Met5-enkephalin or Leu5-enkephalin on nicotine-induced secretion from bovine adrenal chromaffin cells

Eighteen endogenous opioid peptides, all containing the sequence of either Met5- or Leu5-enkephalin, were tested for their ability to modify nicotine-induced secretion from bovine adrenal chromaffin cells. ATP released from suspensions of freshly isolated cells was measured with the luciferin-luciferase bioluminescence method as an index of secretion. None of the peptides affected 5 microM nicotine-induced ATP release at 10 nM. Three peptides inhibited secretion at 5 microM: dynorphin1-13, dynorphin1-9, and rimorphin inhibited by 65%, 37%, and 29% respectively. Use of peptidase inhibitors (bestatin, thiorphan, bacitracin, or 1,10-phenanthroline) did not result in any of the other peptides showing potent actions on the nicotinic response, although bestatin and thiorphan did enhance the inhibitory actions of dynorphin1-13 and dynorphin1-9 by 20-30%. Nicotine-induced secretion of endogenous catecholamines from bovine chromaffin cells cultured for 3 days was also studied to assess any selective actions of the peptides on adrenaline or noradrenaline cell types. Dynorphin1-13 was 1,000-fold more potent than Leu5-enkephalin at inhibiting endogenous catecholamine secretion. Dynorphin1-13 was slightly more potent at inhibiting noradrenaline release than adrenaline release whereas Leu5-enkephalin showed the opposite selectivity. The structure-activity relationships of opioid peptide actions on the chromaffin cell nicotinic response are discussed in relation to the properties of the adrenal opioid binding sites.

Interaction of dynorphin with kappa opioid receptors in bovine adrenal medulla

Dynorphin (Dyn) and various prototypic kappa opioid ligands were tested for their ability to bind to opioid receptors in a membrane preparation of bovine adrenal medulla and to modulate the release of catecholamines (CA) from isolated adrenal chromaffin cells. Saturation binding studies with [3H]-ethylketocyclazocine ([3H]-EKC) were performed at 37 degrees C for 30 min in the presence of [D-Ala2,Me-Phe4,Gly-ol5]-enkephalin (DAGO) and [D-Ser2,Thr6]-Leu-enkephalin (DSLET), two specific ligands for crossreacting mu and delta opioid receptors, respectively. Scatchard plot analysis of the data revealed the presence of two receptor sites: a high affinity binding site (kappa) with a KD of 0.66 nM and a Bmax of 12 pmoles/g protein and a low affinity binding site (kappa 2) with a KD of 11.1 nM and a Bmax of 56 pmoles/g protein. The presence of kappa opioid receptors in the membrane preparation was also supported by competition studies. U-50, 488H and Dyn-(1-13), two selective kappa opioid ligands, were potent inhibitors of [3H]-EKC binding with Ki (high affinity binding sites) of 2.5 and 2.3 nM, respectively. Among the various ligands tested for each class of opioid receptors (mu, delta, kappa), U-50, 488H and Dyn-(1-13) were the most potent inhibitors of the acetylcholine-evoked CA secretions from isolated adrenal chromaffin cells with IC50 of 0.31 and 1.14 microM, respectively. The inhibitory effect of U-50, 488H was significantly antagonized by diprenorphine and MR-2266, two opioid antagonists with a high affinity for the kappa opioid receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of opioid drugs on the release of dopamine and 5-hydroxytryptamine from rat striatum following activation of nicotinic-cholinergic receptors

The effect of (Met5)enkephalin, (D-Ala2,D-Met5)enkephalin, (Leu5)enkephalin, (D-Ala2,D-Met5)enkephalin and morphine on the release of [3H]dopamine, endogenous dopamine and [3H]5-hydroxytryptamine produced by the nicotinic-cholinergic agonist, dimethylphenyl piperazinium iodide (DMPP), was examined in rat striatal slices. The DMPP-induced release of [3H]dopamine and endogenous dopamine was reduced by the presence of (Met5)enkephalin, (D-Ala2,D-Met5)enkephalin (1-10 microM) or morphine (10 microM) but not by (Leu5)enkephalin or (D-Ala2,D-Leu5)enkephalin. The DMPP-induced release of [3H]5-hydroxytryptamine was reduced by (Leu5)enkephalin, (D-Ala2,D-Leu5)enkephalin, (Met5)enkephalin, (D-Ala2,D-Leu5)enkephalin (1-10 microM), and morphine (10 microM). All three opioids failed to alter the release of [3H]dopamine induced by field stimulation or potassium depolarization (30 microM). The inhibitory effects of opioid peptides and morphine demonstrated in the present study appear to be due to an initial interaction with nicotinic-cholinergic receptors in the striatum.

Bovine adrenal chromaffin cells: high-yield purification and viability in suspension culture

A method for purifying chromaffin cells from adult, bovine, adrenal medullae and the techniques for maintaining the cells in suspension culture for at least 14 days are presented. Perfusion of medullae with a collagenase-containing medium produced a cell fraction that contained, in addition to chromaffin cells, a significant percentage of non-chromaffin cells. These cells were found to attach more rapidly than chromaffin cells to glass and tissue-culture plasticware. Using this property, we devised a selective plating procedure that yielded approximately 1-2 x 10(8) chromaffin cells per adrenal medulla at a purity of 95% or higher. On the basis of catecholamine levels and enzyme activities, suspension (as opposed to monolayer) cultures were chosen to further investigate their potential as a model system for the regulation of adrenergic function. In contrast to chromaffin cells cultured in monolayer, chromaffin cells in suspension had a more rounded appearance and formed multicellular aggregates with time in culture. Very few neurite-like structures, commonly observed in monolayer cultures, were present in the suspension cultures. Also, inhibitors of mitosis were not necessary to prevent overgrowth by non-chromaffin cells as there was little or no cell division in the suspension cultures. Catecholamine levels were relatively stable for at least 2 weeks, although a gradual decline in epinephrine occurred after day 5. Unlike other enzymes involved in catecholamine metabolism, phenylethanolamine N-methyl transferase activity declined significantly with time in culture in parallel to the gradual loss of epinephrine. In addition, both oxygen consumption and amino acid incorporation into proteins were relatively stable. Thus, the primary suspension cultures of adult, bovine chromaffin cells seem to offer several advantages for studying long-term regulation of chromaffin cell function and provide a stable source of adrenergic cells for examining short-term regulatory processes.

Distinct distribution of immunoreactive dynorphin and leucine enkephalin in various populations of isolated adrenal cromaffin cells

The distribution of immunoreactive-dynorphin (ir-Dyn) in isolated subpopulations of bovine adrenal chromaffin cells was examined and compared with that of adrenaline (A), noradrenaline (NA) and ir-Leucine-Enkephalin (ir-Leu-Enk). Using a stepwise bovine serum albumin (BSA) gradient, various populations of catecholamine-storing cells were separated and designated as cell layers I, II and III. Cell layer I contained more NA than A; cell layer II contained slightly more A than NA whereas cell layer III was highly enriched in A. The original cell preparation contained 2.9 times more ir-Leu-Enk than ir-Dyn (4.7 and 1.6 pmoles per 10(6) cells, respectively). After separation of the cells on BSA gradient, ir-Dyn was mainly detected in cell layer I (4.0 pmoles/10(6) cells) whereas ir-Leu-Enk was concentrated in cell layer III (8.3 pmoles/10(6) cells). Both peptides were secreted in response to acetylcholine (5 x 10(-5) M), but the amount secreted was in accordance with the cell content in each peptide. After subcellular fractionation of the adrenal medulla, the neuropeptides were found in close association with catecholamines in the secretory granules. These results indicate that bovine adrenal chromaffin cells can be isolated according to their specific content in A, NA and opioid peptides and are consistent with the hypothesis of distinct biosynthetic pathways for Dyn and the Enk.

Use of isolated chromaffin cells to study basic release mechanisms

An account is given of the authors' work with isolated adrenal chromaffin cells to study the synthesis, storage and release of catecholamines and of a number of neuropeptides endogenous to the adrenal medulla. A review of other studies in the literature with the isolated chromaffin cell system is included. It is seen that the isolated chromaffin cells are a convenient in vitro system well-suited to studies of basic release mechanisms. The isolated adrenal chromaffin cells maintain high levels of catecholamines and opiates and release them by exocytosis. The cells have both nicotinic and muscarinic receptors but only the nicotinic are involved in the agonist-evoked release of catecholamines (EC50 nicotine 5 X 10(-6) M: ACh 5 X 10(-5) M). The cells can synthesize AChE and selectively release the 10S molecular form by a mechanism different from exocytosis. Substance P (SP) modulates the secretion of catecholamines and ATP evoked by ACh or nicotine but not that evoked by K+ or veratridine. SP appears to interact with the nicotinic receptor-ionophore complex to regulate Na+ entry. SP receptors on the chromaffin cells show similar structural requirements to SP receptors in other SP responsive tissues. Binding studies on isolated chromaffin cell membranes with [4-3H-Phe]SP have shown specific binding in the nM range. In addition, at high concentrations of ACh, SP protects against nicotinic receptor desensitization. Since SP is contained in the splanchnic nerve terminals that innervate the medulla, the demonstration of SP action and SP receptors on the chromaffin cells suggests a physiological role for SP in the regulation of secretion from the adrenal medulla. Somatostatin (SS) and a number of SS analogues also inhibit release, but are approximately 15-fold less potent than SP. Leu- and Met-enkephalin, which are co-stored with adrenaline in the bovine adrenal medullary cells produce a non-specific inhibition of the nicotine-evoked release of CA, but enhance the basal release of endogenous catecholamines by a mechanism that is Ca2+-dependent, stereospecific and reversible by naloxone and naltrexone. The implication of these peptide-amine interactions for physiological processes regulating homeostasis in the adrenal are discussed.

Opiate binding sites in bovine adrenal medulla

Previous studies using a variety of opiate ligands have suggested the existence of several subclasses of opiate receptors in crude membrane fractions of rat brain, and a similar diversity in bovine adrenal medulla. To examine the receptor profile of bovine adrenal medulla in detail we have studied the binding of classical ligands for mu (mu), delta (delta) and kappa (kappa) opiate receptors. [3H]naloxone ([3H]NAL), [3H]morphine ([3H]MOR), [3H]D-Ala2-D-Leu5-enkephalin ([3H]DAL) and [3H]ethyl-ketocyclazocine ([3H]EKCZ) were used as tracers; unlabeled competitors were NAL, MOR, DAL and ketocyclazocine (KCZ). In adrenal medulla [3H]NAL was specifically bound with a hierarchy of displacement NAL greater than MOR greater than KCZ much greater than DAL. No specific binding of [3H]DAL or [3H]EKCZ was found; for [3H]MOR very low levels of binding were seen, with no displacement by NAL or DAL, inconsistent displacement by KCZ and substantial displacement by MOR with an ED50 of 1.5 nM. In parallel studies rat brain membranes bound each labeled ligand with affinity and specificity consistent with previously published reports. Identical results were obtained in membranes from both tissues prepared with a preincubation step including 100 mM Na+, suggesting that the results were not influenced by occupation of binding sites by endogenous ligands. We interpret these data as supporting the existence of opiate receptors of the mu subtype in bovine adrenal medulla. We find, however, no evidence of delta or kappa sites in this tissue.

Localization of opiate binding sites in kidney and adrenal gland of the rat

[3H]ethylketocyclazocine (EKC) and [3H]etorphine bind to an apparent single class of sites in the rat kidney (kd = 7.3 and 5.2 nM; Bmax = 33.2 and 59.6 fmol/mg protein, respectively). No detectable binding was observed for [3H]dihydromorphine and [3H]D-Ala2,D-Leu5 enkephalin. Ligand selectivity pattern strongly suggests that both [3H]EKC and [3H]etorphine label a kappa opiate binding site since (-)bremazocine greater than EKC greater than etorphine greater than naloxone greater than dynorphin A much greater than beta-endorphin. In the adrenal gland, [3H]EKC also labels a single class of sites (Kd = 20.1 nM; Bmax = 74.7 fmol/mg protein) while no specific binding was seen with mu and delta ligands. Autoradiographically, [3H]EKC and [3H]etorphine binding sites are highly localized in kidney cortex compared to outer and inner medulla. Rather surprisingly, [3H]EKC binding sites in the adrenal are highly localized in the cortex with only low densities in the medulla. We are currently investigating the possible physiological roles of kappa agonists in kidney and adrenal gland functions.

Endogenous opiates: 1981

This paper is the fourth of an annual series reviewing the research concerning the endogenous opiate peptides. This installment covers only work published during 1981 and attempts to provide a comprehensive, but not exhaustive, survey of the area. Previous papers in the series have dealt with research done before 1981. Topics concerning endogenous opiates reviewed here include a delineation of their receptors, their distribution, their precursors and degradation, behavioral effects resulting from their administration, their possible involvement in physiological responses, and their interactions with other peptides and hormones. Due to the burgeoning literature in this field, the comprehensive nature of this review in the future will be limited to considerations of behavioral phenomena related to the endogenous opiates.

Evidence that inhibition of nicotine-mediated catecholamine secretion from adrenal chromaffin cells by enkephalin, beta-endorphin, dynorphin (1-13), and opiates is not mediated via specific opiate receptors

The opioid peptides Met- and Leu-enkephalin, dynorphin (1-13), and beta-endorphin and the narcotic analgesics, morphine, levorphanol, and dextrorphan all produced a dose-dependent inhibition of nicotine (5 x 10(-6) M)-mediated release of [3H]norepinephrine ([3H]NE) from bovine adrenal chromaffin cells in culture. None of these agents affected [3H]NE release induced by high K+ (56 mM). Although the above results suggest that the opioid peptides and narcotic analgesics inhibit catecholamine release from adrenal chromaffin cells in culture, we suggest that these effects are not mediated by specific opiate binding sites, since (1) the inhibition was only produced with high concentrations of the agents--the threshold concentrations were 10(-7) to 10(-5)M and higher; (2) the inhibition produced by the narcotic analgesics did not display stereospecificity, because the d-isomer, dextrorphan, was slightly more active than the l-isomer, levorphanol; (3) the narcotic antagonists naloxone, naltrexone, and levallorphan did not reverse the inhibition produced by either the narcotic analgesics (e.g., morphine) or the opioid peptides (e.g., dynorphin). These three antagonists themselves inhibited the nicotine-mediated release of [3H]NE from the adrenal chromaffin cells in culture. Finally (4), the I2-Tyr1 substituted analogues of beta-endorphin and dynorphin that are biologically less active than the parent compounds produced an inhibition of the nicotine-mediated [3H]NE release similar to that of their parent compounds. These results do not support the idea that high-affinity stereospecific opiate binding sites are involved in the inhibitory modulation of nicotinic evoked catecholamine release from bovine adrenal chromaffin cells in culture.

Effects of pro-opiomelanocortin fragments on release of catecholamines from adrenal chromaffin cells

The effects of pro-opiomelanocortin (POMC) peptide fragments on the basal and agonist-induced release of catecholamines (CAs) from monolayer cultures of purified bovine adrenal chromaffin cells were tested. None of the 5 peptides tested, i.e. beta-MSH, ACTH1-39, gamma-MSH1-13, gamma 3-MSH and N-terminal POMC fragment, had any effect on basal CA release. However, beta-MSH (10(-5) M), gamma-MSH1-13 (10(-6)-10(-5) M), gamma 3-MSH (10(-5) M) and N-terminal POMC fragment (10(-5) M) inhibited the nicotine-induced release of CAs from the chromaffin cells. The possible physiological significance of this inhibitory neuromodulation is discussed.