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

The chromaffin vesicle: advances in understanding the composition of a versatile, multifunctional secretory organelle

Chromaffin vesicles (CV) are highly sophisticated secretory organelles synthesized in adrenal medullary chromaffin cells. They contain a complex mixture of structural proteins, catecholamine neurotransmitters, peptide hormones, and the relative processing enzymes, as well as protease inhibitors. In addition, CV store ATP, ascorbic acid, and calcium. During the last decades, extensive studies have contributed to increase our understanding of the molecular composition of CV. Yet, the recent development of biochemical and imaging procedures has greatly increased the list of CV-soluble constituents and opened new horizons as to the complexity of CV involvement in acute stress responses. Thus, a coherent picture of CV molecular composition is still to be drawn. This review article will provide a detailed account of the content of CV soluble molecules as it emerges from the most recent analytical studies. Moreover, this review article will attempt at focussing on the physiological and pathophysiological implications of the products released by CV.

Primary culture of bovine chromaffin cells

This protocol describes the primary culture of individual chromaffin cells derived by enzymatic digestion from the adrenal medulla of the bovine adrenal gland. Since the late 1970s, such cells have provided a useful model system to study neurotransmitter biosynthesis, storage and release in the catecholaminergic system. The protocol can be divided into three stages: isolation of cells (4-6 h), determination of viable cell numbers (approximately 30 min) and growth in culture (3-7 d). An alternative procedure is to perform studies in a continuous chromaffin (pheochromocytoma) cell line, such as PC12, although such transformed cells are typically less highly differentiated than primary cells. The bovine chromaffin cell procedure should yield approximately 10-20 million cells, suitable for several experiments over the subsequent 3-7 d. Typical experiments involve transmitter biosynthesis, vesicular storage, exocytotic release, stimulus coupling (signal transduction) toward secretion or transcription, or morphology, including ultrastructure. The total time, from adrenal gland harvest until functional experiments, is typically 4-8 d.

Neurotransmitters and neuropeptides in the differential regulation of steroidogenesis in adrenocortical-chromaffin co-cultures

Adrenocortical steroidogenesis is regulated in addition to a central regulation via the hypothalamus-pituitary-adrenal axis by intra-adrenal mechanisms involving the adrenal medulla. We could previously show that adrenocortical steroidogenesis is stimulated by co-culturing bovine adrenocortical cells with medullary chromaffin cells. This stimulation was due to soluble factors released from the chromaffin cells under basal, unstimulated conditions and involved the increased expression of P450 enzymes, StAR and de novo protein synthesis. In the present study we analyzed the differential regulation of the three cortical zones and characterized secretagogues involved in this stimulation. While cortisol and androstenedione release were increased 10 fold by incubation with chromaffin cell-conditioned medium, aldosterone secretion was not influenced. 80% of the stimulation proved to be due to adrenomedullary epinephrine, norepinephrine, ACTH, PACAP and PG-dependent mechanisms. Other adrenomedullary secretory products, serotonin, Met-enkephalin, Leu-enkephalin, galanin, CGRP, substance P, VIP or NPY did not stimulate steroidogenesis in this system. Our data show that adrenomedullary cells differentially regulate the three adrenocortical zones. This stimulation predominantly depended on epinephrine, norepinephrine, PACAP, and ACTH released from the chromaffin cells and prostaglandin-dependent mechanisms such as interleukin-1.

Posttranslational processing of proenkephalins and chromogranins/secretogranins

Posttranslational processing of peptide-precursors is nowadays believed to play an important role in the functioning of neurons and endocrine cells. Both proenkephalins and chromogranins/secretogranins are considered as precursor molecules in these tissues, resulting in posttranslationally formed degradation products with potential biological activities. Among the proteins and peptides of neuronal and endocrine secretory granules, the enkephalins and enkephalin-containing peptides have been most extensively studied. The characterization of the post-translationally formed degradation products of the proenkephalins have enabled the understanding of their processing pathway. Chromogranins/secretogranins represent a group of acidic glycoproteins, contained within hormone storage granules. The biochemistry, biogenesis and molecular properties of these proteins have already been studied for 25 years. The chromogranins/secretogranins have a widespread distribution throughout the neuroendocrine system, the adrenal medullary chromaffin granules being the major source of these storage components. Recent data provide evidence for a precursor role for all members of the chromogranins/secretogranins family although also several other functions have been proposed. In this review, some of the methods applied to study proteolytic processing are described. In addition, the posttranslational processing of chromogranins/secretogranins and proenkephalins, especially the biochemical aspects, will be discussed and compared. Recent exciting developments on the generation and identification of potential physiologically active fragments will be covered.

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)

Source of Stress-Induced Increase in Plasma Met-Enkephalin in Rats: Contribution of Adrenal Medulla and/or Sympathetic Nerves*

Abstract The contribution of the adrenal medulla and/or the sympathetic nerves to the plasma levels of Met-enkephalin was investigated. Rats were divided into four groups: sham-operated/saline, sham-operated/guanethidine, adrenal-demedullated/saline, demedulla-ted/guanethidine. After 4 weeks of injection with either saline or guanethidine (25 mg/kg/day), animals were cannulated in the left carotid artery for blood sampling. Three days later, blood samples were taken before and at 2 and 30 min of restraint stress. Adrenal demedullation lowered basal plasma epinephrine levels markedly and prevented entirely the increase induced by restraint stress. Chronic guanethidine treatment lowered basal plasma norepinephrine levels and decreased the response to stress. Guanethidine treatment increased the basal plasma epinephrine level without affecting the response to stress. The combination of guanethidine plus adrenal demedullation lowered basal plasma concentrations of all three catecholamines and further attenuated the norepinephrine response. Restraint stress increased plasma native and peptidase-derivable Met-enkephalin. Adrenal demedullation, resulting in greater than 95% depletion of adrenal catecholamines and significant depletion of adrenal Met-enkephalin, did not inhibit the stress-induced increase in plasma Met-enkephalin, and in fact, was associated with a potentiated response to stress. Guanethidine treatment with or without demedullation increased baseline plasma native Met-enkephalin and abolished the stress-induced increase in plasma native and peptidase-derivable Met-enkephalin. Thus, the stress-induced increase in plasma Metenkephalin results from release from sympathetic nerves, rather than adrenal medulla. However, the sympathetic nerves and adrenal medulla together do not appear to account entirely for basal concentrations of circulating Met-enkephalin. Hepatic portal vein plasma concentration of native Met-enkephalin was greater than that in the carotid artery, suggesting contribution from the gastrointestinal tract; however, evisceration did not decrease plasma native Met-enkephalin. Some compensatory mechanism results in elevation of basal plasma native Met-enkephalin in sympathectomized rats. Also, in the absence of the adrenal medulla there is a compensatory increase in the amount of Met-enkephalin released into the circulation in response to stress.

Neuronal and adrenal enkephalins and catecholamines in response to acute CNS ischemia and reserpine in pig

Co-storage of enkephalins and catecholamines in coronary artery, mesenteric artery and vein, middle cerebral artery, vas deferens and adrenal medulla was studied in domestic pig (Sus scrofa). Responses to acute CNS ischemia were correlated with time to peak plasma levels of central venous and adrenal vein outflow samples in controls, during reserpine treatment and after drug withdrawal. Endogenous enkephalins are co-stored in chromaffin granules of adrenal epinephrine-type cells and large dense cored vesicles of noradrenergic terminals. After a lag period, reserpine at near 'therapeutic' doses caused an apparent induction of opioid peptide precursor synthesis accompanied by processing to enkephalins in adrenal medulla up to 8-fold by 30 days and in mesenteric vein up to 4.5-fold by 14 days. Upon 14 days recovery from reserpine, elevated adrenal enkephalins were maintained and depleted catecholamines were largely replenished. Acute CNS ischemia produced rises in MAP (approx. 80 mmHg), marked net depletions of noradrenergic enkephalin stores, and net increases in adrenal vein outflow and central venous levels of enkephalins and catecholamines. Noradrenergic terminals contributed significantly to circulating enkephalins as well as norepinephrine. Reserpine for 7 days nearly abolished all tested responses to acute CNS ischemia, but immediate net 200-400% elevations of endogenous enkephalin stores occurred in coronary artery and mesenteric artery and vein (apparent processing of reserpine-induced neuronal precursor stores). Thus, induction of new synthesis of precursor opioid peptides by reserpine, with or without parallel processing to enkephalins, occurs in noradrenergic terminals in many tissues. All effects of reserpine on endogenous enkephalins implicate a central mechanism to inhibit sympathoadrenal outflow to the periphery. At 14 days recovery from reserpine, when near normal cardiovascular responses to acute CNS ischemia were regained, there was increased net release of the elevated adrenal enkephalins, exaggerated peak plasma enkephalin concentrations, but only minimal depletions of enkephalins from noradrenergic terminals.

Separation and culture of living adrenaline- and noradrenaline-containing cells from bovine adrenal medullae

Separation of viable adrenaline-containing from noradrenaline-containing chromaffin cells in large amounts has been achieved. The procedure involves collagenase digestion of bovine adrenomedullary tissue, isolation of cells through gentle filtration, separation of chromaffin from nonchromaffin cells on discontinuous gradients of the radiopaque contrast Renografin, and separation of adrenaline-enriched from noradrenaline-enriched fractions after centrifugation on self-generated Percoll gradients. Collection of 1-ml Percoll fractions gave two clear-cut catecholamine peaks. The denser peak was enriched in adrenaline and phenylethanolamine-N-methyltransferase (PNMT), suggesting that over 90% of cells were adrenergic. The lighter peak was preferentially enriched in noradrenaline but not in PNMT. With this information, we could collect by gentle aspiration two main fraction layers of larger volumes; one at the bottom of the Percoll gradient, which contained essentially adrenaline-storing cells and the other at the top of the gradient, enriched in noradrenaline cells. Those cells could be maintained viable for at least 1 week in primary monolayer cultures, as shown by neutral red staining and trypan blue exclusion. This method will allow the identification of chemical components, receptors, or ionic channels present in one specific type of cell, to determine their relevance to the regulation of the differential secretion of specific materials present in one but not in the other cell type and to ascertain whether the released materials from one cell type affect the functions of the other.

Differential distribution of neuropeptides and serotonin in pig adrenal glands

A differential distribution of vasoactive neuropeptides and serotonin in chromaffin cells and nerve fibers within the adrenal glands of the pig (Sus scrofa) was found using immunohistochemical methods. Met- and leu-enkephalins, present at high levels in the medulla (measured by radioimmunoassay), occurred in adrenaline storing cells, some of which contained calcitonin gene-related peptide. Islets of chromaffin cells beneath the capsule also contained enkephalins and calcitonin gene-related peptide. Nerve fibers with enkephalin-like immunoreactivity were sparse, but many varicose fibers in the inner cortex and medulla showed calcitonin gene-related peptide immunofluorescence in a pattern similar to vasoactive intestinal polypeptide. Neuropeptide Y was mainly associated with perivascular fibers and neither neuropeptide Y nor vasoactive intestinal polypeptide immunoreactive chromaffin cells were detected. In contrast to the neuropeptides, most serotonin-like immunoreactivity coincided with noradrenaline histofluorescence. It is concluded that the distribution of nerve fibers with calcitonin gene-related peptide and vasoactive intestinal polypeptide would allow interactions between chromaffin and inner cortical cells. Stimuli activating noradrenaline chromaffin cells could release serotonin while stimulation of adrenaline storage cells would release enkephalin and, to a lesser extent, calcitonin gene-related peptide. Met-enkephalin, which occurs 3 4:1 over leu-enkephalin, is the most likely of the co-released peptides to reach distant receptors via the venous outflow.

Opiate and alpha receptor antagonists block the pressor responses of conscious rats given intravenous dynorphin

Conscious, unrestrained rats were used to determine the hemodynamic (blood pressure and heart rate) responses following intravenous (IV) injection of dynorphin A(1-13) and the possible receptor mechanisms mediating those changes. Male Sprague-Dawley rats (300 g) were given IV bolus injections (via femoral venous catheter) of 6.0 to 600 nmoles/kg of dynorphin A(1-13), 8.0 nmoles/kg of norepinephrine HCl (NE), 14.3 pmoles/kg of angiotensin II or a vehicle control solution. Blood pressure (BP) and heart rate (HR) were monitored via femoral arterial catheter (into abdominal aorta) over 90 sec postpeptide or -amine administration before and 10 min after IV injection of 4.2 mumoles/kg of naloxone HCl (opiate antagonist), yohimbine HCl (alpha 2 receptor antagonist) or prazosin HCl (alpha 1 receptor antagonist). Dynorphin A(1-13) caused a transient but dose-related rise in mean arterial pressure (MAP) whereas mean pulse pressures (MPP) and mean heart rates (MHR) concomitantly fell, from preinjection control values in a dose-dependent fashion. Pretreatment with naloxone blocked the pressor response of only a subsequent injection with 20 nmoles/kg but not 60 nmoles/kg of dynorphin A or NE (8.0 nmoles/kg). Pretreatment with yohimbine suppressed the marked pressor responses of subsequent NE or Dyn A (60 nmoles/kg) administration whereas prazosin antagonized the rise in MAP of only the lower doses of dynorphin as well as NE. The suppression of the pressor responses of dynorphin by opiate or alpha receptor antagonists were not caused by tachyphylaxis for repeated injections of 6.0 or 60 nmoles/kg of dynorphin caused the same rise in MAP.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y is localized together with enkephalins in adrenergic granules of bovine adrenal medulla

The subcellular localization of neuropeptide Y in the bovine adrenal medulla was studied. After differential centrifugation, a large part of total neuropeptide Y immunoreactivity (66%) was recovered in the large granule fraction. This fraction also contained 42% of the total catecholamines and 52% of the total free [Met]enkephalin. Thus neuropeptide Y co-sedimented with these chromaffin granule markers. The large granule fraction was analysed by the technique of rate zonal centrifugation in hypertonic sucrose media (molarities ranging from 1.6 to 2.2 M). Noradrenaline vesicles were preferentially enriched at high sucrose concentration. Adrenaline vesicles as well as enkephalin and neuropeptide Y immunoreactivity pelleted mainly at lower sucrose concentrations. The large granule fraction was also separated by successive centrifugation in self-generating gradients of Percoll-sucrose into two subpopulations, one containing lighter adrenergic vesicles and the other the dense noradrenergic vesicles. Like [Met]enkephalin immunoreactivity, neuropeptide Y immunoreactivity was concentrated in fractions containing the lighter adrenergic vesicles. In these fractions the molar ratio of adrenaline to free [Met]enkephalin to neuropeptide Y was 5000:12:1. This biochemical study supports immunohistochemical studies which described co-localization of neuropeptide Y in adrenaline cells in the rat, mouse, cat, guinea-pig and man and co-localization of neuropeptide Y with enkephalins in bovine adrenal chromaffin cells. Our results are however in contrast with the report of other immunohistochemical work which claimed co-localization of neuropeptide Y in noradrenaline cells of rat, cat, dog, horse and cow.

Specific insulin binding in bovine chromaffin cells; demonstration of preferential binding to adrenalin-storing cells

Insulin binding was studied in subpopulations of bovine chromaffin cells enriched in adrenalin-producing cells (A-cells) or noradrenalin-producing cells (NA-cells). Binding of 125I-insulin was carried out at 15 degrees C for 3 hrs in the absence or presence of excess unlabelled hormone. Four fractions of cells were obtained by centrifugation on a stepwise bovine serum albumin gradient. The four fractions were all shown to bind insulin in a specific manner and the highest binding was measured in the cell layers of higher densities, containing mainly A-cells. The difference in binding of insulin to the four subpopulations of chromaffin cells seemed to be related to differences in numbers of receptors as opposed to receptor affinities. We conclude that bovine chromaffin cells possess high affinity binding sites for insulin and that these binding sites are mainly confined to A-cells.

Effects of hemorrhage and naloxone on adrenal release of methionine-enkephalin and catecholamines in halothane anesthetized dogs

Concurrent levels of methionine-enkephalin and catecholamines in adrenal vein, femoral vein and femoral artery were measured under baseline conditions and during graded hemorrhage in halothane anesthetized dogs and compared to a non-bled control group. Naloxone was administered in both groups at the end of the experiment. Normotensive hypovolemia with a remaining blood volume of 76% led to a moderate decrease in mean arterial blood pressure from baseline and a 15- to 20-fold increase in norepinephrine, epinephrine and dopamine, and a 5-fold increase in enkephalin in the adrenal vein. Subsequent induction of hypotensive hypovolemia with a remaining blood volume of 51% resulted in a profound drop in blood pressure and evoked a further increase in the level of catecholamines (40- to 50-fold from baseline) and enkephalin (8-fold from baseline) in the adrenal vein. In the control group only a 3- to 4-fold increase from baseline in adrenal vein hormone levels was observed over time. Naloxone administration at the end of the experiment, led to a 2- to 6-fold further increase in hormones at the 3 collection sites in both groups of dogs. Joint calculation of the partial correlation coefficients for the influence of preceding blood volume and blood pressure, and concurrent blood volume and blood pressure on hormone secretion in the adrenal vein revealed that these variables explained the variation in hormone levels between 56 and 92% during normotensive hypovolemia and 62-83% during hypotensive hypovolemia. In one dog with bilateral adrenalectomy, hemorrhage was poorly tolerated, and naloxone administration did not lead to increased systemic plasma levels of catecholamines and enkephalin or improved hemodynamics. In the hemorrhage group, molar ratios of norepinephrine/epinephrine in the adrenal vein showed a significant increasing trend during the experiment. Findings in these experiments support the idea of differential monoaminergic and enkephalinergic regulation in adrenal medullary cells.

Endocrine cells producing regulatory peptides

Recent data on the immunolocalization of regulatory peptides and related propeptide sequences in endocrine cells and tumors of the gastrointestinal tract, pancreas, lung, thyroid, pituitary (ACTH and opioids), adrenals and paraganglia have been revised and discussed. Gastrin, xenopsin, cholecystokinin (CCK), somatostatin, motilin, secretin, GIP (gastric inhibitory polypeptide), neurotensin, glicentin/glucagon-37 and PYY (peptide tyrosine tyrosine) are the main products of gastrointestinal endocrine cells; glucagon, CRF (corticotropin releasing factor), somatostatin, PP (pancreatic polypeptide) and GRF (growth hormone releasing factor), in addition to insulin, are produced in pancreatic islet cells; bombesin-related peptides are the main markers of pulmonary endocrine cells; calcitonin and CGRP (calcitonin gene-related peptide) occur in thyroid and extrathyroid C cells; ACTH and endorphins in anterior and intermediate lobe pituitary cells, alpha-MSH and CLIP (corticotropin-like intermediate lobe peptide) in intermediate lobe cells; met- and leu-enkephalins and related peptides in adrenal medullary and paraganglionic cells as well as in some gut (enterochromaffin) cells; NPY (neuropeptide Y) in adrenaline-type adrenal medullary cells, etc.. Both tissue-appropriate and tissue-inappropriate regulatory peptides are produced by endocrine tumours, with inappropriate peptides mostly produced by malignant tumours.

Adrenal enkephalin and catecholamine contents following subarachnoid hemorrhage in cats

A "closed space" subarachnoid hemorrhage (SAH) was produced experimentally in cats by rupture of the right middle cerebral artery to test the working hypothesis that a stressful event which provokes powerful sympathoadrenal discharge: causes a massive release of co-stored endogenous enkephalins together with catecholamines, induces an increased rate of opioid peptide precursor processing and/or synthesis, and eventually results in markedly elevated tissue levels of enkephalins relative to controls and to co-stored catecholamines. Adrenal medulla and other tissues were analyzed for met- and leu-enkephalins by RIAs and norepinephrine and epinephrine by HPLC-EC at 4 hrs, 3, 10, 16 and 30 days post-SAH. Catecholamines of adrenal medulla were already decreased at 4 hrs and by 3 days post-SAH depletion of epinephrine reached 86% and norepinephrine 53% compared to controls. Concurrently, at 4 hrs and 3 days post-SAH, the adrenal medulla was depleted 47% of met- and 53% of leu-enkephalins. By 10 days post-SAH, when catecholamines had regained control levels, met-enkephalin was elevated to 240% of control and 435% compared to the 3 day depletion; it remained elevated through 30 days post-SAH. In comparison, after 10 days reserpine treatment when catecholamines were markedly depleted, met-enkephalin rose to 970% and leu-enkephalin to 360% relative to controls, confirming recent reports in the literature. The data suggest that release of enkephalins originates primarily from epinephrine-type cells of the adrenal medulla in cat.

Modulation of bovine adrenal gland secretion by etorphine and diprenorphine

Retrograde perfusion was used to investigate the effect of an opiate agonist and an opiate antagonist on the release of catecholamines and [Met5]-enkephalin immunoreactive material (ME-IRM) from bovine adrenal glands. Etorphine (5 X 10(-7) M) inhibited the spontaneous outflow of ME-IRM by approximately 10 percent but had no significant effect on the spontaneous catecholamine release. Acetylcholine (ACh, 5 X 10(-5) M) or 1,1-dimethyl-4-phenylpiperazinium (DMPP, 5 X 10(-5) M) stimulated release of ME-IRM and catecholamines was significantly decreased by the addition of etorphine. Diprenorphine (5 X 10(-7) M) had no significant effect on the spontaneous outflow of either ME-IRM or catecholamines. Diprenorphine reversed the inhibition of the DMPP-stimulated release caused by etorphine. After submaximal stimulation of the gland with DMPP (1 X 10(-5) M), a further stimulation of release of ME-IRM and catecholamines was observed after the addition of diprenorphine alone, i.e., in the absence of etorphine. These results provide further evidence supporting the contention that opiates modulate the secretion of catecholamines and ME-IRM from the adrenal gland.

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.

Bombesin-like immunoreactivity in bovine adrenal medulla

The presence of immunoreactive (ir)-bombesin in bovine adrenal medulla, isolated adrenal chromaffin cells and subcellular fractions of the adrenal medulla was demonstrated using a specific antibody to the synthetic peptide. High levels of ir-bombesin were detected in acid (HCl) extracts of the adrenal tissue (27 pmol/g) and isolated cells (0.35 pmol per 10(6) cells). Subpopulations of adrenal chromaffin cells were also obtained by centrifugation of the original cell preparation through a stepwise bovine serum albumin gradient (cell layers I, II and III). The highest concentration of ir-bombesin (0.77 pmol/10(6) cells) was found in a cell population (cell layer I) enriched in noradrenaline (adrenaline/noradrenaline ratio of 0.6). At the subcellular level, ir-bombesin was mainly concentrated in the secretory granules (0.61 pmol/mg protein) along with catecholamines (1097 nmol/mg protein), but a relatively high concentration of ir-bombesin (0.26 pmol/mg protein) was also found in the microsomal fraction. Isolation and high performance liquid chromatography (HPLC) analysis of adrenomedullary ir-bombesin revealed the presence of four molecular forms, one of them corresponding to gastrin releasing peptide (GRP), another one (major peak) eluting closely to synthetic neuromedin B and another one coeluting with GRP-(18-27). HPLC analysis of the molecular forms of ir-bombesin in the microsomes and secretory granules indicated that GRP- and neuromedin B-like materials can be generated between the two fractions.

Glycoproteins of the chromaffin-granule matrix: use of lectin blotting to distinguish several separate classes

The soluble proteins released by hypotonic lysis of highly purified bovine adrenal chromaffin granules were analysed by one- and two-dimensional electrophoresis, followed by transfer to nitrocellulose and decoration with lectins or specific antibodies. The effects of neuraminidase treatment, and of chemical deglycosylation by trifluoromethanesulphonic acid, were investigated. It was shown that lectins could be used to distinguish the two major series of chromogranins from each other, from dopamine beta-hydroxylase and from several minor, unidentified glycoprotein components of the lysate. Antibody decoration revealed a complex series of peptides containing enkephalin sequences, some of which changed their electrophoretic mobility on treatment with trifluoromethanesulphonic acid.

New bovine adrenal medullary peptide and its precursor

We have isolated a previously unknown peptide and its precursor from bovine adrenal medullary chromaffin granules. The peptide sequence is Leu-Pro-Val-Asn-Ser-Pro-Met-Asn-Lys-Gly-Asn-Glu-Val-Met-Lys. The peptide is cleaved from the precursor at a Lys site. The sequence shows no homology to any known protein in the largest sequence data bank available.

Multiple populations of neuropeptide-containing cells in cultures of the bovine adrenal medulla

Cell populations containing vasoactive intestinal polypeptide (VIP), enkephalins, and catecholamines were identified in bovine adrenal medullary cultures by immunofluorescence and radioimmunoassay. Addition of forskolin to the culture medium increased the cellular levels of both VIP and the enkephalins. These changes resulted from an increase in the number of VIP-positive cells and an increase in cellular enkephalin content.

Release of catecholamines and [Met5]enkephalin immunoreactive material from perfused bovine adrenal glands

Retrogradely perfused bovine adrenal glands were stimulated by acetylcholine (ACh) and 1,1-dimethyl-4-phenyl-piperazinium (DMPP), with or without hexamethonium. Stimulation by either agent resulted in an increased release of both [Met5]enkephalin immunoreactive material (ME-IRM) and catecholamines as measured by radioimmunoassay and high performance liquid chromatography with electrochemical detection, respectively. ACh (5 X 10(-5) M) and DMPP (5 X 10(-5) M) stimulated the release of norepinephrine greater than the release of epinephrine. The action of these agents was antagonized by hexamethonium (5 X 10(-4) M). DMPP produced the same percentage increase in the release of ME-IRM and norepinephrine but produced a greater percentage increase in the release of ME-IRM compared to the release of epinephrine. There was no apparent correlation between the percentage increase in the release of ME-IRM and either norepinephrine or epinephrine after ACh.

Neuroimmunomodulation with enkephalins: enhancement of human natural killer (NK) cell activity in vitro

To further define the effects of enkephalins on immune function, the effect of methionine-enkephalin and leucine-enkephalin on natural killer cell (NK) activity in isolated human peripheral blood lymphocytes was investigated. Incubation of lymphocytes with either enkephalin resulted in significant increases in natural killer cell activity. At effector:target cell ratios of 11:1 methionine-enkephalin significantly (P less than 0.05) enhanced NK activity at dilutions of 10(-6), 10(-8), 10(-10), and 10(-14) mg/ml, while leucine-enkephalin significantly (P less than 0.05) enhanced NK activity at dilutions of 10(-4), 10(-6), 10(-8), 10(-10), and 10(-14) mg/ml. Cells from individuals with low NK activity showed greater percentage increases in NK activity following enkephalin than did cells from individuals with high NK activity.

'Dynorphin' in plasma: enzymatic artifact and authentic immunoreactivity

The potent opioid peptide dynorphin (DYN) is found in posterior pituitary vasopressinergic neurones and in adrenal medullary cells suggesting that secretion into plasma is likely. We have developed a sensitive radioimmunoassay in order to study plasma DYN in man. It transpired that extraction prior to assay was essential since unextracted plasma caused gross and non-parallel inhibition of binding of tracer. Plasma extracted using leached silica glass ( Vycor ) caused inhibition of tracer binding which diluted in parallel to synthetic DYN suggesting the presence of substantial amounts of DYN-like immunoreactivity ( irDYN ) in plasma. Further investigation however demonstrated that this irDYN was artifactual and caused by enzymatic degradation of tracer. Although use of Seppak C18 cartridges resulted in reliable extraction of synthetic porcine DYN from acidified plasma, we have not detected irDYN in any plasma so far studied using this technique. However, extraction of non-acidified plasma using our antibody coupled to Sepharose CNBr-activated 4B followed by gel filtration chromatography demonstrated a single peak of irDYN of molecular size similar to DYN. These data suggested that a small amount of a DYN-like peptide does circulate in human plasma although this is not identical to porcine DYN(1-17). The implication of our results for the measurement of other similar peptides in plasma is discussed.

Methionine-enkephalin, leucine-enkephalin methionine-enkephalin-Arg6-Phe7 and methionine-enkephalin-Arg6-Gly7-Leu8 in human pheochromocytoma

Methionine-enkephalin(met-enkephalin)-, leucine-enkephalin(leu-enkephalin)-, methionine-enkephalin-Arg6-Phe7(met-enkephalin-Arg-Phe)- and methionine-enkephalin-Arg6-Gly7-Leu8(met-enkephalin-Arg-Gly-Leu)-like immunoreactivities(-LI) were studied in 16 pheochromocytomas by radioimmunoassays (RIAs) for these four opioid peptides. Met-enkephalin-Arg-Phe-LI and met-enkephalin-Arg-Gly-Leu-LI existed together with met-enkephalin-LI and leu-enkephalin-LI in 16 pheochromocytomas. Significant positive correlations were observed among contents of these four opioid peptides in 16 pheochromocytomas. The concentrations of these four opioid peptides in epinephrine producing pheochromocytomas were much higher than those in norepinephrine producing tumors. HPLC and gel exclusion chromatography followed by the RIAs showed the presence of met-enkephalin, leu-enkephalin, met-enkephalin-Arg-Phe and met-enkephalin-Arg-Gly-Leu together with their high molecular weight forms. These results indicate the co-existence of met-enkephalin, leu-enkephalin, met-enkephalin-Arg-Phe, met-enkephalin-Arg-Gly-Leu and their high molecular weight forms derived from preproenkephalin A in human pheochromocytomas and suggest the association of preproenkephalin A synthesis with epinephrine production in human pheochromocytomas.