Reserpine increases opiate-like peptide content and tyrosine hydroxylase activity in adrenal medullary chromaffin cells in culture

Protein synthesis blockade differentially affects the degradation of constitutive and nicotinic receptor-induced tyrosine hydroxylase protein level in isolated bovine chromaffin cells

Continuous incubation of bovine adrenal chromaffin cells with the nicotinic receptor agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) causes a twofold increase in the steady-state level of catalytically active tyrosine hydroxylase (TH) protein by 3-4 days. The present study examined the processes that control the time course of enzyme induction. In cells exposed to DMPP for 36 or 54 h, incorporation of [3H]leucine into TH was increased 1.9- and 2.2-fold, respectively, compared with control (non-DMPP-treated) cells. The increase correlated with a twofold rise in TH mRNA level, indicating the absence of translational control of TH synthesis by DMPP. Also absent was an effect by DMPP on the rate of degradation of TH protein because pulse-chase analysis estimated a half-life for TH of 26 +/- 5 h in DMPP-treated cells, a value that was (a) essentially the same as that estimated in control cells (29 +/- 3 h), (b) within the same range as that estimated by approach to steady state (t(1/2) = 19 +/- 4 h), which measured the decline of TH protein content from the DMPP-induced steady-state level back to the basal value during deinduction with the nicotinic antagonist hexamethonium, and (c) consistent with the time course of accumulation of TH protein to a new steady-state level in response to DMPP. However, different rates of degradation for TH protein were observed in control and DMPP-treated cells under conditions in which protein synthesis was blocked. In control cells incubated with 100 microM puromycin or 20 microM cycloheximide for 3 days, the level of catalytically active TH protein failed to decline and exhibited a half-life of > or = 250 h. This finding indicated that TH protein was stabilized. TH protein level also failed to decline when cells were incubated for 3 days with a concentration of the transcription inhibitor alpha-amanitin that caused a >90% loss of TH mRNA. Thus, degradation of constitutively expressed TH protein appears to be controlled by processes dependent on ongoing transcription and translation. In contrast, the increased amount of TH induced by DMPP was not stabilized but instead underwent a decline to the basal level following addition of puromycin or cycloheximide. It is important to note, however, that the decline occurred at a slower rate (t(1/2) > or = 45 h) than that measured during deinduction. Taken together, these data suggest that alterations in the rate of degradation of TH protein may play a role in controlling TH level when TH synthesis is blocked but not when TH synthesis is increased, such as during nicotinic receptor stimulation.

Processing of chromogranins in chromaffin cell culture: effects of reserpine and alpha-methyl-p-tyrosine

Bovine chromaffin cell cultures were treated with either reserpine or alpha-methyl-p-tyrosine for up to 10 days. Afterwards the cells were harvested and the degree of proteolytic processing of secretogranin II, chromogranin A and chromogranin B was determined by immunoblotting and HPLC followed by RIA. There was a significant increase in the proteolysis of all three chromogranins after 4-6 days in the presence of reserpine. The small peptides formed in the presence of reserpine in vitro are also produced in vivo. A similar effect was observed with alpha-methyl-p-tyrosine, an inhibitor of tyrosine hydroxylase, but the response took up to 10 days to develop. Both drugs decreased catecholamine levels but reserpine was more effective, reaching a high degree of depletion after 4 days. In addition, experiments in vitro indicate that low millimolar amounts of either adrenaline (IC50 5.2 mM) or noradrenaline (IC50 2.4 mM) can significantly impair the proteolytic activity of recombinant murine prohormone convertase 1 when assayed with synthetic fluorogenic and/or peptidyl substrates. We conclude that a lowering of catecholamine levels in chromaffin granules leads to a concomitant increase in proteolytic processing of all secretory peptides. Apparently within chromaffin granules the endoproteases are inhibited by catecholamines and thus their removal leads to increased proteolysis.

Modulation of the enkephalinergic phenotype of rat sympathetic neurons by hormonal and transsynaptic mechanisms

Most sympathetic neurons contain one or more neuropeptides in addition to catecholamines. Although the regulation of catecholamines has been studied extensively, comparatively little is known about the regulation of neuropeptides. Since glucocorticoids and preganglionic innervation regulate catecholaminergic properties in chromaffin cells, we examined the effects of these factors on a co-localized neuropeptide, leucine enkephalin (L-Enk), in adult rat sympathetic neurons in vivo. Lowered serum glucocorticoid levels as a consequence of bilateral adrenalectomy resulted in a reduction of ganglionic L-Enk content that was reversed by exposure of adrenalectomized animals to the synthetic glucocorticoid, dexamethasone. Surgical denervation of the SCG eliminated L-Enk-IR preganglionic fibers and caused a dramatic increase in the number of L-Enk-IR neurons. Inhibition of the enkephalinergic component of the preganglionic innervation by chronic exposure to the opiate receptor antagonist naloxone increases the number of L-Enk-IR cell bodies and total ganglionic L-Enk content. None of the experimental manipulations noticeably altered the number or distribution of NPY-IR neurons, suggesting that the effects of glucocorticoids and the innervation on ganglionic L-Enk levels were specific and not simply an alteration of the biosynthetic state of the cells. These results demonstrate that circulating glucocorticoids and the preganglionic innervation regulate L-Enk levels in sympathetic neurons. Since both glucocorticoid levels and preganglionic activity are known to be altered by stressful stimuli, acute regulation of sympathetic L-Enk levels may constitute an important component of the autonomic response to stress.

Reserpine-induced processing of chromogranin A in cultured bovine adrenal chromaffin cells

The effect of reserpine on the processing of the secretory granule protein chromogranin A (CgA) in isolated bovine adrenal chromaffin cells was investigated using two radioimmunoassays employing site-specific antisera. The two antisera were directed against closely associated regions of the CgA molecule which would be exposed by specific processing: antiserum L331 was raised against the C-terminus of the regulatory peptide pancreastatin, and the second antiserum, L300, was raised against the synthetic peptide [Tyr0]CgA306-313 (YLSKEWEDA), a sequence that lies immediately C-terminal to pancreastatin and adjacent to a dibasic amino acid cleavage site. Chronic reserpine treatment of chromaffin cells produced a time- and dose-dependent increase in processing, as demonstrated by an increase in pancreastatin- and YLSKEWEDA-immunoreactivity (ir). The reserpine-induced rise in pancreastatin-ir was due predominantly to an increase in pancreastatin 1-47, whereas the rise in YLSKEWEDA-ir was due to increases in three polypeptides: a 51-kDa YLSKEWEDA-ir polypeptide, CgA297-313, and CgA248-313. The latter predominated. The action of reserpine on both pancreastatin- and YLSKEWEDA-ir was found to be largely inhibited by the protein synthesis inhibitor cycloheximide. The results show that treatment of isolated chromaffin cells with reserpine induces both the selective proteolytic processing and peptidyl-glycine amidation of CgA and its derived fragments. As reserpine has a similar effect on proenkephalin in chromaffin cells, the results suggest that reserpine induces a general increase in the activity of the processing enzymes, partially by an increase in protein synthesis.

Coordinate and differential regulation of phenylethanolamine N-methyltransferase, tyrosine hydroxylase and proenkephalin mRNAs by neural and hormonal mechanisms in cultured bovine adrenal medullary cells

Primary cultures of bovine adrenal medullary cells (AM) in a chemically defined media were used to examine the role of neural and hormonal factors in the expression of proenkephalin A (pEK), phenylethanolamine N-methyltransferase (PNMT) and tyrosine hydroxylase (TH) genes. Acetylcholine or nicotine reduced cellular content of catecholamines by 30% and increased the relative abundance of pEK, TH, and PNMT mRNAs. The increases produced by acetylcholine were +129%, +147%, and +43% for pEK, TH, and PNMT mRNA, respectively. The kinetics of increases produced by nicotine were different for the 3 mRNAs, with pEK and TH showing enhanced levels over 48 h incubation, while PNMT showed increase during the initial 18 h (+90%) followed by decline to control levels at 48 h. 8-Br cAMP and forskolin elicited a similar pattern of changes as nicotine, suggesting that cyclic AMP may be involved in the mediation of the nicotinic effects. To examine the role of depletion of cellular catecholamines in the regulation of mRNA levels, cells were exposed to tetrabenazine or reserpine. Decreases in cellular catecholamine contents were accompanied by increases in TH and pEK mRNA levels, while the expression of PNMT gene exhibited a transient 4-fold increase and then profound inhibition (60-95%) over a 48-h period. The tetrabenazine effect on TH and pEK mRNA was reduced by alpha-amanitin, suggesting transcriptionally-mediated regulation. Inductions of pEK but not TH or PNMT mRNAs were inhibited by cycloheximide. Hormonal regulation of TH, PNMT, and pEK mRNAs was examined by incubation of cells with dexamethasone. Low concentrations of dexamethasone (0.1, 10 nM) were effective to increase PNMT (+35%, +90%) and pEK (+27%, 45%) mRNA levels. TH mRNA was not affected by similar concentrations of dexamethasone, however, there was a 45% increase at 1 microM. Dexamethasone-elicited increases in PNMT mRNA levels were observed at 48 h and persisted up to 7 days, suggesting that hormonal mechanisms may be distinct from those mediating effects of nicotine, cAMP or tetrabenazine. Taken together, these results indicate that (1) the level of TH, PNMT, and pEK mRNAs are regulated by direct neural (acetylcholine) and hormonal (glucocorticoid) inputs to adrenal medullary cells; (2) effects of acetylcholine could be mediated by cyclic AMP and alterations in catecholamine content; and (3) expression of individual genes is regulated differentially. Such differential regulation of TH, PNMT, and pEK mRNAs may contribute to the long-term selective control of hormonal output from adrenomedullary cells.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Choline acetyltransferase activities in single spinal motor neurons from patients with amyotrophic lateral sclerosis

Activities of choline acetyltransferase (ChAT) were microassayed in individual cell bodies of motor neurons, isolated from freeze-dried sections after autopsy of lumbar spinal cords from four patients with sporadic amyotrophic lateral sclerosis (ALS) and four control patients with nonneurological diseases. Numerous large neurons were found in the anterior horn at the early degeneration stage of ALS, but the cell bodies atrophied and decreased in number at the late advanced stage. The small, atrophied neurons were very fragile and were easily destroyed during the isolation procedure with a microknife. The average activity, expressed on a dry weight basis, of 58 ALS neurons was lower than that of 67 control neurons. The large, well-preserved neurons at the early nonadvanced stage had markedly lower ChAT activities than control neurons. The specific activity gradually increased with the progress of atrophy but did not return to the control level.

Neuropeptide tyrosine in the rat adrenal gland--immunohistochemical and in situ hybridization studies

The adrenal gland of the rat was analysed with immunohistochemistry and antisera to neuropeptide tyrosine, to the catecholamine-synthesizing enzymes tyrosine hydroxylase, phenyl-ethanolamine-N-methyltransferase, and to acetylcholinesterase and with in situ hybridization using a nick-translated 280 base pair deoxyribonucleic acid probe coding for exon 2 of the rat neuropeptide tyrosine gene. Neuropeptide tyrosine-like immunoreactivity was observed in three structures: chromaffin cells, medullary ganglion cells and nerve fibers. The chromaffin cells were of both the noradrenaline- and adrenaline-type. The ganglion cells did not seem to contain any catecholamine-synthesizing enzymes but exhibited a strong immunoreaction for acetylcholinesterase. They were thus in all probability cholinergic neurons. In situ hybridization using the nick-translated deoxyribonucleic acid probe to rat neuropeptide tyrosine messenger ribonucleic acid revealed a very high-grain density over the ganglion cells, a moderate density over the chromaffin cells and a low background over cortex, in agreement with the immuno-histochemical demonstration of neuropeptide tyrosine-like immunoreactivity both in chromaffin and ganglion cells. The intense neuropeptide tyrosine-like immunoreactivity and low content of neuropeptide tyrosine messenger ribonucleic acid suggest that the chromaffin cells have fairly large peptide stores but that the peptide turnover is low. In contrast, the ganglion cell bodies seem to contain low amounts of neuropeptide tyrosine-like immunoreactivity but exhibit a high neuropeptide tyrosine synthesis rate. Preliminary studies with the amine-depleting drug reserpine revealed an increase in messenger ribonucleic acid both in ganglion cells and medullary cells. In the chromaffin cells the highest activity was seen 3 and 4 days after injection, and the levels were down to normal after 8 days. The present findings demonstrate neuropeptide tyrosine synthesis and storage in two cell populations in the adrenal medulla. In situ hybridization with its cellular resolution can provide information on possible differential effects of drugs and experimental procedures on these two neuropeptide tyrosine stores.

Reserpine increases chromaffin cell enkephalin stores without a concomitant decrease in other proenkephalin-derived peptides

Reserpine increases the levels of enkephalins in adrenal medullary chromaffin cells; however, the origin of the newly apparent pentapeptides has been the subject of debate, because no increase in the levels of proenkephalin mRNA has been observed. The present study was performed for determining if the reserpine-induced increase in context of enkephalins was derived from processing of preexisting fragments of proenkephalin. Bovine chromaffin cell enkephalins and larger enkephalin-containing peptides were separated by reversed-phase HPLC and identified by approximate molecular weight, elution with peptide standards, and enkephalin sequences contained. Treatment of the cells with reserpine increased the levels of enkephalins and of enkephalin-containing peptides of up to approximately 3 kilo-daltons without reducing the levels of larger enkephalin-containing peptides. Similar results were obtained with another catecholamine-depleting drug, tetrabenazine. In contrast, treatment of chromaffin cells with theophylline or forskolin increased the levels of both enkephalins and enkephalin-containing peptides of all sizes. The results suggest that new synthesis of proenkephalin is required for the effects of reserpine, although proenkephalin processing is also altered by this drug.

Subcellular compartmentalization of 1-methyl-4-phenylpyridinium with catecholamines in adrenal medullary chromaffin vesicles may explain the lack of toxicity to adrenal chromaffin cells

Cultures of bovine adrenomedullary chromaffin cells accumulated 1-methyl-4-phenylpyridinium (MPP+) in a time- and concentration-dependent manner by a process that was prevented by desmethylimipramine. The subcellular localization of the incorporated [methyl-3H]MPP+ was examined by differential centrifugation and sucrose density gradient fractionation and was found to be predominantly colocalized with catecholamines in chromaffin vesicles, and negligible amounts were detected within the mitochondrial fraction. When chromaffin cell membranes were made permeable with the detergent digitonin in the absence of calcium, there was no increase in the release of [3H]MPP+, indicating that there is negligible accumulation of the neurotoxin in the cytosol. Simultaneous exposure to digitonin and calcium induced cosecretion of MPP+ and catecholamines. Stimulation of the cells with nicotine released both catecholamines and MPP+ at identical rates and percentages of cellular content in a calcium-dependent manner. Last, when cells were incubated with MPP+ in the presence of tetrabenazine (an inhibitor of vesicular uptake), the chromaffin cell toxicity of MPP+ was potentiated. We submit that the ability of the chromaffin cells to take up and store MPP+ in the chromaffin vesicle prevents the toxin's interaction with other structures and, thus, prevents cell damage. As an extension of this hypothesis, the relative resistance of some brain monoaminergic neurons to the toxic actions of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine may result from the subcellular sequestration of MPP+ in the storage vesicle.

Secretion of [Met]enkephalyl-Arg6-Phe7-related peptides and catecholamines from bovine adrenal chromaffin cells: modification by changes in cyclic AMP and by treatment with reserpine

Investigations into the effects of culturing bovine adrenal chromaffin cells in the presence (72 h) of dibutyryl cyclic AMP, forskolin, and reserpine on the level and release of [Met]enkephalyl-Arg6-Phe7 immunoreactivity, noradrenaline, and adrenaline are reported. The assay for [Met]enkephalyl-Arg6-Phe7 immunoreactivity recognises both peptide B, the 31-amino acid carboxy-terminal segment of proenkephalin, and its heptapeptide fragment, [Met]enkephalyl-Arg6-Phe7. Treatments that elevate cyclic AMP increase the amount of peptide immunoreactivity in these cells; this is predominantly peptide B-like immunoreactivity in both control cells and cyclic AMP-elevated cells. Treatment with reserpine gives no change in total immunoreactivity levels, but does not result in increased accumulation of the heptapeptide [Met]enkephalyl-Arg6-Phe7 at the expense of immunoreactivity that elutes with its immediate precursor, peptide B. Cyclic AMP treatment causes either no change or a decrease in levels of accumulated noradrenaline and adrenaline. However, the release of [Met]enkephalin-Arg6-Phe7 immunoreactivity, noradrenaline, and adrenaline is increased by 72-h pretreatment with forskolin or dibutyryl cyclic AMP, whether release is stimulated by nicotine or elevated potassium. In each case the molecular form of [Met]enkephalyl-Arg6-Phe7 immunoreactivity that is released approximately reflects the cell content. Pretreatment with reserpine has no effect on the total [Met]enkephalyl-Arg6-Phe7 immunoreactivity released, but does result in an increased release of the heptapeptide and a decrease in release of peptide B-like immunoreactivity. The studies suggest that the levels of [Met]enkephalyl-Arg6-Phe7 and peptide B available for release are controlled both at the level of proenkephalin synthesis and at the level of double-basic residue proteolysis.

Met-enkephalin concentrations in striatum respond reciprocally to alterations in dopamine neurotransmission

The striatum is richly innervated by both enkephalinergic and dopaminergic neurons, providing an anatomic framework from which intimate functional interrelationships between these neuronal systems may be postulated. Accordingly, many functional processes within dopamine neurons have been shown to be modulated by opioid peptides. In the present study we confirm predictable reciprocal effects in enkephalin neurons, brought about by modification of dopamine neurotransmission. Dopamine receptor blockade reliably increased striatal Met-enkephalin concentrations by about 50%, whereas chronic treatment with a potent long-acting dopamine receptor agonist was necessary to demonstrate a small 10-20% decrease in Met-enkephalin concentrations. Depletion of presynaptic dopamine also resulted in a marked 50-60% augmentation of Met-enkephalin levels, that could be prevented by concomitant treatment with a dopamine analogue. Increasing dopamine turnover and release by a mu-opioid agonist decreased Met-enkephalin concentrations, as might have been predicted. Thus we have shown a marked dopaminergic influence that maintains striatal Met-enkephalin concentrations by near maximal tonic inhibitory effects.

Vasoactive intestinal peptide and substance P increase levels of enkephalin-containing peptides in adrenal chromaffin cells

The neuropeptides substance P and vasoactive intestinal peptide (VIP), reported to exist in the splanchnic nerve terminals innervating the adrenal medulla, elevate the levels of enkephalin-containing peptides (ECPs) in cultured bovine adrenal medullary chromaffin cells. Cellular ECP stores were increased over 48 hr by 72 and 46 percent, respectively, following incubation with 5 microM VIP or 10 microM substance P, maximally effective concentrations. The results suggest that VIP and substance P may be trans-synaptic modulators of chromaffin cell ECP stores.

Met-enkephalyl-Arg6-Phe7 immunoreactivity in a human neuroblastoma cell line: effect of dibutyryl 3':5'-cyclic AMP and reserpine

The carboxy terminal part of the proenkephalin A sequence is the 31 amino acid peptide B, which has as its final seven amino acids the sequence of the opioid peptide Met-enkephalyl-Arg6-Phe7. Using a radioimmunoassay which recognises both these peptides we have investigated the relative amounts of peptide B and Met-enkephalyl-Arg6-Phe7 in a human neuroblastoma cell line. We show that these cells contain peptide B-like immunoreactivity but not its heptapeptide fragment. This may be due to lack of proteolytic activity cleaving Met-enkephalyl-Arg6-Phe7 from its precursor, peptide B. On treatment with dibutyryl cyclic AMP the level of immunoreactivity approximately doubles, due to increased amounts of peptide B-like immunoreactivity. Treatment with reserpine, which increases conversion of peptide B to the heptapeptide in bovine chromaffin cells in culture does not stimulate the accumulation of Met-enkephalyl-Arg6-Phe7 in the human neuroblastoma cells. The results are discussed with respect to peptide processing.

Contrasting monoamine oxidase activity and tyramine induced catecholamine release in PC12 and chromaffin cells

PC12 (phaeochromocytoma derived) cells possess the catecholamine synthesizing enzymes as well as the ability to store and release the catecholamines in response to K+. However, their monoamine oxidase activity and catecholamine release in response to tyramine has not been examined previously. PC12 cells have monoamine oxidase activity which oxidizes type A (noradrenaline and serotonin) and type A-B (dopamine, tyramine and kynuramine) substrates, and is selectively inhibited by clorgyline (IC50 approximately 10(-6) M). In contrast, PC12 cell monoamine oxidase hardly oxidizes phenylethylamine a type B substrate, and is relatively insensitive to inhibition by the selective monoamine oxidase type B inhibitor, 1-deprenyl (IC50 approximately 10(-6) M). By the above criteria it is apparent that the monoamine oxidase in PC12 is solely type A. The kinetics of the oxidase are similar to those of monoamine oxidase type A reported in other tissues including the adrenergic neuron, having apparent Km values of 400, 280, 170 and 227 microM for noradrenaline, dopamine, serotonin and tyramine. The apparent Km value for phenylethylamine is 235 microM. On the other hand, isolated chromaffin cells have the B form of monoamine oxidase with high affinity (Km approximately 25 microM) for phenylethylamine and low affinities for noradrenaline (Km approximately 1100 microM) and adrenaline (Km approximately 1700 microM). This enzyme form is selectively inactivated by the monoamine oxidase type B inhibitor, 1-deprenyl. In similar fashion to peripheral adrenergic neurons, PC12 cells share the capacity to express a tyramine releasable pool of catecholamines, a property entirely lacking in mature cultured chromaffin cells, even though the latter cells are capable of taking up tyramine by a cocaine sensitive process.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex splanchnic nerve stimulation increases levels of proenkephalin A mRNA and proenkephalin A-related peptides in the rat adrenal medulla

The effect of reflex splanchnic nerve stimulation on proenkephalin A biosynthesis was investigated in the rat adrenal medulla. Tissue levels of native [Met5]enkephalin-like immunoreactivity (IR) (measured by direct RIA of tissue extracts), cryptic [Met5]enkephalin-like IR (calculated as the increase in [Met5]enkephalin-like IR detected in tissue extracts after sequential digestion with trypsin and carboxypeptidase B), and proenkephalin A mRNA were determined in adrenal medulla from rats sacrificed at various times after a period of insulin-induced hypoglycemia. Two hours of insulin hypoglycemia, which produced intense reflex stimulation of the splanchnic nerves as evidenced by a 55% decrease in the adrenal medulla catecholamine levels, resulted in a 3-fold increase in proenkephalin A mRNA levels in this tissue. The proenkephalin A mRNA levels reached a maximum 15-fold increase over control values 24 hr after this period of hypoglycemic stress and then gradually declined with an approximate half-life of 4 days. Native and cryptic [Met5]enkephalin-like IR had increased 9-fold and 12-fold, respectively, 24 hr after this period of hypoglycemia, and both demonstrated maximum increases of 130-fold and 50-fold, respectively, after 96 hr. Combined pretreatment (i.p. administration) with the ganglionic and muscarinic blocking agents chlorisondamine (5 mg/kg of body weight) and atropine (1 mg/kg) blocked the increase in levels of proenkephalin A mRNA seen in the rat adrenal medulla following insulin hypoglycemia. These data indicate that reflex splanchnic nerve discharge stimulates proenkephalin biosynthesis, probably at the level of gene expression.

Neuropeptide Y in the adrenal gland: characterization, distribution and drug effects

The occurrence of neuropeptide Y-like immunoreactivity in the adrenal gland was investigated by means of radioimmunoassay, chromatography and immunohistochemistry. The adrenal levels of neuropeptide Y-like immunoreactivity varied considerably between species with lowest amounts in the rat and highest in the cow where immunoreactivity was observed in chromaffin cells and nerve fibres in the capsule and cortex. The distribution of neuropeptide Y-like immunoreactivity in the cow medulla overlapped that of enkephalin-like immunoreactivity. Chromatographic characterisation of rat and cow adrenal extracts showed that the majority of the neuropeptide Y-like immunoreactivity was similar in molecular weight and solubility properties to porcine neuropeptide Y. Rat adrenal contained additional material some of which may represent oxidised neuropeptide Y. The administration of insulin and reserpine to rats in vivo showed that the turnover of adrenal neuropeptide Y-like immunoreactivity is regulated by the splanchnic nerve. Splanchnic activation following insulin-induced hypoglycaemia elicited a 60% depletion of neuropeptide Y-like immunoreactivity 2 h post insulin injection. A smaller (maximum 40%) depletion of neuropeptide Y-like immunoreactivity was measured 24 h after reserpine injections which may be explained by splanchnic activation. Five days after reserpine injections the levels of adrenal neuropeptide Y-like immunoreactivity were increased to 200% of control levels and remained slightly elevated at 25 days. Adrenal enkephalin-like immunoreactivity showed similar but not identical changes following reserpine. The reserpine-induced elevation in neuropeptide Y-like immunoreactivity at the 5-day time point was abolished in rats with a chronic bilateral splanchnectomy. This evidence indicates that neuropeptide Y may be considered as a new adrenal medullary hormone.

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.

Effects of pre- and postnatal administration of antibodies to nerve growth factor on the morphological and biochemical development of the rat adrenal medulla: a reinvestigation

Whether or not adrenal medullary (chromaffin) cells which respond to nerve growth factor (NGF) both in vitro and in vivo require NGF for their normal development is controversial. Systemic deprivation of endogenous NGF by injection of anti-NGF antibodies into rat fetuses or by transfer of anti-NGF to the offspring of autoimmunized mothers has provided conflicting results. We have reinvestigated the effects of a specific antiserum to NGF on the morphology, catecholamine (CA) and neuropeptide (Met-enkephalin, Met-ENK; substance P, SP) content, and choline acetyltransferase (ChAT) activity of the rat adrenal medulla. Fetuses were injected with anti-NGF antibodies on day 17 of gestation and postnatally at daily intervals for 7 days. The histological appearance of adrenal medullae of anti-NGF injected animals was not altered as compared to controls. Ultrastructurally, no degenerative changes or developmental retardation of chromaffin cells could be detected. However, numbers of chromaffin granules per micron 2 of cytoplasmic area were greater and the mean diameters of the cores of adrenaline storage granules were smaller in antibody-treated than in control animals. CA and SP content, ratios of adrenaline to noradrenaline and ChAT activities were identical in anti-NGF-treated and control animals. Anti-NGF antibodies caused a reduction of adrenal Met-ENK by 40% as compared to controls. Superior cervical ganglia from the same animals were used to document immunosympathectomy induced by the antiserum. They displayed the well-established structural alterations and a marked reduction of the CA content. We conclude that administration of anti-NGF antibodies to embryonic and early postnatal rats induces only subtle changes in the ultramorphology of chromaffin cells without altering the development of normal CA levels. The small, yet significant effects of anti-NGF antibodies on adrenal Met-ENK, however, may suggest a role for endogenous NGF in the regulation of opioid peptide metabolism in developing chromaffin cells.

Regulation of guanosine triphosphate cyclohydrolase and tetrahydrobiopterin levels and the role of the cofactor in tyrosine hydroxylation in primary cultures of adrenomedullary chromaffin cells

Selective modification of the tetrahydrobiopterin levels in cultured chromaffin cells were followed by changes in the rate of tyrosine hydroxylation. Addition of sepiapterin, an intermediate on the salvage pathway for tetrahydrobiopterin synthesis, rapidly increased intracellular levels of tetrahydrobiopterin and elevated the rate of tyrosine hydroxylation in the intact cell. Tyrosine hydroxylation was also enhanced when tetrahydrobiopterin was directly added to the incubation medium of intact cells. When the cultured chromaffin cells were treated for 72 h with N-acetylserotonin, an inhibitor of sepiapterin reductase, tetrahydrobiopterin content and the rate of tyrosine hydroxylation were decreased. Addition of sepiapterin or N-acetylserotonin had no consistent effect on total extractable tyrosine hydroxylase activity or on catecholamine content in the cultured chromaffin cells. Three-day treatment of chromaffin cell cultures with compounds that increase levels of cyclic AMP (forskolin, cholera toxin, theophylline, dibutyryl- and 8-bromo cyclic AMP) increased total extractable tyrosine hydroxylase activity and GTP-cyclohydrolase, the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin. Tetrahydrobiopterin levels and intact cell tyrosine hydroxylation were markedly increased after 8-bromo cyclic AMP. The increase in GTP-cyclohydrolase and tetrahydrobiopterin induced by 8-bromo cyclic AMP was blocked by the protein synthesis inhibitor cycloheximide. Agents that deplete cellular catecholamines (reserpine, tetrabenazine, and brocresine) increased both total tyrosine hydroxylase and GTP-cyclohydrolase activities, although treating the cultures with reserpine or tetrabenazine resulted in no change in cellular levels of cyclic AMP. Brocresine and tetrabenazine increased tetrahydrobiopterin levels, but the addition of reserpine to the cultures decreased catecholamine and tetrahydrobiopterin content and resulted in a decreased rate of intact cell tyrosine hydroxylation in spite of the increased activity of the total extractable enzyme. These data indicate that in cultured chromaffin cells GTP-cyclohydrolase activity like tyrosine hydroxylase activity is regulated by both cyclic AMP-dependent and cyclic AMP-independent mechanisms and that the intracellular level of tetrahydrobiopterin is one of the many factors that control the rate of tyrosine hydroxylation.

Naloxone provokes catecholamine release in phaeochromocytomas and paragangliomas

The effects of low- (2 mg) and high-dose (10 mg) intravenous naloxone administration on circulating plasma catecholamines in four patients with proven and two patients with suspected phaeochromocytomas have been evaluated. In three out of four patients with confirmed phaeochromocytomas or paragangliomas, 10 mg naloxone resulted in a marked rise (290-575%) in circulating noradrenaline; despite combined alpha and beta-adrenoceptor blockade, in two out of four cases systolic and diastolic pressures rose whilst pulse rate fell. No response was seen to 2 mg naloxone in any patient. No humoral or pressor response was obtained in the fourth patient, who may have been secreting maximal levels of plasma noradrenaline at the time of study. In the two patients with suspected phaeochromocytoma, there was no response to naloxone: further investigations failed to reveal a source of abnormal catecholamine secretion in these patients. It is concluded that naloxone represents a new pharmacological agent which can provoke catecholamine release in patients with phaeochromocytomas; in such patients, endogenous opioids may regulate catecholamine release either from the tumour itself or from the enhanced peripheral catecholamine stores.

Relationship between the regulation of enkephalin-containing peptide and dopamine beta-hydroxylase levels in cultured adrenal chromaffin cells

Adrenal medullary chromaffin cells were maintained under conditions known to increase their cellular levels of enkephalin-containing peptides and the effects of these treatments on another chromaffin vesicle component, dopamine beta-hydroxylase, were examined. Catecholamine-depleting drugs, such as tetrabenazine, and cyclic nucleotide-elevating drugs, including forskolin, 8-bromo-cyclic AMP, and theophylline, increase chromaffin cell enkephalin-containing peptide levels but fail to increase dopamine beta-hydroxylase. In contrast, insulin treatment increases the levels of both enkephalin-containing peptides and dopamine beta-hydroxylase. The increased amounts of enkephalin-containing peptides produced by tetrabenazine and by insulin are stored in subcellular particles with properties identical to chromaffin vesicles on density-gradient centrifugation. These results suggest that following insulin treatment chromaffin cells synthesize new chromaffin vesicles with a full complement of enkephalin-containing peptides, but that after treatment with catecholamine-depleting or cyclic nucleotide-related agents enkephalin-containing peptides can be inserted into preexisting vesicles or that new vesicles, made as a part of the normal turnover of cellular components, contain elevated peptide levels.

Purification of peptides derived from proenkephalin A on Bio-Rex 70

The weakly acidic, cation-exchange resin Bio-Rex 70 was used at a low pH for chromatography of enkephalins and other peptides containing enkephalin sequences. Recoveries of various peptide standards and peptides in adrenal chromaffin cell extracts were greater than 85%. Catecholamines and other substances such as density gradient media are not retained by the resin under the conditions employed. A significant purification of enkephalins and larger peptides containing enkephalin sequences with respect to total protein was also obtained by this method. This chromatographic technique should be useful where a low-cost, preliminary purification of samples containing peptides derived from proenkephalin A is required and may be adaptable to other peptides as well.

Reserpine-induced potentiation of the inhibitory action of neuropeptide Y on the rat vas deferens neurotransmission

The inhibitory action of neuropeptide Y (NPY) on the muscular activity of the prostatic end of the rat vas deferens elicited by transmural electrical stimulation was examined in control and in reserpinized rats. Pretreatment with 1 mg/kg reserpine for 48 h induced a 6-fold increase in NPY potency. Likewise, the potency of clonidine to inhibit the electrically induced muscular activity or noradrenaline to contract the ductus musculature was also potentiated. It is hypothesized that reserpine via a denervation super-sensitivity-like process increases the density of the NPY receptors. The functional significance of NPY in the motor activity of the vas deferens is discussed.

Reserpine induction of tyrosine hydroxylase in paraplegia

Reserpine induction of tyrosine hydroxylase (TH) activity reflects the biochemical adaptability of sympathetic neurons. Midthoracic spinal cord transection in adult animals precludes TH induction in the sixth lumbar (L6) ganglion, a ganglion innervated by spinal segments caudal to the lesion. However, in animals receiving lesions as neonates, an elevation in L6 ganglion TH activity occurred after reserpine. This retained biochemical adaptability indicates an increased recuperative capacity of developing neurons.

Opioid peptides and catecholamines in human pheochromocytoma

Opioid peptides (OP) and catecholamines (CA) were measured in twelve human pheochromocytomas (PHEO). In all tumors the CA concentrations were much higher than those OP (range: 300-85,000 fold higher). Large intertumor variability in the levels of both substances was encountered (mean +/- S.E.M. = CA: 44.9 +/- 7.7 mumoles/g; OP: 38.1 +/- 17.1 nmoles/g; range = CA: 10.1-93.1 mumoles/g; OP: 0.7-181 nmoles/g). Norepinephrine (NE) was the main CA in seven of the 12 tumors. In four of these PHEO, NE accounted for 85% or more of the total CA. These "noradrenergic PHEO" derived from the right adrenals, were of smaller size (36 +/- 15g), had the lowest levels of OP (1.1 +/- 0.3 nmoles/g) and CA (28 +/- 10 mumoles/g), produced moderate to severe sustained hypertension (MBP: 160 +/- 11 mmHg) and the most severe and persistent clinical manifestations. Epinephrine (EPI) was the main CA in five of the 12 tumors. These PHEO had intermediate levels of OP (12 +/- 3 nmoles/g), and four of them were of left adrenal origin. Patients bearing these tumors were generally normotensive (MBP: 103 +/- 4 mmHg) and asymptomatic, with occasional paroxysmal crisis. The highest levels of OP (132 +/- 24 nmoles/g) were found in two tumors of extra-adrenal location and in one of right adrenal origin. The proportion of NE and EPI ranged between 60-80% and 20-40% respectively, of total tumor CA. The two extra-adrenal PHEO were the largest of this series (180 and 245g). These patients had mild hypertension (MBP: 118 +/- 7 mmHg) of sustained or paroxysmal course, and frequent symptomatic episodes. Differences in the synthesis, storage, metabolism and release of CA and OP in PHEO probably account for their variable tumoral content, as well as for the clinical heterogeneity produced by these tumors. It remains to be seen whether OP can contribute to the clinical manifestations of patients with pheochromocytomas.

Localization of substance P- and enkephalin-like immunoreactivity in relation to catecholamine-containing cell bodies in the cat dorsolateral pontine tegmentum: an immunofluorescence study

The distribution of tyrosine hydroxylase-, substance P- and enkephalin-immunoreactive neurons in the cat dorsolateral pons was studied using the indirect immunofluorescence method of Coons. To allow for the visualization of substance P- and enkephalin-immunoreactive cell bodies, colchicine was injected either in the ventricular space or in the cerebral tissue. The distribution of the tyrosine hydroxylase-immunoreactive cell bodies corresponded with the well-known distribution of catecholamine cells in this area of the brain. The observation of adjacent sections treated separately with tyrosine hydroxylase- and enkephalin-antiserum revealed that most catecholaminergic cells contain enkephalin-immunoreactivity. In addition to this catecholamine-enkephalin cell population, a moderate number of substance P-immunoreactive cell bodies was found in dorsolateral pons. The peribrachial nuclei were found to be densely supplied with substance P- and enkephalin-immunoreactive fibers, whereas the medial subdivisions, which contain the majority of the catecholamine cells in the dorsolateral pons, display a moderate number of immunoreactive fibers. These results are suggestive of interactions between peptide-containing and catecholaminergic neurons and also between-peptide-containing and non-catecholamine-containing neurons in the cat dorsolateral pons.

Reserpine inhibits rat anterior pituitary hormone secretion in vitro: effects on prolactin and ACTH and ultrastructural observations

We measured [3H]prolactin ([3H]Prl) synthesis and secretion in female rat anterior hemipituitary glands incubated in vitro, and immunoassayable Prl secretion from dispersed anterior pituitary cells in a perfused column. Anterior pituitary glands which were incubated in 9 microM reserpine showed a marked inhibition of [3H]Prl secretion but no change in hormone synthesis, thus causing [3H]Prl accumulation within the gland. The same concentration of reserpine produced a similar effect in pituitary glands taken from rats depleted of dopamine with alpha-methyl-p-tyrosine. Reserpine inhibited Prl secretion from dispersed anterior pituitary cells with a gradual onset and prolonged duration. Thyrotropin-releasing hormone (TRH), but not dibutyryl cyclic AMP (dbcAMP), the calcium ionophore A23187 or excess Ca2+, stimulated both [3H]Prl and Prl secretion in the presence of reserpine. In contrast, neither basal nor vasopressin-stimulated ACTH (bio- and immunoassayable) secretion was inhibited by 9 microM reserpine. Ultrastructurally, pituitary glands incubated in reserpine had an increased content of Prl secretory granules. Reserpine thus selectively inhibited Prl secretion, secondarily causing accumulation of both measurable hormone and Prl secretory granules within the pituitary gland. We hypothesize that reserpine interrupted calcium-dependent mechanisms in the stimulus-secretion coupling process to inhibit Prl release.

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.

The adrenal chromaffin cell as a model to study the co-secretion of enkephalins and catecholamines

The enkephalins, endogenous opioid pentapeptides first discovered in brain, are present in high concentrations in the adrenal medulla chromaffin cell. The enkephalins and other peptides containing enkephalin sequences are stored with catecholamines in the secretory organelles (chromaffin vesicles); these peptides are apparently incorporated into the vesicles at the time of their biosynthesis as opposed to later accumulation, as is the case with catecholamines. The enkephalins, catecholamines and other soluble components of the vesicle are co-secreted by the process of exocytosis. Regulatory mechanisms, apparently triggered by a critical catecholamine pool, control the synthesis of enkephalins. These mechanisms allow for rapid recovery of enkephalin content after secretion. These findings have been extended from the chromaffin cell to the ontogenically related sympathetic neurons and pheochromocytoma tumors. Secreted enkephalins and related peptides reach ubiquitous opiate receptors through the synaptic gap or the circulation and may modulate a number of important systemic functions. The co-storage and co-secretion of adrenomedullary opioid peptides and catecholamines is only one of a growing number of examples of co-existence of multiple messengers in single neuronal or endocrine cell types. Co-secreted multiple messengers may act in a co-ordinated fashion to produce integrated organismal responses.

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.

Opioid peptides and noradrenaline co-exist in large dense-cored vesicles from sympathetic nerve

The possibility that opioid peptides and noradrenaline co-exist not only in the desheathed bundle of bovine splenic nerve which contains approximately 98% sympathetic C-fibers, but also in the population of large dense-cored noradrenergic vesicles from these fibers, has been investigated. The primary fraction of large dense-cored vesicles which can be prepared at about 85% purity has been further subjected to density gradient and fractional centrifugation procedures, including D2O-loading and unloading on modified second gradients, in an attempt to separate any minor population of particles which potentially could contain opioid peptides and contaminate the large dense-cored vesicle fraction. Measurement of opioid peptides, noradrenaline, dopamine and dopamine beta-hydroxylase activity supports the conclusion that opioid peptides are stored in the primary population of large dense-cord vesicles per se, rather than in a minor population of contaminating particles from cells other than sympathetic C-fibers. This conclusion has implications for exocytotic release and the physiological role of the opioid peptides intra- and extra-neuronally. Nerve vesicle opioid peptides have a size less than 5000 daltons, in contrast to the high proportion of large peptides containing enkephalin sequences in the bovine adrenal medulla.

Adrenal medullary enkephalin-like peptides may mediate opioid stress analgesia

Different patterns of fact shock activate opioid and nonopioid mechanisms of stress analgesia in the rat. Opioid, but not nonopioid, stress analgesia is reduced by adrenal demedullation and denervation and is potentiated by reserpine, a drug known to increase concentrations of adrenal medullary enkephalin-like peptides. It is suggested that adrenal enkephalins mediate opioid stress analgesia.

Catecholamine transport and energy-linked function of chromafffin granules isolated from a human pheochromocytoma

The structure and function of chromaffin granules of human pheochromocytoma was extensively investigated in a highly purified granule fraction obtained from a single specimen of human pheochromocytoma tissue. Pheochromocytoma chromaffin granules were analyzed for catecholamine, ATP, enkephalin, phospholipid, cytochrome and ion content. Using a variety of techniques it was found that the membrane of these granules is highly impermeable to Na+, K+, and H+, and that the intragranular pH was maintained at 5.1 irrespective of suspending media. The presence of MgATP induces a transmembrane potential (delta psi) across the membrane of these granules which is positive inside and which corresponds to 90 mV. Both delta pH and delta psi are coupled to biogenic amine accumulation into the granules in a process which is reserpine sensitive. These properties are compared with those of chromaffin granules isolated from normal human tissue or from other animal species and are discussed in terms of possible explanation at a biochemical or subcellular level of the clinical manifestation of the pheochromocytoma.

Biopterin cofactor biosynthesis: independent regulation of GTP cyclohydrolase in adrenal medulla and cortex

Guanosine triphosphate cyclohydrolase, the enzyme that is apparently rate-limiting in biopterin biosynthesis, is increased in adrenal cortex and medulla of rats treated with insulin or reserpine. Denervation and hypophysectomy block the increase in medullary and cortical enzyme activity, respectively, whereas cycloheximide presents the increase in both tissues. These results provide evidence for induction and regulation of guanosine triphosphate cyclohydrolase.

Tetrahydrobiopterin increases in adrenal medulla and cortex: a factor in the regulation of tyrosine hydroxylase

Tetrahydrobiopterin, the cofactor for tyrosine hydroxylase and other monooxygenases, is present in tissues at apparent concentrations much less than those necessary to saturate the corresponding enzymes. Reserpine treatment or insulin-induced hypoglycemia in rats produces a statistically significant increase in the tetrahydrobiopterin content of both the adrenal medulla and the cortex. Adrenal denervation and hypophysectomy selectively block the increases in cofactor level in medulla and cortex, respectively, while cycloheximide prevents the increase in both tissues. Reserpine did not increase cofactor levels in liver, kidney, or corpus striatum but decreased that of the pineal gland. These results suggest that tetrahydrobiopterin is under neural control in the medulla and hormonal control in the cortex and that increases in cofactor may result from induction of enzyme(s) in the biosynthetic pathway. These results demonstrate regulation of tissue tetrahydrobiopterin and are consistent with the suggestion that cofactor levels participate in the regulation of tyrosine hydroxylase in the adrenal medulla and may have a function, as yet undetermined, in the adrenal cortex.