Enkephalin and neuropeptide Y: two colocalized neuropeptides are independently regulated in primary cultures of bovine chromaffin cells

Regulated expression of atrial natriuretic peptide-like immunoreactivity in cultured bovine adrenomedullary chromaffin cells

We show that cultured bovine adrenal chromaffin cells can be stimulated to produce atrial natriuretic peptide-like immunoreactivity (ANP). ANP levels increased 5-fold in response to either forskolin or phorbol ester treatment, and 17-fold after depolarization by 40 mM potassium. These agents appear to act through distinct second messenger mediated pathways to cause increased accumulation of ANP. When forskolin and phorbol ester were added simultaneously, their effects were synergistic: ANP levels increased 30-fold, more than the product of the increases achieved by treatment with either drug alone. The ANP present in bovine chromaffin cell extracts appeared immunologically identical to human ANP(1-28). By gel filtration, the immunoreactive ANP extracted from chromaffin cells was in a high molecular weight form, although HPLC fractionation revealed that a portion of the total immunoreactivity could be eluted with the same retention time as synthetic ANP standards.

Is PACAP the major neurotransmitter for stress transduction at the adrenomedullary synapse?

It has been known for more than a decade that the neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) is co-stored with acetylcholine in the splanchnic nerve terminals innervating the adrenal medulla. Both transmitters are robust secretagogues for catecholamine release from chromaffin cells. Here, we review the unique contribution of PACAP to the functioning of the splanchnic-adrenal synapse in stress. While acetylcholine is released across a wide range of firing frequencies, PACAP is released only at high frequencies of stimulation, and its role in the regulation of epinephrine secretion and biosynthesis is highly specialized. PACAP is responsible for long-term catecholamine secretion using secretory mechanisms different from the rapidly desensitizing depolarization evoked by acetylcholine through nicotinic receptor activation. PACAP signaling also maintains catecholamine synthesis required for sustained secretion during prolonged stress via induction of the enzymes TH and PNMT, and enhances transcription of additional secreted molecules found in chromaffin cells that alter further secretion through both autocrine and paracrine mechanisms. PACAP thus mediates chromaffin cell plasticity via functional encoding of cellular experience. These features of PACAP action at the splanchnic-adrenal synapse may be paradigmatic for the general actions of neuropeptides as effectors of stimulus-secretion-synthesis coupling in stress.

PACAP activates calcium influx-dependent and -independent pathways to couple met-enkephalin secretion and biosynthesis in chromaffin cells

Pituitary adenylate cyclase activating polypeptide-27 (PACAP-27) caused a dose-dependent increase in met-enkephalin secretion and increased production of met-enkephalin peptide and proenkephalin A (PEnk) mRNA in bovine chromaffin cells, at concentrations as low as 300 pM. PACAP-38 was less potent than PACAP-27, but had similar effects. Vasoactive intestinal polypeptide (VIP) (1-100 nM) was without appreciable effect on either enkephalin secretion or biosynthesis, implicating PACAP type I receptors in PACAP-stimulated enkephalin secretion and synthesis. PACAP type I receptors can activate adenylate cyclase and stimulate phospholipase C through heterotrimeric G protein interactions, leading to increased intracellular cyclic AMP (cAMP), inositol triphosphate (IP3)-mediated calcium mobilization, and calcium- and diacylglycerol (DAG)-mediated protein kinase C (PKC) activation. Enkephalin secretion evoked by 10-100 nM PACAP-27 was not inhibited by 1 microM (-)-202-791, an L-type specific dihydropyridine calcium channel blocker, but was inhibited 65-80% by the arylalkylamine calcium channel blocker D600. Forty mM potassium-evoked secretion was inhibited > 90% by both D600 and (-)-202-791, 25 microM forskolin-induced secretion was blocked < 50% by D600 and was unaffected by (-)-202-791, and 100 nM phorbol myristate acetate (PMA)-induced secretion was unaffected by either D600 or (-)-202-791. Enkephalin biosynthesis was increased by 10 nM PACAP-27, as measured by increased met-enkephalin pentapeptide content and PEnk A mRNA levels. PACAP-, forskolin-, and PMA-stimulated enkephalin synthesis were not blocked by D600 or (-)-202-791. Elevated potassium-induced enkephalin biosynthesis upregulation was completely blocked by either D600 or (-)-202-791 at the same concentrations. PACAP acting through type I PACAP receptors couples calcium influx-dependent enkephalin secretion and calcium influx-independent enkephalin biosynthesis in chromaffin cells. Restriction of the effects of enhanced calcium influx to stimulation of secretion, but not of biosynthesis, is unique to PACAP. By contrast, potassium-induced enkephalin biosynthesis upregulation is completely calcium influx dependent, specifically via calcium influx through L-type calcium channels. We propose that subpopulations of voltage-dependent calcium channels are differentially linked to intracellular signal transduction pathways that control neuropeptide gene expression and secretion in chromaffin cells.

Nicotine and prostaglandin E induce secretogranin II levels in bovine chromaffin cells

The synthesis regulation of secretogranin II was investigated in bovine chromaffin cells by treatment with various first messengers. Nicotine and prostaglandin E2 elevated secretogranin II mRNA and protein up to three-fold. Angiotensin II, atrial natriuretic peptide, apomorphine, bradykinin and clonidine on the other hand had no effect. The prostaglandin E induced elevation of secretogranin II mRNA was transduced via the calcium/calmodulin pathway but not via the protein kinase A or C pathways as shown by using specific inhibitors. Exposure of chromaffin cells to drugs specifically activating second messenger pathways both elevated and decreased secretogranin II mRNA. The calcium channel agonist Bay K, forskolin and phorbol esters increased secretogranin II mRNA whereas 8-Br-cGMP repressed the secretogranin II message. Thus, although secretogranin II expression can be altered by all major second messenger transduction systems, regulation of secretogranin II in vivo occurs mainly via the calcium/calmodulin pathway. Chromogranin A and B mRNA were not changed by any of the first messengers investigated indicating a differential synthesis regulation of components co-stored in bovine chromaffin granules.

Depolarization effects on the peptidergic phenotypes of chick sympathetic and adrenal cells

Depolarizing stimuli are among the factors known to influence the phenotypic plasticity of nerve cells. In order to determine the prevalence of the depolarization effects in terms of cell and neuropeptide phenotypes, we have analyzed the effect of potassium (K+)-induced depolarization on the avian sympathoadrenal system. The expression of three peptidergic phenotypes, somatostatin (SS), neuropeptide Y (NPY) and enkephalin (Enk) by two cell types, adrenal and sympathetic, was studied under different depolarizing regimens. Cells from the sympathetic paravertebral ganglion and adrenal gland of 10-11-day chick embryos were cultured and the peptide levels were measured by radioimmunoassays. Chronic depolarization causes differential effects on the peptidergic phenotypes increasing NPY and Enk but decreasing SS in both adrenal and sympathetic cultures. However, shorter exposures to depolarizing stimuli revealed diverse effects on NPY and Enk phenotypes and even between adrenal and sympathetic cells. Moreover, the maintenance of the effects after removal of the depolarizing stimuli showed additional differences among the phenotypes. Our results are not compatible with a previously established hypothesis stating that depolarization increases the synthesis of whichever neurotransmitters a neuron is already producing. They provide evidence indicating that the depolarization effect is much more complex than originally thought, and serve to initiate an in depth probe into the effect of depolarization of cellular plasticity.

Immunologically induced sympathectomy of preganglionic nerves by antibodies against acetylcholinesterase: increased levels of peptides and their messenger RNAs in rat adrenal chromaffin cells

Systemic administration of murine monoclonal acetylcholinesterase antibodies to rats has been shown to cause selective degeneration of sympathetic preganglionic neurons. In the present study rats were subjected to a single i.v. injection of these acetylcholinesterase antibodies, or to normal IgG or saline for control. Exophthalmos, piloerection and eyelid-drooping (ptosis) were observed within 1 h after administration of the antibodies. Rats were killed at different time-points after antibody administration, and the adrenal glands were analysed by means of indirect immunohistochemistry and in situ hybridization histochemistry. As soon as 3 h after the antibody treatment, a marked increase in the number of chromaffin cells expressing mRNA encoding, respectively, enkephalin, calcitonin gene-related peptide, galanin, neurotensin and substance P was seen. At 12 h the peptide mRNA levels were still elevated and there was a concomitant increase in the number of peptide-immunoreactive cells. All peptide levels remained high for at least 48 h; however, 77 days after the antibody treatment only enkephalin-immunoreactive cells could be encountered. A disappearance of acetylcholinesterase- and enkephalin-immunoreactive cells could be encountered. A disappearance of acetylcholinesterase- and enkephalin-positive fibers was already seen 3 h after the antibody treatment, and after 24 h no fibers were encountered. In contrast, up until 48 h there was no apparent change in the number or intensity of immunofluorescent fibers expressing calcitonin gene-related peptide, galanin, neurotensin or substance P. However, 77 days after the antibody treatment the number of calcitonin gene-related peptide- and substance P-immunoreactive fibers was increased as compared to controls. In addition, reappearance of acetylcholinesterase- and enkephalin-immunoreactive fibers was seen 77 days after antibody administration, although their number was still low as compared to controls. Double-labeling immunohistochemistry revealed that the chromaffin cells expressing peptides after the antibody treatment preferentially were adrenaline storing cells (noradrenaline-negative). The majority of these cells expressed only one peptide. Both surgical transection of the splanchnic nerve as well as treatment with acetylcholine receptor antagonists mimicked the effects seen after the acetylcholinesterase-antibody treatment, although changes were less pronounced. The present results show that interruption of splanchnic transmission induces fast, marked, and selective increases in peptide expression in rat adrenal chromaffin cells.

The expression of neuropeptide Y immunoreactivity in the avian sympathoadrenal system conforms with two models of coexpression development for neurons and chromaffin cells

We have studied the expression and development of neuropeptide Y-like immunoreactivity (NPY-LI) in the sympathoadrenal system of the chicken using single and double immunocytochemical techniques and radioimmunoassay. NPY-LI is expressed by neurons of the paravertebral sympathetic ganglia and by chromaffin cells of the adrenal gland in embryonic and adult chickens. The peptide is coexpressed with catecholaminergic properties in neurons. In chromaffin cells, it is also expressed with immunoreactivity to somatostatin and serotonin. We have used the expression of NPY-LI to analyze how cells that coexpress two or more neuroactive substances arrive at their final phenotype. Our results suggest that the ontogeny of coexpression in neurons of the avian paravertebral sympathetic ganglia occurs in a sequential pattern, where the expression of the peptide follows the initial expression of the “classical neurotransmitter”. In contrast, in chromaffin cells, expression of the peptides occurs concomitantly with expression of catecholaminergic properties or soon after. Initially, coexpression of several neuroactive substances occurs, but this is followed by further specialization where the expression of one peptide prevails over the other. We believe that the two models of coexpression shown by our results can be used to describe the ontogeny of coexpression in other cells of the nervous system.

Developmental and strain-specific heterogeneity of rat adrenal chromaffin cells recognized by a monoclonal antibody against intact chromogranin B

We have raised a monoclonal antibody (MAB-1E10) reactive with the intact forms but not the processing products of the chromaffin cell vesicle protein chromogranin B (CgB). The antibody recognizes rat and human, but not bovine and chick adrenal chromaffin cells. In addition, MAB-1E10 immunoreactivity was detected in rat PC 12 pheochromocytoma cells and in pituitaries. Several other tissues, including pancreas, small intestine and superior cervical ganglia, which are known to contain CgB in endocrine cells or neurons, respectively, were found not to be reactive with MAB-1E10. Using short-term cultures of dissociated adrenal chromaffin cells from Hannover-Wistar rats, we found that the expression of intact CgB is developmentally regulated. Between embryonic day 19 and postnatal day 40, about 80% of adrenal chromaffin cells--identified by their reactivity with an antibody against the enzyme dopamine-beta-hydroxylase--were found to be reactive with MAB-1E10. The proportion of positive cells subsequently decreased to about 5% at postnatal day 90. In the presence of glucocorticoids, this decrease was reduced to about 45% CgB-positive cells at postnatal day 90. In another rat strain, Sprague-Dawley rats, the proportion of MAB-1E10-immunoreactive chromaffin cells (about 50%) remained constant from birth to adulthood. Our results indicate that CgB is differentially expressed and/or processed in different rat tissues, strains and during development, and furthermore, that expression or processing in rat chromaffin cells might be regulated by glucocorticoids. Intact CgB appears to be a marker for a subpopulation of chromaffin cells, but its function(s) remains to be clarified.

Comparative incorporation of proenkephalin-derived peptides, chromogranin A, and dopamine beta-hydroxylase into chromaffin vesicles

The incorporation of enkephalin-containing peptides (ECPs) derived from proenkephalin into chromaffin vesicles was examined in primary cultures of adrenal medullary chromaffin cells. Cells were pulse-labeled with [35S]methionine and chased for periods up to 24 h. Chromaffin vesicles in cell homogenates were then fractionated by density gradient centrifugation and the presence of [35S]Met-enkephalin sequences in gradient fractions determined. 35S-ECPs were incorporated into particles suggestive of immature vesicles within 1-2 h after radiolabeling. Vesicle maturation, measured by co-equilibration of 35S-ECPs and total ECPs in the gradients, was complete within 9-12 h and was unaffected by treatments that increase proenkephalin synthesis. Incorporation of [35S]chromogranin A into chromaffin vesicles followed a similar time course, but 35S-labeled dopamine beta-hydroxylase was much more slowly incorporated, possibly reflecting differences in incorporation of membrane and soluble components. In summary, the data demonstrate that ECPs are rapidly sequestered in immature chromaffin vesicles, a process unaltered by changing rates of proenkephalin synthesis.

Modulation of neuropeptide expression in avian embryonic sympathetic cultures

Two distinct neuropeptide-related phenotypes are found in avian paravertebral sympathetic ganglia, corresponding to somatostatin- (SS) and vasoactive intestinal polypeptide- (VIP) expressing cells. We have detected the same cell phenotypes in cultures of embryonic quail sympathetic ganglia and have used this system to study the modulation of their expression by the environment. The cell phenotypes were identified using immunocytochemistry and induced catecholamine fluorescence and quantitative data were obtained by radioimmunoassay. Dissociation of the ganglia caused a profound increase in the expression of VIP but had no effect on SS levels. Addition of corticosterone (10(-6) M) increased the expression of SS without modifying VIP levels. In contrast, depolarization of the cells induced changes in levels of both neuropeptides. The modulation of VIP correlates with the modulation of cholinergic properties. The regulation of neuropeptide expression in the avian system shows both similarities and differences to what has been found in the mammalian system.

Enkephalin-like immunoreactivity in ganglionic cells in the larynx and superior cervical ganglion of the rat

The distribution of enkephalin-like immunoreactivity (ENK-LI) in the larynx, the superior cervical ganglion (SCG) and the nodose ganglion of adult rats was examined in the present study. A substantial number of the local acetylcholinesterase (AChE)-positive, presumably parasympathetic, ganglionic cells in the larynx displayed ENK-LI. These cells also exhibited neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-LI. Varicose nerve fibers showing ENK-LI were observed close to the acini and ducts of the glands, in the perichondrium and in the lamina propria. The varicosities exhibiting ENK-LI frequently displayed NPY- and VIP-LI. The ENK-LI was detected in a subpopulation of AChE-positive nerve fibers in the laryngeal tissue. In the SCG, only a small number of the ganglionic cells displayed ENK-LI. These cells, in contrast to other ganglionic cells of the SCG, did not show NPY-LI. None of the ganglionic cells of the nodose ganglion exhibited ENK-LI. Sympathectomy and vagotomy affected neither the number nor the distribution of fibers showing ENK-LI in the larynx. In conclusion, ENK appears to be present together with NPY and VIP in the parasympathetic innervation of the larynx and in a very limited number of the ganglionic cells of a sympathetic ganglion, the SCG, of the adult rat.

Effects of the catecholaminergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) on adrenal chromaffin cells in culture

N-(2-Chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) is an inhibitor of noradrenaline uptake and a neurotoxin known to deplete noradrenaline levels with little effect on dopamine, serotonin or adrenaline in the central nervous system. The present study tested the effects of DSP-4 on catecholamine uptake, release and content in cultures of isolated bovine adrenal chromaffin cells. DSP-4 selectively inhibited the acute uptake of [3H]noradrenaline with little or no effect on [3H]adrenaline or [3H]dopamine uptake. In cultures preloaded with [3H]catecholamines, DSP-4 stimulated the release of [3H]noradrenaline and, to a small extent, also [3H]adrenaline and [3H]dopamine. However, the drug did not stimulate the release of appreciable amounts of endogenous adrenaline, noradrenaline or dopamine. A high concentration of DSP-4 inhibited the carbachol-stimulated release of adrenaline, noradrenaline and dopamine from the cells. Following a 1-hr exposure to the drug, DSP-4 decreased adrenaline, noradrenaline and dopamine levels in the cells with no gross morphologic changes in the cells. Reductions in adrenaline and noradrenaline levels were almost equal in magnitude, while dopamine was depleted to a somewhat greater extent under some conditions. Longer exposure to DSP-4 resulted in morphological changes in the cells, suggesting that the drug is also toxic to chromaffin cells in culture.

Differential colocalization of neuropeptide Y- and methionine-enkephalin-Arg6-Gly7-Leu8-like immunoreactivity in catecholaminergic neurons in the rat brain stem

The present study, using a combination of catecholamine (CA) histofluorescence and peptide immunocytochemistry in the same tissue sections, investigated the coexistence of neuropeptide Y (NPY) and methionine-enkephalin-Arg6-Gly7-Leu8 (MEAGL)-like immunoreactivity (LI) in catecholaminergic neurons of colchicine-treated rat brain stems. Of the total number of catecholaminergic neurons in the A1/C1, A2/C2, A3, A4, and A6 regions approximately 83, 28, 98, 76, and 36%, respectively, contained both NPY-LI and CA. Of the total number of catecholaminergic neurons in A1/C1, A2/C2, A3, and A5 regions, approximately 47, 4, 8, and 17%, respectively, contained both MEAGL-LI and CA. Moreover, about 24% of the catecholaminergic neurons in the A1/C1 region contained both NPY- and MEAGL-LI. Neither the noradrenergic neurons (A7) in the pons nor any of the dopaminergic neurons in the midbrain (A8, A9, A10) contained NPY- or MEAGL-LI. Neurons containing both NPY- and MEAGL-like immunoreactive peptides without CA were not found in the rat brain stem. These findings indicate that catecholaminergic neurons in the brain stem of the rat can be subdivided into distinct subgroups on the basis of the coexistence of specific peptides.

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.

Coexistence of catecholamine and methionine enkephalin-Arg6-Gly7-Leu8 in neurons of the rat ventrolateral medulla oblongata. Application of combined peptide immunocytochemistry and histofluorescence method in the same vibratome section

An overlapping distribution of catecholamine-containing cells and proenkephaline-A derived peptide-containing neurons have been identified in the rat medulla oblongata. However, it is not evident whether the coexistence of these bioactive substances occurs in the same neurons or not. Therefore, we examined the coexistence of catecholamine and methionine-enkephalin-Arg6-Gly7-Leu8 (MEAGL), a proenkephaline-A derived peptide, using a combination of histofluorescence and peroxidase-anti-peroxidase (PAP) immunohistochemical (modified formaldehyde-glutalaldehyde (Faglu)) methods on the same tissue sections. We found one third of A1/C1 catecholamine fluorescent cells show MEAGL-like immunoreactivity.

Neural and humoral factors separately regulate neuropeptide Y, enkephalin, and chromogranin A and B mRNA levels in rat adrenal medulla

The influence of neurogenic versus humoral factors on mRNA levels of several secretory proteins of rat adrenal medulla was studied in vivo. Increased splanchnic nerve activity was generated (reflexly) with insulin treatment. Twenty-four hours after insulin injection, levels of mRNAs encoding neuropeptides (enkephalin and neuropeptide Y) were increased 6.5-fold, whereas those of mRNAs for the major secretory proteins (chromogranins A and B) were unchanged. Bilateral transection of the splanchnic nerves completely prevented this increase. Hypophysectomy decreased levels of chromogranin A mRNA to 32% of control, suggesting a dependence on hormones of the pituitary-adrenal axis. Treatment of hypophysectomized rats with dexamethasone restored chromogranin A mRNA to basal levels. Chromogranin B mRNA levels were not changed by either insulin treatment or hypophysectomy. These results demonstrate (i) that different classes of secretory proteins present in chromaffin granules are regulated by different mechanisms, (ii) that this regulation occurs at a pretranslational site, and (iii) that the relative concentration of secretory constituents of chromaffin granules may vary. The significance of an altered composition of secretory-granule constituents, which may be important in hypotension or stress, is discussed.

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.

Leucine-enkephalin- and neuropeptide Y-modulation of [3H]noradrenaline release in the oviduct of mature and juvenile rabbits

1. The effects of leucine-enkephalin and neuropeptide Y (NPY) on [3H]noradrenaline release induced by electrical field stimulation were studied in the isthmic part of the oviduct of juvenile and mature rabbits. 2. [3H]noradrenaline and total tritium overflow in the presence of cocaine, corticosterone and hyoscine were determined by liquid scintillation spectrometry. 3. Tritium overflow evoked by electrical stimulation (1 or 4 Hz, 1 msec) was calcium dependent. [3H]noradrenaline content (measured by ion exchange chromatography) accounted for 85% of the total tritium overflow. 4. Leucine-enkephalin (1 microM) in the presence of the peptidase inhibitor bacitracin reduced the stimulation-evoked tritium overflow in mature rabbits by 26.1 +/- 1.6% and in juvenile rabbits by 11.9 +/- 1.9%. Naloxone (1 microM) antagonized the effect of leucine-enkephalin. 5. NPY (0.2 microM) reduced the evoked tritium overflow in mature rabbits by 23.4 +/- 2.4% and in juvenile rabbits by 17.2 +/- 4.3%. 6. It is concluded that leucine-enkephalin and NPY inhibited [3H]noradrenaline release in rabbit oviduct and the modulatory effect of leucine-enkephalin depends on maturity while NPY modulation is a more independent system.

Stress-induced changes of circulating neuropeptide Y in the rat: comparison with catecholamines

Circulating concentrations of neuropeptide Y-like immunoreactivity (NPY), noradrenaline (NA) and adrenaline (AD) were measured in conscious, chronically catheterized rats submitted to various stress protocols. Basal plasma levels of NPY, NA and AD (194 +/- 52 fmol/ml, 0.90 +/- 0.11 pmol/ml and 0.52 +/- 0.07 pmol/ml) were increased by handling (+132%, +76% and +629%, respectively) and rose further during electric shock treatment. Adrenalectomy resulted in the complete disappearance of circulating adrenaline but did not alter either control or stress values of noradrenaline. In comparison circulating levels of NPY were reduced, but not significantly in adrenalectomized animals. Insulin stress induced a large increase in plasma AD levels and cold stress induced an increase in plasma NA levels, without any parallel change in NPY concentrations. These results demonstrate that NPY, which is colocalized with catecholamines in the peripheral nervous systems, is also released during stress responses and that its release parallels more closely changes in circulating NA than AD. Furthermore, stress-induced changes in circulating NPY-like immunoreactivity do not originate from the adrenal gland but mainly from the peripheral nervous system, and the release of NPY is dependent upon the nature of the stimulus.

Rat adrenal medulla: levels of chromogranins, enkephalins, dopamine beta-hydroxylase and of the amine transporter are changed by nervous activity and hypophysectomy

The levels of several constituents of chromaffin granules were determined in rat adrenal medulla after treatment with insulin or reserpine and after hypophysectomy. Insulin treatment induced increased levels of enkephalins, dopamine beta-hydroxylase, the amine carrier and of chromogranin B whereas catecholamines, cytochrome b-561 and chromagranin A remained slightly below control levels. Administration of reserpine led to similar changes with the exception of the enkephalins which increased much less. After hypophysectomy, chromogranin A was reduced to low levels; dopamine beta-hydroxylase, the amine carrier and catecholamines showed an intermediate reduction, whereas the other components remained at control levels. We can conclude that nervous stimulation of the adrenal medulla (by insulin and reserpine) induces the synthesis of enkephalins, dopamine beta-hydroxylase, the amine carrier and chromogranin B whereas the level of chromogranin A apparently depends on corticosteroids. Thus, major components of the secretory content and the membranes of chromaffin granules are regulated separately, which allows the biogenesis of chromaffin granules with a significantly altered composition.

Cytochrome b561 can be detected in many neuroendocrine tissues using a specific monoclonal antibody

CG7 is a monoclonal antibody that recognizes cytochrome b561, a major protein component of adrenal medullary chromaffin granules. Immunocytochemical studies using this antibody have demonstrated that cytochrome b561 is present in many neural and endocrine tissues and that its distribution is correlated with the presence of either catecholamines or amidated peptides in the tissue. These tissues include neuronal cell bodies and/or fibers in the gut, blood vessels, retina, and posterior pituitary, endocrine cells of the gut, anterior and intermediate lobes of the pituitary, heart muscle, and all adrenal medullary chromaffin cells. The discovery of cytochrome b561 in many neuropeptide-containing tissues regardless of the presence of catecholamines is consistent with a general role for cytochrome b561 as a secretory granule membrane electron carrier. Its expression may be linked to an ascorbic acid requirement by both catecholamine and neuropeptide biosynthetic enzymes.

Monoclonal antibodies to chromaffin cells can distinguish proteins specific to or specifically excluded from chromaffin granules

I have prepared a number of monoclonal antibodies to chromaffin cell membranes. One of these antibodies recognizes a number of antigenically related proteins that are present in all tissues examined. In the adrenal, these proteins are completely excluded from chromaffin granules but are present in other subcellular membrane fractions. This non-granule membrane-specific antibody has been designated NG3. A second antibody, CG7, binds to a single protein which segregates specifically into chromaffin granules. The protein recognized by CG7 is cytochrome b561, or chromomembrin B, one of the major protein components of chromaffin granule membranes. CG7 also labels a protein (the identical cytochrome b561) in bovine posterior pituitary neurosecretory vesicle membranes indicating that it functions in both peptidergic and catecholaminergic secretory granules. These two monoclonal antibodies provide useful probes of both granule and extra-granule membrane proteins for studies of membrane trafficking in chromaffin cells.

Chromogranin A synthesis and secretion in chromaffin cells

A sensitive and selective radioimmunoassay for chromogranin A (Chrg A) has been developed to quantitate content, release, and biosynthesis of this secretory protein in neuroendocrine tissues. An antiserum raised against Chrg A from bovine adrenal medulla was found to detect predominantly only the Mr 70-75 kilodalton Chrg A in its native form, allowing the use of this antiserum as a quantitatively specific probe for Chrg A in cell-free extracts of the adrenal medulla and chromaffin cells. Chrg A comprises about 10% of the total protein of the chromaffin cell. It is released in parallel with Met-enkephalin and catecholamines from the bovine chromaffin cell in primary culture in response to nicotine and nicotinic cholinergic agonists. From 14 to 22% of total Chrg A is released from the cell during a 15-min exposure to a maximally stimulatory dose of nicotine (10-100 microM). Chrg A release on nicotinic stimulation is blocked by D-600 and hexamethonium to the same extent as Met-enkephalin and catecholamine release. The parallel time course and percent release of Chrg A and Met-enkephalin indicate that these secretory polypeptides are contained in, and released from, functionally identical cellular compartments. Chrg A and Met-enkephalin pentapeptide sequences are present in the chromaffin cell at a ratio of about 2:1, although Chrg A is far more abundant on a mass basis. Chrg A and Met-enkephalin biosynthesis appear to be differentially regulated within the chromaffin cell, since chronic treatment of cells with nicotine and forskolin causes an elevation of Met-enkephalin pentapeptide without a concomitant elevation of intracellular levels of Chrg A.