Bovine chromaffin granules: immunological studies with antisera against neuropeptide Y, [Met]enkephalin and bombesin

PACAP signaling in stress: insights from the chromaffin cell

Pituitary adenylate cyclase-activating polypeptide (PACAP) was first identified in hypothalamus, based on its ability to elevate cyclic AMP in the anterior pituitary. PACAP has been identified as the adrenomedullary neurotransmitter in stress through a combination of ex vivo, in vivo, and in cellula experiments over the past two decades. PACAP causes catecholamine secretion, and activation of catecholamine biosynthetic enzymes, during episodes of stress in mammals. Features of PACAP signaling allowing stress transduction at the splanchnicoadrenomedullary synapse have yielded insights into the contrasting roles of acetylcholine's and PACAP's actions as first messengers at the chromaffin cell, via differential release at low and high rates of splanchnic nerve firing, and differential signaling pathway engagement leading to catecholamine secretion and chromaffin cell gene transcription. Secretion stimulated by PACAP, via calcium influx independent of action potential generation, is under active investigation in several laboratories both at the chromaffin cell and within autonomic ganglia of both the parasympathetic and sympathetic nervous systems. PACAP is a neurotransmitter important in stress transduction in the central nervous system as well, and is found at stress-transduction nuclei in brain including the paraventricular nucleus of hypothalamus, the amygdala and extended amygdalar nuclei, and the prefrontal cortex. The current status of PACAP as a master regulator of stress signaling in the nervous system derives fundamentally from the establishment of its role as the splanchnicoadrenomedullary transmitter in stress. Experimental elucidation of PACAP action at this synapse remains at the forefront of understanding PACAP's role in stress signaling throughout the nervous system.

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.

Combinatorial code of growth factors and neuropeptides define neuroendocrine differentiation in PC12 cells

Adrenal chromaffin cells constitute one of the first cell types to have been defined as a neuroendocrine cell type. Since they produce dopamine, these cells have been proposed for the treatment of neuronal deficits in human Parkinson's disease. However, the factors involved in the development of chromaffin cells are still poorly understood. Based on recent insights from stem cell research, we decided to study the role of extracellular matrices, growth factors and neuropeptides on the neuroendocrine differentiation in a serum-free medium of PC12 cells. Employing immunohistochemistry, quantitative PCR and HPLC analysis, neuroendocrine differentiation was determined by evaluating neurite outgrowth, catecholamine biosynthesis and release as well as neuropeptide and vesicular protein mRNA expression. The combination of bFGF, NGF and PACAP could prevent the inhibition of neurite process development induced by dexamethasone in PC12 cells cultured on ECM. Whereas glucocorticoids were essential in the regulation of enzymes of catecholamine biosynthesis and metabolism, growth factors and PACAP were more efficient in inducing neuropeptide and chromogranin B expression as well as release of dopamine and 3-methoxytyramine. Therefore, in addition to glucocorticoids, chromaffin cells need a gradient of matrix, growth factors, and neuropeptides to develop the full functional phenotype of a neuroendocrine cell.

Deletion of tyrosine hydroxylase gene reveals functional interdependence of adrenocortical and chromaffin cell system in vivo

Catecholamines are produced in the medulla of the adrenal gland and may participate in the intraglandular regulation of its cortex. We analyzed the adrenal structure and function of albino tyrosine hydroxylase-null (TH-null) mice that are deficient in adrenal catecholamine production. Adrenal catecholamines were markedly reduced, and catecholamine histofluorescence was abrogated in 15-day-old TH-null mice. Chromaffin cell structure was strikingly altered at the ultrastructural level with a depletion of chromaffin vesicles and an increase in rough endoplasmic reticulum compared with wild-type mice. Remaining chromaffin vesicles lined up proximally to the cell membrane in preparation for exocytosis providing a "string-of-pearls" appearance. There was a 5-fold increase in the expression of proenkephalin mRNA (502.8 +/- 142% vs. 100 +/- 17.5%, P = 0.016) and a 2-fold increase in the expression of neuropeptide Y (213.4 +/- 41.2% vs. 100 +/- 59.9%, P = 0.014) in the TH-null animals as determined by quantitative TaqMan (Perkin-Elmer) PCR. Accordingly, immunofluorescence for met-enkephalin and neuropeptide tyrosine in these animals was strongly enhanced. The expression of phenylethanolamine N-methyl transferase and chromogranin B mRNA was similar in TH-null and wild-type mice. In TH-null mice, adrenocortical cells were characterized by an increase in liposomes and by tubular mitochondria with reduced internal membranes, suggesting a hypofunctional state of these steroid-producing cells. In accordance with these findings, plasma corticosterone levels were decreased. Plasma ACTH levels were not significantly different in TH-null mice. In conclusion, both the adrenomedullary and adrenocortical systems demonstrate structural and functional changes in catecholamine-deficient TH-null mice, underscoring the great importance of the functional interdependence of these systems in vivo.

The adrenomedullary venous vasculature as a target for endothelins: comparison of the porcine and bovine central adrenomedullary veins

The functional properties of the isolated porcine and bovine central adrenomedullary veins were compared, with emphasis on the active tension responses to high K+, endothelin-1 (ET-1) and neuropeptide Y (NPY). In the porcine vein, the contraction evoked by ET-1 was 4--5-fold higher than with high K+, as in the bovine vein. The potencies for ET-1 were similar in ring and strip preparations of the porcine vein, with EC50 values 5--7-fold higher than in the bovine vein. In preparations previously exposed to ET-1 the contractions evoked by high K+ and NPY were potentiated and facilitated, respectively,. However, only in the porcine vein was the ET-1 contraction sustained. This contraction was effectively relaxed by milrinone, indicating a role for cGMP inhibited cyclic nucleotide phosphodiesterase in the sustained contraction. Caffeine and forskolin were also effective relaxants of contractions evoked by ET-1 in both veins, suggesting relaxation by elevated levels of cAMP. The K(+)-contracted porcine, but not bovine, vein was relaxed by acetylcholine (ACh) and vasointestinal polypeptide in a concentration-dependent manner, indicating species differences with respect to signal transduction leading to increases in cyclic nucleotides. In conclusion, these results demonstrate that ET-1 is the main constrictor of the porcine central adrenomedullary vein, with significant species differences in mode of contraction and relaxation. These findings suggest roles for the endogeneously released ET-1 and NPY in regulation of venous contractility within the adrenal gland of mammals.

Expression of neurotrophins and their receptors in the developing and adult rat adrenal gland

We have studied the postnatal expression of neurotrophins, their cognate high-affinity trk receptors and the low-affinity NGF receptor (p75LNGFR) in the rat adrenal gland using RT-PCR. Neurotrophin mRNAs were detectable during the whole postnatal period. Strongest signals were obtained for BDNF and NT4/5. Expression of trkA, trkB, trkC and p75LNGFR was found at all ages studied. Signals for trkA were highest in the adult adrenal medulla, whereas signals for p75LNGFR were highest in the adult adrenal cortex. Cur data suggest still largely enigmatic roles for neurotrophins in functions of the adrenal medulla and possibly also the cortex.

Differences in the composition of chromaffin granules in adrenaline and noradrenaline containing cells of bovine adrenal medulla

Several constituents of chromaffin granules were quantitatively determined in noradrenaline and adrenaline cells purified from bovine adrenal medulla. As far as secretory peptides are concerned noradrenaline granules contained slightly more secretogranin II, but much less chromogranin A than adrenaline granules. This can be explained by the dependence of the biosynthesis of chromogranin A on corticosteroids. Proteolytic processing of chromogranin A and secretogranin II was higher in noradrenaline cells which was paralleled by a higher content of the prohormone convertase PC2. Noradrenaline granules also contained a higher concentration of the vesicular monoamine transporter (vMAT2). No differences were found for dopamine beta-hydroxylase, prohormone convertase PC1, carboxypeptidase H and synaptophysin. These results indicate that the secretory cocktail of peptides released from these cells differs significantly between adrenaline and noradrenaline storing cells.

The transcriptional regulation of the preproenkephalin gene

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Identification of a 7B2-derived tridecapeptide from bovine adrenal medulla chromaffin vesicles

1. A novel tridecapeptide was isolated from extracts of bovine adrenal medulla chromaffin vesicles and the primary structure determined to be SVPHFSDEDKDPE. 2. This peptide is identical to the C termini of human and porcine 7B2 and is highly homologous to the same region of the mouse and Xenopus lavis protein. 3. In all these species the homologous peptide is preceded by a pair of lysine residues, a potential proteolytic processing site. 4. Ser6 is part of a well-conserved casein kinase II consensus phosphorylation sequence. Evidence for phosphorylation of this residue was obtained during Edman sequencing. 5. Thus, this novel adrenal medullary probably arises from the posttranslational processing of the bovine 7B2 protein.

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.

Screening of adrenal medullary neuropeptides for putative neurotrophic effects

Chromaffin granules, the secretory organelles of the neuron-like adrenal medullary chromaffin cells, have previously been shown to store and liberate neurotrophic activities that support in vitro survival of several neuron populations including those innervating the adrenal medulla. Molecules resembling fibroblast growth factor and ciliary neurotrophic factor have been identified among these activities. Since chromaffin granules store a variety of neuropeptides and many neuropeptides can have pleiotropic effects on neuronal growth and maintenance we have tested 24 different neuropeptides for their capacities to promote survival of embryonic chick ciliary, dorsal root and sympathetic ganglionic neurons. Peptides tested included several derivatives of proenkephalin (Leu- and met-enkephalin, fragments BAM 22, B, F and E), somatostatin, substance P, neuropeptide Y, neurotensin, VIP, bombesin, secretin, pancreastatin, dynorphin B, dynorphin 1-13, beta-endorphin, alpha-, beta-, and gamma-MSH. Control cultures received saturating concentrations of ciliary neurotrophic or nerve growth factor (CNTF; NGF), or no trophic supplements. At 1 x 10(-5) M leu- and met-enkephalin as well as somatostatin supported sympathetic neurons to the same extent as NGF. At the same concentrations, leu-enkephalin, the proenkephalin fragments BAM 22 and E, and somatostatin maintained about half of the dorsal root ganglionic neurons supported by NGF, but were not effective on ciliary neurons. VIP promoted the survival of approximately 50% of the ciliary and embryonic day 10 dorsal root ganglionic neurons as compared to saturating amounts of CNTF, but required the presence of non-neuronal cells in the cultures to be effective. Neurotensin (1 x 10(-5) M had a small effect on ciliary neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y inhibits nicotinic cholinergic currents but not voltage-dependent calcium currents in bovine chromaffin cells

The effects of neuropeptide Y (NPY; 1-36) and NPY fragment (16-36) on nicotinic currents (IACh) and voltage-dependent calcium currents (ICa) were studied in bovine chromaffin cells using the whole-cell patch-clamp technique. The peak amplitude of inward nicotinic currents was markedly depressed by both NPY (1-36) and NPY (16-36). In contrast, ICa was unaffected by either NPY (1-36) or NPY (16-36). Both pertussis toxin pretreatment and including GDP [beta-S] in the patch pipette solution completely abolished the inhibitory effect of NPY on IACh. It is concluded that inhibition of IACh probably represents the mechanism by which NPY decreases catecholamine release from adrenal medulla. This effect appears to be mediated by a G-protein-coupled Y2 receptor.

Neuropeptide Y and catecholamine synthesizing enzymes and their mRNAs in rat sympathetic neurons and adrenal glands: studies on expression, synthesis and axonal transport after pharmacological and experimental manipulations using hybridization techniques and radioimmunoassay

The effects of reserpine treatment (10 mg/kg, i.p.) on the content of neuropeptide Y-like immunoreactivity and catecholamines were compared with the levels of mRNA coding for neuropeptide Y, tyrosine hydroxylase and phenylethanolamine N-methyltransferase in rat sympathetic neurons and adrenal gland. A reversible depletion of neuropeptide Y-like immunoreactivity was observed in the right atrium of the heart, kidney and masseter muscle, while the immunoreactive neuropeptide Y content in the stellate and lumbar sympathetic ganglia and its axonal transport in the sciatic nerve increased following reserpine. The increase in the stellate ganglion was maximal at 48 h and absent 9 days after reserpine treatment. The expression of neuropeptide Y mRNA and tyrosine hydroxylase mRNA in both the stellate and the superior cervical ganglion increased earlier than the neuropeptide Y content, with a clear cut two-fold elevation at 24 h after reserpine. The increase in both mRNAs in the superior cervical ganglion and the depletion of neuropeptide Y, but not of noradrenaline, in terminal areas was prevented after pretreatment both with a nicotinic receptor antagonist (chlorisondamine) and with surgical preganglionic denervation. A marked (75-90%) depletion of neuropeptide Y-like immunoreactivity and adrenaline in the adrenal gland, concomitant with 3-4-fold increases in neuropeptide Y mRNA and tyrosine hydroxylase mRNA expression, was present at 24 h after reserpine treatment. Also in the adrenal gland, there was a reversal of the reserpine-induced increase in neuropeptide Y mRNA and tyrosine hydroxylase mRNA and depletion of neuropeptide Y and adrenaline following splanchnic denervation. Pharmacological, ganglionic blockade prevented the depletion of neuropeptide Y and the increased expression of neuropeptide Y mRNA, but not fully, the tyrosine hydroxylase mRNA elevation. In addition, a marked decrease in phenylethanolamine N-methyltransferase mRNA levels was noted after reserpine. This decrease was reversed by denervation and by ganglionic blockade. Denervation alone led to a small but significant decrease in all mRNAs examined both in the superior cervical ganglion and the adrenal medulla. The present data suggest that the depletion of neuropeptide Y-like immunoreactivity in sympathetic nerves and in the adrenal gland after reserpine is associated with a compensatory increase in neuropeptide Y synthesis and axonal transport, most likely due to increased nicotinic receptor stimulation. Whereas the reserpine depletion of neuropeptide Y in both sympathetic nerves and adrenal gland is related to neuronal activation, adrenal but not nerve terminal depletion of catecholamines can be prevented by the ganglionic blocker chlorisondamine.4+e difference in effect of pharmacological ganglionic

Co-localization of chromogranin A and B, secretogranin II and neuropeptide Y in chromaffin granules of rat adrenal medulla studied by electron microscopic immunocytochemistry

The co-localization of various antigens in rat chromaffin granules was investigated by the immunogold staining procedure. In ultrathin serial sections staining of chromaffin granules was obtained with antisera against chromogranin A, chromogranin B, secretogranin II and neuropeptide Y. These results indicated that these antigens are costored within chromaffin granules. To further corroborate this point a double immunogold staining procedure was used. This method unequivocally established that chromogranin A, chromogranin B, secretogranin II and neuropeptide Y are co-localized in the same chromaffin granules. These results are relevant for studies demonstrating changes in the level of these peptides in adrenal medulla. The co-localization makes it likely that such changes lead to a different relative composition of the secretory quanta of chromaffin granules.

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.

Two-dimensional immunoblotting analysis and immunocytochemical localization of the secretory polypeptide 7B2 in adrenal medulla

The soluble proteins of bovine chromaffin granules were subjected to 2D-electrophoresis followed by immunoblotting with an antiserum against the pituitary peptide 7B2. One immunoreactive spot was visualized at a position corresponding to a molecular weight of 24,000 and to a pI of 5.2. Using peroxidase-antiperoxidase (PAP) pre-embedding immunocytochemical technique for electron microscopy, 7B2 has been localized within secretory granules with diameters of approximately 115 and 190 nm in noradrenergic and adrenergic cells respectively. These data establish that in chromaffin granules 7B2 represents a minor component of the acidic proteins which include the chromogranins A and B, secretogranin II and the enkephalin-containing peptides.

Effect of local injection of cysteamine and cystamine on somatostatin and neuropeptide Y levels in the rat striatum

Cysteamine and its dimeric form cystamine have been applied to the rat striatum by local injection. Both compounds resulted in a dose-dependent decrease of somatostatin levels. Maximal reduction of somatostatin (by about 50%) was obtained at a dose of 50 micrograms of cysteamine or cystamine after about 6 h. All three molecular weight forms of somatostatin--somatostatin-14, somatostatin-28, and the 13,000 molecular weight form of somatostatin--were reduced, as shown by size exclusion HPLC. Injection of radiolabeled cystamine revealed a fast conversion of the compound to cysteamine, suggesting it is active in the monomeric form. The levels of neuropeptide Y, which is colocalized with somatostatin in striatal neurons, failed to be changed by local or intraperitoneal injection of cysteamine, suggesting that this treatment does not affect vesicles of somatostatin/neuropeptide Y neurons.

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 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.

The adrenal contribution to the neuroendocrine responses to splanchnic nerve stimulation in conscious calves

1. The extent to which the adrenal gland contributes to neuroendocrine responses to electrical stimulation of the peripheral end of the splanchnic nerve has been investigated in conscious calves in which the right nerve was stimulated either at 4 Hz continuously for 10 min or at 40 Hz in 1 s bursts at 10 s intervals for the same period. 2. It was confirmed that the release of neuropeptide Y (NPY) and of gastrin-releasing peptide (GRP) is potentiated by stimulation in bursts at a relatively high frequency and shown that the adrenal gland made a negligible contribution to these responses. 3. There was no detectable change in the concentration of vasoactive intestinal peptide (VIP) in the arterial plasma but the existence of a very small but highly significant rise in the output of VIP from the adrenal provided evidence that it was released within the gland in response to splanchnic nerve stimulation. 4. The concentration of calcitonin gene-related peptide (CGRP) in the arterial and adrenal venous effluent plasma was consistently below the level of detection of the assay. 5. Splanchnic nerve stimulation resulted in an abrupt rise in the output of both free and total met5-enkephalin-like immunoreactivity from the adrenal gland which was substantially potentiated by stimulating in bursts. This pattern of stimulation also increased the proportion released in a high-molecular-weight form. 6. Stimulation in bursts significantly enhanced the output of both adrenaline and noradrenaline from the adrenal and resulted in the release of proportionately more noradrenaline. Small amounts of dopamine and DOPAC were also released during splanchnic nerve stimulation and the output of dopamine was significantly increased by stimulating in bursts. 7. Both patterns of stimulation elicited an abrupt rise in mean plasma adrenocorticotrophic hormone (ACTH) concentration, which was associated with an increase in mean adrenal cortisol output and the former effect was significantly enhanced by stimulating in bursts. 8. It is concluded that certain responses to splanchnic nerve stimulation are significantly potentiated by an intermittent high-frequency pattern of stimulation, including all those that are attributable to adrenal medullary activity, whereas others are apparently unaffected by changes in stimulus pattern.

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.

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.

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.

The primary structure of human secretogranin I (chromogranin B): comparison with chromogranin A reveals homologous terminal domains and a large intervening variable region

We have determined and analyzed the primary structure of human secretogranin I (chromogranin B), a tyrosine-sulfated secretory protein found in a wide variety of peptidergic endocrine cells. A 2.5-kb cDNA clone, hybridizing to an mRNA of similar length, was isolated from a cDNA library of human pheochromocytoma. The identity of the clone was established by comparison of its deduced amino acid sequence with N-terminal and several internal secretogranin I sequences as well as by immunoprecipitation of the protein produced by in vitro transcription-translation of the cloned cDNA. Secretogranin I is a 657 amino acid long polypeptide of 76 kd and is preceded by a cleaved N-terminal signal peptide of 20 residues. Comparison of the predicted amino acid sequence of human secretogranin I with that of bovine chromogranin A reveals significant homologies near the N termini and at the C termini. The N-terminal homologous domains contain the only two cysteine residues of both proteins and form disulfide-stabilized loop structures. The sequences between the homologous terminal domains in both proteins differ but are characterized by a remarkable hydrophilicity, an abundance of acidic amino acids and potential dibasic cleavage sites for the generation of smaller, perhaps hormone-like, peptides.

Isolation and characterization of chromogranins A, B, and C from bovine chromaffin granules and a rat pheochromocytoma

Bovine chromaffin granules from adrenal medulla contain three acidic secretory proteins: chromogranins A, B, and C. For isolation of these proteins, methods based mainly on high performance liquid chromatography were developed. After removal of contaminating glycoproteins by lectin affinity chromatography, chromogranins were separated by high performance anion-exchange, gel-filtration, and reverse phase liquid chromatography. As a final purification step sodium dodecyl sulfate-gel electrophoresis was performed. Amino acid analysis of isolated bovine chromogranins revealed a similar composition of all three proteins, with glutamic acid being the most prominent amino acid. The methods developed for bovine proteins also proved suitable for isolating rat chromogranins A and B from a transplantable pheochromocytoma. Chromogranin C was not present in sufficient amounts to be isolated from this tissue. The chromogranins purified by these methods were used to raise specific antibodies in rabbits. The use of purified chromogranins together with specific antisera may be valuable in understanding the still undiscovered function of these proteins.

Identification of two glycoproteins of chromaffin granules as the carboxypeptidase H

An antiserum against carboxypeptidase H, an enzyme involved in the biosynthesis of neuropeptides such as the enkephalins, was used to identify the enzyme proteins in bovine chromaffin granules. Two-dimensional immuno- and lectin-blots revealed that two closely migrating glycoproteins which have been previously named J and K represented the enzyme. The same protein doublet was present in the membrane preparation and the soluble lysate of bovine chromaffin granules; however, the membrane contained significantly more enzyme protein.

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.