Chromogranin A: a multipurpose prohormone?
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Animals↗
Biomedical subjects
K B Helle
Publications and source records attributed to K B Helle.
Vasoinhibitory activity of synthetic peptides from the amino terminus of chromogranin A.
Naturally occurring amino terminal fragments of chromogranin A (CGA), the calcium-binding protein found in all endocrine secretory vesicles, have vasoinhibitory activity when tested in isolated segments of the endothelium-denuded human saphenous vein. Synthetic peptides corresponding to sequences within the first 76 residues of chromogranin A have been made and tested for biological activity. Full length vasostatin I (CGA1-76) (40 nM), but not the truncated vasostatin I, CGA1-40 (100 nM) mimics natural chromogranin A fragments in its inhibition of contractions induced by endothelin-1 (ET-1) in calcium containing medium. CGA1-40 (100 nM) mimics the inhibitory effect of the vasostatins on the contractions induced in the absence of extracellular calcium by high potassium and noradrenaline, but not by ET-1. The iodinated peptides both exhibit saturable binding in an aortic smooth muscle cell line, indicative of a single class of high affinity binding protein ('receptor' with an apparent KD of approximately 45 nM. This binding is not affected by endothelin-1. Iodinated peptides can be crosslinked to a single polypeptide in binding experiments performed on intact calf aortic smooth muscle cells.
Animals↗
Role of the endothelium in regulation of vascular functions in two teleosts.
Functional and structural aspects of the vascular endothelium were studied in major blood vessels from two distantly related species, the Atlantic salmon (S. salar) and the cod (G. morhua). The ventral aorta (VA) of both teleosts and the dorsal aorta (DA) and the coeliaco mesenteric artery (CMA) of the cod and the salmon respectively were examined for endothelium dependent and independent responses to acetylcholine (ACh), adrenaline (A) and endothelin-1 (ET-1). In the salmon, endothelial probing resulted in reduced contractile responses to high K+ in both VA and CMA while the responses to ACh and A were reduced only in CMA. Indomethacin, but not L-NMMA, enhanced vasoconstrictions to high K+, ACh and A in the unprobed CMA. In the cod vessels the endothelial probing caused reduced contractile responses to the two effective vasoconstrictors in both vessels, to high K+ and A in VA and to high K+ and ET-1 in DA. Both indomethacin and L-NMMA enhanced contractile tension to A in VA, while indomethacin, but not L-NMMA, enhanced the constrictions by high K+ in VA and by ET-1 in DA. These experiments have revealed heterogeneous patterns of endothelial function in blood vessels of two teleosts, reflecting differences in endothelial morphology and in production of potent endothelial derived contracting factors as well as prostanoic and non-prostanoic endothelium-derived dilating factors.
Acetylcholine↗
Human chromostatin inhibits endothelin-1-induced contractures in human blood vessels.
Isolated endothelium-denuded segments of the human internal thoracic artery (ITA) and saphenous vein (SV) have been used for characterization of vasoinhibitory effects of the chromostatin (hChs) sequence of human chromogranin A (CGA124-143). In SV preincubation with hChs inhibited the response to depolarizing high K+ in Ca(2+)-free medium in a concentration dependent manner (EC50 approximately 2 nM). At 200 nM hChs the tension response to high K+ (80 mM) was inhibited by 44% (n = 8) and the tension response to noradrenaline (2.6 microM) was inhibited by 20% (n = 6), but the tension response to endothelin-1 (65 nM) (ET-1) was not affected. In ITA no effect of hChs was observed on tension response to K+ or ET-1 in Ca(2+)-free medium. On the other hand, in Ca(2+)-containing medium the tension evoked by 65 nM ET-1 was no longer sustained in segments preincubated with 200 nM hChs and declined spontaneously to 76 +/- 12% (n = 6) of maximal tension after 6 min. A vascular function for the Chs sequence of the human CGA is thus indicated, inhibiting different components of vasoconstrictor responses in the human SV and ITA segments.
Calcium↗
Functional aspects of the adrenal medullary chromogranins.
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Adrenal Medulla↗
Vasostatins, comprising the N-terminal domain of chromogranin A, suppress tension in isolated human blood vessel segments.
Chromogranin A (CGA) belongs to a family of highly acidic proteins which are co-stored and co-released with the catecholamines from the mammalian adrenal gland and occur in nmolar concentrations in the human circulation. A vascular function for the adrenomedullary released and circulating CGA has yet to be established. The present study reports on the novel vasoinhibitory effect of the N-terminal domain of the adrenomedullary CGA in isolated segments of the human internal thoracic artery (ITA) and saphenous vein (SV). The collective term vasostatin(s) refers to N-terminal fragments (CGA1-76 and CGA1-113) of apparent molecular weights 7 to 22 kD, to indicate their vascular inhibitory effects. The sustained contractions evoked by the potent vasoconstrictor peptide, endothelin-1 (ET-1) were suppressed when ITA and SV segments were preincubated for 15 min with vasostatins (72 nM). The vasoinhibitory effects were not dependent on an intact endothelium and suppression of the response to 35 nM ET-1 was approximately 77% and approximately 40% in endothelium-denuded ITA and SV segments, respectively. In endothelium-denuded SV segments the vasostatins suppressed the maximal sustained tension response but not the potency for ET-1, indicating that the vasostatin effect did not involve interference with ET-1 binding to its vascular receptor. Preincubation of endothelium-denuded SV segments with nifedipine (1 microM) inhibited the sustained response to ET-1 > or = 10 nM by 50%.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Sequence↗
Chromogranin A: secretion of processed products from the stimulated retrogradely perfused bovine adrenal gland.
Chromogranin A (CGA) is a member of a family of highly acidic proteins co-stored and co-secreted with adrenaline and noradrenaline in the adrenal medulla. A number of biologically active fragments of CGA (CGAFs) have been characterized including a group of small N-terminal fragments collectively named vasostatins due to their vascular inhibitory activity. In the present study, the release of CGAFs, including CGA N-terminal fragments, from the isolated, retrogradely perfused bovine adrenal gland, has been studied under basal conditions and during nerve stimulation and perfusion with acetylcholine. The CGAFs were characterized by SDS-PAGE followed by immunoblotting with antisera to specific sequences within the CGA molecule. Many different CGAFs were released during stimulation of the glands. Antisera to CGA1-40 and CGA44-76 detected a 7 kD protein whose release was increased during stimulation. This component co-migrated with synthetic CGA1-76, was not immunoreactive to antisera to CGA79-113 or CGA124-143, and was seen whether or not the serine protease inhibitor aprotinin was present in the perfusion medium. The release of an approximately 18 kD component, which stained with antisera to CGA1-40, CGA44-76 and CGA79-113, but not to chromostatin (CGA124-143), was also increased during stimulation. Components of 22 kD and larger were detected with antisera to chromostatin, but not with antisera to CGA1-40, CGA44-76 and CGA79-113. Two of these components of 22 to 24 kD were enhanced during nerve stimulation in the presence of aprotinin. The results indicate that processed chromogranin A fragments are secreted from the bovine adrenal medulla during stimulation of chromaffin cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Acetylcholine↗
The vasoinhibitory activity of bovine chromogranin A fragment (vasostatin) and its independence of extracellular calcium in isolated segments of human blood vessels.
Endothelium-independent vasoconstrictor responses in isolated segments of human internal thoracic artery (ITA) and saphenous vein (SV) were used as a bioassay system for the vasoinhibitory activity of bovine chromogranin A (CGA). Preincubation with vasostatin (0.8 micrograms/ml), containing the N-terminal domain of CGA, (CGA1-76, CGA1-113 and CGA1-143ff), inhibited the contractile responses evoked by 80 mM K+, 2.6 microM noradrenaline (NA), or 65 nM endothelin-1 (ET-1) in Ca(2+)-free solution in SV but not in ITA. The results demonstrate a vasoinhibitory activity in vasostatin and show that there is a marked difference between the arterial and venous segments in the Ca2+ independent component of the inhibitory response. A vascular role for the N-terminal domain of CGA is indicated, presumably by inhibiting Ca2+ release from intracellular stores in the human vein but not the artery.
Calcium↗
Distribution and vasomotor effects of neuropeptides in angular oculi and facial veins of reindeer.
1. The vasomotor responses to neuropeptides of the angular oculi and facial veins of reindeer were examined in vitro and correlated with the neuropeptide distribution in the perivascular nerves, as demonstrated by immunohistochemistry. 2. Nerves displaying calcitonin gene related peptide (CGRP)- or neuropeptide Y (NPY)-like immunoreactivity (-LI) were observed in the media of both veins, while very few fibers were immunoreactive to vasoactive intestinal polypeptide (VIP) or substance P (SP) in either vein. 3. The staining pattern for NPY-LI was largely identical to that of dopamine-beta-hydroxylase, a marker for noradrenaline (NA) producing fibers, indicating coexistence of NPY and NA. 4. Administration of NPY in vitro elicited contractions in both veins in the presence of propranolol, though more conspicuously in the angular oculi vein. 5. The peptide was without any modulating effect on NA-stimulated contractions in the angular oculi vein, whereas a small enhancement of the NA-induced tone was seen in the facial vein. 6. CGRP caused partial relaxation of both veins, whereas atrial natriuretic polypeptide caused relaxation only in the facial vein. VIP and SP had no effect on either vein. 7. The results suggest that in reindeer the sympathetic nerve fibres to both facial and angular oculi veins contain the vasoconstrictor neuropeptide NPY besides NA, even though these fibres exert a vasodilator action on the myogenically active facial vein. 8. The vasodilator neuropeptide CGRP, which is present in other more sparse perivascular nerve fibres mainly in angular oculi vein, is perhaps of afferent nature in which case CGRP might subserve axon reflex functions. 9. If, however, also the CGRP fibres are truly efferent in nature, chances for a central reciprocal control of flow through angular oculi vein might be at hand.
Animals↗
In vitro responses to atrial natriuretic polypeptide in human vessels commonly used as aortocoronary bypass grafts.
Vascular effects of atrial natriuretic polypeptide (APII), i.e. the peptide hormone released from the atrial myocardium, were investigated in segments of the human internal thoracic artery (ITA) and saphenous vein (SV) with intact (+E) or injured (-E) endothelium. All segments were subject to several cycles of agonists in order to detect tachyphylactic or facilitatory responses. Opposite, indirect effects on the noradrenaline contracted ITA and SV were obtained in response to APII at a supranormal concentration (50 nM) which had no direct relaxing action on the isolated segments in vitro. In ITA the noradrenaline contractures in subsequent cycles were reduced to 41 +/- 21% (+E) and 28 +/- 9% (-E), but in SV they were enhanced to 211 +/- 115% (+E) and 483 +/- 242% (-E) of those before APII exposure. Thus under in vitro conditions ITA could be indirectly relaxed by APII via tachyphylactic effect on the noradrenaline contracture. SV, on the other hand, was markedly potentiated by APII in its noradrenaline response. In injured endothelium these opposite effects were aggravated.
Atrial Natriuretic Factor↗
Inhibition by VIP and atriopeptin II on the field stimulation evoked release of [3H]noradrenaline in the rat portal vein.
The modulatory effects of vasodilatory peptides on noradrenaline release from sympathetic nerve terminals have been studied in the rat portal vein model. Transmural field stimulation of the longitudinally mounted vein preparation evoked concomitant increases in the [3H]noradrenaline overflow and the integrated tension. Both responses were abolished by guanethidine or tetrodotoxin, whereas only the tension response was blocked by phentolamine. CGRP and VIP, both being present in intramural nerve fibers in the rat portal vein, were compared with atriopeptin II for modulatory effects. CGRP (100 nM) had no effect on the overflow of [3H]noradrenaline or the integrated tension response to transmural stimulation. VIP (30 nM) and atriopeptin II (30 nM) both caused significant reductions of both [3H]noradrenaline overflow and the integrated tension. These results indicate that the decreased tension response to transmural stimulation in the presence of VIP or AP II reflects the sum of both pre- and postsynaptic inhibitions.
Animals↗
Effects of calcitonin gene-related peptide (CGRP) on regional haemodynamics and on selected hepato-splanchnic arteries from the rat: a comparison with VIP and atriopeptin II.
The neuropeptides calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were compared with atriopeptin II (AP II) for vasodilatory responses in the rat. The haemodynamic changes following intravenous infusion of non-hypotensive doses were measured by the microsphere technique. Isolated segments of arteries from the hepato-splanchnic region were assayed for tension responses. CGRP (2.9 pmol kg-1 min-1) caused significant reductions in vascular resistances in the spleen, the stomach and the myocardium. VIP was without detectable effects at a similar dose. At a 10-times higher dose, AP II was still without hypotensive effect and vascular resistance was reduced only in the submaxillary gland. CGRP, VIP and AP II produced endothelium-independent relaxations of isolated segments of the left gastric artery, the splenic artery and the hepatic artery. In the superior mesenteric artery (SMA) the response to CGRP was reduced by 90% after the endothelium was disrupted. When a functional endothelium was present, the potencies for CGRP were higher in the gastric artery, the splenic artery and the SMA than in the hepatic artery. The orders of potencies for the peptides were, for the gastric artery and the SMA CGRP greater than AP II greater than VIP, and for the splenic artery and the hepatic artery CGRP = AP II greater than VIP. In conclusion, vasodilations in the spleen and the stomach occurred only in response to infusion of CGRP. Consistently, significantly higher potency values were found for CGRP than for VIP in isolated arteries from these organs. However, there were examples of discrepancies between the in vitro and the in vivo responses to CGRP and AP II.
Animals↗
Vasodilation by calcitonin gene-related peptide (CGRP) and by transmural stimulation of the methoxamine-contracted rat hepatic artery after pretreatment with guanethidine.
Non-cholinergic, non-adrenergic vasodilation has been studied by transmural field stimulation of the isolated rat hepatic artery and compared with responses in the splenic artery. In the hepatic artery with rubbed endothelium, transmural stimulation caused a contracture that was blocked by phentolamine and potentiated after capsaicin. After pretreatment with guanethidine in order to deplete the neuronal stores of noradrenaline, the methoxamine-contracted hepatic artery was significantly relaxed by transmural stimulation; more efficiently than the splenic artery. This relaxation of the hepatic artery was attenuated following a 30 min exposure to capsaicin and largely blocked by tetrodotoxin (TTX). The relaxation by exogenous CGRP was independent of a functional endothelium. In contrast, vasodilation by substance P (SP) and neurokinin A (NKA), was completely dependent on an intact endothelium. Exogenous CGRP caused a near-complete relaxation of the methoxamine-contracted hepatic artery both before and after capsaicin treatment. CGRP was a more efficient relaxant of the hepatic than the splenic artery. These findings show that responses to transmural stimulation of the hepatic artery are modulated after pretreatment with capsaicin, indicating release of relaxing substances such as CGRP, presumably from capsaicin-sensitive neuronal stores. In conclusion, CGRP is a likely mediator of neuronal vasodilation in the rat liver, independent of the state of the endothelium.
Animals↗
Comparative aspects of the endocrine myocardium.
Secretory organelles are common features of the myocardium, from cyclostomes to man, and occur in the atria of all vertebrates, in the ventricle of the lower vertebrates and in the embryonic and foetal ventricles of mammals. These organelles constitute the final step in the regulated secretory pathway for the atrionatriuretic polypeptides collectively termed atriopeptins. At birth, however, the mammalian ventricle shifts to constitutive secretion, with low levels of atriopeptins in the normal and elevated levels in the hypertrophied adult ventricle. In the mammalian atria the atriopeptins are costored with the calcium-binding, highly acidic chromogranins A and B, and the secretory organelles account also for the highest subcellular calcium concentration in the myocardium. These similarities between the myocardium and the neuroendocrine system confirm and extend the earlier observations and point to new aspects of the endocrine heart; as a source of prohormones not only for the atriopeptins but also for members of the chromogranin family. A significant role is also apparent for the secretory organelles in the intracellular sequestration of calcium in both the normal and the overstimulated myocardium. Down-regulation of excess in blood volume appears to be mediated by atriopeptins via indirect and direct relaxations of vascular smooth muscle in the aorta and other large arteries. Apart from their natriuretic actions, the atriopeptins also contribute to substantial fluid loss via the gastrointestinal tract.
Animals↗
Differential patterns of relaxation by synthetic atrial peptide (APII) in the pulmonary artery, ascending and distal abdominal aorta.
The vasodilatory effects of the synthetic rat atriopeptin (APII) have been studied in vitro in agonist-contracted, endothelium-denuded segments of the rat pulmonary artery, the ascending, and the distal abdominal aorta. In the pulmonary artery the contractures to methoxamine were inhibited more potently by APII (pD2 = 9.10 +/- 0.40, n = 6) than by the vasodilatory neuropeptide VIP (pD2 = 7.37 +/- 0.66, n = 6). The intrinsic activity of APII was 0.46 +/- 0.16 (n = 6). In segments previously exposed to either VIP or the beta 2-agonist salbutamol, APII was a near complete agonist (alpha = 0.82 +/- 0.17, n = 7 and 0.84 +/- 0.14, n = 6, respectively) without significant changes in the potencies. APII was a complete agonist also for the inhibition of the alpha-agonist-contracted segments of the aorta, however, with potencies 10-fold lower than in the pulmonary artery. VIP was without functionally significant effects in the aorta. The tachykinins (CGRP, SP, Neurokinins A and B) were without effects in all segments tested. In the ascending aorta, APII induced a long-lasting tachyphylaxis to the alpha-agonists, nearly completely abolishing the subsequent responsiveness to NA and methoxamine for more than 4 h.
Albuterol↗
Chromogranin A: osmotically active fragments and their susceptibility to proteolysis during lysis of the bovine chromaffin granules.
Osmotically active fragments of chromogranin A (Chr A) were studied in lysates from bovine chromaffin granules (CG) disrupted in the presence or absence of inhibitors of endogenous proteolytic activities. The effects of various methods of lysis were examined by micro-osmometry, PAGE-SDS electrophoretic techniques and immunoblots with polyclonal anti-Chr A sera. Osmotically active 'small' Chr A fragments (below 30 kDa) were conspicuous in lysates containing cocktails of leupeptin, pepstatin A, pHMB, PMSF and aprotinin. The osmotically inactive native Chr A in the 68-100 kDa range and the osmotically active fragments below 47 kDa were degraded in lysates at neutral or acid pH in the absence of inhibitors. However, degradation of the native Chr A and intermediates below 47 kDa could be prevented by extraction directly from intact CG, notably in cold or boiling distilled water. On the other hand, the main product after large-scale extraction of CG in 1 M acetic acid (pH 1.9, 100 degrees C) was a novel, osmotically active fragment (22 kDa), immunostaining only for the N-terminal sequence (Chr A1-40). The heat-stable fraction (Mr,n 23 kDa) exhibited concentration-independent colloid osmotic pressures even in the absence of phosphate, a property which may distinguish this N-terminal-containing fragment from the larger intermediates, probably containing the pancreastatin sequence, and other regions at the C-terminal side of the prohormone molecule. The functional roles of these osmotically active intermediates in the processing of Chr A are not yet known.
Acids↗
Arterial and venous coronary bypass grafts: differential responses to alpha-natriuretic polypeptide on the noradrenaline contractures in vitro.
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Atrial Natriuretic Factor↗
Comparison of atriopeptins II and III, VIP and beta 2-adrenoceptor-evoked relaxations of the two layers of smooth muscle in the rat portal vein.
The relative importance of vascular relaxations induced by atriopeptins (AP), the beta-adrenoceptor agonist isoprenaline and of the neuropeptide VIP was studied in vitro on circular and longitudinal preparations of the rat portal vein. Two members of the rat atriopeptins (AP II and III) were equipotent with respect to relaxation of the spontaneously contracting outer, longitudinal layer and of the alpha 1-contracted inner, circular layer. The potency for AP II was about 13 times lower in the inner (pD2 = 7.48 +/- 0.73, n = 6) than in the outer layer (pD2 = 8.60 +/- 0.34, n = 6). No significant difference was apparent between the intrinsic activities for AP II in the two layers. The potencies for AP II were for both layers higher than those for VIP while the intrinsic activities for AP II were significantly lower than for VIP and for the reference agonist, isoprenaline in both layers. Atriopeptin II was equally efficient in relaxing the K+-depolarized and alpha 1-contracted longitudinal segments. Neither the beta-antagonist, propranolol nor the guanylate cyclase inhibitor, methylene blue, modified the potency or the intrinsic activity of AP II. These results suggest that concentrations of circulating atriopeptins above 10 nM may contribute to reduction of vascular tone by the methylene blue insensitive receptors for AP II and III in the portal-mesenteric vein region.
Animals↗