Biomedical subjects

R J Parmer

Publications and source records attributed to R J Parmer.

At least 73 records · Page 4Linked to original sources

PubMed1993

Chromogranin A immunoreactivity in human cerebrospinal fluid: properties, relationship to noradrenergic neuronal activity, and variation in neurologic disease.

Although measurement of chromogranin A in the bloodstream is of value in sympathoadrenal investigations, little is systematically known about chromogranin A in cerebrospinal fluid, despite substantial knowledge about its occurrence and distribution in brain. We therefore applied a homologous human chromogranin A radioimmunoassay to cerebrospinal fluid, in order to evaluate the properties and stability of cerebrospinal fluid chomogranin A, as well as its relationship to central noradrenergic neuronal activity, to peripheral (plasma) chromogranin A, and to disease states such as hypertension, renal failure and Parkinsonism. Authentic, physically stable chromogranin A immunoreactivity was found in cerebrospinal fluid (at 37-146 ng/ml; mean, 87.0 +/- 6.0 ng/ml in healthy subjects), and several lines of evidence (including 3.39 +/- 0.27-fold higher chromogranin A in cerebrospinal fluid than in plasma) indicated that it originated from a local central nervous system source, rather than the periphery. Cerebrospinal fluid chromogranin A values were not influenced by administration of effective antihypertensive doses of clonidine or propranolol, and were not related to the cerebrospinal fluid concentrations of norepinephrine, methoxyhydroxyphenylglycol, or dopamine-beta-hydroxylase; thus, cerebrospinal fluid chromogranin A was not closely linked to biochemical or pharmacologic indices of central noradrenergic neuronal activity. Cerebrospinal fluid chromogranin A was not changed (P > 0.1) in essential hypertension (84.2 +/- 14.0 ng/ml) or renal failure (72.2 +/- 13.4 ng/ml), despite a marked (7.1-fold; P < 0.001) increase in plasma chromogranin A in renal failure, and a modest (1.5-fold; P = 0.004) increase in plasma chromogranin A in essential hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗

PubMed1993

Catecholamine secretory vesicles. Augmented chromogranins and amines in secondary hypertension.

Chromogranins A and B are major soluble proteins in chromaffin granules. Their adrenomedullary content is increased in the spontaneously (genetic) hypertensive rat. Is augmented catecholamine vesicular storage of the chromogranins a specific feature of genetic hypertension? To explore this question, we measured chromogranin A immunoreactivity, using a novel, synthetic peptide radioimmunoassay, in rat adrenal medullas 4-6 weeks after induction of the two-kidney, one clip Goldblatt model of renovascular hypertension and in unmanipulated control animals. We also measured messenger RNAs of chromogranins A and B and dopamine beta-hydroxylase by Northern blot. Immunoreactive adrenal chromogranin A was 3.3-fold higher (p < 0.01) in clipped rat adrenals. Adrenal catecholamine concentrations and phenylethanolamine-N-methyltransferase activity were also higher in clipped rats. Adrenal dopamine beta-hydroxylase activity (both membrane-bound and soluble forms) and corticosterone (glucocorticoid) concentration did not significantly differ between the groups. Adrenal medullary chromogranin A messenger RNA levels in clipped rats were 3.2-fold higher (p = 0.029) than those in the control group, and chromogranin B messenger RNA levels were 4.6-fold higher (p = 0.05). Dopamine beta-hydroxylase messenger RNA levels were 2.9-fold higher (p = 0.038). Thus, augmented synthesis and storage of adrenomedullary chromogranins A and B, catecholamines, and their biosynthetic enzymes appear to be characteristic of both acquired and genetic hypertension.

Adrenal Medulla↗

PubMed1993

Secretory protein traffic. Chromogranin A contains a dominant targeting signal for the regulated pathway.

Secretory proteins are targeted into either constitutive (secreted upon synthesis) or regulated (stored in vesicles and released in response to a secretagogue) pathways. To investigate mechanisms of protein targeting into catecholamine storage vesicles (CSV), we stably expressed human chromogranin A (CgA), the major soluble protein in human CSV, in the rat pheochromocytoma PC-12 cell line. Chromaffin cell secretagogues (0.1 mM nicotinic cholinergic agonist, 55 mM K+, or 2 mM Ba++) caused cosecretion of human CgA and catecholamines from human CgA-expressing cells. Sucrose gradients colocalized human CgA and catecholamines to subcellular particles of the same buoyant density. Chimeric proteins, in which human CgA (either full-length [457 amino acids] or truncated [amino-terminal 226 amino acids]) was fused in-frame to the ordinarily nonsecreted protein chloramphenicol acetyltransferase (CAT), were expressed transiently in PC-12 cells. Both constructs directed CAT activity into regulated secretory vesicles, as judged by secretagogue-stimulated release. These data demonstrate that human CgA expressed in PC-12 cells is targeted to regulated secretory vesicles. In addition, human CgA can divert an ordinarily non-secreted protein into the regulated secretory pathway, consistent with the operation of a dominant targeting signal for the regulated pathway within the peptide sequence of CgA.

Amino Acid Sequence↗

PubMed1992

Baroreflex sensitivity and heredity in essential hypertension.

BACKGROUND: Abnormalities in baroreflex control of heart rate may be important in the pathogenesis of essential hypertension. METHODS AND RESULTS: To investigate the influence of heredity on baroreflex function, we measured baroreflex sensitivity in 40 untreated patients with essential hypertension grouped by the presence (FH+) or absence (FH-) of a family history of hypertension and in 24 normotensive counterparts. Baroreflex sensitivity was assessed by both high-pressure (phenylephrine bolus) and low-pressure (amyl nitrite inhalation) stimuli. Subject groups were matched for age, blood pressure, body weight, and race. Baroreflex sensitivity (in milliseconds per millimeter of mercury) assessed by amyl nitrite inhalation was 24.3 +/- 2.8 in FH- normotensives, 12.3 +/- 1.7 in FH+ normotensives, 15.4 +/- 3.3 in FH- hypertensives, and 8.1 +/- 1.2 in FH+ hypertensives. Baroreflex sensitivity assessed by phenylephrine bolus was 28.8 +/- 5.6 in FH- normotensives, 19.3 +/- 2.8 in FH+ normotensives, 19.1 +/- 2.0 in FH- hypertensives, and 13.6 +/- 1.3 in FH+ hypertensives. Two-factor analysis of variance showed significant effects on baroreflex sensitivity for blood pressure status (normotensive versus hypertensive) and for family history of hypertension. After control line (controlling) for the effects of several variables, including age, mean arterial pressure, body weight, and race through multiple linear regression analysis, the effect of family history of hypertension on baroreflex sensitivity was still highly significant. Indeed, of all variables investigated, family history of hypertension was the strongest unique baroreflex sensitivity predictor. CONCLUSIONS: These data suggest that the impairment in baroreflex sensitivity in hypertension is in part genetically determined and may be an important hereditary component in the pathogenesis of essential hypertension.

Administration, Inhalation↗

PubMed1991

Structure and function of the chromogranin A gene. Clues to evolution and tissue-specific expression.

Chromogranin A is the index member of a family of acidic proteins stored and released throughout the neuroendocrine system with peptide hormones and neurotransmitters. To better understand its functional domains, its evolutionary lineage, and the basis of its tissue-specific pattern of expression, we obtained a mouse chromogranin A cDNA and used it to isolate the chromogrannin A gene from the mouse genome. We then characterized the gene's exon/intron structure, and the structure and function of its 5'-regulatory region (promoter/enhancer). The chromogranin A gene was complex, its eight exons and seven introns spanning about 11 kilobase pairs. The eight exons displayed some correspondence to putative functional domains suspected within the cDNA-deduced primary structure of the protein. Three exons also displayed both length and sequence homology to exons in another member of the chromogranin/secretogranin family, chromogranin B, suggesting an evolutionary relationship. A 1.2-kilobase pair genomic fragment just 5' of the coding region was able to program cell type-specific gene expression in a transfection/reporter system. Both pituitary corticotropes and adrenal chromaffin cells recognized this promoter. The promoter possessed some known consensus transcriptional control elements (TATA box, cyclic AMP-response element, and Sp1 site), but otherwise novel transcriptional control elements seem to be operative. The results suggest that this complex gene is encoded by exon modules with evolutionary links to homologous modules in other chromogranin/secretogranin protein family members, and that the 5'-flanking region of the gene is sufficient to confer neuroendocrine tissue-specific expression of the chromogranin A gene.

Amino Acid Sequence↗

PubMed1991

Suppression of chromogranin-A release from neuroendocrine sources in man: pharmacological studies.

Chromogranin-A (CgA) is an acidic soluble protein with a virtually ubiquitous occurrence in normal human neuroendocrine tissues. Of the many potential tissue sources of CgA immunoreactivity, which contribute to basal (unstimulated) circulating CgA? To explore this question we studied the effects of selective and nonselective suppression of secretion at several sites within the neuroendocrine system. Selective disruption of sympathetic outflow by trimethaphan decreased basal CgA by 25%, suggesting that sympathetic neurons contribute to circulating CgA. Plasma CgA in patients with unilateral and bilateral adrenalectomy fell within the range observed in normal subjects, weighing against the adrenal medulla as a major source of basal circulating CgA. Selective suppression of a variety of anterior and posterior pituitary cell types decreased plasma levels of the usual resident peptide hormones, but left plasma CgA unperturbed. After propranolol treatment, plasma CgA remained unaltered. Secretin suppressed plasma PTH and calcitonin, but did not alter plasma CgA levels. On the other hand, widespread nonselective suppression of a variety of neuroendocrine secretory cells by somatostatin decreased plasma CgA by 48%. Plasma catecholamines were unaltered by somatostatin infusion, suggesting that somatostatin inhibited CgA release from nonsympathoadrenal sources. During the infusion of somatostatin, the plasma epinephrine increment in response to insulin-induced hypoglycemia was maintained, and plasma CgA did not fall, nor did it rise after somatostatin cessation. Taken together, these findings suggest that somatostatin did not inhibit transport of stimulation-released CgA from the adrenal medulla to the circulation. In conclusion, although the adrenal medulla is the major tissue source of CgA immunoreactivity in man, other neuroendocrine sites, including sympathetic axons and multiple endocrine glands, appear to influence the basal circulating concentration of CgA.

Adrenal Glands↗

PubMed1991

Comparison of the steady-state pharmacokinetics of fosinopril, lisinopril and enalapril in patients with chronic renal insufficiency.

The phosphinyl ester prodrug fosinopril, a new angiotensin converting enzyme (ACE) inhibitor, is fully hydrolysed after oral administration to the pharmacologically active diacid, fosinoprilat. This metabolite is cleared by both hepatic and renal routes, while most other ACE inhibitors are cleared exclusively by the kidney. In the present study, after administration of multiple fixed oral doses the accumulation of the active moieties of fosinopril, enalapril and lisinopril was compared in patients with renal insufficiency. 29 patients with creatinine clearances (CLCR) less than 30 ml/min received either fosinopril 10mg (n = 9), enalapril 2.5mg (n = 10) or lisinopril 5mg (n = 10) once daily for 10 days in a nonblind (open-label) parallel study. Pharmacokinetic parameters including area under the serum concentration-time curve (AUC), peak serum concentration (Cmax) and time to peak concentration (tmax), as well as renal function, blood pressure, and plasma renin activity (PRA) and aldosterone levels, were determined on the first and last days of the study. The percentage (+/- SEM) increases in AUC from day 1 to day 10 for fosinoprilat, enalaprilat and lisinopril were 26.8 +/- 9.9 (nonsignificant), 76.6 +/- 16.6 (p less than 0.001) and 161.7 +/- 31.8% (p less than 0.001), respectively. These results indicate that there was significantly less accumulation of fosinoprilat, based on accumulation indices, relative to either enalaprilat (p less than 0.05) or lisinopril (p less than 0.001) during the study. The Cmax of fosinopril increased significantly less than that of lisinopril (21.1 vs 123.6%; p less than 0.01). Renal function was not altered in any group, and blood pressure changed modestly.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1991

Chromogranin A storage and secretion: sensitivity and specificity for the diagnosis of pheochromocytoma.

Chromogranin A, co-stored and co-released with catecholamines from adrenal medullary and sympathetic neuronal vesicles, is elevated in the plasma of patients with pheochromocytoma. The usefulness of the hormone in the differential diagnosis of hypertension is examined. An elevated level of chromogranin A had comparable diagnostic sensitivity (83%, 24/29) to, but greater diagnostic specificity (96%, 86/90) than the level of plasma catecholamines when subjects with pheochromocytoma (n = 29) were evaluated in comparison to several reference groups, including normotensive controls (n = 49), subjects with essential hypertension (n = 28), subjects with renovascular hypertension (n = 5), and subjects with primary aldosteronism (n = 3). Subjects with signs or symptoms suggesting pheochromocytoma, but in whom the diagnosis was ultimately ruled out (n = 5) had normal plasma levels of chromogranin A. A modest rise in chromogranin A in those with essential hypertension, and correlation of chromogranin A with diastolic blood pressure in normotensive patients and patients with essential hypertension did not impair the diagnostic usefulness of chromogranin A for pheochromocytoma. Renal failure was associated with an elevated plasma chromogranin A independently of blood pressure. Plasma chromogranin A correlated with tumor mass, tumor chromogranin A content, tumor norepinephrine content, and urinary vanillylmandelic acid excretion; it did not correlate with plasma or urinary catecholamines, nor with blood pressure in patients with pheochromocytoma. Plasma chromogranin A levels did not differ in subjects with pheochromocytoma when stratified by age, sex, tumor location, or tumor pathology. Several drugs used in the diagnosis or treatment of pheochromocytoma (clonidine, metoprolol, phentolamine, and tyramine) had little effect on plasma chromogranin A concentration. Within the pheochromocytoma, chromogranin A was localized along with catecholamines to the soluble core of chromaffin granules, where it accounted for 18 +/- 5% of vesicle soluble protein. We conclude that 1) chromogranin A emerges along with catecholamines from pheochromocytoma chromaffin granules; 2) plasma chromogranin A is a sensitive and specific diagnostic tool in evaluation of actual or suspected pheochromocytoma; 3) plasma chromogranin A predicts pheochromocytoma tumor size and overall catecholamine production; and 4) drugs commonly employed in the diagnosis or treatment of pheochromocytoma have little effect on plasma chromogranin A level, preserving the usefulness of chromogranin A in evaluating pheochromocytoma. Thus, measurement of chromogranin A provides a useful adjunct to the diagnosis of pheochromocytoma.

Adrenal Gland Neoplasms↗

PubMed1990

Chromogranin A in familial pheochromocytoma: diagnostic screening value, prediction of tumor mass, and post-resection kinetics indicating two-compartment distribution.

PURPOSE: Chromogranin A, co-released with catecholamines from the adrenal medullary and sympathetic neuronal vesicles, is elevated in plasma from patients with pheochromocytoma. We assessed its diagnostic screening value, its plasma level in correlation with tumor mass, and its disposition kinetics in familial pheochromocytoma and sporadic pheochromocytoma. PATIENTS AND METHODS: The sensitivity and specificity of chromogranin A's diagnostic value for pheochromocytoma were established through one kindred with familial pheochromocytoma associated with von Hippel-Lindau syndrome (13 available members) and in seven subjects with sporadic pheochromocytoma. Serial postoperative plasma samples were also obtained (5 minutes to 4 days) from eight subjects with pheochromocytoma in order to study chromogranin A post-resection kinetics. Chromogranin A was measured by radioimmunoassay based on purified pheochromocytoma chromogranin A. RESULTS: In this kindred, elevations of chromogranin A (greater than 52 ng/mL) were sensitive (83%, five of six) and specific (100%, 10 of 10) in detecting familial pheochromocytoma; these diagnostic values comparable to those achieved by conventional evaluations for pheochromocytoma, such as urinary catecholamines, urinary catecholamine metabolites or imaging methods. Elevated levels of plasma chromogranin A specifically indicated pheochromocytoma, rather than von Hippel-Lindau syndrome gene carrier status. In 13 preoperative subjects with either familial or sporadic pheochromocytoma, plasma chromogranin A concentration predicted tumor size (r = 0.81, p less than 0.01). The change in chromogranin A plasma concentration after pheochromocytoma resection best fit a two-compartment model, with an initial rapid half-life time of 16 minutes, followed by a longer half-life time of 520 minutes. The model also predicted a 23.8:1 compartmental ratio of extravascular/intravascular chromogranin A, suggesting substantial tissue sequestration or binding of chromogranin A. CONCLUSIONS: (1) Plasma chromogranin A is a valuable (sensitive and specific) diagnostic tool in detecting both familial and sporadic pheochromocytoma. (2) The concentration of plasma chromogranin A predicts the size of the pheochromocytoma. (3) Chromogranin A post-resection kinetics suggest extravascular sequestration of chromogranin A.

Adolescent↗

PubMed1990

Chromogranin A in the olfactory system of the rat.

The olfactory bulb of the rat contains chromogranin A at a similar level as the adrenal gland or the hypophysis as revealed by immunoblots. Olfactory chromogranin A also displays the same size as chromogranin A of endocrine cells. In the hippocampus and other brain regions, we could not detect chromogranin A by immunoblotting. In contrast, chromogranin A messenger ribonucleic acid (using S1 nuclease protection assays) was observed in all brain regions examined, including the olfactory bulb. By in situ hybridization histochemistry with a complementary ribonucleic acid probe (280 nucleotides), and by immunocytochemistry, chromogranin A synthesis could be localized to cell bodies of the mitral cell layer, of the external plexiform layer and of the periglomerular region of the olfactory bulb. Immunocytochemically, chromogranin A was also detected in the central projection areas of mitral and tufted cells in the primary olfactory cortex and the anterior amygdaloid area but not in the olfactory glomeruli, where the incoming olfactory nerve fibers of the primary olfactory neurons establish synaptic contacts. Taken together the data show that chromogranin A, following biosynthesis in the perikarya of the mitral and tufted cells, is specifically transported into their axonal terminals but not into their primary dendrites. We propose that the rat olfactory system could serve as a model for the study of chromogranin A regulation and function in neurons.

Adrenal Glands↗

PubMed1990

Molecular cloning, structure, and expression of dopamine-beta-hydroxylase from bovine adrenal medulla.

Dopamine-beta-hydroxylase (DBH), the enzyme that catalyzes the conversion of dopamine to norepinephrine, remains the topic of many unanswered questions. We isolated DBH cDNA clones from a bovine adrenal medulla cDNA library in the vector lambda gt10. The longest cDNA had an open reading frame encoding an entire mature DBH 578 amino acid (64,808 dalton) polypeptide chain, though lacking a portion of the signal peptide. Additional 5' clones, obtained by the polymerase chain reaction, established the sequence of a 19 amino acid signal peptide. The mature protein sequence was 84% homologous to that of human pheochromocytoma DBH, including preservation of four potential copper ligand sites (HH or HXH) and substrate binding domains. There were no hydrophobic (putative membrane spanning) domains, other than the signal peptide. All available DBH peptide and protein sequence data can be accounted for by the cDNA-deduced 578 amino acid mature protein primary structure. Prokaryotic DBH expression yielded a 65-kilodalton DBH-immunoreactive peptide that differed from eukaryotic adrenal DBH only in N-linked, endoglycosidase F-sensitive glycosylation in the latter. Southern analysis suggested one DBH gene, whereas Northern analysis suggested a single 2.6 kbp tissue-specific DBH transcript. Comparison of the DBH primary structure with other reported sequences [Protein Identification Resource (PIR), New Atlas (NEWAT)] did not indicate that DBH is a member of any known gene family. The results suggest that a single DBH gene encodes a message specifying a single DBH polypeptide chain.

Adrenal Medulla↗

PubMed1990

Is physiologic sympathoadrenal catecholamine release exocytotic in humans?

In cultured cells and isolated perfused organs, catecholamines are coreleased with chromogranin A (CgA) from adrenal chromaffin cells and sympathetic neurons. The corelease suggests that exocytosis is the mechanism of catecholamine secretion. To investigate whether physiologic catecholamine secretion is exocytotic in humans, we measured plasma norepinephrine, epinephrine, and CgA responses to differentiated stimuli of sympathoadrenal discharge. The CgA radioimmunoassay antibody recognized authentic CgA in normal human adrenal chromaffin vesicles. Insulin-induced hypoglycemia and caffeine ingestion, in decreasing order of potency, selectively stimulated epinephrine release from the adrenal medulla. During hypoglycemia, plasma levels of epinephrine and CgA rose, and peak plasma levels of epinephrine and CgA correlated, suggesting that gradations in epinephrine release represented gradations in exocytosis. However, significant increments in plasma CgA were not observed after caffeine ingestion. Furthermore, the rise of CgA levels during hypoglycemia lagged 60 minutes behind those of epinephrine. A less-pronounced temporal dissociation between CgA and epinephrine release was also shown in isolated chromaffin cells in vitro. Selective adrenal vein catheterization suggested a barrier to CgA transport across the adrenal capillary wall. Short-term, high-intensity dynamic exercise, assumption of the upright posture, prolonged low-intensity dynamic exercise, and smoking, in decreasing order of potency, stimulated norepinephrine release from sympathetic nerve endings. Only the first sympathetic neuronal stimulus resulted in significant increments in plasma CgA, increments considerably less than those attained during adrenal medullary activation by insulin hypoglycemia. During high-intensity exercise, peak plasma norepinephrine and CgA levels correlated, suggesting that gradations in norepinephrine release represented gradations in exocytosis. The human adrenal medulla was a far more prominent tissue source of CgA than human sympathetic nerves--adrenal medullary homogenates contained 97-fold more CgA (micrograms/g) than sympathetic nerve homogenates. In conclusion, catecholamine secretion during selective stimulation of either sympathetic nerves or the adrenal medulla is, at least in part, exocytotic. Furthermore, stimulation of the former results in comparatively modest changes in plasma CgA compared with changes attained during stimulation of the latter. CgA appears to be transported by a route different from that of catecholamines from adrenal medullary chromaffin cells to the circulation in vivo.

Adrenal Glands↗

PubMed1990

Autonomic function in hypertension. Are there racial differences?

Previous biochemical assessment of sympathetic nervous system activity including plasma catecholamines, plasma renin activity, and plasma dopamine-beta-hydroxylase levels has suggested racial differences in the contribution of the sympathetic nervous system to the pathogenesis or maintenance of hypertension. We, therefore, performed physiological and pharmacological studies in white and black subjects with essential hypertension and their age-matched normotensive counterparts to assess autonomic and sympathetic nervous system function. One hundred one male subjects (47 white hypertensive, 17 black hypertensive, 22 white normotensive, and 15 black normotensive subjects) were evaluated for baroreceptor reflex sensitivity to low-pressure (amyl nitrite inhalation) and high-pressure (phenylephrine infusion) stimuli; cold pressor test heart rate and blood pressure responses; and blood pressure response to phentolamine alpha-adrenergic blockade. Hypertensive subjects exhibited an increase in resting heart rate, a decrease in baroreceptor reflex sensitivity, and an exaggerated decline in mean arterial pressure in response to phentolamine. These abnormalities were present to a comparable degree in black and white hypertensive subjects. Cold pressor testing revealed greater increases in heart rate in blacks as compared with whites; however, this racial difference was present regardless of blood pressure status, occurring in black normotensive and black hypertensive subjects to a comparable degree. Cold pressor test blood pressure increments were similar in the four groups. We conclude that both white hypertensive and black hypertensive subjects demonstrate similar abnormalities in autonomic and sympathetic nervous system function including blunting of baroreceptor reflex sensitivity and an increased alpha-adrenergic receptor participation in blood pressure maintenance. The results do not suggest major racial differences in autonomic pathogenetic mechanisms in hypertension.

Adrenergic alpha-Antagonists↗

PubMed1990

Chromogranin A. Storage and release in hypertension.

The chromogranins/secretogranins are a family of acidic, soluble proteins with widespread neuroendocrine distribution in secretory vesicles. Although the precise function of the chromogranins remains elusive, knowledge of their structure, distribution, and potential intracellular and extracellular roles, especially that of chromogranin A, has greatly expanded during recent years. Chromogranin A is coreleased with catecholamines by exocytosis from vesicles in the adrenal medulla and sympathetic nerve endings. Thus, measurement of its circulating concentration by radioimmunoassay may be a useful probe of exocytotic sympathoadrenal activity in humans, under both physiological and pathological conditions. Here, we explore the storage, structure, and function of chromogranin A, and parameters that influence its circulating levels. We have also measured plasma chromogranin A concentrations in different groups of patients with hypertension, including those with pheochromocytoma.

Chromogranins↗

PubMed1990

Circulating chromogranin A as a diagnostic tool in clinical chemistry.

Chromogranin A, measured in the circulation by radioimmunoassay, has emerged as a useful tool in the evaluation of exocytotic sympathoadrenal activity in man, as well as the diagnosis of the presence and extent of neuroendocrine neoplasia. Here we present current thoughts on the structure and function of chromogranin A, and describe known parameters affecting its plasma concentration.

Adrenal Gland Neoplasms↗

PubMed1989

Molecular cloning of chromogranin A from rat pheochromocytoma cells.

Chromogranin A (CgA) is the major soluble protein in catecholamine storage vesicles. To gain insight into its function, we isolated CgA clones from a size-selected lambda gt10 rat pheochromocytoma complementary DNA (cDNA) library. The longest cDNA insert identified was 2.2 kb and encoded the entire 462-amino acid open reading frame of rat CgA including an 18-amino acid hydrophobic signal peptide. Comparison of rat CgA with the recently published sequences of bovine CgA and human CgA revealed regions of strong homology at the N-and COOH-termini as well as variant areas predominantly in the middle portion of the molecule. Regions highly conserved and therefore suggestive of functional importance included 1) multiple paired basic residues, which may serve as proteolytic processing signals; 2) a region homologous to porcine pancreastatin, a putative modulator of peptide hormone release; and 3) a short hydrophobic disulfide loop region near the N-terminus that may have a role in the targeting of CgA to secretory vesicles. On the other hand, lack of conservation of the membrane attachment sequence arginine-glycine-aspartic acid argues against its functional importance in CgA. In addition, the presence of a unique polyglutamine region in rat CgA points to a possible messenger RNA (mRNA) splice junction. Northern blot experiments demonstrated the presence of an approximately 2.2 kb rat CgA mRNA in a neuroendocrine distribution (adrenal, brain, pheochromocytoma cells, but not skeletal muscle, heart, or kidney). Southern blot studies were consistent with the presence of a single CgA gene within the rat pheochromocytoma cell genome. Finally, comparison of the present rat pheochromocytoma cDNA clones with those recently obtained from normal rat adrenal gland reveals minor but apparently real differences that suggest CgA microheterogeneity.

Amino Acid Sequence↗

PubMed1988

Enkephalins in human phaeochromocytomas: localization in immunoreactive, high molecular weight form to the soluble core of chromaffin granules.

Enkephalins, endogenous opioid pentapeptides, are found in normal chromaffin tissue and may influence blood pressure regulation. We studied the subcellular localization and precursor-product status of enkephalin immunoreactivity in 11 human phaeochromocytomas (seven adrenal, four extra-adrenal). Enkephalin immunoreactivity was found in all phaeochromocytomas, it paralleled radio-immunoassay standard curves and was not destroyed by boiling or protease inhibitors i.e. ethylenediaminetetraacetic acid (EDTA) and phenylmethylsulfonyl fluoride (PMSF). Sucrose gradients localized enkephalin immunoreactivity to chromaffin granules (55 +/- 17% of total immunoreactivity; n = 6). In vitro granule lysis released 81% of the enkephalins and 91% of the catecholamines. Thus, phaeochromocytoma enkephalins are present in the soluble core of chromaffin granules, along with catecholamines. Enkephalin immunoreactivity was not contained in purified chromogranin A, either before or after trypsin cleavage. High pressure liquid chromatography (HPLC) elution of enkephalin immunoreactivity matched that of synthetic methionine-enkephalin, leucine-enkephalin, and methionine-sulfoxide-enkephalin standards. Enkephalin immunoreactivity was augmented by trypsin alone and by trypsin plus carboxypeptidase B (by 352 +/- 56%), suggesting that the majority of the enkephalins were present in higher molecular weight precursor form. Sephacryl S-200 gel filtration of chromaffin granule lysate revealed a trypsin-augmented putative human enkephalin precursor with a molecular weight of 2000-4000 daltons as well as product enkephalins. Enkephalin concentration in phaeochromocytoma closely paralleled the epinephrine, but not the norepinephrine content of the tumours. However, it was not statistically different in adrenal versus extra-adrenal tumours. Thus, these peptides are contained in high molecular weight form in the soluble core of catecholamine storage vesicles, predominantly epinephrine vesicles.

Adrenal Gland Neoplasms↗

PubMed1987

Serum zinc is unaffected by effective captopril treatment of hypertension.

Captopril, a sulfhydryl compound that lowers blood pressure by inhibiting the zinc metalloenzyme, angiotensin converting enzyme, may occasionally result in ageusia, a symptom also associated with zinc deficiency. We therefore studied serum zinc and copper concentrations in a group of 14 essential hypertensive subjects before treatment and after 5-6 months of antihypertensive oral monotherapy with either captopril (50 mg, twice daily; n = 7) or other drugs (propranolol or alphamethyldopa; n = 7). Serum zinc and copper were unaltered by either regimen. Thus, zinc depletion is an unlikely consequence of long-term exposure to captopril, at least in the dosages commonly used for treatment of hypertension.

Blood Pressure↗