Multiple heritable traits are associated with essential (genetic) hypertension in humans. Because chromogranin A is increased in both human and rodent genetic hypertension, we examined the influence of heredity and blood pressure on chromogranin A in humans. In estimates derived from among- and within-pair variance in monozygotic versus dizygotic twins, plasma chromogranin A displayed significant (F15,18 = 2.93, P = .016) genetic variance (sigma 2 g), and its broad-sense heritability was high (h2B = 0.983). Plasma chromogranin A was increased in essential hypertension (99.9 +/- 6.7 versus 62.8 +/- 4.7 ng/mL, P < .001) but was influenced little by genetic risk for (family history of) hypertension (in normotensive or hypertensive subjects), by race, or by several antihypertensive therapies (angiotensin-converting enzyme inhibitor, diuretic, or beta-adrenergic antagonist). In normotensive subjects at genetic risk for essential hypertension, neither basal nor sympathoadrenal stress-evoked chromogranin A differed from values found in subjects not at risk. In established essential hypertension, plasma chromogranin A responses to adrenal medullary (insulin-evoked hypoglycemia) or sympathetic neuronal (dynamic exercise) activation were exaggerated, whereas responses to sympathoadrenal suppression (ganglionic blockade) were diminished, suggesting increased vesicular stores of chromogranin A and an adrenergic origin of the augmented chromogranin A expression in this disorder. We conclude that plasma chromogranin A displays substantial heritability and is increased in established essential hypertension. Its elevation in established hypertension is associated with evidence of increased vesicular stores of the protein and with adrenergic hyperactivity but is influenced little by customary antihypertensive therapies. However, the chromogranin A elevation is not evident early in the course of genetic hypertension.

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(,ug/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 resultsin 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. (Circulation 1990;81:185-195) C atecholamine release in isolated cells and by corelease of the catecholamine storage vesicle organs is exocytotic from both adrenal medcore constituents chromogranin A (CgA)2,5 and dopa-

The primary structure of chromogranin A indicates multiple domains which might be subject to posttranslational modification. We explored chromogranin A's proteolytic cleavage, glycosylation, and possible intermolecular disulfide links, using biochemical and cell biological approaches. Anti-chromogranin A region-specific immunoblots on chromaffin granules suggested bidirectional endoproteolytic cleavage of chromogranin A; control experiments ruled out artifactual cleavage during granule isolation or lysis. Isolation of chromogranin A-derived peptides by gel filtration chromatography or sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), followed by N-terminal amino acid sequencing, established several cleavage sites, including at least two at dibasic sites. Secretion of chromogranin A from bovine chromaffin cells did not initiate further cleavage, nor did prolonged exposure of secreted chromogranins to the secretory cells. The chromogranin A cleavage pattern was qualitatively similar in other neuroendocrine tissues, though cleavage was more complete in adrenal medullary than in anterior pituitary hormone storage vesicles, and N-terminal fragments of 45 and 55 kilodaltons were more prominent in the hypothalamus. A similar cleavage pattern was seen in human pheochromocytoma granules, as judged by chromogranin A region-specific immunoblots, fragment isolation by SDS-PAGE, and microsequencing. The presence of full-length chromogranin A as the core protein of a chromaffin granule soluble proteoglycan was suggested in bovine (but not human) chromaffin granules by glycoprotein staining, chondroitinase ABC digestion, chemical deglycosylation, and region-specific immunoblotting. Human (but not bovine) chromogranin A displayed intermolecular disulfide crosslinks on SDS-PAGE gels and immunoblotting. These results document diverse structural paths that the chromogranin A molecule may take in endocrine secretory cells after its translation.

Previous studies from our laboratory have demonstrated that the Y chromosome from the spontaneously hypertensive rat (SHR) is responsible for a significant portion of the elevated blood pressure and also produces an earlier pubertal rise in plasma testosterone. We performed the following studies to determine whether the SHR Y chromosome raises blood pressure by sympathetic nervous system responses as measured by adrenal chromogranin A and plasma and tissue catecholamines. Male SHR from the University of Akron colony were studied from 5 to 20 weeks of age. Blood pressure was measured by tail-cuff, tail artery cannulation, and aortic telemetry (Data Sciences); acute (air stress) and chronic (territorial colony) social stressors were compared; blood was collected for determination of plasma catecholamines; and adrenal glands were analyzed at 15 weeks for catecholamines. Rats with the SHR Y chromosome had higher blood pressure and plasma norepinephrine than those with the normotensive Wistar-Kyoto (WKY) Y chromosome. However, the SHR Y chromosome did not significantly change responsiveness to acute or chronic stressors. Phentolamine and clonidine prevented the stress responses. Adrenal chromogranin A levels were elevated 37% and 40% and adrenal norepinephrine content 29% and 100% at 4 and 10 weeks of age, respectively, in rats with an SHR Y chromosome compared with WKY. Chemical sympathectomy normalized blood pressure in all strains and significantly reduced norepinephrine (36% to 41%) in all strains except in WKY, which already had a normal blood pressure. In conclusion, the SHR Y chromosome appears to increase the chronic sympathetic nervous system. A potential mechanism could be a Y locus that influences chronic sympathetic nervous system activity, which may reinforce neurohumoral factors and structural components of the vessel wall, accelerating the development of hypertension.