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.

Addition of rosiglitazone 2 mg bd and 4 mg bd to metformin therapy improved glycemic control in Mexican patients whose type 2 diabetes was inadequately controlled by metformin alone. Furthermore, the combination of rosiglitazone plus metformin was well tolerated.

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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. (Hypertension 1990;15:237-246)