Endothelin-3 immunoreactivity in gonadotrophs of the human anterior pituitary.

Endothelin (ET), originally discovered in vascular endothelial cells, has also been demonstrated in nonvascular tissues. The present study was undertaken to elucidate the presence of ET in the human pituitary. The avidin-biotin complex method with antiserum to ET-1 (and ET-2) or ET-3 was used to identify ET in human pituitaries obtained by autopsy. ET-3 immunoreactivity was found in the cytoplasm of large ovoid cells of the anterior pituitary. Using the double staining method, the cells containing ET-3 immunoreactivity were differentiated from cells containing ACTH, TSH beta, GH, PRL, and protein S-100. By staining with anti-LH beta antiserum in adjacent sections and using the double staining method, the cells were identified as gonadotrophs. No staining was observed in the posterior pituitary. In addition, no ET-1 (and ET-2) immunoreactivity was detected. The specific localization of ET-3 immunoreactivity in the gonadotrophs of the human pituitary suggests a possible role of ET-3 in the regulation of anterior pituitary function.

Atrial natriuretic peptide and brain natriuretic peptide coexist in the secretory granules of human cardiac myocytes.

To elucidate the intracellular localization of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in human cardiac myocytes, an immunocytochemical study was carried out by a double immunogold technique using antisera highly specific for ANP and BNP. Surgical and autoptic tissue specimens of human heart were studied. In the atrial myocytes, ANP was localized in almost all of the secretory granules, whereas BNP was colocalized with ANP in some of the granules. Although very few secretory granules were observed in ventricular myocytes, colocalization of ANP and BNP was basically the same as in atrial myocytes. No immunoreactive products were found in the control studies. These results suggest that secretion of BNP is under a regulatory mechanism similar to that of ANP.

Plasma immunoreactive endothelin, but not thrombomodulin, is increased in patients with essential hypertension and ischemic heart disease.

To ascertain an involvement of vascular endothelial cells in cardiovascular disease, we have determined plasma levels of two endothelium-derived substances, endothelin (ET) and thrombomodulin (TM), in essential hypertension (EH) and ischemic heart disease. Plasma ET was determined by radioimmunoassay (RIA) after extraction. Plasma TM levels were determined by enzymunoimmunoassay. Plasma ET levels were significantly elevated in patients with EH involving target organ damage, vasospastic angina pectoris (VSA), and acute myocardial infarction (AMI), especially in those associated with cardiogenic shock. There was a weak but significant correlation between plasma ET levels and serum creatinine concentration in patients with EH. Plasma ET levels were elevated even before the coronary spasm in patients with VSA, whereas they did not show any further increase during the spasm. In contrast, plasma TM levels in patients with EH and VSA did not show a significant difference from that in normal subjects. These results suggest that ET plays an important role in the pathophysiology of EH and ischemic heart disease, and also that increases in plasma ET cannot be simply attributed to a leakage of the peptide from the injured endothelial cells.

Molecular form of immunoreactive endothelin in plasma and urine of normal subjects and patients with various disease states.

To elucidate the pathophysiologic significance of the family of endothelin (ET) peptides, we have investigated plasma and urinary immunoreactive (ir-) ET levels and its molecular forms in normal and pathological conditions. Plasma and urine ET were extracted with an Amprep C2 column. The molecular form of ET was determined by a combination of radioimmunoassay and reverse-phase high-performance liquid chromatography. Although plasma ir-ET was composed mainly of big ET and endothelin-1 (ET-1) in normal subjects, that in acute myocardial infarction, chronic renal failure (CRF), essential hypertension, and vasospastic angina pectoris was characterized by an increase of high molecular ir-ET in addition to increases in big ET and ET-1. Urinary ir-ET in both normal subjects and patients with CRF was composed mainly of a high molecular form in addition to big ET and ET-1. These results suggest that the biosynthetic and/or degradation process of ET under pathological conditions appears to be different from that under normal conditions.

Is big endothelin converted to endothelin-1 in circulating blood?

Although evidence has been accumulating to support an intracellular processing of big endothelin-1 (big ET-1) to ET-1, molecular conversion in the circulating blood remains to be elucidated. The present study was undertaken to investigate whether big ET-1 was converted to ET-1 in human blood. In the first experiment, normal serum with synthetic big ET-1 exogenously added or serum from patients with chronic renal failure was incubated in vitro at 37 degrees C for 1 h. In the second experiment, synthetic big ET-1 was incubated in the whole blood at 37 degrees C for 1 h. In the third experiment, synthetic big ET-1 was administered intravenously in anesthetized rat and a plasma sample was obtained before and after 15 min and 1 h. After respective incubation, molecular forms of ET were determined by a combination of reverse-phase high-performance liquid chromatography and radioimmunoassay. There was no significant conversion of big ET-1 to ET-1 in the serum obtained from normal and CRF patients. However, there was a slight but significant increase of ET-1 after incubation of big ET-1 in the whole blood or after administration of big ET-1 in anesthetized rat. The conversion in the whole blood was inhibited by 5 mM EDTA. These results suggest that circulating blood may not be a major site of molecular conversion from big ET-1 to ET-1, although conversion does occur in the circulation by blood cell-mediated process.