Hyoichiro Sakurai

Atrial natriuretic factor inhibits vasopressin secretion from rat posterior pituitary

The effects of synthetic atrial natriuretic factor (ANF) were studied in superfused rat posterior pituitary gland. ANF (10(-6)M, 10(-10)M) significantly inhibited basal as well as KC1 (50 mM) or angiotensin II-stimulated immunoreactive arginine vasopressin secretion. The magnitude of inhibition was greater at 10(-6)M than at 10(-10)M. ANF also decreased cAMP secretion and increased cGMP secretion from the posterior pituitary. These results suggest that ANF directly acts on the posterior pituitary to inhibit arginine vasopressin secretion and that this effect is, at least, partly mediated by the changes in cyclic nucleotide production.

逆相C18シリカカラムを用いた高感度Radioimmunoassayによる血漿8-arginine vasopressinの測定法

A highly sensitive and simple radioimmunoassay for the measurement of 8-arginine vasopressin (AVP) in human plasma has been developed. The dose response curve ranges from 0.025 to 8 pg/tube. This simple extraction technique employing an ODS C18 column recovered 87.1 +/- 10.4 (mean +/- SD)% of AVP in the range of 1-10 pg/ml added to 0.5 ml plasma. Determination of AVP in each fraction of plasma, which was gel-filtrated through a Sephadex G25 (1 X 25 cm), revealed that the fraction of plasma AVP was superimposed on that of authentic AVP, and interference of non-specific substances was completely eliminated by an ODS C18 column. Using the assay, 13 of 16 patients with diabetes insipidus (DI) showed plasma AVP concentrations ranging from 0.03 to 0.21 pg/ml, and the other 3 patients had less than 0.03 pg/ml. The AVP concentrations of DI were clearly distinguished from those obtained in normal subjects (0.30-4.20 pg/ml, n = 65). The within and between assay variability was about 10% each. Plasma AVP concentrations (mean +/- SD) of normal subjects (n = 6) standing, sitting, and supine after an overnight of fluid deprivation were 2.41 +/- 1.15, 1.95 +/- 0.85 and 0.97 +/- 0.48 pg/ml (30 min after) respectively. Plasma AVP concentrations of normal subjects (n = 6) after water load (20 ml/kg wt) were clearly reduced from 1.89 +/- 1.00 (before) to 0.42 +/- 0.21 (standing for 60 min) and also from 0.89 +/- 0.41 to 0.40 +/- 0.22 pg/ml (supine for 60 min).

Radioimmunoassay for endothelin and immunoreactive endothelin in culture medium of bovine endothelial cells

Using a synthetic 21-residue endothelin as antigen, we have produced an antiserum for endothelin and developed a specific and sensitive radioimmunoassay (RIA) for endothelin. The minimum detection limit of the RIA was 1 pg/tube. Immunoreactive (ir-) endothelin was extracted from the culture medium by Bondelute C8 column. The ir-endothelin in the culture medium of endothelial cells (EC) from bovine pulmonary artery and carotid artery was 1.48 ng/ml and 3.31 ng/ml, respectively. Reverse-phase high performance liquid chromatography coupled with the RIA revealed that ir-endothelin in the culture medium comprised one major component corresponding to synthetic endothelin. In addition, the cultured EC of bovine pulmonary artery were specifically stained by immunohistochemical technique. These results suggest that endothelin could be produced in the EC of the pulmonary and carotid arteries besides the aorta. The RIA presented in this study could be an useful tool to investigate the pathophysiologic significance of endothelin.