Kazuo Takaori

Atrial natriuretic polypeptide in atria and plasma in experimental hyperthyroidism and hypothyroidism.

To investigate the involvement of thyroid hormone on the release of atrial natriuretic polypeptide (ANP), we have measured immunoreactive ANP in the atria and plasma of experimental hyperthyroid and hypothyroid rats. Plasma ANP was higher (p less than 0.05) in hyperthyroid rats and was lower (p less than 0.05) in hypothyroid rats than in euthyroid rats. ANP content and concentration in the atria were lower (p less than 0.01) in hyperthyroid rats than in hypothyroid rats. An inverse correlation was found between the plasma ANP and ANP concentration in the atria (n = 15, r = 0.60, p less than 0.01). The results indicate an increased systemic release of ANP from the atria in hyperthyroidism and a decreased systemic release in hypothyroidism.

Protein kinase c activity in platelets from spontaneously hypertensive rats (SHR) and normopensive wistar Kyoto rats (WKY)

Calcium-activated phospholipid dependent protein kinase (protein kinase C) activity in platelets was measured in 4, 12, and 20-week-old SHR and WKY. At age 4-weeks, there was no significant difference in protein kinase C activity and systolic blood pressure between SHR and WKY. In 12 and 20-week-old SHR, both protein kinase C activity and systolic blood pressure were significantly higher than in the age-matched WKY. These results suggest that protein kinase C may be involved in the control of blood pressure in SHR and WKY.

Effect of Chronic Treatment with Angiotensin I Converting Enzyme Inhibitors on Circulating Atrial Natriuretic Polypeptide in Spontaneously Hypertensive Rats

We have recently shown that circulating atrial natriuretic polypeptide (ANP) in adult spontaneously hypertensive rats (SHR) is higher than that in age-matched Wistar-Kyoto rats (WKY). The present experiment was designed to examine the possible effects of chronic treatment with angiotensin I converting enzyme inhibitors (ACEI) on plasma ANP levels in SHR. Captopril and enalapril lowered blood pressure and reduced relative ventricular weight in SHR but not to the level of WKY. Plasma ANP levels were decreased by captopril and enalapril compared with untreated SHR. These results suggest that the ANP release may be suppressed in ACEI-treated SHR compared with untreated SHR. We speculate that a reduction of cardiac overload by ACEI may in part explain the decline of circulating ANP.

Intracellular pH in platelets from spontaneously hypertensive rats and Wistar-Kyoto rats

Intracellular pH in platelets from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY) was measured using a pH-sensitive fluorescent dye, 2‘,7’-bis(carboxyethyl)carboxyfluorescein tetraacetoxy methyl ester (BCECF). Intracellular pH in platelets was significantly higher in SHR than in WKY (7.12 ± 0.04 versus 7.06 ± 0.02, P < 0.01; n = 10). There was a close correlation between intracellular pH and systolic blood pressure (r = 0.66, P < 0.01). Addition to platelets of 1-(5-isoquinolinesulphonyl)-2-methylpiperazine (H-7), a specific inhibitor of protein kinase C, produced a significantly larger decrease in intracellular pH in SHR than in WKY (0.06 ± 0.02 versus 0.03 ± 0.00, P < 0.01, n = 5). These results suggest that protein kinase C may play an important role in the increased intracellular pH in SHR.

Biochemical Properties of the Renin Binding Substance of Rat Kidney

Renin extracted from isolated renin granules of the rat is a low molecular weight form (40,000 daltons). The renin binding substance which is capable of binding with the low molecular weight renin to form a high molecular weight renin (60,000 daltons) under sulfhydryl oxidation was found to be contained in the crude extract of rat renal cortex. This substance is presumably a protein with molecular weight of over 47,000 daltons by gel filtration. The most striking event was that rat renin binding substance was bound with dog renin and vice versa.

Increased Na+/H+ exchange activity in vascular smooth muscle cells of spontaneously hypertensive rats and possible involvement of protein kinase C

1. Na+ influx into cultured vascular smooth muscle cells (VSMC) obtained from spontaneously hypertensive rats (SHR) and from Wistar‐Kyoto rats (WKY) was measured. Na+ influx via the Na+/H+ exchange system was measured as the rate of 22Na+ influx into cultured VSMC sensitive to ethylisopropylamiloride (EIPA), a specific inhibitor of the exchange system.

Intrarenal localization of renin binding substance in rats.

Renin binding substance is a protein that reacts with renin (Mw:40,000) to form a high-molecular-weight renin (Mw:60,000). There is evidence that this substance is present in the renal cortex. However, the exact localization has not been determined. We now report that when glomeruli and tubular segments were isolated from the rat kidney cortex and were frozen and thawed to extract proteins, the high-molecular-weight renin was detected by high performance liquid chromatography, when renin was mixed with an extract of tubular segments, but was not detected with an extract of the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli, and the renin binding substance probably does not contribute to the process of biosynthesis of renin in juxtaglomerular cells. Rather, this substance may play a role in tubular functions in the kidney.

High molecular weight renin identified in cytosol fractions of mouse renal cortices

Abstract In an attempt to confirm that high molecular weight renin was indeed true renin, we used a specific renin antibody and high performance liquid chromatography to determine characteristics of this protein. In mouse renin granules, renin was stored in a low molecular weight form of 38,000 daltons (LMW renin) and this molecular weight remained unchanged with application 20 mM of sodium tetrathionate. In the cytosol fraction of the renal cortex, LMW renin was partially converted to high molecular weight renin (HMW renin) of 65,000 daltons, as determined using tetrathionate. In both the LMW and HMW renin, enzymatic activity was completely neutralized by application of a specific antiserum of renin and an absolute amount of renin was identified by direct radioimmunoassay. The Km values of HMW and LMW renin were similar. Thus, LMW renin probably binds with renin binding substance and forms HMW renin.

Chronic Antihypertensive Drug Treatment Decreases Protein Kinase C Activity in Platelets from SHR

There is evidence that protein kinase C activity in platelets from adult SHR is significantly higher than this activity in age-matched WKY. In the present study, protein kinase C activity in the SHR was measured following antihypertensive drug treatment. Chronic administration of enalapril to SHR for 2 weeks decreased both systolic blood pressure and protein kinase C activity to the levels seen in the WKY. Similar results were obtained in case of chronic treatment of SHR with hydralazine or nifedipine. These results suggest that enhanced protein kinase C activity of SHR can be suppressed by lowering blood pressure by antihypertensive drugs.

INVOLVEMENT OF SYMPATHETIC NERVOUS SYSTEM INHIBITION IN THE HYPOTENSIVE EFFECT OF BROMOCRIPTINE IN SPONTANEOUSLY HYPERTENSIVE RATS

The hypertensive effect of bromocriptine in young (6 week old) spontaneously hypertensive rats (SHR) was studied. Blood pressure and plasma norepinephrine level in bromocriptine‐treated SHR were significantly lower than those in vehicle‐treated SHR after 3 weeks of treatment (5 mg/kg per day, i.p.), while no significant decrease of blood pressure or plasma norepinephrine level was observed after 2 weeks of treatment. These results suggest the involvement of sympathetic nervous system inhibition in the hypotensive effect of bromocriptine in SHR.