Pharmacological studies on a new antihypertensive agent, S-2150, a benzothiazepine derivative: 1. Antinecrotic and antiarrhythmic effects in reperfused rat hearts

S-2150 is a new 1,5-benzothiazepine derivative that inhibits [3H]diltiazem and [3H]WB4101 bindings to the membrane of rat tissue. The effects of S-2150 on ischemia/ reperfusion injury were studied in anesthetized rats. S-2150 reduced the myocardial infarct size (IS) induced by 20-min coronary artery occlusion followed by reperfusion. To evaluate reperfusion-induced ventricular tachycardia and fibrillation (VT, VF), we occluded the coronary artery for 4 min and then reperfused it. The incidence of arrhythmia was blocked by S-2150, and this effect offered protection against cardiac death. Prazosin did not modify the IS or incidence of reperfusion arrhythmias, but combined treatment with a noneffective dose of diltiazem showed significant cardioprotective effects. We also compared the direct effects of S-2150 and diltiazem on cardiac function and coronary perfusion flow using isolated rat hearts. Both drugs decreased mechanical function and increased coronary flow, with S-2150 being less cardiodepressive and more vasodilatory. S-2150 is cardioprotective at doses comparable to hypotensive doses even though its cardiodepressant effect is much weaker than that of diltiazem. This effectiveness may be partly explained by its dual characteristics: blocking the Ca channel and the alpha 1-adrenoceptor.

Impaired catecholamine secretion as a cause of diabetic autonomic neuropathy

Human and animal studies were performed to investigate the causes of diabetic autonomic neuropathy. Human diabetics, with and without autonomic neuropathy, were measured for plasma catecholamine response to insulin hypoglycemia and for urinary catecholamine excretion. In streptozotocin-diabetic rats, plasma catecholamine response and tissue catecholamine concentrations were measured at various stages of the disease. As the duration of the diabetic state lengthens in rats, there is a time-proportional stepwise decrease in plasma catecholamine response. This is similar to the clinical course observed in human diabetics, which also includes a reduction of catecholamine excretion after the appearance of autonomic neuropathy. After 6 weeks of diabetes, rat tissue is found to have an increased concentration of catecholamines; this may represent a compensatory reaction to the difficulties of secretion. At 13 weeks of diabetes, tissue catecholamine concentrations return to almost normal, when plasma responses have disappeared. These results suggest that the impaired secretion of catecholamines in diabetics may be a cause of diabetic autonomic neuropathy.

Age related changes of N-acetyl-beta-D-glucosaminidase and L-alanine aminopeptidase in mouse kidney, urine and plasma

Age and sex dependent differences of N-acetyl-beta-D-glucosaminidase (NAG) and L-alanine aminopeptidase (AAP) activities in kidney, urine and plasma of male and female mice were studied. The sex difference in NAG activity appeared between 27 and 38 days of age with the manifestation of significant differences in body weight and kidney growth. NAG activity in male kidneys was 3-fold that in females and its urinary level in mature males was over 10-fold higher. Androgenic regulation was found not only in the NAG contents in the kidneys and in the urinary excretion but also in the plasma NAG level, which showed higher in females. On the other hand, AAP activity in kidney, urine and plasma did not show much sex differences. Age related changes in AAP activity were not found except in the kidney and marked androgenic regulation was also not found in AAP. These results indicate that NAG and AAP, which are both urinary enzymes used as indicators of renal lesions, may be regulated differently.

Abnormalities in plasma catecholamine response and tissue catecholamine accumulation in streptozotocin diabetic rats: a possible role for diabetic autonomic neuropathy

Plasma catecholamine levels, determined by high performance liquid chromatography, were elevated in response to blood withdrawal in normal rats. Such a response was also observed in streptozotocin diabetic rats 2 and 6 weeks after disease onset, but was no longer seen at 13 weeks. Tissue (adrenal, heart, skin, kidney) catecholamine levels in diabetic rats were increased at 6 weeks as well as at 13 weeks. These abnormalities were corrected by insulin treatment in at least a part of diabetic rats. The present data suggest that there might be a catecholamine accumulation, which is later accompanied with an impairment of catecholamine secretion, in diabetic rats, and they gave a basis for an inference that similar changes might play some role in the pathogenesis of diabetic autonomic neuropathy in man.

Sex difference of N-Acetyl-beta-D-glucosaminidase activity in the kidney, urine, and plasma of mice

N-Acetyl-beta-D-glucosaminidase (NAG) activities in urine, kidney, and plasma were compared in an age-matched group of male and female ds mice. In males, the NAG activity in the kidney was significantly higher (p less than 0.001), and the urinary NAG activity (unit/g creatinine) was 8-fold higher than those for females, while plasma NAG levels were significantly lower (p less than 0.001). These findings indicate that when using urinary NAG activity to detect drug nephrotoxicity in mice, the different basal levels between males and females should be considered before drug administration.

Renin-angiotensin system and prostacyclin biosynthesis in streptozotocin diabetic rats

The relationship between the renin-angiotensin system (RAS) and prostacyclin (PGI2) biosynthesis was studied in experimental diabetic rats. The group with diabetes induced by streptozotocin (STZ, 3.3 mmol/kg i.v.) showed prolonged hypertension, and plasma renin activity decreased markedly from 8.4 +/- 0.7 to 2.4 +/- 0.3 and 1.2 +/- 0.3 ng angiotensin I/ml per h at 2 and 8 weeks after STZ treatment. Plasma PGI2, determined as 6-keto-PGF1 alpha, decreased significantly at 8 weeks, with the values for the STZ-treated and control groups being 1490 +/- 99 and 2210 +/- 90 pg/ml, respectively. Significant suppression of renin release from renal cortical slices was observed at 8 weeks in the diabetic group, although no significant change was found in the renal renin content when compared with that of the controls. The release of PGI2 from the renal medullary slices of the diabetic group was suppressed at 2 and 8 weeks, with the suppression in aorta and renal cortical slices being apparent only at 8 weeks. These results indicate that suppression of the RAS may be related to PGI2 biosynthesis in diabetes mellitus.

Decreased response of plasma catecholamine to stress in diabetic rats

Previously we reported that the heart norepinephrine concentration was markedly increased in diabetic rats. To further study the relationship between a disturbance in the autonomic nervous system and catecholamine metabolism in diabetes mellitus, the plasma catecholamine response to stress and catecholamine concentration of heart and adrenals were measured. Wistar male rats were made diabetic by streptozotocin and kept for 13 weeks. A silicon catheter was placed in the superior V. cava 1 week prior to the experiment. Insulin was injected subcutaneously for 3 days once daily. After an overnight fast and without anesthesia, 1 ml of blood, a control sample, was obtained and then the animals were exsanguinated. The blood was mixed with 1 mM EGTA at a final concentration and centrifuged. The tissue was homogenized with 0.4 N perchloric acid containing 1 mM EGTA and centrifuged at 10,000 x g for 20 minutes. Catecholamines were determined by high performance liquid chromatography. Normal rats responded to blood withdrawal stress, and plasma catecholamines were markedly increased, but almost no increase or an actual decrease was observed in diabetic rats. These abnormal responses were improved by insulin treatment. Heart norepinephrine was increased significantly in the diabetic rats compared with the control rats and was reduced significantly by insulin injections. Adrenal epinephrine was also significantly increased in the diabetic rats compared with the control rats, but was not significantly reduced by insulin. These result suggest a possible disturbance of catecholamine secretion in the diabetic rats.

Increased norepinephrine content in diabetic rat heart

In an attempt to clarify the mechanism of cardiac neuropathy in diabetes mellitus, Wister male rats were made diabetic by streptozotocin injection for 11 to 13 weeks, and catecholamine concentrations of hearts were determined by high performance liquid chromatography. No apparent histological changes were found in hearts and kidneys of any group of rats. Controls used were age-matched normal rats and Goldblatt-hypertensive rats, because streptozotocin induced diabetic rats appeared to be significantly hypertensive. Heart norepinephrine concentrations of diabetic rats and diabetic-Goldblatt-hypertensive rats were markedly higher (8,380 +/- 300 pmol/g tissue and 6,980 +/- 390, respectively) compared with those of controls and Goldblatt-hypertensive rats (2,700 +/- 470 and 2,010 +/- 300, respectively). These results suggest some disturbances in catecholamine secretion in diabetic hearts before typical microangiopathic changes take place.

Characteristics of a renin-binding substance for the conversion of renin into a higher-molecular-weight form in the dog

1. Renal cortical homogenates of the dog were subjected to sieve separation, a Nucleopore Filter being used to separate the renin granules. 2. The molecular weight of renin in the granules was estimated to be about 40 000 by gel filtration. Renin was converted into a higher-molecular-weight form (60 000) by mixing with cytosol in the presence of sodium tetrathionate, a thiol inhibitor. 3. When cytosol was pretreated with acid (pH 3.0) or heating (100 degrees C), the molecular-weight conversion did not occur. 4. Cytosol was separated into three parts by gel filtration. Fraction A included substances with a molecular weight of over 47 000, fraction B from 47 000 to 32 000, and fraction C from 32 000 to 15 000. The mixture of renin in the granules with fraction A and sodium tetrathionate resulted in the formation of a higher-molecular-weight form of the enzyme, but no change in molecular weight was detected when renin was mixed with fractions B or C and sodium tetrathionate.

Relationship between molecular weight conversion and renin activity in dog renal renin

A normal size form of renin, which seems to be a storage form in renin granules, changed neither in molecular weight nor activity by acidification to pH 3.0. High molecular weight (HMW) renin fractionated by gel chromatography from crude renal extract prepared with thiol group blockers was converted into normal size renin by acdification, accompanied with an increase in renin activity by about 50%. The molecular weight conversion by acidification appeared due to destruction or loss of binding ability of the renin binding substance which was present in the cytosol of renal cortical tissue. Renin and renin binding substance could combine into HMW renin at neutral pH in the presence of thiol group blockers and renin activity decreased.

Conversion between renin and high-molecular-weight renin in the dog

Two forms of renin, one of mol.wt. 43,000 and the other 60,000, were found in the dog kidney. Conversion between the two forms of renin was reversible at neutral pH. Though the molecular weight of renin in kidney-cortex homogenate was 43,000, it was completely converted into high-molecular-weight renin in the presence of substances that react with thiol groups. On the contrary, stored renin in the granules was the form of normal size (mol. wt. 43,000) regardless of the absence or presence of such substances. The present experiments indicated that renin is stored in the granules as the form of normal size and might be converted into high-molecular-weight renin when it is released from the granules and attached to some substance in the soluble fraction of renal-cortical tissue.

Renin release from renin granules in the dog

1. Renin release from isolated dog renin granules was limited to within 20% of the total renin during incubation at 37 degrees C in isotonic medium and did not depend on the external concentration of renin. 2. Although the renin granules were osmotically and mechanically fragile, they were quite stable at 0 degrees C in isotonic medium. 3. The bulk of renin activity appeared in the supernatant when the granules were ruptured by osmotic lysis. About 8% of the total renin still remained in the membrane fraction of the granules after treatment by freezing and thawing. 4. Therefore stored renin in the granules can be described as comprising three components: a readily released soluble form; a soluble but hard-to-release form; a membrane-bound form.

Storage form of renin in the dog kidney

A large part of renin was revealed to be stored in the remin granules as a soluble but hard to release form. Over 70% of the total renin in the granules could be released when the granules were ruptured by hypo-osmotic shock. Renin release from the isolated granules was limited within 20% of the total renin during incubation at 37C in an isotonic medium. 2. Without mechanical or osmotic shock renin granules were quite stable in a cold isotonic solution. Renin release from the isolated granules was not so much influenced by addition of cations which significantly stimulate renin release in vivo. Some cellular components may be required for the release process of renin from the granules as a mediator. 3. The molecular weight of the stored renin in the granules was shown to be 43,000 which was the regular size. Acidification of the extract of the renin granules altered neither molecular size of renin nor renin activity.