M. L. Overturf

Effects of moderate hypertension on cardiac function and metabolism in the rabbit.

To study the early effects of hypertension on the heart, we examined isolated hearts from rabbits with slowly developing hypertension of up to 64 weeks in duration after unilateral nephrectomy and renal artery stenosis. Normotensive animals kept under identical conditions served as controls. Mean arterial blood pressure rose from 83 to 155 mm Hg in the hypertensive group of longest duration, but the ratio of left ventricular weight to body weight was not different between the experimental and control groups. Although left ventricular hypertrophy was not present, left ventricular peak systolic pressure of perfused hearts was significantly higher in hypertensive than in normotensive hearts. Furthermore, while in hypertensive hearts the left ventricular end-diastolic volume was increased, the peak systolic pressure did not respond to an increase in left ventricular end-diastolic volume. Functional changes were accompanied by metabolic changes in the left ventricle. Rates of glucose utilization were increased and rates of ketone body utilization were decreased in hypertensive hearts. Activities of key enzymes of carbohydrate metabolism (phosphorylase, hexokinase, phosphofructokinase, and lactate dehydrogenase) were increased, while those of ketone body metabolism (3-oxoacid-CoA transferase, acetoacetyl-CoA synthase) were decreased and those of the citric acid cycle (citrate synthase, 2-oxoglutarate dehydrogenase) were not different between groups. In summary, moderate hypertension for a period of more than 1 year resulted in functional and metabolic changes of the left ventricle in hypertensive animals that were already manifest at 8 weeks of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension and atherosclerosis in cholesterol-fed rabbits: Part 1. Mild, two-kidney, one-clip goldblatt hypertension treated with enalapril

Ten groups of New Zealand white rabbits were used to study the effects of mild, chronic two-kidney, one-clip hypertension (HT) and long-term antihypertensive therapy on atherogenesis. Five groups were fed a normal diet (ND) over the 8-month study period; 2 groups, one of which was given enalapril, remained normotensive (NT) throughout the study. Of the 3 HT groups, one was hypertensive for 7 months; the blood pressures of the other groups were normalized after 2 months with enalapril, or by removal of the clipped kidney. The other 5 groups were similar except that they were fed at 0.1% cholesterol diet (CD). The results showed that: neither mild chronic HT nor abrupt, short-term HT exacerbated atherogenesis in the CD-animals; although fibromuscular vascular lesions were present in the aorta of normal-diet, HT animals no atheroma was observed; enalapril therapy had no effect on atherogenesis; enalapril therapy reduced the total weight and the cholesterol and triglyceride content of the aorta of the ND groups regardless of blood pressure history; the aortic triglyceride content, but not the cholesterol content, of the CD group, was reduced by enalapril; and although heart size was unaffected by either diet or blood pressure levels, the mitochondria volume per unit volume of the left ventricle was reduced in both NT-ND and HT-CD groups treated with enalapril.

Purification of human renin and inhibition of its activity by pepstatin

Several proteases from human kidney tissue were partially purified by ammonium sulfate precipitation followed by Sephadex G-75 gel filtration chromatography. The incubations of column fractions with 14C-tetradecapeptide renin substrate indicated four major renin activity peaks between the molecular weights of 25,000 and 80,000. The highest specific activity was found in Fraction B (mol. wt 39,500). Significant renin-like activity was also found in Fraction A (mol. wt 58,000) and Fraction C (mol. wt 33,500). None of the fractions contained angiotensinase activity. Disc-gel electrophoresis indicated that Fractions B and C were heterogeneous. The conversion of 14C-tetradecapeptide renin substrate to angiotensin I by major fractions was differentially inhibited by low concentrations of pepstatin. Both the rate of substrate conversion and the sensitivity to pepstatin were influenced by pH. Generally, the proteases were more sensitive to pepstatin at physiological pH. Regardless of pH, all of the kidney proteases were completely inhibited by 10−3 M pepstatin. The conversion of human substrate by human plasma proteases was found to be even more sensitive to pepstatin. The concentration of 10−5 M pepstatin essentially eliminated plasma renin activity. These results indicate that pepstatin can serve as an efficient inhibitor of both human kidney and plasma renin proteases and as such will be useful in the study of the kinetics of these systems in both research and clinical situations.

Hypertension and atherosclerosis in cholesterol-fed rabbits II. One-kidney, one clip Goldblatt hypertension treated with nifedipine

Eight groups of New Zealand white rabbits were used to study the effects of moderate chronic one-kidney, one clip hypertension (HT) and long-term nifedipine therapy on atherogenesis. Four groups were fed a normal diet (ND) over an 8-month study period; two groups, one of which was given nifedipine, remained normotensive (NT) throughout the study. Of the two HT groups, one remained hypertensive for 7 months; the blood pressure of the other group was normalized after 2 months with nifedipine. The other four groups of animals were similarly constructed except that they were fed a 0.1% cholesterol diet (CD). The results showed that: although scattered fibromuscular vascular lesions were present in the aortas of normal-diet, HT animals no atheroma was observed; neither moderate chronic HT nor abrupt, short-term HT exacerbated atherogenesis in the CD-animals; nifedipine therapy had no suppressive effect on either fibromuscular lesions or atherogenesis; nifedipine therapy reduced the aorta weight of the normotensive ND and CD groups; the aortic triglyceride content of both dietary groups was reduced by nifedipine; cholesterol content was unaffected; left ventricular hypertrophy was evident only in HT-untreated groups; and only the weight of the left ventricle of the ND-NT-treated group was significantly reduced, but the mitochondria volume per unit volume of left ventricle myocardial cells was reduced only in the NT-CD group treated with nifedipine. It is concluded that an antihypertensive dosage of nifedipine administered to animals with atherosclerosis does not suppress subsequent atherogenesis.

Structure of neutral glycerides and phosphoglycerides of human kidney

Abstract 1. 1. Neutral lipids and phospholipids of human kidney have been isolated and the fatty acid composition of each determined. 2. 2. Triglycerides were fractionated into 7 bands by argentation chromatography. The major class (49%) was saturated, monoene, monoene. Stereospecific analysis revealed that both positions 1 and 2 contained an approximate ratio of 1:1 saturated to unsaturated fatty adds. 3. 3. Positional distribution of fatty acids in phosphatidylcholine, the major phospholipid component (27.2%), was determined by phospholipase A2 and pancreatic lipase hydrolysis. 4. 4. Overall results indicated similarities and differences when compared to kidney lipids of other mammalian species.

Renin as a risk factor for atherogenesis: Effects of hypercholesterolemia and two-kidney-one-clip hypertension in the rabbit

Four groups of New Zealand rabbits were used to study the effect of plasma renin activity (PRA) on atherogenesis. Control groups were fed normal rabbit chow (Group I) or chow supplemented with 0.25% cholesterol and 0.75% corn oil (Group II). The two-kidney--one-clip (2K-1C) hypertensive model was produced in 2 additional groups; Group III (normal diet) and Group IV (atherogenic diet). The latter 2 groups were subgrouped according to PRA levels. Each group was examined over a 7-month period. Group II became hyperlipidemic and developed extensive lipoidal vascular lesions. Mean arterial pressure remained normal throughout the experimental period; PRA fell below normal. Group III and Group IV rabbits developed sustained hypertension irrespective of circulating PRA. The atheromas of Group III were predominantly microscopic and fibromuscular; the extent of aortic and coronary artery involvement was independent of renin response. The most extensive and complicated atheromas were seen in the 2K-1C rabbits consuming the atherogenic diet (Group IV). The lesions were mostly lipoidal, although some were fibromuscular. These results demonstrated that cardiovascular lesions and atherogenesis were exacerbated in the 2K-1C rabbits on a high cholesterol diet; however, PRA was excluded as the cause.

Cholesterol metabolism in hypercholesterolemia-resistant rabbits.

Normal rabbits typically respond to a diet high in cholesterol with a large increase in the concentration of plasma cholesterol. We have previously described the breeding and partial characterization of a variant rabbit which does not respond to a high cholesterol diet with changes in plasma cholesterol concentration. In the present report we have characterized three components involved in cholesterol homeostasis: the B/E (LDL) receptor, 3-hydroxy-3-methylglutaryl coenzyme A reductase activity (HMG-CoA reductase, EC 1.1.1.34) and acyl-coenzyme A: cholesterol acyltransferase activity (ACAT, EC 2.3.1.26) in the livers of the hypercholesterolemia-resistant rabbits. Using normal cholesterol-fed rabbit [125I] beta-VLDL as a ligand, liver membranes prepared from resistant rabbits fed a low-cholesterol diet had 70% higher binding capacity than membranes from normal rabbits fed the same diet. Similar experiments demonstrated that the resistant rabbits had a 240% higher B/E receptor binding capacity compared to normal animals when liver membranes were prepared from animals fed a 0.25% cholesterol-enriched diet. No difference in the binding affinity of [125I]beta-VLDL was detected in membranes prepared from normal or resistant animals. When fed a low-cholesterol diet, the resistant rabbits had approximately 2-fold higher hepatic HMG-CoA reductase activity (97.4 +/- 3.5 pmol product/mg/min in resistant animals compared to 45 +/- 1.1 pmol product/min/mg in normal animals). The difference was exaggerated in animals fed the 0.25% cholesterol-enriched diet, 73.3 +/- 5.5 vs 2.4 +/- 0.56 pmol product/min/mg for resistant and normal membranes respectively. The basal activity of ACAT in hepatic membranes was significantly lower in the resistant rabbits compared to normal rabbits (138 +/- 11 vs 268 +/- 19 pmol cholesteryl ester/min/mg in resistant and normal rabbits respectively); when fed a 0.25% cholesterol-enriched diet, the enzyme was induced 6-fold in normal animals but was increased only 2-fold in the resistant animal. These biochemical data suggested that the resistant rabbit maintained low intracellular cholesterol even when fed a cholesterol-enriched diet. Direct measurement of cellular cholesterol and cholesteryl esters demonstrated that the concentration of these lipids was significantly lower in the resistant animal than in normal animals with the largest differences found in the cytoplasmic rather than the membrane compartment. These studies demonstrate that the resistant rabbit manifests several quantitative differences in cholesterol metabolism and in the regulation of cholesterol metabolism; but these studies do not directly explain the underlying cause of the resistance to hypercholesterolemia in the resistant rabbit.

Cortical and medullary lipids of normal and nephrosclerotic human kidney

Abstract 1. 1. Major lipid classes from cortical and medullary zones of normal and nephrosclerotic human kidneys have been isolated and the fatty acid composition of each determined. 2. 2. The nephrosclerotic tissue contained two times more total lipid than the normal kidney but, irrespective of kidney pathology, phospholipids were the major cortical lipids and neutral lipids were the predominant lipids in medullary zones. 3. 3. Human kidney contained large amounts of phosphatidylcholines, phosphatidylethanolamines and sphingomyelins and although these were slightly increased in the sclerotic kidney, anatomical differences in phospholipid content were not significant. 4. 4. Quantitative differences between the zones of normal kidney were found with triglycerides, diglycerides. free fatty acids and cholesterol; overall, the sclerotic tissue contained more triglycerides and small amounts of cholesterol esters with less significant regional differences. 5. 5. Palmitic, oleic and stearic acid were the major fatty acids of neutral lipids; these plus linoleic acid were prevalent in phospholipids.

RENIN AS A PREDICTOR OF HYPERTENSIVE COMPLICATIONS

Prior to the beginning of this decade, the interest in plasma renin activity (PRA) was mainly because of its association with malignant hypertension, renovascular hypertension, and primary aldosteronism. Considerable research effort was expended in defining proper PRA assay methods. The majority of the clinical studies were aimed at appraising the usefulness of PRA measurements, both in terms of screening patients for renovascular involvement as a basis for their hypertension (peripheral PRA), and for detecting specific, functional renovascular lesions (split renal vein plasma samples). Now, at the end of this decade, PRA assays can be performed reliably, if critical protocols are followed. Functional lesions can thus be isolated and surgical corrections can usually effect a cure for this group of patients. The value of peripheral PRA measurements as a hypertension screening device is still uncertain. In this paper, we examine the value of PRA in the prediction of cardiovascular risk.

Effect of human kidney lipids on human kidney renin activity.

Abstract The major lipids of human kidney tissue were isolated by solvent extraction, and the lipid composition was determined by thin-layer chromatographic techniques. The positional distribution of fatty acyl groups in ethanolamine and choline phosphatides was determined after enzymatic hydrolysis. Major phosphatides were assayed for plasmalogen content. Triglycerides were characterized by argentation chromatography. The fatty acyl composition of these lipids was also determined. The effect of intact triglycerides, phospholipids, 1- and 2-monoacyl phosphatides and ether lipids on renin activity in vitro was determined by incubations with 3-[U 14 C]valyl tetradecapeptide renin substrate. Kidney triglycerides, 1-monoacyl and 2-monoacyl phosphatidylethanolamines and phosphatidylcholines significantly inhibited renin activity. The renin-inhibitory effect of these lipids was comparable to inhibition by hog kidney phospholipid inhibitor. The intact phospholipids and cholesterol potentiated human kidney renin activity. Phosphatidylserines and synthetic glyceryl ether lipids have no significant effect. These results indicate that lipid-induced inhibition of human renin activity does not require the ethanolamine moiety, acyl group unsaturation, or the presence of a hydroxyl group at the 2-position. Additionally, no specific structure-activity relationships can describe lipid-renin interactions.