Effects of two forms of hypertension on atherosclerosis in the hyperlipidemic baboon

Hypertension Enhances Advanced Atherosclerosis and Induces Cardiac Death in Watanabe Heritable Hyperlipidemic Rabbits

Hypertension is a major risk factor for the development of atherosclerosis. Cardiovascular risk has been reported to be significantly increased in hyperlipidemic patients with hypertension. However, it is not clear whether hypertension can directly destabilize plaques, thereby enhancing cardiovascular events. To examine whether hypertension enhances the development of atherosclerosis and increases plaque vulnerability, we generated hypertensive Watanabe heritable hyperlipidemic (WHHL) rabbits by surgical removal of one kidney and partial ligation of the other renal artery and compared the nature of aortic and coronary atherosclerosis in hypertensive WHHL rabbits with normotensive WHHL rabbits. All hypertensive WHHL rabbits died from 34 to 56 weeks after surgery, whereas no normotensive WHHL rabbits died. Pathologic examinations revealed that hypertensive WHHL rabbits showed different degrees of myocardial infarction caused by severe coronary stenosis along with myocardial hypertrophy. Furthermore, aortic lesions in hypertensive WHHL rabbits exhibited a higher frequency of intraplaque hemorrhage and vulnerable plaques than those in normotensive WHHL rabbits. These results indicate that hypertension induced by the surgical removal of one kidney and partial ligation of the other renal artery method in WHHL rabbits may not only enhance the development of atherosclerosis but also destabilize the plaques, increasing cardiac death.

A Cross-Sectional Study of Ageing and Cardiovascular Function over the Baboon Lifespan

Background

Ageing is associated with changes at the molecular and cellular level that can alter cardiovascular function and ultimately lead to disease. The baboon is an ideal model for studying ageing due to the similarities in genetic, anatomical, physiological and biochemical characteristics with humans. The aim of this cross-sectional study was to investigate the changes in cardiovascular profile of baboons over the course of their lifespan.

Methods

Data were collected from 109 healthy baboons (Papio hamadryas) at the Australian National Baboon Colony. A linear regression model, adjusting for sex, was used to analyse the association between age and markers of ageing with P < 0.01 considered significant.

Results

Male (n = 49, 1.5–28.5 years) and female (n = 60, 1.8–24.6 years) baboons were included in the study. Age was significantly correlated with systolic (R² = 0.23, P < 0.001) and diastolic blood pressure (R² = 0.44, P < 0.001), with blood pressure increasing with age. Age was also highly correlated with core augmentation index (R² = 0.17, P < 0.001) and core pulse pressure (R² = 0.30, P < 0.001). Creatinine and urea were significantly higher in older animals compared to young animals (P < 0.001 for both). Older animals (>12 years) had significantly shorter telomeres when compared to younger (<3 years) baboons (P = 0.001).

Conclusion

This study is the first to demonstrate that cardiovascular function alters with age in the baboon. This research identifies similarities within cardiovascular parameters between humans and baboon even though the length of life differs between the two species.

The baboon kidney transcriptome: analysis of transcript sequence, splice variants, and abundance

The baboon is an invaluable model for the study of human health and disease, including many complex diseases of the kidney. Although scientists have made great progress in developing this animal as a model for numerous areas of biomedical research, genomic resources for the baboon, such as a quality annotated genome, are still lacking. To this end, we characterized the baboon kidney transcriptome using high-throughput cDNA sequencing (RNA-Seq) to identify genes, gene variants, single nucleotide polymorphisms (SNPs), insertion-deletion polymorphisms (InDels), cellular functions, and key pathways in the baboon kidney to provide a genomic resource for the baboon. Analysis of our sequencing data revealed 45,499 high-confidence SNPs and 29,813 InDels comparing baboon cDNA sequences with the human hg18 reference assembly and identified 35,900 cDNAs in the baboon kidney, including 35,150 transcripts representing 15,369 genic genes that are novel for the baboon. Gene ontology analysis of our sequencing dataset also identified numerous biological functions and canonical pathways that were significant in the baboon kidney, including a large number of metabolic pathways that support known functions of the kidney. The results presented in this study catalogues the transcribed mRNAs, noncoding RNAs, and hypothetical proteins in the baboon kidney and establishes a genomic resource for scientists using the baboon as an experimental model.

Cardiovascular structure and function in baboons with Type 1 diabetes -- a transvenous ultrasound study

Diabetes mellitus is an important risk factor for both macrovascular and cardiac disease in humans. The availability of a novel intravenous ultrasound probe allows detailed interrogation of a large proportion of the vasculature, as well as the heart, during the same examination. Six male baboons (Papio hamadryas) with Type 1 diabetes and known microangiopathy, and six control animals were studied. Vascular structure in the major large arteries and cardiac function were studied using transvenous ultrasound introduced via the right femoral vein and positioned under fluoroscopy. All arteries were examined for atherosclerotic plaque and for presence of increased intima-media thickness (IMT). Left ventricular function was assessed at rest and following infusions of dobutamine (positive inotrope) and esmolol (negative inotrope). The procedure was performed safely and successfully in all cases. No atherosclerotic plaque was seen in either diabetic or normal baboons. There was no difference in the aortic IMT (0.38+/-0.04 vs. 0.37+/-0.05 mm, normal vs. diabetic, P=NS) or in doppler flow in the renal or iliac arteries between diabetic and normal baboons. Left ventricular wall thickness and systolic tissue velocity were similar in the two groups at rest (6.9+/-2.5 vs. 6.2+/-1.4 cm/s, normal vs. diabetic, P=NS), after dobutamine (15.5+/-2.2 vs. 12.7+/-3.9 cm/s, normal vs. diabetic, P=NS), and after esmolol (4.3+/-1.0 vs. 5.6+/-1.0 cm/s, normal vs. diabetic, P=NS). In a high primate model of diabetes with microangiopathy, the presence of hyperglycemia for 7 years per se does not produce abnormalities of macrovascular or cardiac structure.

Hypercholesterolemia superimposed by experimental hypertension induces differential distribution of collagen and elastin

We studied the mural distribution of collagen types I and III and tropoelastin in enhanced experimental atherogenesis induced in rabbits by hyperlipidemia superimposed by hypertension. Animals were fed a high-cholesterol diet for 5 weeks and also subjected to midthoracic aortic coarctation for 4 weeks. Serum cholesterol levels were increased and blood pressure was elevated proximal to the coarctation. Foam cell lesions developed in the aorta proximal to the coarctation. In situ hybridization and immunohistochemistry showed that gene expression of collagen types I and III and tropoelastin was upregulated, with a differential distribution across the arterial wall. New collagen type I was mainly distributed in the intima, the outer media, and the adventitia. New collagen type III was spread more uniformly across the wall, including the adventitia, whereas tropoelastin was mainly localized in intimal foam cell lesions. Morphometric data showed an increase in wall thickness. These results suggest that collagen types I and III play a role in remodeling of the aortic wall in response to hypertension. The remarkable involvement of the adventitia in this response indicates that the adventitia is an important component of the arterial wall. Tropoelastin is closely associated with foam cell lesion formation, suggesting a role for this component in atherogenesis as well.

Stretch force on vascular smooth muscle cells enhances oxidation of LDL via superoxide production

Hemodynamic forces on vasculature profoundly influence atherogenesis. We examined the effect of stretch force on the oxidation of low-density lipoprotein (LDL) by rat aortic smooth muscle cells (RASM) and superoxide production. Stretch force was imposed on RASM cultured on deformable dishes by stretching the dishes. Incubation of native LDL with static RASM for 24 h resulted in LDL oxidation as indicated by increases in thiobarbituric acid-reacting substances from 9.5 +/- 2.3 to 24.5 +/- 2.3 nmol malondialdehyde/mg. Stretch force on RASM augmented cell-mediated LDL oxidation to 149.3 +/- 17.1% concomitantly with increase in superoxide production. LDL oxidation was inhibited by superoxide dismutase or depletion of the metal ion in the culture medium, indicating that it was a metal ion-dependent and superoxide-mediated process. The enhancement of LDL oxidation by stretch force was inhibited by diphenyliodonium, indicating the involvement of the NADH/NADPH oxidase system. Our findings suggest that the increased oxidant stress induced by stretch force is one of the potential mechanisms whereby hypertension facilitates atherosclerosis.

Effect of natriuretic peptide family on the oxidized LDL-induced migration of human coronary artery smooth muscle cells

The migration of medial smooth muscle cells (SMCs) into the intima is proposed to be an important process of intimal thickening in atherosclerotic lesions. The present study examined the possible effect of a novel endothelium-derived relaxing peptide, C-type natriuretic peptide (CNP), on oxidized low-density lipoprotein (LDL)-induced migration of cultured human coronary artery SMCs by the Boyden's chamber method. The effect of CNP was compared with that of atrial and brain natriuretic peptides (ANP and BNP, respectively). Oxidized LDL stimulates SMC migration in a concentration-dependent manner between 20 and 200 micrograms/mL. This stimulation was chemotactic in nature but was not chemokinetic. By contrast, native LDL was without significant activity. CNP-22 clearly inhibited SMC migration stimulated with 200 micrograms/mL oxidized LDL in a concentration-dependent manner between 10(-9) and 10(-6) mol/L. ANP-(1-28) and BNP-32 also inhibited oxidized LDL-induced SMC migration at concentrations of 10(-7) and 10(-6) mol/L, but these effects were weaker than the effect of CNP-22. Such inhibition by these natriuretic peptides was paralleled by an increase in the cellular level of cGMP. Oxidized LDL-induced migration was significantly inhibited by a stable analogue of cGMP, 8-bromo-cGMP, or an activator of the cytosolic guanylate cyclase, sodium nitroprusside. These natriuretic peptides did not suppress the cell adhesion either in the absence or presence of oxidized LDL. These data indicate that oxidized LDL stimulates migration of human coronary artery SMCs and that natriuretic peptides, especially CNP, inhibit this stimulated SMC migration, at least in part, through a cGMP-dependent process. Taken together with the finding that oxidized LDL is present in the intima, CNP may play a role as a local antimigration factor during the process of intimal thickening in hypercholesterolemia-induced coronary atherosclerosis.

Relation of a postmortem renal index of hypertension to atherosclerosis in youth. The Pathobiological Determinants of Atherosclerosis in Youth (PDAY) Research Group

In a cooperative multicenter study, Pathobiological Determinants of Atherosclerosis in Youth, of 1164 young men 15 through 34 years of age who died of external causes and were autopsied in forensic laboratories, we measured atherosclerosis of the aorta and the right coronary artery. Using the ratio of intimal thickness to outer diameter of the small renal arteries to predict mean arterial pressure (MAP) during life, we classified the cases as either normotensive (MAP < 110 mm Hg) or hypertensive (MAP > or = 110 mm Hg). By this criterion, the prevalence of hypertension in blacks was 16%; in whites, 12%. Hypertension was associated directly with blood level of glycohemoglobin (an indicator of blood glucose concentration) and with body mass index (BMI) but inversely with thickness of the panniculus adiposus. Among hypertensive compared with normotensive cases, the extent of raised lesions (mainly fibrous plaques) was greater in the aortas of 30- to 34-year-old men and in the right coronary arteries of 25- to 34-year-old men. The prevalence of raised lesions involving 5% or more of the intimal surface was twofold greater in the aortas and right coronary arteries of hypertensive men throughout the 15-to-34-year age span of the study cases. The association of hypertension with raised lesions was not accounted for by adjusting for glycohemoglobin level, BMI, or thickness of the panniculus adiposus. Hypertension is associated with accelerated atherosclerosis in youth.

Hypertensive cerebrovascular disease and the renin-angiotensin system

BACKGROUND

Arterial hypertension is the leading cause of cardiovascular disease and is associated with an increased risk of stroke and heart attack. These complications have been largely attributed to the remodeling of the arterial wall, including accelerated atherosclerosis occurring in hypertensive patients. Although the risk of haemorrhagic stroke seems to be directly related to the level of blood pressure elevation, no such tight relationship has been found between blood pressure levels and atherosclerosis. This observation has led to the concept that a number of genetic, humoral, and cellular factors may be involved in atherogenesis in hypertensive patients.

SUMMARY OF REVIEW

The experimental and clinical evidence concerning the role of the renin-angiotensin system in cardiovascular remodeling and atherogenesis of the cerebrovascular bed as well as the data supporting an association between angiotensin II and thrombotic stroke are examined.

CONCLUSIONS

The contribution of the renin-angiotensin system to the pathogenesis of accelerated carotid artery atherosclerosis and particularly of cerebrovascular disease remains to be definitively proven. However, the bulk of experimental and clinical data are consistent with the hypothesis that the renin-angiotensin system may play a detrimental role.

Dissociation between the antiatherosclerotic effect of trandolapril and suppression of serum and aortic angiotensin-converting enzyme activity in the Watanabe heritable hyperlipidemic rabbit

This study was undertaken to determine whether low doses of the angiotensin-converting enzyme (ACE) inhibitor trandolapril affected atherosclerosis in the Watanabe heritable hyperlipidemic (WHHL) rabbit. Trandolapril (10 micrograms/kg body weight per 48 hours) was begun at 3 months of age and continued for 9 months. The selected dose reduced serum ACE activity but did not influence blood pressure. Both serum and aortic ACE activity were reduced by more than 80% in the trandolapril-treated compared with control WHHL rabbits, similar to the suppression achieved with the 25-fold-higher dose that in our previous studies induced marked inhibition of aortic atherosclerotic lesions in the WHHL rabbit. In contrast to these prior findings, low-dose trandolapril had no effect on aortic surface involvement by atherosclerosis, aortic cholesterol content, or aortic morphology. The data suggest that the antiatherosclerotic action of ACE inhibitors in the WHHL rabbit may not be related directly to arterial enzyme inhibition.

Combined antihypertensive and lipid-lowering therapy in experimental glomerulonephritis

We examined the interrelation between systemic hypertension, hyperlipidemia, and progressive renal injury in experimental glomerulonephritis. Induction of nephrotoxic serum nephritis in Sprague-Dawley rats led to systemic hypertension and hyperlipidemia. Four groups of rats were studied over a 16-week period: (1) untreated nephritic rats; (2) nephritic rats treated with hydralazine, reserpine, and lasix (AH); (3) nephritic rats treated with lovastatin (4 mg/kg) (Lova); and (4) nephritic rats treated with combined antihypertensive/lipid-lowering therapy (AH/Lova). Systolic blood pressure rose progressively in untreated rats (152 +/- 4 mm Hg at 16 weeks). Blood pressure was reduced by antihypertensive therapy (P < .001) (108 +/- 2 mm Hg in the AH group and 111 +/- 3 mm Hg in the AH/Lova group) but remained elevated in animals treated with lovastatin alone (P > .05) (156 +/- 3 mm Hg in the Lova group). Serum cholesterol rose progressively in untreated rats (3.70 +/- 0.85 mmol/L [143 +/- 33 mg/dL] at 16 weeks). The rise in serum cholesterol was prevented by lovastatin therapy (P < .001) (2.22 +/- 0.41 mmol/L [86 +/- 16 mg/dL] in the Lova group and 2.09 +/- 0.52 mmol/L [81 +/- 2 mg/dL] in the AH/Lova group) but not antihypertensive therapy (P > .05) (2.92 +/- 0.65 mmol/L [113 +/- 25 mg/dL] in the AH group). Proteinuria was reduced by antihypertensive therapy (P < .001) and lipid-lowering therapy (P < .05) (16-week values: 1.069 +/- 0.167 g/d in untreated rats, 0.663 +/- 0.164 g/d in the Lova group, 0.392 +/- 0.051 g/d in the AH group, and 0.176 +/- 0.035 g/d in the AH/Lova group).(ABSTRACT TRUNCATED AT 250 WORDS)

X-linked glucose-6-phosphate dehydrogenase (G6PD) and autosomal 6-phosphogluconate dehydrogenase (6PGD) polymorphisms in baboons

Electrophoretic polymorphisms of glucose-6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) were examined in captive colonies of five subspecies of baboons (Papio hamadryas). Phenotype frequencies and family data verified the X-linked inheritance of the G6PD polymorphism. Insufficient family data were available to confirm autosomal inheritance of the 6PGD polymorphism, but the electrophoretic patterns of variant types (putative heterozygotes) suggested the codominant expression of alleles at an autosomal locus. Implications of the G6PD polymorphism are discussed with regard to its utility as a marker system for research on X-chromosome inactivation during baboon development and for studies of clonal cell proliferation and/or cell selection during the development of atherosclerotic lesions in the baboon model.

Beta-blocker effects on 24-h activity in normotensive and renovascular hypertensive baboons

Spontaneous motor activity of normotensive and renovascular hypertensive baboons was measured during oral dosing with the beta-adrenergic antagonists atenolol HCl (2.6 mg/kg/day) and d,l-propranolol HCl (6.8 mg/kg twice daily) in separate studies. Each study administered active drug for 21 consecutive days. Piezoelectric monitors sensitive to movement were worn continuously by the baboons. Propranolol decreased overall 24-h average activity during the third week of dosing in normotensive baboons but not in renovascular hypertensive baboons. The greatest reductions in activity averaged 20% at those times of day corresponding to the second daily drug dose both in normotensive baboons and, at this time of day only, in the majority of hypertensive baboons. Activity decreases reversed to baseline levels when propranolol was discontinued. For atenolol, most normotensive but no hypertensive baboons showed decreases in activity at the time of day corresponding to the daily drug dose.

Albumin transport characteristics of rat aorta in early phase of hypertension

The effects of early-stage hypertension on the macromolecular transport characteristics of the aorta have been investigated in rats 1 week after the ligature of the abdominal aorta between the two renal arteries. The animals were left untreated or treated for 1 week with an angiotensin converting enzyme inhibitor (enalapril, 6 mg/kg per day). Blood pressure of a subgroup of hypertensive rats was acutely lowered to a normal level by injection of enalaprilat (1.5 mg/kg) at the time of the experiment. 131I-Albumin and 125I-albumin were injected 90 minutes and 5 minutes, respectively, before the rats were killed. The transmural distribution of the relative tissue concentrations across the wall was obtained using a serial frozen-section technique. Short-term albumin uptake permitted calculation of apparent endothelial permeability coefficients, and 90-minute uptake was used to estimate the steady-state albumin distribution within the media. The effect of early-stage hypertension on the characteristics of the arterial macromolecular transport depended on the aortic site; the ascending aortic arch appeared not to be affected. In the thoracic and abdominal aorta, the endothelial permeability coefficients increased significantly in hypertensive rats. This increase was not a direct effect of the arterial pressure, since the values were not significantly different when the pressure was acutely normalized. The 90-minute albumin concentration in the media was enhanced in hypertensive rats and returned to the normal value by acutely lowering the blood pressure, indicating that the increase observed in hypertensive rats resulted from a direct effect of pressure, possibly increased pressure-driven convection and/or pressure-induced stretching of the wall. Treatment by angiotensin converting enzyme inhibitor prevented hypertension and protected against its effects in hypertensive animals.

Effects of hypertension and hyperlipidemia on the myocardium and coronary vasculature of the WHHL rabbit

This study was undertaken to study the effects of hyperlipidemia and hypertension on the coronary circulation and on the myocardium of Watanabe heritable hyperlipidemic (WHHL) rabbits. Surgery to induce hypertension by the one-kidney, one-clip technique was performed on the WHHL rabbits at 3 months of age. At 3 and 6 months after surgery, the right and left coronary arteries and the left ventricle and posterior papillary muscle from normotensive and hypertensive animals were assessed. Atherosclerotic involvement was found at the coronary origin in 94% of the arteries evaluated. Lesions were usually confined to the proximal 1-2 mm of the coronary artery. The prevalence of coronary atherosclerosis in the WHHL rabbit was found to be higher than previously reported in rabbits of the same age. Hypertension-induced muscular and vascular changes such as left ventricular hypertrophy, medial thickening of the arteries, and hyaline arteriolosclerosis were found in most of the hypertensive animals. These changes were rarely seen in the normotensive rabbits. Characteristics of ischemia and cell injury such as eosinophilic fibers, fiber vacuolization, and contraction band necrosis were found more often in hypertensive than in normotensive WHHL rabbits. Confluent areas of severe necrosis indicative of myocardial infarction were not found; myocardial damage was diffuse and involved individual cells and small microscopic areas. This model may be valuable in further studies of coronary artery disease and myocardial injury that result from the combination of hypercholesterolemia and hypertension.

Behavioral performance effects of verapamil in normotensive and renovascular hypertensive baboons

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with verapamil. Performances during a five-color simultaneous match-to-sample task were measured for two doses (2.0, and 3.2 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 9% during the lower dose of verapamil, compared to vehicle; choice reaction times were unchanged at the higher dose. At baseline and during vehicle administration, the yellow and white stimuli were the most difficult to discriminate correctly; discrimination of these colors was slightly impaired by the lower, but not the higher dose of verapamil. Verapamil's behavioral effects were not modulated by blood pressure changes since both baboon groups showed equivalent changes in behavioral performance, but only renovascular hypertensive baboons showed blood pressure decreases. Verapamil appears to be an effective hypotensive and does not produce profound psychomotor impairment at clinically used doses during the first weeks of treatment.

Chronic hydrochlorothiazide and verapamil effects on motor activity in hypertensive baboons

Spontaneous motor activity was measured in six baboons during chronic oral dosing with a diuretic (hydrochlorothiazide/triamterene), a calcium channel blocker (verapamil), and a combination of the two drugs. Piezoelectric monitors sensitive to movement were attached to leather collars and were worn continuously by the baboons throughout the protocol. Baboons were made hypertensive during a preexperimental period by either 1) chronic administration of deoxycorticosterone acetate (DOCA)-salt or 2) surgical renal artery stenosis. Total inactive periods/day increased over baseline levels during diuretic alone and increased further during diuretic + verapamil combined. The total number of inactive periods/day returned toward baseline levels in the subsequent conditions of verapamil alone and baseline recovery. Activity levels decreased during combination dosing mainly during morning hours (0700-1100 h). Overall changes in activity occurred in the second week of dosing; this time period was found earlier to maximally decrease blood pressure and to impair behavioral performances.

Effects of chronic aortic coarctation on atherosclerosis and arterial lipid accumulation in the Watanabe hereditary hyperlipidemic (WHHL) rabbit

The effects of high blood pressure on atherosclerosis were examined in the Watanabe heritable hyperlipidemic (WHHL) rabbit. For this purpose, the subdiaphragmatic aorta of rabbits was partially ligated (coarctation) to increase blood pressure. Atherosclerosis was assessed 4 months later by morphometric analyses and quantitation of arterial lipids. Results were compared to control WHHL rabbits with matched plasma triglycerides and cholesterol levels. A marked increase in atherosclerotic lesions was observed in the thoracic aorta of the hypertensive rabbits without qualitative changes in its morphometric features. The cross sectional area of the atherosclerotic plaques of the ascending and descending aorta in the hypertensive rabbits was two- and six-times larger than in normotensive rabbits, respectively. Lesions represented 12.0% +/- 3.5% of the total medial cross sectional area of the descending aorta of normotensive rabbits, versus 45.0% +/- 5.7% in hypertensive rabbits. No lesions were observed downstream of the coarctation in hypertensive rabbits, nor in the normotensive rabbits. Accumulation of cholesterol and choline-containing phospholipids in the descending aorta of hypertensive rabbits was increased 3.2- and 1.5-fold, respectively, when compared to normotensive rabbits. Hypertension did not change the unesterified cholesterol/total cholesterol and sphingomyelin/lecithin + lysolecithin molar ratios. In conclusion, chronic coarctation enhances the atherosclerotic response in WHHL rabbits in the high blood pressure compartment, and reduces the variability of this response.

Lysolecithin actions on vascular smooth muscle cells

Oxidation of low density lipoprotein increases its atherogenic potential. During oxidation there is an extensive conversion of lecithin to lysolecithin. In rat aortic smooth muscle cells, 2-25 micrograms/ml lysolecithin elevated cytosolic calcium concentration up to 560%. Lysolecithin (10-20 micrograms/ml) increased [3H]thymidine incorporation from 15 cpm/mg cell protein (controls) up to 189 cpm/mg cell protein. Lysolecithin (10 micrograms/ml) potentiated the PDGF-induced (50 ng/ml) [3H]thymidine incorporation up to 6.3 times. The results indicate that lysolecithin could induce mechanisms, by which oxidized low density lipoproteins could promote cell growth and thus contribute to atherosclerosis.

Performance of baboons under a repeated acquisition procedure during chronic oral exposure to atenolol and propranolol

Repeated acquisition behavioral performances of normotensive and renovascular hypertensive baboons were tested before, during, and following chronic oral dosing with the beta-adrenergic antagonists atenolol HCl (2.6 mg/kg/day PO), and d,l propranolol HCl (6.8 mg/kg twice daily PO) in separate studies. Each study administered active drug for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Animals pressed five keys in sequence for food reinforcement during daily experimental sessions which consisted of alternating acquisition (new sequence learning) and performance (previously learned) task components. Atenolol increased response latencies during acquisition in comparison to performance components, and during early portions of sessions. Propranolol also increased response latencies during acquisition components in early periods of sessions, but fewer dependent measures were affected, and the magnitude of increases in response latencies was smaller (12% +/- 5 SEM) as compared with atenolol (47% +/- 13). Test doses of phencyclidine HCl (PCP) increased latencies to the same degree as atenolol. PCP markedly reduced accuracy, while atenolol or propranolol did not. Blood pressures remained stable under atenolol, and decreased by approximately 10-15 mmHg under propranolol. No differences between renovascular hypertensive and normotensive baboons were found as a function of drug conditions. Drug effects were not dependent on plasma propranolol concentration.

Hypertension sustains plaque progression despite reduction of hypercholesterolemia

To assess the effect of hypertension on diet-induced coronary artery plaques after a return to a nonatherogenic diet, 10 cynomolgus monkeys were fed an induction regimen containing 2% cholesterol and 25% peanut oil for 6 months and then were subjected to midthoracic aortic coarctation to induce hypertension. The animals were then fed a nonatherogenic "prudent" ration for 6 additional months (hypertension-regression group). Twelve additional monkeys were fed the atherogenic diet for 6 months; six were killed (lesion-induction control group) and six were changed to the prudent diet for 6 additional months without coarctation (normotension-regression control group). At the end of the induction period, cholesterol levels averaged 744 +/- 178 mg/dl for the 22 animals and were similar for the three groups throughout the induction period. For the animals restored to the nonatherogenic diet (hypertension-regression and normotension-regression groups), serum cholesterol levels fell to 486 +/- 252 mg/dl at 1 month, to 341 +/- 162 mg/dl at 2 months, and to 234 +/- 78 mg/dl at 6 months. There was no significant difference between the hypertensive and normotensive animals. Six months after coarctation, blood pressure proximal to the coarctations for the hypertension-regression group ranged from 100/60 to 220/145 mm Hg with a mean of 166/103 +/- 36/28 mm Hg. Cross-sectional area of coronary plaques was somewhat lower for the normotension-regression control group compared with the lesion-induction control group, but the difference was not significant. Plaque area was, however, markedly greater in the hypertension-regression group than in either the lesion-induction or the normotension-regression groups (p less than 0.05 for each) despite progressive reduction in hyperlipidemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral effects of chronic, orally administered diuretic and verapamil in baboons

Behavioral performances of six baboons were tested during chronic oral dosing with diuretic (hydrochlorothiazide/triamterene), a calcium channel blocker (verapamil), and a combination of the two drugs. Reaction times and color matching-to-sample performances as well as physiological measures were obtained in deoxycorticosterone acetate (DOCA)-salt baboons and in renovascular hypertensive baboons. Combined diuretic and verapamil impaired color matching to a small degree in comparison to baseline performance, while drug administered alone had no effect. Weekly systolic and diastolic blood pressures decreased maximally from baseline during the drug combination period, and were accompanied by maximal increases in serum sodium. The largest behavioral impairments during combination dosing were observed for colors that were most difficult to discriminate during baseline. Significant positive correlations were found between systolic blood pressure and color matching accuracy. No differences between the animal hypertension groups were found as a function of drug condition either in physiological or behavioral responses. Only the combination of diuretic and verapamil produced a deleterious effect on color discrimination, which suggests further study of commonly administered drug combination therapies in hypertension.

Atherogenesis, calcium and calcium antagonists

Hypercholesterolemia and arterial hypertension are highly interrelated risk factors of atherosclerosis. Early lesions in nonhuman primates with dietary hypercholesterolemia resemble atherosclerotic lesions demonstrable in the arteries of American children with comparably elevated plasma cholesterol levels. Lesion formation depends upon calcium-regulated cellular processes such as chemotaxis, adhesion, migration, proliferation, lipid uptake and necrosis. Interventions acting on cell calcium uptake including treatment with calcium chelating agents, lanthanum trichloride, and calcium antagonists may retard atherogenesis in fat-fed animals in the absence of hypolipidemic effects. Recent controlled coronary angiographic trials in patients with coronary artery disease suggest that calcium antagonists may retard the progression of coronary atherosclerosis in humans. Large-scale long-term studies are needed to determine the utility of these agents for the treatment of coronary artery disease.

Novel cellular activities for low density lipoprotein in vascular smooth muscle cells

Hyperlipidemia and hypertension play important roles in the pathogenesis of atherosclerosis. To investigate the underlying intracellular mechanisms, we studied the effect of various concentrations of low density lipoprotein from normolipidemic subjects on concentrations of free intracellular calcium, intracellular pH, DNA synthesis, and vascular tone in vascular smooth muscle cells and rings from rat aortas. Low density lipoprotein in the range of 1-15 micrograms/ml induced a dose-dependent increase of concentration of free intracellular calcium and a biphasic change of the intracellular pH. Similar concentrations of low density lipoprotein led to an enhanced DNA synthesis. Furthermore, cumulative addition of 1-15 micrograms/ml low density lipoprotein produced a dose-dependent increase in contractile tension of thoracic aortic rings from rats. The maximal low density lipoprotein-induced contractile response was approximately 70% of that induced by 40 mM KCl. These findings indicate that low concentrations of low density lipoprotein occurring, for example, in the extravascular fluid might contribute to the pathogenesis of cardiovascular diseases by enhancing cell proliferation and vasoconstriction by changing intracellular calcium and intracellular pH.

Behavioral performance effects of nifedipine in normotensive and renovascular hypertensive baboons

Behavioral performances of normotensive and hypertensive adult male baboons were tested before, during, and following chronic oral dosing with nifedipine. Performances during a five-color simultaneous match-to-sample task were measured during three dosing schedules (0.20, 0.68, and 1.14 mg/kg/day) and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14-day baseline and recovery periods, respectively. Choice reaction times increased by 191 ms over baseline at the 0.68 mg/kg dose. Choice reaction times above the 95th percentile (i.e., the slowest reaction times) were the most slowed by nifedipine. Accuracy of color matching was decreased at 0.20 and 0.68 mg/kg by an average range of 2-4%. The yellow and white stimuli were the most difficult to discriminate correctly, and were also the most impaired by nifedipine. Nifedipine's behavioral effects were not modulated by blood pressure changes because daily changes in choice reaction time and systolic blood pressure were not correlated, and hypertensive status did not determine the behavioral effects. Potential sources of nifedipine's behavioral performance effects are discussed, with blood pressure changes excluded as a probable mechanism.

Matching to sample, blood pressure and hormonal effects of chronic enalapril in baboons

Sensory and behavioral performance of three normotensive and one renovascular hypertensive baboon was tested before, during and following chronic oral dosing with the angiotensin converting enzyme (ACE) inhibitor enalapril. Performance measurements during a five-color simultaneous matching to sample task were obtained during enalapril dosing of 0.18 and 0.61 mg/kg/day, and vehicle. Each dose was administered for 21 consecutive days preceded and followed by 14 baseline and recovery periods, respectively. BP from awake animals as well as serum ACE activity were measured. Systolic BPs decreased by a maximum of 6-8% (8 mmHg). ACE activity was decreased in a dose-dependent fashion by 54.01% and 81.63% for 0.18 mg/kg and 0.61 mg/kg doses, respectively. At 0.61 mg/kg, the duration of simple key-press motor behavior increased by 15% in the first week and then progressively returned to baseline levels. Systematic changes in choice reaction times or color discrimination accuracy were not observed. Although the renovascular hypertensive baboon displayed greater hypotension and ACE inhibition, behavioral effects were not significantly different from normotensive baboons. The present study extends to sensory functions the lack of adverse behavioral side-effects of enalapril.

Influence of hypertension on aortic atherosclerosis in the Watanabe rabbit

The effects of one-kidney, one clip Goldblatt hypertension on aortic atherosclerosis have been studied in the Watanabe heritable hyperlipidemic (WHHL) rabbit. Renovascular surgery was performed on WHHL rabbits at 3 months of age, and the rabbits were followed for periods of 3-6 months. Aortic atherosclerosis was assessed by measurement of intimal surface involvement with atherosclerotic lesions, determination of aortic free and ester cholesterol content, and microscopic examination. Systolic blood pressure increased by approximately 40-60 mm Hg in the renovascular surgical group as compared with the sham-operated group, but body weight, heart rate, serum cholesterol, and serum triglyceride were unaffected. Aortic atherosclerosis was increased in the hypertensive rabbits, even after 2-3 months of hypertension. At 3 months after renovascular surgery, the aortic surface area covered by atherosclerotic disease averaged 77 +/- 4.4% in hypertensive as compared with 16 +/- 3.3 in control rabbits. At 6 months after surgery, the values were 62 +/- 8.2% and 30 +/- 5.3% in the hypertensive and control rabbits, respectively. The differences in surface involvement and cholesterol content as a result of hypertension were particularly prominent in the descending thoracic aorta. Atherosclerotic lesions in the descending thoracic and abdominal aortic regions of normotensive WHHL rabbits were localized primarily to the ostia of branch vessels, but in the hypertensive rabbits, the involvement was typically very diffuse. No major differences in the nature of atherosclerotic lesions of comparable size were apparent by light microscopy. The results indicate that hypertension accelerates atherogenesis in the WHHL rabbit and suggest that this model may be valuable for studying the mechanisms by which such acceleration is induced.

Cardiac beta myosin heavy chain diversity in normal and chronically hypertensive baboons

We have identified two distinct beta-myosin heavy chains (MHCs) present in baboon myocardium by electrophoresis in gradient pore gels and by Western blots with anti-MHC MAb. The two beta-MHCs have molecular masses of 210 and 200 kD and share several antigenic determinants including an epitope recognized by a beta-MHC-specific MAb. A fivefold increase in the level of the 200-kD beta-MHC was observed in the hypertrophied left ventricles of baboons with chronic (5.3 +/- 0.7 yr) renal hypertension. A 60% increase (P less than 0.01) in BP and a 100% increase (P less than 0.001) in left ventricular mass to body weight ratio occurred in hypertensive baboons compared with normotensive animals. The Ca2+-activated myosin ATPase activity in hypertrophied left ventricles was decreased by 35% (P less than 0.05) compared with controls. Normal levels of the 200-kD MHC were detected in the right ventricles and intraventricular septa of the hypertensive animals. These data suggest that cardiac MHCs of primates may exist in alternative molecular forms that are indistinguishable by nondenaturing gel electrophoresis and that increased concentration of a second beta-MHC is associated with ventricular hypertrophy (r = 0.55). The functional significance and mechanisms that control the concentration of beta-MHC subspecies remain to be determined.

Growth factor expression in aorta of normotensive and hypertensive rats

Hypertension causes biochemical and morphological changes in the vessel wall by unknown mechanisms. Locally produced substances may have a role in mediating these vascular changes. We have studied the expression of platelet-derived growth factor (PDGF) B chain and PDGF A chain, insulin-like growth factor (IGF)-I and IGF-II, endothelial cell growth factor (ECGF), basic fibroblast growth factor (bFGF), and transforming growth factor-beta (TGF-beta) in aortic tissue from normotensive rats and rats made hypertensive by deoxycorticosterone (DOC)/salt treatment. Using Northern blotting, we found that genes for each of these growth factors were transcriptionally active in the aorta of both normotensive and hypertensive rats. TGF-beta aortic mRNA levels increased up to threefold as a result of DOC/salt hypertension. In contrast, no major changes in the expression of either PDGF chain, IGF-I or II, ECGF, or bFGF were detectable. The results indicate that at least seven genes coding for growth factors that were shown previously to influence growth and function of vascular cells in vitro, are expressed in rat aorta in vivo. These findings support the hypothesis that synthesis and release of growth factors in the arterial wall are involved in autocrine and/or paracrine regulatory mechanisms. In addition, the increased expression of TGF-beta in vivo may have a role in mediating the aortic changes induced by hypertension.

Intimal changes in the aorta of prehypertensive rats

Intimal changes were quantitated in several rat models of arterial hypertension. One kidney-one clip rats drinking water (1K-1C-water), one-kidney rats treated with deoxycorticosterone acetate and drinking 1% NaCl (1K-DOCA-salt), and two-kidney rats drinking 1% NaCl (2K-salt) were studied after 1 to 8 weeks. The thoracic aorta was examined en face and by electron microscopy. Surprisingly, all 2K-salt, most 1K-DOCA-salt (17 out of 19), and two-thirds of 1K-1C-water rats (12 out of 18) had normal arterial pressure at sacrifice. In these normotensive 2K-salt, 1K-1C-water, and 1K-DOCA-salt animals, intimal mononuclear cells (which emigrated from the blood) increased between three- and ninefold. In these same normotensive 1K-1C-water and 1K-DOCA-salt rats, endothelial cell mitoses increased three- to sixfold with a corresponding increase in endothelial cell numbers. In the latter two groups, there was no evidence of endothelial cell denudation or changes in aortic circumference, and the subendothelial space widened mainly with reticular basement membrane presumably synthesized by the endothelium. In normotensive 1K-DOCA-salt rats, most of the endothelial cells were thick and there were several intercellular gaps. Endothelial proliferation, synthesis of macromolecules, and gap formation, as well as increased mononuclear cell emigration, indicate functional changes in mononuclear cells and in endothelial cells. We suggest that the experimental procedures designed to produce hypertension also generate factor(s) which activates mononuclear cells and/or endothelial cells. This cellular activation leads to intimal changes independent of hypertension.

Ventricular/vascular coupling and regional arterial dynamics in the chronically hypertensive baboon: correlation with cardiovascular structural adaptation

Ventricular/vascular coupling dynamics and regional hemodynamics of five hypertensive baboons with concentric left ventricular (LV) hypertrophy (mean arterial pressure +/- SD, 148 +/- 16 mm Hg; LV mass/body weight ratio 3.42 +/- 0.8) were compared with five normotensive controls (mean arterial pressure 89 +/- 3 mm Hg; LV mass/body wt ratio 2.73 +/- 0.5) at different mean arterial pressures. Ventricular/vascular dynamics were assessed by aortic input impedance, pulsatile/total power ratio, effective arterial elastance and compliance from a three-element Windkessel "lumped" model of the circulation. Regional arterial dynamics were assessed by pulse-wave velocities and local reflection coefficients. Systemic arterial compliance was similarly decreased with elevated pressure in both groups but was significantly more reduced for the hypertensive group compared with control animals at control (0.49 +/- 0.16 vs. 0.96 +/- 0.09 ml/mm Hg; p less than 0.05) and acutely lowered arterial pressure (0.62 +/- 0.26 vs. 1.41 +/- 0.24 ml/mm Hg, respectively). Changes in compliance were paralleled by differences in effective arterial elastance derived from cineventriculographic pressure-volume ratios. Regional foot-foot and apparent phase pulse-wave velocities were significantly increased for distal aortic segments of the hypertensive animals during elevated pressures compared with controls (cff, 17.5 +/- 7.5 vs. 8.7 +/- 3.0 m/sec; p less than 0.05). Histology of the aorta revealed significant increases in collagen content (microgram/mg dry wt) from proximal to distal aortic segments (27 +/- 2 vs. 38 +/- 6; p less than 0.005) in hypertensive animals but not in controls (27 +/- 2 vs. 32 +/- 6; NS). With pharmacological normalization of systemic arterial pressures, hypertensive baboons developed aortic wave speeds similar to controls but manifested significantly reduced compliance compared with controls. In contrast, with acute elevations of pressure, systemic arterial aortic compliances were similar for both groups, but distal pulse-wave velocities were significantly increased for hypertensive animals compared with controls. We conclude that measures of ventricular/vascular coupling and arterial dynamics are determined by both the level of arterial pressure and the physical characteristics of the cardiovascular system in chronic systemic hypertension and pressure overload ventricular hypertrophy.

Cigarette smoking, dietary hyperlipidemia, and experimental atherosclerosis in the baboon

In separate experiments, we fed 30 male and 25 female baboons a diet enriched in cholesterol and saturated fat for periods of 3.3 and 2.6 years. Using operant conditioning with water rewards, we trained the animals to puff on smoking machines in a human-like manner. Half of the animals smoked more than 40 cigarettes per day, while the remaining animals (controls) puffed air. Initially, the diet produced twofold (males) and threefold (females) elevations from baseline levels in serum cholesterol concentrations, but over the course of the experiments, the serum cholesterol decreased to 1.5 (males) and 2.0 (females) times baseline levels in both cigarette smokers and controls. Blood carbon monoxide concentration, plasma thiocyanate concentration, and urine cotinine concentration were significantly greater in smokers than in controls. Responses to smoking in males included lymphocytosis, elevated fasting blood glucose concentration, and decreased seminal vesicle weight. In females, hemoglobin and mean corpuscular hemoglobin concentrations were elevated. The extent of atherosclerosis was examined after 2.8 (males) and 1.6 (females) years of smoking. Among males, the extent of lesions in carotid arteries was significantly greater in smokers than in controls, but there were no significant differences in atherosclerosis in the aorta or the brachial, iliac-femoral, or coronary arteries. Among females, there were no significant differences in atherosclerosis between smokers and controls in any artery. These experiments show little effect of 2 to 3 years of cigarette smoke inhalation and concurrent modest elevation of blood carboxyhemoglobin on experimental atherosclerosis in the presence of moderate hyperlipidemia.

Echocardiographic left ventricular mass and function in the hypertensive baboon

Nonhuman primates with chronic systemic hypertension provide an ideal model for studying structural and functional alterations associated with compensatory cardiac hypertrophy. Since noninvasive techniques are useful for the longitudinal evaluation of these animals, we sought to critically asses the M-mode echocardiographic estimation of left ventricular mass in the baboon and to characterize estimates of left ventricular size and function in baboons with chronic renal hypertension. In 23 baboons (12 normotensive, 11 chronic hypertensive), M-mode echocardiography-determined left ventricular mass was 73 +/- 13 (SE) g as compared with the necropsy weight of 69 +/- 11 g (p = NS), and the correlation was excellent (r = 0.94). When 30 chronically hypertensive baboons being observed longitudinally were compared with 10 normotensive control animals studied under identical conditions, several differences were noted in measures derived from echocardiography and high fidelity pressure measurements. Left ventricular systolic pressure was considerably higher in the hypertensive baboons (113 +/- 23 vs 90 +/- 11 mm Hg; p less than 0.001), as was left ventricular mass (148 +/- 60 vs 103 +/- 38 g; p less than 0.03). However, since the ratio of posterior wall thickness to cavity dimension was larger in the hypertensive baboons (0.52 +/- 0.17 vs 0.43 +/- 0.07; p less than 0.05), this concentric hypertrophy maintained values for left ventricular meridional stress at the same level as in the control animals. Despite matched heart rate and left ventricular stress, the rates of change in left ventricular dimensions and wall thickness in systole and diastole were all approximately 25% less in the hypertrophied baboons.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of an unusual lipoprotein similar to human lipoprotein a isolated from the baboon, Papio sp

An unusual lipoprotein was detected and purified from the blood of some members of a large colony of baboons, Papio sp. This lipoprotein was found to be similar to human lipoprotein a in all respects and is therefore termed lipoprotein a. Baboon lipoprotein a had a density of 1.052 g/ml and was located between low- and high-density lipoproteins in a density gradient ultracentrifugation. However, despite its greater density, baboon lipoprotein a was larger than low-density lipoprotein, based on gradient gel electrophoresis and gel filtration. The lipoprotein contained a very large apolipoprotein (apolipoprotein-lipoprotein a) which was found to consist of an apolipoprotein B linked to another protein called apolipoprotein a by a disulfide bridge(s). In all these characteristics, baboon lipoprotein a was similar to human lipoprotein a.