[The effect of aortic coarctation on nitric oxide production by the vascular endothelium]

Nitric oxide is an important regulator of vascular tone. Deficiencies in nitric oxide release have been implicated in hypertension. In the present study we evaluated vascular reactivity to phenylephrine and acetylcholine in isolated aorta ring preparations from sham and aortic coarctation-induced hypertensive rats and nitric oxide release under resting conditions and after stimulation with acetylcholine. Aortic vessels were divided in upper segment and lower segment in relation to the coarctation; both segments were tested for vascular reactivity and nitric oxide release. Phenylephrine produced higher vasoconstriction in upper segments from hypertensive rats compared to sham operated animals. Lower segments in both experimental groups were not significantly different. Relaxation produced by acetylcholine showed a higher EC50 in the upper segments from hypertensive rats; lower segments in both experimental groups were not significantly different. Aortic rings from hypertensive rats had a higher level of nitric oxide release compared to sham operated rats. Lower segments from hypertensive rats released significantly more nitric oxide. These results suggest that shear stress induced nitric oxide release in lower aortic segments from aortic coarctation-induced hypertensive rats.

Hypoplastic aortic arch morphology pertinent to growth after surgical correction of aortic coarctation

BACKGROUND

Whether a hypoplastic transverse arch will grow after successful coarctectomy remains controversial.

METHODS

We studied 15 coarctation specimens with hypoplastic transverse arch. Eight patients were less than 1 month old and 7 were between 1 and 3 months. The diameter and length of the various segments of the aortic arch were measured. The number of elastin lamellae was determined histologically. Collagen density was quantified with a microdensitophotometer. Using immunohistochemistry, we determined alpha-actin-positive smooth muscle cells in the media of the ascending aorta and the hypoplastic transverse arch.

RESULTS

Despite a hypoplastic transverse arch, the ascending and descending aorta grew. The absolute number of elastin lamellae in the hypoplastic transverse arch was low, but when expressed as a ratio versus its diameter, this number was high (p < 0.05). Collagen density showed high absolute values in the descending aorta. In the older group, 4 of 7 showed no staining for alpha-actin in the hypoplastic transverse arch, whereas under 1 month of age, only 2 of 8 cases were negative.

CONCLUSIONS

The hypoplastic transverse arch is characterized by a relatively high number of elastin lamellae. Fewer alpha-actin-positive cells in the hypoplastic transverse arch occur in older specimens, which could indicate a diminished potential growth.

Excessive anaerobic metabolism during exercise after repair of aortic coarctation

OBJECTIVES

To determine whether survivors of surgery for coarctation of the aorta (CoA) have an excessive reliance on anaerobic metabolism during exercise.

BACKGROUND

Patients with peripheral vascular disease cannot increase blood flow to their muscles normally during exercise. Consequently they acquire an early, excessive reliance on anaerobic metabolism and have depression of the ventilatory anaerobic threshold (VAT) and of the slope of the oxygen consumption-work rate relationship (delta VO2/delta WR). We speculated that the capacity to augment blood flow to the lower extremities during exercise may be impaired after CoA surgery and would result in similar metabolic disturbances.

STUDY DESIGN

Progressive exercise tests were performed on 15 patients (ages 19 +/- 7 years; range, 10 to 32) after successful repair of CoA (residual resting gradient, 7.7 +/- 7.1 mm Hg; range, 0 to 18), 15 age- and sex-matched healthy control subjects, and 10 patients (ages 13 +/- 3 years; range, 10 to 20) who had undergone ligation of a patent ductus arteriosus.

RESULTS

The CoA patients' VAT averaged 14.8 +/- 3.8 ml O2/kg per minute versus 19.3 +/- 3.1 ml O2/kg per minute for the control subjects (p < 0.01), and their delta VO2/delta WR averaged 8.2 +/- 1.8 ml/watt compared with 10.1 +/- 1.4 ml/watt for control subjects (p < 0.01). Furthermore, 10 of 15 CoA patients had a VAT of less than 40% of predicted maximal oxygen consumption, and 9 of 16 had a delta VO2/delta WR of less than 8.7 ml O2/watt (generally accepted abnormal values). Patients with patent ductus arteriosus resembled the healthy control subjects with regard to anaerobic metabolism during exercise.

CONCLUSIONS

Patients who have had CoA repairs commonly manifest an excessive reliance on anaerobic metabolism during exercise. This phenomenon may result from persistent blood flow abnormalities across the aortic arch during exercise, which may be present even after apparently successful surgery.

Eflornithine alters changes in vascular responsiveness associated with coarctation hypertension

This study examined the temporal effects of the polyamine synthesis inhibitor eflornithine (alpha-difluoromethylornithine) on vascular responses to KCI, norepinephrine, sodium nitroprusside and acetylcholine in aortic rings from coarctation hypertensive rats. Coarctation hypertension reduced the contractile response of aortic rings to KCI and norepinephrine, increased sensitivity (reduced the EC50 value) to norepinephrine and attenuated relaxation to acetylcholine by 14 days of hypertension. Treatment of coarctation hypertensive rats with eflornithine resulted in a normalization of the contractile intensity to KCI and norepinephrine and relaxations to acetylcholine by 14 days of hypertension. Responses to sodium nitroprusside were similar in all groups at all time points. Hyperresponsiveness to norepinephrine produced by coarctation of the aorta was not affected by eflornithine. These studies indicate that normalization of vascular function can occur in the presence of significantly elevated blood pressure upon chronic administration of eflornithine. This functional normalization correlates with eflornithine-mediated regression of structural abnormalities normally associated with pressure overload hypertension.

Multiple polyamine regulatory pathways control compensatory cardiovascular hypertrophy in coarctation hypertension

While a number of factors may initiate structural alterations within the cardiovascular system in response to hypertension, there are obligate cellular signaling mechanisms, such as the polyamines, through which they must operate. This study examined the effects of polyamine synthesis inhibition using eflornithine, a suicide inhibitor of ornithine decarboxylase on blood pressure, compensatory remodeling of the cardiovascular system, and cardiac and aortic polyamine contents using an aortic coarctation model in rats. Eflornithine treatment failed to reduce carotid arterial blood pressure and actually significantly elevated vascular pressure above and below the coarctation site by 14 days of hypertension. Eflornithine only transiently reduced aortic polyamine content of hypertensive rats while this agent reduced coarctation-induced aortic medial wall thickening and the synthesis/deposition of fibronectin and laminin in the hypertensive aorta. Increases in left ventricular mass and polyamine content were concomitantly reduced in hypertensive rats administered eflornithine. These results suggest that multiple polyamine regulatory pathways may maintain vascular polyamine content in response to aortic coarctation; however de novo polyamine synthesis is essential for select aspects of vascular remodeling, including matrix synthesis. Cardiac tissue, in contrast, may rely principally on de novo polyamine synthesis.

Hypertension increases insulin-like growth factor binding protein-4 mRNA levels in rat aorta

Insulin-like growth factor-I (IGF-I) is an endocrine and autocrine/paracrine growth factor. Recently, we have demonstrated that interrenal aortic coarctation in the rat increases IGF-I mRNA levels in the thoracic aorta, consistent with a role for this mitogen in hypertensive vascular remodeling. The effects of IGF-I are modulated by several IGF binding proteins including IGFBP-3, the main circulating carrier of IGF-I, and IGFBP-4, the main IGF binding protein produced by vascular smooth muscle cells in vitro. To obtain insights into the regulation of IGF-I and more specifically to study potential changes in IGF binding proteins in high-renin hypertension, we studied male Sprague-Dawley rats that had undergone abdominal aortic coarctation. Compared with sham-operated rats, the study rats showed a rapid increase in IGFBP-4 mRNA levels in the hypertensive (thoracic) aorta, reaching a plateau at 3 days (2.5-fold increase) and persisting for at least 14 days. In striking contrast, IGFBP-4 mRNA decreased slightly in the normotensive (abdominal) aorta at 14 days. IGFBP-3 mRNA levels did not change in either vascular bed after coarctation. Study of hepatic tissue indicated that in coarcted rats IGFBP-4 and IGFBP-3 mRNA levels decreased transiently (approximately 50% at 7 days compared with sham). Circulating IGF-I in coarcted animals decreased slightly (P = .08), and Western ligand analysis indicated that circulating levels of IGF binding proteins were not altered.(ABSTRACT TRUNCATED AT 250 WORDS)

Guanine nucleotide-binding proteins in aortic smooth muscle from hypertensive rats

To explore the hypothesis that altered vascular muscle signal transduction may underlie some of the vascular changes observed in hypertensive models, we measured expression of GTP-binding protein (G protein) alpha-subunits, Gs, G(i), and Gq, in aortic muscle of reduced renal mass and sham-operated rats and proximal and distal aortic segments from rats with interrenal aortic coarctation (IR-AC). G protein expression was measured by immunoblot analysis. When we probed aortic muscle membrane with G(i) and Gq alpha-subunit antibodies, we identified 41- and 42-kD immunoreactive proteins, respectively. Three immunoreactive bands specific to Gs alpha-subunit antibody were resolved. Immunoreactive blot densities were compared. In aortic muscle membrane of reduced renal mass rats (blood pressure, 148 +/- 7 mm Hg), we found significantly reduced Gs and G(i) blot densities compared with sham-operated controls (blood pressure, 99 +/- 12 mm Hg). There were no differences in Gq blot densities between reduced renal mass and control rats. Gs and G(i) blot densities were significantly lower in IR-AC proximal aortic segments (carotid pressure, 165 +/- 5 mm Hg) and distal aortic segments (femoral pressure, 121 +/- 4 mm Hg) than in aortas of sham-operated controls. In contrast, Gq expression was significantly increased in the high-pressure proximal aortic segments compared with low-pressure distal aortic segments from IR-AC rats. Thus, altered G protein expression occurs in aortic muscle from nongenetic rat models of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Membrane current changes in left ventricular myocytes isolated from guinea pigs after abdominal aortic coarctation

OBJECTIVE

The aim was to look for membrane current changes as a basis for the prolongation of action potential duration in left ventricular myocytes following abdominal aortic coarctation.

METHODS

Immature female guinea pigs underwent laparotomy and an aortic coarctation was fashioned immediately distal to the renal arteries. After 20 weeks the hearts were removed and single myocytes were isolated from the left ventricles by standard enzymatic techniques. The switch-clamp technique was used.

RESULTS

Heart weight:body weight ratio was increased by 7% in the coarctation group (p < 0.01). Systolic left ventricular pressure was 59(SEM 4) mm Hg in control and 76(7) mm Hg in coarctation animals (p < 0.05). Cell capacity was increased by 21% in the coarctation group (p < 0.05), and mean resting potential was 4.6 mV more negative in this group (p < 0.001). Action potential duration at 90% repolarisation was 310(17) ms in the control group (n = 22) and 358(13) ms in the coarctation group (n = 34, p < 0.05). Peak density of L-type calcium current was -8.6(0.4) pA.pF-1 in control and -11.1(0.7) pA.pF-1 in coarctation cells (p < 0.01). The regression line for calcium current versus cell capacity was shifted to higher calcium currents in the coarctation group. The half inactivation potential for this current was shifted by 11.5 mV (p < 0.01). Calcium-activated tail currents were larger and the envelope of tail currents was prolonged in the coarctation cells. No significant differences were found in the amplitude of IK or of IKl.

CONCLUSIONS

After infrarenal aortic coarctation, action potential duration of left ventricular myocytes is prolonged. This prolongation may be attributed to an increase in calcium current density and a shift of its inactivation variable, together with an increased magnitude and prolonged time course of sodium-calcium exchange current. These current changes are potentially arrhythmogenic.

Decreased perfusion pressure modulates renin and ANG II type 1 receptor gene expression in the rat kidney

To determine whether decreased perfusion pressure affects the abundance and distribution of renin and its mRNA and the expression of the angiotensin II type 1 (AT1) receptor gene within the kidney, adult male Sprague-Dawley rats were subjected to aortic coarctation proximal to the renal arteries (Coarc, n = 8) and compared with sham-operated rats (Sham, n = 6). Renal renin distribution was determined by immunocytochemistry using a specific polyclonal antibody against rat renin. Renin mRNA was assessed by in situ hybridization to a 35S-labeled oligonucleotide complementary to rat renin mRNA. Kidney AT1 mRNA levels were determined by Northern analysis using a 1,133-base pair rat AT1 cDNA. Femoral arterial blood pressure, measured 24 h after surgery, was lower in Coarc than in Sham rats (75 +/- 5.4 vs. 122 +/- 2.3 mmHg, P < 0.05). Aortic coarctation increased the percent of juxtaglomerular apparatuses (%JGA) containing renin and its mRNA (85 +/- 2.5 and 66 +/- 2.8 vs. 49 +/- 5.3 and 36 +/- 1.7%, Coarc vs. Sham, P < 0.05) and the intensity of hybridization signals (497 +/- 89 vs. 71 +/- 12 grains/JGA, Coarc vs. Sham, P < 0.05). In addition, recruitment of renin gene expressing cells was observed along afferent arterioles in Coarc rats, whereas renin and its mRNA were limited to the JGAs in Sham rats. Renal AT1 receptor gene expression was threefold lower in Coarc than in Sham rats. We conclude that reduction of perfusion pressure after abdominal aortic coarctation acutely enhances renin gene expression and downregulates AT1 receptor gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

The vascular smooth muscle alpha-actin gene is reactivated during cardiac hypertrophy provoked by load

Cardiac hypertrophy triggered by mechanical load possesses features in common with growth factor signal transduction. A hemodynamic load provokes rapid expression of the growth factor-inducible nuclear oncogene, c-fos, and certain peptide growth factors specifically stimulate the "fetal" cardiac genes associated with hypertrophy, even in the absence of load. These include the gene encoding vascular smooth muscle alpha-actin, the earliest alpha-actin expressed during cardiac myogenesis; however, it is not known whether reactivation of the smooth muscle alpha-actin gene occurs in ventricular hypertrophy. We therefore investigated myocardial expression of the smooth muscle alpha-actin gene after hemodynamic overload. Smooth muscle alpha-actin mRNA was discernible 24 h after coarctation and was persistently expressed for up to 30 d. In hypertrophied hearts, the prevalence of smooth muscle alpha-actin gene induction was 0.909, versus 0.545 for skeletal muscle alpha-actin (P less than 0.05). Ventricular mass after 2 d or more of aortic constriction was more highly correlated with smooth muscle alpha-actin gene activation (r = 0.852; P = 0.0001) than with skeletal muscle alpha-actin (r = 0.532; P = 0.009); P less than 0.0005 for the difference in the correlation coefficients. Thus, smooth muscle alpha-actin is a molecular marker of the presence and extent of pressure-overload hypertrophy, whose correlation with cardiac growth at least equals that of skeletal alpha-actin. Induction of smooth muscle alpha-actin was delayed and sustained after aortic constriction, whereas the nuclear oncogenes c-jun and junB were expressed rapidly and transiently, providing potential dimerization partners for transcriptional control by c-fos.

Dynamics of shear-induced redistribution of F-actin in endothelial cells in vivo

The steady-state responses of endothelial cell F-actin distribution to changes in in vivo shear stress have been well documented. The purpose of the current work was to define the dynamics of redistribution of F-actin in the period immediately after experimental changes in shear. We used abdominal aortic coarctation in rabbits to experimentally increase shear stress downstream from the coarctation by approximately twofold. In situ staining was employed to track subsequent F-actin redistribution. Within 12-15 hours, the number of stress fibers in the central regions of the cells decreased, and some separation of junctional actin in adjacent cells occurred. Long, central stress fibers of variable thickness were evident at 24 hours, but the band of actin normally seen at the periphery of the cells could no longer be distinguished. The redistribution of F-actin was completed over the next 24 hours by an increase in thickness of central stress fibers. Restoration of normal F-actin distribution after coarctations were removed proceeded more slowly. The long, thick stress fibers that were induced by high shear were replaced by thinner or shorter microfilament bundles 48 hours after the coarctations were removed. At 72 hours, central stress fibers were primarily long, thin structures. Peripheral F-actin was not fully restored at this time. Peripheral F-actin was restored at 1 week after removal of the coarctation, but there were still more and longer stress fibers at this time than were observed in control aortas.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic glutathione-related antioxidant defences in rabbits subjected to suprarenal aortic coarctation hypertension

In seven rabbits subjected to suprarenal aortic coarctation hypertension, the segments above and below the coarctation were tested for the antioxidant defences (i.e. acid-soluble thiol compounds, selenium-dependent and selenium-independent glutathione peroxidase, glutathione reductase, glutathione transferase) and thiobarbituric acid-reactive substances. Seven sham-operated rabbits served as controls. Systolic blood pressure proximal to the ligature increased significantly with respect to pre-operative values after 16 days (117 +/- 8.3 vs 71.7 +/- 5.2 mmHg, P less than 0.05), while pressure distal to the ligature remained normotensive. Higher values of acid-soluble thiol compounds, thiobarbituric acid-reactive substances and increased activities of selenium-dependent glutathione peroxidase, glutathione reductase and glutathione transferase were assayed in the suprarenal with respect to the subrenal segment in both groups. However, the values of the upper segments were more elevated in the experimental group than in controls, but no differences were observed in the lower segments. Glutathione peroxidase activity assayed with cumene hydroperoxide was higher than the activity assayed with hydrogen peroxide in the hypertensive segments, but no differences were detected in the substenotic and control segments. Furthermore, an isoenzymatic form of glutathione transferase, analogous to rat 8-8 glutathione transferase isoenzyme, was detected by immunodiffusion in the hypertensive aorta. The following conclusions may be drawn: (1) a biochemical gradient in glutathione-related enzymes, acid-soluble thiol compounds and thiobarbituric acid-reactive substances between the proximal and distal aorta seems to exist in control rabbits; (2) suprarenal aortic coarctation induces a significant increase in glutathione-related antioxidant defences and thiobarbituric acid-reactive substances of the hypertensive aortic wall.

[The system of cyclic nucleotides during myocardial hyperfunction and hypertrophy in rats of various ages]

Simulation of myocardial hyperfunction and hypertrophy in rats exhibited the age- and hypertrophy step-dependent alterations in the system of cyclic nucleotides. Significant activation of the HC-cGMP system, decrease in content of cAMP and stimulation of the AC activity were detected in old animals at the emergency step. At the later steps content of cAMP and the AC stimulated activity were increased more distinctly in adult rats as compared with old animals. These alterations were responsible for age-related peculiarities of myocardial contractility at the emergency step as well as for development of hypertrophy at the later steps. The cyclase system appears to facilitate the age-related adaptation of myocardium to overloading during the old age.

Localization of cytoplasmic collagen mRNA in human aortic coarctation: mRNA enhancement in high blood pressure-induced intimal and medial thickening

Enhanced synthesis and deposition of extracellular matrix components, including collagen, contribute significantly to arteriosclerotic changes in the arterial vessel wall. We localized cells actively synthesizing collagen by hybridizing 35S-labeled RNA probes complementary to type I and III collagen mRNA with cytoplasmic mRNA in frozen sections of surgically removed aortic coarctations. These were chosen as a model for comparing mRNA levels in areas of high blood pressure-induced wall thickening and in unaffected post-stenotic areas. In situ hybridization revealed increased expression of type I and III collagen mRNA in intimal cells and in cells adjacent to the medial-adventitial border in the pre-stenotic part of the coarctation. In contrast, cells of the post-stenotic area showed only a very low signal. No immunohistologically detectable macrophages were seen in the pre-stenotic subendothelial areas where mRNA levels were enhanced. Higher collagen mRNA levels therefore occur in particular regions of high blood pressure-induced arterial wall thickening in the absence of macrophages. The results suggest that in situ hybridization is suitable for detection of locally occurring transcriptional activation of cells for collagens in the vessel wall.

[The lipid and phospholipid composition of the myocardium in hyperfunction caused by aortic coarctation]

It is shown that in the first 10-12 days of heart hyperfunction caused by subdiaphragmatic constriction of the aorta adaptational changes in lipid metabolism develop in the myocardium in addition to its hypertrophy. These changes are capable of leading to reduced viscosity of the myocardial membranes and activation of enzymatic processes providing for the intensified work of the heart.

Atrial natriuretic peptide and its messenger ribonucleic acid in overloaded and overload-released ventricles of rat

To study the occurrence of atrial natriuretic peptide (ANP) in overloaded ventricles, suprarenal aortic coarctation was performed on adult rats (n = 60) to induce overloaded left ventricle. In 36 rats, the overloads were released in 2 weeks. The hearts (6 rats in each group) were examined 2, 7, and 14 days after overload and 2, 7, 19, 47, and 77 days after overload release. Another group of 6 rats was coarctated for the second time for 1-6 days after 14 days of coarctation and 7 days of release. ANP immunoreactivity was examined by light and electron microscopic immunocytochemistry. ANP mRNA was studied by RNA-RNA tissue in situ hybridization. ANP immunoreactivity and ANP mRNA were found in the left ventricle 2 days after coarctation, and their amounts increased in proportion to the intraventricular pressure and the duration of coarctation. Two days after release, ANP and its mRNA began to decrease, but at 77 days ANP-containing granules still existed in the ventricular myocytes, whereas its mRNA became undetectable. The second coarctation triggered the release of the remaining ventricular ANP from the first overload and induced another cycle of increased ANP synthesis. Specific granules that do not contain ANP were found in overload-released ventricles, indicating the possible existence of other peptide hormones. These findings suggest that the extents of ventricular ANP gene expression and ANP synthesis and release are regulated by intraventricular pressure, and the occurrence of ANP in overloaded ventricles may not be a transient, immediately reversible phenomenon.

Aortic hypertrophy and "waterlogging" in the development of coarctation hypertension

To study the mechanisms and roles of vascular structural changes during the development of hypertension, we coarcted or sham-coarcted the abdominal aorta of rats. At intervals of 3 to 56 days later, we obtained standardized segments of thoracic and abdominal aortas for measurement of dry weight, water content, and amino acid content. Carotid arterial pressure was elevated by day 5 in coarcted rats and remained elevated. Femoral and tail arterial pressures remained normal. Cardiac ventricular weight and dry weight of the thoracic aorta, normalized for body weight, rose rapidly over 3-10 days in coarcted rats, remaining constant at 50-60% above levels in sham-coarcted rats thereafter. In contrast, water content of thoracic aorta in coarcted rats peaked at 123% of control values on day 7 (p less than 0.001), falling rapidly thereafter to levels about half of peak. Increments in dry weight and water content of the normotensive abdominal aortic segments were of far lesser magnitude and occurred 1 to 2 weeks later, probably reflecting the effects of initial hypotension of the hindquarters. Percent hydroxyproline of intima-media segments of the thoracic aorta remained normal during the 8-week period, indicating that increases in aortic dry weight did not represent disproportional fibrosis and thus are attributable to muscular hypertrophy. These results provide support for the hypothesis that arterial wall "waterlogging" is primarily an early manifestation of the hypertensive process. The greatest magnitude of waterlogging coincides with the rapid early increase in aortic dry weight, representing hypertrophy, which suggests common mechanisms, such as activation of Na+-H+ antiport.

Atrial natriuretic factor gene expression in rat ventricle during experimental hypertension

Activation of atrial natriuretic factor (ANF) gene expression has been reported in the rat ventricle in several models of hemodynamic overload, including hypertension. However, nothing is known about the potential trigger(s) and the time course of this activation during the development of hypertension. We measured aortic blood pressure, left ventricular hypertrophy (LVH), and left ventricular ANF mRNA concentration (LV ANF mRNA) in a first group of rats (study A) killed at 5 and 18 h and 2, 4, 6, 9, 15, and 30 days after suprarenal coarctation of the abdominal aorta. Coarctation induced a progressive rise in aortic blood pressure and left ventricular mass. We observed a biphasic accumulation of ANF mRNA in the left ventricle with a peak at day 4 averaging 20 times the control value long before stable hypertension and hypertrophy were achieved, followed by a decrease until day 9. This decrease was followed by a new rise, which stabilized around 10 times the control value seen during stable hypertension and hypertrophy. In a second group of rats killed at days 4 and 30 (study B), we determined, in addition to the previous parameters, left ventricular end-diastolic pressure (LVEDP), plasma renin (PRC), and plasma ANF concentrations. LVEDP and PRC were markedly increased at day 4, but at day 30, during stable hypertension and hypertrophy, these parameters returned to control values, whereas plasma ANF was increased. Using immunocytochemistry, we looked in a third group of rats (study C) for the presence of the immunoreactive peptide at days 4 and 30.(ABSTRACT TRUNCATED AT 250 WORDS)

Exaggerated renal thromboxane and prostaglandin release by angiotensin II in suprarenal aortic coarctation hypertension

The ability of angiotensin II and arachidonic acid to release immunoreactive prostaglandins into venous and ureteral effluents of rabbit isolated perfused kidneys was examined 7 days after suprarenal aortic coarctation (SRAC) or sham operation (SHAM). Renal vascular responses to angiotensin II were significantly enhanced in SRAC and accompanied by an enhanced venous efflux of bioassayable prostaglandins. Angiotension II-induced release of immunoreactive PGE2, PGF2 alpha, 6-keto PGF1 alpha and TxB2 into the venous effluent was exaggerated in SRAC. As angiotensin II did not stimulate TxB2 efflux in the SHAM group the induction of TxB2 release by SRAC is particularly noteworthy. These changes in eicosanoid release in response to angiotensin II were not mimicked by arachidonic acid administration. These results suggest that in renovascular hypertension angiotensin II-induced prostaglandin release is primarily augmented in the vascular compartment and is consistent with the sensitivity of renal function to cyclooxygenase inhibitors in renovascular hypertension.

Direct correlation between calcium content and blood pressure: a study of aortic coarctation in rats

The calcium content of aorta was measured by atomic absorption after coarctation in the rat. At 7 and 14 days, the calcium content was elevated on the proximal side of the coarctation, where pressure was increased significantly. On the distal, low pressure side of the aortic coarctation, calcium was reduced significantly. There is a direct correlation between the blood pressure and the content of calcium (r = 0.69, P less than 0.001). The width of the aortic media on the high pressure side was increased significantly at 7 and 14 days after coarctation, whereas no significant changes in width were present on the low pressure side of the constriction. We conclude that pressure regulates the aortic calcium content, likely acting through a local effect.

Aortic wall metabolism in relation to susceptibility and resistance to experimental atherosclerosis

Different segments of the aorta and its branches show differing susceptibilities to atherosclerosis. To identify metabolic features that may account for plaque formation and sparing, we studied aortic wall respiration and glycolysis proximal and distal to an aortic coarctation in 30 rabbits fed a standard or atherogenic diet. Three months after coarctation, blood pressure in the proximal aorta was elevated, and plaque occupied 98% +/- 28% of the intimal surface compared with 57% +/- 26% for control animals (p less than 0.05). Aortic pressure distal to the stenosis remained normal, but plaque formation was markedly decreased (5% +/- 4%) compared with controls (30% +/- 27%, p less than 0.05). Metabolic studies included measurement of oxygen consumption of proximal and distal aortic walls, lactic acid production, and 2-deoxyglucose uptake. Elevated pressure or hyperlipidemia increased respiration (22.6 +/- 4.0 or 16.3 +/- 6.0 pmol oxygen consumed/min/microgram deoxyribonucleic acid [DNA] vs 5.8 +/- 5.2 for controls; p values less than 0.05) without increasing glycolytic metabolism. The coexistence of hypertension and hyperlipidemia resulted in maximal plaque formation and a sevenfold increase in both oxidative metabolism (46.6 +/- 27.2 pmol oxygen consumed/min/microgram DNA vs 5.8 +/- 5.2 for controls, p less than 0.004) and glycolytic metabolism (44 +/- 10 ng lactic acid produced/90 min/microgram DNA vs 6 +/- 3 for controls, p less than 0.004). In the spared aortic segment distal to coarctation, glycolytic metabolism was increased (10 +/- 8 ng lactic acid produced/90 min/microgram DNA vs 2 +/- 1 for controls, p less than 0.05) but oxidative metabolism remained normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial beta-receptors in experimental renal and aortic coarctation hypertensive rabbits

We investigated the effect of inducing two-kidney, one clip (2K, 1C) and aortic coarctation (AC) hypertension in rabbits, on myocardial beta-adrenoreceptor number and affinity, using 3H-dihydroalprenolol as a beta-ligand. Six weeks after surgery, mean arterial blood pressures were: sham-operated controls C, 75.6 +/- 2.3 mmHg (n = 11); 2K-1C 96.3 +/- 2.5 mmHg (n = 6, P less than 0.005); and AC, 114.1 +/- 4.8 mmHg (n = 10, P less than 0.0005). Bmax values at six weeks for C, 2K,-1C and AC were 234.5 +/- 35.7, 139.0 +/- 10.3 (P less than 0.05) and 121.0 +/- 12.8 (P less than 0.005) fmol/mg protein respectively. There were no differences in KD. Both 2K, 1C and AC hypertension significantly decreased myocardial beta-receptor density; this may be a 'down-regulatory' response to increased circulating or myocardial catecholamine concentrations or to enhanced sympathetic activity.

Muscle substrate levels, muscle enzyme activities and muscle morphology in the vastus lateralis and deltoideus muscles in normal children and in children with coarctation of the aorta

Muscle biopsies from the deltoideus dx and vastus lat. dx muscles were taken in 17 children with coarctation of the aorta, aged 5.0 to 13.8 years, prior to surgery. Higher concentrations of glycogen, ATP and CP were found in the vastus lat. muscle compared to the deltoideus muscle. The same differences between these two muscles were also found in healthy controls. No differences were found between the patients with coarctation of the aorta and the control group. Nor were any differences found for the other variables studied; glucose, glucose-6-phosphate, lactate, muscle enzyme activities (SDH, LDH and phosphorylase), muscle fibre composition or fibre sizes. It seems reasonable to assume that the differences in muscle substrate levels found between the vasus lat. and the deltoideus muscles in the two groups were due to a higher degree of activity during daily life for the legs as compared to the arms. Patients with coarctation of the aorta do not seem to be influenced by the altered haemodynamic situation with regard to the studied variables.