From the Outside In: Biological Mechanisms Linking Social and Environmental Exposures to Chronic Disease and to Health Disparities

The ongoing epidemic of chronic diseases involves a spectrum of clinical entities now understood to represent late manifestations of progressive metabolic dysfunction initiated in early life. These diseases disproportionately affect disadvantaged populations, exacerbating health disparities that persist despite public health efforts. Excessive exposure to stressful psychosocial and environmental forces is 1 factor known to contribute to population-level disparities in at-risk settings. Yet increasing evidence reveals that even a single adverse environmental exposure-especially during very early developmental years-can become literally biologically embedded, inducing long-lasting disease-promoting pathways that amplify responses (e.g., cortisol, immune, inflammatory) to all future adverse stressors, thus enhancing their disease-promoting impacts. The same pathways may also interact with ancestrally linked genetic variants to modify chronic disease risk. We address how, in at-risk populations, environmentally activated disease-promoting pathways can contribute to a biologically based disease-susceptible phenotype; this is likely to be uniquely damaging in populations with multiple adverse exposures and is capable of cross-generational transmission. Intended to complement existing models, this biological perspective highlights key research opportunities and life-stage priorities with potential to enhance the reduction of health disparities.

Altered vertebral and femoral bone structure in juvenile offspring of microswine subject to maternal low protein nutritional challenge

Epidemiological studies suggest skeletal growth is programmed during intrauterine and early postnatal life. We hypothesize that bone development may be altered by maternal diet and have investigated this using a microswine model of maternal protein restriction (MPR). Mothers were fed a control diet (14% protein) or isocaloric low (1%) protein diet during late pregnancy and for 2 weeks postnatally. Offspring were weaned at 4 weeks of age to ad lib or calorie-restricted food intake groups. Femur and vertebra were analysed by micro computed tomography in offspring 3-5 months of age. Caloric restriction from 4 weeks of age, designed to prevent catch-up growth, showed no significant effects on bone structure in the offspring from either maternal dietary group. A maternal low protein diet altered trabecular number in the proximal femur and vertebra in juvenile offspring. Cortical bone was unaffected. These results further support the need to understand the key role of the nutritional environment in early development on programming of skeletal development and consequences in later life.

Effects of postweaning calorie restriction on accelerated growth and adiponectin in nutritionally programmed microswine offspring

Poor prenatal development, followed by rapid childhood growth, conveys greater cardiometabolic risk in later life. Microswine offspring exposed to perinatal maternal protein restriction [MPR; "low protein offspring" (LPO)] grow poorly in late-fetal/neonatal stages. After weaning to an ad libitum (AL) diet, LPO-AL exhibit accelerated growth and fat deposition rates with low adiponectin mRNA, despite low-normal body fat and small intra-abdominal adipocytes. We examined effects of caloric restriction (CR) on growth and metabolic status in LPO and normal protein offspring (NPO) randomized to AL or CR diets from weaning. CR transiently reduced growth in both LPO and NPO, delaying recovery in female LPO-CR. Over 7.5-12.5 weeks, linear growth rates in LPO-CR were slower than LPO-AL ( P < 0.001) but exceeded NPO-AL; body weight growth rates fell but were lower in LPO-CR versus NPO-CR. Linear acceleration ceased after 12 weeks. At 16 weeks, percent catch-up in LPO-CR was reduced versus LPO-AL ( P < 0.001). Plasma growth hormone was low in LPO ( P < 0.02). CR normalized fat deposition rate, yet adiponectin mRNA remained low in LPO-CR ( P < 0.001); plasma adiponectin was low in all LPO-AL and in female LPO-CR. Insulin sensitivity improved during CR. We conclude that in LPO: 1) CR delays onset of, but does not abolish, accelerated linear growth, despite low growth hormone; 2) CR yields stunting via delayed onset, plus a finite window for linear growth acceleration; 3) MPR lowers adiponectin mRNA independently of growth, adiposity, or adipocyte size; and 4) MPR reduces circulating adiponectin in LPO-AL and female LPO-CR, potentially enhancing cardiometabolic risk.

Cardiovascular and systemic microvascular effects of anti-vascular endothelial growth factor therapy for cancer

OBJECTIVES

This study sought to evaluate the contribution of microvascular functional rarefaction and changes in vascular mechanical properties to the development of hypertension and secondary ventricular remodeling that occurs with anti-vascular endothelial growth factor (VEGF) therapy.

BACKGROUND

Hypertension is a common side effect of VEGF inhibitors used in cancer medicine.

METHODS

Mice were treated for 5 weeks with an anti-murine VEGF-A monoclonal antibody, antibody plus ramipril, or sham treatment. Microvascular blood flow (MBF) and blood volume (MBV) were quantified by contrast-enhanced ultrasound in skeletal muscle, left ventricle (LV), and kidney. Echocardiography and invasive hemodynamics were used to assess ventricular function, dimensions and vascular mechanical properties.

RESULTS

Ambulatory blood pressure increased gradually over the first 3 weeks of anti-VEGF therapy. Compared with controls, anti-VEGF-treated mice had similar aortic elastic modulus and histological appearance, but a marked increase in arterial elastance, indicating increased afterload, and elevated plasma angiotensin II. Increased afterload in treated mice led to concentric LV remodeling and reduced stroke volume without impaired LV contractility determined by LV peak change in pressure over time (dp/dt) and the end-systolic dimension-pressure relation. Anti-VEGF therapy did not alter MBF or MBV in skeletal muscle, myocardium, or kidney; but did produce cortical mesangial glomerulosclerosis. Ramipril therapy almost entirely prevented the adverse hemodynamic effects, increased afterload, and LV remodeling in anti-VEGF-treated mice.

CONCLUSIONS

Neither reduced functional microvascular density nor major alterations in arterial mechanical properties are primary causes of hypertension during anti-VEGF therapy. Inhibition of VEGF leads to an afterload mismatch state, increased angiotensin II, and LV remodeling, which are all ameliorated by angiotensin-converting enzyme inhibition.

p21 is decreased in polycystic kidney disease and leads to increased epithelial cell cycle progression: roscovitine augments p21 levels

Background

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease with few treatment options other than renal replacement therapy. p21, a cyclin kinase inhibitor which has pleiotropic effects on the cell cycle, in many cases acts to suppress cell cycle progression and to prevent apoptosis. Because defects in cell cycle arrest and apoptosis of renal tubular epithelial cells occur in PKD, and in light of earlier reports that polycystin-1 upregulates p21 and that the cyclin-dependent kinase inhibitor roscovitine arrests progression in a mouse model, we asked whether (1) p21 deficiency might underlie ADPKD and (2) the mechanism of the salutary roscovitine effect on PKD involves p21.

Methods

p21 levels in human and animal tissue samples as well as cell lines were examined by immunoblotting and/or immunohistochemisty. Apoptosis was assessed by PARP cleavage. p21 expression was attenuated in a renal tubular epithelial cell line by antisense methods, and proliferation in response to p21 attenuation and to roscovitine was assessed by the MTT assay.

Results

We show that p21 is decreased in human as well as a non-transgenic rat model of ADPKD. In addition, hepatocyte growth factor, which induces transition from a cystic to a tubular phenotype, increases p21 levels. Furthermore, attenuation of p21 results in augmentation of cell cycle transit in vitro. Thus, levels of p21 are inversely correlated with renal tubular epithelial cell proliferation. Roscovitine, which has been shown to arrest progression in a murine model of PKD, increases p21 levels and decreases renal tubular epithelial cell proliferation, with no affect on apoptosis.

Conclusion

The novelty of our study is the demonstration in vivo in humans and rat models of a decrement of p21 in cystic kidneys as compared to non-cystic kidneys. Validation of a potential pathogenetic model of increased cyst formation due to enhanced epithelial proliferation and apoptosis mediated by p21 suggests a mechanism for the salutary effect of roscovitine in ADPKD and supports further investigation of p21 as a target for future therapy.

Diabetic nephropathy and proximal tubule ROS: challenging our glomerulocentricity

Diabetic nephropathy is currently viewed as a predominantly glomerular process with glomerular injury driving secondary tubular loss. Brezniceanu and colleagues apply transgenic methods to support a prominent role for reactive oxygen species as mediators and for the proximal tubule as a major site of early disease activity in diabetes. Results support evidence for early tubular apoptosis and atrophy in human diabetic nephropathy.

Maternal nutrition, low nephron number, and hypertension in later life: pathways of nutritional programming

A large body of epidemiologic literature supports an inverse relation between birth weight and both systolic blood pressure and prevalence of hypertension, but mechanisms through which lower birth weight increases risk for hypertension are not established. This article advances the view that 1) permanently reduced nephron number is essential but not alone sufficient to mediate nutritionally induced hypertension; and 2) fetally programmed propensity for increased appetite and accelerated postnatal growth, thus generating inappropriately increased body mass, is a necessary "second hit" to actualize hypertension vulnerability. Based on decades of nephrologic research, this increased ratio of body mass (excretory load) to nephron number (excretory capacity) induces intrarenal compensations (tubular and glomerular hypertrophy with single-nephron hyperfiltration and intrarenal renin-angiotensin II activation), which maintain normal glomerular filtration rate at the expense of systemic and glomerular hypertension and at the risk of progressive renal disease. The vigor of the intrarenal compensatory responses is markedly greater in the immature than in the mature kidney, potentially explaining the greater risk of nephron deficits being present early in life as compared with the minimal risk in adult kidney donors. Effective interventions have not yet been defined. Suboptimal maternal nutrition, pervasive in both developed and developing countries, offers a window of opportunity to enhance the cardiovascular and renal health of future generations.

Mechanisms of Disease: in utero programming in the pathogenesis of hypertension

Nutritional and other environmental cues during development can permanently alter the structure, homeostatic systems, and functions of the body. This phenomenon has been referred to as 'programming'. Epidemiological and animal studies show that programmed effects operate within the normal range of growth and development, and influence the risk of chronic disease in adult life. We review the evidence that these effects include reduced nephron number and compensatory adaptations, which might lead to hypertension, and perhaps accelerate the decline in renal function that accompanies aging. These processes might be exacerbated by programmed changes in vascular structure and function, and alterations in endocrine and metabolic homeostasis. Programmed effects might be initiated as early as the periconceptual phase of development, and could involve epigenetic changes in gene expression or altered stem cell allocation. Better understanding of these processes could lead to the development of novel diagnostic and preventive measures, and to early detection of at-risk individuals. By monitoring blood pressure, weight, and renal function in children, it might be possible to reduce the risk of cardiovascular and renal disease in later life.

Developmental antecedents of cardiovascular disease: a historical perspective

Knowledge of the fetal antecedents of cardiovascular disease has increased rapidly since the association between low birth weight and the disease was demonstrated 20 yr ago. It now is known that individuals who had low birth weight or who were thin or short at birth are at increased risk for both cardiovascular disease and type 2 diabetes. This has been shown in studies in different countries and cannot be explained by confounding variables. Through clinical and animal studies, the biologic processes that underlie the epidemiologic associations and how their effects are modified by postnatal growth and by living conditions in childhood and adult life are beginning to be understood. One such process is altered renal development, with reduced nephron numbers, which may initiate hypertension.

Chymase-like Angiotensin II-Generating Activity in End-Stage Human Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by exuberant inflammation and fibrosis, a process believed to contribute to progressive loss of normal renal function. Despite early-onset hypertension and intrarenal renin/angiotensin II (AngII) activation, angiotensin-converting enzyme (ACE) inhibition does not consistently confer renal protection in ADPKD. The hypothesis was that mast cells within the inflammatory interstitium release chymase, an enzyme capable of efficient conversion of AngI to AngII, providing an ACE-independent route of AngII generation. End-stage ADPKD renal tissue extracts and cyst fluids were assayed for time-dependent, chymostatin-inhibitable conversion of (125)I-AngI to (125)I-AngII under conditions of ACE and aminopeptidase inhibition by means of HPLC. Thirteen of 14 ADPKD kidney extracts exhibited chymase-like AngII-generating capacity; calculated initial reaction rates averaged 3.9 +/- 2.9 fmol AngII/min/ micro g protein with a mean maximal conversion of 55% +/- 30% of added substrate. AngII-generating activity was both protein and substrate dependent. All five cyst fluid samples were negative. Chymase-like activity was detectable in only three of six non-ADPKD kidney extracts. Immunoreactive chymase protein was present in/around mast cells within the fibrotic renal interstitium in all samples. Findings demonstrate for the first time the presence of mast cells, mast cell-associated immunoreactive chymase protein, and chymase-like AngII generating capacity in ADPKD cystic kidneys. Results support the potential for ACE-independent AngII generation and for mast cell-initiated inflammatory processes in ADPKD, each with therapeutic implications for ADPKD renal progression.

ANG II AT(1) and AT(2) receptors in developing kidney of normal microswine

To identify an appropriate model of human renin-angiotensin system (RAS) involvement in fetal origins of adult disease, we quantitated renal ANG II AT(1) and AT(2) receptors (AT1R and AT2R, respectively) in fetal (90-day gestation, n = 14), neonatal (3-wk, n = 5), and adult (6-mo, n = 8) microswine by autoradiography ((125)I-labeled [Sar(1)Ile(8)]ANG II+cold CGP-42112 for AT1R, (125)I-CGP-42112 for AT2R) and by whole kidney radioligand binding. The developmental pattern of renal AT1R in microswine, like many species, exhibited a 10-fold increase postnatally (P < 0.001), with maximal postnatal density in glomeruli and lower density AT1R in extraglomerular cortical and outer medullary sites. With aging, postnatal AT1R glomerular profiles increased in size (P < 0.001) and fractional area occupied (P < 0.04), with no change in the number per unit area. Cortical levels of AT2R by autoradiography fell with age from congruent with 5,000 fmol/g in fetal kidneys to congruent with 60 and 20% of fetal levels in neonatal and adult cortex, respectively (P < 0.0001). The pattern of AT2R binding in postnatal pig kidney mimicked that described in human and simian, but not rodent, species: dense AT2R confined to discrete cortical structures, including pre- and juxtaglomerular, but not intraglomerular, vasculature. Our results provide a quantitative assessment of ANG II receptors in developing pig kidney and document the concordance of pigs and primates in developmental regulation of renal AT1R and AT2R.

Angiotensin II type 1 and 2 receptors in conduit arteries of normal developing microswine

OBJECTIVE

To identify vascular cells capable of responding to angiotensin II (Ang II) generated in conduit arteries, we examined the Ang II type 1 receptor (AT1R) and Ang II type 2 receptor (AT2R) in the thoracic aorta (TA) and abdominal aorta (AA) and branches in 90-day fetal, 3-week postnatal, and 6-month adult microswine.

METHODS AND RESULTS

By autoradiography ((125)I-[Sar(1)Ile(8)]-Ang II with or without AT1R- or AT2R-selective analogues or (125)I-CGP 42112), there were striking rostrocaudal differences in (1) AT2R binding at all ages (prominent in AA wall and branches, sparse in TA wall and branches) and (2) a non-AT2R binding site for CGP 42112 (consistently evident in postnatal TA and branches but absent in AA and branches). Furthermore, patterns of AT2R distribution in infradiaphragmatic arteries were developmentally distinct. In fetal AAs, high-density AT2Rs occupied the inner 60% of the medial-endothelial wall. In postnatal AAs, AT2Rs were sparse in the medial-endothelial wall but prominent in a circumferential smooth muscle alpha-actin-negative cell layer at the medial-adventitial border, occupying approximately 20% to 25% of the AA cross-sectional area. AT1R density in the TA and AA medial-endothelial wall increased with age, whereas AT2R density decreased after birth.

CONCLUSIONS

A novel AT2R-positive cell layer confined to postnatal infradiaphragmatic arteries physically links adventitial and medial layers, appears optimally positioned to transduce AT2R-dependent functions of local Ang II, and suggests that adventitial Ang II may elicit regionally distinct vascular responses.

A crossover study of gabapentin in treatment of restless legs syndrome among hemodialysis patients

Restless legs syndrome (RLS) is a common entity affecting hemodialysis patients. Although the cause of RLS remains unclear, a number of therapies have been used successfully to treat the disorder. Gabapentin is an anticonvulsant shown to alleviate symptoms of RLS in two small studies of nonhemodialysis patients. Because it is excreted renally, gabapentin has a long half-life among hemodialysis patients and may be advantageous if proven effective. We conducted a randomized, double-blind, placebo-crossover study of gabapentin in the treatment of RLS among a population of hemodialysis patients. Sixteen patients identified with RLS were randomized to either gabapentin or placebo. After 6 weeks of treatment with 200 to 300 mg of gabapentin after each hemodialysis session, patients' RLS was reassessed. After a 1-week washout period, patients were switched from gabapentin to placebo or placebo to gabapentin. After another 6 weeks, patients' RLS was assessed again. Patient data were analyzed using both parametric and nonparametric means. Thirteen of the 16 original patients completed the study. Two patients dropped out because of lethargy (believed to be secondary to gabapentin), and 1 patient died secondary to myocardial infarction. Eleven patients responded to gabapentin, but not placebo (P < 0.01). One patient responded to both, and 1 patient responded to placebo, but not gabapentin. Gabapentin is an effective treatment for RLS in hemodialysis patients.

Accuracy of an automated blood pressure device in stable inpatients: optimum vs routine use

BACKGROUND

Despite widespread use of the automated blood pressure (BP) device (IVAC model 4200, IVAC Corporation, San Diego, Calif), there is little formal validation in the literature on its accuracy.

OBJECTIVE

To assess the accuracy of the IVAC 4200 device, both under standardized conditions and as routinely used by ward staff, compared with the true indirect BP measured by mercury manometer (MM).

METHODS

One hundred forty-five stable inpatients were randomly selected for BP measurements by 3 randomly ordered protocols: (1) MM performed by certified investigators, (2) IVAC 4200 BP performed by trained investigators (research automated [RA]), and (3) IVAC 4200 BP performed by ward personnel (ward automated [WA]).

RESULTS

For RA compared with MM ("true" indirect BP), 59% of systolic and 54% of diastolic readings were within 5 mm Hg and 83% of systolic and 86% of diastolic were within 10 mm Hg for a British Hypertension Society grade C for both. For WA compared with MM, 40% of systolic and 50% of diastolic readings were within 5 mm Hg and 70% of systolic and 80% of diastolic readings were within 10 mm Hg for British Hypertension Society grades D and C, respectively. The presence of arrhythmias and/or low K5 values (fifth phase of Korotkoff sounds <30 mm Hg) significantly increased the inaccuracy for diastolic values. Inappropriate cuff selection significantly increased inaccuracy of systolic BP (WA vs MM).

CONCLUSIONS

The IVAC 4200 yields substandard estimates of systolic and diastolic BP even under standardized, thus optimum conditions. The presence of arrhythmias or low K5 values and the selection of inappropriate cuff size by the ward staff also contributed to inaccuracy.

Proliferative synergy of ANG II and EGF in porcine aortic vascular smooth muscle cells

To test growth effects of angiotensin II (ANG II) in porcine vascular smooth muscle cells (VSMC) and potential ANG II synergy with epidermal growth factor (EGF), we exposed subconfluent, near-quiescent porcine aortic VSMC to ANG II, EGF, or ANG II + EGF (each 10(-9) M) in Dulbecco's modified Eagle's-Ham's F-12 medium with insulin + 0.4% fetal calf serum (FCS) selected for minimal ANG II-degrading capacity. Cell number and DNA and protein synthesis (by [3H]-thymidine and [35S]methionine incorporation, respectively) were determined serially over 1-6 days. ANG II alone induced an early 20% increase and then a plateau in cell number over the 0.4% FCS control (P < 0.01; n = 8), thus without sustained increase in proliferation rate. Yet ANG II alone did not increase fractional DNA or protein synthesis (each as cpm/10(3) cells) and, by flow cytometry, reduced S phase fraction without increase in cell size. EGF alone induced brisk DNA synthesis yet minimal cell division over days 0-4, thus late-cycle arrest. ANG II + EGF, despite no increase in fractional DNA or protein synthesis rates over EGF alone, induced significant indomethacin-resistant dose-dependent (P < 0.001) increase in cell proliferation rate over EGF alone with a median effective dose of 5 x 10(-10) M ANG II, thus proliferative synergy. We propose that 1) ANG II induces a subpopulation of cells arrested in or beyond S phase to proceed through mitosis but does not influence G1 traversal or S phase entry and 2) ANG II + EGF achieve proliferative synergy by complementary actions at sequential cell cycle loci, with EGF supporting progression from G0/G1 to S phase and ANG II inducing completion of mitosis by cells already in or beyond S phase ("late-cycle completion").

Influence of growth oxygen level on eicosanoid release from lung endothelial cells during hypoxia

Eicosanoid products of arachidonic acid are suspected modulators of hypoxic vasoconstriction in the pulmonary vasculature. Vascular endothelial cells (EC) release several eicosanoids, but there is disagreement regarding the effect of hypoxia on EC eicosanoid release. We postulated that the oxygen level of growth in culture might influence the release of eicosanoids during acute hypoxia. We studied EC cultured from the main pulmonary arteries of pigs and grown at either 5% or near 20% oxygen, representing the normal limits of oxygen exposure to endothelium in normal lungs. Although cultures grown in 5% oxygen grew slightly faster by 4 days, the confluent cell number, protein content, and baseline eicosanoid release were no different compared with paired cultures grown in 20% oxygen. However, with an acute decrease in oxygen level, cultures grown in 5% oxygen released less prostaglandin E2, F2 alpha, and 6-ketoprostaglandin F1 alpha compared with amounts released at the growth oxygen level. In contrast, cultures grown in 20% oxygen released increased amounts of these eicosanoids compared with release at the growth oxygen level. Release of thromboxane B2 was not significantly different during hypoxia between cultures grown at 5% vs. 20% oxygen. In other experiments, cyclooxygenase activity, stimulated arachidonic acid release by calcium ionophore A23187, and uptake of arachidonic acid were no different in cultures grown at 5% vs. 20% oxygen. However, arachidonic acid release during hypoxia was reduced in 5% cultures and increased in 20% cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Nontraditional combination pharmacotherapy of hypertension

Traditional drug combinations that have additive hypotensive effect include double therapy with a diuretic and any other antihypertensive agent and triple therapy with a diuretic, direct vasodilator, and either a beta blocker or reserpine. Due to the availability of new classes of antihypertensive agents, other combinations of drugs are now increasingly used. The effectiveness of combination therapy for hypertension has been investigated; the results of these studies are reviewed.

EGF is incomplete mitogen in porcine aortic smooth muscle cells: DNA synthesis without cell division

To characterize growth effects of epidermal growth factor (EGF) in subconfluent quiescent porcine aortic vascular smooth muscle cells (VSMC), we measured DNA and protein synthesis by [3H]thymidine (Thd) and [35S]methionine (Met) incorporation, respectively, and cell proliferation rates over 0-6 days in Dulbecco's modified Eagle's-Ham's F-12 media containing 0.4% fetal calf serum (FCS) and insulin. EGF induced dose-dependent [3H]Thd uptake (P less than 0.001); after 10(-9) M EGF, DNA synthesis rate peaked at 24 h, averaging 77% of the response to 10% FCS, and then declined steeply with nadir at 48-60 h. Unexpectedly, EGF failed to induce cell proliferation in the first 4 days, leaving this initial burst of DNA synthesis (12-60 h) uncoupled from cell division. A second lesser but sustained phase of increased DNA synthesis, apparent by day 3-4, was associated with a small increase in cell number on day 6 (P less than 0.05). The early unsustained burst of DNA synthesis reflects EGF's potent mitogenic efficacy for DNA synthesis (G1- to S-phase traversal), probably acting on a subset of cells partially synchronized initially at an EGF-responsive G0/G1 locus; the minimal cell division despite brisk DNA synthesis documents EGF's limited efficacy for (or inhibition of) late cell-cycle events required for completion of mitosis. Late cell-cycle processes are thus rate limiting. EGF also increased protein synthetic rate over control (P less than 0.03) but to a lesser degree (P less than 0.01) than 10% FCS. Indomethacin (10(-6) M) did not alter DNA or proliferative responses to 10(-9) M EGF but transiently augmented EGF-induced protein synthesis (P less than 0.025) at 24 h only.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive function in hypertensives treated with atenolol or propranolol

STUDY OBJECTIVE

To test reports that beta blockers, particularly lipophilic forms, impair cognitive function and cause psychiatric disturbances.

DESIGN

Randomized, double-blind, controlled crossover trial with eight-week treatment periods.

PATIENTS

Sequential sample of 42 male veterans, with untreated diastolic blood pressures (DBP) between 90 and 110 mmHg, aged 35-64 years.

INTERVENTIONS

Propranolol-LA, 80-mg tablets, or atenolol, 50-mg tablets, were given daily, incremented by one tablet at weekly intervals until DBP less than or equal to 90 mmHg. Hydrochlorothiazide was added, if necessary.

MAIN RESULTS

Repeated-measures ANOVA was performed on all cognitive tests. Cognitive test performance was not affected by beta blocker therapy in seven of nine tests and was enhanced on Trail Making Test. Performance was impaired only on Digit Cancellation. Neither Speilberger's State Trait Anxiety Inventory nor the Beck Depression Inventory was affected by either beta blocker.

CONCLUSIONS

Atenolol or propranolol therapy does not impair cognitive function or contribute significantly to psychiatric side effects.

An in vitro system for study of effects of angiotensin I on cultured endothelial cells

Since certain non-vascular angiotensin II (AII) receptors may be activated by angiotensin I (AI), and since sustained increase in AI levels accompanies chronic treatment with converting enzyme inhibitors (CEI) which block conversion of AI to AII, the question of whether AI has significant biological effects is of clinical relevance. We therefore sought to develop an in vitro culture system in which effects of angiotensin I, independently of its conversion to AII, could be studied in cloned aortic vascular endothelial cells (VEC). This was complicated by peptide degradation during the period of observation, both by angiotensin converting enzyme (ACE) on the surface of VEC and by angiotensinases in either the serum component of culture media or associated with the cell monolayer. Accordingly, we examined the half life of AI under relevant cell culture conditions, with and without confluent fetal bovine aortic endothelial cells (FBAEC). Factors assessed included (1) fetal calf serum: commercial source, concentration in culture media, effects of converting enzyme inhibitor (CEI: MK422) and/or heat inactivation (superimposed on the commercially performed process); and (2) effect of FBAEC in monolayer culture, with and without CEI. Results showed that (1) in the absence of cells, loss of AI in culture media, when present, was solely due to the presence of fetal calf serum (FCS) and showed a dose dependent response; (2) FCS from differing sources may vary dramatically in capacity for AI breakdown; and (3) serum related AI disappearance included a heat resistant ACE like component (inhibitable by CEI) and a heat sensitive/CEI resistant component dominant at concentrations of FCS exceeding 5%.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic CEI alters effect of low Na+ diet in normal and coarcted pups. I. BP, renin, and GFR

To assess the renin-angiotensin (RA) dependence of evolving neonatally induced coarctation hypertension (NICH) in inbred pups, we randomized sex-matched littermates to a high dose of converting-enzyme inhibitor (CEI:MK-421) or placebo from the time of neonatal aortic banding (coarcted) vs. no banding (control). In phase 1 studies, pups were examined serially on normal diet (Bagby and Fuchs, Hypertension In press.): chronic CEI lowered systolic blood pressure (BP) equally in coarcted and controls and failed to prevent systolic BP excess in coarcted dogs. In phase 2 studies, the same pups were exposed to a low sodium (LS) diet at 4 mo of age, a time when the untreated NICH model exhibits increased forelimb systolic BP. Measurements of systolic BP, RA components, renal function, and extracellular volume (ECV) were made before and serially during 12 days on the LS diet. Responses of coarcted and control pups to the LS diet were similar, with or without CEI, providing no evidence for exaggerated angiotensin II (ANG II) dependence in evolving NICH. Independently of coarctation status, chronic CEI significantly modified RA and renal functional responses to the LS diet: a greater renin rise but abnormal renin substrate fall, thus no rise in ANG I or ANG I generation rate; a greater rise in creatinine and a trend toward a greater fall in glomerular filtration rate (GFR). Despite these findings compatible with sustained ANG II deficit, chronic CEI unexpectedly failed to impair maintenance of systolic BP during a superimposed LS diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic CEI alters effect of low Na+ diet in normal and coarcted pups. II. Na+ and H2O balance

To assess angiotensin (ANG II) dependence of evolving neonatally induced coarctation hypertension (NICH) in inbred pups, we randomized sex-matched littermates to high-dose converting enzyme inhibitor (CEI: MK-421, 3 mg/kg) or placebo from the time of neonatal aortic banding (coarcted) vs. no banding (control). During phase 1 studies over 4 mo postbanding during ad libitum Na+ intake (Bagby and Fuchs, Hypertension Dallas in press). CEI failed to prevent evolution of proximal blood pressure (BP) excess or to impair renal function. Phase 2 studies examine, in the same pups, responses to low Na+ (LS) diet superimposed on chronic CEI at 4 mo, timed to allow development of BP increase in untreated NICH. The present report details metabolic handling and balances of Na+, K+, and fluid for 3 days before (normal Na+ intake) and daily for 11 days after initiation of LS diet, a companion paper describes BP, renin-angiotensin (RA), and renal functional responses. In no case did metabolic responses of coarcted pups to LS diet differ from those of controls, whether on CEI or placebo, whereas responses to LS diet and to CEI reveal positive findings of independent interest. LS diet induced expected renal and fecal Na+ conservation, no net effect on K+ balance, and, despite unexpected free-water diuresis, mild hyponatremia. Chronic CEI impaired maximal renal (but not fecal) Na+ conservation during LS diet, caused exaggerated free-water diuresis but no change in fluid balance, and thus, with the larger Na+ deficit, accounted for greater hyponatremia. CEI caused no net effect on K+ balance. Results indicate normal renal handling of fluid, Na+, and K+ in evolving NICH and provide no evidence for selective intrarenal RA activation or exaggerated ANG II dependence. Findings also suggest that, during LS diet, ANG II is 1) essential for maximum renal Na+ conservation and normal free-water handling, and 2) not essential for fecal Na+ and water conservation or for maintenance of normal water and K+ balances. Results are also compatible with a CEI-induced thirst stimulation and/or osmotic insensitivity and with functional vasopressin deficiency during LS diet.

Chronic MK421 fails to modify evolution of hypertension in neonatally coarcted pups

In inbred dogs with neonatally induced coarctation hypertension, prior serial studies during the first year after aortic banding showed extracellular volume excess with normal plasma renin activity (PRA). The present studies test the hypothesis that slowly evolving aortic constriction in this model will yield intrarenal angiotensin II excess, peripherally undetectable, with continuous slightly positive sodium balance, and thus that chronic blockade of angiotensin II formation will prevent generation of hypertension. Accordingly, we used MK421 (enalapril, 3 mg/kg twice daily), a long-acting angiotensin converting enzyme inhibitor, or placebo, administered orally, from the time of banding through 4 months after banding in sex-matched littermates randomly assigned to one of four groups: coarcted/MK421; control/MK421; coarcted/placebo; control/placebo. Results indicate that MK421 caused identical lowering of absolute forelimb systolic blood pressure in coarcted and control pups but failed to modify evolution of a significant (p less than 0.005) systolic blood pressure difference in coarcted versus control dogs. Thus, neither temporal course nor final magnitude of relative hypertension was altered by MK421. Efficacy of MK421 was documented by 83% inhibition of the pressor response to angiotensin I at nadir of drug effect and by sustained increases in angiotensin I and renin concentration throughout the period of study. Coarcted and control pups responded similarly to MK421 for all measured variables. Glomerular filtration rate and extracellular volume (measured by [14C]inulin disappearance) did not differ among groups. Thus, chronic administration of MK421 failed to prevent hypertension and did not impair maintenance of normal renal function in the evolving phase of neonatally induced coarctation hypertension. We conclude that, although angiotensin II may participate in the untreated model, it does not appear essential to generation of hypertension. We propose that the renal pressure-natriuresis mechanism regulates distal pressure, that stenosis-related resistance independently determines the proximal-distal difference, and that chronic converting enzyme inhibition lowers the set point of the former without influencing stenosis evolution, thus secondarily lowering proximal pressure by an equal degree.

Canine neonatally induced coarctation hypertension in the second year. Variably hyperresponsive plasma renin activity

In canine neonatally-induced coarctation hypertension, we reported abnormally elevated plasma renin activity (PRA) during sodium restriction in 2-year-old dogs, but found normal PRA responses to sodium restriction +/- furosemide in coarcted dogs studied serially over the first year postaortic banding (PAB). To resolve this apparent discrepancy in PRA response, longitudinal studies were extended to 2 years PAB. In two separately-studied groups, each with three coarcted and three littermate controls, measurements of indirect forelimb blood pressure (BP) at 15 to 18 months, direct brachial arterial BP at 24 months, and serial measurement of PRA and extracellular volume (ECV, as 24Na space) were made over a 15- to 24-month age range during three sodium-volume levels: ad libitum sodium intake (NS), low-sodium diet alone (LS), and low-sodium plus Lasix (LS/Lasix). While PRA in coarcted dogs of both groups was comparable to controls at NS and LS, PRA in Group 1 coarcted dogs significantly exceeded that of littermates during LS/Lasix in both 18- and 24-month studies. In contrast, PRA in Group 2 coarcted dogs was not hyperresponsive to LS/Lasix as compared to simultaneously-studied littermates. The hyperresponsive PRA in Group 1 coarcted dogs could not be attributed to larger absolute or relative ECV deficits. Overall, ECV in coarcted dogs of each group was higher on the average but was not statistically different from controls. Results indicate that the hyperresponsive PRA in this canine model is: 1) a variable feature, developing secondarily in the late established phase; 2) reproducible for a given animal; and 3) not attributed to exaggerated ECV deficits during the LS/Lasix protocol.

Extracellular volume expansion and delayed resolution of hypertension after canine aortic coarctectomy

The hemodynamic changes occurring after surgical correction of thoracic aortic coarctation were studied in two neonatally coarcted dogs at six months of age and compared to sham surgery in two littermate controls. Excision of the tight iatrogenic aortic band with direct aortic reanastomosis abolished pressure gradients. Post-coarctectomy systemic pressure rose, after an early transient fall, to pre-operative proximal levels and was sustained for two to four weeks before decreasing to control normotensive values. Femoral systolic pressure (and renal perfusion pressure) rose by 47-57 mmHg in coarcted dogs (p less than .001). Extracellular volume (ECV) increased in both coarcted animals, peaking 28-32 cc/kg (7.1-7.6% increase) above precoarctectomy levels. Peak ECV expansion coincided with the peak post-coarctectomy blood pressure. Fluid administration, blood losses and plasma renin activity (PRA) were comparable in all animals. Post-coarctectomy tachycardia was also noted in coarcted dogs (p less than .001), whereas neither ECV nor heart rate changes occurred in control animals. We postulate that post-coarctectomy baroreceptor stimulation results in sympathetically-mediated renal sodium retention, not only preventing a pressure diuresis, but resulting in overt volume expansion. Failure of PRA suppression despite increased distal pressure and volume excess may also reflect sympathetic activation. Data are compatible with the view that sympathetic activation and consequent volume expansion transiently sustain hypertension in the post-coarctectomy setting until baroreceptor re-adjustments permit normalization of blood pressure.

Acute responses to arterial pressure and plasma renin activity to converting enzyme inhibition (SQ 20,881) in serially studied dogs with neonatally-induced coarctation hypertension

In six inbred dogs with neonatally-induced coarctation hypertension, and in seven littermate controls, acute responses of proximal arterial pressure and plasma renin activity (PRA) to converting enzyme inhibitor (CEI; SQ 20,881, 0.5 mg/kg i.v.) were serially examined. Studies were performed at 2, 6, and 12 months post-aortic banding under sodium-replete and -deplete conditions. Both in normotensive controls and in coarcted dogs, depressor responses (pre- minus post-CEI values) were positively correlated, not only with initial (pre-CEI) PRA, but also independently with initial blood pressure. Although absolute depressor responses in coarcted dogs exceeded those of the control group, there were no significant group differences when, by analysis of covariance, depressor responses were adjusted for the physiologic influence of initial pressure. Similarly, depressor responses expressed as a percent of initial pressure were comparable in coarcted and control groups. Initial PRA and PRA response to CEI in coarcted dogs were also comparable to control dogs; the PRA response correlated with initial PRA in both groups. CEI did not significantly diminish the magnitude of blood-pressure difference between coarcted and control dogs. Thus, in neonatally-induced coarctation hypertension, under both sodium replete- and -deplete conditions: 1) acute depressor and PRA responses to CEI are modulated by the same factors that influence responses of normotensive controls; 2) larger absolute depressor responses to CEI appear to be a physiologic function of higher initial pressure; and 3) blood pressure excess over littermate controls is largely sustained by CEI-resistant factors, potentially including the known volume excess in coarcted dogs.

In vitro determinants of plasma renin activity in serially-studied inbred dogs with neonatally induced coarctation hypertension: renin reactivity, renin substrate, and renin concentration

Increased renin activity of plasma, suggesting an excess of circulating accelerators and/or deficit of inhibitors of the renin reaction, has been reported in a number of hypertensive states; however, its contribution to genesis and/or maintenance of hypertension is unknown. To longitudinally assess the evolution of plasma renin reactivity in relation to blood pressure in neonatally-induced coarctation hypertension, we have made serial observations in 6 coarcted dogs and in 7 littermate controls over 1-12 months post-aortic-banding during varied steady-state sodium intake. Measurements of renin activity (defined as the increment of angiotensin I-generation rate following addition of exogenous renin to plasma), renin substrate concentration (RS), and plasma renin activity (PRA), together with calculation of plasma renin concentration (PRC) (as PRC = PRA divided by renin reactivity) provided estimates of the three major determinants of PRA. RS values were adjusted for variability due to assay-control and to age via covariate analysis. Results indicate no difference in adjusted RS between coarcted and control dogs, thus obviating the influence of RS differences on renin reactivity results. Renin reactivity and PRC in coarcted dogs were also comparable to control values. Furthermore, responses of RS, renin reactivity and PRC to dietary sodium manipulation were similar in coarcted and control animals. We conclude that circulating modifiers of the renin reaction play no role in the genesis or in the first-year maintenance of neonatally-induced coarctation hypertension.

Serial renin-angiotensin studies in spontaneously hypertensive and Wistar-Kyoto normotensive rats. Transition from normal- to high-renin status during the established phase of spontaneous hypertension

To characterize the renin-angiotensin system in the Aoki-Okamoto spontaneously hypertensive rat (SHR) more fully, serial measurements of plasma renin activity (PRA), plasma renin concentration (PRC), renin reactivity (as relative index of circulating modifiers of the renin reaction) and renin substrate concentration were made in 6- to 64-week-old SHR and in age-matched Wistar-Kyoto normotensive rats (WKY). In the evolving phase of SHR hypertension (6 and 13 weeks of age), PRA was comparable to WKY control values, whereas mature SHR with established hypertension developed, between 13 and 35 weeks of age, a high-PRA state persisting through 64 weeks of age. In 64-week-old SHR, increased plasma volume (3.54 +/- 0.91 in SHR vs. 3.18 +/- 0.90 ml/100 g body weight in WKY, p less than 0.025), together with increased PRA (24.9 +/- 3.8 in SHR vs. 13.1 2.2 ng AI/ml plasma/hr in WKY, p less than 0.025), suggest that volume decrease cannot explain increased PRA. In 42-week-old SHR, PRA was incompletely suppressed by deoxycorticosterone acetate plus 1% saline orally for 4 days: 4.9 +/- 1.2 in SHR vs. 0.6 +/- 0.8 ng angiotensin I/ml plasma/hr in WKY, p less than 0.001. Modestly increased renin reactivity of plasma was observed in SHR at all ages studied, supporting the ubiquity of increased circulating accelerators (or decreased inhibitors) of the renin reaction in hypertensive states. However, elevated renin reactivity did not account for the transition from normal to high PRA observed in mature SHR, nor did renin substrate concentration, which was consistently lower in SHR than in age-matched WKY. Temporal patterns of, and strain differences in PRA were closely paralleled by variations in PRC but not by other reaction components. Significant elevation of serum creatinine in old SHR support the presence of renal injury. We conclude that PRA and PRC are normal in evolving SHR hypertension and progress to abnormally elevated levels after hypertension is established. We postulate that "high-renin" hypertension may develop as a consequence of the hypertensive state per se, perhaps due to nephrosclerotic vascular disease.

Abnormalities of renal perfusion and the renal pressor system in dogs with chronic aortic coarctation

To clarify the role of the renin-angiotensin system in coarctation hypertension, 2-year-old inbred dogs with chronic neonatally induced thoracic aortic coarctation were subjected to 6 days of rigorous salt restriction. The following parameters were then measured: glomerular filtration rate, renal plasma flow, plasma renin activity, plasma renin concentration, renin reactivity, and renin substrate concentration. Glomerular filtration rate and renal plasma flow were significantly lower in salt-restricted coarcted dogs: 3.0 +/- 0.2 and 9.0 +/- 1.5 ml/min kg-1, respectively, compared with values of 4.0 +/- 0.2 (P less than 0.005) and 13.2 +/- 0.6 (P less than 0.025) ml/min kg-1 in salt-restricted controls. Plasma renin activity was abnormally high in experimental dogs: 13.5 +/- 2.5 vs. 4.5 +/- 1.5 ng angiotensin I/ml hour-1 in controls (P less than 0.005). In addition, a significant elevation of renin reactivity (indicating a relative increase in circulating accelerators or a relative decrease in inhibitors of the renin reaction) was apparent in the plasma of coarcted dogs. Plasma renin concentration was elevated but to an insignificant degree in coarcted dogs, and renin substrate concentration was comparable with that of controls. The impaired renal perfusion and abnormal elevation of plasma renin activity during salt restriction is analogous to clinical and experimental observations in hypertensive states associated with total renal underperfusion and supports a major role for the renal pressor system in the pathogenesis of coarctation hypertension. The insignificant elevation of plasma renin concentration is not incompatible with this view. The demonstration of increased renin reactivity in coarctation hypertension provides additional evidence that acceleration of the renin reaction is common to all hypertensive states.