Integrative echocardiographic assessment of post-operative obstruction severity and restenosis after balloon valvuloplasty in 81 dogs with pulmonary stenosis

INTRODUCTION/OBJECTIVES

Pulmonary stenosis (PS) is a congenital defect in the dog that is managed with balloon valvuloplasty (BV). Obstruction severity is routinely assessed using transthoracic echocardiography. The objectives of this study were to describe the short-term changes and long-term restenosis by retrospectively evaluating flow-dependent and flow-independent echocardiographic variables for dogs with PS after BV.

ANIMALS, MATERIALS, AND METHODS

Medical records and stored echocardiographic images were reviewed from dogs that received BV for PS. The following echocardiographic variables were measured or calculated: maximum systolic ejection velocity (Vmax_PV) and velocity-derived maximal pressure gradient (PV maxPG) across the pulmonary valve; ratio of aortic to pulmonary velocity time integral (VTI_AV/VTI_PV); ratio of aortic to pulmonary maximal velocity.

RESULTS

Eighty-one dogs with PS that had a BV were included. Each of these dogs had pulmonary obstruction severity assessed in at least three timepoints. Forty-nine dogs had at least one additional examination performed, the last of which occurred a median of 504 days after the BV. Echocardiographic variables at the first follow-up had increased by a clinically relevant quantity in 20-34% of the dogs when comparing to the immediate post-BV examination. The last follow-up examination identified valve restenosis in 18-38% of the dogs in this study. Valve type and pre-BV obstruction severity did not have a significant effect (P > 0.1).

CONCLUSIONS

For the assessment of BV efficacy, the immediate post-BV echocardiogram may not be as useful as the first follow-up examination several months later. Pulmonary restenosis after BV may be more prevalent than previously reported.

Long-term relief of obstruction in a dog with double-chambered right ventricle using combined cutting balloon and high-pressure balloon dilation

A 4-month-old intact female Golden Retriever dog was diagnosed with double-chambered right ventricle (DCRV) without infundibular stenosis, tricuspid valve dysplasia, and subsequent severe right atrial enlargement and was referred for combined cutting balloon and high-pressure balloon dilation. On presentation, these diagnoses were confirmed, and the peak systolic pressure gradient across the DCRV obstructive lesion assessed by continuous wave Doppler interrogation was 80 mm Hg. The obstructive lesion within the mid-right ventricle had a diameter of 6 mm through which blood flowed from the proximal right ventricular (RV) chamber to the distal RV chamber. The following day, general anesthesia was induced, and a minimally invasive balloon dilation was performed. A cutting balloon was inflated across the mid-RV obstructive lesion, followed by an inflation of a high-pressure balloon across this lesion. The high-pressure balloon catheter that was used had a diameter roughly 1.5 times the diameter of the pulmonary annulus. The following day, echocardiographic evaluation of the patient revealed a peak systolic pressure gradient across the DCRV obstructive lesion of 16 mm Hg, with a RV diameter at the level of obstruction of 11 mm. Twelve months later, the dog remains asymptomatic, right atrial size has decreased, and has a peak systolic pressure gradient across the DCRV lesion of 20 mm Hg.

FRAX calculated without BMD does not correctly identify Caucasian men with densitometric evidence of osteoporosis

The FRAX algorithm assesses the patient's probability of sustaining an osteoporotic fracture and can be calculated with or without densitometric data. This study seeks to determine whether in men, FRAX scores calculated without BMD, correctly identify patients with BMD-defined osteoporosis.

INTRODUCTION

The diagnosis of osteoporosis is based on densitometric data, the presence of a fragility fracture or increased fracture risk. The FRAX algorithm estimates the patient's 10-year probability of sustaining an osteoporotic fracture and can be calculated with or without BMD data. The purpose of this study is to determine whether in men, FRAX calculated without BMD, can correctly identify patients with BMD-defined osteoporosis.

METHODS

Retrospectively retrieved data from 726 consecutive Caucasian males, 50 to 70 years old referred to our Osteoporosis Center.

RESULTS

In the population studied, 11.8 and 25.3% had BMD-defined osteoporosis when female and male reference populations were used respectively. When the National Osteoporosis Foundation thresholds to initiate treatment are used, only 27% of patients with BMD-defined osteoporosis, but 4% with normal BMD reached/exceeded these thresholds. Lowering the threshold increased sensitivity, but decreased specificity.

CONCLUSIONS

Our results suggest that FRAX without BMD is not sensitive/specific enough to be used to identify Caucasian men 50 to 70 years old with BMD-defined osteoporosis.

Gbetagamma affinity for bovine rhodopsin is determined by the carboxyl-terminal sequences of the gamma subunit

Two native betagamma dimers, beta(1)gamma(1) and beta(1)gamma(2), display very different affinities for receptors. Since these gamma subunits differ in both primary structure and isoprenoid modification, we examined the relative contributions of each to Gbetagamma interaction with receptors. We constructed baculoviruses encoding gamma(1) and gamma(2) subunits with altered CAAX (where A is an aliphatic amino acid) motifs to direct alternate or no prenylation of the gamma chains and a set of gamma(1) and gamma(2) chimeras with the gamma(2) CAAX motif at the carboxyl terminus. All the gamma constructs coexpressed with beta(1) in Sf9 cells yielded beta(1)gamma dimers, which were purified to near homogeneity, and their affinities for receptors and Galpha were quantitatively determined. Whereas alteration of the isoprenoid of gamma(1) from farnesyl to geranylgeranyl and of gamma(2) from geranylgeranyl to farnesyl had no impact on the affinities of beta(1)gamma dimers for Galpha(t), the non-prenylated beta(1)gamma(2) dimer had significantly diminished affinity. Altered prenylation resulted in a <2-fold decrease in affinity of the beta(1)gamma(2) dimer for rhodopsin and a <3-fold change for the beta(1)gamma(1) dimer. In each case with identical isoprenylation, the beta(1)gamma(2) dimer displayed significantly greater affinity for rhodopsin compared with the beta(1)gamma(1) dimer. Furthermore, dimers containing chimeric Ggamma chains with identical geranylgeranyl modification displayed rhodopsin affinities largely determined by the carboxyl-terminal one-third of the protein. These results indicate that isoprenoid modification of the Ggamma subunit is essential for binding to both Galpha and receptors. The isoprenoid type influences the binding affinity for receptors, but not for Galpha. Finally, the primary structure of the Ggamma subunit provides a major contribution to receptor binding of Gbetagamma, with the carboxyl-terminal sequence conferring receptor selectivity.

Independent and synergistic interaction of retinal G-protein subunits with bovine rhodopsin measured by surface plasmon resonance

We have used surface plasmon resonance (SPR) measurements for the kinetic analysis of G-protein-receptor interaction monitored in real time. Functionally active rhodopsin was immobilized on an SPR surface, with full retention of biochemical specific activity for catalysis of nucleotide exchange on the retinal G-protein alpha subunit, via binding to immobilized concanavalin A. The binding interactions of bovine retinal alpha(t) and beta(1)gamma(1) subunits with rhodopsin measured by SPR were profoundly synergistic. Synergistic binding of the retinal G-protein subunits to rhodopsin was not observed for guanosine 5'-[gamma-thio]triphosphate-bound Galpha(t), nor was binding observed with squid retinal Galpha(q), which is not activated by bovine rhodopsin. The binding affinity (336+/-171 nM; mean value+/-S.D.) of retinal betagamma for rhodopsin in the presence of retinal alpha subunit measured by SPR confirmed the apparent affinity of 254 nM determined previously by nucleotide exchange assays. Binding of beta(1)gamma(1), beta(1)gamma(2), and beta(1)gamma(8-olf) dimers to rhodopsin, independently of the alpha subunit, was readily observable by SPR. Further, these dimers, differing only in their gamma subunit compositions, displayed markedly distinct binding affinities and kinetics. The beta(1)gamma(2) dimer bound with a kinetically determined K(d) of 13+/-3 nM, a value nearly identical with the biochemically determined K(1/2) of 10 nM. The physiologically appropriate beta(1)gamma(1) displayed rapid association and dissociation kinetics, whereas the other beta(1)gamma dimers dissociated at a rate less than 1/100 as fast. Thus rhodopsin interaction with its native signalling partners is both rapid and transient, whereas the interaction of rhodopsin with heterologous Gbetagamma dimers is markedly prolonged. These results suggest that the duration of a G-protein-coupled receptor signalling event is an intrinsic property of the G-protein coupling partners; in particular, the betagamma dimer.

Percutaneous vertebroplasty: a novel treatment for acute vertebral fractures

Acute vertebral fracture is a painful and debilitating complication of osteoporosis which has been extremely difficult to manage. Percutaneous vertebroplasty--injecting cement to stabilise the fractured end plate--represents a major management breakthrough. We report the first four patients with osteoporotic vertebral fractures treated by this technique at our hospital. They are, to our knowledge, among the first to be successfully treated in this way in Australia.

Contribution of individual projections alone and in combination for radiographic detection of ankle fractures

OBJECTIVE

We wanted to determine whether the standard three-view ankle radiographic series could be replaced by a two-view combination, and if so, which two-view combination (anteroposterior with lateral or mortise with lateral) would be superior.

MATERIALS AND METHODS

During a 12-month period, we retrospectively reviewed 556 consecutive ankle radiographic studies consisting of anteroposterior, mortise, and lateral views. One hundred twenty patients with at least one ankle fracture were paired with 140 healthy control subjects. Each image in the three-view examination was separated and sorted by view and studied independently; all images were reviewed by two skeletal radiologists and two orthopedic surgeons. Each radiograph was evaluated for fracture of the medial, lateral, and posterior malleoli and the foot using a five-point confidence rating. Performance of each view and modeled two- and three-view combinations of views was evaluated with modified receiver operating characteristic analysis.

RESULTS

The data provide little support for preferring either two-view combination (anteroposterior-lateral or mortise-lateral) for any type of fracture. The three-view combination does detect significantly more fractures than some two-view combinations in some locations, and there is a statistically significant cost in diagnostic accuracy for eliminating the anteroposterior or mortise view.

CONCLUSION

Reducing the ankle radiographic series from three to two views would result in a small but significant decrease in the detection of fractures of the ankle and foot. Both two-view combinations are equivalent for fracture detection.

TEM analysis of tweed structure in high-palladium dental alloys

Transmission electron microscopy and convergent-beam electron diffraction were used to study three high-palladium dental alloys: an as-cast Pd-Ga alloy, a cast Pd-Cu-Ga alloy aged at room temperature for over 5 years, and a cast Pd-Cu-Ga alloy annealed at 1023 K for 2 h and slowly cooled to room temperature. Bands containing a tweed structure in the Pd-Ga alloy were 120degrees twins with (1 1 0 mirror planes. Within these bands the alloy had a face-centered tetragonal structure with a c/a ratio of 1.03. The aged Pd-Cu-Ga alloy contained a larger amount of tweed structure than the original as-cast alloy, along with randomly oriented bands and thin lath-like regions. The annealed Pd-Cu-Ga alloy contained rectangular particles of a secondary phase that may be Pd2Ga, Pd5Ga2 or Pd13Ga5. The microtwinned band structure relieves the strain energy arising from transformation of the f.c.c. palladium solid solution on cooling.

Electrocardiographic patterns of patients with echocardiographically determined biventricular hypertrophy

The numerous criteria proposed for the electrocardiographic (ECG) diagnosis of biventricular hypertrophy (BVH) suffer from inadequate correlative data. We used two-dimensional (2D) echocardiography to identify BVH and analyzed the ECG patterns in these patients. The study group had 69 such patients with BVH and the control group had 22 patients with isolated left ventricular hypertrophy (LVH) demonstrated by 2D echocardiography. The electrocardiograms were analyzed for the presence of established criteria used in the diagnosis of LVH and right ventricular hypertrophy (RVH). Of the 69 patients in the study group, 17 (25%) had ECG findings of BVH, 25 (36%) had LVH, and 14 (20%) had RVH. An S wave in V5/V6 of >7 mm was most the frequent finding in the 17 patients with BVH on the electrocardiogram. The sensitivity of ECG criteria for BVH was 24.6%, specificity was 86.4%, and positive predictive value was 85%. This study reemphasizes the difficulty of ECG diagnosis of BVH. The electrocardiogram has a low sensitivity but satisfactory specificity and positive predictive accuracy for BVH.

Effect of long-term beta-blockade on aortic root compliance in patients with Marfan syndrome

BACKGROUND

This study was undertaken to assess the effect of long-term beta-blockade on the aortic root stiffness index and distensibility in patients with Marfan syndrome.

METHODS

Aortic root stiffness index and distensibility were calculated according to the formulas of Stefanadis and Hirai, respectively, with 2-dimensional guided M-mode echocardiogram before and after an average of 26 months of atenolol administration.

RESULTS

Twenty-three asymptomatic patients were studied (11 men and 12 women, aged 31 +/- 14.2 years). The follow-up was 4 +/- 2.2 years. The dose of atenolol was individualized (mean 43.5 +/- 21.6 mg/d). Heart rate decreased from 79 +/- 9 beats/min to 64 +/- 9 beats/min (P =. 01), and systolic blood pressure decreased from 124 +/- 13 mm Hg to 114 +/- 2 mm Hg (P =.01). Distensibility increased from 1.85 +/- 0. 70 x 10(-6) cm2/dynes-1 to 2.21 +/- 0.76 x 10-6 cm2/dynes-1 (P =.02), and the stiffness index decreased from 9.68 +/- 3.78 to 8.85 +/- 3. 15 ( P =.2). Two groups of responses to treatment were identified. Compared with baseline values 15 (65%) patients who responded to treatment had increased distensibility and decreased stiffness index of the aortic root (P =.05). Eight patients (35%) who did not respond to treatment had no significant change. Body weight >91 kg and baseline end-diastolic aortic root diameter >40 mm were significantly associated with no response (P =.05). Two patients in the nonresponding group had echocardiographic progression of aortic insufficiency.

CONCLUSIONS

There was a heterogeneous response in the aortic root elastic properties after long-term treatment with atenolol in asymptomatic patients with Marfan syndrome. Stiffness index and distensibility are more likely to respond when the baseline end-diastolic aortic root diameter is <40 mm.

The bombesin receptor subtypes have distinct G protein specificities

We used an in situ reconstitution assay to examine the receptor coupling to purified G protein alpha subunits by the bombesin receptor family, including gastrin-releasing peptide receptor (GRP-R), neuromedin B receptor (NMB-R), and bombesin receptor subtype 3 (BRS-3). Cells expressing GRP-R or NMB-R catalyzed the activation of squid retinal Galphaq and mouse Galphaq but not bovine retinal Galphat or bovine brain Galphai/o. The GRP-R- and NMB-R-catalyzed activations of Galphaq were dependent upon and enhanced by different betagamma dimers in the same rank order as follows: bovine brain betagamma > beta1gamma2 >> beta1gamma1. Despite these qualitative similarities, GRP-R and NMB-R had distinct kinetic properties in receptor-G protein coupling. GRP-R had higher affinities for bovine brain betagamma, beta1gamma1, and beta1gamma2 and squid retinal Galphaq. In addition, GRP-R showed higher catalytic activity on squid Galphaq. Like GRP-R and NMB-R, BRS-3 did not catalyze GTPgammaS binding to Galphai/o or Galphat. However, BRS-3 showed little, if any, coupling with squid Galphaq but clearly activated mouse Galphaq. GRP-R and NMB-R catalyzed GTPgammaS binding to both squid and mouse Galphaq, with GRP-R activating squid Galphaq more effectively, and NMB-R also showed slight preference for squid Galphaq. These studies reveal that the structurally similar bombesin receptor subtypes, in particular BRS-3, possess distinct coupling preferences among members of the Galphaq family.

Mechanism of allosteric regulation of the rod cGMP phosphodiesterase activity by the helical domain of transducin alpha subunit

The G protein alpha subunit (Galpha) is composed of two distinct folding domains: a GTP-binding Ras-like domain and an alpha helical domain (HD). We have recently reported that the helical domain (HDt) of the vertebrate visual transducin alpha subunit (Galphat) synergizes activation of retinal cyclic GMP phosphodiesterase (PDE) by activated Galphat (Liu, W., and Northup, J. K., (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 12878-12883). Here, we examine the molecular basis for this HD-based signaling regulation, and we provide a new model for the activation of the target effector. The HD proteins derived from visual transducin or taste gustducin alpha subunits, but no other Galpha HD proteins, each attenuate the PDE catalytic core (Palphabeta) and synergize Galphat stimulation of the holoPDE (Palphabetagamma2) with similar apparent affinities. The data from studies of both HDt-mediated attenuation and stimulation indicate that the HDt and the PDE inhibitory subunit (Pgamma) interact with PDE at independent sites and that Palphabeta contains the binding sites for HD. The saturation of both processes by HDt displays positive cooperativity with Hill coefficients of 1.5 for the attenuation of Palphabeta activity and 2.1 for synergism of holoPDE activation. Our data suggest the that Galphat-HDt regulates PDE by allosterically decreasing the affinity of Palphabeta for Pgamma and thus simultaneously facilitating the interaction of the activated Galphat-Ras-like domain with Pgamma. Thus, we propose a new model for the high efficiency of PDE activation as well as deactivation, and, overall, a novel mechanism for controlling fidelity, sensitivity, and efficacy of G protein signaling.

Cell contact as an independent factor modulating cardiac myocyte hypertrophy and survival in long-term primary culture

Cardiac myocytes maintained in cell culture develop hypertrophy both in response to mechanical loading as well as to receptor-mediated signaling mechanisms. However, it has been shown that the hypertrophic response to these stimuli may be modulated through effects of intercellular contact achieved by maintaining cells at different plating densities. In this study, we show that the myocyte plating density affects not only the hypertrophic response and features of the differentiated phenotype of isolated adult myocytes, but also plays a significant role influencing myocyte survival in vitro. The native rod-shaped phenotype of freshly isolated adult myocytes persists in an environment which minimizes myocyte attachment and spreading on the substratum. However, these conditions are not optimal for long-term maintenance of cultured adult cardiac myocytes. Conditions which promote myocyte attachment and spreading on the substratum, on the other hand, also promote the re-establishment of new intercellular contacts between myocytes. These contacts appear to play a significant role in the development of spontaneous activity, which enhances the redevelopment of highly differentiated contractile, junctional, and sarcoplasmic reticulum structures in the cultured adult cardiomyocyte. Although it has previously been shown that adult cardiac myocytes are typically quiescent in culture, the addition of beta-adrenergic agonists stimulates beating and myocyte hypertrophy, and thereby serves to increase the level of intercellular contact as well. However, in densely-plated cultures with intrinsically high levels of intercellular contact, spontaneous contractile activity develops without the addition of beta-adrenergic agonists. In this study, we compare the function, morphology, and natural history of adult feline cardiomyocytes which have been maintained in cultures with different levels of intercellular contact, with and without the addition of beta-adrenergic agonists. Intercellular contact, communication, and transmission of contractile forces between myocytes appears to play a primary role in remodeling the 2-dimensional cell layer into a parallel alignment of elongated myocytes with highly developed intercalated disk-like junctions. This highly differentiated state is very stable, and cultures which achieve this state exhibit significantly greater longevity than more sparsely plated myocytes. These myocytes typically continue beating, and survive from 6 to more than 12 weeks in culture. When this level of contact and differentiation are not achieved, even among beta-adrenergic stimulated myocytes, contractile activity is not sustained, myofibrils atrophy, there is little or no development of junctional complexes, and the period of myocyte viability is typically no more than 5 weeks in vitro.

Transmission electron microscopic investigation of high-palladium dental casting alloys

OBJECTIVE

The purpose of this study was to use transmission electron microscopy to examine four representative high-palladium alloys and gain insight into possible strengthening mechanisms.

METHODS

Castings of two Pd-Cu-Ga alloys and two Pd-Ga alloys were thinned by jet polishing and ion milling, followed by plasma cleaning, to yield foil specimens. Multiple specimens were prepared for each alloy. Bright-field images, dark-field images and selected-area electron diffraction patterns for the alloys in the as-cast condition, after simulated porcelain-firing heat treatment, and after annealing at 980 degrees C were analyzed by standard transmission electron microscope (TEM) techniques. The overall compositions of the ultrastructures for the specimen foils were determined by conventional standardless energy-dispersive spectroscopic analyses with the TEM, and mean values of the elemental compositions were compared to the nominal alloy compositions provided by the manufacturers.

RESULTS

There was generally good agreement (differences less than 2 wt%) between the overall ultrastructure composition and each nominal alloy composition, except for Protocol from which in may have been lost during casting or formed intermetallic compounds that were not detected by TEM. The same fine-scale tweed structure within parallel bands of approximately 100-200 nm width was observed for all four alloys in the as-cast condition and after simulated porcelain-firing heat treatment. The persistence of the ultrastructure in the specimens of the two Pd-Cu-Ga alloys annealed at 980 degrees C and quenched in ice water indicated very rapid formation from the palladium solid solution. The presence of ¿100¿ and ¿110¿ forbidden reflections for the <001> zone suggested that the tweed structure is ordered, although further research is necessary to establish this conclusion.

SIGNIFICANCE

The presence of a similar tweed structure in both the Pd-Cu-Ga alloys and the Pd-Ga alloys of substantially lower hardness shows that some other strengthening mechanism accounts for the high hardness and strength generally observed for Pd-Cu-Ga alloys.

Intermittent inotropic therapy in an outpatient setting: a cost-effective therapeutic modality in patients with refractory heart failure

Patients with intractable heart failure (New York Heart Association [NYHA] class III and IV) who were receiving maximal conventional treatment were enrolled in an outpatient program that included inotropic infusions, intensive patient education, and close follow-up. The effects of this approach to therapy were evaluated on (1) the number of hospital admissions, (2) length of stay, and (3) number of emergency room visits during the ensuing year. These data were compared with similar data from the year before entry in the program for each patient. Thirty-six patients with stable NYHA class III and IV heart failure received milrinone or dobutamine to manage chronic heart failure in an outpatient setting. The cause of heart failure was ischemic heart disease in 12, idiopathic in 11, hypertension in 8, and pulmonary hypertension in 5. Four patients received dobutamine and 32 patients received milrinone. The mean period of observation was 294 days. For the period before entry in the program, patients had 21 emergency room visits, 75 admissions, and 528 days spent in the hospital. After enrollment, patients had 10 emergency room visits, 34 admissions, and 150 days spent in the hospital. In conclusion, this therapeutic regimen reduced the number of hospital admissions, days spent in the hospital, and emergency room visits. Our study supports the concept that the use of intermittent inotropic therapy in the outpatient setting plays an important role in managing this severely ill group of patients.

Scale effects in international migration to the United States

This study concerns regional variability in flows of international migration to the United States. Specifically, the author focuses on "the geographic concentration of flows by examining the variation in the characteristics of the flows to the largest immigrant states. The flows are analysed by country of origin and by age, skill levels and labour force participation. The paper also examines flows at a finer scale to counties within the largest receiving state, California. Just as across states in the United States, the variations across counties within California create disproportionate effects on particular localities. The paper documents the range of regional and local variation and argues that the scale effects are likely to increase because future flows are more likely to be dominated by network flows than by employment opportunities." (SUMMARY IN FRE AND GER)

Programmed myocyte cell death affects the viable myocardium after infarction in rats

To determine whether apoptotic and necrotic myocyte cell death occur acutely and chronically after infarction, the formation of DNA strand breaks and the localization of myosin monoclonal antibody labeling were analyzed in the surviving myocardium from 20 min to 1 month. DNA strand breaks in myocyte nuclei were detected as early as 3 h following coronary artery occlusion and were still present at 1 month. This cellular process was characterized biochemically by internucleosomal DNA fragmentation which produced DNA laddering on agarose gel electrophoresis. Quantitatively, 155 myocyte nuclei per 10(6) cells exhibited DNA strand breaks in the portion adjacent to the infarcted tissue at 3-12 h. This parameter increased to 704 at 1-2 days and subsequently decreased to 364 at 7 days, 188 at 14 days, and 204 at 1 month. In the remote myocardium, the number of myocyte nuclei with DNA strand breaks was 84 per 10(6) at 3-12 h and remained essentially constant up to 1 month. Programmed myocyte cell death was accompanied by a decrease in the expression of bcl-2 and an increase in the expression of bax. The changes in the expression of these genes were present at 1 and 7 days after coronary artery occlusion. In conclusion, the mechanical load produced by myocardial infarction and ventricular failure may affect the regulation of bcl-2 and bax in the viable myocytes, triggering programmed cell death and the remodeling of the ventricular wall.

Apoptotic and necrotic myocyte cell deaths are independent contributing variables of infarct size in rats

Programmed cell death in the myocardium has been linked to ischemia reperfusion injury as well as to excessive mechanical forces associated with increases in ventricular loading. Moreover, hypoxia activates the suicide program of cardiac myocytes in vitro. Because the supplied portion of the ventricular wall is ischemic and subjected to high levels of systolic and diastolic stresses (acutely after coronary artery occlusion), apoptosis and necrosis may contribute independently to myocyte cell death after infarction. Therefore, myocardial infarction was produced in rats, and, after the determination of ventricular hemodynamics, the contribution of apoptotic and/or necrotic myocyte cell death to infarct size was measured quantitatively from 20 minutes to 7 days after coronary artery occlusion. Programmed cell death was assessed by the terminal deoxynucleotidyl transferase assay and by the electrophoretic detection of DNA laddering. Myocyte necrosis was evaluated by myosin monoclonal Ab labeling. Moreover, the expression of Bcl-2, Bax, and Fas proteins in myocytes was examined by immunocytochemistry. Myocyte cell death by apoptosis and necrosis comprised nearly 3 million myocytes at 2 hours. Apoptotic cell death involved 2.8 million cells and necrotic cell death only 90,000 myocytes. Apoptosis continued to represent the major independent form of myocyte cell death, affecting 6.6 million myocytes at 4.5 hours. Myocyte necrosis peaked at 1 day, including 1.1 million myocytes. DNA electrophoretic analysis confirmed these observations by showing nucleosomal ladders at 2-3 hours, 4.5 hours, 1 day, and 2 days after coronary artery occlusion. Myocytes showing both DNA strand breaks and myosin labeling were a prominent aspect of myocardial damage only after 6 hours. Finally, the expression of Bcl-2 and Fas in myocytes increased 18-fold and 131-fold, respectively. In conclusion, programmed myocyte cell death is the major form of myocardial damage produced by occlusion of a major epicardial coronary artery, whereas necrotic myocyte cell death follows apoptosis and contributes to the progressive loss of cells with time after infarction. The enhanced expression of Fas may be implicated in the activation of apoptosis in spite of the increase in Bcl-2, which tends to preserve cell survival.

Demographic foundations of political empowerment in multiminority cities

As U.S. cities accommodate increasing ethnic and racial diversity, political choices may unify or divide their local populations. Those choices pull communities toward two different modes of pluralism: traditional "melting pot" assimilation or a complex mosaic of racial and ethnic assertiveness. Central to this issue is equity and empowerment, which may be accentuated by minority populations' size, structure, and spatial concentration. We examine two potential modes of local empowerment: "dominance," whereby each group is the majority of voters in single election districts (reinforcing separative tendencies), and "influence," whereby a group gains "influential minority" status in several districts (reinforcing unifying tendencies).

Myosin heavy chain synthesis is independently regulated in hypertrophy and atrophy of isolated adult cardiac myocytes

Hypertrophy of isolated adult feline cardiac muscle cells may be induced in culture by either alpha- or beta-adrenergic agonists. However, it has been shown previously that each of these agonists activate different subsets of immediate-early response genes and have different effects on expression of "fetal" protein isoforms and stimulation of protein synthesis. Moreover, in adult feline heart cells, beta-adrenergic agonists, such as isoproterenol, activate sustained synchronous beating and sarcomeric reorganization while alpha-adrenergic agonists, such as phenylephrine, do not. The objective of the present study was to determine whether these differences in proximal signaling events converged in a common signal pathway during activation of contractile protein synthesis. By direct comparisons of actin and myosin heavy chain (HC) synthesis and accumulation following isoproterenol and phenylephrine, it was determined that both agonists stimulate a coordinated accumulation of these proteins during cardiomyocyte growth. However, each agonist stimulated a very different program of contractile protein synthesis. During phenylephrine-induced hypertrophy, actin and myosin HC syntheses were rapidly and coordinately activated and continuously maintained at rates 10-25% greater than untreated cultures. The pattern of myosin HC synthesis following isoproterenol was very much more complex with periods during which it was as much as 40% greater or 25% less than in control cultures. Furthermore, there was no correlation between rates of actin and myosin HC synthesis following isoproterenol. It was concluded that actin and myosin HC syntheses and accumulation were regulated independently and in a very different manner following isoproterenol or phenylephrine. Since protein accumulation was not correlated with synthesis rates during development of hypertrophy, it was also concluded that post-translational mechanisms played a significant role in the maintenance of contractile protein stoichiometry during beta-adrenergic/beating-induced hypertrophy. Myosin HC synthesis also appeared to be independently regulated during cardiomyocyte atrophy induced by the calcium channel blocker nifedipine. Unlike the case in hypertrophy, however, protein balance was not maintained in nifedipine, and the depression of myosin HC synthesis and loss of myosin HC content were much greater than in the case of other contractile proteins.

Regulation of hypertrophy and atrophy in cultured adult heart cells

Mechanical loading and alpha-adrenergic receptor stimulation have both been shown to induce hypertrophy in isolated neonatal heart cells. The present study examined the effects of adrenergic hormones and contractile activity on the hypertrophic response in isolated adult feline cardiomyocytes maintained for more than 14 days in insulin- and serum-supplemented medium. Measurements of the hypertrophic response included cell size, total protein content, myosin heavy chain content, and the time course of activation of increased protein synthesis. Reactivation of the "fetal" gene program was evaluated by secretion of atrial natriuretic factor (ANF) into the medium. Significant myocyte hypertrophy was induced in both quiescent myocytes treated with alpha 1-adrenergic agonists and in beating myocytes treated with beta-adrenergic agonists. However, there were both quantitative and qualitative differences in the response to each type of stimulation. alpha-Adrenergic agonists promoted an increase in cell size, protein content, and ANF secretion but not myofibrillar reorganization, which was observed only in beating myocytes. In contrast to results reported for neonatal heart cells, determinants of hypertrophy in beating myocytes exceeded those in nonbeating alpha 1-adrenergic agonist-treated heart cells in every parameter examined. In addition, in the case of both beating and alpha-adrenergic stimulation, there were marked time-dependent variations in rates of protein synthesis over the interval of 4 hours to 7 days of treatment with each type of stimulus. Differences were also encountered in correlations between rates of protein synthesis and protein accumulation over this interval. The effect of beating was particularly important both to the reorganization of myofibrillar structure and the metabolism of myosin heavy chain. In cultures in which beating was inhibited with the calcium channel antagonist nifedipine, the loss of myosin heavy chain was significantly greater than that of total protein.

Contractile activity and cell-cell contact regulate myofibrillar organization in cultured cardiac myocytes

Adult feline ventricular myocytes cultured on a laminin-coated substratum reestablish intercellular junctions, yet disassemble their myofibrils. Immunofluorescence microscopy reveals that these non-beating heart cells lack vinculin-positive focal adhesions; moreover, intercellular junctions are also devoid of vinculin. When these quiescent myocytes are stimulated to contract with the beta-adrenergic agonist, isoproterenol, extensive vinculin-positive focal adhesions and intercellular junctions emerge. If solitary myocytes are stimulated to beat, an elaborate series of vinculin-positive focal adhesions develop which appear to parallel the reassembly of myofibrils. In cultures where neighboring myocytes reestablish cell-cell contact, myofibrils appear to reassemble from the fascia adherens rather than focal contacts. Activation of beating is accompanied by a significant reduction in the rate of total and cytoskeletal protein synthesis; in fact, myofibrillar reassembly, redevelopment of focal adhesions and fascia adherens junctions require no protein synthesis for at least 24 h, implying the existence of an assembly competent pool of cytoskeletal proteins. Maturation of the fasciae adherens and the appearance of vinculin within Z-line/costameres, does require de novo synthesis of new cytoskeletal proteins. Changes in cytoskeletal protein turnover appear dependent on beta agonist-induced cAMP production, but myofibrillar reassembly is a cAMP-independent event. Such observations suggest that mechanical forces, in the guise of contractile activity, regulate vinculin distribution and myofibrillar order in cultured adult feline heart cells.

Evidence for post-translational kinetic compartmentation of protein turnover pools in isolated adult cardiac myocytes

The kinetics of protein metabolism were evaluated in isolated adult feline cardiomyocytes maintained in long term cell culture. The results of these studies suggested that, rather than individual proteins entering a kinetically homogeneous pool, most newly synthesized proteins were segregated into different kinetic compartments with different probabilities of being degraded. Evidence for this conclusion was developed from two types of experiment. The first line of evidence was derived from the kinetics of labeled amino acid incorporation into protein when labeling was conducted over very short or long periods (4 h to 32 days). The observed rates of isotope incorporation over different periods did not fit the expected pattern for a homogeneous pool. A close approximation of observed rates of label incorporation over both short and long labeling intervals could, however, be fit to results predicted using a two-compartment model. When the results of long term equilibration labeling studies were also evaluated relative to short and long term labeling ratios, then it was also possible to identify a unique set of parameters for a two-compartment model which could account for label incorporation in both types of experiment. From this analysis it was estimated that the fast kinetic compartment represented a steady-state level of 10% of total cellular protein with a mean half-life of 21.9 h (ks = 75.9% d-1). The slow kinetic compartment comprised the remaining 90% of protein with a mean t1/2 equal to 15.6 days (ks = 4.4% d-1). Both the observed and predicted equilibration rate of this two compartment mixture was best fit by a single exponential function with an equilibration rate of 5.48% d-1. Based on this outcome, it was also predicted that mixing of nascent and long lived proteins could be followed using a protocol of long and short term labeling in different isotopes followed by a chase period without label. By tracking the isotope ratios in total proteins and SDS-polyacrylamide gel electrophoresis separated proteins, as well as in counts released into the culture medium during the chase period it was determined that nascent proteins were preferentially degraded for a period of at least 48 h following synthesis. Up to 20% of nascent proteins in both the total protein compartment as well as individual proteins, such as myosin heavy chain, were preferentially degraded prior to achieving a state of homogeneous mixing with long lived proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

Stress activation of mesocorticolimbic dopamine neurons: effects of a glycine/NMDA receptor antagonist

Restraint of brief duration causes a metabolic activation of mesocortical and some mesolimbic dopaminergic systems with little effect on the nigrostriatal system. We have examined the ability of an antagonist of the allosteric glycine site of the N-methyl-D-aspartate receptor complex to block the stress-induced response in dopamine utilization. Thirty minutes of restraint stress elevated dopamine metabolism, as measured by the ratio between 3,4-dihydroxyphenylacetic acid (DOPAC) and dopamine, in both the medial prefrontal cortex and nucleus accumbens. An antagonist for the glycine/N-methyl-D-aspartate receptor complex, 1-hydroxy-3-aminopyrrolidone-2 ((+)-HA-966), given systemically or injected into the ventral tegmental area, prevents the stress-induced increase in dopamine metabolism in the prefrontal cortex without altering the response in the nucleus accumbens. Similarly, systemic administration of the non-competitive antagonist for the N-methyl-D-aspartate receptor, dizocilpine ((+)-MK-801), blocked the stress-induced rise in dopamine metabolism in the medial prefrontal cortex but not the nucleus accumbens. The negative enantiomer of HA-966 did not produce a selective antagonism of the stress-induced dopamine metabolism in the medial prefrontal cortex. These results support previous work which suggest the mesocortical and mesoaccumbens dopamine neurons respond to excitatory input through different glutamate receptor mechanisms. Additionally, the specific blockade of the stress-induced change in dopamine metabolism in the medial prefrontal cortex by a glycine antagonist implies a role for such an antagonist in treatment of disease states which may involve disruptions of N-methyl-D-aspartate receptor function.

Cultured adult cardiac myocytes maintain protein synthetic capacity of intact adult hearts

Previous studies have shown that the rates of protein synthesis observed in embryonic and neonatal heart cells in culture are as much as nine times greater than the rates of synthesis observed in the intact adult heart either in situ or in isolated perfusion studies. This study addressed whether adult cardiomyocytes in long-term culture maintain the protein synthetic capacity of the adult myocardium or, rather, whether the protein synthetic capacity expands or falls as adult cardiac myocytes progress in culture. Protein synthesis was evaluated in isolated adult feline cardiomyocytes maintained in serum and insulin-supplemented medium for up to 53 days in vitro. With the use of both pulse- and saturation-labeling techniques it was determined that the rate of protein synthesis in adult cardiomyocytes was maintained at a level very close to that observed in the intact heart for over 1 mo in culture. Saturation-labeling studies indicate a fractional rate of protein synthesis at 6.1%/day and an absolute synthesis rate of 1,300 nmol leucine incorporated.g protein-1.h-1. Pulse-labeling studies revealed an initial increase in protein synthesis rates during adaptation to culture and a further increase after activation of beating and cellular hypertrophy.

Comparing cross-sectional and longitudinal analyses of residential mobility and migration

"A reevaluation of cross-sectional versus longitudinal models of residential mobility...casts doubt on the study by Davies and Pickles in 1985 in which it was argued that cross-sectional analysis is inadequate.... With the use of data from the [U.S.] Panel Study of Income Dynamics (PSID), the conclusion of this reevaluation is that longitudinal analysis increases our understanding of the processes and provides a richer understanding of migration and mobility but does not undermine the work that has been produced from cross-sectional analysis."

Residential preferences and residential choices in a multiethnic context

A study of the expressed preferences of four different ethnic groups in the Los Angeles metropolitan area shows strong desires for own-race combinations in the ethnicity of neighborhoods that individuals say they would choose when seeking a new residence. The results also show that Anglos are not the only group to practice "avoidance" of other racial/ethnic neighborhoods, although avoidance behavior by Anglos is the strongest. Because the issues of racial composition are socially sensitive, additional tests examined the relationship of preferences to behavior. Although many behaviors generally follow expressed preferences, members of households who expressed "no preference" also were found to largely choose own race neighborhoods. The results of this study suggest that the expressed preference for own race/own ethnicity, in combination with short-distance local moves, is likely to maintain present patterns of separation in U.S. metropolitan areas.

Adrenergic receptor desensitisation may serve a cardioprotective role

OBJECTIVE

The aim was to test the hypothesis that beta adrenoceptor desensitisation is a form of cardioprotection whereby the myocardium is protected from the injurious effects of excessive adrenergic stimulation by isoprenaline.

METHODS

A new sensitive and specific method of identifying cardiac myocyte necrosis with monoclonal antimyosin was employed. Antibody labelled necrotic cardiomyocytes from male Sprague-Dawley rats (190-300 g) were identified by immunofluorescence. Homologous beta adrenoceptor desensitisation was induced by 9 d pretreatment with isoprenaline infusion (20 mg.kg-1.d-1), and heterologous desensitisation by treatment with 0.15% propylthiouracil in the diet for six weeks. The effects of isoprenaline induced cardiomyocyte injury in these animals were compared with those in control rats.

RESULTS

In euthyroid control rats, treatment with the beta adrenergic agonist, isoprenaline, produced prolonged tachycardia and hypotension, and a significant amount of cardiac myocyte necrosis subendocardially. When the same isoprenaline challenge was given to rats pretreated for 9 d with an isoprenaline infusion, the haemodynamic response was markedly attenuated and very little myocyte necrosis was noted. In the model of heterologous desensitisation occurring in hypothyroidism, isoprenaline challenge produced markedly diminished haemodynamic response and little cardiac myocyte necrosis.

CONCLUSIONS

In both homologous and heterologous models of beta adrenoceptor desensitisation, the susceptibility of the myocardium to isoprenaline induced cytotoxicity is markedly reduced.

Effects of 6-hydroxydopamine lesions of the prefrontal cortex on tyrosine hydroxylase activity in mesolimbic and nigrostriatal dopamine systems

The effects of prefrontal cortical dopamine depletion on subcortical dopamine function in the rat were examined. 6-Hydroxydopamine lesions of the dopaminergic innervation of the prefrontal cortex did not alter concentrations of dopamine or its metabolite 3,4-dihydroxyphenylacetic acid in either the striatum or nucleus accumbens. Similarly, the activity of the catecholamine biosynthetic enzyme tyrosine hydroxylase in the striatal complex was not changed in animals with prefrontal cortical lesions. Animals sustaining neurotoxic lesions of the prefrontal cortex were challenged with haloperidol in order to activate submaximally tyrosine hydroxylase activity. The magnitude of the haloperidol-induced increase in enzyme activity in the nucleus accumbens was significantly greater in lesioned subjects than in control animals. These data suggest that lesions of the prefrontal cortical dopamine innervation do not result in significant alterations in basal dopaminergic function in the striatal complex. However, lesions of the dopaminergic innervation of the prefrontal cortex significantly increase the responsiveness of mesolimbic dopamine afferents to pharmacological challenge.

Hypertrophy of isolated adult feline heart cells following beta-adrenergic-induced beating

Catecholamine-induced beating and myocardial hypertrophy were evaluated in isolated adult feline cardiomyocytes maintained in culture for up to 30 days. Adult feline cardiomyocytes were used in this study because they displayed several unique characteristics that facilitated assessment of factors regulating cardiomyocyte hypertrophy in vitro. These characteristics included the following. 1) A single heart provides a high yield of 20-40 x 10(6) calcium-tolerant rod-shaped myocytes. 2) In culture, isolated adult feline cardiomyocytes maintain a stable population of differentiated myocytes that could be maintained without the dramatic loss of cell number, DNA content, or cell structure seen in adult rat cardiomyocyte cultures. 3) Cultured feline cardiomyocytes remained quiescent in culture unless appropriately stimulated to begin beating. 4) Sustained regular beating activity could be readily initiated up to 3 wk in culture by addition of 1 x 10(-5) M isoproterenol, other beta-adrenergic agonists, or agents known to elevate adenosine 3',5'-cyclic monophosphate. Beating could be maintained indefinitely in the presence of isoproterenol, but ceased upon removal of isoproterenol from the medium. Initiation of beating in 7-day-old cultures resulted in a profound restructuring of cardiomyocyte morphology compared with quiescent cultures. Beating heart cells were 66% larger with increased protein content, and they had significantly greater development of striated myofibrillar structure than quiescent myocytes at the same age in culture. We conclude that maintenance of an organized myofibrillar structure in cultured adult cardiac myocytes requires activation of intrinsic beating. Cardiomyocyte hypertrophy also develops following beta-adrenergic activation of beating, but it is unclear whether beating per se is required for inducing hypertrophy in isolated adult cardiomyocytes in vitro.

Autoimmune determinants of rheumatic carditis: localization of epitopes in human cardiac myosin

Rheumatic carditis is a sequela of group A streptococcal throat infection. Although the pathogenic mechanisms which lead to heart damage in acute rheumatic fever (ARF) are not well understood, autoimmune processes have been implicated, involving molecular mimicry between streptococci and the human heart. We have studied the immunological cross-reactions between the group A Streptococcus and human heart to understand their molecular and immunological basis. Human and mouse monoclonal antibodies (mAb) and affinity-purified anti-myosin antibodies from acute rheumatic fever sera were characterized and shown to cross-react with group A streptococcal M protein and myosin. Studies of proteolytic fragments of human cardiac myosin identified sites of cross-reactivity in the rod region of the myosin heavy chain. Murine monoclonal antibodies cross-reactive with streptococcal M protein and myosin recognized epitopes located in the S2 and light meromyosin (LMM) subfragments of the heavy chain. None of the cross-reactive monoclonal antibodies recognized the S1 subfragment. One broadly cross-reactive monoclonal antibody was highly cytotoxic for heart cells in vitro and reactive with the LMM fragment. The data suggest that the cross-reactive epitopes recognized by these antibodies are conformational, dependent upon their alpha-helical structures, and potentially damaging to host tissues.

Cell shape and organization of the contractile apparatus in cultured adult cardiac myocytes

The isolation and culture of adult cardiac myocytes has proved to be an ideal model system to explore myocardial biology at the cellular level. A major criticism of this model, however, has been that organ-specific characteristics such as cell shape and subcellular structural organization cannot be retained in vitro for prolonged periods of time. Encasing freshly isolated myocytes in a matrix of calcium alginate enables one to maintain the rod-like, three-dimensional (3D) shape of the cultured myocyte. Such preparations more closely resemble their in vivo counterparts with respect to the organization of the contractile apparatus, the transverse tubular system and the sarcoplasmic reticulum than do heart cells cultured on a two-dimensional (2D) plastic surface. Stereologic measurements reveal that myofibrillar volume density (VvMYF) decreases in both non-beating preparations over a 2-week interval, but VvMYF is conserved in cells cultured in an alginate matrix when compared to those myocytes maintained on a laminin-coated substratum. The present observations suggest that in the absence of contractile function myofibrillar atrophy appears responsible for the decline in VvMYF in alginate (3D) preparations, whereas atrophy and subcellular remodelling probably mediate the myofibrillar loss and reorganization that develops when adult heart cells are cultured on a 2D surface.

Residential preferences and neighborhood racial segregation: a test of the Schelling segregation model

The debate over the role of the forces that create the patterns of residential separation has identified neighborhood preferences as one of the explanatory variables, but although we possess some empirical data on the nature of neighborhood racial preferences, the theoretical contributions have received only limited empirical evaluation. Among the theoretical statements, Schelling's model of the effects of small differences in preferences on residential patterns has provided a basic building block in our understanding of preferences, choices, and patterns. Several recent surveys of residential preferences provide the data with which to evaluate the underpinnings of the Schelling model. The preference/tolerance schedules that are derived from the data have a different functional form from that suggested by Schelling, but confirm the view that stable integrated equilibria are unlikely.

Subcellular compartmentalization of myosin isoforms in embryonic chick heart ventricle myocytes during cytokinesis

Embryonic chick heart ventricle myocytes retain the ability to alternate between proliferation and functional differentiation. A cytoplasmic isoform of myosin is present in cleavage furrows of various nonmuscle cells during cytokinesis, whereas one or more of the cardiac myosin isoforms are localized in sarcomeres of beating cardiomyocytes. Antibodies were employed to reveal the subcellular localizations of cytoplasmic and cardiac myosin isoforms in embryonic chick ventricle cardiomyocytes during cytokinesis. Monoclonal anticytoplasmic myosin antibodies were prepared against myosin purified from brains of 1-day-posthatched chickens and shown to react with chick brain myosin heavy chain by Western blots and/or ELISA tests. One monoclonal antibrain myosin antibody also cross-reacted with chick cardiac myosin but not with skeletal or smooth muscle myosins. Two antichick cardiac myosin monoclonal antibodies and one antichick skeletal myosin polyclonal antibody that cross-reacts with cardiac myosin were employed to identify cardiac sarcomeric myosin. Cells were isolated from day 8 embryonic chick heart ventricles, enriched for myocytes, grown in vitro for 3 days, and then examined by immunofluorescence techniques. Monoclonal antibodies against cytoplasmic myosin preferentially localized in the cleavage furrows of both cardiofibroblasts and cardiomyocytes in all stages of cytokinesis. In contrast, antibodies that recognize cardiac myosin were distributed throughout cardiomyocytes during early stages of cytokinesis, but became progressively excluded from the furrow area during middle and late stages of cytokinesis. These data suggest that in cells that contain both cytoplasmic and sarcomeric myosin isoforms, only cytoplasmic myosin isoforms are mobilized to from the contractile ring for cytokinesis.

Elderly mobility and mobility outcomes: households in the later stage of the life course

Recent research has demonstrated that elderly residential mobility is conditioned more often by economic factors than is mobility in general. This article explores these issues, specifically those related to the effects of mobility, aging in place, and migration on elderly economic well-being. Using the American Housing Survey national file for 1985, different types of mobility and migration for households in the later stages of the life course are examined. The evidence reiterates central city/suburban locational differences for the elderly, emphasizes the role of house costs, and house cost/income ratios in creating stress for the elderly, and strongly suggests that the elderly population is not simply grouped into young-old, old, and old-old, but is better treated in a continuum of life course changes.

Dose response of dairy cows to ammonium salts of volatile fatty acids

In previous studies ammonium salts of a mixture of isobutyrate, 2-methylbutyrate, isovalerate, and valerate were fed in a corn silage, corn, corn gluten meal, and urea diet to Holstein cows throughout lactation to define the optimum level of ammonium salts of milk production. The objective of this work was to conduct another dose response study using other forage and protein sources and to determine the effects of decreasing VFA intakes as lactation advanced. The concentrate portion of the diet contained 0, .4, .8, 1.2, or 1.6% ammonium salts of VFA. The forage to concentrate ratio was 50:50, 60:40, and 70:30 for the first, middle, and last third of lactation, respectively. The study was conducted at four university locations using 191 Holstein cows. Feeds used included corn silage, alfalfa silage or hay, corn, soybean meal, minerals, and vitamins. Treatment x location interactions were significant for milk yield during early lactation. During mid- and late lactation, supplemental VFA (.8%) improved milk and protein yield. Milk composition was not greatly affected by feeding VFA. In mid-lactation, cows fed .8% ammonium salts of VFA ate more feed than did controls. Feed efficiencies were similar among groups throughout the experiment. Cows fed VFA tended to gain less BW during lactation than did controls. Health and reproduction were not different among groups.

Prefrontal cortical dopamine depletion enhances the responsiveness of mesolimbic dopamine neurons to stress

Mild footshock stress results in the metabolic activation of the prefrontal cortical dopamine (DA) innervation, but does not augment DA utilization in mesolimbic areas (such as the nucleus accumbens septi, NAS) or the striatum. However, increases in either the intensity or duration of footshock stress increase DA utilization in the subcortical sites. DA afferents to the prefrontal cortex (PFC) hold corticofugal projection neurons under tonic inhibition. Previous data suggest that removal of these corticofugal glutamatergic neurons from tonic DA inhibition results in a transsynaptic alteration in the NAS, such that the DA innervation of the NAS is rendered hyperresponsive to certain perturbations. We therefore examined the effects of stress on subcortical DA systems in rats previously subjected to 6-hydroxydopamine lesions of the PFC DA innervation. Mild footshock stress resulted in an increase in concentrations of the DA metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the PFC, but not NAS or striatum, of sham-lesioned animals. Footshock resulted in a significant increase in the concentration of DOPAC in the nucleus accumbens of animals sustaining PFC lesions two weeks previously. The PFC lesion did not result in a stress-induced increase in DA release in the striatum. These results suggest that disruption of the PFC DA innervation results in an enhanced responsiveness of the mesolimbic DA innervation to stress. These data may help explain the stress-elicited exacerbation of the psychotic process in schizophrenia.

Relation between left ventricular systolic resistance and contractile rate processes

To test the hypothesis that left ventricular (LV) systolic resistance is determined by the intrinsic rate processes of the contractile system, we studied 40 spontaneously hypertensive male rats (SHR). Thyroid hormone manipulation was used to alter isomyosin composition and consequently the rate processes of the contractile system. Seven groups of rats were studied: control (SHRC, n = 9); propylthiouracil (PTU) treated for 10 days (SHRP-10, n = 5), 20 days (SHRP-20, n = 5), and 30 days (SHRP-30, n = 6); and thyroxine treated for 5 days (SHRT-05, n = 5), 10 days (SHRT-10, n = 5), and 15 days (SHRT-15, n = 5). In situ (n = 40) and isolated (n = 14; 5 SHRP-30, 5 SHRC, and 4 SHRT-15) heart experiments were performed. In comparison to SHRC, we observed the following: 1) LV pump performance was not different in any of the thyroxine-treated groups, whereas with PTU, pump performance was significantly depressed in rats with greater than 80% slow myosin. 2) Normalized LV peak elastance (Emaxn) was significantly increased in the SHRP-30, whereas it was not altered after thyroxine. These observations were further confirmed in the isolated heart on the basis of peak isovolumetric stress-strain relations. 3) Thyroxine increased and PTU decreased theoretical maximum flow (Qmax; a measure of LV resistance); thus an inverse relation between Qmax and percent slow myosin was observed (r2 = 0.86). 4) The time to peak isovolumetric pressure was increased in SHRP-30 and decreased in SHRT-15. The relaxation process was significantly slower for SHRP-30 group and was unchanged for SHRT-15 group. These observations support our hypothesis that LV systolic resistance quantifies an intrinsic rate-dependent property of the myocardium and that isomyosin composition is one of its determinants. In addition, with changes in isomyosin composition toward predominantly slow myosin, the responses in Emaxn and Qmax are discordant, which may be responsible for the preservation of pump performance. This underscores the importance of quantifying both LV systolic resistance and elastance in the assessment of the functional status of the LV as a mechanical pump.

Isoproterenol-induced myocardial fibrosis in relation to myocyte necrosis

Treatment of rats with the beta-adrenergic agonist isoproterenol results in cardiac hypertrophy, myocyte necrosis, and interstitial cell fibrosis. Our objectives in this study have been to examine whether hypertrophy and fibrosis occur in a compensatory and reparative response to myocyte loss or whether either process may be occurring independently of myocyte loss and thus be a reactive response to adrenergic hormone stimulation. We have examined this question by evaluating each of these responses in rats treated with different doses and forms of isoproterenol administration. Myocyte necrosis was evaluated using in vivo labeling with monoclonal antimyosin for identification of myocytes with permeable sarcolemma, which was indicative of irreversible injury. Myocardial fibrosis was evaluated by morphometric point counting of Gomori-stained tissue sections and by assessment of the stimulation of fibroblast proliferation by determination of increased levels of DNA synthesis. Stimulation of fibroblast DNA synthesis was determined from DNA specific radioactivities and radioautography after pulse labeling with [3H]thymidine. The evidence provided by this study suggests that the degree and timing of myocardial hypertrophy does not follow the course of myocyte loss and, thus, appears to be either a response to altered cardiac loading or a reactive response to beta-adrenergic hormone stimulation rather than a compensation for myocyte loss. Myocardial fibrosis, on the other hand, appears to be more closely related to myocyte necrosis with respect to collagen accumulation in the same areas of the heart, its dose-response relation to the amount of isoproterenol administered, and the timing of increased DNA synthesis, or fibroblast proliferation, after myocyte loss.

Tissue plasminogen activator-mediated thrombolysis of cerebral emboli and its effect on hemorrhagic infarction in rabbits

Tissue plasminogen activator (tPA) dissolves intravascular thrombus and restores blood flow after thromboembolic vascular occlusion. The utility of this agent for treatment of stroke in humans may be limited by post-reperfusion hemorrhagic complications. We studied tPA-mediated thrombolysis in an animal model of cerebrovascular occlusion in order to determine what factors, if any, predispose tPA-treated animals to suffer hemorrhage. Small blood clot emboli were injected into the internal carotid arteries of rabbits. Angiograms confirmed occlusion of the middle cerebral artery or internal carotid artery in 100% of subjects. tPA or saline was administered as a 30-minute infusion at various times after embolization. Hemorrhage rates were similar in all groups regardless of treatment. tPA increased the prothrombin time and the thrombin time but not the partial thromboplastin time. There was no correlation between these changes in blood coagulation and the finding of cerebral hemorrhage. We observed a significant association between stroke severity and cerebral hemorrhage. We conclude that tPA treatment successfully causes thrombolysis of cerebral emboli without causing an increase in the incidence of cerebral hemorrhage in rabbits.

Cardiac myosin isoenzyme shifts in non-insulin treated spontaneously diabetic rats

We evaluated myocardial myosin isoform distribution in a group of diabetic BB/W rats from which insulin was withheld for varying periods in order to evaluate the time course and extent of myosin isoform shifts in these animals. Prior studies of myosin isoform distribution in diabetic rats have utilized chemically induced diabetic rats or insulin-treated BB/W rats. Following a stabilization period on insulin therapy, insulin was withheld for 9-28 days during which the animals received supplemental parenteral bicarbonate and Ringer's lactate. Left ventricular myocardial myosin isoform distribution was determined by nondenaturing pyrophosphate gel electrophoresis. We found that the normal predominance of V1 isomyosin in these rats was shifted to V3 predominance by approximately two weeks after the cessation of insulin therapy. This was significantly sooner than was seen in another study which utilized insulin treated BB/W rats, and is similar to the time course seen with chemically induced diabetic rats. In addition, the normal V1 myosin isoform distribution observed during insulin therapy and the progressive shift to the V3 isoform distribution during increasing periods without insulin suggest that this shift can be prevented with insulin alone.