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Biomedical subjects

G Cooper

Publications and source records attributed to G Cooper.

At least 91 records · Page 5Linked to original sources
PubMed1996

Translational initiation factor eIF-4E. A link between cardiac load and protein synthesis.

To define the coupling mechanism between cardiac load and the rate of protein synthesis, changes in the extent of eIF-4E phosphorylation were measured after imposition of a load. Electrically stimulated contraction of adult feline cardiocytes increased eIF-4E phosphorylation to 34% after 4 h, as compared with 8% phosphorylation in quiescent controls. However, eIF-4E phosphorylation did not increase upon electrical stimulation in the presence of 7.5 mM 2,3-butanedione monoxime, an inhibitor of actin-myosin cross-bridge cycling and active tension development. Treatment of adult cardiocytes with either 0.1 microM insulin or 0.1 microM phorbol 12-myristate 13-acetate increased eIF-4E phosphorylation to 23 and 64%, respectively, but these increases were not blocked by 2,3-butanedione monoxime. In canine models of acute hemodynamic overload in vivo, eIF-4E phosphorylation increased to 23% in response to left ventricular pressure overload as compared with 7% phosphorylation in controls. Acute volume overload had no effect on eIF-4E phosphorylation. These changes in eIF-4E phosphorylation account for differences in anabolic responses to acute pressure versus acute volume overload. These data suggest that eIF-4E phosphorylation is a mechanism by which increased cardiac load is coupled to accelerated rates of protein synthesis.

Animals↗
PubMed1996

Basis for increased microtubules in pressure-hypertrophied cardiocytes.

BACKGROUND: We have shown the levels of the sarcomere and the cardiocyte that a persistent increase in microtubule density accounts to a remarkable degree for the contractile dysfunction seen in pressure-overload right ventricular hypertrophy. In the present study, we have asked whether these linked phenotypic and contractile abnormalities are an immediate and direct effect of load input into the cardiocyte or instead a concomitant of hypertrophic growth in response to pressure overloading. METHODS AND RESULTS: The feline right ventricle was pressure-overloaded by pulmonary artery banding. The quantity of microtubules was estimated from immunoblots and immunofluorescent micrographs, and their mechanical effects were assessed by measuring sarcomere motion during microtubule depolymerization. The biogenesis of microtubules was estimated from Northern and Western blot analyses of tubulin mRNAs and proteins. These measurements were made in control cats and in operated cats during and after the completion of right ventricular hypertrophy; the left ventricle from each heart served as a normally loaded same-animal control. We have shown that the alterations in microtubule density and sarcomere mechanics are not an immediate consequence of pressure overloading but instead appear in parallel with the load-induced increase in cardiac mass. Of potential mechanistic importance, both these changes and increases in tubulin poly A+ mRNA and protein coexist indefinitely after a new, higher steady state of right ventricular mass is reached. CONCLUSIONS: Because we find persistent increases both in microtubules and in their biosynthetic precursors in pressure-hypertrophied myocardium, the mechanisms for this cytoskeletal abnormality must be sought through studies of the control both of microtubule stability and of tubulin synthesis.

Animals↗
PubMed1996

Incidence and outcome of overt gastrointestinal bleeding in patients undergoing bone marrow transplantation.

The purpose of this study was to determine the prevalence, clinical patterns, and outcomes of gastrointestinal bleeding in consecutive patients treated at one bone marrow transplant center. We reviewed the clinical course of 579 consecutive bone marrow transplant recipients who underwent therapy from January 1986 through December 1993. These patients were evaluated for overt gastrointestinal bleeding, defined as hematemesis, melena, hematochezia, or a combination. Overt gastrointestinal bleeding was defined in 43 of 579 patients (7.4%), including 25 men and 18 women undergoing transplantation for hematologic disorders (N = 29) and solid tumors (N = 14). After high-dose cytotoxic chemotherapy, patients were given allogeneic (N = 10) or autologous (N = 33) hematopoietic progenitor cell support obtained from bone marrow, peripheral blood, or both. H2 blockers, sucralfate, or a combination were administered to all patients as prophylactic therapy. Bleeding manifestations included hematemesis(N = 24, melena (N = 8), hematochezia (N = 7), and combinations (N = 4). The median time from bone marrow infusion to the onset of overt gastrointestinal bleeding was 7.5 days (range: 0-45 days). Fourteen patients had evidence of orthostatic hypotension attributable to gastrointestinal bleeding. Esophagogastroduodenoscopy was performed in 26 patients; 18 had diffuse esophagitis and gastritis. Two patients with bleeding ulcers underwent successful electrocautery. Colonoscopy was performed in five patients and revealed a cecal ulcer in one subject, tumor recurrence in one patient, and colitis in another. No patients underwent surgical intervention. Only ine patient died as a result of gastrointestinal bleeding. Overt gastrointestinal bleeding is uncommon in patients undergoing bone marrow transplantation; most episodes are self-limited and do not contribute to overall mortality. Endoscopy is primarily diagnostic as most patients do not have lesions amenable to therapeutic procedures.

Adolescent↗
PubMed1996

A self-help approach for high-risk drinking: effect of an initial assessment.

A self-help book was offered to persons wanting to quit or cut down on their alcohol use. Study participants (99 men, 56 women) were recruited through advertisements, screened by telephone, and randomly assigned to 1 of 2 conditions. Book by mail or Assessment + Book (30-min telephone motivational interview plus book by mail). At 3-month follow-up, significantly more participants qualified as moderate drinkers in the Assessment + Book condition (65% vs. 43%), by this criterion: < or = 12 drinks/week and < or = 10% heavy drinking days (5 + drinks if male and 4 + drinks if female; 13.6 g of ethanol per drink). At 12 months there was no effect of condition, but significantly more women than men were rated as moderate drinkers (71% vs. 52%). Collateral informants corroborated the participants' reports of drinking.

Adult↗
PubMed1996

Network analysis of human Y microsatellite haplotypes.

To investigate the utility of Y chromosome microsatellites for studying human male-lineage evolution, we typed samples from three populations for five tetranucleotide repeats and an Alu insertion polymorphism. We found very high levels of haplotype diversity and evidence that most mutations involve the gain or loss of only one repeat unit, implying that any given microsatellite haplotype may have arisen independently on two or more Y-chromosome lineages. Together, these factors suggest that interpretation of small sample sizes (< 30) will be problematic. By typing a large sample of individuals (n = 174) from one population, East Anglia, we were able to construct a haplotype network. The network exhibits a well-connected core structure of commoner haplotypes. Computer simulations based on this network estimate the convergence time for African and Caucasian groups may be between 1.4 and 1.8 times as long as the convergence of the East Anglian population. Based on our comparison between large and small sample sizes, we suggest that large sample sizes are necessary in order to interpret Y-microsatellite haplotypes, and that a network analysis of the type we describe may prove informative in future studies.

Base Sequence↗
PubMed1996

Effects of anisosmotic stress on cardiac muscle cell length, diameter, area, and sarcomere length.

The purpose of this study was to examine the effects of anisosmotic stress on adult mammalian cardiac muscle cell (cardiocyte) size. Cardiocyte size and sarcomere length were measured in cardiocytes isolated from 10 normal rats and 10 normal cats. Superfusate osmolarity was decreased from 300 +/- 6 to 130 +/- 5 mosM and increased to 630 +/- 8 mosM. Cardiocyte size and sarcomere length increased progressively when osmolarity was decreased, and there were no significant differences between cat and rat cardiocytes with respect to percent change in cardiocyte area or diameter; however, there were significant differences in cardiocyte length (2.8 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05) and sarcomere length (3.3 +/- 0.3% in cat vs. 6.1 +/- 0.3% in rat, P < 0.05). To determine whether these species-dependent differences in length were related to diastolic interaction of the contractile elements or differences in relative passive stiffness, cardiocytes were subjected to the osmolarity gradient 1) during treatment with 7 mM 2,3-butanedione monoxime (BDM), which inhibits cross-bridge interaction, or 2) after pretreatment with 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N, N,N',N'-tetraacetic acid (EGTA), a bivalent Ca2+ chelator. Treatment with EGTA or BDM abolished the differences between cat and rat cardiocytes. Species-dependent differences therefore appeared to be related to the degree of diastolic cross-bridge association and not differences in relative passive stiffness. In conclusion, the osmolarity vs. cell size relation is useful in assessing the cardiocyte response to anisosmotic stress and may in future studies be useful in assessing changes in relative passive cardiocyte stiffness produced by pathological processes.

Animals↗
PubMed1996

Comparative effects of contraction and angiotensin II on growth of adult feline cardiocytes in primary culture.

The purposes of this study were 1) to determine whether angiotensin II causes growth of adult feline cardiocytes in long-term culture, 2) to compare the growth effects of angiotensin II with those resulting from electrically stimulated contraction, and 3) to determine whether the anabolic effects of contraction are exerted via the angiotensin type 1 receptor. Adult feline cardiocytes were cultured on laminin-coated trays in a serum-free medium. Cardiocytes were either electrically stimulated to contract (1 Hz, 5-ms pulse duration, alternating polarity) or were nonstimulated and quiescent. Quiescent cells were studied as controls and after treatment with angiotensin II (10(-8) M), losartan (10(-6) M; an angiotensin type 1-receptor antagonist), or angiotensin II plus losartan. Contracting cells were studied in the presence and absence of angiotensin II or losartan. In quiescent cardiocytes, angiotensin II treatment on day 7 significantly increased protein synthesis rates by 22% and protein content per cell by 17%. The effects of angiotensin II were completely blocked by losartan. Electrically stimulated contraction on days 4 and 7 in culture significantly increased protein synthesis rate by 18 and 38% and protein content per cell by 19 and 46%, respectively. Angiotensin II treatment did not further increase protein synthesis rate or protein content in contracting cardiocytes. Furthermore, losartan did not block the anabolic effects of contraction on protein synthesis rates or protein content. In conclusion, angiotensin II can exert a modest anabolic effect on adult feline cardiocytes in culture. In contracting feline cardiocytes, angiotensin II has no effect on growth. Growth caused by electrically stimulated contraction occurs more rapidly and is greater in magnitude than that caused by angiotensin II. Growth of contracting adult feline cardiocytes is not dependent on activation of the angiotensin receptor.

Angiotensin II↗
PubMed1996

Effects of pressure- or volume-overload hypertrophy on passive stiffness in isolated adult cardiac muscle cells.

It has been hypothesized that the changes in myocardial stiffness induced by chronic hemodynamic overloading are dependent on changes in the passive stiffness of the cardiac muscle cell (cardiocyte). However, no previous studies have examined the passive constitutive properties of cardiocytes isolated from animals with myocardial hypertrophy. Accordingly, changes in relative passive stiffness of cardiocytes isolated from animals with chronic pressure- or volume-overload hypertrophy were determined by examining the effects of anisosmotic stress on cardiocyte size. Anisosmotic stress was produced by altering superfusate osmolarity. Hypertrophied cardiocytes were enzymatically isolated from 16 adult cats with right ventricular (RV) pressure-overload hypertrophy induced by pulmonary artery banding (PAB) and from 6 adult cats with RV volume-overload hypertrophy induced by creating an atrial septal defect (ASD). Left ventricular (LV) cardiocytes from each cat served as nonhypertrophied, normally loaded, same-animal controls. Superfusate osmolarity was decreased from 305 +/- 3 to 135 +/- 5 mosM and increased to 645 +/- 4 mosM. During anisosmotic stress, there were no significant differences between hypertrophied RV and normal LV cardiocytes in pressure overload PAB cats with respect to percent change in cardiocyte area (47 +/- 2% in RV vs. 48 +/- 2% in LV), diameter (46 +/- 3% in RV vs. 48 +/- 2% in LV), or length (2.4 +/- 0.2% in RV vs. 2.0 +/- 0.3% in LV), or sarcomere length (1.5 +/- 0.1% in RV vs. 1.3 +/- 0.3% in LV). Likewise, there were no significant differences in cardiocyte strain between hypertrophied RV and normal LV cardiocytes from ASD cats. In conclusion, chronic pressure-overload hypertrophy and chronic volume-overload hypertrophy did not alter the cardiocyte response to anisosmotic stress. Thus chronic overload hypertrophy did not alter relative passive cardiocyte stiffness.

Animals↗
PubMed1996

Cytoskeletal role in the contractile dysfunction of cardiocytes from hypertrophied and failing right ventricular myocardium.

We have shown on the levels of the sarcomere and the cardiocyte that increased microtubule density accounts, to a remarkable degree, for the contractile dysfunction characteristic of pressure-overload right ventricular hypertrophy. In this study, we have asked whether these linked phenotypic and contractile abnormalities persist during the transition to right heart failure in this model and whether, following this transition, microtubule depolymerization remains effective in restoring normal cellular contractile function when characterized in terms of sarcomere mechanics. The feline right ventricle was pressure overloaded by pulmonary artery banding. The quantity of microtubules was estimated from immunoblots and immunofluorescent micrographs, and their mechanical effects were assessed by measuring sarcomere motion during microtubule depolymerization. These measurements were made in control cats and in operated cats having right ventricular hypertrophy alone or hypertrophy with associated right heart failure; the left ventricle from each heart served as a normally loaded same-animal control. We show here both that alterations in microtubule density and sarcomere mechanics are a persistent and progressive feature of the hypertrophied and then failing cat right ventricle and that the ratio of polymerized to free tubulin is selectively increased in the failing right ventricle. The mechanical defect, though more severe in failing than in hypertrophied right ventricles, was normalized by microtubule depolymerization. Because we find persistent and progressive increases both in microtubules and in the functional consequence of aberrant sarcomere mechanics during the transition from hypertrophy to failure when right ventricular pressure overloading is severe, this cytoskeletal abnormality may well contribute to the contractile dysfunction characteristic of right heart failure in this model.

Animals↗
PubMed1995

Contraction accelerates myosin heavy chain synthesis rates in adult cardiocytes by an increase in the rate of translational initiation.

The purpose of this study was to determine the mechanism by which contraction acutely accelerates the synthesis rate of the contractile protein myosin heavy chain (MHC). Laminin-adherent adult feline cardiocytes were maintained in a serum-free medium and induced to contract at 1 Hz via electrical field stimulation. Electrical stimulation of contraction accelerated rates of MHC synthesis 28%, p < 0.05 by 4 h as determined by incorporation of [3H]phenylalanine into MHC. MHC mRNA expression as measured by RNase protection was unchanged after 4 h of electrical stimulation. MHC mRNA levels in messenger ribonucleoprotein complexes and translating polysomes were examined by sucrose gradient fractionation. The relative percentage of polysomebound MHC mRNA was equal at 47% in both electrically stimulated and control cardiocytes. However, electrical stimulation of contraction resulted in a reproducible shift of MHC mRNA from smaller polysomes into larger polysomes, indicating an increased rate of initiation. This shift resulted in significant increases in MHC mRNA levels in the fractions containing the larger polysomes of electrically stimulated cardiocytes as compared with nonstimulated controls. These data indicate that the rate of MHC synthesis is accelerated in contracting cardiocytes via an increase in translational efficiency.

Animals↗
PubMed1995

Conversion of the sodium channel activator aconitine into a potent alpha 7-selective nicotinic ligand.

Methyllycaconitine (MLA) is a competitive antagonist of nicotinic acetylcholine receptors, with a remarkable preference for neuronal [125I]alpha Bgt binding sites. We have begun to investigate the structural basis of its potency and subtype selectivity. MLA is a substituted norditerpenoid alkaloid linked to a 2-(methylsuccinimido)benzoyl moiety. Hydrolysis of the ester bond in MLA to produce lycoctonine diminished affinity for rat brain [125I]alpha Bgt binding sites 2500-fold and abolished affinity for [3H]nicotine and muscle [125I]alpha Bgt binding sites. The voltage-gated Na+ channel activator aconitine, also a norditerpenoid alkaloid, but with significant structural differences from lycoctonine, displayed comparable weak or absent nicotinic activity. Addition of a 2-(methylsuccinimido)benzoyl sidechain to O-demethylated aconitine, to mimic MLA, abolished Na+ channel activation and conferred nanomolar affinity for brain [125I]alpha Bgt binding sites, comparable to that of MLA. We propose that the ester-linked 2-(methylsuccinimido)benzoyl group is necessary for nicotinic potency, but alpha 7 selectivity resides in the norditerpenoid core of the molecule.

Aconitine↗
PubMed1995

Load effects on gene expression during cardiac hypertrophy.

Hemodynamic load is a primary regulator of cardiac mass. A potential proximal event in this regulatory pathway is thought to be the induction of immediate early genes, and markers of this process include the re-expression of genes for fetal sarcomeric proteins and the ventricular expression of atrial natriuretic factor (ANF). Previous in vivo models which have examined these questions have often neither quantified myocardial loading nor accounted for covariables which may affect gene expression such as the renin-angiotensin-aldosterone system, the sympathetic nervous system, or baroreceptors. Thus, whether load alone is sufficient to induce immediate early genes, which may ultimately result in cardiac hypertrophy, remains unknown. In the present study two models of right ventricular (RV) pressure overload were created by partially occluding the pulmonary artery (PA), either with a balloon catheter for 1 or 4 h, or with a surgically placed PA band for 12, 24, or 48 h. Serum catecholamine concentrations were determined in a subset of RV pressure overload cats at basal state, after 5 min of balloon inflation, and after 1 h of balloon inflation to examine the effects of this systemic trophic factor on IEG induction. Northern blot analysis for c-fos, egr-1, alpha-skeletal actin, and ANF from paired RV and left ventricular (LV) RNA allowed the effect of load (selectively increased in the RV) to be separated from other systemic variables (present in both ventricles). The relative signal intensities of the optical density of RV and LV mRNA autoradiograms were determined from northern blots, alternate lanes of which were loaded with 7.5 micrograms of total RNA from RV and LV tissue from the same cat. Partial PA occlusion caused RV systolic pressure to increase from a control value of 22 +/- 1 mmHg to 57 +/- 6 mmHg after 1 h, 59 +/- 5 mmHg after 4 h, and 58 +/- 5 mmHg after 48 h of RV pressure overload (RVPO). Serum norepinephrine and epinephrine levels at both 5 and 60 min of RVPO were not significantly different from basal levels. The RV/LV ratios of mRNA for both egr-1 and c-fos were equal in control and 48 h PA banded animals, but were increased in the 1 and 4 h balloon RVPO cats. The RV/LV ratio of mRNA for alpha-skeletal actin was equal in the basal state and did not increase after 12, 24, or 48 h of RVPO. After 48 h of RVPO, total RNA was increased in the RV compared with the LV (1.9 +/- 0.1 v 1.1 +/- 0.1 micrograms/g tissue, P < 0.05). ANF expression was present in the RV after 48 h of RVPO, but absent in same-animal LV and all control ventricles. Thus, while increased load alone did not alter the expression of alpha-skeletal actin, it was sufficient both to induce increased expression of two distinct classes of immediate early genes, as well as ANF, and to increase total RNA, indicating hypertrophic growth initiation.

Animals↗
PubMed1995

Response to influenza immunisation in asymptomatic HIV infected men.

OBJECTIVE: This study aimed to determine if patients with HIV infection can develop a significant antibody response to influenza immunisation, and whether such immunisation is detrimental to the progression of their HIV illness. DESIGN: Prospective, non-randomised study. METHODS: The titres of antibody response to influenza immunisation were determined in 44 asymptomatic HIV positive men and compared with 16 HIV presumed seronegative controls. The magnitude of response were correlated with patients' CD4 lymphocyte counts. The rate of CD4 lymphocyte count decline over a median of 12 months before and after immunisation were also evaluated. RESULTS: Thirty-two of the 44 HIV positive subjects (73%) were able to mount a four-fold or greater response to at least one of the influenza strains, and 14 of them (32%) did so to all four strains. In comparison, 15 of the 16 controls (93.5%) had a four-fold or greater response to at least one, and six of them (38%) to all influenza strains, which was not significantly different from the HIV positive group. The magnitude of increase in antibody titre was not significantly different between the two groups either. CD4 lymphocyte count change for a median of 12 months after immunisation was not different from a median of 12 months before immunisation. CONCLUSIONS: Asymptomatic HIV infected patients are able to mount antibody response to influenza immunisation, which appears to be safe in respect to HIV illness progression in the short term.

Adolescent↗
PubMed1995

Growth effects of electrically stimulated contraction on adult feline cardiocytes in primary culture.

The purpose of this study was to determine effects of long-term electrical stimulation of cardiocyte contraction on protein synthesis rates and total protein content. Adult feline cardiocytes were plated on laminin-coated culture trays and maintained in a serum-free medium consisting of M199 supplemented with ascorbate, bovine serum albumin, creatine, carnitine, taurine, and 10(-7) M recombinant insulin. Cardiocytes were electrically stimulated to contract with use of continuous electrical pulses of alternating polarity at a frequency of 1 Hz and pulse duration of 5 ms. Nonstimulated cardiocytes are normally quiescent and were used as the control group. In control quiescent cardiocytes, protein synthesis rate decreased by 14% between days 1 and 4 in culture and then remained stable through day 7. In electrically stimulated cardiocytes, protein synthesis rates increased by 19% between days 1 and 7. Protein synthesis rates were 18% higher on day 4 and 43% higher on day 7 in electrically stimulated than in quiescent cardiocytes. Protein content per cell was determined by measuring total fluorescence per cell by use of confocal microscopy of fluorescein isothiocyanate-stained cells. Electrical stimulation significantly increased cellular protein content by 52% after 7 days compared with controls. Quiescent and electrically stimulated cardiocytes remained rod shaped, retained their myofibrillar architecture, and were responsive to electrical stimulation over the 7-day period. These data demonstrated that electrically stimulated contraction of adult cardiocytes resulted in cell growth, as assessed by an increase in protein content per cell over 7 days in culture. This increase was due, at least in part, to an acceleration of steady-state protein synthesis rates.

Animals↗
PubMed1995

Inhibition of collagen cross-linking: effects on fibrillar collagen and ventricular diastolic function.

The fibrillar collagen network is postulated to be a primary determinant of left ventricular diastolic stiffness. This hypothesis was tested by examining the structural and physiological effects of a reduction in fibrillar collagen content and cross-linking in the intact left ventricle. Collagen cross-linking was inhibited by treating five normal adult pigs with beta-aminopropionitrile (BAPN; 10 g/day po) for 6 wk; five normal untreated pigs served as controls. Left ventricular volume, mass, and function were determined by simultaneous echocardiography and catheterization. Chamber stiffness, defined by pressure vs. volume data, and myocardial stiffness, defined by stress vs. dimension data, were determined from variably loaded beats during dextran infusion. Collagen distribution (% area) and integrity (% confluence) were determined by light microscopy. Collagen content was measured by hydroxyproline assay, and collagen cross-linking was measured by salt extraction. BAPN decreased collagen distribution (% area decreased from 12 +/- 1% in control to 7 +/- 1% in BAPN, P < 0.05), collagen integrity (% confluence decreased from 8 +/- 1% in control to 4 +/- 1% in BAPN, P < 0.05), collagen content (from 36 +/- 2 mg/g dry wt in control to 27 +/- 2 mg/g dry wt in BAPN, P < 0.05), and collagen cross-linking (extractable collagen increased from 21 +/- 2% in control to 28 +/- 2% in BAPN, P < 0.05). BAPN decreased chamber stiffness (0.13 +/- 0.02 in control to 0.06 +/- 0.01 in BAPN, P < 0.05) and myocardial stiffness (10.4 +/- 0.5 in control to 6.6 +/- 0.5 in BAPN, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopropionitrile↗