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Biomedical subjects

S Sen

Publications and source records attributed to S Sen.

At least 379 records · Page 21Linked to original sources
PubMed1987

A factor that initiates myocardial hypertrophy in hypertension.

A lack of correlation between blood pressure and myocardial hypertrophy was established in spontaneously hypertensive rats, suggesting that factors other than blood pressure control might be responsible for the modulation of myocardial hypertrophy. An in vitro system that is independent of blood pressure and hemodynamic effects was developed by use of isolated myocytes to study myocardial protein synthesis. The validity of this system was determined by means of morphology, by receptor integrity, and by studying the incorporation of tritiated leucine into myocyte protein (dpm/mg/hr). Addition of a supernatant of spontaneously hypertensive rat myocardial homogenate (centrifuged at 1500 g) to the myocyte system resulted in a significant increase in tritiated leucine incorporation into myocyte protein when compared with the addition of homogenates from normal controls. The protein from the homogenate was partially purified by high performance liquid chromatography. The resultant purified protein also stimulated protein synthesis by 70%. Furthermore, a significant increase in the specific activity of the transfer RNA and the rate of protein synthesis was observed after addition of homogenate from hypertrophied heart (4.02 +/- 0.3 vs 7.0 +/- 0.2 pmol leucine/microgram protein/hr; p less than 0.05). These data demonstrate the existence of a soluble factor in the hypertrophied myocardium that stimulated protein synthesis. This factor may play a key role in modulation of myocardial structure during development or regression of myocardial hypertrophy in hypertension.

Animals↗
PubMed1987

The effect of hyperthyroidism and hypothyroidism on alpha 1- and alpha 2-adrenergic responsiveness in rat aortic smooth muscle.

We report the role of thyroid hormones on in vitro responsiveness of rat aortic smooth muscle to alpha-adrenergic stimulation. Four groups of rats: hypothyroid, hyperthyroid, thyroxine (0.1 mg/kg) treated hypothyroid and controls were employed. Response of alpha 1- and alpha 2-adrenoceptors was evoked with 6 incremental doses (10(-9) to 10(-4) M) of preferential alpha 1-agonist, phenylephrine and alpha 2-agonist, clonidine respectively. alpha 1-Adrenoceptors were also evoked by phenylephrine after blockade of alpha 2-adrenoceptors with 10(-7) M yohimbine. Similarly, alpha 2-adrenoceptors were stimulated with clonidine after blocking alpha 1-adrenoceptors with selective antagonists prazosin (10(-7) M). Aortic responsiveness to alpha-agonist norepinephrine was compared between the aortae of hypothyroid and euthyroid rats after blockade of alpha 2-adrenoceptors with 10(-4) M corynanthine. We report that in hypothyroid aortae, alpha 1-adrenergic response was significantly decreased, the dose response curve shifted to the right and the maximal response was 30% less than the normal; alpha 2-adrenergic response was completely inhibited in hypothyroid state; also, IP injections of 0.1 mg/kg thyroxine twice in 48 h to thyroidectomized rats reversed the effects of hypothyroidism on both alpha 1- and alpha 2-adrenergic response. Hyperthyroidism did not alter alpha 1- and alpha 2-adrenergic response. These results signify the role of thyroid hormones in the regulation of alpha-adrenergic response in rat aortae.

Animals↗
PubMed1987

Evaluation of isomers of octopamine for in vitro alpha-adrenergic stimulation of the aortic smooth muscle from spontaneously hypertensive rats.

Isomers of octopamine were tested for in vitro alpha-adrenergic stimulation of aortic smooth muscle of spontaneously hypertensive rats (SHR). In order to test the response of alpha 1-adrenoceptors to meta-, para-, and ortho-octopamine, alpha 2-adrenoceptors were blocked with 10(-7) M yohimbine, and to measure the response of alpha 2-adrenoceptors the alpha 1-adrenoceptors were blocked with 10(-7) M prazosin. The contractile response of aortic smooth muscle of SHR to stimulation by phenylephrine, m-, p-, and o-isomers of octopamine in the presence of yohimbine was not appreciably altered. However, administration of prazosin severely attenuated the response of muscles of these compounds indicating that like phenylephrine, the isomers of octopamine stimulate mainly alpha 1-adrenoceptors. The attenuation of contractile response to isomers of octopamine in the presence of prazosin was not as pronounced as in the case of phenylephrine. The comparative potencies of phenylephrine, m-, p-, and o-octopamine in the presence of 10(-7) M prazosin were 1:1.2:2.5:0.75, respectively. Thus, it appears that the isomers of octopamine, especially para- and meta-octopamine, play a much more important role in the physiology of vascular smooth muscle than has been thus far perceived.

Animals↗
PubMed1987

Factors regulating myocardial hypertrophy in hypertension.

Evidence for the existence of factor(s) other than blood pressure responsible for modulation of myocardial hypertrophy accompanying hypertension is well documented. A factor that has been isolated from the myocardium of the spontaneously hypertensive rat and partially purified has been shown to stimulate protein synthesis in vitro. Three indexes of protein synthesis, namely incorporation of 3H-leucine into myocyte myosin, specific activity of the leucyl tRNA, and rate of protein synthesis, also were observed to significantly increase on exposure to this factor, which may play a key role in the modulation of myocardial hypertrophy that accompanies hypertension. Evidence has also been presented demonstrating the role of unknown factors that control the shift of myosin isozymes from V1 (a high-ATPase, high-contractile protein type) to V3 (a slow ATPase type myosin), and vice versa. This study demonstrates that the modulation of the myocardial mass can be controlled at different levels: first at an intrinsic intracellular level by the mechanism of a local growth factor, and then at the level of the contractile protein, the quality rather than quantity of which was found to be important. Both of these were observed to be modulated by factor(s) independent of blood pressure and myocardial mass. However, it remains to be determined what is responsible at the genetic level for transmitting the signal that selects what type of protein will be synthesized and whether there is a common pathway among all the controlling factors.

Animals↗
PubMed1986

Construction of a genomic library from germinating seedlings of mung bean (Vigna radiata). Evidence for the presence of a class of repetitive sequences and selection of beta-tubulin specific recombinant phage.

We have constructed a genomic library of Vigna radiata from its total DNA in the phage charon 4A. Recombinant phages were used to hybridize with a family of mung bean repetitive DNA. At least 30% of recombinant phages showed positive hybridization with a specific type of sequences. These phages were also used to screen for beta-tubulin-specific recombinants and a recombinant phage with beta-tubulin gene was identified.

Autoradiography↗
PubMed1986

[Neurogenic cardiac arrhythmias in acute intracranial increase in pressure (recurrent hemorrhage in subarachnoid hemorrhages)].

Neurogenic cardiac arrhythmias during 5 cases of subarachnoid rebleeding in 4 patients were analyzed by using long-term ECG (Holter). The initial onset of rebleeding was characterized by an abrupt decrease of heart rate from 93.3 +/- 7.85 (beats/min) to 63.3 +/- 14.6 (beats/min). This was immediately followed by pronounced tachycardia of 163.0 +/- 20.9 (beats/min) and subsequently, alterations of the P wave, ST depression with an increase in T wave amplitude. Frequent premature ventricular contractions, couplets, and self-terminating episodes of ventricular tachycardia for 2-8 minutes were observed during 2 episodes of rebleeding, an idioventricular rhythm in one case. The ECG returned to normal in the 3 non-lethal cases. Pathogenetically, the initial heart rate decrease with varying P wave configuration can be explained through activation of the baroreceptor reflex. Elevated intracranial pressure causes a blood pressure increase thus stimulating the baroreceptors and consequently, the afferent and efferent tracts of the vagus nerve. The sympathicotonus appears to have a modulating effect.

Adult↗
PubMed1986

DNA amplification in multidrug, cross-resistant Chinese hamster ovary cells: molecular characterization and cytogenetic localization of the amplified DNA.

Vincristine-resistant (VCR) Chinese hamster ovary (CHO) cells have been established by stepwise selection in increasing concentrations of vincristine. These cells exhibit multidrug cross-resistance to a number of drugs that have no structural or functional similarities. Cytogenetic analyses of resistant cells revealed the presence of double minutes and expanded chromosomal segments, thus implicating gene amplification as a possible mechanism of resistance. An amplified DNA segment isolated from other multidrug cross-resistant CHO cell lines (Roninson, I. B., H. T. Abelson, D. E. Housman, N. Howell, and A. Varshavsky, 1984, Nature (Lond.), 309:626-628) is also amplified in our VCR lines. This DNA segment was used as a probe to screen a cosmid library of VCR genomic DNA, and overlapping clones were retrieved. All of these segments, totaling approximately 45 kilobases (kb), were amplified in VCR cells. Using in situ hybridization, we localized the amplification domain to the long arm of CHO chromosome 1 or Z1. Northern hybridization analysis revealed that a 4.3-kb mRNA was encoded by this amplified DNA domain and was over-produced in the VCR cells. Suggestions for the involvement of these amplified DNA segments in the acquisition of multidrug cross-resistance in animal cells are also presented.

Animals↗
PubMed1986

Withdrawal of long-term amrinone therapy in patients with congestive heart failure: a placebo controlled trial.

To verify favourable long-term effects, 14 patients with chronic congestive heart failure, NYHA class II-IV, who had been treated with oral amrinone for 8-15 months with apparent clinical benefit, had the drug withdrawn according to a 12 week placebo controlled double-blind crossover protocol. Evaluation was performed noninvasively by means of exercise stress test, echocardiogram, radionuclide angiography and systolic time intervals. None of these variables were significantly changed after discontinuation of amrinone, regardless of whether placebo was introduced during the first (group B, N = 7) or the second 6 week period (group A, N = 5), nor when the medication was finally openly withheld for another 6 weeks. In 2 further group A patients, premature termination of the trial was due to deterioration of symptoms on blinded amrinone. Hence, no sustained drug related effects could be proven by controlled withdrawal of long-term amrinone in this trial.

Adult↗
PubMed1986

Free proline changes in Pinus taeda L. callus in response to drought stress.

The amino acid, proline (PRO), may have an important role in plant adaptation to drought stress. To study the effect of drought stress on PRO content of pine tissues, we measured free PRO by high pressure liquid chromatography in control ( -0.4 MPa) and drought-stressed ( -0.8, -1.0, -1.3, -1.6 MPa) callus tissue of Pinus taeda L. after eight weeks of growth. Drought stress was induced by adding polyethylene glycol (PEG) to the nutrient media. The relation between PRO accumulation and water potential was influenced by composition of the medium and temperature. Callus growing in media with water potentials of -0.8 MPa showed no increase in PRO compared to control callus in media at -0.4 MPa. When callus tissue was subjected to low water potentials (-1.6 MPa), endogenous PRO concentration increased 40-fold, while callus fresh weight decreased by more than 90%. When exogenous PRO was added to the nutrient media, endogenous PRO was directly proportional to the exogenous PRO concentration rather than reduction in callus growth. Thus low water potential in callus results in endogenous PRO accumulation and large reductions in callus fresh weight growth. Proline accumulation in pine cells appears to be related to mechanisms associated with tolerance to desiccation.

Journal Article↗
PubMed1986

Noise reversion of a dual chamber pacemaker without noise.

Three patients are reported whose DDD pacemakers reverted to the asynchronous mode in the absence of skeletal muscle or electromagnetic (EMI) interference. In all three cases, the basic cardiac rhythm was atrial fibrillation with fast ventricular response due to intrinsic AV conduction. Noise reversion was triggered by the patients' own ventricular activity at cycle lengths shorter than the ventricular refractory period of the pulse generator. In one patient, asynchronous AV sequential pacing during atrial fibrillation was noted shortly after resuscitation from ventricular fibrillation; however, the initiation of the malignant ventricular arrhythmia by the pacemaker remains unproven. The mechanism of noise reversion by rapid cardiac activity and possible solutions to the problem by adequate pacemaker design are discussed.

Aged↗
PubMed1986

Multidrug-resistant phenotype cosegregates with an amplified gene in somatic cell hybrids of drug-resistant Chinese hamster ovary cells and drug-sensitive murine cells.

Gene amplification has been associated with multidrug resistance (MDR) in several drug-resistant Chinese hamster ovary (CHO) cell lines which exhibit cross-resistance to other unrelated, cytotoxic drugs. In situ hybridization studies (Teeter et al., J. Cell Biol., in press) suggested the presence of an amplified gene associated with the MDR phenotype on the long arm of either of the largest CHO chromosomes (1 or Z1) in vincristine-resistant cells. In this study, somatic cell hybrids were constructed between these vincristine-resistant CHO cells and drug-sensitive murine cells to determine the functional relationship between the chromosome bearing the amplified sequences and the MDR phenotype. Hybrids exhibited primary drug resistance and MDR in an incomplete dominant fashion. Hybrid clones and subclones segregated CHO chromosomes. Concordant segregation between vincristine resistance, the MDR phenotype, the presence of the MDR-associated amplified sequences, overexpression of the gene located in those sequences, and CHO chromosome Z1 was consistent with the hypothesis that there is an amplified gene on chromosome Z1 of the vincristine-resistant CHO cells which is responsible for the MDR in these cells. A low level of discordance between CHO chromosomes Z8 and 2 and the drug resistance phenotype suggests that these chromosomes may contain genes involved with the MDR phenotype.

Animals↗