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Biomedical subjects

M K Sharma

Publications and source records attributed to M K Sharma.

At least 37 records · Page 2Linked to original sources
PubMed1998

Corneoscleral burn during phacoemulsification surgery.

We report a case in which a severe corneoscleral burn occurred during phacoemulsification surgery. The equipment-tuning process was uneventful and routine surgery was expected. Severe tissue injury occurred because the anterior chamber collapsed momentarily and the phaco tip touched corneoscleral tissue. We discuss mechanisms by which this type of injury may occur and the likely cause in our case. We also suggest methods to reduce the incidence.

Aged↗
PubMed1998

Changes in superoxide dismutase activity and estradiol-17 beta content in follicles of different sizes from ruminants.

Subcellular distribution of oxygen free radical scavenging enzymes has recently been demonstrated in goat ovary. In the present study the follicles of the follicular phase were isolated mechanically from goat and sheep ovaries and grouped as small (< 3 mm), medium (3-6 mm) and large (> 6 mm) follicles. The specific (units/mg protein) and total (units/g tissue) activity of superoxide dismutase (SOD) was estimated in homogenate of different sizes of follicles. The small follicles of both the species contained highest specific and total activity (6.99 +/- 1.49, 107.9 +/- 3.1 in sheep and 3.57 +/- 0.09, 76.5 +/- 4.0 in goat, respectively), whereas large follicles showed lowest specific and total activity (32.02 +/- 0.25, 80.4 +/- 5.5 in sheep and 1.71 +/- 0.06, 63.20 +/- 2.20 in goat, respectively). The estradiol-17 beta was also estimated and expressed as ng/follicle. The results show that estradiol-17 beta content was highest in large follicle (8.00 +/- 0.46 in sheep and 4.5 +/- 0.73 in goat). The content of estradiol-17 beta was increased progessively as the size of the follicles increased. From these findings, an inverse relationship was observed between SOD activity and estradiol-17 beta content in the follicles of different sizes from ruminants which may have functional role in follicle development and steroidogenesis.

Animals↗
PubMed1996

Prolonged coronary artery occlusion-reperfusion sequences reduce myocardial free radical production: an electron paramagnetic resonance study.

Our purpose was to determine whether prolonged myocardial ischemia attenuates free radical production after early reperfusion. Twenty-two mongrel dogs underwent left anterior descending coronary artery occlusion for 20, 40, or 60 minutes followed by 30 minutes of reperfusion. Electron paramagnetic resonance spectroscopy was used to measure ascorbate free radical in the coronary vein effluent. Ascorbate free radical production during reperfusion was significantly (p < 0.05) reduced in the dogs undergoing 60 minutes of coronary artery occlusion compared with the dogs undergoing 40 and 20 minutes of occlusion. We conclude that prolonged myocardial ischemia results in less free radical production on reperfusion than do shorter periods of ischemia followed by reperfusion.

Animals↗
PubMed1994

Ascorbyl free radical as a real-time marker of free radical generation in briefly ischemic and reperfused hearts. An electron paramagnetic resonance study.

The role of free radicals in myocardial reperfusion injury remains controversial. We have developed a new method using ascorbyl free radical (AFR) as a real-time, quantitative marker of free radical generation during myocardial reperfusion. A total of 35 dogs were studied. Twelve open-chest dogs underwent either 5 minutes (n = 5) or 20 minutes (n = 7) of coronary artery occlusion and 30 minutes of reperfusion. Seven additional animals undergoing 20 minutes of coronary occlusion also received the antioxidant enzymes superoxide dismutase and catalase, beginning 10 minutes before occlusion through the end of reperfusion. Exogenous ascorbate was infused intravenously, and the concentration of AFR in the great cardiac vein was continuously measured by electron paramagnetic resonance spectroscopy. Preocclusion AFR concentration was similar in the three groups. Upon reperfusion, AFR rose significantly in each animal group (P < .05). However, the AFR rise in the 20-minute-occlusion group, 38 +/- 17%, was significantly greater than in the 5-minute-occlusion group, 27 +/- 14% (P < .002). In addition, in the animals that received superoxide dismutase and catalase, the rise in the AFR was markedly attenuated, 13 +/- 6% (P < .002). Two dogs that received ascorbate but did not undergo coronary artery occlusion/reperfusion sequences showed no change in coronary venous AFR signal, indicating the stability of the signal over time. Five dogs received ascorbate while undergoing interventions to alter coronary venous flow: intravenous saline, dobutamine, dipyridamole, and nitroglycerin. Coronary venous AFR changes were minimal despite large coronary flow alterations, indicating that the AFR signal is independent of changes in coronary venous flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Cardiac geometry and mass changes associated with pacing-induced cardiomyopathy in the dog.

We evaluated the effects of chronic rapid pacing (240 beats/min) on ventricular geometry and function and on cardiac mass in a canine model. Forty dogs were studied by two-dimensional echocardiography before and after 45 days of pacing. Compared with sham-operated control animals, the paced animals had significant increases in end-diastolic and end-systolic volume and a decrease in ejection fraction. The increase in ventricular volume was primarily the result of dilation of the short axis of the ventricular lumen, without significant changes in the long-axis dimension. Paced animals had biatrial hypertrophy but no change in ventricular or total cardiac mass.

Animals↗
PubMed1993

Comparative measures of systolic ejection during treadmill exercise by impedance cardiography and Doppler echocardiography.

Measurements of systolic ejection dynamics by impedance cardiography were compared with simultaneous Doppler echocardiography in normal subjects and coronary artery disease patients. Patients with chest pain admitted for elective coronary angiography were monitored by simultaneous impedance cardiography and Doppler echocardiography before, during, and after treadmill exercise. Ensemble-averaged ECG, impedance cardiogram (ICG), the first derivative of ICG (dZ/dt), and Doppler waveforms were analyzed to identify systolic ejection variables. The timing of aortic valve opening was well correlated (r = 0.78) the timing of peak ejection velocity was very well correlated (r = 0.86), and the timing of aortic valve closure was moderately correlated (r = 0.69 and r = 0.73) in these subjects. The thoracic electrical impedance acceleration and normalized impedance acceleration indices were moderately correlated with Doppler model acceleration (r = 0.74, r = 0.79). The impedance cardiogram waveforms are of complex origin and are related to both aortic blood velocity and aortic blood acceleration. Users of dZ/dt timing features for determining aortic valvular events might consider alternative impedance features to improve ejection time accuracy.

Adult↗
PubMed1993

Interaction of vitamin C and vitamin E during free radical stress in plasma: an ESR study.

To study the interaction of the antioxidant vitamins C and E in a biological system, we used electron spin resonance (ESR) spectroscopy to make serial measurements of ascorbate and tocopheroxyl free radicals in plasma subjected to continuous free radical-mediated oxidative stress. Upon initiation of a continuous oxidative stress, we observed an immediate increase in the concentration of ascorbate radical, which reached a peak, and then steadily declined. Only after the virtual disappearance of the ascorbate radical did we observe the appearance of the tocopheroxyl radical. These data are consistent with the hypothesis that ascorbate is the terminal small-molecule antioxidant in biological systems. This is the first experimental demonstration that the predicted thermodynamic hierarchy of ascorbate, alpha-tocopherol, and their free radicals holds in a biological system containing endogenous levels of these antioxidant vitamins.

Antioxidants↗
PubMed1993

The syringe nitroxide free radical--Part II.

Some plastic syringes introduce a nitroxide free radical into the fluids they contain. The EPR spectrum shows a triplet with aN = 17.0 +/- 0.1 G in plasma. We report here that this nitroxide/hydroxylamine couple serves as an antioxidant system, whose redox potential appears to be between that of vitamin C and vitamin E. This adventitious antioxidant can alter the course of free radical processes.

Ascorbic Acid↗
PubMed1992

Modulation of pituitary gonadotropins and prolactin secretion by testosterone in vitro.

Investigations were undertaken to study the differential modulation of LH, FSH and PRL secretion by testosterone (T) using whole pituitary (PI) or pituitary-hypothalamus coincubates (PHC) as in vitro constructs. PI and PHC from intact and castrated rats were incubated with or without T thrice, for 24 h each, (24 h x 3, total incubation period 72 h). The spent media was replenished every 24 h. At the end of 72 h, a few of the pituitary glands were challenged with 10 nM LHRH for 4 h. The spent media and pituitary glands were analyzed for LH, FSH and PRL using specific RIAs. Incubation of PI or PHC from intact rats with T stimulated the release of LH and FSH but inhibited the release of PRL. T had no effect on the intrapituitary contents of LH but inhibited intrapituitary contents of FSH and PRL, as compared to controls incubated without T. Castration increased intrapituitary contents of LH and FSH with concomitant decrease in PRL levels. Incubation of PI or PHC from castrated rats with T inhibited intrapituitary contents of LH to intact pituitary levels, while PRL levels were further reduced instead of being ameliorated. It is concluded that PI or PHC can be used as convenient in vitro models to monitor the effect of castration or of T modulation of pituitary and hypothalamus functions. T does not affect the synthesis of LH at the gonadotroph level but facilitates the regulation of intracellular LH and FSH levels. It is postulated that T inhibits the synthesis of FSH/PRL at the gonadotroph/lactotroph levels.

Animals↗
PubMed1991

Detection of paradoxical cerebral echo contrast embolization by transcranial Doppler ultrasound.

Contrast echocardiography has been shown to be a sensitive method for detecting patent foramen ovale in embolic stroke, implying paradoxical embolization. However, not all two-dimensional echocardiographic studies are of diagnostic quality, and direct evidence for paradoxical cerebral embolization remains lacking. We addressed these problems by simultaneously using transcranial Doppler ultrasound and contrast echocardiography to compare relative sensitivity and concordance in the detection of right-to-left vascular shunting. Forty-six patients with stroke, transient neurologic defect, or question of atrial septal defect underwent study at rest and during Valsalva strain. Two-dimensional echocardiography detected shunting in 26% at rest and 15% during Valsalva strain, whereas transcranial Doppler study returned rates of 41% and 41%, respectively. Concordance was 82% and 75%, respectively. Discordant studies almost always had evidence of paradoxical contrast embolization by transcranial Doppler and intermediate findings by two-dimensional echocardiography. Transcranial Doppler is a sensitive, unambiguous technique for the detection of anatomic substrates and target organ involvement in patients suspected to have paradoxical cerebral embolization.

Adult↗
PubMed1991

Circulating immune complexes in pre-eclampsia.

Serum samples from 20 non-pregnant women, 30 women with normal pregnancy and 50 women with pregnancy associated with pre-eclampsia were tested for circulating immune complexes using the polyethyleneglycol precipitation method. A highly significant positive correlation was found between circulating immune complexes and severe pre-eclampsia (BP greater than 140/90 mm Hg, albuminuria greater than 0.25 g/l). In contrast to this the difference in immune complex levels between non-pregnant subject, normal pregnancy cases and patients with mild pre-eclampsia was not statistically significant. A significant positive correlation was found between the level of circulating immune complexes and the severity of albuminuria. These findings suggest that circulating immune complexes, though not seeming to play an aetiological role in pre-eclampsia may very well be involved in its pathogenesis.

Antigen-Antibody Complex↗
PubMed1988

Long-term bepridil monotherapy for angina pectoris.

The long-term efficacy of bepridil as once-a-day monotherapy was studied in 19 men with stable angina pectoris. After 2 weeks of single-blind placebo therapy and a 12-week parallel placebo-controlled, dose-response study, each patient received open-label bepridil. After a dose-titration period of 3 months, patients received bepridil (100 to 400 mg once a day, mean 290 mg) for 24 months. The response to treatment was assessed by patient diaries and serial treadmill exercise testing 24 hours after dose administration, every 3 months. Only 2 patients were released from the study due to therapeutic failure. Compared with placebo, 3 months of bepridil therapy resulted in a significant reduction in the weekly frequency of angina from 10.3 +/- 9.1 to 1.8 +/- 3.5 (p less than 0.002) and nitroglycerin consumption from 5.0 +/- 5.4 to 1.4 +/- 2.3 (p less than 0.01). In addition, there was a simultaneous significant increase in the walking time to angina from 5.2 +/- 2.3 to 7.9 +/- 2.6 minutes (p less than 0.001) and total exercise time from 7.1 +/- 2.2 to 8.8 +/- 1.9 minutes (p less than 0.001). These favorable effects were sustained throughout the 24 months of the study. Although resting QTc interval was prolonged by 36 to 42 ms (p less than 0.001) during bepridil therapy, ventricular dysrhythmias were not observed immediately before or during exercise testing and were not manifested by symptoms. Neurologic and gastrointestinal side effects of mild to moderate severity were observed, but none required discontinuation of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗