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Biomedical subjects

R M Levin

Publications and source records attributed to R M Levin.

At least 55 records · Page 3Linked to original sources
PubMed1999

Mitochondrial and mitochondrial-related nuclear genetic function in rabbit urinary bladder following reversal of outlet obstruction.

Partial outlet obstruction of the rabbit urinary bladder causes increased tissue hypertrophy and decreased contractility of that organ; we showed that, in an experimental rabbit model, both correlate closely with alterations in the status and expression of mitochondrial (mt), and mt-related nuclear, genetic parameters in bladder smooth muscle. Here we investigate the rate and overall level of recovery of mt and nuclear genetic function following reversal of outlet obstruction in the same animal model. Release from outlet obstruction at 28 days resulted in improvement in both level of hypertrophy and contractile function in all bladders studied. However, bladders fell into two groups based on whether relative copy mt genome number per cell was above or below that of unobstructed controls. Bladders with high mt DNA content adjusted organellar genome copy number toward normal post-reversal but did not properly adjust mt transcript levels; mt-related nuclear transcripts in these samples showed recovery. Bladders with low mt DNA content showed no adjustment of those levels toward normal post-reversal but did show some adjustment in other mt and nuclear genetic parameters. Thus, a limiting factor for return of normal bladder function following reversal of outlet obstruction may be recovery of normal mt genetic performance.

Animals↗
PubMed1999

Metabolic basis for contractile dysfunction following chronic partial bladder outlet obstruction in rabbits.

Prior studies have shown that partial outlet obstruction of the rabbit bladder causes a progressive increase in bladder mass, a progressive decrease in the contractile response to different forms of stimulation, and a selective decrease in the activity of mitochondrial enzymes. In this investigation the contractile responses to field stimulation and bethanechol were directly correlated with the activity of citrate synthase as a function of both the duration of obstruction and the bladder mass. Partial bladder outlet obstruction was surgically induced in twenty New Zealand White rabbits. The bladders were then rapidly excised at 30, 40, 90, 105 or 150 days post obstruction. The contractile responses to field stimulation (32 Hz) and bethanechol (250 microM) were determined. The remainder of the bladders were frozen and used for citrate synthase activity determinations. The data were grouped for analysis both by the duration of obstruction and by the bladder mass. Chronic partial outlet obstruction caused a parallel decline in the activity of citrate synthase and in the response of the obstructed tissue to stimulation.

Animals↗
PubMed1999

Mitochondrial involvement in bladder function and dysfunction.

Benign bladder pathology resulting from prostatic hypertrophy or other causes is a significant problem associated with ageing in humans. This condition is characterized by increased bladder mass, decreased urinary flow rate, decreased compliance, and these and other changes in bladder function often subject patients to increased risk of urinary tract infection. While the physiologic attributes of benign bladder pathology have been extensively described in humans and in various animal model systems, the biochemical and molecular genetic bases for that pathology have only recently been investigated in detail. Studies demonstrate that mitochondrial energy production and utilization are severely impaired in bladder smooth muscle during benign bladder disease, and to a large extent this realization has provided a rational basis for understanding the characteristic alterations in urinary flow and compliance in bladder tissue. Recent investigations targeting the detailed molecular basis for impaired mitochondrial function in the disease have shown that performance of the organellar genetic system, and to a large extent that of relevant portions of the nuclear genetic system as well, is severely aberrant in bladder tissue. In this article, we discuss the physiologic aspects of benign bladder disease, summarize biochemical evidence for the altered mitochondrial energy metabolism that appears to underlie bladder pathology, review the structure and function of the mitochondrial genetic system, and discuss molecular genetic studies of that system which have begun to provide a mechanistic explanation for the biochemical and physiological abnormalities that characterize the disease. We also discuss areas for further research which will be critically important in increasing our understanding of the detailed causes of benign bladder pathology.

Aging↗
PubMed1999

Metabolic aspects of urinary bladder filling.

Urinary bladder compliance allows the bladder to fill to near capacity without a large increase in intravesical pressure. Bladder compliance is composed of two interrelated factors: passive characteristics of the connective tissue elements of the bladder, and active properties of the smooth muscle elements. The tension generated by the smooth muscle elements can significantly affect bladder compliance. This study utilized an in-vitro whole-bladder model in rabbits to determine the effects of hypoxia, alterations in calcium concentrations, and muscarinic agonists and antagonists on bladder capacity and compliance. The urinary bladder was excised together with a short segment of proximal urethra. A catheter was inserted into the bladder via the dome and the urethra was canulated with a saline-filled tube. The bladder was mounted in an isolated bath containing Tyrode's buffer. The catheter was connected to a pressure transducer to monitor the intravesical pressure and connected to a saline-filled i.v. bag. The weight of the saline bag was continually monitored. The height of the saline bag was set to 80 mmH2O above the baseline intravesical pressure. Bladder filling was started by opening the bladder to the saline reservoir. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin, respectively. Results are summarized as follows: (a) control bladder filling was biphasic, there was an initial rapid rise in intravesical pressure followed by a slower linear rise to the pre-set pressure; (b) hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and significantly increased final bladder volume; (c) incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and also significantly increased the final bladder volume; (d) high concentrations of calcium increased the initial rate of rise in intravesical pressure; (e) carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and significantly decreased final bladder volume; (f) atropine and tetrodotoxin (TTX) had no effects on bladder filling. In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.

Animals↗
PubMed1999

Struma ovarii and hyperthyroidism.

Struma ovarii is a teratoma of the ovaries that contains a large amount of thyroid tissue. Like the cervical thyroid gland, this ectopic thyroid tissue can become autonomous. We present a case of hyperthyroidism caused by thyroid tissue in a large ovarian cystic teratoma and provide detailed endocrinological, radiological, and pathological preoperative and postoperative data. This is also the first documented case of struma ovarii in association with a secreting pituitary tumor. In addition, we provide a retrospective pathological analysis of 1390 surgically removed ovarian tumors at 2 major academic centers.

Adult↗
PubMed1999

Correlation of EGTA and calcium-blocking agents on the response of the bladder to in vitro ischemia.

The effects of repetitive field stimulation (model of hyperrelexia) on the responses of isolated strips of rabbit urinary bladder to FS and carbachol were evaluated under a variety of incubation conditions. Compared to control conditions, 2 h of repetitive FS in normal, oxygenated Tyrode's solution followed by incubation for 1 h with no stimulation resulted in a 50% decrease in contractile response to FS and a 30% decrease in the response to carbachol. Incubation in the absence of O2 and glucose was used as an in vitro model for ischemia. Repetitive stimulation during in vitro ischemia resulted in a significantly greater decrease in the contractile responses to FS and carbachol than did in vitro ischemia without repetitive stimulation. The magnitude of contractile dysfunctions in response to both stimuli were significantly reduced in the presence of EGTA (calcium chelator), diltiazem (calcium channel blocker) or pincidil (potassium channel opener). Incubation with thapsigargin (SR calcium uptake inhibitor) + ryanodine (SR calcium storage inhibitor) had no effect. The results of these studies indicate that inhibition of Ca2+ entry reduces the contractile dysfunctions induced by repetitive stimulation in the presence of in vitro ischemia. Inhibition of Ca2+i storage and release had no significant effect on the magnitude of contractile dysfunctions induced by repetitive stimulation an in vitro ischemia.

Animals↗
PubMed1999

Rabbit versus rat urinary bladder: effects of in vitro hypoxia.

PURPOSE: Studies indicate that bladder hypoxia may be an etiological factor for lower urinary tract dysfunction. Rat and rabbit are two species of experimental animals used frequently to study lower urinary tract function and dysfunction. The objective of this study was to compare directly effects of in vitro hypoxia on contractile responses of rat and rabbit urinary bladder to different forms of stimulation. METHODS: Sexually mature male New Zealand White rabbits and Sprague-Dawley rats were compared. Each bladder was excised while the animal was anesthetized, and longitudinal bladder strips were cut, then mounted in organ baths. A tension of 2 g was placed on all strips. Effects of 1, 2, 3 and 4 h hypoxia followed by 1 h of reoxygenation on contractile responses of bladder strips to field stimulation (FS), carbachol (100 micromol/l), ATP (1 mmol/l) and KCl (120 mmol/l) were determined. RESULTS: Contractility, per unit tissue mass, of rat bladder strips was significantly greater than that of rabbit bladder strips in response to FS (all frequencies), carbachol, KCl and ATP. Hypoxia (followed by reoxygenation) resulted in time-dependent progressive reduction in contractile responses of bladder strips to all stimuli. Rat bladder was significantly more sensitive to hypoxia than rabbit bladder in response to FS and carbachol. Hypoxia induced similar effects on rat and rabbit bladder responses to ATP and KCl. CONCLUSION: Rat bladder neurogenic and cholinergic responses are significantly more sensitive to hypoxia than are those of rabbit bladder, which may be due to the rat bladder's greater contractile force generation and previously reported higher Ca2+-ATPase activity.

Animals↗
PubMed1999

Effects of in vivo ischemia on contractile responses of rabbit bladder to field stimulation, carbachol, ATP and KCl.

Rabbits were subjected to bilateral ischemia for 3, 6, or 18 h then euthanized and their bladders excised. Isolated strips of rabbit bladder detrusor were incubated in normal Tyrode's solution and contractile responses to FS, carbachol, ATP, and KCl measured. Maximal contraction, maximal rate of tension generation, and length of time to maximal contraction were determined. These studies revealed that contractile responses to FS (neurogenic stimulation) were most affected by ischemia. Contractile responses to carbachol, ATP and KCl were all similarly sensitive to ischemia.

Adenosine Triphosphate↗
PubMed1998

Use of abdominal fascia to create partial outlet obstruction in rabbits.

Partial outlet obstruction has been used for a considerable period of time as an animal model for the urodynamic changes that occur with the progressive obstruction of benign prostatic hyperplasia (BPH). Although there are many models of partial outlet obstruction, one common feature is that the degree of obstruction produced is inconsistent. The current study evaluates the responses of the bladder to a partial outlet obstruction created using an autologous fascial collar from harvested rectus fascia. The results demonstrate that although there was a moderate and variable increase in bladder mass, the alterations in the contractile responses to field stimulation (FS), carbamyl choline (carbachol), KCl, and adenosine 5'-triphosphate (ATP) were less severe than other models of partial outlet obstruction. Specifically, there was an approximate 40% decrease in the magnitude of the contractile response to FS but no significant changes in the magnitude of the contractile responses to carbachol, KCl, or ATP. Further analysis of the contractile responses demonstrated that there was a greater decrease in the rate of tension generation than in the magnitude of response for FS, and a significant increase in the time to maximal tension. Although there were no decreases in the magnitude of the responses to carbachol, KCl, or ATP, there were significant reductions in the rate of tension generation for carbachol and KCl and significant increases in the time to maximal tension for carbachol and ATP. Applying less tension over a wider area, the fascial collar provided a consistent and reproducible mild partial outlet obstruction.

Adenosine Triphosphate↗
PubMed1998

Effects of hypoxia, calcium, carbachol, atropine and tetrodotoxin on the filling of the in-vitro rabbit whole bladder.

PURPOSE: The urinary bladder stores urine at low intravesical pressure and empties the urine efficiently and completely. Bladder compliance is the property that allows the bladder to fill to near capacity without a large increase in intravesical pressure. The current study utilized an in vitro whole bladder model to determine the effects of hypoxia, alterations in extracellular calcium concentration, carbachol and atropine on bladder capacity and compliance. METHODS: Mature male New Zealand White rabbits were used in this study. The urinary bladder was excised from the rabbit together with a short segment of proximal urethra and mounted in a 400 ml. isolated bath containing Tyrode's buffer. Bladder filling was started by opening the bladder to a saline reservoir placed 80 cm. above the bladder. Intravesical pressure, rate of pressure increase, rate of volume increase, and maximal volume were digitally recorded. The bladder filling was repeated while the whole bladder was subjected to hypoxia, high calcium concentration, the presence of EGTA, carbachol, atropine and tetrodotoxin respectively. RESULTS: Results are summarized as follows: 1) Bladder filling was biphasic. There was an initial rapid rise in intravesical pressure followed by a slower rise. The final bladder volume averaged 46 ml. 2) Hypoxia significantly decreased the initial rate of the rise in intravesical pressure, increased the rate of bladder filling, and increased bladder volume by 43%. 3) Incubation of the bladder in the presence of EGTA also significantly decreased the initial rate of intravesical pressure rise, increased the rate of filling and increased bladder volume by 39%. 4) High concentrations of calcium increased the initial rate of rise in intravesical pressure. 5) Carbachol significantly increased the rate of intravesical pressure rise, decreased the rate of bladder filling, and decreased bladder volume. 6) Atropine and tetrodotoxin (TTX) had no effects on bladder filling. CONCLUSION: In summary, alterations in muscle tone had significant effects on bladder capacity and compliance.

Animals↗
PubMed1998

Effect of partial outlet obstruction on the myogenic response to field stimulation.

1. Experimental studies of outlet obstruction have been performed on rats, rabbits, guinea pigs, cats, dogs and pigs. There is evidence that partial outlet obstruction can alter the membrane properties of the bladder smooth muscle and result in progressive denervation. The current studies were designed to evaluate the effects of moderate partial outlet obstruction on the response of isolated strips of rabbit bladder smooth muscle to field stimulation in the absence and presence of tetrodotoxin (TTX). 2. The results are as follows: In the absence of TTX, partial outlet obstruction resulted in a significant reduction in the neurogenic response at all frequencies. In the presence of 1 microM TTX, which caused maximal inhibition of the release of neurotransmitters, partial outlet obstruction caused a significant increase in the myogenic response to field stimulation. 3. These studies clearly demonstrate that partial outlet obstruction results both in a significant decrease in the neurogenic response of the obstructed bladder to field stimulation and in a significant increase in the myogenic component.

Animals↗
PubMed1998

Effect of calcium and calcium chelator on the response of the bladder to in vitro ischaemia.

OBJECTIVE: To examine the effect of different concentrations of calcium on the contractile responses of isolated strips of rabbit bladder detrusor to various forms of stimulation after 2 h incubation in the presence of substrate and oxygen depletion (in vitro ischaemia), followed by 1 h of recovery. The resultant contractile responses were correlated with the level of lipid peroxidation as determined by malonedialdehyde (MDA) concentration. MATERIALS AND METHODS: Isolated strips of rabbit bladder detrusor smooth muscle were incubated in Tyrode's solution containing different concentrations of calcium (0-5.4 mmol/L). The effect of 2 h of incubation in oxygen- and substrate-free medium (in vitro ischaemia), followed by a 1-h incubation in the presence of oxygen and substrate, on the contractile responses to field stimulation, carbachol and KCl were determined. The effects of repetitive stimulation (15 s of stimulation at 32 Hz applied every 5 min during the 2-h experimental period) were also assessed. RESULTS: The contractile responses to all stimuli increased as the extracellular calcium concentration was increased from 0.6 to 5.4 mmol/L. A 2 h exposure to in vitro ischaemia, followed by a return to normal solution, resulted in a diminished response to all stimuli. This contractile dysfunction was least in the presence of calcium chelator (EGTA) and greatest in the presence of 5.4 mmol/L calcium. Repetitive stimulation during in vitro ischaemia also exacerbated the contractile dysfunction. Lipid peroxidation increased during in vitro ischaemia in proportion to the calcium concentration and was enhanced by repetitive stimulation during this period. Regardless of the incubation conditions, the reduction in the contractile response was significantly greater for field-stimulated tissues than for those stimulated with carbachol or KCl. CONCLUSIONS: These results show that the magnitude of contractile dysfunction induced by incubation in the presence of substrate and oxygen depletion is reduced in the presence of low calcium concentrations, increased in the presence of high calcium levels and increased in the presence of repetitive stimulation. In addition, the level of lipid peroxidation after the recovery period was proportional to the magnitude of contractile dysfunction present.

Animals↗
PubMed1998

Physiological effects of macrocycle 1 on the rabbit corpus cavernosum.

When the penis is in the flaccid state, the corpus cavernosum smooth muscle is under adrenergic control in order to maintain the sinusoids in a contracted condition (primarily via alpha-adrenergic stimulation). Penile erection is mediated by relaxation of corporal smooth muscle through a variety of direct and indirect mechanisms. Pharmacological agents that either inhibit alpha-adrenergic transmission or facilitate corporal smooth muscle relaxation will be beneficial for penile erection. Preliminary studies on macrocycle 1, a novel bioactive agent, demonstrated that this compound inhibits receptor-stimulated contraction without significantly altering field-stimulated contraction. The current study was designed to determine the physiological effects of macrocycle 1 on the response of the rabbit corpus cavernosum to various forms of stimulation. Sexually mature male New Zealand White rabbits were used in this study. The corpus cavernosum was dissected sharply from the removed penis and two longitudinal strips were prepared for isometric tension studies. Each strip was prestimulated with 200 mumol/l phenylephrine to produce a maximal contraction. The influences of macrocycle 1 (15.6, 62.5, 250, 1,000 mumol/l) on both the contractile response to phenylephrine and the relaxant effects of field stimulation, carbachol, ATP and nitroprusside were determined. The results demonstrated that although basal tension was not altered, the contractile response to phenylephrine was decreased by 5, 18, 47 and 57%, respectively, by the different concentrations of macrocycle 1. The degree of relaxation induced by field stimulation of various frequencies was significantly enhanced by macrocycle 1 in a concentration-dependent manner. Similarly, the degrees of relaxation induced by bethanechol, ATP and nitroprusside were all significantly enhanced in a concentration-dependent manner. The conclusion from this study is that macrocycle 1 significantly inhibits phenylephrine-stimulated contraction and significantly enhances field-stimulated and pharmacologically induced relaxation. Although the mechanisms of action are not clear, its physiological effects on the rabbit corpus cavernosum implicate a potential for the treatment of erectile dysfunction.

Adenosine Triphosphate↗
PubMed1998

Digital analysis of the pharmacological effects of in vitro ischemia on rabbit corpus cavernosum.

PURPOSE: Regulation of corporal smooth muscle tone is essential for the initiation of penile erection. In recent years, in vitro isometric tension studies using isolated corpus cavernosal tissue have been used extensively to investigate the mechanisms regulating corporal smooth muscle tone and tension. In the present study, we utilized digital analysis of contractile data generated from investigation of contractile and relaxation responses of isolated rabbit corpus cavenosum to various forms of stimulation. Digital analysis of the contractile and relaxation data allows quantitation of both maximal and mean rates of tension change, and time elapsed to maximal response. Rates of tension changes may provide additional important information regarding cellular events that mediate corporal tone and tension changes. METHODS: Sexually mature male New Zealand White rabbits were used. Each corpus cavernosum was dissected sharply from the removed penis, then two longitudinal strips were prepared for isometric tension studies and placed in individual baths. Tension was monitored continually using an 8-channel Grass Polygraph. The Grass PolyVIEW system simultaneously converted analog signals to digital information and stored data using a 486 PC computer. Each corporal strip was prestimulated with 300 mumol/l phenylephrine to produce a maximal contraction, then field stimulation (FS), carbachol and nitroprusside were applied consecutively to determine relaxation effects. This procedure was repeated after strips were deprived of glucose and oxygen (in vitro ischemia) for 1 h. The following parameters were quantitated for all responses: maximal tension change; maximal and mean rates of tension change, and time to maximal response. RESULTS: Effects of 1-hour in vitro ischemia on rabbit corporal tissue were as follows: (1) an 85% decrease in contractile response to phenylephrine, and (2) a marked increase in rate of contractile response to phenylephrine. Phenylephrine precontracted strips exhibited: (3) no change in relaxant response to FS; (4) increased relaxant responses to carbachol and nitroprusside; (5) no change in rates of relaxation in response to FS; (6) increased rates of relaxation in response to carbachol and nitroprusside, (7) no change in elapsed time to maximal relaxation in response to FS, and (8) decreased elapsed time to maximal relaxation in response to carbachol and nitroprusside. CONCLUSION: Digital analysis of the data generated facilitates recording, reviewing and analyzing of in vitro isometric tension studies on rabbit corpus cavernosum. Digital analysis allows quantification of additional parameters that have important implications for determination of mechanisms by which specific pathological processes occur.

Animals↗
PubMed1998

Effect of repetitive stimulation on the contractile response of rabbit urinary bladder subjected to in vitro hypoxia or in vitro ischemia followed by reoxygenation.

PURPOSE: We studied the effects of hypoxia followed by reoxygenation and an in vitro model of ischemia (hypoxia + substrate [glucose] deprivation) followed by reperfusion (reoxygenation + substrate replacement) on the contractile response of rabbit urinary bladder strips to nonrepetitive and repetitive field stimulation (FS), and correlated the results with the rate of lipid peroxidation. We view repetitive FS as a model for hyperreflexia. METHODS: The effects of repetitive and nonrepetitive FS on the contractile responses of isolated strips of rabbit bladder to FS, carbachol, and KCl were determined in the presence of 3 different incubation media: O2 + glucose (normal physiological medium); N2 + glucose (in vitro hypoxia), and N2 - glucose (in vitro ischemia). Then, all strips were incubated for 1 h in normal physiological medium ('reperfusion') followed by a final stimulation; the resultant contractile responses were correlated with the level of lipid peroxidation as determined by malonedialdehyde (MDA) concentration. RESULTS: Repetitive stimulation, a model of hyperreflexia, significantly increased the rate of development of contractile dysfunction in bladder tissue strips incubated in all 3 media as compared to nonrepetitive stimulation, which caused no degradation of the contractile response in normal physiological medium. The rate of development of contractile dysfunction was significantly greater in bladder tissue strips incubated in the in vitro ischemia medium (N2 - glucose) than in strips incubated in the hypoxia medium (N2 + glucose); which, in turn, was significantly greater than in those incubated in the normal physiological medium (O2 + glucose). Repetitive stimulation ('hyperreflexia') during all 3 incubation conditions resulted in increased [MDA] after reoxygenation or 'reperfusion'. Incubation in in vitro ischemia buffer (N2 - glucose) followed by 1 h reoxygenation + substrate replacement stimulated lipid peroxidation to a significantly greater extent than did incubation in hypoxia buffer (N2 + glucose) followed by 1 h of reoxygenation; the level of lipid peroxidation, [MDA], paralleled the magnitude of the contractile dysfunctions present. Independent of the incubation medium, the magnitude of FS-induced contractile dysfunction after reoxygenation or 'reperfusion' was significantly greater than the magnitude of dysfunction in response to carbachol or KCl. CONCLUSIONS: The results demonstrate that the rate of contractile failure induced by in vitro ischemia is greater than that induced by in vitro hypoxia, and that the contractile response to FS is significantly more sensitive to both hypoxia and in vitro ischemia than is the contractile response to either carbachol or KCl. Repetitive stimulation ('hyperreflexia') increases the rate of contractile failure under all conditions tested, and the magnitude of the contractile failure may be due, in part, to the generation of free radicals and subsequent stimulation of lipid peroxidation upon reoxygenation or 'reperfusion'.

Animals↗