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Biomedical subjects

R M Levin

Publications and source records attributed to R M Levin.

At least 217 records · Page 12Linked to original sources
PubMed1991

Changes in bladder function in the one year spontaneously diabetic BB rat.

Micturition characteristics and in vitro urinary bladder function were investigated in insulin-treated spontaneously diabetic BB rats and age-matched non-diabetic controls one year after the onset of diabetes. BB rats weighed less than controls and were hyperglycemic. Diabetic rats consumed larger volumes of water and excreted larger volumes of urine than controls. The frequency of micturitions and the mean volumes of urine excreted per micturition were significantly increased in BB rats compared to age-matched controls. Associated with the micturition changes in the BB rats were significant increases in bladder body mass. Contractile responses of strips from bladder bodies and bases were measured in response to nerve stimulation, carbachol, phenylephrine, ATP, and KCl. No significant differences between controls and diabetics were found in the absolute contractile responses of bladder body strips to nerve stimulation, carbachol, ATP, or KCl. However, if the data were transformed to correct for the increases in tissue mass in the diabetics, there were significant decreases in the responses of bladder body strips from BB rats to carbachol, ATP, and KCl, but not to nerve stimulation. Even after transformation, there were no differences in the responses of bladder base strips to carbachol, phenylephrine, or KCl. The data indicate that significant changes in micturition characteristics are evident one year after the onset of diabetes in the spontaneously diabetic BB rat. These changes are slow in development, since they are absent six months after the onset of diabetes. The changes in micturition and bladder strip contractility are qualitatively similar to, but quantitatively modest in comparison with those caused by streptozotocin-induced diabetes mellitus. The quantitative differences are probably attributable to an ameliorative effect of the insulin received by the BB rat.

Adenosine Triphosphate↗
PubMed1991

Indigocarmine as a quantitative indicator of urothelial integrity.

There is increasing evidence that the urothelium of the bladder mucosa prevents the penetration of solutes from the urine into the bladder wall. In the current study, in vivo treatments of rabbit urinary bladder with DMSO, acetone and overdistension resulted in damage to the physical integrity of the bladder mucosa as quantitated by the penetration of the dye indigocarmine (1% in saline) into submucosal tissues. Penetration of the dye can be quantitated, because the dye can be extracted from the tissue and measured spectrophotometrically. Indigocarmine does not penetrate normal, control, bladder mucosae. Bladders treated with gentle 20, 30 and 50% acetone washes for one minute permit dye penetration which is proportional to the acetone concentration utilized. Intravesical 50% DMSO ("RIMSO 50") administration permits modest dye penetration. Distension by slow filling with saline to volumes 90% of capacity and greater causes a marked increase in dye penetration which is proportional to the magnitude of overdistension. Although pretreatment of the bladder with heparin did not reduce the dye penetration following acetone administration, it completely abolished penetration of the dye following overdistension. Indigocarmine is potentially useful as both a quantitative and qualitative indicator of bladder mucosal integrity.

Animals↗
PubMed1991

Creation of a feline model of obstructive uropathy.

The aim of this project was to create a reproducible, quantifiable feline model of obstructive uropathy. Seventy-three adult female cats of comparable age were evaluated to obtain the normal control urodynamic data base. Twenty-four cats had a silastic cuff installed around the urethra to induce bladder outlet obstruction, and eight underwent a sham operation. Repeated urodynamic evaluations were performed at predetermined postoperative intervals. The obstructed and normal cats inhibited detrusor contractility by reflex striated urethral sphincter activity. Measurements of voiding pressure to verify the presence, and to assess the degree of induced outlet obstruction, required paralysis of the sphincter by curare. Following cuff implantation, voiding pressure increased from a mean normal of 17.2 cm./H2O to 31.6 to 42.5 cm./H2O in animals designated as moderately obstructed, and to 101.7-125.0 cm./H2O in animals designated as severely obstructed. 84.6% of the high pressure bladders developed vesicoureteral reflux. Analysis of resting, low bladder volume, urethral pressure profile (UPP) data and voiding pressures indicate a compensatory sphincteric response to filling in non-curarized animals, and a lack of that response in curarized animals. It appears that implantation of a silastic cuff to prevent full opening of the urethra during voiding, without actually compressing it, is a reasonable model of obstructive uropathy. The observation that the relationship between striated urethral sphincter activity and inhibition of detrusor contractility is influenced by administration of curare was unexpected, and may have clinical implications.

Animals↗
PubMed1991

Experimental hyperreflexia: effect of intravesical administration of various agents.

In anesthetized rabbits, we can induce a significant degree of spontaneous activity in the urinary bladder by placing a ligature around the proximal portion of the external urethra. Previous studies characterized the activity as primarily reflex in nature, since intravesical hexamethonium selectively inhibited the hyperreflexia. In this current study we determined the effect of intravesical administration of a variety of compounds to inhibit the induced hyperreflexia. The following agents were tested at concentrations of 1, 10, 100 and 500 mumol/l (intravesically): verapamil, cromakalim, nifedipine, diltiazem, and atropine; lidocaine was tested in 0.05, 0.5 and 5% solutions. The results are summarized as follows: (1) Lidocaine was the most effective agent tested, virtually eliminating both the amplitude and frequency of the spontaneous activity at the lowest concentration (0.5%). (2) Verapamil and nifedipine were somewhat more potent than cromakalim and diltiazem. Atropine sulfate was the least potent, inhibiting both the amplitude and frequency of the hyperreflexia by less than 50% at 500 mumol/l. (3) In all cases, the amplitude of the spontaneous activity was inhibited to a significantly greater degree than the frequency of the spontaneous activity. (4) In general, there was no effect of any of the agents on mean arterial pressure at 1 or 10 mumol/l. At 100 and 500 mumol/l, all agents except for lidocaine and cromakalim decreased arterial pressure. These two agents produced no consistent fall in blood pressure at any concentration. In conclusion, the acute hyperreflexic (rabbit) preparation provides a highly reproducible and consistent model for the study of the effect of drugs on hyperreflexia.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Comparison of the contractile and metabolic effects of muscarinic stimulation with those of KCl.

Urinary bladder emptying is mediated primarily by a coordinated contraction of the bladder body in response to parasympathetic stimulation and muscarinic receptor activation. In previous studies we presented evidence that the contractile response to bethanechol stimulation could be dissociated from the metabolic response through the use of diltiazem (calcium channel blockade). The conclusion from these studies was that muscarinic stimulation resulted in a significant increase in metabolic activity which was not directly associated with contraction. KCl stimulates contraction in isolated strips by directly depolarizing the membrane rather than from binding to specific membrane receptors. The current study directly compares the metabolic and contractile activity of bethanechol (muscarinic stimulation) with KCl (direct membrane depolarization). Isolated strips of rabbit urinary bladder body were monitored in vitro for changes in intracellular-free calcium, NADH/NAD ratio, and contraction. Intracellular-free calcium was monitored by preincubation of isolated bladder smooth muscle strips with FURA-2 AM and continuously measuring the fluorescence with an MB2 surface spectrofluorometer using excitation wavelengths of 340 and 380 nm, and an emission wavelength of 510 nm. The NADH/NAD ratio was monitored with the MB2 surface spectrophotometer using an excitation wavelength of 366 nm and an emission wavelength of 450 nm. Contraction was monitored using a isometric force transducer connected to a Grass model D polygraph. The results can be summarized as follows. (1) Both bethanechol and KCl stimulate a sharp decrease in the NADH/NAD ratio, a rapid increase in intracellular-free calcium, and a slower increase in contractile force.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Role of substrates in the maintenance of contractility of the rabbit urinary bladder.

Recent studies have shown that muscarinic stimulation causes an increase in the breakdown of glucose and glycogen leading to an increase in lactate and CO2 production and a decrease in the ratio of NADH/NAD. Similar studies using palmitate as substrate showed that bethanechol did not change the rate of palmitate oxidation. Using both isolated strips of rabbit bladder dome, and the rabbit in vitro whole-bladder model, the present study compares the ability of glucose, pyruvate, palmitate, succinate and malate to support contraction and correlates the results with the intracellular concentration of high-energy phosphates. The results can be summarized as follows. In the absence of substrate, the peak response of muscle strips to field stimulation (32 Hz, 80 V, 1 ms) decreased progressively with time to 85% of the initial response at 60 min and 72% at 160 min. In contrast, the plateau phase of the response decreased to 45 and 23% of the initial response at 60 and 160 min, respectively. When glucose was present in the incubation medium, the peak and plateau tensions were 86 and 73% of the initial values at 160 min. Similar experiments with pyruvate as substrate showed that at 160 min both peak and plateau were elevated above initial values (peak = 119%; plateau = 123%). In the presence of palmitate, succinate or malate, the peak and plateau tensions decreased with time at a similar rate as in the absence of substrate. The reduction in tissue content of pre-formed high energy phosphates was similar for zero substrate and when palmitate, succinate or malate were present in the bath.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Developmental aspects of bladder contractile function: sensitivity to extracellular calcium.

The urinary bladders of 1-day and 1-week-old rabbits generate higher intravesical pressures in response to bethanechol and field stimulation than bladders isolated from mature 8-week-old rabbits. Yet the density of cholinergic receptors in the rabbit bladder does not change with maturation (1 day to 8 weeks). In an effort to better understand the molecular mechanisms by which newborn rabbit bladders generate greater pressures than the bladders of adult rabbits, we studied the effect of maturation on the relationship between extracellular calcium and contraction. Our results showed quite clearly that (1) at physiologic concentrations of calcium (2.5 mumol/l), isolated bladder strips of 1-day- and 1-week-old rabbits contracted in response to bethanechol to 98% of their maximal tension as opposed to 68% for their 8-week-old counterparts, (2) the ED50 (for calcium) for the 1-day and 1-week bladders was 0.4 mmol/l whereas the ED50 for the adult bladder strips was 2.2 mmol/l, and (3) the neonatal bladders demonstrated a much greater sensitivity to diltiazem than the adult bladders. The contractile response to calcium of the neonatal bladders was significantly inhibited by 1 mumol/l diltiazem whereas the 8-week-old bladders showed no inhibition at this concentration. In a second series of experiments, the effect of extracellular calcium on concentration was correlated with the intracellular concentration of free calcium using the calcium fluoride FURA-2 and surface spectrofluorometry. These studies confirmed that the increased contractile response of the neonatal bladder strips to calcium or cholinergic agonists was associated with an increase in the maximal intracellular free calcium concentration.

Animals↗
PubMed1991

Effects of pregnancy on muscarinic receptor density and function in the rabbit urinary bladder.

The contractile response of the rabbit urinary bladder to field stimulation consists of both cholinergic and purinergic components. In general, approximately 60% of the contractile response to field stimulation is cholinergic and 40% is purinergic. Although the purinergic response represents a significant proportion of the initial (phasic) pressure response to field stimulation of the isolated whole bladder, it contributes only 10-15% of the ability of field stimulation to empty the bladder. The current study investigates the effects of pregnancy on the contractile responses of the isolated urinary bladder to cholinergic and purinergic stimulation. The results of these studies indicate that pregnancy induces substantial changes in the physiology and pharmacology of the urinary bladder. The following data are consistent with the theory that pregnancy substantially increases the relative purinergic component of the response to field stimulation (and presumably neuronal stimulation): (1) there was a significantly greater response of the bladders isolated from pregnant rabbits to low-frequency field stimulation; (2) atropine was more effective at inhibiting the pressure generation of bladders isolated from virgin female rabbits; (3) field stimulation was more effective at emptying bladders isolated from virgin female rabbits; (4) the response of the bladders from pregnant rabbits to bethanechol was significantly reduced, whereas the response to ATP was significantly increased. In addition to these effects of pregnancy on bladder physiology, pregnancy induced a 50% decrease in the muscarinic receptor density of the urinary bladder body, which correlated very well with the 50% decrease in the contractile response to bethanechol.

Animals↗
PubMed1991

Effect of anoxia on in vitro bladder function.

Previous studies have demonstrated that the ability of the in vitro whole bladder to empty in response to bethanechol administration was inhibited by anoxia while its ability to generate pressure decreased only slightly. One question was not addressed by these early studies: Is the anoxic effect selective for receptor-mediated contractile stimulation (as opposed to non-receptor-mediated contractile stimulation)? The present study was designed to compare the effect of anoxia on the ability of the in vitro bladder to generate pressure, sustain pressure, and empty in response to field stimulation (FS), bethanechol and KC1 administration. Each New Zealand white rabbit was anesthetized with pentobarbital and the bladder removed. The bladder was mounted as a whole-bladder preparation in a 300-ml isolated bath containing Tyrode's solution at 37 degrees C and equilibrated with 95% O2, 5% CO2. Anoxia was produced by changing the gas mixture to 95% nitrogen, 5% CO2. The effect of anoxia on the response to FS, bethanechol, and KCl was determined at different times after the initiation of anoxia. The results of these studies can be summarized as follows. (1) Anoxia induced a time-dependent decrease in the rate of pressure generation, the magnitude of pressure generation, and the percent volume emptied in response to FS and bethanechol. (2) At all time periods of anoxia, the ability of the bladder to empty was inhibited to a significantly greater degree than either the rate of magnitude of pressure generation (for both FS and bethanechol administration).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

In vitro intravesical instillation of anticholinergic, antispasmodic and calcium blocking agents to decrease bladder contractility.

We investigated the effect of intravesical administration of atropine, oxybutynin, verapamil, diltiazem, and imipramine on pressure responses of the rabbit in vitro whole bladder model. All drugs investigated suppressed the pressure responses to field stimulation and bethanechol in a time-dependent manner (maximum inhibition at 90-120 min). Atropine and oxybutynin suppressed the contractile response to bethanechol to a much greater extent than that to field stimulation. These results suggest that the use of self-intravesical instillation might be a good therapeutic approach for patients with detrusor hyperreflexia, especially those who are already managed by intermittent catheterization.

Administration, Intravesical↗
PubMed1990

Creatine kinase activity of urinary bladder and skeletal muscle from control and streptozotocin-diabetic rats.

The urinary bladder depends on intracellular ATP for the support of a number of essential intracellular processes including contraction. The concentration of ATP is maintained constant primarily via the rapid transfer of a phosphate from creatine phosphate (CP) to ADP catalyzed by the enzyme creatine kinase (CK). Since muscular pathologies associated with diabetes are in part related to intracellular alterations in metabolism, we have characterized the CK activity in both skeletal muscle and urinary bladder from control and streptozotocin-diabetic rats. The following is a summary of the results: 1) Bladder tissue from control rats showed linear kinetics with a Vmax = 390 nmoles/mg protein/min, and a Km = 275 microM. 2) Urinary bladder tissue isolated from diabetic rats displayed biphasic kinetics with Vmax = 65 and 324 nmoles/mg protein/min, and Km's = 10 microM and 190 microM respectively. 3) Skeletal muscle isolated from control rats showed linear kinetics with an approximate Vmax of 800 nmoles/mg protein/min and a Km of 280 microM CP. 4) Homogenates of skeletal muscle from diabetic rats showed complex kinetics not separable into distinct component forms. 5) The Km for ADP for both skeletal muscle and bladder was approximately 10 microM. These studies demonstrate that whereas bladders isolated from both control and diabetic rats possess a low-affinity isomer(s) of CK with similar maximum enzymatic activity, there is a high affinity isomer present within the urinary bladder muscle of diabetic rats that is not present in bladder tissue isolated from control rats. Skeletal muscle isolated from both diabetic and control rats exhibited a maximal activity 2 to 3 times higher than that of the bladder.

Animals↗
PubMed1990

The effect of dilevalol on cardiac autonomic neural discharge, plasma catecholamines, and myocardial beta receptor density associated with coronary occlusion.

Cats anesthetized with alpha chloralose received saline or dilevalol (1 mg/kg, IV) during a 10-minute infusion. Fifteen minutes later, the left anterior descending coronary artery was subjected to coronary occlusion 2 mm below its origin. Regional differences in the beta receptor densities were found for the atria and ventricles and for the areas within the left ventricle in cats with no coronary occlusion and dilevalol or saline. The variation in beta receptor density distribution may be related to functional differences. Coronary occlusion and saline or dilevalol did not modify the myocardial beta receptor density regional distribution. Mean times to arrhythmia and death in five saline cats were 5.8 +/- 3.6 (N = 3) and 5.4 (N = 2) minutes; three cats were killed 6 hours after coronary occlusion. In five dilevalol cats the times to arrhythmia and death were 2.2 +/- 0.8 (N = 5) and 75.9 +/- 70.7 (N = 4); 1 cat was killed. Dilevalol induced a significant decrease in blood pressure and heart rate prior to coronary occlusion. Coronary occlusion decreased blood pressure and heart rate in both groups. Twenty-five minutes after dilevalol but prior to coronary occlusion, postganglionic cardiac sympathetic neural discharge decreased to 81%. In the minutes prior to arrhythmia, postganglionic cardiac sympathetic neural discharge was 95% and was significantly increased to 121% 3 minutes after coronary occlusion. The postganglionic cardiac sympathetic neural discharge values after coronary occlusion were similar to those in the saline cats. Dilevalol depressed postganglionic cardiac sympathetic neural discharge prior to coronary occlusion but did not prevent the nonuniform (i.e., increases, decreases, or no change) discharge in the postganglionic cardiac sympathetic neural discharge associated with coronary occlusion-induced arrhythmia. Norepinephrine and epinephrine values in saline cats increased the first 5 minutes after coronary occlusion; this increase was associated with arrhythmia. Norepinephrine and epinephrine values from minute 15 to minute 360 did not differ from control. Dilevalol prevented the increase in norepinephrine and epinephrine levels associated with arrhythmia and death.

Adrenergic beta-Antagonists↗
PubMed1990

Effect of bladder outlet obstruction on the morphology, physiology, and pharmacology of the bladder.

Bladder outlet obstruction secondary to benign prostatic hyperplasia induces numerous changes in bladder morphology, physiology, and pharmacology. These changes have been studied experimentally in various animal models, and while each species has advantages and disadvantages, it is unclear which is most like man. It has been shown that tissue hypertrophy leading to an increase in tissue mass develops rapidly after bladder outlet obstruction. Ischemia induced by the obstruction results in acute muscle dysfunction. The degree of functional impairment is directly related to the degree of tissue hypertrophy. However, the bladder contractile apparatus appears to have a surprising regenerative ability, such that recovery of bladder function becomes obvious 14 days after obstruction. Urodynamic changes include an increase in urinary frequency and voiding pressure and a decrease in voided volume. Clinically, involuntary bladder contractions are often present. Determination of which of these specific aspects of outlet obstruction the investigator is interested in studying will dictate the selection of the most appropriate animal model.

Animals↗
PubMed1990

Comparative length-tension relationship of urinary bladder strips from hamsters, rats, guinea-pigs, rabbits and cats.

1. Comparative passive tension-active tension curves were constructed for urinary bladder body strips from hamster, rat, guinea-pig, rabbit and cat. 2. Equally sized strips from rabbit and cat bladders had a significantly greater mass and cross-sectional area than strips from other species. 3. There was a greater change in cross-sectional area of strips from rabbit and cat bladders with increasing length than in strips from other species. 4. Cat bladder strips developed a significantly greater absolute active tension than did strips from all other species at passive tensions greater than 5 g. 5. The length-tension relationships of the urinary bladder differs from skeletal or vascular smooth muscle in that there is no significant decrease in active tension at strip lengths greater than L0. 6. The ability of the urinary bladder to generate active tension at tissue lengths considerably greater than L0 is a prime importance in the physiological role of the urinary bladder to accommodate and store urine.

Animals↗
PubMed1990

The influence of intravesical volume upon contractile responses of the whole bladder preparation from streptozotocin-diabetic rats.

1. The in vivo whole bladder preparation was used to correlate bladder volume with the ability of urinary bladders from control, sucrose-drinking, and diabetic rats to develop pressure in response to bethanechol or nerve stimulation. 2. Both streptozotocin-induced diabetes mellitus and sucrose-diuresis caused an increase in rat urinary bladder capacity and mass. 3. There were significant decreases in the ability of bladders from control rats to develop pressure in response to bethanechol at 1.0 ml intravesical volume, but no change in responsiveness of bladders from sucrose-drinking or diabetic rats at different intravesical volumes. Bladders from sucrose-drinking and diabetic rats developed significantly less pressure in response to bethanechol stimulation at low intravesical volumes than did bladders from control rats. 4. Bladders from diabetic rats developed significantly less pressure in response to 32 Hz stimulation at 0.2 ml intravesical volume compared to larger volumes, however, there were no differences in the responses of bladders from sucrose-drinking or control rats at any intravesical volume. 5. Bladders from control and sucrose-drinking rats had a reduced ability to empty in response to bethanechol and field stimulation at large intravesical volumes. 6. Bladders from 8-week streptozotocin-diabetic rats are able to contract and empty efficiently in response to nerve stimulation and bethanechol over a wide range of intravesical volumes.

Animals↗
PubMed1990

Bladder purinergic receptors.

In rabbits the contractile response of the urinary bladder is only partially due to cholinergic innervation since atropine does not completely block neuronally mediated contractions. In the human bladder this atropine resistance is controversial with some reporting atropine resistance in vitro while others have stated that the atropine resistance is also tetrodotoxin resistant. Results of the present investigation demonstrate that an atropine resistant, tetrodotoxin sensitive contraction can be evoked in some, but not all human bladder strips. Evidence accumulated over the past few decades indicates that this atropine resistant contraction may be mediated by ATP or a related purine compound. Studies presented herein are designed to develop a radioligand assay for this purinergic receptor. Initial studies indicated that the hydrolysis resistant ATP analog beta, gamma methylene ATP offers several advantages over ATP as a potential radioligand. It is only slowly hydrolyzed by endogenous ATPase and does not inhibit the hydrolysis of ATP indicating that it probably does not bind to the active sites of endogenous ATP hydrolyzing enzymes. In addition beta, gamma methylene ATP is 10-100 fold more potent than ATP itself in stimulating contractions of the urinary bladder in-vitro. The radioligand binding assay herein described can be used to quantitate the density of purinergic receptors, an essential step for determining the role of this system in urinary bladder function and dysfunction. Application of this assay could form the foundation for development of a new class of therapeutic agents for the treatment of urinary bladder dysfunction based on modulation of the purinergic nervous system.

Adenine Nucleotides↗
PubMed1990

Ontogeny of bladder function in the rabbit.

Although numerous experimental studies have addressed urinary bladder innervation, physiology and pharmacology, little information is available concerning the ontogeny of bladder function. The present study describes the developmental aspects of bladder mass, bladder capacity, pressure development and emptying in white New Zealand rabbits one day of age through maturity (11 to 15 weeks of age). The following studies were performed: Cystometry, pressure generation, rate of pressure generation, and emptying responses to field stimulation, cholinergic and purinergic stimulation using the in vitro whole bladder model. The results of these studies can be summarized as follows: 1) body weight and bladder weight increased in proportion to each other, bladder capacity increase proportionally with development until eight weeks of age, then increased substantially greater than body and bladder weight between eight and 11 to 15 weeks of age; 2) the ability to empty is similar for all ages; 3) pressure responsiveness to field stimulation, bethanechol, and ATP is greater at one day? of age, intermediate at one week of age, and similar for the other age groups; 4) The response to ATP (purinergic transmitter) is of an equal magnitude to the cholinergic response at one day, and reduces rapidly to approximately 45% of the cholinergic response by four weeks. Desensitization of the bladders to ATP reduced the response to field stimulation in the one day bladders to a significantly greater degree than the other age groups. These functional results indicate a marked alteration in cholinergic and purinergic response between the one day and the four week old rabbit bladders, with the response of the one week old bladders in between. The responses of the four, eight, and 11 to 15 week bladders was similar for equal volumes even though the bladder mass increased over threefold. This indicates that the ability of the bladder to generate pressure (during development) is not directly related to bladder mass.

Adenosine Triphosphate↗