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Biomedical subjects

R M Levin

Publications and source records attributed to R M Levin.

At least 271 records · Page 15Linked to original sources
PubMed1987

Comparison of calcium antagonist properties of antispasmotic agents.

Several agents commonly employed for the treatment of detrusor hyperreflexia or instability are characterized as antispasmotics. Their mechanism of action is not completely understood but it has been proposed that their actions are dependent on anticholinergic activity, CNS mediated relaxation, or local anesthetic properties. The purpose of this study was to determine if imipramine, flavoxate HCl, or oxybutynin HCl possess any calcium antagonist properties. This was accomplished by determining the ability of these agents to inhibit a standard cholinergic stimulus (200 uM bethanechol) over a range of extracellular calcium concentrations (0.5 to 10.0 mM). In-vitro isolated smooth muscle strips of rabbit bladder dome were utilized. Control tissues displayed a reproducible response to bethanechol stimulation at different calcium concentrations with an ED50 of 0.4 mM calcium and a peak response of 5.0+/-0.4 grams tension. Flavoxate (2.5 mM), oxybutynin (2.5 uM), and imipramine 25 uM) all significantly reduced peak tension generation. The ED 50's for extracellular calcium in the presence of flavoxate and oxybutynin were not significantly different from controls. Imipramine at both 3 and 25 uM significantly increased the ED50 for calcium. The above data demonstrate that imipramine possesses competitive calcium antagonism. The relative contribution of calcium antagonism toward the inhibitory effects of imipramine is unknown but may play a significant role in its clinical activity.

Animals↗
PubMed1987

In vitro studies of glucose metabolism of the rabbit urinary bladder.

The urinary bladder, as do all smooth muscle organs, depends on the delivery of oxygen and metabolic substrates for proper functioning. Although glucose metabolism has been studied and evaluated for a variety of smooth muscle systems, little is known about carbohydrate metabolism of the urinary bladder. In the present investigation glucose metabolism and glycogen formation of the urinary bladder of the rabbit was studied in vitro. Isolated urinary bladder strips were prepared from bladder base and body and the following metabolic determinations were made: glucose utilization, glycogen formation, CO2, and lactic acid formation. In addition, the effect of insulin on glucose metabolism was investigated. Glucose utilization was similar in bladder base and body (6.57 +/- 0.67 mumols/gm./2 hours in combined tissues). Eighty-one percent of the glucose utilized was metabolized to lactate whereas 11% was oxidized to CO2 and 4.7% was incorporated into glycogen. Insulin caused a small but significant increase in glucose utilization by bladder strips.

Animals↗
PubMed1986

The effect of acute and chronic administration of timolol on cardiac sympathetic neural discharge, arrhythmia, and beta adrenergic receptor density associated with coronary occlusion in the cat.

The effect of timolol (5 mg/kg, p.o., b.i.d. 7 or 14 days) on cardiac beta adrenergic receptor density, the times to arrhythmia (AR) and death (D), heart rate, mean arterial blood pressure, and postganglionic cardiac sympathetic neural discharge after acute coronary occlusion in cats was examined. In the control animals, receptor densities in the left and right atria did not differ, but were lower than the right ventricle. Left ventricle and septum receptor densities were higher, with the left ventricle the highest. The importance of the gradation of beta receptors with increasing density from base to apex appears to be its relation to cardiac contractile function. Occlusion in cats not treated with timolol did not alter the cardiac beta receptor densities. After timolol for 7 or 14 days, no occlusion, receptor density increased in left ventricle and septum although the increase was only significant after 14 days. A comparison of the beta adrenergic receptor densities in cats pretreated with timolol for 7 or 14 days with or without occlusion revealed that, in general, a decrease (p greater than 0.05) occurred for the occlusion group. Timolol decreased heart rate and blood pressure prior to occlusion. The mean times to AR and D were not significantly increased by either dosing regimen of timolol, although the trend was for an increase in the time to D after 7 days of timolol and an increase in the time to AR and D after 14 days of timolol. When compared with data obtained in saline cats, chronic timolol produced minimal changes in postganglionic cardiac sympathetic neural discharge. Timolol given chronically (p.o.) or acutely (5 mg/kg, i.v. given 15 min prior to occlusion) also did not prevent the cardiac sympathetic discharge associated with the development of AR. The time to AR and D in the acutely treated cats was increased but not significantly. Since cardiac sympathetic neural discharge increased as blood pressure fell in the control period but did not increase after occlusion in the timolol treated animals, the combination of timolol and occlusion may have modified neural discharge via an action on the baroreceptor mechanism. That chronic administration of timolol produces an effect not present in cats in which only occlusion was done is supported by the observation that chronic treatment produced an occlusion-induced decrease in beta adrenergic receptor density.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1986

Regional distribution of myocardial beta-adrenoceptors in the cat.

The purpose of this study was to delineate the distribution of beta-adrenoceptor density in the cat heart, with an emphasis on areas within the left ventricle. beta-Adrenoceptor densities, determined for hearts obtained from five cats, were not significantly different in the left and rights atria, i.e. 47.6 +/- 7.2 and 32.8 +/- 7.5 fmol/mg protein, respectively. beta-Adrenoceptor densities for the septum and right ventricle were 105.4 +/- 15.0 and 65.0 +/- 14.0 fmol/mg protein, respectively. The beta-adrenoceptor density for the proximal distribution of the left anterior descending artery LV1, distal distribution of the left anterior descending artery LV2 and posterior wall of the left ventricle LV3 were: 81.3 +/- 11.5, 145.1 +/- 20.8 and 165.4 +/- 35.8 fmol/mg protein, respectively. Thus, the distribution of the beta-adrenoceptor densities was greatest in the apex of the left ventricle. The data suggest that there are regional differences in the beta-adrenoceptor densities among the areas of the heart and within the left ventricle. These differences may be related to functional differences.

Animals↗
PubMed1986

Escherichia coli adherence to anion exchange resin. In vitro model for initial screening of potential antiadherence agents.

The first step in developing a bladder infection is attachment of bacteria to the bladder epithelium. Removing the bladder mucin increases bacterial adherence up to a thousand-fold, and this increase can be prevented by pretreating the mucin-deficient bladder with heparin. To develop a rapid, in vitro antiadherence screening assay, we studied the adherence of Escherichia coli to various chromatography resins and the ability of heparin and other agents to antagonize this attachment. The results can be summarized as follows: Although E. coli attached to all resins, only the adherence to the anion exchange resin was inhibited by heparin (up to 95%). Agents which did not effect E. coli adherence to the resin did not affect attachment to the bladder. Agents which inhibited E. coli adherence to the bladder also inhibited E. coli adherence to the resin. Similar to the effect of heparin on E. coli attachment, the adherence of Klebsiella ozaene, Proteus mirabilis, and Streptococcus fecalis to both bladder epithelium and anion exchange resin were also antagonized. These studies indicate that the adherence of E. coli (as well as other bacterial species) to anion exchange resin responds to heparin and other chemical agents in a similar manner as does adherence to the mucin-deficient rabbit urinary bladder. Because of the ease and rapid nature of this in vitro assay, it serves as a useful screen for potential bacterial antiadherence agents and could be used to help elucidate mechanisms of bacterial attachment.

Adhesiveness↗
PubMed1986

Heparin inhibition of increased bacterial adherence following overdistension, ischemia and partial outlet obstruction of the rabbit urinary bladder.

While it is well established clinically that urinary tract infection in the presence of outflow obstruction may be associated with difficulty in eradicating bacteria, it is not clear whether this is secondary to the presence of residual urine volume or other local effects of the obstruction such as attenuation of the intrinsic antibacterial defense mechanisms of the mucosal surface. Experiments in our laboratory and others over the past several years have demonstrated that the primary antibacterial defense mechanism of the bladder is the antiadherence effect of the bladder surface mucin layer. Additional studies have shown that heparin can duplicate this antiadherence activity of bladder mucin. The present report demonstrates that one hour of overdistension or ischemia and one week of partial outlet obstruction cause a functional defect in the intrinsic antiadherence effect of the bladder mucosa as evidenced by increased bacterial adherence. This defect can be reversed by heparin exposure prior to bacterial challenge. These results indicate that partial outlet obstruction and its potential sequelae such as overdistension and, particularly, mucosal ischemia, have dramatic adverse effects on the intrinsic antiadherence defense mechanism of the bladder. These effects can be reversed by intravesical exposure to an exogenous anionic polyelectrolyte (heparin).

Animals↗
PubMed1986

Relevance of spontaneous activity to urinary bladder function: an in vitro and in vivo study.

The presence and functional significance (if any) of spontaneous activity in the normal urinary bladder during filling is a controversial subject. One model used by many investigators to study spontaneous activity has been isolated urinary bladder smooth muscle strips. Although spontaneous activity is a property commonly observed in isolated urinary bladder strip preparations, the in vitro whole bladder preparation (rabbit) is devoid of spontaneous activity. Additionally, under normal conditions the in vivo rabbit bladder does not display spontaneous activity during the filling phases of micturition. The present study compares the spontaneous activity of isolated smooth muscle strips, the whole bladder preparation, and the catheterized in vivo bladder (rabbit). The results are as follows: The spontaneous activity (frequency and amplitude) of isolated strips is extremely variable among strips of the same bladder. Spontaneous activity is not affected by the following specific inhibitory compounds: tetrodotoxin, atropine, phentolamine, propranolol and hexamethonium. This indicates that spontaneous activity observed in isolated strips is myogenic in nature and not dependent on the activation of specific autonomic receptors. The in vitro whole bladder preparation shows no spontaneous activity at any volume or pressure unless longitudinal tension is applied. The spontaneous activity of the whole bladder subjected to longitudinal tension is not affected by the same compounds mentioned above. Spontaneous activity of the in vivo bladder is absent at low intravesical volumes and pressures. Spontaneous activity develops upon reaching a critical pressure. However, this activity is completely inhibited by intravenous ganglionic blockade (hexamethonium). In the presence of hexamethonium, the in vivo bladder is devoid of spontaneous activity at any volume or pressure, thus the in vivo "spontaneous activity" is mediated through neuronal reflexes. It is concluded that under normal circumstances the rabbit bladder is devoid of myogenic spontaneous activity and that the spontaneous activity observed in isolated strips is directly related to longitudinal stretch. Since under normal conditions the bladder is not subjected to longitudinal stretch, the spontaneous activity observed in the isolated strip studies has little physiological significance under normal conditions, but could help explain the pathophysiology of certain dysfunctions during the filling stage of micturition.

Animals↗
PubMed1986

Acute biochemical and functional alterations in the partially obstructed rabbit urinary bladder.

Rapid structural and functional alterations have been noted in several models of partial outlet obstruction. To better characterize the rapid progression of alterations, the partially obstructed urinary bladders of mature NZW male rabbits were studied at 1, 3, 5, 7 and 14 days of outlet obstruction with respect to muscarinic receptor density, DNA, RNA, lipid and hydroxyproline content. Functional characteristics were assessed by measuring the in vitro response of the whole bladder to cholinergic and field stimulation. Wet weight increased eight-fold by day 7, decreasing to four-fold at day 14. Receptor density decreased by 50% by day 1 and remained low throughout. Although DNA concentration varied only slightly from controls, RNA increased four-fold by day 7. Hydroxyproline concentration per mg. tissue decreased in the obstructed bladder, yet total hydroxyproline content of the obstructed bladder significantly increased. Total lipids increased significantly during day 3 through 7 and decreased by day 14. Cystometry revealed a large capacity low pressure system at day 1 which rapidly changed to a low compliance system of lesser volume by day 14. Bladder emptying was significantly impaired in all obstructed specimens. Additionally, electrical field stimulation was significantly less effective than cholinergic stimulation in effecting bladder emptying. The above findings suggest that rapid changes in biochemical parameters occur during the early stage of acute obstruction which may in part be secondary to metabolic or inflammatory alterations in the detrusor. It additionally suggests that the myogenic alterations in partial outlet obstruction are rapid and partially adaptive, while neurogenic alterations appear degenerative and display a lesser degree of short term adaptation.

Animals↗
PubMed1986

Functional effects of in vitro obstruction on the rabbit urinary bladder.

Bladder outlet obstruction has been the subject of numerous clinical and experimental investigations. Although these studies have demonstrated that the bladder can respond to outlet obstruction with muscular hypertrophy and hyperplasia, resulting in markedly altered morphological and functional characteristics, the nature of the direct effect of obstruction on the ability of the bladder to empty is relatively unknown. If one regards the bladder as a simple pump mechanism, decreasing the diameter of the outlet port (obstruction) would be expected to increase the work the bladder muscle would have to do in order to empty. The purpose of this present investigation is to better define the physical nature of the increased stress placed on the normal bladder via partial outlet obstruction. For these studies, the in vitro whole bladder is an appropriate model for several reasons: 1) one has complete control of initial intravesical volume, pressure, outlet diameter, and outlet resistance, and 2) this model quantitatively measures the effect of pharmacological agents and electrical stimulation on intravesical pressure and the ability of the bladder to empty. The results of these studies indicate that the obstructed bladder requires an increased pressure to empty. Although the obstructed bladder can empty completely, the rate of emptying is reduced significantly and the time required to completely empty is significantly increased. The obstructed bladder fatigues rapidly with repetitive stimulations, whereas the normal bladder is far less subject to fatigue. The physical alterations observed in these studies would play a direct role in the development of the functional alterations observed in in vivo obstruction.

Animals↗
PubMed1986

Functional effects of the purinergic innervation of the rabbit urinary bladder.

Although it is generally agreed that micturition is primarily under the control of the parasympathetic nervous system, there is good evidence that an atropine insensitive, nonadrenergic-noncholinergic neuronal component exists. Recent evidence indicates that the purinergic transmitter ATP (or an other purinergic analog) may be responsible for the atropine-insensitive portion of the contraction. Although isolated muscle strip studies have identified the purinergic response, the functional significance of this response has not been determined. Utilizing an in vitro whole-bladder model, we have investigated the functional ability of the purinergic component of field stimulation to empty the bladder under standard conditions. The results indicate: the response of the bladder to both cholinergic stimulation and field stimulation is characterized by a rapid rise in intravesical pressure followed by a prolonged plateau phase; expulsion of fluid from the bladder occurs primarily during the plateau phase of the contraction; in the presence of atropine, field stimulation produces only a transient rapid rise in tension, similar to the response to exogenous ATP; and this "purinergic" response does not result in significant bladder emptying. These results suggest that the bladder response to this purinergic stimulation may be complimentary to, but functionally different from that which occurs in response to cholinergic transmission alone.

Adenosine Triphosphate↗
PubMed1985

Mannose inhibition of Escherichia coli adherence to urinary bladder epithelium: comparison with yeast agglutination.

The adherence of piliated strains of Escherichia coli (E. coli) to mammalian epithelial cells has been reported by several investigators to be specifically inhibited by D(+)-mannose or its derivatives. Much of this work utilized mannose type compounds to inhibit agglutination of mannan containing yeast cells by E. coli to demonstrate mannose sensitivity. This report investigates the ability of the neotype strain of E. coli (which is sensitive to mannose inhibition of yeast cell agglutination) to bind and metabolize radiolabeled D(+)-mannose. In addition the relative efficacy of D(+)-mannose and heparin to inhibit the adherence of E. coli to rabbit bladder mucosa was compared. Results showed that although D(+)-mannose did block E. coli--yeast cell agglutination in a reversible manner, radiolabeled D(+)-mannose binding by E. coli could not be displaced by 1,000 fold excess unlabeled D(+)-mannose. This suggests uptake of the sugar as opposed to a surface binding phenomenon which was confirmed by the demonstration of significant metabolism of mannose by E. coli. The same concentration of D(+)-mannose which prevented E. coli--yeast cell agglutination was not particularly effective in preventing E. coli adherence to the acid denuded rabbit bladder. Heparin treatment of the acid denuded bladder was very effective in preventing E. coli adherence but was ineffective in preventing E. coli--yeast cell agglutination. This indicates that E. coli--yeast cell agglutination should not be correlated with E. coli adherence to mammalian epithelial tissue.

Agglutination↗
PubMed1985

Recovery from short-term obstruction of the rabbit urinary bladder.

Partial bladder outlet obstruction is a commonly encountered pathophysiologic state. Recently we have reported on the rapid nature of the contractile and functional changes that occur in the rabbit urinary bladder within one week of chronic partial obstruction. The purpose of this present study is to investigate the ability of the bladder to recover from one week of partial obstruction. Twenty-six mature male white New Zealand rabbits were separated into 3 groups. Each rabbit was anesthetized with ketamine-xylazine and a partial obstruction of the bladder established by gently securing a 2.0 silk suture around the temporarily catheterized bladder neck. The rabbits in group 1 were sacrificed following one week of partial obstruction. For groups 2 and 3, the obstructing suture was surgically removed after one week of obstruction adn the rabbit was allowed to recover for either two or four weeks. At the end of one week of obstruction the bladder displayed a 9-fold increase in tissue mass, 50 per cent reduction in contractile response to bethanechol and a 76 per cent reduction in the ability of the bladder to expel saline. After the two week recovery period, the bladder mass was reduced to approximately twice the control mass, the contractile and pressure responses to bethanechol were returned to control levels, and the ability of the bladder to expel saline recovered to approximately 75 per cent of control levels. No further improvements were observed following the four week recovery period. It appears that although the contractile response recovers completely following the one week obstruction period, the ability of the bladder to empty remains partially impaired.

Adenosine Triphosphate↗
PubMed1985

Further characterization of bacterial adherence to urinary bladder mucosa: comparison with adherence to anion exchange resin.

Bacterial adherence to anion exchange resin has recently been reported to provide a useful, rapid, in vitro screening assay for identifying putative antiadherence agents. The studies presented in this report provide additional evidence that adherence to anion exchange resin is similar to urinary bladder mucosa adherence. Results are as follows. 1) Heparin inhibits the adherence of Escherichia coli, Klebsiella ozaenae, Proteus mirabilis, Streptococcus fecalis and Pseudomonas aeruginosa to both the mucin deficient bladder and anion exchange resin. 2) Drugs which inhibit E. coli adherence to the bladder also inhibit E. coli adherence to the resin and conversely, drugs which do not effect E. coli adherence to the resin do not affect attachment to the bladder. 3) Extracts from mammalian urinary bladder mucosa prevent E. coli adherence to both the bladder and resin. 4) The ability of heparin to displace preattached bacteria from anion exchange resin is inversely proportional to the time the bacteria are in contact with resin. Similar results were obtained for the ability of heparin to displace bacteria from the bladder. These studies indicate that bacterial adherence to anion exchange resin responds to heparin and other chemical agents in a manner similar to the mucin deficient rabbit urinary bladder. Because of the ease and rapid nature of this in vitro assay, it serves as a useful screen for potential bacterial antiadherence agents and could be used to help elucidate mechanisms of bacterial attachment.

Adhesiveness↗
PubMed1985

The effect of parasympathetic decentralization on the feline urinary bladder.

To examine the pharmacologic nature of parasympathetic decentralization on feline vesical smooth muscle, male cats were subjected to bilateral ventral rhizotomy from levels lumbar 7 to coccygeal 1 and studied at 1 and 3 months. By employing manual bladder decompression twice daily, compensatory bladder hypertrophy was absent or minimal in all specimens. In vitro muscle bath studies of bladder body demonstrated no significant end organ pharmacologic supersensitivity to cholinergic or alpha and beta adrenergic stimulation. Membrane receptor assays displayed a rise in muscarinic cholinergic and beta adrenergic receptors at 1 month which decreased at 3 months. The cholinergic receptor data parallels ultrastructural studies which demonstrate early cholinergic nerve terminal degeneration after motor decentralization followed by subsequent regrowth of cholinergic axons. Alpha 1 and alpha 2 adrenergic receptor densities remained constant in control, 1 month, and 3 month preparations. This lack of classic end organ denervation supersensitivity in the decentralized urinary bladder suggests that other mechanisms may be responsible for eliciting a positive response with the clinical denervation supersensitivity test.

Animals↗
PubMed1985

Effect of diltiazem on in vitro rabbit bladder function.

The relationship between extracellular calcium and urinary bladder function was investigated by studying the effect of the specific calcium antagonist diltiazem on the functional ability of the in vitro whole rabbit urinary bladder to empty in response to pharmacological stimulation. The bladder was found to require an extracellular calcium concentration of 4.5 X 10(-4) M to elicit near complete cholinergic-mediated emptying. Diltiazem (1 X 10(-6) - 1 X 10(-4) M) inhibition of bladder function was competitively antagonized by increasing the extracellular calcium concentration (0.45 X 10(-4) - 3.6 X 10(-4) M). In the absence of diltiazem, alterations in the extracellular calcium concentration between 0.45 X 10(-4) and 3.6 X 10(-4) M had no significant effects on bladder response to bethanechol. KCl-mediated bladder emptying was significantly more sensitive to diltiazem inhibition than was bethanechol-stimulated emptying. Even at the intermediate diltiazem concentration of 1 X 10(-5) M, increasing the extracellular calcium concentration did not completely reverse the inhibitory effect of diltiazem on bladder response to KC1. These findings are consistent with the hypothesis that diltiazem at low concentrations may inhibit extracellular calcium influx while at higher concentrations translocation of intracellular stores of calcium may be inhibited as well. The study also suggests that diltiazem is capable of inhibiting urinary bladder function and deserves further consideration as a possible therapeutic agent in certain forms of urinary bladder dysfunction.

Animals↗