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Biomedical subjects

R M Levin

Publications and source records attributed to R M Levin.

At least 253 records · Page 14Linked to original sources
PubMed1989

Effects of muscarinic stimulation on intracellular calcium in the rabbit bladder: comparison with metabolic response.

Urinary bladder emptying is mediated primarily by a co-ordinated contraction of the bladder body in response to parasympathetic stimulation and muscarinic receptor activation. In a previous study using surface spectrophotometry to monitor the nicotinamide adenine dinucleotide (oxidized form)/nicotinamide adenine dinucleotide (reduced form) (NADH/NAD) ratio, we demonstrated that muscarinic stimulation results in a rapid decrease in this ratio which precedes the contractile response, and that the ED50 for the NADH response is significantly lower than the ED50 for contraction. The current study was designed to correlate changes in intracellular free calcium using FURA-2 fluorescence with both the contractile and metabolic response to muscarinic stimulation. Isolated strips of 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 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 an isometric force transducer connected to a Grass model D polygraph. The results can be summarized as follows: (1) Bethanechol stimulates a sharp decrease in the NADH/NAD ratio, a rapid increase in intracellular free calcium, and a slower increase in contractile force. (2) The ED50 for NADH fluorescence was significantly less than the ED50 for either contraction or calcium fluorescence which were equal to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Pharmacological comparison of the isolated whole urethra model to urethral strip methodology.

Urethral strips provide a sensitive method for quantitative pharmacology; however, it is not clear if the physiological response of the whole urethra to pharmacological agents can be extrapolated from these data. The intent of this study was to investigate whether the linear contraction of strips is consistent with the ability of the intact urethra to alter resistance to flow. To measure the effect of drugs on the ability of the intact urethra to alter resistance to flow in the absence of endogenous influences, we developed an in vitro whole rabbit urethra model. We characterized the effect of norepinephrine in the absence and presence of alpha-adrenergic antagonists (prazosin, yohimbine, and LY253352) on intraurethral pressure which was measured during constant saline infusion using a Statham pressure transducer. We compared this to the contractile function of urethral strips. The pA2 values for alpha-adrenergic antagonists, LY253352, prazosin, and yohimbine were 8.17 +/- 1.5, 6.49 +/- 1.2, and 5.58 +/- 0.9, respectively, as determined in the whole urethra. The pA2 values for these antagonists determined in urethral strips were as follows: LY253352 8.72 +/- 1.2; prazosin 7.52 +/- 1.5, and yohimbine 5.6 +/- 0.84. Pharmacologically, the whole urethra model and isolated strips appeared to respond similarly to alpha-adrenergic agonists and antagonists, and thus both models would be suitable for pharmacological studies on the normal urethra.

Animals↗
PubMed1988

The effect of chronic timolol in an animal model for myocardial infarction.

The effect of no drug or timolol (5 mg/kg, PO, for 1, 2, or 8 weeks on postganglionic cardiac sympathetic neural discharge, blood pressure, heart rate and beta-receptor density after acute coronary occlusion of the left anterior descending artery was compared. Beta-receptor density, determined by binding of 3H-dihydroalprenolol, was examined in the myocardium (LA = left atrium, RA = right atrium, LV1 = proximal and LV2 = distal left anterior descending artery distribution, LV3 = posterior left ventricle, S = septum, and RV = right ventricle). In control cats (no coronary occlusion or timolol) beta-receptor density of LV2 and LV3 was greater (P less than .05) than LA, RA, LV1, and RV. LV3 was greater (P less than .05) than S and RA, and LA was less than S. Longer treatment with timolol increased beta-receptor density. When compared with no timolol, beta-receptor density was greater in RA after 8 weeks and in LV1 after 2 weeks and not different in LV2 and S. Beta-receptor density and LV3 and RV were greater after 8 weeks than after 1 week or no timolol. Spearman rank correlation coefficients between dose and beta-receptor density revealed an increase (P less than .05) for all heart areas. Heart rate did not vary before timolol and was decreased after all doses of timolol. Timolol increased the mean times to coronary occlusion-induced death although the increase was not statistically significant. Timolol did not prevent postganglionic cardiac sympathetic neural discharge associated with arrhythmia. Timolol may increase beta-receptor density and decrease synaptic norepinephrine, causing a decreased release per cardiac sympathetic nerve impulse. Alternatively, molecules of timolol may accumulate in nerve endings and be released in greater concentrations at the receptors. This could explain the protection against coronary occlusion-induced arrhythmia and death.

Anesthesia↗
PubMed1988

Dissociation of the metabolic from the contractile response to muscarinic stimulation in the rabbit urinary bladder.

The calcium dependence of contraction and NADH fluorescence was investigated in rabbit bladder stimulated with bethanechol or KCl. The absence of calcium in the bathing solution induced a rightward shift in the dose response to bethanechol for both contraction and NADH fluorescence. The contractile response was shifted to a greater degree than the fluorescence response and the maximal response to bethanechol was reduced by 80% for contraction but only 20% for NADH fluorescence. This rightward shift was also induced by the benzothiazepine calcium antagonist diltiazem (200 microM) and again the contractile response was shifted significantly more than the fluorescence response. The combination of zero calcium and 200 microM diltiazem virtually abolished contractions but only inhibited the NADH fluorescence by 65% at maximally effective bethanechol concentrations. Unlike the effect of diltiazem on the response to bethanechol, diltiazem (200 microM) shifted both the contraction and fluorescence curves to the right equally in response to KCl stimulation. These results indicate that a metabolic response to muscarinic stimulation (decreased NADH) can occur in the absence of any observable contractile response. This metabolic response may be due to post receptor signal processing events. For KCl stimulation, the NADH response is probably secondary to and a result of the contractile response.

Animals↗
PubMed1988

Defective antiadherence activity of bladder extracts from patients with recurrent urinary tract infection.

A substantial body of animal work indicates that the initial first line defense against invading microorganisms in the urinary tract is the antiadherence activity of the surface mucin layer. Previous work has demonstrated that bacterial adherence to anion exchange resin can be used as a model for adherence to the mucin deficient rabbit bladder. This anion exchange resin adherence model can also be used as a rapid screen for potential antiadherence agents. In vitro saline extracts of bladder mucosa from various mammalian species including man have been shown to inhibit bacterial adherence to both anion exchange resin and the mucin deficient rabbit bladder. The present report investigates the ability of in vivo saline bladder washes from several groups of patients to inhibit bacterial adherence to anion exchange resin. This has an advantage over other methods of quantitation or visualization of mucin since it is the ability of the bladder extract to prevent bacterial adherence, and not merely the quantity of mucin, that determines the effectiveness of the mucin lining in preventing bacterial attachment. Bladder washes from patients with recurrent urinary tract infection were significantly less potent at inhibiting bacterial adherence than extracts from other groups of patients. This decreased functional antiadherence activity of bladder extracts may help explain the frequency of urinary tract infection in this group of patients.

Adult↗
PubMed1988

The functional effect of mild outlet obstruction on the rabbit urinary bladder.

Bladder outlet obstruction has been the subject of numerous studies. In previous studies on severe obstruction, the initial response of the bladder has been to produce an acute overdistension of the bladder resulting in severe tissue damage and functional disorders. This is quite different from the slow onset of outlet obstruction seen in association with benign prostatic hypertrophy (BPH). The present study describes the functional effect of mild outlet obstruction created in a rabbit model, and compares it to a previously described model of severe obstruction. Mild bladder outlet obstruction was created by placing a silicon sleeve (inner circumference 30 mm.) around the bladder neck of mature male NZW rabbits. Individual groups of rabbits were studied at one, seven, and 14 days following the creation of the outlet obstruction. The following studies were performed on each group of rabbits: in vivo and in vitro cystometry, field stimulation and cholinergic stimulation using the in vitro whole bladder model. In addition, the tissue concentration of ATP (adenosine triphosphate) and CP (creatine phosphate) and the muscarinic receptor density were determined. The obstructed bladders showed no significant cystometric difference at one day, but revealed a marked decrease of compliance and capacity at one and two weeks. Unlike the response to severe outlet obstruction, there was no initial acute overdistension of the bladder wall. Although the ability of the obstructed bladders to generate intravesical pressure in response to both field stimulation and bethanechol did not decrease, the ability of both forms of stimulation to empty the obstructed bladders was markedly impaired. The response to field stimulation was reduced to a significantly greater extent than the response to bethanechol, indicating neuronal damage. The muscarinic receptor number per bladder was increased above control at all time periods. The intracellular concentration of ATP and CP in the obstructed bladders was similar to that of control. Our present model of mild obstruction was not accompanied by a massive increase in tissue mass nor was there an overdistension of the detrusor; thus, this model would be a more suitable model for the study of clinical outlet obstruction.

Adenosine Triphosphate↗
PubMed1988

Effect of chronic nitrofurantoin on the rabbit urinary bladder.

Interstitial cystitis is a pathological condition whose symptoms mimic urinary tract infection and include urgency, frequency, and moderate to severe pain. Many more women than men are affected, with antibiotic therapy being the usual first treatment approach based on symptomology. Some clinicians believe that chronic antibiotic therapy may play an etiological role in interstitial cystitis; however neither clinical nor experimental data support their opinion. The implied pathogenesis of antibiotic injury is an alteration of the bladder mucosa and its protective mucin coating to allow urine-mediated damage to the bladder wall. The purpose of this study is to evaluate rabbit urinary bladder function and morphology during chronic nitrofurantoin administration. The results demonstrate that up to twelve months of chronic nitrofurantoin administration produce no changes in 1) bacterial adherence to the rabbit bladder mucosa, 2) specific antibacterial adherence activity of the bladder mucin, and 3) ultrastructure of the mucosa, submucosa, and muscularis.

Animals↗
PubMed1988

Effect of age on in vivo urinary bladder function in the rat.

The effects of age on micturition in male Fischer 344 rats, ages five to seven, 16 to 18 and 22 to 24 months, were studied. The 24 hr. water intake, 24 hr. urine output, frequency and volume of each micturition were obtained from rats housed individually in metabolic cages. Intravesical pressure and volume at which the micturition contraction occurred were evaluated using natural-fill cystometry. The 24 hr. water intake and urine output increased significantly with advancing age; 22 to 24 months rats showed a 39% increase in water intake and a 93% increase in urine output compared to five to seven month rats. The increase in urine output observed in the 22 to 24 month old rats was manifested by a 95% increase in volume per micturition and a 52% increase in frequency of micturition compared to five to seven month old rats. The pressure at micturition (PAM) was 100% greater in 22 to 24 and 16 to 18 month old rats compared to five to seven month old rats with no age-related difference in bladder volume at micturition (BVM). These studies demonstrate that in vivo micturition changes with age in the male F344 rat. Although there were no overt urological dysfunctions observed in the aging rats, the alterations in function would indicate that there were changes in either the mechanisms controlling micturition, or changes in the musculature itself. These possibilities will be the subject of further investigations.

Aging↗
PubMed1988

Effect of bethanechol on glycolysis and high energy phosphate metabolism of the rabbit urinary bladder.

The urinary bladder, similar to other smooth muscles, utilizes glucose as one of its primary sources of metabolic energy. We have studied the effect of bethanechol on both glycolysis and high energy phosphate metabolism. The results can be summarized as follows: bethanechol administration in vitro stimulates a 30% decrease in intracellular glycogen, a 100% increase in lactic acid production, and an 80% increase in CO2 generation. Although there was a rapid and sustained decrease in the intracellular concentration of creatine phosphate, there was only a minor decrease in the intracellular concentration of ATP. There were no changes in adenine uptake or de novo ATP synthesis.

Adenine↗
PubMed1988

Identification of receptor subtypes in the rabbit and human urinary bladder by selective radio-ligand binding.

Recent advances in receptor technology have demonstrated that subtypes of each autonomic receptor exist. Using both direct radio-ligand studies and the inhibition of receptor binding by subtype-selective pharmacological antagonists, we have studied the distribution of subtypes of alpha and beta adrenergic receptors and muscarinic cholinergic receptors in the urinary bladder of the rabbit and man. Alpha adrenergic receptors were quantified by direct binding of tritiated prazosin (alpha-1), yohimbine (alpha-2), and the non-selective alpha adrenergic ligand dihydroergocriptine (DHE). These studies demonstrated that the distribution of alpha receptor subtypes in the bladder base (for both rabbit and human) is approximately 80% alpha-1 and 20% alpha-2. Beta receptor subtypes were identified by the inhibition of the non-selective ligand 3H-dihydroalprenalol (DHA) by the beta-1 selective inhibitor ICI-89 and the beta-2 selective inhibitor ICI-118. Initial studies demonstrated that the beta adrenergic density of the bladder body was 92 fmol per mg. protein for the rabbit and 32 fmol per mg. protein for human bladder body. Inhibition of DHA binding by ICI-118 demonstrated a single class of receptor with an IC50 of approximately 0.013 microM for both rabbit and human. Inhibition of DHA binding by ICI-89 also demonstrated one class of receptors with an IC50 of approximately 9.0 microM for both species. These results indicate that there are primarily beta-2 receptors in the rabbit and human bladder body. Although the number of muscarinic subtypes in existence is currently being re-evaluated, there are at least two which can be identified by the selective muscarinic agent pirenzepine (PZP). The brain has been shown to contain both high and low affinity PZP sites. Using both direct PZP binding to the bladder body, and the inhibition by PZP of the non-selective radio-ligand quinuclidinyl benzylate (QNB), we have demonstrated that both the rabbit and human bladder body have no observable high affinity PZP-selective binding and the inhibition of 3H-QNB by PZP demonstrated that there was only the low-affinity PZP binding site. Although receptor subtypes in the bladder have been the subject of numerous investigations, this is the first study describing the distribution of both adrenergic and cholinergic receptor subtypes in both the rabbit and human.

Animals↗
PubMed1988

Effect of chronic atropine administration on the rat urinary bladder.

Micturition is accomplished via a coordinated contraction of the urinary bladder body mediated primarily by muscarinic receptor stimulation. Theoretically, bladder function may be modified by pharmacologically altering either the muscarinic receptor density and/or the magnitude of the response to receptor activation. In the central nervous system, autonomic receptor density can be modified by chronic administration of specific receptor agonists and antagonists. The chronic administration of receptor agonists induces a decrease in the specific receptor density whereas the chronic administration of antagonists induces an increase in the specific receptor density. Although these induced alterations in receptor density occur in the CNS, there have been few studies on peripheral tissue. For the current study, we have administered L-atropine chronically to rats (five mg./kg./day) using implanted osmotic pumps. Using direct radioligand binding techniques, the muscarinic receptor density of the rat brain (cortex) and urinary bladder were determined following six hours, 12 hours, one, two, four, seven, 11 and 14 days of atropine administration. In addition, we have also determined the effect of atropine administration on bladder weight and the response of isolated strips of the bladder to bethanechol, a specific muscarinic agonist. For both the brain and the bladder, the receptor density increased progressively and reached a maximum by seven days. At 14 days of atropine administration, the density of muscarinic receptors in rat brain increased significantly (p less than .05) from 2956 +/-74 fmoles/mg. protein to 3800 +/-170 fmoles/mg. protein. The muscarinic receptor density of the rat urinary bladder increased significantly from 115 +/-10 fmole/mg. protein to 165 +/-14 fmole/mg. protein. Although there was a 42% increase in bladder mass, the contractile response of isolated strips to bethanechol did not change significantly. This study demonstrates that the urinary bladder can respond to the chronic administration of atropine with a significant increase in the density of muscarinic receptors. The magnitude of the increase observed was slightly greater than the magnitude observed for muscarinic receptors isolated from the brain cortex.

Animals↗
PubMed1988

The effects of short-term in-vivo ischemia on the contractile function of the rabbit urinary bladder.

The proper functioning of any smooth muscle requires adequate perfusion with oxygen and nutrients. Ischemia compromises both these factors and results in dysfunction, the extent depending on the degree and duration of ischemia. This study determined the effects of one, two and four weeks in vivo ischemia on the capacity, compliance and contractile function of the rabbit urinary bladder. Morphological changes were also studied with light microscopy. Different degrees of ischemia were achieved as follows. In the unilateral group the vesical artery was tied on one side and the animals were sacrificed at one week or two weeks. In the bilateral group the vesical arteries on both sides were tied and the animals were sacrificed one week later. In the bilateral staged group the vesical artery was tied on one side and after one week the contralateral artery was ligated, and the animals sacrificed one week after the second procedure. Muscle strips were studied for contractile response, with a distinction being made between the ipsilateral and contralateral side of vessel ligation in the unilateral group. The results were as follows. 1) In the unilateral group there was a 72% reduction in the contractile response of the dome of the bladder to bethanecol on the side of vessel ligation and a 32% reduction on the contralateral side. The response to methoxamine on the base was reduced by 44%, with no difference between the ipsilateral and contralateral side. 2) Bilateral vessel ligation resulted in a 97% reduction in contractile response to bethanechol on the dome and a 75% in the response of the base to methoxamine. 3) Staged bilateral ligation resulted in a 69% reduction in the contractile response of the dome to bethanechol and a 18% reduction in the response of the base to methoxamine. Ischemia caused a marked reduction in the compliance and capacity of the bladder in all the three groups, with the most marked changes in the bilateral group. Multiple spontaneous contractions were noted in the three groups during the filling phase of the cystometrograms. Histological features correlated well with the functional changes in the different groups.

Animals↗
PubMed1988

Functional effects of imipramine on the rabbit urinary bladder: an in-vitro study.

Imipramine is a tricyclic antidepressant that has been demonstrated to be useful in the treatment of certain voiding dysfunctions. Imipramine has a variety of pharmacological effects including direct antimuscarinic activity, inhibition of catecholamine reuptake, direct muscle relaxant, and calcium antagonism. Using the in-vitro whole bladder model we have studied the effect of imipramine on the rate and magnitude of both intravesical pressure generation and bladder emptying in response to field stimulation. The results can be summarized as follows: at concentrations as low as 1 mumol/l imipramine causes a significant inhibition of volume expulsion without significantly affecting pressure generation. Imipramine produced a dose-dependent inhibition of both pressure development and percent volume emptying; however, it was substantially more potent in inhibiting the ability of the bladder to empty than to generate pressure.

Animals↗
PubMed1988

Group A streptococcal infection in children younger than three years of age.

We evaluated 758 sick children younger than 3 years of age for Group A beta-hemolytic streptococcal (GABHS) upper respiratory infection (URI) to determine the usual clinical presentation of the disease in this age group, indications for culture and the optimal site(s) from which to isolate the organism. GABHS infection was documented in 35 subjects (4.6%). The classic presentation (as proposed in the 1940s) of GABHS URI in children younger than 3 years of age was not confirmed by this study. In 32 of the GABHS cases there were pharyngitis, common cold symptoms or both, and these were associated with acute otitis media 10 times and with otitis media with effusion 3 times. Clinical impetigo was associated with GABHS URI (4 of 32 cases). GABHS URI would not have been documented in 6 of 32 cases if cultures of the anterior nares had not been performed. Children between 18 and 36 months of age were more likely to have GABHS disease than were younger children. Hoarseness and vomiting occurred less frequently in children younger than 36 months with GABHS infection than in those of that age who had non-beta-hemolytic streptococcal illnesses. A history of two or more siblings at home or a family member with a recent streptococcal infection and the presence of irritability, a reddened throat or palate or uvular edema were each associated with GABHS URI. We concluded that sick children between 18 and 36 months of age with a reddened throat should have cultures taken of the throat and anterior nares for GABHS.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacteriological Techniques↗
PubMed1988

Effect of contractile activity on muscarinic receptor density and the response to muscarinic agonists.

Autonomic receptor density can be modulated by alterations in neuronal activity over a relatively short period of time (hours). The current study investigates whether increased in vivo stimulation of urinary bladder smooth muscle can alter muscarinic receptor density and response to muscarinic stimulation. A high degree of reflex stimulation of the urinary bladder (rabbits) was initiated by stricture of the external urethra. Intravesical pressure and intra-abdominal pressure were monitored continuously over a 4-hr time period. At the end of the 4-hr period, the rabbits were sacrificed and isolated strips of bladder body were either mounted in isolated smooth muscle baths for contractile studies or frozen and stored in liquid nitrogen for muscarinic receptor analysis. These studies demonstrated that over 4 hr of urethral stricture there was a significant reduction in muscarinic receptor density from a Bmax of 34 +/- 3.4 fmol/mg of protein in control bladder strips to 22 +/- 2.4 fmol/mg of protein in the experimental group. In association with the decreased muscarinic receptor density, there was a significant and selective decrease in the contractile response to muscarinic stimulation. Similar to the in vivo studies, repetitive field stimulation of in vitro strips resulted in a significant decrease in muscarinic receptor density and a significant and selective decrease in the contractile response to muscarinic stimulation. The results from these studies indicate that muscarinic receptor density, and response to muscarinic stimulation, can be modulated over a relatively short period of time by alterations in the level of neuronal stimulation.

Animals↗
PubMed1987

Nitrofurantoin not surface active agent in rabbit urinary bladder.

It has been recently suggested that nitrofurantoin may induce symptoms of interstitial cystitis by acting as a surface active agent that destroys glycosaminoglycan (GAG) on the bladder surface. Evidence accumulated over the past decade has demonstrated that the bladder surface GAG prevents bacterial adherence. In this experiment, exposure of the bladder lumen to nitrofurantoin at more than twice the therapeutic concentration did not destroy the bladder GAG layer (as evidenced by periodic acid-Schiff histochemistry) nor increase bacterial adherence as did a true surface active agent (Triton X-100). Acid treatment as well as all tested organic solvents except 50% dimethyl sulfoxide (DMSO) also removed the bladder GAG layer and increased bacterial adherence. These results indicate that neither nitrofurantoin nor 50% DMSO has adverse effects on the bladder surface and thus is unlikely to initiate the interstitial cystitis symptom complex by means of surfactant activity.

Animals↗
PubMed1987

Reduction of bacterial adherence to catheter surface with heparin.

Despite many advances in catheter design and use, the most common cause of hospital-acquired infections is catheterization of the urinary tract. In the present investigation the adherence of bacteria to catheters coated with heparin was studied. Since heparin itself does not coat the plastic catheter surface, a complex of heparin with tridodecylmethylammonium chloride (TDMAC) was used which results in hydrophobic association of hydrocarbon chains of the TDMAC with the catheter leaving the quaternary ammonium moiety of TDMAC exposed to the surface forming ionic bonds with the highly anionic sulfate groups of heparin. Coating latex catheter material with TDMAC without heparin resulted in 3.6-fold higher adherence whereas coating with the TDMAC-heparin complex reduced adherence to less than 10% of control untreated latex. TDMAC-heparin also significantly reduced bacterial adherence to teflon coated latex (Bardex) and vinyl catheter material. Less than 30% of the original heparin was removed after wash periods of up to one week. These results indicate that TDMAC-heparin coating of urethral catheters reduces bacterial adherence and thereby may delay the acquisition of catheter associated urinary tract infection.

Bacterial Adhesion↗