Diuretic Rats Research Articles

Short‐term diabetes‐ and diuresis‐induced alterations of the bladder are mostly reversible in rats

To determine whether diabetes mellitus- and diuresis-induced alterations in the bladder can be reversed in rats. Male Sprague-Dawley rats were randomly distributed into eight groups (n = 16 per group): 3 weeks and 11 weeks age-matched controls, 3 weeks and 11 weeks after streptozotocin-induced diabetes mellitus, 3 weeks after diabetes mellitus induction then treated with insulin for 8 weeks, 3 weeks and 11 weeks after 5% sucrose-induced diuresis, and 3 weeks after 5% sucrose-induced diuresis followed by removal of 5% sucrose for 8 weeks. Bodyweight, blood glucose and glycated hemoglobin A1c were monitored. At the designated time-points, 24-h urinary habits were examined, and cystometry was carried out in half of the animals. The bladders from the remaining animals were harvested for histological examination, and quantification of smooth muscle, urothelium and collagen components. Insulin treatment reversed hyperglycemia and polyuria in diabetic animals successfully, which was shown by normalization of blood glucose, glycated hemoglobin A1c and 24-h urinary habits. Subsequently, bodyweight, bladder weight and percentage change of bladder components (smooth muscle, collagen, urothelium) in total bladder cross-sectional area were reversed to almost normal levels, and the bladder dysfunction was mostly reversed by 8 weeks of glycemic control, seen in the cystometry study. Similar alterations and reversed effects were seen in diuretic rats without and with 5% sucrose removal, respectively. Short-term (3-week induction) diabetes- and polyuria-induced functional and morphological alterations of the bladder can mostly be reversed in rats.

Berberine improves neurogenic contractile response of bladder detrusor muscle in streptozotocin-induced diabetic rats

Ethnopharmacological relevanceCoptidis Rhizoma has been used to treat diabetes mellitus for more than 1400 years in China. Berberine, one of the main alkaloids of Coptidis Rhizoma, is a principal antidiabetic component of Coptidis Rhizoma. To investigate the effects of berberine on impaired neurogenic contractility of detrusor muscle from urinary bladder of rats with early stage diabetes. Materials and methodsThe detrusor muscle strips were isolated from urinary bladders of streptozotocin-induced diabetic rats, 5% sucrose-induced diuretic rats or normal rats, and were placed in organ bath. The contractions induced by electrical field stimulation (EFS), carbachol, KCl, adenosine triphosphate, and the effects of berberine on those contractions were measured. ResultsThe EFS- or KCl-induced contraction of detrusor muscle was significantly decreased in diabetic rats as compared with diuretic or normal rats. Atropine and suramin inhibited EFS-induced contraction. In diabetic rats, the atropine sensitive components were decreased in EFS-induced contraction of detrusor muscle, and the adenosine triphosphate-induced contraction was significantly increased. The carbachol-induced contrations were not different among groups. Berberine significantly potentiated EFS-induced contractions of detrusor muscle both from normal and diabetic rats, but the potentiated effect of BBR was more sensitive to atropine in diabetic rats. Berberine also potentiated adenosine triphosphate-induced contraction of detrusor muscle, but did not change carbachol- or KCl-induced contraction. ConclusionThe neurogenic contraction of urinary bladder detrusor muscle is decreased while purinergic contraction of bladder detrusor muscle is increased in rats with early stage diabetes. Berberine increases the neurogenic contractile response to EFS possibly via both presynaptic increasing neurotransmitters release and postsynaptic potentiation of purinergic transmitter-regulated response in rat urinary bladder detrusor; and in diabetic rats, berberine increases neurogenic contractile response mainly via the presynaptic increasing acetylcholine release.

Calcineurin and Akt expression in hypertrophied bladder in STZ-induced diabetic rat

Diabetes causes significant increases in bladder weight but the natural history and underlying mechanisms are not known. In this study, we observed the temporal changes of detrusor muscle cells (DMC) and the calcineurin (Cn) and Akt expressions in detrusor muscle in the diabetic rat. Male Sprague–Dawley rats were divided into 3 groups: streptozotocin-induced diabetics, 5% sucrose-induced diuretics, and age-matched controls. The bladders were removed 1, 2, or 9weeks after disease induction and the extent of hypertrophy was examined by bladder weights and cross sectional area of DMC. Cn and Akt expression were evaluated by immunoblotting. Both diabetes and diuresis caused significant increases in bladder weight. The mean cross sectional areas of DMC were increased in both diabetic and diuretic animals 1, 2, or 9weeks after disease induction. The expression levels of both the catalytic A (CnA) and regulatory B (CnB) subunits of Cn were increased at 1 and 2weeks, but not at 9weeks. Expression of Akt was similar among control, diabetic, and diuretic rat bladder at all time points. In conclusion, diabetes and diuresis induce similar hypertrophy of detrusor muscle during the first 9weeks, indicating that bladder hypertrophy in the early stage of diabetes is in response to the presence of increased urine output in diabetes. Our results suggest that the Cn, but not the Akt signaling pathway may be involved in the development of bladder hypertrophy.

Temporal diabetes and diuresis‐induced alteration of nerves and vasculature of the urinary bladder in the rat

• To characterize the temporal changes of the nerves and vasculature of the bladder in diabetic rats. • A total of 36 Sprague-Dawley rats were divided into three groups: streptozotocin-induced diabetics, 5% sucrose-induced diuretics and age-matched controls. • The characteristics of the nerves and vasculature in the equatorial cross-sectional areas of the bladder were examined by immunofluorescence staining of their specific markers, neurofilament 200 (NF200) and CD31, at 1, 9 or 20 weeks after induction. • The distributions of the nerves and blood vessels were observed and the densities were quantified. • Diabetes caused a significant reduction in body weight. Bladder weight increased in diabetic and diuretic rats, but not in controls. • The total cross-sectional wall area and detrusor muscle area at the equatorial midline were greater in bladders of diabetic and diuretic rats than in controls. • Neurofilament 200-immunoreactive (NF200-IR) nerves were mainly distributed in the detrusor muscle. CD31-immunoreactive blood vessels were mainly distributed in the mucosa/submucosa. • There were no significant differences in the NF200-IR nerve terminal area among control, diabetic and diuretic groups. However nerve density was decreased at 9 and 20 weeks in the muscle, and at 20 weeks in the mucosa/submucosa in diabetic and diuretic animals. • Blood vessel density decreased in the diabetic and diuretic groups at 20 weeks in the muscle. • Diabetes induced time-dependent changes in the density of the nerves and vasculature in the bladder tissues. • Diabetes-related polyuria plays an important role in these changes.

Improvement in Neurogenic Detrusor Overactivity by Peripheral C Fiber's Suppression With Cyclooxygenase Inhibitors

Cyclooxygenase inhibitors decrease micturition frequency in animals with bladder inflammation but to our knowledge the influence of cyclooxygenase inhibitors on detrusor overactivity has not been investigated. We evaluated the effects, and the site and mechanism of action of cyclooxygenase inhibitors on detrusor overactivity induced by cerebral infarction. Cerebral infarcted rats underwent cumulative intravenous administration of the selective cyclooxygenase-1 inhibitor SC-560 (Sigma), the selective cyclooxygenase-2 inhibitor rofecoxib (Kemprotec, Middlesbrough, United Kingdom) or the nonselective cyclooxygenase inhibitor FYO-750 hourly plus a single intravenous administration of SC-560, rofecoxib or SC-560 plus rofecoxib. To evaluate the site of action cerebral infarcted rats underwent single intracerebroventricular or intrathecal administration of FYO-750. To evaluate the mechanism of action FYO-750 was intravenously administered in diuretic rats or cerebral infarcted rats pretreated with resiniferatoxin. For cumulative administration SC-560 (0.3 mg/kg), rofecoxib (0.3 mg/kg) and FYO-750 (0.1 to 1 mg/kg) significantly increased bladder capacity. For single administration neither SC-560 (0.03 mg/kg) nor rofecoxib (0.03 mg/kg) affected bladder capacity but SC-560 plus rofecoxib significantly increased bladder capacity vs vehicle. Intracerebroventricular and intrathecal administration of FYO-750 did not affect bladder capacity. FYO-750 did not affect urinary production in diuretic rats and the effects of FYO-750 were blocked by resiniferatoxin except at the highest drug dose. Results indicate that cyclooxygenase inhibitors improve detrusor overactivity caused by cerebral infarction by suppressing peripheral C fiber's without affecting urinary production. The nonselective cyclooxygenase inhibitor showed more potent efficiency than the selective cyclooxygenase-1 or the cyclooxygenase-2 inhibitor alone.

Diabetes-induced Alternations in Biomechanical Properties of Urinary Bladder Wall in Rats

To determine whether diabetes mellitus and the associated changes in bladder function will trigger bladder wall tissue remodeling and concomitant alterations in the mechanical properties. We investigated the time course of changes in function and mechanical properties of diabetic and diuretic rat bladders using both in vivo and in vitro techniques Cystometry was performed at 2, 4, and 8 weeks on female Sprague-Dawley rats that had received either a single injection of streptozotocin (65 mg/kg intraperitoneally) or 5% sucrose in drinking water for the duration of the experiments. At each point, the biaxial mechanical properties of 10 x 10-mm tissue specimens obtained from the posterior part of bladder wall were quantified. The changes in overall tissue compliance and mechanical anisotropy as a function of time were examined Both diabetic and diuretic conditions led to increases in bladder weight, bladder capacity, and in vivo compliance compared with the controls at all points tested. Under biaxial loading, all bladder wall tissues exhibited a nonlinear stress-strain relationship and mechanical anisotropy, with greater tissue compliance in the circumferential direction than in the longitudinal direction. Although the compliance of the bladder wall increased progressively and synchronously in both diabetic and diuretic bladders for < or = 4 weeks, only the diabetic bladders continued to increase the compliance for < or = 8 weeks (diabetic 0.64 +/- 0.04 vs diuretic 0.48 +/- 0.05, P = .03) The results of our study have shown that diuresis mainly contributes to the "early" changes of mechanical properties of the bladder, with diabetes inducing additional "late" changes of mechanical properties of the rat bladders after 4 weeks.

Time-Dependent Alterations of Select Genes in Streptozotocin-Induced Diabetic Rat Bladder

To investigate time-course changes in the expression of select genes and extracellular matrix proteins in the bladder of rats with streptozotocin-induced diabetes, so as to examine the mechanisms underlying changes in mechanical properties of the bladder due to diabetic cystopathy. Female Sprague-Dawley rats were injected with streptozotocin (65 mg/kg). Rats that were fed with 5% sucrose in drinking water served as diuretic controls, in addition to normal control rats. At the end of 2, 4, and 8 weeks, total ribonucleic acid (RNA) isolated from the detrusor layer of the bladders was reverse transcribed, and then complementary deoxyribonucleic acid was amplified with polymerase chain reaction primer sets for type I collagen, type III collagen, tropoelastin, and transforming growth factor beta 1 (TGF-beta-1). Collagen and elastin contents of the bladders were quantified with commercially available assays. Both diabetic and diuretic rat bladders exhibited significantly (P <0.05) lower expression of type I collagen and TGF-beta-1 messenger RNA (mRNA) compared with normal controls at all time points tested. In contrast, downregulation of type III collagen mRNA expression in both diabetic and diuretic groups was seen at 4 and 8 weeks. Furthermore, tropoelastin mRNA expression in the diabetic rat bladders was, compared with normal and diuretic rats, significantly (P <0.05) greater at 2 weeks. Both diabetic and diuretic rat bladders exhibited significantly (P <0.05) decreased collagen and increased elastin protein content at 2 and 8 weeks. The results of the present study suggest that increases in compliance of the bladders in diabetic cystopathy result not only from diuresis-driven reduction of collagen synthesis but also from increased elastin synthesis.

Temporal diabetes- and diuresis-induced remodeling of the urinary bladder in the rat

The natural history of diabetes mellitus-induced remodeling of the urinary bladder is poorly understood. In this study, we examined temporal remodeling of the bladder in diabetic and diuretic rats. Male Sprague-Dawley rats were divided into three groups: streptozotocin-induced diabetic, 5% sucrose-induced diuretic, and age-matched control. Micturition and morphometric characteristics were evaluated using metabolic cages and light-microscopic examination of the bladder 4 days and 1, 2, 3, and 9 wk after induction. Digital image analysis was used to quantify equatorial cross-sectional areas of bladder tissue and lumen, as well as relative content of the three primary tissue components: smooth muscle, urothelium, and collagen. Diabetes and diuresis caused significant increases in fluid intake, urine output, and bladder weight. In both groups, progressive increases were observed in lumen area from 4 days to 3 wk after induction and in wall area from 2 to 3 wk after induction. Wall thickness decreased within the first 2 wk in the diabetic and diuretic rats but returned to control at 3 and 9 wk. As a percentage of total cross-sectional area, smooth muscle area increased, urothelium area was unchanged, and collagen area decreased in diabetic and diuretic rats after 2-3 wk compared with control rats. In conclusion, diabetes and diuresis induced similar bladder remodeling. Diabetes-induced diuresis caused adaptive physical changes in rat bladder by 4 days after induction; remodeling was observed by 2-3 wk after induction and remained stable from 3 to 9 wk.

Alterations in neurogenically mediated contractile responses of urinary bladder in rats with diabetes

Diabetic bladder dysfunction (DBD) is among the most common and bothersome complications of diabetes mellitus. Autonomic neuropathy has been counted as the cause of DBD. In the present study, we compared the alterations in the neurogenically mediated contractile responses of urinary bladder in rats with streptozocin-induced diabetes, 5% sucrose-induced diuresis, and age-matched controls. Male Sprague-Dawley rats were divided into three groups: 9-wk diabetic rats, diuretic rats, and age-matched controls. Micturition and morphometric characteristics were evaluated using metabolic cage and gross examination of the bladder. Bladder detrusor muscle strips were exposed to either periodic electrical field stimulation (EFS) or to EFS in the presence of atropine, alpha,beta-methylene adrenasine 5'-triphosphate, or tetrodotoxin. The proportions of cholinergic, purinergic, and residual nonadrenergic-noncholinergic (NANC) components of contractile response were compared among the three groups of animals. Diabetes caused a significant reduction of body weight compared with diuresis and controls, although the bladders of diabetic and diuretic rats weighed more than the controls. Both diabetes and diuresis caused significant increase in fluid intake, urine output, and bladder size. Diabetes and diuresis caused similarly increased response to EFS and reduced response to cholinergic component compared with controls. However, the purinergic response was significantly smaller in diuretic bladder strips compared with controls but not in diabetic rats. A residual NANC of unknown origin increased significantly but differently in diabetics and diuretics compared with controls. In conclusion, neurogenically mediated bladder contraction is altered in the diabetic rat. Diabetic-related changes do not parallel diuretic-induced changes, indicating that the pathogenesis of DBD needs further exploration.

The effect of AVP-V receptor stimulation on local GFR in the rat kidney.

Arginine vasopressin (AVP) might influence urinary concentration ability by altering the intrarenal distribution of glomerular filtration rate (GFR). To study this possibility we have measured the intracortical distribution of GFR following acute AVP-V1 receptor stimulation in anaesthetized female Sprague-Dawley (SPD) rats during euvolemia and water diuresis by the aprotinin method, allowing two consecutive measurements of zonal GFR in the same kidney. Acute i.v. bolus injection of 50 ng V1 receptor agonist ([Phe2, Ile3, Orn8]-vasopressin) followed by a continuous infusion of 5 ng min(-1) in euvolemic rats reduced GFR by 25% in outer cortex (OC), 20% in middle cortex (MC) and 19% in inner cortex (IC) relative to vehicle infusion (all P < 0.05). In water diuretic rats V1 receptor agonist reduced GFR by 22% in OC, 10% in MC and 11% in IC relative to vehicle infusion (P < 0.05). GFR decreased slightly more in OC than in MC and IC in both euvolemic and water diuretic rats (P < 0.05) indicating a distribution of GFR towards MC and IC. Acute infusion of the selective non-peptide V1 receptor antagonist OPC-21268 in euvolemic rats reduced GFR by 14% in OC, 13% in MC and 11% in IC relative to vehicle infusion (P < 0.05), with no significant difference between the layers. The change in distribution of GFR not only between OC and IC, but also between OC and MC suggests that the afferent/efferent arterioles and not the medullary vasa recta is the main site of resistance change. We conclude that acute i.v. infusion of V1 receptor agonist in high doses reduces GFR more in superficial than in deep cortex in both euvolemic and water diuretic rats and that this may be of some importance for water conservation, adding to the V2- receptor effect on water permeability of the collecting ducts.

The effect of AVP-V2 receptor stimulation on local GFR in the rat kidney.

The effect of AVP-V2 receptor agonist desmopressin, dDAVP, its non-peptide antagonist OPC-31260 and vehicle infusion on glomerular filtration rate (GFR) in the outer, middle and inner cortex was studied in both hydropenic and water diuretic Inactin anaesthetized female Sprague-Dawley rats using the aprotinin method. Two subsequent GFR measurements were carried out in the same kidney by injection of 125I- and 131I-labelled aprotinin before and after i.v. infusion of dDAVP, OPC-31260 or the vehicle. Acute infusion of dDAVP in hydropenic rats increased total GFR by 14% relative to vehicle infusion, whereas in water diuretic rats it had no effect relative to vehicle. No significant changes in arterial pressure (Pa) or renal blood flow (RBF) were recorded. Infusion of OPC-31260 reduced total GFR by 11% compared with vehicle. These results are consistent with the findings that a presensitization of the vasculature by high plasma levels of AVP is necessary for the renal vascular effects mediated by the V2 or V2-like receptors to occur. The ratio between inner and outer cortex GFR remained unchanged from control to experimental condition as follows: dDAVP infusion in hydropenic rats, 0.504 vs. 0.494 in control; vehicle infusion in hydropenic rats, 0. 393 vs. 0.392; OPC-31260 infusion in hydropenic rats, 0.517 vs. 0. 523; dDAVP in water diuretic rats, 0.547 vs. 0.543; vehicle in water diuretic rats, 0.413 vs. 0.417. Thus no significant difference in the GFR response was observed between superficial and deep cortical layers of the rat kidney.

Expression of aldose reductase, sorbitol dehydrogenase and Na+/myo-inositol and Na+/Cl-/betaine transporter mRNAs in individual cells of the kidney during changes in the diuretic state.

The effect of changes in medullary extracellular tonicity on mRNA expression for aldose reductase (AR), sorbitol dehydrogenase (SDH), Na+/Cl-/betaine (BGT) and Na+/myo-inositol (SMIT) cotransporter in different kidney zones was studied using Northern blot analysis and non-radioactive in situ hybridization in four groups of rats: controls, acute diuresis (the loop diuretic furosemide was administered), chronic diuresis (5 days of diuresis), and antidiuresis [5 days of diuresis followed by 24 h deamino-Cys1, d-Arg8 vasopressin (dDAVP)]. Acute administration of the loop diuretic furosemide significantly reduced AR, SMIT and BGT gene expression in the inner and outer medulla compared with controls. Administration of dDAVP to chronically diuretic rats raised the expression of these three mRNAs in the inner but not the outer medulla compared with the chronically diuretic rats. None of these alterations in medullary tonicity significantly changed SDH expression. The in situ hybridization studies showed AR, BGT and SMIT mRNAs to be expressed in both epithelial and non-epithelial cells of the outer and inner medulla. The various cell types (epithelial, endothelial and interstitial cells) differed in their expression pattern and intensity of AR, SDH, BGT and SMIT mRNA, but the inner medullary cells responded uniformly to a decrease in extracellular tonicity with a reduction, and to an increase with enhancement of their AR, BGT and SMIT expression.

Urea transport processes are induced in rat IMCD subsegments when urine concentrating ability is reduced.

Infusing urea into low-protein-fed mammals increases urine concentration within 5-10 min. To determine which urea transporter may be responsible, we measured urea transport in perfused IMCD3 segments [inner medullary collecting duct (IMCD) segments from the deepest third of the IMCD] from low-protein-fed rats. Basal facilitated urea permeability increased 78%, whereas active urea secretion was completely inhibited. This suggests that upregulation of facilitated urea transport may mediate the rapid increase in urine concentration. Next, expression of active urea transporter(s) in perfused IMCDs was determined in rats with other causes of reduced urine concentrating ability. In untreated and water diuretic rats, IMCD1 segments showed no active urea transport, nor did IMCD2 segments from untreated or hypercalcemic rats. In IMCD1 segments from hypercalcemic rats, active urea reabsorption was induced. The induced active urea reabsorption was completely inhibited by replacing perfusate Na+ with N-methyl-D-glucamine (NMDG+). Active urea secretion was completely inhibited in IMCD3 segments from hypercalcemic rats. In contrast, water diuresis stimulated active urea secretion in IMCD2 segments. The induced active urea secretion was inhibited by phloretin, ouabain, triamterene, or replacing perfusate Na+ with NMDG+. In conclusion, the response of active urea transporters to reductions in urine concentrating ability follows two paradigms: one occurs with hypercalcemia or a low-protein diet, and the second occurs only in water diuresis.

Evidence for sodium-dependent active urea secretion in the deepest subsegment of the rat inner medullary collecting duct.

Active reabsorption of urea appears in the initial IMCD (IMCD1) of rats fed a low-protein diet. To determine whether active urea transport also occurs in the deepest IMCD subsegment, the IMCD3, we isolated IMCDs from the base (IMCD1), middle (IMCD2), and tip (IMCD3) regions of the inner medulla from rats fed a normal protein diet and water ad libitum. IMCDs were perfused with identical perfusate and bath solutions. A significant rate of net urea secretion was present only in IMCD3s. Replacing perfusate Na+ with NMDG+ reversibly inhibited net urea secretion but replacing bath Na+ with NMDG+ or perfusate Cl- with gluconate- had no effect. Net urea secretion was significantly inhibited by: (a) 250 microM phloretin (perfusate); (b) 100 nM triamterene (perfusate); (c) 1 mM ouabain (bath); and (d) cooling the tubule to 23 degrees C. Net urea secretion was significantly stimulated by 10 nM vasopressin (bath). Next, we perfused IMCD3s from water diuretic rats (given food ad libitum) and found a significant, fivefold increase in net urea secretion. In summary, we identified a secondary active, secretory urea transport process in IMCD3s of normal rats which is upregulated in water diuretic rats. This new urea transporter may be a sodium- urea antiporter.

Experimental Diabetes Upregulates the Expression of Uretereral Endothelin Receptors

NAKAMURA, I., M. SAITO, Y. FUKUMOTO, M. YOSHIDA, K. NISHI, R. M. WEISS AND J. LATIFPOUR.Experimental diabetes upregulates the expression of uretereral endothelin receptors.PEPTIDES 18(7) 1091–1093, 1997.—We investigated the binding characteristics of endothelin (ET) receptors in the ureters of rats with experimentally induced diabetes and diuresis. Receptor binding experiments demonstrated an upregulation in the expression of [125I]ET-1 binding sites in the diabetic rat ureter but not in the diuretic rat ureter. ET-1, ET-3, IRL 1620, and BQ 610 inhibited [125I]ET-binding to the rat ureter consistent with the predominance of ETA receptors in these tissues. The subtype specificity of ET receptors in ureteral tissues was confirmed with inhibition data obtained from cloned human ETA and ETB receptors.

糖尿病ラット膀胱におけるムスカリンレセプターの分布に関する研究

We evaluated the alterations of density, localization and subtype specificity of muscarinic receptors in experimentally-induced diabetic rat bladder. Five groups of rats were maintained for sixteen weeks 1) diabetic, 2) diabetic insulin-treated (insulin started 8 weeks after the onset of diabetes), 3) sucrose-fed diuretic, 4) sucrose-removed and 5) age matched controls. We used radioligand binding technique and light microscopic autoradiography to define the density and distribution of muscarinic receptors in the rat urinary bladder. Saturation experiments showed an increase in the density of muscarinic receptors in the bladders of diabetic and diuretic rats compared with age matched controls. Insulin treatment partially reversed the up-regulatin of muscarinic receptors in rat urinary bladder. Autoradiographic studies also indicated that muscarinic receptors were located in all layers of the bladder muscularis. The muscularis of the bladder dome contained higher densities of muscarinic receptors than that of the bladder base. Lack of [3H]QNB binding to transitional epithelium, lamina propria, and tunica adventitia suggests an absence of muscarinic receptors in these regions. Inhibition of [3H]QNB binding to the bladder sections by selective muscarinic antagonists indicated existence of the M2 and M3 receptor subtypes in the muscularis of the rat bladder.

実験的糖尿病ラットの下部尿路機能に関する研究

Diabetic lower urinary tract disfunction is well known, however, precise mechanism of the lower urinary tract disfunction remains to be solved. The present study is to clarify the lower urinary tract disfunction of diabetic rats by simultaneously measuring bladder and urethral pressures. Female wistar rats were administered with streptozotocin (STZ 65 mg/kg, i.p.) to induce diabetes mellitus. Bladder and urethral pressures during rhythmic bladder contractions were compared under urethane anesthesia (1.0 g/kg, i.v.) between the control rats, diabetic rats, and diuretic rats. The bladder contraction pressures of diabetic rats were decreased initially, but returned to the control values at 8 weeks. Atropine (2.5 mg/kg, i.a.) produced a marked reduction of bladder contraction pressure in the 8 weeks diabetic rats. The diabetic rats showed an increase of urethral pressure simultaneously with an increase of bladder pressure in the initial phase of rhythmic bladder contraction which is totally blocked by striated muscle relaxant. This phenomenon was not observed in the control or diuretic rats. Both group showed an initial decrease of urethral pressure followed by bladder contraction and rhythmic contractions of the urethra. Our results suggest that bladder muscarinic receptors of the 8 weeks diabetic rats are more dominant than those of the other groups, and Mahoney's 4th reflex (urethrosphincteric guarding reflex) is facilitated but Mahoney's 6th reflex (detruthodetrusor facilitative reflex) is suppressed in the diabetic rats. We think that in the diabetic rats, sensory inputs by bladder distension were weak and could not induce Mahoney's 6th reflex until certain threshold values. Diabetic rats might develop changes in the mode of spinal neuronal transmission.

Enhancement of muscarinic receptor-coupled phosphatidyl inositol hydrolysis in diabetic bladder.

We previously have shown an increase in muscarinic receptor density in streptozotocin (STZ)-induced diabetic and sucrose-fed diuretic rat detrusor that correlates with an increase in the contractile response to muscarinic agonist (J Pharmacol Exp Ther 248:81, 1989; Diabetes 40: 265, 1991). To investigate the signal transduction pathway involved in this altered functional response, we examined muscarinic receptor-coupled phosphatidylinositol metabolism in STZ-diabetic, sucrose-fed diuretic and age-matched control rat bladders. [3H]myo-inositol uptake was similar in all groups, but incorporation of myo-inositol into phosphatidylinositol (PI) was significantly increased in the diabetic bladder compared to the sucrose-fed and control rat bladders. Carbachol-induced increase in inositol phosphate (IPs) production was higher in the diabetic bladder than in bladders from control and sucrose-fed animals although the EC50 values were similar for all groups. Enhanced inositol phosphate production after muscarinic agonist stimulation may be due not only to the upregulation of muscarinic receptors but also the increased incorporation of myo-inositol into PI in the STZ-induced diabetic bladder.

Regulation of aldose reductase, sorbitol dehydrogenase, and taurine cotransporter mRNA in rat medulla.

The regulation of mRNA for aldose reductase, sorbitol dehydrogenase, and the Na+/Cl-/taurine cotransporter was studied with three in vivo models in which urinary concentration is reduced: Sprague-Dawley rats undergoing a water diuresis or fed a low-protein diet or Brattleboro rats. In Sprague-Dawley rats, 3 days of water diuresis reduced inner medullary aldose reductase mRNA abundance 6.5-fold compared with untreated rats, whereas sorbitol dehydrogenase and taurine cotransporter mRNA were unchanged. When water diuretic rats were acutely deprived of water, urine osmolality increased significantly after 4 h but aldose reductase mRNA did not increase until 12 h. Heat shock protein-70 mRNA was not increased by water deprivation. Second, in rats fed a low-protein diet for 3 wk, aldose reductase mRNA increased two-fold, whereas sorbitol dehydrogenase and taurine cotransporter mRNA were unchanged. Finally, in Brattleboro rats, urine osmolality and levels of aldose reductase and taurine cotransporter mRNA increased in response to 1 day of water deprivation, whereas sorbitol dehydrogenase mRNA was unchanged. Administering vasopressin (1 U/day) to Brattleboro rats for 8 days also increased urine osmolality and aldose reductase mRNA but did not alter sorbitol dehydrogenase or taurine cotransporter mRNA. This result is consistent with the hypothesis that changes in urine osmolality induce changes in aldose reductase mRNA abundance that are independent of vasopressin. It was concluded that, in rat inner medulla: (1) aldose reductase mRNA abundance varies with changes in water balance or dietary protein, whereas sorbitol dehydrogenase and taurine cotransporter mRNA do not; and (2) heat shock protein-70 mRNA abundance is not increased during acute osmotic stress.

In vivo diuretic actions of renal vasopressin V1 receptor stimulation in rats

The specific vasopressin V1 receptor agonist (V1AG; [Phe2,Ile3,Orn8]vasopressin) was infused (2.0 ng.kg-1.min-1) into the renal medullary interstitial space to determine the effects of selective medullary V1 receptor stimulation on sodium and water excretion in normal rats. Responses were compared with those of arginine vasopressin (AVP) and vasopressin V2 receptor stimulation resulting from infusion of a V1 receptor antagonist with AVP. Medullary infusion of V1AG or AVP in euvolemic rats produced no changes in hemodynamics or glomerular filtration rate. V1AG increased urine flow > 60% in euvolemic rats, whereas no change was observed with AVP. This response could not be explained by a rise of arterial pressure or by volume retention. With V2 stimulation in euvolemic rats, urine flow was decreased. In water diuretic rats, V1AG produced no change, whereas AVP infusion decreased urine flow. The results provide in vivo evidence that tubular V1 vasopressin receptor activity results in increased urine flow and thereby modulates the antidiuretic actions of vasopressin in the euvolemic state.