Rat bladder in the early stages of streptozotocin-induced diabetes: adrenergic and cholinergic innervation

Impaired M3 and enhanced M2 muscarinic receptor contractile function in a streptozotocin model of mouse diabetic urinary bladder

We investigated the contractile roles of M2 and M3 muscarinic receptors in urinary bladder from streptozotocin-treated mice. Wild-type and M2 muscarinic receptor knockout (M2 KO) mice were given a single injection of vehicle or streptozotocin (125 mg kg(-1)) 2-24 weeks prior to bladder assays. The effect of forskolin on contractions elicited to the muscarinic agonist, oxotremorine-M, was measured in isolated urinary bladder (intact or denuded of urothelium). Denuded urinary bladder from vehicle-treated wild-type and M2 KO mice exhibited similar contractile responses to oxotremorine-M, when contraction was normalized relative to that elicited by KCl (50 mM). Eight to 9 weeks after streptozotocin treatment, the EC(50) value of oxotremorine-M increased 3.1-fold in urinary bladder from the M2 KO mouse (N = 5) compared to wild type (N = 6; P < 0.001). Analogous changes were observed in intact bladder. In denuded urinary bladder from vehicle-treated mice, forskolin (5 microM) caused a much greater inhibition of contraction in M2 KO bladder compared to wild type. Following streptozotocin treatment, this forskolin effect increased 1.6-fold (P = 0.032). At the 20- to 24-week time point, the forskolin effect increased 1.7-fold for denuded as well as intact bladders (P = 0.036, 0.01, respectively). Although streptozotocin treatment inhibits M3 receptor-mediated contraction in denuded urinary bladder, muscarinic contractile function is maintained in wild-type bladder by enhanced M2 contractile function. M2 receptor activation opposes forskolin-induced relaxation of the urinary bladder, and this M(2) function is enhanced following streptozotocin treatment.

Using gene chips to identify organ-specific, smooth muscle responses to experimental diabetes: potential applications to urological diseases

OBJECTIVE

To identify early diabetes-related alterations in gene expression in bladder and erectile tissue that would provide novel diagnostic and therapeutic treatment targets to prevent, delay or ameliorate the ensuing bladder and erectile dysfunction.

MATERIALS AND METHODS

The RG-U34A rat GeneChip (Affymetrix Inc., Sunnyvale, CA, USA) oligonucleotide microarray (containing approximately 8799 genes) was used to evaluate gene expression in corporal and male bladder tissue excised from rats 1 week after confirmation of a diabetic state, but before demonstrable changes in organ function in vivo. A conservative analytical approach was used to detect alterations in gene expression, and gene ontology (GO) classifications were used to identify biological themes/pathways involved in the aetiology of the organ dysfunction.

RESULTS

In all, 320 and 313 genes were differentially expressed in bladder and corporal tissue, respectively. GO analysis in bladder tissue showed prominent increases in biological pathways involved in cell proliferation, metabolism, actin cytoskeleton and myosin, as well as decreases in cell motility, and regulation of muscle contraction. GO analysis in corpora showed increases in pathways related to ion channel transport and ion channel activity, while there were decreases in collagen I and actin genes.

CONCLUSIONS

The changes in gene expression in these initial experiments are consistent with the pathophysiological characteristics of the bladder and erectile dysfunction seen later in the diabetic disease process. Thus, the observed changes in gene expression might be harbingers or biomarkers of impending organ dysfunction, and could provide useful diagnostic and therapeutic targets for a variety of progressive urological diseases/conditions (i.e. lower urinary tract symptoms related to benign prostatic hyperplasia, erectile dysfunction, etc.).

Factors underlying the increased sensitivity to field stimulation of urinary bladder strips from streptozotocin-induced diabetic rats

1. The responses of bladder strips from control, streptozotocin-diabetic, and sucrose-drinking rats to electrical field stimulation were investigated. Sucrose-drinking rats were included as additional controls because they have enlarged bladders as a result of non-diabetic diuresis. 2. Bladder strips from diabetic rats developed more spontaneous activity than those from the two control groups. Indomethacin reduced the amplitude and frequency of spontaneous contractions suggesting that they resulted from endogenous prostaglandin formation. Tetrodotoxin (TTX) had little effect, while alpha, beta-methylene ATP caused increases in spontaneous activity. 3. Bladder strips from diabetic rats responded to field stimulation with greater contractions than controls in the absence of antagonists as well as in the presence of atropine and alpha, beta-methylene ATP. Increasing TTX concentrations caused a step-wise depression of the contractile response to electrical stimulation which was not affected by preincubation with either atropine or alpha, beta-methylene ATP. 4. Atropine and indomethacin had no effect on strength-duration curves constructed to measure threshold contractile responses to five pulses stimulation. The curves were shifted to the right by both TTX and alpha, beta-methylene ATP, indicating that the responses were neurogenic in nature and at least partially, the result of stimulation of P2-purinoceptors. In the absence of drugs, bladder strips from diabetics responded at lower voltages and pulse widths than those of control and sucrose-drinking rats, suggesting that they were more excitable. 5. The response curve of bladder strips from diabetics to field stimulation at increasing voltage was shifted upwards and to the left compared to strips from control or sucrose-drinking rats. 6. Bladder strips from diabetics responded to stimulation at increasing pulse width with greater responses than those from control or sucrose-drinking rats. At 1.0 ms pulse width, the TTX-resistant response of strips from diabetic rats was still greater than that of the other groups, indicating that a myogenic component was also involved.7. The data suggest that bladder strips from diabetic rats are more excitable than those of control or sucrose-drinking rats. This may result from diabetes-induced decreases in bladder lipid or other membrane changes, and/or be a result of partial depolarization, perhaps related to diabetic neuropathy.

Differential effect of guanethidine on dopamine and norepinephrine in rat peripheral tissues

The changes of dopamine (DA) and norepinephrine (NE) were investigated in rat peripheral tissues after guanethidine treatment (50 mg/kg i.p. five days each week) during one week (group 1, n = 10, five injections) and during 2.5 weeks (group 2, n = 8, 13 injections). Guanethidine greatly reduced NE levels in all the analyzed tissues but only partially depleted DA in kidney, bladder, stomach, intestine, lung and liver and in sympathetic ganglia. The differential pattern of changes between DA and NE induced by guanethidine suggests that peripheral DA is distributed in several neuronal or non-neuronal pools, whose presence, nature and contribution varies in the different tissues. Both noradrenergic cell bodies and small intensely fluorescent cells (SIF cells) can contribute to the DA in the superior cervical ganglion. Noradrenergic neurons seem to be the main sources of DA in seminal vesicles, vas deferens, heart and spleen. In addition to noradrenergic nerves, extraneuronal sources could account for a meaningful portion of DA in kidney, gastrointestinal tract, lung and liver. The bladder is the peripheral tissue where DA exhibits the highest resistance to the neurotoxin. Accordingly, these tissues may provide meaningful sources of non-precursor DA pools.

The effect of streptozotocin-induced diabetes on cholinergic motor transmission in the rat urinary bladder

1. The effect of streptozotocin (STZ)-induced diabetes on cholinergic motor transmission in the rat urinary bladder was investigated by recording contractile activity of detrusor strips in vitro. 2. The Ca(2+)-channel antagonist, nifedipine, was found to be more effective in blocking the noncholinergic motor transmission than P2-purinoceptor desensitization by alpha,beta-methylene ATP. 3. The neurogenic contractile responses to electrical field stimulation in the presence of nifedipine (cholinergic) were larger in the diabetic detrusor than in the non-diabetic controls. The potentiation of the cholinergic transmission was more evident at higher frequencies. 4. Concentration-response curves for acetylcholine were identical in detrusors from diabetic and non-diabetic animals, thus excluding a postsynaptic supersensitivity to acetylcholine being responsible for the potentiation of cholinergic motor transmission. 5. It is concluded that the potentiation of cholinergic motor transmission is due to enhanced release of acetylcholine in diabetic detrusor. Possible reasons for this enhancement are discussed in relation to diabetes.

Inhibitory effect of streptozotocin-induced diabetes on non-cholinergic motor transmission in rat detrusor and its prevention by sorbinil

1. Non-cholinergic motor transmission in the urinary bladder of streptozotocin (STZ)-diabetic rats was studied by recording contractile activity of strips of detrusor in vitro. 2. The neurogenic contractile responses to electrical field stimulation (EFS) of atropine-treated detrusor strips were decreased in 4, 8 and 12 week STZ-diabetic rats. The decrease was most marked in 12 week diabetic rats and least in 4 week ones. 3. Concentration-response curves showed no change in sensitivity of the detrusor to acetylcholine (ACh) in diabetic rats. The maximum tension generated by ACh was similar in diabetic and non-diabetic animals. 4. The contractile responses to EFS at frequencies greater than or equal to 1 Hz were not maintained during stimulation. The 'fade' was significantly greater in detrusor strips of diabetic rats. 5. The contractile response of detrusor to EFS was significantly greater in 12 week diabetic rats treated with the aldose reductase inhibitor sorbinil, than in untreated 12 week diabetic rats. The sensitivity to ACh was similar in the two groups. 6. It is concluded that the reduction of the neurogenic non-cholinergic responses of detrusor to EFS in STZ-diabetic rats is probably caused by a reduction in the release of the non-cholinergic motor transmitter. The results are discussed in relation to bladder dysfunction in human diabetes mellitus.

Early increase in CGRP- and VIP-immunoreactive nerves in the skin of streptozotocin-induced diabetic rats

We have previously shown depletion of nerves and neuropeptides in skin biopsies of diabetic patients, even in the absence of clinical signs and symptoms of sensory and autonomic neuropathy, but were unable to examine the changes occurring at an early stage of the disease. Therefore, the distribution and relative density of peptide-containing nerves was studied in streptozotocin-treated rats in order to assess the progression of neural changes in the initial stages of diabetes. Skin samples dissected from the lip and footpad of diabetic rats, 2, 4, 8 and 12 weeks after streptozotocin injection and age matched controls were sectioned and were immunostained with antisera to the neuropeptides substance P, calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP) and neuropeptide Y (NPY), and to a general neural marker, protein gene product 9.5 (PGP 9.5). No change was apparent in the distribution or relative density of immunoreactive cutaneous nerve fibres 2, 4 and 8 weeks after streptozotocin treatment. By 12 weeks there was a marked increase in the number of CGRP-immunoreactive fibres present in epidermis and dermis, and of VIP-immunoreactive fibres around sweat glands and blood vessels. A parallel increase was seen in nerves displaying PGP 9.5 immunoreactivity. No differences were detected in nerves immunoreactive for either substance P in the epidermis and dermis, and NPY around blood vessels. The alterations in the peptide immunoreactivities may be similar in the initial stages of human diabetes.

Changes in the somatostatin, substance P and vasoactive intestinal polypeptide content of the gastrointestinal tract following streptozotocin-induced diabetes in the rat

Rats with streptozotocin-induced diabetes of 10 weeks' duration showed significant changes in the total content of somatostatin, substance P and vasoactive intestinal polypeptide in the stomach and small intestine compared with control animals. An increase (p less than 0.05) in the concentration and total content of gastric somatostatin and a decrease (p less than 0.05) in the concentration and content of gastric substance P were seen in the streptozotocin-treated rats. The increase in the vasoactive intestinal polypeptide (VIP) content (54%, p less than 0.05) and the decrease in the substance P content (35%, p less than 0.05) of the gut may contribute to the impaired intestinal motility observed in animals with experimentally produced diabetes. Both the diabetogenic effect of streptozotocin and the changes in regulatory peptide concentrations were prevented by injection of nicotinamide before streptozotocin suggesting that the changes did not arise from a non-specific toxic effect of streptozotocin upon gastrointestinal neurones and/or endocrine cells.