Muscarinic supersensitivity in the rat urinary bladder after capsaicin pretreatment

TRPV1 is involved in stretch-evoked contractile changes in the rat autonomous bladder model: a study with piperine, a new TRPV1 agonist

AIM

Vanilloids like capsaicin and resiniferatoxin (RTX) have been used for more than a decade in the treatment of neurogenic detrusor overactivity. Recently, the vanilloid molecule piperine (PIP) has been shown to have similar pharmacological properties as these drugs. In this study, we looked at PIP-effects on autonomous bladder contractile activity, with particular interest for its selectivity for the transient receptor potential channel 1 (TRPV1) receptor. Additionally, we studied the role of TRPV1 in volume-induced contractile changes using selective and non-selective TRPV1 antagonists.

METHODS

The acute and prolonged effects of PIP were studied on rat bladders. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. In acute experiments, PIP was added directly to the bathing solution. For prolonged effects, animals were pre-treated intravesically with vehicle (ethanol 5%) or PIP (10(-4) M) and sacrificed 72 hr later. The effects of selective (capsazepine (CZP)) and non-selective (ruthenium red (RR)) TRPV1 antagonists on volume-evoked contractile parameters were also studied.

RESULTS

Acute administration of PIP 10(-4) M significantly increased amplitude of bladder contractions (P < 0.05). These effects were significantly antagonized (P < 0.05) by the TRPV1-selective antagonist CZP (10(-5) M) and the non-selective TRP-antagonist RR (10(-5) M). Intravesical pre-treatment with PIP induced shorter contractions with more periods of non-activity (P < 0.05) compared to controls. Inhibition of TRPV1 with CZP and RR significantly reduced the volume-evoked rise in contractile amplitude in isolated bladders (P < 0.05).

CONCLUSION

We found evidence for acute and prolonged effects of PIP on bladder contractility, which seem to be mediated through TRPV1. Furthermore, we found evidence for involvement of TRPV1 in afferent signaling of mechanical stimuli.

Final report on the safety assessment of capsicum annuum extract, capsicum annuum fruit extract, capsicum annuum resin, capsicum annuum fruit powder, capsicum frutescens fruit, capsicum frutescens fruit extract, capsicum frutescens resin, and capsaicin

Capsicum-derived ingredients function as skin-conditioning agents--miscellaneous, external analgesics, flavoring agents, or fragrance components in cosmetics. These ingredients are used in 19 cosmetic products at concentrations as high as 5%. Cosmetic-grade material may be extracted using hexane, ethanol, or vegetable oil and contain the full range of phytocompounds that are found in the Capsicum annuum or Capsicum frutescens plant (aka red chiles), including Capsaicin. Aflatoxin and N-nitroso compounds (N-nitrosodimethylamine and N-nitrosopyrrolidine) have been detected as contaminants. The ultraviolet (UV) absorption spectrum for Capsicum Annuum Fruit Extract indicates a small peak at approximately 275 nm, and a gradual increase in absorbance, beginning at approximately 400 nm. Capsicum and paprika are generally recognized as safe by the U.S. Food and Drug Administration for use in food. Hexane, chloroform, and ethyl acetate extracts of Capsicum Frutescens Fruit at 200 mg/kg resulted in death of all mice. In a short-term inhalation toxicity study using rats, no difference was found between vehicle control and a 7% Capsicum Oleoresin solution. In a 4-week feeding study, red chilli (Capsicum annuum) in the diet at concentrations up to 10% was relatively nontoxic in groups of male mice. In an 8-week feeding study using rats, intestinal exfoliation, cytoplasmic fatty vacuolation and centrilobular necrosis of hepatocytes, and aggregation of lymphocytes in the portal areas were seen at 10% Capsicum Frutescens Fruit, but not 2%. Rats fed 0.5 g/kg day-1 crude Capsicum Fruit Extract for 60 days exhibited no significant gross pathology at necropsy, but slight hyperemia of the liver and reddening of the gastric mucosa were observed. Weanling rats fed basal diets supplemented with whole red pepper at concentrations up to 5.0% for up to 8 weeks had no pathology of the large intestines, livers, and kidneys, but destruction of the taste buds and keratinization and erosion of the gastrointestinal (GI) tract were noted in groups fed 0.5% to 5.0% red pepper. The results of 9-and 12-month extension of this study showed normal large intestines and kidneys. In rabbits fed Capsicum Annuum Powder at 5 mg/kg day-1 in the diet daily for 12 months damage to the liver and spleen was noted. A rabbit skin irritation test of Capsicum Annuum Fruit Extract at concentrations ranging from 0.1% to 1.0% produced no irritation, but Capsicum Frutescens Fruit Extract induced concentration-dependent (at 25 to 500 microg/ml) cytotoxicity in a human buccal mucosa fibroblast cell line. An ethanol extract of red chili was mutagenic in Salmonella typhimurium TA98, but not in TA100, or in Escherichia coli. Other genotoxicity assays gave a similar pattern of mixed results. Adenocarcinoma of the abdomen was observed in 7/20 mice fed 100 mg red chilies per day for 12 months; no tumors were seen in control animals. Neoplastic changes in the liver and intestinal tumors were observed in rats fed red chili powder at 80 mg/kg day-1 for 30 days, intestinal and colon tumors were seen in rats fed red chili powder and 1,2-dimethyl hydrazine, but no tumors were observed in controls. In another study in rats, however, red chile pepper in the diet at the same dose decreased the number of tumors seen with 1,2-dimethylhydrazine. Other feeding studies evaluated the effect of red chili peppers on the incidence of stomach tumors produced by N-methyl-N'-nitro-N-nitrosoguanidine, finding that red pepper had a promoting effect. Capsicum Frutescens Fruit Extract promoted the carcinogenic effect of methyl(acetoxymethyl)nitrosamine (carcinogen) or benzene hexachloride (hepatocarcinogen) in inbred male and female Balb/c mice dosed orally (tongue application). Clinical findings include symptoms of cough, sneezing, and runny nose in chili factory workers. Human respiratory responses to Capsicum Oleoresin spray include burning of the throat, wheezing, dry cough, shortness of breath, gagging, gasping, inability to breathe or speak, and, rarely, cyanosis, apnea, and respiratory arrest. A trade name mixture containing 1% to 5% Capsicum Frutescens Fruit Extract induced very slight erythema in 1 of 10 volunteers patch tested for 48 h. Capsicum Frutescens Fruit Extract at 0.025% in a repeated-insult patch test using 103 subjects resulted in no clinically meaningful irritation or allergic contact dermatitis. One epidemiological study indicated that chili pepper consumption may be a strong risk factor for gastric cancer in populations with high intakes of chili pepper; however, other studies did not find this association. Capsaicin functions as an external analgesic, a fragrance ingredient, and as a skin-conditioning agent--miscellaneous in cosmetic products, but is not in current use. Capsaicin is not generally recognized as safe and effective by the U.S. Food and Drug Administration for fever blister and cold sore treatment, but is considered to be safe and effective as an external analgesic counterirritant. Ingested Capsaicin is rapidly absorbed from the stomach and small intestine in animal studies. Subcutaneous injection of Capsaicin in rats resulted in a rise in the blood concentration, reaching a maximum at 5 h; the highest tissue concentrations were in the kidney and lowest in the liver. In vitro percutaneous absorption of Capsaicin has been demonstrated in human, rat, mouse, rabbit, and pig skin. Enhancement of the skin permeation of naproxen (nonsteroidal anti-inflammatory agent) in the presence of Capsaicin has also been demonstrated. Pharmacological and physiological studies demonstrated that Capsaicin, which contains a vanillyl moiety, produces its sensory effects by activating a Ca2 +-permeable ion channel on sensory neurons. Capsaicin is a known activator of vanilloid receptor 1. Capsaicin-induced stimulation of prostaglandin biosynthesis has been shown using bull seminal vesicles and rheumatoid arthritis synoviocytes. Capsaicin inhibits protein synthesis in Vero kidney cells and human neuroblastoma SHSY-5Y cells in vitro, and inhibits growth of E. coli, Pseudomonas solanacearum, and Bacillus subtilis bacterial cultures, but not Saccharomyces cerevisiae. Oral LD50 values as low as 161.2 mg/kg (rats) and 118.8 mg/kg (mice) have been reported for Capsaicin in acute oral toxicity studies, with hemorrhage of the gastric fundus observed in some of the animals that died. Intravenous, intraperitoneal, and subcutaneous LD50 values were lower. In subchronic oral toxicity studies using mice, Capsaicin produced statistically significant differences in the growth rate and liver/body weight increases. Capsaicin is an ocular irritant in mice, rats, and rabbits. Dose-related edema was observed in animals receiving Capsaicin injections into the hindpaw (rats) or application to the ear (mice). In guinea pigs, dinitrochlorobenzene contact dermatitis was enhanced in the presence of Capsaicin, injected subcutaneously, whereas dermal application inhibited sensitization in mice. Immune system effects have been observed in neonatal rats injected subcutaneously with Capsaicin. Capsaicin produced mixed results in S. typhimurium micronucleus and sister-chromatid exchange genotoxicity assays. Positive results for Capsaicin were reported in DNA damage assays. Carcinogenic, cocarcinogenic, anticarcinogenic, antitumorigenic, tumor promotion, and anti-tumor promotion effects of Capsaicin have been reported in animal studies. Except for a significant reduction in crown-rump length in day 18 rats injected subcutaneously with Capsaicin (50 mg/kg) on gestation days 14, 16, 18, or 20, no reproductive or developmental toxicity was noted. In pregnant mice dosed subcutaneously with Capsaicin, depletion of substance P in the spinal cord and peripheral nerves of pregnant females and fetuses was noted. In clinical tests, nerve degeneration of intracutaneous nerve fibers and a decrease in pain sensation induced by heat and mechanical stimuli were evident in subjects injected intradermally with Capsaicin. An increase in mean inspiratory flow was reported for eight normal subjects who inhaled nebulized 10(-7) M Capsaicin. The results of provocative and predictive tests involving human subjects indicated that Capsaicin is a skin irritant. Overall, studies suggested that these ingredients can be irritating at low concentrations. Although the genotoxicity, carcinogenicity, and tumor promotion potential of Capsaicin have been demonstrated, so have opposite effects. Skin irritation and other tumor-promoting effects of Capsaicin appear to be mediated through interaction with the same vanilloid receptor. Given this mechanism of action and the observation that many tumor promoters are irritating to the skin, the Panel considered it likely that a potent tumor promoter may also be a moderate to severe skin irritant. Thus, a limitation on Capsaicin content that would significantly reduce its skin irritation potential is expected to, in effect, lessen any concerns relating to tumor promotion potential. Because Capsaicin enhanced the penetration of an anti-inflammatory agent through human skin, the Panel recommends that care should be exercised in using ingredients that contain Capsaicin in cosmetic products. The Panel advised industry that the total polychlorinated biphenyl (PCB)/pesticide contamination should be limited to not more than 40 ppm, with not more than 10 ppm for any specific residue, and agreed on the following limitations for other impurities: arsenic (3 mg/kg max), heavy metals (0.002% max), and lead (5 mg/kg max). Industry was also advised that aflatoxin should not be present in these ingredients (the Panel adopted < or =15 ppb as corresponding to "negative" aflatoxin content), and that ingredients derived from Capsicum annuum and Capsicum Frutescens Plant species should not be used in products where N-nitroso compounds may be formed. (ABSTRACT TRUNCATED)

Autonomous contractile activity in the isolated rat bladder is modulated by a TRPV1 dependent mechanism

AIMS

Resiniferatoxin (RTX), a vanilloid compound and agonist of the transient receptor potential channel 1 (TRPV1), is known for its beneficial effects on neurogenic detrusor overactivity. The mainstream rationale for its use is the desensitization of TRPV1 on sensory bladder afferents. However, recent findings showed that TRPV1 is present in other cell types in the bladder. To eliminate the effects of RTX on spinal and central neural circuits, we investigated autonomous contractility in normal and neurogenic rat bladders after treatment with RTX.

METHODS

Female Wistar rats were made paraplegic at vertebral level T8-T9. Animals were intravesically pre-treated with vehicle (ethanol 5%) or RTX (100 nM) and sacrificed after 72 hr. Each bladder was excised and placed in a heated organ bath, where intravesical pressures were measured. Effects on contractile parameters of intravesical volume load, the non-selective muscarinic receptor agonist carbachol (CA) and electrical stimulation (ES) of nerves were studied in both groups.

RESULTS

In RTX-treated normal bladders we found shorter contractions with higher amplitude than in control bladders (P < 0.05). In RTX-treated neurogenic bladders the amplitude and duration of autonomous contractions were increased compared with controls (P < 0.05). Furthermore RTX induced an increased response to CA and to ES (P < 0.05).

CONCLUSIONS

RTX significantly affected the properties of autonomous bladder contractile activity. This provides evidence for local effects of RTX on bladder contractile activity, which are not mediated by afferent neural pathways and which may contribute to the beneficial effects on detrusor overactivity. TRPV1 and TRPV1(+) cells seem to play an important role in (autonomous) bladder contractility.

In vitro functional properties of the rat bladder regenerated by the bladder acellular matrix graft

PURPOSE

To assess the response of rat urinary bladder regenerated by the homologous bladder acellular matrix graft (BAMG) to in vitro electrical and pharmacologic stimuli.

MATERIALS AND METHODS

In Sprague-Dawley rats, partial cystectomy (>50%) was performed, followed by BAMG augmentation cystoplasty. After 4 months, organ bath studies of tissue strips in 10 were used to compare the contractility of the BAMG regenerates and the corresponding host detrusor smooth muscle.

RESULTS

The BAMG regenerates exhibited contractile activity to electrical field stimulation and a qualitatively identical pattern of response to muscarinic, purinergic, alpha- and beta-adrenergic drug administration and nitric oxide. At 4 months after surgery, the maximum forces of contraction of the BAMG regenerates to carbachol stimulation amounted to close to 80% of the host bladder response. With electrical field stimulation, they equaled 44% and 62% of the host bladder response after 2.5 and 4 months, respectively. Histological and immunohistochemical studies confirmed the presence of receptors for neurotransmitters that these functional in vitro studies implied.

CONCLUSIONS

The present study provides further evidence that augmentation cystoplasty with the BAMG leads to functional regeneration of the rat bladder detrusor smooth muscle.

Morphological and functional evidence against a sensory and sympathetic origin of nitric oxide synthase-containing nerves in the rat lower urinary tract

To establish which type of nerves (parasympathetic, sympathetic or sensory) produce nitric oxide in the rat lower urinary tract, chemical denervation of primary afferents and sympathetic nerves was carried out by systemic treatment with capsaicin and 6-hydroxydopamine, respectively, followed by identification of neuronal nitric oxide synthase immunoreactivity. Functional in vitro studies were also performed to examine whether the synthesis and release of nitric oxide was affected following treatment with the respective neurotoxins. Nerve fibres immunoreactive for substance P and calcitonin gene-related peptide were found in control tissue, but could not be detected following capsaicin treatment. In comparison, nitric oxide synthase-immunoreactive fibres appeared to be unaffected by capsaicin treatment. Administration of 6-hydroxydopamine resulted in a complete disappearance of tyrosine hydroxylase-immunoreactive nerves, whereas nitric oxide synthase-containing nerve fibres did not appear to be affected by the treatment. In ultrastructural studies, nitric oxide synthase immunoreactivity, as studied by colloidal gold particles, was found in the axoplasm and not in association with intraneuronal structures or synaptic vesicles. Gold particles representing substance P immunoreactivity were seen as clusters associated with large granular vesicles. In consecutive sections of nerve fibres, substance P and nitric oxide synthase were not found in the same axon profile. In functional studies on urethral tissue, application of capsaicin (1 microM) produced a long-lasting relaxation. The nitric oxide synthase inhibitor NG-nitro-L-arginine (0.1 mM) had no effect on this response. Systemic treatment with capsaicin or 6-hydroxydopamine had no effect on nerve-evoked, nitric oxide-mediated relaxations. The data suggest that nitric oxide synthase-containing nerves in the rat lower urinary tract do not belong to nerve populations sensitive to either the sympathetic neurotoxin, 6-hydroxydopamine, or the sensory neurotoxin, capsaicin.

Effects of denervation on muscarinic receptors in the rat bladder

OBJECTIVE

To demonstrate the specific distribution of muscarinic receptors in the rat urinary bladder and to investigate the effects of afferent and efferent denervation on the density and distribution of muscarinic receptors.

MATERIALS AND METHODS

Urinary bladders were obtained from female rats which had been injected with vehicle (control), or neonatally with capsaicin (NC, afferent denervation) or which had their pelvic plexus removed (post-ganglionic denervation, PGD, efferent denervation). Tissue sections were used in radioligand-binding studies and for autoradiography with the muscarinic receptor ligand l-quinuclidinyl[phenyl-4-3H]benzilate (QNB).

RESULTS

Binding of QNB was saturable and specific to a single population of binding sites, with a mean dissociation constant (Kd) of 1.05 +/- 0.14 nM in controls and 0.90 +/- 0.13 nM in rats with PGD. Post-ganglionic denervation caused a 37% increase in maximal binding (Bmax) of QNB from 437.1 +/- 39.1 fmol/mg protein (control group) to 599.1 +/- 4.5 fmol/mg protein (P < 0.02). Autoradiograms revealed muscarinic binding sites over the smooth muscle, but none over the epithelium. Smooth muscle binding sites were doubled after PGD but were unchanged after NC treatment.

CONCLUSION

Muscarinic receptors were localized over the smooth muscle of the rat bladder and were increased after post-ganglionic denervation. This increase may be responsible for the increased sensitivity to muscarinic agonists reported to occur after bladder denervation.

Contractility of urinary bladder and vas deferens after sensory denervation by capsaicin treatment of newborn rats

1. Capsaicin, a selective sensory neurotoxin, was given to newborn rats and at the age of 3 months the contractile activity of the urinary bladder detrusor muscle and vas deferens evoked by either electrical field stimulation (EFS) or exogenous adenosine 5'-triphosphate (ATP) and carbachol (urinary bladder), or ATP and noradrenaline (vas deferens) were tested. 2. EFS of the urinary bladder evoked contractions which consisted of cholinergic and purinergic components, since they could be partially blocked by either the muscarinic cholinoceptor antagonist, atropine (0.3 microM) or by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP (10 microM). In capsaicin-treated rats, contractions of the urinary bladder evoked by EFS were significantly larger than those of control (vehicle-treated) animals, and this difference remained after the purinergic component of the contractions was blocked by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP. However, when the cholinergic component of the contractions was blocked with atropine, the difference between the groups at 8 Hz and 16 Hz was abolished; EFS caused significantly larger contractions of the capsaicin-treated rat bladder only at frequencies of 2 Hz and 4 Hz. 3. EFS evoked contractions of the vas deferens consisted of adrenergic and purinergic components since they could be partially blocked by either the alpha-adrenoceptor antagonist, phentolamine (3 microM) or by alpha,beta-methylene ATP (10 microM). The contractions of the vas deferens were significantly larger than in the capsaicin-treated rats only at a frequency of 16 Hz. There were no differences between vas deferens contractions of the two groups either after desensitization of P2X-purinoceptors by alpha,beta-methylene ATP or in the presence of phentolamine.4. Contractions of the capsaicin-treated rat urinary bladder evoked by exogenous carbachol (0.1-100 microM) were not significantly different from those of controls, the pD2 values being 1.78 +/- 0.23 micro M and 1.90 +/- 0.20 micro M respectively. There was also no significant difference between the groups in contractions of the bladder evoked by ATP (10 micro M-3 mM).5. Contractions of the vas deferens evoked by either ATP (10 micro M-3 mM) or noradrenaline (1-1000 micro M) in the capsaicin-treated group showed no significant difference between control and capsaicin treated rats.6. In conclusion, the present results indicate that chronic capsaicin treatment increases the amplitude of contractions of the rat urinary bladder, an effect which preferentially involves the cholinergic component of the response; since the response to carbachol is unaffected, the change involves prejunctional mechanisms. In contrast, both the purinergic and adrenergic components of contraction in the vas deferens are unaffected by capsaicin. It is suggested that sensory nerves have a trophic influence on the development of parasympathetic nerves in the rat bladder; removal of sensory nerves shortly after birth results in an increase mainly in the cholinergic, and to a lesser extent purinergic component.

Postnatal development of neuropeptide Y- and calcitonin gene-related peptide-immunoreactive nerves in the rat urinary bladder

The postnatal development of neuropeptide Y- and calcitonin gene-related peptide-immunoreactive (NPY-IR and CGRP-IR) nerve fibers in the rat urinary bladder was investigated using whole-mount preparations and cryostat sections. In newborn and 3-day-old rats, many NPY-IR nerve fibers were observed in the subserous and muscle layers. Many NPY-IR nerve cell bodies clustered at branching points of the subserous nerve bundles. Within 4 weeks after birth, these cell bodies drastically decreased in number and spread along the bundles, although the number of NPY-IR nerve fibers increased moderately. In contrast, CGRP-IR nerve fibers in newborn and 3-day-old rats were less developed, and no CGRP-IR nerve cell body was observed in any rat. However, CGRP-IR nerve fiber distribution in the urinary tissues conspicuously increased within 4 weeks after birth. Especially, an increase of the infraepithelial fibers showing a meshwork appearance was prominent in the fundus and corpus of the bladder. The infra- and intraepithelial CGRP-IR nerve meshwork of the ventral wall was more dense than that of the trigone. At 4 weeks, NPY-IR and CGRP-IR nerves were similar to those of the adult rat (8-12 weeks old). The present study suggests a correlation between the development of the peripheral nervous system in the urinary bladder and maturation of micturition behavior in the rat.

Urinary bladder dysfunction in the BB/W diabetic rat: effect of ganglioside treatment on functional and structural alterations

Urinary bladder dysfunction in the diabetic BB/W rat is characterized by infrequent irregular contractions of high amplitude. Initially these occur in the absence of detectable neuroanatomical lesions of sensory afferent and parasympathetic fibers of the pelvic nerve, which constitute the micturition reflex arc. Structural lesions consisting of progressive axonal atrophy of myelinated and unmyelinated fibers become detectable only after 4 months of diabetes. In the current study we evaluated the effect of ganglioside treatment (10 mg./kg. body weight) for one month. This drug regimen was initiated at 4 months of diabetes, when functional bladder abnormalities were well established, whereas structural lesions were yet to appear. Animals examined 1 or 3 months after termination of the one-month treatment protocol showed sustained normalization of the characteristic functional abnormalities, accompanied by prevention of the neuroanatomical lesions of sensory afferent and parasympathetic efferent myelinated fibers in the pelvic nerve. These data suggest that ganglioside treatment may be beneficial in delaying the progression of diabetic autonomic neuropathy in this experimental animal model.

Effect of capsaicin on distribution of binding sites for tachykinins and calcitonin gene-related peptide in rat urinary bladder: a quantitative autoradiographic study

The autoradiographic localization of binding sites for [125I]BH-[Sar9,Met(O2)11]SP, [125I]NKA, and [125I]CGRP was investigated in adjacent sections of urinary bladder body, from adult rats pretreated 14 days before with capsaicin or vehicle. Location of silver grains was assessed both qualitatively and quantitatively using computerized densitometry. Dense labeling of smooth muscle was seen with both [125I]BH-[Sar9,Met(O2)11]SP ([125I]BHSar-SP) and [125I]NKA; in addition, [125I]BHSar-SP labeled submucosal blood vessels. For these radioligands, no differences were apparent between sections from capsaicin- and vehicle-pretreated rats. Specific binding of [125I]CGRP was observed over the epithelium and weakly over submucosal arterioles, but not over smooth muscle. The density of [125I]CGRP binding sites on the epithelium, but not blood vessels, was increased (p < 0.05) by 22% after chronic capsaicin pretreatment, suggesting receptor upregulation. This study demonstrates that although all three peptides are colocalized in primary afferent sensory fibers in rat urinary bladder, the receptors for these neuropeptides are located on different cell types and may be subject to different neural influences.

Capsaicin induced afferent denervation and receptor-linked responses to CGRP in the rat

We have examined the effect of neonatal capsaicin-induced destruction of primary afferent nerves in rats on the response to calcitonin gene-related peptide (CGRP) in vitro and in vivo. Denervation was confirmed by immunohistochemistry. Rat alpha-CGRP (rCGRP) activated adenylate cyclase in homogenates of rat spleen (basal activity 45 +/- 8.27, delta Vmax 75 +/- 16 pmol cyclic AMP min-1 protein; K(act) 2.04 +/- 0.44 nM). A single specific binding site for [125I]hCGRP was demonstrated in homogenates of spleen (Kd = 4.84 +/- 0.66 nM, Bmax = 1.43 +/- 0.35 pmol mg-1 protein). Neither adenylate cyclase activation nor binding site characteristics were affected by capsaicin-induced denervation. In addition, hypotensive responses to intravenous boluses of rCGRP were examined in anaesthetized rats. Neither the basal blood pressure nor the blood pressure fall in response to rCGRP were altered by neonatal denervation by capsaicin. In conclusion, there is no evidence of denervation hypersensitivity of receptor mediated responses to CGRP in vivo or in vitro, following capsaicin-induced denervation in the rat. This suggests that CGRP is unlikely to exert a sustained tonic influence on cardiovascular regulation in the rat.

Urinary bladder function in rats with hereditary diabetes insipidus; a cystometrical and in vitro evaluation

Bladder function was investigated in female rats with hereditary diabetes insipidus (DI) and in healthy controls, in vivo by means of recordings of micturition pattern and cystometry, and in vitro in organ bath experiments. Rats with DI exhibited bladder hypertrophy, the weight of the bladder in these rats being two times that of controls. Recordings of micturition pattern showed that DI-rats had an increased 24 hour diuresis and micturition volume, and decreased micturition interval in comparison with controls. Cystometry recordings revealed increased bladder capacity and micturition volume in DI-rats. However, in these rats basal bladder pressure and threshold pressure were lower than in controls. No significant changes in micturition pressure or bladder compliance were observed, and none of the rats had residual urine. In organ bath studies, a lower maximal response to electrical field stimulation was obtained in bladder strips from DI-rats, than in the control strips, when expressed relative to the response elicited by K(+)-solution. When activated by field stimulation, the DI-bladder strips and the control strips had similar sensitivity to muscarinic receptor blockade with scopolamine at all stimulation frequencies. The sensitivity to carbachol was similar in the two groups. The results suggest that the increased functional demands of DI on the detrusor do not result in major changes pre- or postjunctionally. Further, several of the previously reported urinary bladder changes observed in rats with diabetes mellitus (DM) are similar to those now reported in rats with DI, emphasizing the importance of an increased diuresis per se for the development of alterations in bladder function. However, in contrast to the findings in DM rats, the sensitivity to electrical stimulation of nerves during blockade of muscarinic receptors was similar in DI-rats and their controls. This supports our previous suggestion that the increased resistance to muscarinic receptor blockade of the bladder in DM-rats at low stimulation frequencies is induced by the disease (diabetes mellitus) as such and not by the increased diuresis.

Effects of age and streptozotocin-induced diabetes on contents and effects of substance P and vasoactive intestinal polypeptide in the lower urinary tract of the rat

The urinary bladder and urethral content of substance P and vasoactive intestinal polypeptide and the in vitro effects of the peptides on the bladder were studied at 6 weeks and 6 months of streptozotocin-induced diabetes in the rat. The results were compared with those obtained in age-matched control animals. Both short-term and long-term streptozotocin treatment induced a clearcut increase in bladder weight. Bladder substance P content was increased in both groups of diabetic animals but substance P concentration was similar in control and diabetic animals. Vasoactive intestinal polypeptide content was slightly higher in diabetic animals than in controls but vasoactive intestinal polypeptide concentration was significantly lower in the bladders from both short-term and long-term diabetic animals. The bladder contractile response to substance P was similar in all groups of animals and vasoactive intestinal polypeptide was found to be devoid of contractile or relaxatory effects in the rat bladder. No change in urethral weight was seen with diabetes. There were no clear-cut changes in the urethral contents or concentrations of substance P and vasoactive intestinal polypeptide. The study also enabled comparisons between younger (3 months) and older (9 months) rats. This comparison showed a decrease in the concentrations and contents of substance P and vasoactive intestinal polypeptide between young and older rats. The changes were seen in both the bladder and the urethra and were similar in diabetic and normal animals.

On the reversibility of functional bladder changes induced by infravesical outflow obstruction in the rat

Rats were subjected to infravesical outflow obstruction for six weeks. The bladder function was followed by cytometrical and in vitro investigations and by recordings of micturition pattern before and after removal of the obstruction. Cytometrical investigations showed that outflow obstruction for six weeks induced a bladder instability. Further, in the presence of obstruction the micturition pressure was large as was the bladder capacity and the rats had residual urine. After removal of the obstruction the bladder function rapidly normalized. The bladder instability disappeared within one week, bladder capacity decreased as did the micturition pressure. Moreover, only a minor amount of residual urine was present post-obstruction. In vitro investigation showed that the response to carbachol and to electrical stimulation was similar in normal and obstructed bladders. However, after removal of the obstruction a supersensitivity to carbachol as well as to electrical stimulation had developed. Obstructed bladders showed a markedly decreased response to substance P. The sensitivity to substance P was rapidly enhanced post-obstruction and after four days the response was restored to the control level. The present study shows that the bladder function in rats with infravesical outflow obstruction rapidly normalized after removal of the obstruction. The disappearance of the bladder instability despite the developed supersensitivity to muscarinic receptor stimulation supports the opinion that the bladder instability is not of muscarinic origin.