Biomedical subjects

J B Tuttle

Publications and source records attributed to J B Tuttle.

At least 19 recordsLinked to original sources

PubMed2001

Chronic reduction in complex I function alters calcium signaling in SH-SY5Y neuroblastoma cells.

Sporadic, non-familial Parkinson's disease is characterized by a 15-30% reduction in complex I activity of the electron transport chain. A pharmacological model of reduced complex I activity was created by prolonged treatment of SH-SY5Y cells with low doses (5-20 nM) of rotenone, a selective inhibitor of complex I. Short-term (less than 2 week) exposure to rotenone did not influence calcium signaling, production of reactive oxygen species, or mitochondrial morphology. However, following 2 weeks of rotenone exposure, SH-SY5Y cells showed unusual calcium dynamics, specifically multiple calcium responses to carbachol, a muscarinic agonist. These secondary calcium responses were not seen in control SH-SY5Y cells and were dependent upon calcium influx. Mitochondrial membrane potential was also reduced in low dose rotenone-treated cells. These results demonstrate that a chronic, partial reduction in complex I activity, such as that seen in Parkinson's disease, can alter cell signaling events and perhaps increase the susceptibility of cells to calcium overload and subsequent cell death.

Animals↗

PubMed2001

Treatment of aged rat sensory neurons in short-term, serum-free culture with nerve growth factor reverses the effect of aging on neurite outgrowth, calcium currents, and neuronal survival.

Impaired NGF production and release has been documented in aged animals, suggesting that decreased NGF receptor stimulation may be one factor contributing to neuronal dysfunction with aging. Other studies have suggested that aging may be associated with impaired intracellular responses to NGF. Because aging-associated neuronal dysfunction contributes to morbidity and mortality in the geriatric population, it is important to determine whether the effects of aging on sensory neuron function and survival are reversible. In the present study, we observed significantly decreased neurite outgrowth and neuronal survival in short-term cultures (0-96 h) of dorsal root ganglion (DRG) neurons from aged (>22 months) Fisher 344 x Brown Norway F1 hybrid rats, compared to young (4-6 month) and middle-aged (14 month) animals. From 24 to 96 h in culture, diminished survival of aged neurons appeared to be due to an increased rate of apoptotic cell death. DRG neurons from aged animals also exhibited significantly decreased whole cell, high-threshold voltage-dependent calcium currents, with a larger proportion of L-type current, compared to youthful and middle-aged animals. Treatment of aged DRG neurons with NGF restored neurite outgrowth, neuronal survival and calcium current amplitude and subtype distribution to those observed in youthful DRG neurons.

Animals↗

PubMed2001

Activation of the transcription factors nuclear factor-kappaB and activator protein-1 in bladder smooth muscle exposed to outlet obstruction and mechanical stretching.

PURPOSE: Transcriptional control of bladder genes in response to outlet obstruction, growth factors and mechanical force is poorly understood. We analyzed the effects of bladder obstruction, mechanical stretching and platelet derived growth factor on the activation of the major growth controlling transcription factors nuclear factor-kappaB and activator protein-1. MATERIALS AND METHODS: Complete outlet obstruction was created in female rats by proximal urethral ligation and bladders were harvested 3, 6 and 24 hours later, respectively. Bladder cells were grown in culture and stimulated with 10 ng./ml. platelet derived growth factor or 10 cycles per minute of mechanical stretching for 0.5 to 4 hours. Nuclear proteins were high salt extracted and incubated with 32phosphorus double strand oligonucleotides containing a consensus binding sequence for activator protein-1 or nuclear factor-kappaB. The resulting DNA protein complexes were analyzed by electrophoretic mobility shift assay. RESULTS: Nuclear extract isolated from obstructed bladders showed intense activator protein-1 binding activity 3, 6 and 24 hours after obstruction as well as increased nuclear factor-kappaB binding activity after 6 and 24 hours. Binding activity was absent or minimal in sham operated rats. Cultured cells exposed to mechanical stretching for 2 and 4 hours showed increased activator protein-1 and nuclear factor-kappaB DNA binding compared with unstretched cells. Likewise stimulation with platelet derived growth factor caused a consistent increase in activator protein-1 and nuclear factor-kappaB binding activity. The binding of nuclear proteins was abolished by a 40-fold excess of an unlabeled specific oligonucleotide but not by excess irrelevant oligonucleotide. Thus, the assays were specific for the factors involved. CONCLUSIONS: Bladder obstruction and mechanical stretching cause the formation of activator protein-1 and nuclear factor-kappaB DNA complexes, consistent with a role of these transcription factors in the control of hypertrophy associated gene activation.

Animals↗

PubMed2001

In vivo and in vitro investigation of the effects of sildenafil on rat cavernous smooth muscle.

PURPOSE: We investigated the effect of sildenafil on rat erectile tissues in vivo and in vitro. MATERIALS AND METHODS: Intracavernous pressure was recorded in pentobarbital anesthetized, male Sprague-Dawley rats and we studied the effect of 100 or 200 microg/kg(-1) sildenafil given intravenously. In an isolated endothelin-1 contracted strip preparation of rat corpus cavernosum we also assessed the effect of sildenafil on the response to electrical field stimulation of the nerves. RESULTS: Electrical stimulation of the cavernous nerve induced a frequency dependent increase in intracavernous pressure of a mean plus or minus standard error of mean 55 +/- 3 mm Hg at 20 Hz, corresponding to a mean of 47% +/- 2% of mean arterial pressure. The 100 microg/kg(-1) dose did not increase intracavernous pressure but significantly increased mean decay time of the pressure response from 16 +/- 3 to 35 +/- 3 seconds (p <0.001). In vitro sildenafil significantly enhanced the amplitude and duration of the relaxation induced by the electrical stimulation of corpus cavernosum strips in a concentration dependent fashion. CONCLUSIONS: In anesthestized rats sildenafil significantly prolonged the decay period of the intracavernous pressure response induced by electrical stimulation of the cavernous nerve but it did not increase the amplitude. Sildenafil enhanced the amplitude and duration of the relaxant response to electrical field stimulation in isolated corpus cavernosum tissue.

Animals↗

PubMed2001

Histological and neurotrophic changes triggered by varying models of bladder inflammation.

PURPOSE: We determined whether bladder inflammation causes elevated expression of nerve growth factor by bladder parenchymal cells, leading to alterations in neurons innervating the bladder. To answer this question biochemical, histological and neuronal size data were obtained in rats following various experimental models of bladder inflammation. MATERIALS AND METHODS: Chemical (2.5% formalin), immune (lipopolysaccharide 2 x 104 cfu/ml.) and mechanical (chromic catgut) inflammation was evaluated at various times and compared to control bladders. Hematoxylin and eosin, and Giemsa staining was done to characterize inflammation and quantify mast cells in the bladder. Nerve growth factor protein and messenger RNA were assayed in the bladder and major pelvic ganglion using 2-site enzyme-linked immunosorbent assay and reverse transcriptase-polymerase chain reaction, respectively. Retrograde axonal tracing was done to size bladder neurons in the major pelvic and dorsal root ganglia. RESULTS: All forms of inflammation increased bladder weight and produced diffuse hyperplasia, intramural edema, acute and chronic inflammatory cells, infiltration and mastocytosis. Generally bladder inflammation resulted in a 50% increase in nerve growth factor and 52% to 58% enlargement of peripheral neurons. CONCLUSIONS: Inflammation results in altered nerve growth factor content of the bladder, and morphological changes in sensory and motor neurons innervating the bladder. Such neuroplasticity may be a possible explanation for the association of bladder inflammation with long-term symptoms and pain after inflammation subsides.

Animals↗

PubMed2000

Mitochondrial DNA-depleted neuroblastoma (Rho degrees) cells exhibit altered calcium signaling.

To investigate the role of chronic mitochondrial dysfunction on intracellular calcium signaling, we studied basal and stimulated cytosolic calcium levels in SH-SY5Y cells and a derived cell line devoid of mitochondrial DNA (Rho degrees ). Basal cytosolic calcium levels were slightly but significantly reduced in Rho degrees cells. The impact of chronic depletion of mitochondrial DNA was more evident following exposure of cells to carbachol, a calcium mobilizing agent. Calcium transients generated in Rho degrees cells following application of carbachol were more rapid than those in SH-SY5Y cells. A plateau phase of calcium recovery during calcium transients was present in SH-SY5Y cells but absent in Rho degrees cells. The rapid calcium transients in Rho degrees cells were due, in part, to increased reliance on Na(+)/Ca(2+) exchange activity at the plasma membrane and the plateau phase in calcium recovery in SH-SY5Y cells was dependent on the presence of extracellular calcium. We also examined whether mitochondrial DNA depletion influenced calcium responses to release of intracellular calcium stores. Rho degrees cells showed reduced responses to the uncoupler, FCCP, and the sarcoplasmic reticulum calcium ATPase inhibitor, thapsigargin. Acute exposure of SH-SY5Y cells to mitochondrial inhibitors did not mimic the results seen in Rho degrees cells. These results suggest that cytosolic calcium homeostasis in this neuron-like cell line is significantly altered as a consequence of chronic depletion of mitochondrial DNA.

Calcium↗

PubMed2000

Stretch-activated signaling of nerve growth factor secretion in bladder and vascular smooth muscle cells from hypertensive and hyperactive rats.

Elevated vascular (VSMC) and bladder smooth muscle (BSMC) NGF are associated with altered visceral innervation in the spontaneously hypertensive rat (SHR: hypertensive, behaviorally hyperactive) compared with control Wistar-Kyotos (WKYs). Stretch stimulates increased NGF production in BSMCs. To elucidate whether stretch induces NGF synthesis in VSMCs, and to determine if disturbances in stretch-mediated NGF production contribute to the elevated tissue levels of NGF in SHRs, we subjected VSMCs and BSMCs cultured from four established inbred rat strains (WKY, WKHA: hyperactive; SHR and WKHT: hypertensive) to several stretch paradigms. For VSMCs, acute and cyclic stretch affected cells derived from hypertensive rats (80-100% increase over control) but not from normotensive strains. For BSMCs, cyclic and static stretch increased NGF secretion in all four strains, but had a two- to threefold greater effect in cells from SHRs and WKHTs (increase up to 600%) at early time points. At later time points of a 24-h experimental period, stretch increased NGF output up to 400% in SHR and WKHA cultures. Thus, defects that influence early induction of stretch-mediated SHR NGF secretion cosegregate with the hypertensive phenotype. Stretch-gated ion channel inhibitors, voltage-gated ion channel inhibitors, and protease inhibitors failed to affect stretch-induced BSMC NGF secretion. In contrast, gene transcription, intracellular calcium, protein kinase C (PKC), and autocrine release of an unknown factor may play a role in the elevated NGF secretion observed in smooth muscle from hypertensive animals. Altered stretch-induced smooth muscle NGF secretion may contribute to the augmented vascular and bladder NGF content associated with high blood pressure and hyperactive voiding in SHRs.

Animals↗

PubMed2000

Altered neural control of micturition in the aged F344 rat.

The purpose of this study was to determine whether micturition reflexes are altered in aged rats. Voiding frequencies and awake cystometrograms (CMGs) were measured in young (3-5 months old) and aged (24 months) F344 male rats. Bladder contractions induced by subcutaneous apomorphine and intravesical capsaicin stimulation were measured using awake CMGs. Urodynamic parameters were compared. Aged rats voided less frequently (4.1 vs 6.9 times/18 h, P = 0.006), with a higher volume per void (1.1 vs 0.7 ml, P = 0.02) and had a higher micturitional threshold pressure (8.7 vs 4.6 mmHg, P = 0.0001) than the young rats. Apomorphine induced a higher frequency of bladder contractions in aged animals compared to young animals (5.5 vs 3.1 contractions/min, P = 0.03). Intravesical capsaicin caused a lower pressure bladder response in the aged rats (38.5 vs 70.6 mmHg, P = 0.01) compared to the young rats. Bladder afferents and central micturition pathways may be altered in aged rats. Impaired bladder contractility in the elderly may be exacerbated by reduced sensory input, whereas the propensity for detrusor instability could result from altered central processing. This study demonstrated the utility of the F344 animal model to study micturitional changes resulting from aging.

Aging↗

PubMed2000

Calcium homeostasis and nerve growth factor secretion from vascular and bladder smooth muscle cells.

Bladder and vascular smooth muscle cells cultured from four rat strains (WKY, SHR, WKHA, WKHT) differing in rates of nerve growth factor (NGF) production were used to determine whether a relationship exists between intracellular calcium and NGF secretion. Basal cytosolic calcium was related to basal NGF secretion rates in bladder and vascular smooth muscle cells from all four strains with the exception of WKHT bladder muscle cells. Thrombin is a calcium-mobilizing agent and increases NGF production from vascular but not bladder smooth muscle cells. Strain differences were found in the magnitude of the calcium peak induced by thrombin in vascular smooth muscle cells, but these differences did not correlate with NGF secretion. Thrombin caused a calcium response in bladder smooth muscle cells without influencing NGF production. Quenching the calcium transient with a calcium chelator had no effect on thrombin-inducted NGF secretion rates in vascular smooth muscle cells. Thus, basal intracellular calcium may establish a set point for NGF secretion from smooth muscle. In addition, transient elevations in cytosolic calcium were unrelated to the induction of NGF output.

Animals↗

PubMed1999

Mitochondrial impact on nerve growth factor production in vascular smooth muscle-derived cells.

Ht30</=Ht10>/=Ht5). Cells with reduced mitochondrial activity also showed abnormal responses to the stimulation of NGF output. Thrombin and phorbol ester elevated NGF production from Ht100, Ht30 and Ht10 cells, but not from Ht5 cells. Ht30 cells, despite secreting less NGF basally than Ht100 cells, reached a similar or greater NGF output upon stimulation. Mitogens increased NGF output and NGF mRNA levels with the largest effect on NGF protein in Ht30 cells. Free radical production and the ability of cells to respond to NGF-inducing agents were related. These data suggest that chronic impairment of mitochondrial function associates with disturbances in cellular production of a signaling protein.

Animals↗

PubMed1999

The spontaneously hypertensive rat: insight into the pathogenesis of irritative symptoms in benign prostatic hyperplasia and young anxious males.

Recent epidemiological studies have shown that hypertensive men are more likely to undergo surgical intervention for irritative voiding symptoms from BPH than age-matched controls. Indeed, noradrenergic nerves which regulate vascular tone also participate in the functional component of bladder outlet obstruction due to BPH. Newer, less invasive therapies for BPH such as thermal therapy can relieve symptoms yet do not eliminate obstruction based on urodynamic studies. Coincidentally, drugs such as alpha-adrenoceptor antagonists, which have been thought to relieve obstruction due to a peripheral effect, can be given intrathecally in animals to relieve urinary frequency due to obstruction. Taken together these observations implicate both peripheral and central sympathetic pathways in the motor control of the urinary bladder especially with disease states. We have used the hypertensive and behaviourally hyperactive spontaneously hypertensive rat (SHR), to investigate the roles sympathetic pathways or micturition. Elevated nerve growth factor (NGF) derived from vascular and bladder smooth muscle cells of the SHR appears to direct morphological, biochemical, and functional changes. The increase in NGF can apparently be explained by stabilization of its mRNA leading to increased synthesis in NGF. Bladders from SHRs develop a profuse noradrenergic hyperinnervation compared with the control WKY strain. Since afferents supplying the SHR bladder are hypertrophied, changes in afferent pathways are also likely. These differences in innervation and NGF in the SHR may explain changes in function. SHRs void 3 times as frequently as their genetic controls. Urinary frequency can be reduced by alpha-adrenoceptor antagonists. Cystometrograms performed in SHRs reveal lower bladder capacities and micturition volumes and the presence of unstable contractions compared with the WKY rat. Intrathecal, rather than intra-arterial administration of the alpha-adrenoceptor antagonist doxazosin reduces unstable contractions in the SHR. In vitro muscle bath studies have shown enhanced responses of SHR bladder smooth muscle to alpha-adrenoceptor agonists. It is likely that upregulation of NGF production causes sensory and possibly noradrenergic pathways to elicit hyperactive voiding. Increase in NGF in the adult bladder due to pathological conditions yields similar, yet distinct, consequences for voiding behaviour and innervation. Likewise, increased NGF in adult bladders following obstruction or inflammation triggers neuronal hypertrophy, enhanced reflex activity and urinary frequency. In contrast to the SHR, hyper-innervation is not observed. Moreover, peripheral or spinal alpha-adrenoceptor blockade eliminates urinary frequency following obstruction. These observations support the role for sympathetic pathways in the motor function of the bladder, especially in congenital or adult disease states. A similar process may underlie the neuroplasticity involved in alterations after obstruction or inflammation of the lower urinary tract in humans. The SHR strain raises the possibility that a common genetic defect exists capable of predisposing to both hypertension and overactivity of the urinary bladder. Whether a genetic predisposition to sustained bladder overactivity in response to inflammatory stimuli in obstruction exists in humans is an intriguing prospect.

Animals↗

PubMed1999

Altered NGF regulation may link a genetic predisposition for hypertension with hyperactive voiding.

PURPOSE: Hyperactive voiding and elevated smooth muscle NGF output are traits of the spontaneously hypertensive rat (SHR). Elevated target-derived NGF is associated with hypertension and hyperactive voiding in SHRs. In the present study, we tested for possible genetic links between hypertension, hyperactive voiding and augmented bladder smooth muscle cell (BSMC) NGF secretion. MATERIALS AND METHODS: We crossed SHRs with WKYs to produce a gene segregating F2 population. We measured F2 mean arterial blood pressure (BP) and six-hour voiding frequency. BSMCs were cultured from 'Low BP F2s' (95+/-2) and 'High BP F2s' (141+/-3 mm. Hg) and conditioned medium tested for NGF with a two-site ELISA. The NGF regulators isoproterenol, platelet-derived growth factor (PDGF) and phorbol-12-myristate-13-acetate were tested in F2 BSMC cultures. RESULTS: A positive correlation (r = 0.75) between blood pressure and voiding frequency existed in this F2 population. As BP rose voiding frequency increased and volume per void decreased such that there were no significant changes in total urine voided (Low BP F2s: 1.0+/-0.5; High BP F2s: 6.2+/-0.5 voids/6 hours). Low BP F2s (2.0+/-0.2) secreted NGF at a higher basal rate than High BP F2s (0.7+/-0.1 fg NGF/hr/100 cells). However, High BP F2s (1,620 and 3,850) were oversensitive to isoproterenol and PDGF-induced increases in NGF output, compared with Low BP F2s (219 and 1,282% control, respectively). CONCLUSIONS: Elevated tissue NGF due to a hypersensitivity to NGF regulating stimuli, rather than alterations in basal NGF, may genetically link hypertension and hyperactive voiding.

Animals↗

PubMed1999

Persistently increased voiding frequency despite relief of bladder outlet obstruction.

PURPOSE: Bladder outlet obstruction (BOO) can increase urinary frequency. Even after surgical relief of obstruction, up to 30% of patient are still bothered by irritative voiding symptoms. We tested the hypothesis that deligation of a partial bladder outlet obstruction model mimics this clinical observation. MATERIALS AND METHODS: Female Wistar rats were obstructed for 3 weeks by partial urethral ligation and then were relieved of obstruction by urethral deligation. Measurements of voiding frequency and voided volumes were measured preoperatively, after ligation, and after deligation. Relief of obstruction was confirmed by measuring flow rates through ex vivo perfusion of deligated urethras. Urine osmolality and bladder weights were determined. Awake cystometrograms (CMGs) were performed 3 weeks after deligation to measure bladder function. RESULTS: Neither sham ligation nor sham deligation altered voiding frequency. Ligation doubled mean voiding frequency (in cc) from 2.01 +/- 0.32 to 3.96 +/- 0.22 per 4 hours (p = 0.0002). Three weeks after deligation, voiding behavior of the animals segregated into 2 groups: 20% had persistent hyperactive voiding frequency (6.67 +/- 1.23 per 4 hours) while 80% normalized voiding frequency (1.53 +/- 0.20 per 4 hours). The difference in voiding frequency in these 2 groups could not be attributed to alterations in urine osmolality, persistence of urethral obstruction, difference in bladder weights or severity of initial obstruction created. Awake CMGs revealed a higher peak micturition pressure and lower voided volume in the hyperactive voiders. CONCLUSIONS: 20% of the animals after urethral deligation had persistent hyperactive voiding which parallels clinical observations. Because the CMG data suggested persistent obstruction, yet urethral perfusion and bladder weights indicated no obstruction, we propose that these 20% of animals have a "functional" bladder outlet obstruction and can be used to study mechanisms underlying hyperactive voiding.

Animals↗

PubMed1999

The effect of sildenafil on apomorphine-evoked increases in intracavernous pressure in the awake rat.

PURPOSE: The aim of this study was to develop a quantitative, awake animal model to investigate the effect of sildenafil on centrally-evoked erectile activity. METHODS: Intracavernous pressures were recorded in awake, male Sprague Dawley rats after administration of apomorphine (100 or 250 microg./kg. subcutaneously). Sildenafil (100 microg./kg. intravenously) was then given 10 min. after a second dose of apomorphine. The time to first response, duration of response, and peak intracavernous pressure and area under the response, were measured before and after sildenafil. RESULTS: Apomorphine produced rhythmic increases in intracavernous pressure. The pressure increase consisted of two components. The amplitude of the first, tonic response was 58 +/- 3 mm. Hg, and a superimposed, burst-like increase in pressure elevated this further to 81 +/- 6 mm. Hg. Bilateral transection of the pudendal nerves abolished the burstlike pressure changes; bilateral transection of the cavernous nerves prevented both responses. The duration of the apomorphine-induced increase in intracavernous pressure was significantly (p = 0.003) prolonged by sildenafil (100 microg./kg.) from 37 +/- 4 to 62 +/- 11 s (n = 6). The overall intracavernous pressure response to apomorphine (100 microg./kg.), measured as the area under the curve, was significantly (p = 0.003) increased by sildenafil (100 microg./kg.) from 67 +/- 8 to 142 +/- 31 units (n = 6). N-nitro-L-arginine methyl ester (40 mg./kg. intravenously) prevented the apomorphine-induced responses. CONCLUSIONS: Monitoring intracavernous pressures in the awake rat represents a simple model to evaluate the effect of drugs on erectile function. Using this model we have shown that apomorphine elicits a rise in intracavernous pressure that can be prolonged by sildenafil. These results suggest that there may be a role for the combination of apomorphine and sildenafil in the management of erectile dysfunction.

Animals↗

PubMed1998

Increased nerve growth factor mRNA stability may underlie elevated nerve growth factor secretion from hypertensive vascular smooth muscle cells.

Altered nerve growth factor (NGF) regulation has been linked to the pathophysiology of hypertension. Vascular smooth muscle cells from an inbred hypertensive, but normoactive rat strain (WKHT) secreted NGF at a greater rate than from a hyperactive, normotensive strain (WKHA). Exposure to phorbol ester increased NGF secretion rates from WKHT by 400-800% but not from WKHA vascular muscle. NGF secretion rates from both WKHT and WKHA vascular cells were elevated by co-application of platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) by 300-1000%. This response was partially attenuated by actinomycin D, an inhibitor of RNA transcription. These results suggest that regulation of NGF production does not occur solely at the level of transcription and post-transcriptional mechanisms operate. Analysis of NGF mRNA stability in the two strains following PDGF and TGF-beta1 treatment showed that NGF mRNA in WKHT had a half-life of 126.2+/-11.68 min while in WKHA vascular smooth muscle cells, the half-life was 47. 33+/-11.98 min. In addition to increased NGF mRNA stability in WKHT vascular muscle, these cells have an increased translational efficiency of NGF protein; elevated synthesis of NGF protein per unit NGF mRNA. Differences in signaling pathways may result in increased NGF mRNA stability and translational efficiency that may account for the elevated NGF protein in WKHT vascular smooth muscle cells.

Animals↗

PubMed1998

Arterial nerve growth factor (NGF) mRNA, protein, and vascular smooth muscle cell NGF secretion in hypertensive and hyperactive rats.

Elevated levels of nerve growth factor (NGF) protein and NGF mRNA have been reported in the vessels of spontaneously hypertensive rats (SHR: hypertensive, hyperactive) compared to Wistar-Kyoto (WKY) rats. Elevated NGF may be involved in the development of hypertension in SHRs. We examined vascular NGF mRNA and protein content and the regulation of NGF secretion by vascular smooth muscle cells (VSMCs) from two inbred strains (WKHT: hypertensive; WKHA: hyperactive) derived from SHRs and WKYs. Our goal was to determine if receptor-mediated defects in NGF regulation play a role in increased secretion of VSMC NGF from hypertensive animals. Tissue NGF mRNA content was determined by competitive, quantitative RT-PCR. Tissue NGF and NGF content in cultured VSMC-conditioned medium was quantified using a two-site ELISA. Tail artery NGF mRNA was elevated in WKHTs compared to WKHAs. Tissue NGF protein was elevated in WKHT aorta, mesenteric, and tail artery compared to WKHAs. Pharmacologically induced increases in NGF output were blocked with inhibition of transcription or protein synthesis. Basal NGF secretion by WKHT VSMCs was significantly higher than WKHAs. The observed increases in VSMC NGF output in SHRs over WKYs in response to beta-adrenergic agents are not preserved in the WKHT:WKHA comparison. Protein kinase C-dependent increases in SHR VSMC NGF appear in both WKHTs and WKHAs. In contrast, elevated NGF levels due to disturbances in alpha-adrenergic, peptidergic, and purinergic control of NGF output are features common to both genetic models of hypertension (SHR and WKHT). These results suggest that the defect in smooth muscle NGF metabolism observed in SHRs cosegregates with a hypertensive rather than a hyperactive phenotype. Moreover, altered receptor-mediated regulation (alpha-adrenergic, peptidergic, and purinergic) of VSMC NGF production may contribute to elevated vascular tissue NGF, suggesting a mechanism leading to the high levels of NGF associated with hypertension in SHRs and WKHTs.

Adenosine Triphosphate↗

PubMed1998

Mechanisms of increased NGF production in vascular smooth muscle of the spontaneously hypertensive rat.

The spontaneously hypertensive rat (SHR) was developed as a genetic model of essential hypertension. In vivo and in vitro evidence demonstrates that vascular smooth muscle cells (VSMCs) from the SHR produce more nerve growth factor (NGF) than the normotensive Wistar-Kyoto (WKY) control strain. This increased NGF production is accompanied by excessive innervation of target tissues in the SHR. In the present study, a sensitive, competitive, quantitative, reverse-transcriptase polymerase chain reaction (C Q RT-PCR) assay is characterized and used to analyze levels of NGF mRNA in cultured VSMCs derived from the SHR and WKY strains as well as bladder tissue. Differences in NGF secretion rates between SHR and WKY VSMCs were partially due to an increased stability of NGF mRNA in SHR VSMCs. Following treatment with platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta 1) to elevate NGF production, the half-life of the NGF mRNA was 104.5 +/- 18.0 min in SHR VSMCs, compared to only 36.5 +/- 11.6 min in WKY VSMCs. Sequence analysis of the 3' untranslated region (UTR) revealed no strain differences in cis-acting sequences potentially involved in determining mRNA stability. Thus, it seems unlikely to be a 3'UTR mutation that prolongs mRNA lifetime. Rather, differential regulation of an RNA-binding protein may play a role in the abnormal NGF mRNA stability in SHR VSMCs. SHR VSMCs also demonstrate an increased translational efficiency of NGF protein; more NGF protein is synthesized per unit of NGF mRNA. The use of a C Q RT-PCR assay has allowed the determination that abnormal NGF mRNA stabilization as well as altered translational efficiency may contribute to excess NGF synthesis and progressive hypertension in the SHR.

Animals↗

PubMed1998

Neurally mediated hyperactive voiding in spontaneously hypertensive rats.

The development of hypertension in spontaneously hypertensive rats (SHR) and hyperactive voiding in rats with urethral obstruction are characterized by abnormal smooth muscle growth, increased tissue levels of nerve growth factor (NGF) and altered patterns of innervation. The present study was undertaken to determine if bladder smooth muscle from SHRs contains and secretes elevated levels of NGF, and if so, whether the augmented NGF contributes to changes in bladder innervation and function without tissue hypertrophy. Voiding behavior was monitored using specially designed metabolic cages. NGF levels in tissue homogenates and conditioned cell culture media were measured by ELISA. NGF mRNA in cultured bladder smooth muscle cells (BSMCs) was quantified using reverse transcriptase PCR. Noradrenergic innervation was assessed by staining with glyoxylic acid and assaying norepinephrine (NE) content in bladders with high performance liquid chromatography. SHRs voided more frequently than WKY rats. NGF content was higher in bladders from adult SHRs when compared to Wistar-Kyoto normotensive rats (WKYs). No significant difference in NGF mRNA content was observed between SHR and WKY BSMCs. However, SHR BSMCs secreted NGF at a higher rate and amount per unit mRNA than did WKY BSMCs. SHR bladders contained more NE and were more densely stained for catecholaminergic fibers than bladders from WKY rats. The results support the hypothesis that elevated NGF secretion by bladder smooth muscle is associated with hyperinnervation of bladder and hyperactive voiding in SHRs. Thus, the SHR strain may represent a genetic model to study changes in bladder function resulting from altered patterns of innervation.

Adrenergic Fibers↗