Salicylate induced tinnitus: Behavioral measures and neural activity in auditory cortex of awake rats

Neurophysiological studies of salicylate-induced tinnitus have generally been carried out under anesthesia, a condition that abolishes the perception of tinnitus and depresses neural activity. To overcome these limitations, measurement of salicylate induced tinnitus were obtained from rats using schedule induced polydipsia avoidance conditioning (SIPAC) and gap pre-pulse inhibition of acoustic startle (GPIAS). Both behavioral measures indicated that tinnitus was present after treatment with 150 and 250 mg/kg of salicylate; measurements with GPIAS indicated that the pitch of the tinnitus was near 16 kHz. Chronically implanted microwire electrode arrays were used to monitor the local field potentials and spontaneous discharge rate from multiunit clusters in the auditory cortex of awake rats before and after treatment with 150 mg/kg of salicylate. The amplitude of the local field potential elicited with 60 dB SPL tone bursts increased significantly 2h after salicylate treatment particularly at 16-20 kHz; frequencies associated with the tinnitus pitch. Field potential amplitudes had largely recovered 1-2 days post-salicylate when behavioral results showed that tinnitus was absent. The mean spontaneous spike recorded from the same multiunit cluster pre- and post-salicylate decreased from 22 spikes/s before treatment to 14 spikes/s 2h post-salicylate and recovered 1 day post-treatment. These preliminary physiology data suggest that salicylate induced tinnitus is associated with sound evoked hyperactivity in auditory cortex and spontaneous hypoactivity.

Differential damage to auditory neurons and hair cells by ototoxins and neuroprotection by specific neurotrophins in rat cochlear organotypic cultures

Therapeutic ototoxic drugs are one of the major causes of damage in the peripheral auditory system, leading to hearing loss. In this study, we have examined the toxic actions of three classes of ototoxins (sodium salicylate, gentamicin and cisplatin) in organotypic cultures of postnatal cochlear explants. In these cultures, afferent innervation of hair cells by primary auditory neurons remained intact. Double labelling with a monoclonal antibody against neurofilament protein and a phalloidin-fluorescein isothiocyanate conjugate revealed that the three types of drugs induced differential damage to auditory neurons and hair cells in the cochlea. While gentamicin preferentially caused hair cell death, sodium salicylate specifically induced degeneration of auditory neurons. In contrast, cisplatin resulted in destruction of both auditory neurons and hair cells. Neuronal degeneration was largely prevented by the addition of neurotrophin-4/5, brain-derived neurotrophic factor and neurotrophin-3 to the culture media together with the ototoxins, while nerve growth factor and other growth factors had no effect. In contrast, the hair cell loss caused by cisplatin or gentamicin was not attenuated by the presence of neurotrophins. These results suggest that ototoxic mechanisms of salicylates, aminoglycosides and chemotherapeutic agents are different. Auditory neuronal loss induced by ototoxins may be prevented by specific neurotrophins.

An animal model for tinnitus

Subjective tinnitus remains obscure, widespread, and without apparent cure. In the absence of a suitable animal model, past investigations took place in humans, resulting in studies that were understandably restricted by the nature of human investigation. Within this context, the development of a valid animal model would be considered a major breakthrough in this field of investigation. Our results showed changes in the spontaneous activity of single neurons in the inferior colliculus, consistent with abnormally increased neuronal activity within the auditory pathways after manipulations known to produce tinnitus in man. A procedure based on a Pavlovian conditioned suppression paradigm was recently developed that allows us to measure tinnitus behaviorally in conscious animals. Accordingly, an animal model of tinnitus is proposed that permits tests of hypotheses relating to tinnitus generation, allowing the accommodation of interventional strategies for the treatment of this widespread auditory disorder.

Effects of salicylate on neural activity in cat primary auditory cortex

The effect of systemically applied salicylate on single-unit firing activity in primary auditory cortex was investigated in six cats. A dose of 200 mg/kg sodium salicylate was administered intraperitoneally, and recordings from the same units were performed prior to application and continuously up to, on average. 6 h after administration. Local field potentials were used to track the threshold shifts and general input-output (I/O) behavior following salicylate administration. All animals showed 20-30 dB of threshold shift about 2 h after administration and showed no recovery during the following 4 h. I/O curves were invariably of the recruitment type. Significant changes were found in spontaneous firing rates for two groups of unit separately. Low-spontaneous rate units (initial firing rate < 1 spike/s) showed an increase in spontaneous rate and high-spontaneous rate units (initial firing rate > 1 spike/s) showed a decrease in spontaneous firing rate. There were no significant changes in modal and mean values for interspike-interval (ISI) histograms. The duration-to-rebound peak in the autocorrelation function for spontaneous firings was prolonged significantly after salicylate administration. Peak cross-correlation coefficients for the firing patterns of simultaneously recorded cells showed no significant change but the correlogram's central peak was significantly narrower after salicylate application. The percentage of firings occurring in bursts showed no significant change after administration of salicylate. The best modulation frequency in response to stimulation with periodic click trains decreased after administration. Both the changes in the spontaneous autocorrelogram and in the temporal modulation transfer function suggest a prolongation in the duration of the Ca(2+)-activated K+ conductance of the cortical pyramidal cells following salicylate. This suggests that salicylates affect both the auditory periphery and the auditory cortex.

Too much of a good thing: long-term treatment with salicylate strengthens outer hair cell function but impairs auditory neural activity

Aspirin has been extensively used in clinical settings. Its side effects on auditory function, including hearing loss and tinnitus, are considered as temporary. A recent promising finding is that chronic treatment with high-dose salicylate (the active ingredient of aspirin) for several weeks enhances expression of the outer hair cell (OHC) motor protein (prestin), resulting in strengthened OHC electromotility and enhanced distortion product otoacoustic emissions (DPOAE). To follow up on these observations, we carried out two studies, one planned study of age-related hearing loss restoration and a second unrelated study of salicylate-induced tinnitus. Rats of different strains and ages were injected with salicylate at a dose of 200 mg/kg/day for 5 days per week for 3 weeks or at higher dose levels (250-350 mg/kg/day) for 4 days per week for 2 weeks. Unexpectedly, while an enhanced or sustained DPOAE was seen, permanent reductions in the amplitude of the cochlear compound action potential (CAP) and the auditory brainstem response (ABR) were often observed after the chronic salicylate treatment. The mechanisms underlying these unexpected, permanent salicylate-induced reductions in neural activity are discussed.

Salicylate-induced cochlear impairments, cortical hyperactivity and re-tuning, and tinnitus

High doses of sodium salicylate (SS) have long been known to induce temporary hearing loss and tinnitus, effects attributed to cochlear dysfunction. However, our recent publications reviewed here show that SS can induce profound, permanent, and unexpected changes in the cochlea and central nervous system. Prolonged treatment with SS permanently decreased the cochlear compound action potential (CAP) amplitude in vivo. In vitro, high dose SS resulted in a permanent loss of spiral ganglion neurons and nerve fibers, but did not damage hair cells. Acute treatment with high-dose SS produced a frequency-dependent decrease in the amplitude of distortion product otoacoustic emissions and CAP. Losses were greatest at low and high frequencies, but least at the mid-frequencies (10-20 kHz), the mid-frequency band that corresponds to the tinnitus pitch measured behaviorally. In the auditory cortex, medial geniculate body and amygdala, high-dose SS enhanced sound-evoked neural responses at high stimulus levels, but it suppressed activity at low intensities and elevated response threshold. When SS was applied directly to the auditory cortex or amygdala, it only enhanced sound evoked activity, but did not elevate response threshold. Current source density analysis revealed enhanced current flow into the supragranular layer of auditory cortex following systemic SS treatment. Systemic SS treatment also altered tuning in auditory cortex and amygdala; low frequency and high frequency multiunit clusters up-shifted or down-shifted their characteristic frequency into the 10-20 kHz range thereby altering auditory cortex tonotopy and enhancing neural activity at mid-frequencies corresponding to the tinnitus pitch. These results suggest that SS-induced hyperactivity in auditory cortex originates in the central nervous system, that the amygdala potentiates these effects and that the SS-induced tonotopic shifts in auditory cortex, the putative neural correlate of tinnitus, arises from the interaction between the frequency-dependent losses in the cochlea and hyperactivity in the central nervous system.

Salicylate-induced degeneration of cochlea spiral ganglion neurons-apoptosis signaling

Aspirin, whose active ingredient is sodium salicylate, is the most widely used drug worldwide, but it is not recommended for children because it may cause Reye's syndrome. High doses of salicylate also induce temporary hearing loss and tinnitus; while these disorders are believed to disappear when treatment is discontinued some data suggest that prolonged treatment may be neurotoxic. To investigate its ototoxicity, immature, postnatal day 3 rat cochlear organotypic cultures were treated with salicylate. Salicylate did not damage the sensory hair cells, but instead damaged the spiral ganglion neurons (SGN) and their peripheral fibers in a dose-dependent manner. The cross-sectional area of SGN decreased from 205 microm(2) in controls to 143, 116, and 91 microm(2) in cultures treated with 1, 3, or 5 mM salicylate, respectively. Morphological changes and caspase upregulation were indicative of caspase-mediated apoptosis. A quantitative RT-PCR apoptosis array identified a subset of genes up- or down regulated by salicylate. Eight genes showed a biologically relevant change (P<0.05, > or =2 fold change) after 3 h treatment with salicylate; seven genes (Tp53, Birc3, Tnfrsf5, Casp7, Nfkb1, Fas, Lta, Tnfsf10) were upregulated and one gene (Pycard) was downregulated. After 6 h treatment, only one gene (Nol3) was upregulated and two genes were downregulated (Cideb and Lhx4) while after 12 h treatment, two genes (Il10, Gadd45a) were upregulated and 4 (Prok2, Card10, Ltbr, Dapk1) were downregulated. High doses of salicylate in a physiologically relevant range can induce caspase-mediated cell death in immature SGN; changes in the expression of apoptotic genes particularly among members of the tumor necrosis factor (TNF) family appear to play an important role in the degeneration.

Effectiveness and toxicity screening of various absorption enhancers using Caco-2 cell monolayers

We studied the enhancing and toxic effects of five different absorption enhancers on the transport of FITC-dextran with an average molecular weight of 4000 (FD-4) across Caco-2 cell monolayers, and their enhancing effects were also compared with those in rat intestine. The enhancing and cytotoxic properties of these enhancers were characterized using the following tests: measurement of the permeability coefficients of FD-4 and the transepithelial electrical resistance (TEER) in Caco-2, the release of cytosolic lactate dehydrogenase (LDH) and intracellular mitochondrial dehydrogenase (MDH) activity. All the absorption enhancers increased the permeability of FD-4 across Caco-2 cell monolayers and a good relationship was observed between the enhancement and their toxic effects. However, EDTA and Na-Cap were effective for improving the transport of FD-4 across Caco-2 cells without serious cytotoxicity. At concentrations with low cytotoxicity, various absorption enhancers exihibited reversible effects on the TEER values in Caco-2 cell monolayers, except for 50 mM sodium salicylate (Na-Sal). Moreover, we obtained a good correlation between the enhancement of these enhancers in Caco-2 cell monolayers and in rat large intestine. This finding indicated that the effectiveness of absorption enhancers in the Caco-2 monolayer system was similar to an in vivo rat system. Therefore, the screening system using Caco-2 cell monolayers is useful for examining the effectiveness and toxicity of absorption enhancers.

Suppression of Japanese encephalitis virus infection by non-steroidal anti-inflammatory drugs

Japanese encephalitis virus (JEV) infection generates a rapid inflammatory response including peripheral neutrophil leucocytosis and infiltration of neutrophils into extraneural tissue. The level of inflammation correlates well with the clinical outcome in Japanese encephalitis patients. Non-steroidal anti-inflammatory drugs (NSAIDs), used medicinally for their analgesic and anti-inflammatory properties, are being considered for prevention of cardiovascular disease and cancer, as well as for treatment of human immunodeficiency virus infection. Apart from their ability to inhibit prostaglandin synthesis, the mechanisms underlying the beneficial therapeutic effects are largely unknown. We used aspirin, indomethacin and sodium salicylate to study the role of NSAIDs in JEV propagation in vitro. We found that NSAIDs suppressed JEV propagation in neuronal and non-neuronal cells. Blockade of cyclooxygenase activity by NSAIDs caused decreased production of free radicals and prostaglandins. However, these pharmacological alterations did not seem to correlate well with the antiviral effects. When cells were treated with the mitogen-activated protein kinase (MAPK) inhibitors PD 98059 and SB 203580, salicylate lost its antiviral effect. The activation of MAPK by anisomycin mimicked the action of salicylate in suppressing JEV-induced cytotoxicity. The decreased phosphorylation of extracellular signal-regulated kinase (ERK) was induced by JEV infection and the decrease in ERK was reversed by salicylate. Our data suggest that the signalling pathways of MAPK play a role in the antiviral action of salicylate.

Altered neuronal intrinsic properties and reduced synaptic transmission of the rat's medial geniculate body in salicylate-induced tinnitus

Sodium salicylate (NaSal), an aspirin metabolite, can cause tinnitus in animals and human subjects. To explore neural mechanisms underlying salicylate-induced tinnitus, we examined effects of NaSal on neural activities of the medial geniculate body (MGB), an auditory thalamic nucleus that provides the primary and immediate inputs to the auditory cortex, by using the whole-cell patch-clamp recording technique in MGB slices. Rats treated with NaSal (350 mg/kg) showed tinnitus-like behavior as revealed by the gap prepulse inhibition of acoustic startle (GPIAS) paradigm. NaSal (1.4 mM) decreased the membrane input resistance, hyperpolarized the resting membrane potential, suppressed current-evoked firing, changed the action potential, and depressed rebound depolarization in MGB neurons. NaSal also reduced the excitatory and inhibitory postsynaptic response in the MGB evoked by stimulating the brachium of the inferior colliculus. Our results demonstrate that NaSal alters neuronal intrinsic properties and reduces the synaptic transmission of the MGB, which may cause abnormal thalamic outputs to the auditory cortex and contribute to NaSal-induced tinnitus.

Chemically induced alterations in maternal homeostasis and histology of conceptus: their etiologic significance in rat fetal anomalies

Possible relationships between maternal acid-base-electrolyte imbalance, histological changes in the maternal/extraembryonic tissues (decidua, placenta, membranes enclosing cavities), and fetal anomalies induced by maternotoxic doses of ethylene glycol, sodium salicylate, and cadmium chloride in rats were investigated. Acid-base-electrolyte, histologic and, teratologic studies were conducted concurrently with, as far as feasible, a similar protocol. Ethylene glycol caused 1) maternal homeostatic changes including metabolic acidosis and hyperosmolality, 2) extraembryonic lesions with degeneration of allantois and reduced villigenesis being more prevalent, and 3) materno-fetal effects such as decreases in fetal and maternal body weights, decreased maternal food intake, and fetal abnormalities (vertebral, rib, and sternebral defects). Few of these changes occurred when NaHCO3, an endogenous agent known to correct metabolic acidosis, was coadministered with ethylene glycol. Ethylene glycol-induced maternal metabolic acidosis, concurrent with hyperosmolality, was suspected to contribute toward reduction in villigenesis and fetal anomalies, including body weight reductions. Sodium salicylate induced the following: 1) mild maternal acidosis, hypokalemia, and hypophosphatemia with no significant change in pH; 2) maternal hemorrhage in extraembryonic cavities, papillary proliferation of the visceral yolk sac endoderm, and failure to form the chorioallantoic labyrinth; and 3) resorptions, hydrocephaly, rib defects, and fetal body weight reduction. Upon simultaneous treatment with sodium salicylate, NaHCO3 significantly reduced, and NH4Cl enhanced the incidence of the above histologic and teratologic effects, without significantly altering acid-base values. An etiologic association between the above salicylate-induced maternal and extraembryonic lesions and teratogenicity was likely. Cadmium chloride, whether administered by the intraperitoneal (ip) or intravenous (iv) route, caused 1) hydrocephaly, anophthalmia, vertebral and rib defects, reduction in fetal body weight, resorptions and maternal toxicity (acute peritonitis by the ip route only), and 2) extensive necrosis and hemorrhage in the decidua basalis, hemorrhage in the ectoplacental cone and around Reichert's membrane, and absence of chorioallantoic labyrinth. An etiologic relationship between these teratologic and histologic effects seemed probable, since both were dose-related. From the above studies, it was hypothesized that maternal factors--metabolic acidosis, hyperosmolality, hemorrhages in the ectoplacental cone, extraembryonic cavities, and around Reichert's membrane, and necrosis of decidua basalis--may have, directly or indirectly, reduced fetal nutrition and materno-embryonic gaseous exchange, which ultimately altered fetal development.

Parenteral aspirin and sodium salicylate are equally injurious to the rat gastric mucosa

The effects of parenteral aspirin (ASA) or sodium salicylate (SA) on the gastric mucosa were investigated in anesthetized pylorus-ligated rats 3 h after a bolus intravenous injection of ASA or SA, 150 mg/kg, or NaCl (control). Aspirin or SA produced similar extensive gross mucosal hemorrhagic lesions and similar microscopic damage in the presence of luminal acid (luminal pH 1.3 +/- 0.05). Neither ASA nor SA produced gastric mucosal injury with intragastric instillation of saline (luminal pH 3.7 +/- 0.5). Pretreatment for 1 h with luminal or subcutaneous 16,16-dimethyl prostaglandin E2 completely prevented the formation of red streaks in ASA-treated rats but not in SA-treated rats, although prostaglandin E2 pretreatment significantly reduced the gross lesion area in SA-treated rats (p less than 0.05). We conclude the following: (a) Intravenous SA is as damaging as intravenous ASA as long as luminal acid is present. (b) 16,16-Dimethyl prostaglandin E2 completely protected the gastric mucosa from injury by intravenous ASA, and to a lesser extent by intravenous SA. (c) In view of the damaging effects of SA on the gastric mucosa and the rapid conversion of ASA to SA, the mechanism of the gastric mucosal injury by intravenous ASA is much more complex than simple inhibition of endogenous prostaglandin synthesis.

The vascular component of sodium salicylate ototoxicity in the guinea pig

Drugs of the salicylate family (aspirin-like drugs) are reversibly ototoxic. Electrophysiologic and ultrastructural evidence suggests an impairment of the sensory hair cells of the cochlea following salicylate treatment. In addition, since these drugs can cause vasoconstriction, the ototoxicity of salicylates may also involve an impairment of the blood circulation in inner ear. However, a vascular hypothesis of salicylate toxicity has not received much attention. In the current study, we simultaneously measured cochlear blood flow (by laser Doppler flowmetry) and the sound-evoked potentials from the round window. Sodium salicylate caused a decrease in cochlear blood flow that appeared within 30 min following an intramuscular injection of a low dose of sodium salicylate (100 mg/kg). This sodium salicylate dose did not cause a change in auditory sensitivity. For higher doses (200 mg/kg and 300 mg/kg), both cochlear blood flow and auditory sensitivity were affected. The 300 mg/kg dose decreased blood flow by about 25% and elevated compound action potential thresholds by 10 to 25 dB for high frequencies (> or = 8 kHz). Further experiments showed that salicylate-induced threshold shifts were significantly reduced for the mid-frequencies when cochlear blood flow is increased by the vasodilating drug hydralazine (negating the flow reduction caused by salicylate). These data indicate that in addition to the direct effect of systemically administered salicylate on neurosecretory function a decreased blood flow contributes to the ototoxicity of salicylates.

Salicylate and quinine affect the central nervous system

Spontaneous local field potential (LFP) spindle frequencies in cat primary auditory cortex (AI) were estimated from the LFP-trigger autocorrelogram before and after application of sodium salicylate and quinine sulfate. A significant decrease (from 8.7 Hz to 7.6 Hz) was observed. The best modulation frequencies for 251 single units recorded in AI response to periodic click train stimulation also decreased (from 10 Hz to 8.6 Hz) after application of these tinnitus-inducing drugs. The results strongly suggest a central effect of salicylates and quinine in addition to their peripheral ototoxic effects.

Direct effects of salicylate on renal function in the dog

Sodium salicylate was administered to anesthetized dogs in doses sufficient to produce concentrations in plasma comparable to those common in human salicylate toxicity. Salicylate administration increased the rates of excretion of water, sodium, and chloride in the urine. Salicylate administration also increased the rate of excretion of potassium so that its clearance often exceeded that of creatinine. This enhancement of potassium excretion was dissociated from the alkalosis that accompanies salicyate toxicity. Administration of 5% CO(2) in inspired gas did not attenuate the excretion of potassium; injection of salicylate into one renal artery caused a unilateral kaliuresis. Phosphate excretion increased progressively after administration of salicylate. On several occasions the clearance of phosphate equalled that of creatinine. Salicylate reduced renal tubular glucose reabsorption. When salicylate was injected into a renal artery, a glycosuria occurred ipsilaterally at filtered loads of glucose far below the reabsorptive capacity of the dog kidney. Salicylate administration also was associated with early elevation of glucose, phosphate, and potassium concentration in plasma. Salicylate administration reduced the content of adenosine triphosphate in the renal medulla. Salicylate was concentrated within the medulla between 1.5 and 3 times that of the cortex, a gradient equal to that for chloride.

The effect of age on salicylate-induced nephrotoxicity in male rats

The administration of 500 mg/kg sodium [14C]salicylate to 3- and 12-month-old male rats produced proximal tubular necrosis in the older animals but only mild nonspecific cellular changes in the younger group. The onset of renal damage was similar for both 3- and 12-month-old rats but recovery time was prolonged in the older rats. Covalent binding of salicylate equivalents was present in renal cortices from all rats and was largely confined to the mitochondrial fraction; however, older rats displayed five times more binding to this organelle than younger rats. Also the mitochondrial pathway for salicylurate synthesis was significantly inhibited in the older animals. These results demonstrate the existence of an age-dependent susceptibility to salicylate nephrotoxicity and suggest that mitochondrial injury may play an important role in the development of salicylate-induced proximal tubular necrosis.

Induction of hepatic cytochrome P4502E1 in rats by acetylsalicylic acid or sodium salicylate

Studies were conducted on the mechanism of the ethanol-inducible cytochrome P450 (cytochrome P4502E1, CYP 2E1) induction by acetylsalicylic acid (ASA) or its metabolite salicylate (SAL). Many exogenous inducers of CYP 2E1 seem to increase CYP 2E1 by post-transcriptional activation without elevation of its mRNA level. Administration of a single high dose of ASA or SAL produces a significant increase in the activity of the hepatic microsomal p-nitrophenol hydroxylase in rats. Pretreatment of ASA-treated rats with a blocker of mRNA transcription, actinomycin D, or a blocker of protein synthesis, cycloheximide, markedly suppressed this enhanced activity of microsomal p-nitrophenol hydroxylase. The CYP 2E1 mRNA levels in livers of control rats and rats treated with ASA or SAL were measured by Northern blot analysis. Significantly elevated CYP 2E1 mRNA levels were measured in livers of treated rats compared with mRNA amounts of the control group. These data suggest that mRNA elevation seems to be characteristic for ASA induction, while other inducing agents show different patterns and mechanisms of activation.

Induction of a heat shock response (HSP 72) in rat embryos exposed to selected chemical teratogens

A monoclonal antibody to the 72 kD heat shock protein (HSP 72), Western blot analysis and 2-D gel electrophoresis/autoradiography were used to determine whether selected chemical teratogens induced the synthesis and accumulation of HSP 72 in postimplantation rat embryos exposed in vitro. The chemical teratogens studied include N-Acetoxy-2-acetylaminofluorene (N-Ac-AAF), cadmium chloride (CAD), cyclophosphamide (CP), sodium arsenite (AS), and sodium salicylate (SAL). Exposures to test chemicals were selected that produced obvious embryotoxicity characterized by abnormal development and growth retardation. Of the five chemical teratogens studied, AS and SAL induced the synthesis and accumulation of HSP 72 in day 10 rat embryos. The kinetics of HSP 72 accumulation, however, differed between AS- and SAL-treated embryos. Maximal levels of HSP 72 were observed 24 hours after AS exposure and 10 hours after SAL exposure. N-Ac-AAF, CD, and CP induced obvious embryotoxicity; however, none of these chemical teratogens induced HSP 72 at any of the timepoints assayed. Although only a small sample of chemical teratogens was studied, our results suggest that the heat shock response, characterized by the synthesis and accumulation of HSP 72, is not a general biomarker for chemical teratogens.

Prevention of reoxygenation injury by sodium salicylate in isolated-perfused rat liver

Sodium salicylate can be used as a chemical trap for hydroxyl radicals, the most damaging reactive oxygen species. Because reactive oxygen species are involved in the pathogenesis of hepatic hypoxia/reoxygenation injury, the goal of this study was to determine if trapping hydroxyl radicals with salicylate would prevent or at least ameliorate such injury. Isolated rat livers, continuously perfused with Krebs-Henseleit bicarbonate buffer in the presence or absence of salicylate (2 mM), were exposed, after 30 min of recovery, to 60 min of hypoxia, followed by 30 min of reoxygenation. During reoxygenation, control livers experienced a sharp increase in the rate of lactic dehydrogenase release, taken as index of cell injury, protein carbonyl content, and malondialdehyde, taken as index of protein oxidation and lipid peroxidation, respectively. The presence of salicylate in the solution perfusion significantly reduced the rate of lactic dehydrogenase release, protein carbonyl content, and malondialdehyde production during reoxygenation. Hepatic histology documented a significantly reduced cell injury in salicylate-perfused livers compared to control livers. These data suggest that the hydroxyl radical chemical trap sodium salicylate, acting as an antioxidant, may represents an effective agent to reduce liver injury due to hypoxia/reoxygenation in a model of isolated-perfused rat liver.

Effects of noise and salicylate on hair cell loss in the chinchilla cochlea

Chinchillas were exposed to octave band noise, sodium salicylate (300 mg/kg per day intraperitoneally), or the combination of both agents for 15 days. The octave band noise exposure was centered at 500 Hz at an intensity of either 80 or 105 dB sound pressure level. The effects of the experimental treatments were evaluated by determining the number of missing hair cells after recovery as a function of location within the cochlea using a surface preparation technique. Average cochleograms were calculated for each of five experimental groups. Animals given salicylate alone showed little or no hair cell loss. Noise exposure at 80 dB resulted in a mild (less than 30%) outer hair cell loss in the apical turn of the cochlea, whereas exposure at 105 dB resulted in moderate (50%) outer hair cell loss (outer hair cell first row particularly) in the apical half of the cochlea, mild outer hair cell loss in the basal region of the cochlea, and a mild loss of inner hair cells. The amount of hair cell loss in the groups exposed to the combination of salicylates and noise was not significantly different from the corresponding groups exposed to noise alone. Statistical analysis of the data suggest that the combination of salicylate plus noise does not produce any greater hair cell loss than noise alone.

Postnatal evolution of supernumerary ribs in rats after a single administration of sodium salicylate

Radiographs were used to follow the postnatal evolution of 14th ribs in rat pups. Initially, 30 pregnant female rats were randomly distributed into two groups receiving 0 or 300 mg kg(-1) sodium salicylate on day 9 of pregnancy. In the treated group, adverse effects were noted on body weight changes and food consumption during the 2 days following dosing. At birth, a high majority of pups had extra ribs at the 300 mg kg(-1) dose. Radiographs done on postnatal days 1, 6, 14, 28 and 54 showed a reduction in the incidence of rudimentary ribs only, whereas extra ribs, often associated with 27 presacral vertebrae, had the same incidence from birth to adult stage. Furthermore, extra ribs seemed to exhibit similar growth evolution to the other thoracic ribs. This work helps to clarify the postnatal evolution of supernumerary ribs because it was performed on the same animals from birth to adult stage, showing that the reversibility was related to rib length and, in consequence, concerned the rudimentary ribs only. The coexistence of additional presacral vertebrae primarily with extra ribs suggests that both kinds of supernumerary ribs (rudimentary and extra) might be different phenomena and could be considered separately in developmental toxicology studies.

Protection by free oxygen radical scavenging enzymes against salicylate-induced embryonic malformations in vitro

Salicylates are among the oldest and most widely used drugs and are known to lead to foetal death, growth retardation and congenital abnormalities in experimental animals. In this study, the effects of acetyl salicylic acid (ASA), salicylic acid (SAL) and sodium salicylate (NaSAL) on early organogenesis and the interaction of these molecules with free radicals has been investigated. Postimplantation rat embryos were cultured in vitro from day 9.5 of gestation for 48 hr. ASA, SAL and NaSAL were added to whole rat serum at concentrations between 0.1 and 0.6 mg/ml. Also, the lowest effective concentration of ASA for all parameters (0.3 mg/ml) and the same concentration of NaSAL and SAL was added to the culture media in the presence of superoxide dismutase (SOD) (30 U/ml) or glutathione (0.5 micromol/ml). The growth and development of embryos was compared and each embryo was evaluated for the presence of any malformations. When compared to growth of control embryos, the salicylates decreased all growth and developmental parameters in a concentration-responsive manner. There was also a concentration-related increase in overall dysmorphology, including the incidence of haematoma in the yolk sac and neural system, open neural tube, abnormal tail torsion and the absence of fore limb bud. When SOD was added in the presence of ASA, growth and developmental parameters were improved and there was a significant decrease in the incidence of malformations. Addition of SOD also decreased the incidence of malformations in the presence of SAL, but did not effect the growth and developmental parameters of SAL and NaSAL. There was no significant difference between the embryos grown in the presence of these three molecules on the addition of glutathione. The effects of salicylates might involve free oxygen radicals by the non-enzymatic production of the highly teratogenic metabolites 2,3- and 2,5-dihydroxybenzoic acid. An enhanced production of these metabolites in embryonic tissues may be directly related to the increased risk of congenital malformations.