Hirokazu Tsubone

Characteristics of vagal afferent activity in rats: Three types of pulmonary receptors responding to collapse, inflation, and deflation of the lung

To elucidate the characteristics of vagal afferent fibers arising from rat lungs, single-unit activity from pulmonary stretch receptors and two other types of pulmonary receptors was recorded. In the latter, one type of receptor, termed deflation-sensitive receptors in this study, was stimulated only in the expiratory phase of normal respiration. Moreover, this type of receptor exhibited persistent discharges resulting in a train or burst of impulses with collapse and forced deflation, respectively. The decrease of discharge frequency during collapse was slow and the average adaptation index was 20%, indicating a slowly adapting characteristic. Upon forced deflation, the discharge frequency increased with increasing negative pressure to -158 mm H2O intratracheal pressure. The other type of receptor, termed irritant-like receptors, responded to both deflation and inflation. In addition, they displayed rapidly adapting and irregular discharges during maintained inflation. These results indicate that rat vagus nerves deliver afferent information from at least three types of pulmonary receptors: pulmonary stretch and lung irritant-like receptors and the receptors specifically sensitive to expiration or lung deflation. Furthermore, the possibility is postulated that vagal deflation-sensitive receptors are related to the peripheral mechanism in normal respiration and Hering-Breuer deflation reflex in rats.

Alterations of nitrite and nitrate concentrations in the blood of mice exposed to nitrogen dioxide

Abstract Blood nitrite and nitrate of mice were determined using naphthylethylenediamine and a Cu-Cd reduction column. When mice were exposed to 40 ppm nitrogen dioxide, nitrite became constant in 10 min. Nitrite declined rapidly, with a half-life of several minutes, when mice were removed to room air. Nitrate showed changes similar to those of nitrite; however, the concentration in the blood was higher and the half-life was longer. Dose-effect relationships were also determined at concentrations ranging between 5 and 40 ppm for 1 hr exposure. No increase of methemoglobin was observed at these concentrations. Addition of fresh mouse blood to sodium nitrite in vitro indicated a rapid conversion of nitrite to nitrate with an increase of methemoglobin, whereas addition to sodium nitrate did not cause any changes. The fate of inhaled nitrogen dioxide in the living body is discussed based on the results obtained.

Biochemical studies on strain differences of mice in the susceptibility to nitrogen dioxide

Strain differences of mice in their susceptibility to nitrogen dioxide (NO2) were examined by measuring the activities of antioxidative protective enzymes, and the amounts of antioxidants and lipid peroxides in lungs. Four strains of mice: ICR, BALB/c, ddy and C57BL/6 were used in this study and their LC50 values after exposure to NO2 for 16 hr were: 38, 49, 51 and 64 ppm, respectively (1). Genetic strain differences were observed in the enzyme activities, the antioxidant contents and lipid peroxide contents among these four different strains. The activities of glutathione peroxidase (GPX), glutathione S-transferase, and superoxide dismutase (SOD), and the contents of non-protein sulfhydryls (NPSH), alpha-tocopherol (alpha-Toc) and total lipids in lungs of the four strains were related to their LC50, while TBA reactants in lungs of the four strains were inversely related to their LC50. After exposure to 20 ppm NO2 for 16 hr, the activities of the protective enzymes and the contents of NPSH decreased, while the level of alpha-Toc increased markedly. The activities of GPX, 6-phosphogluconate dehydrogenase, SOD and disulfide reductase, and the contents of NPSH, alpha-Toc and total lipids were also related to their LC50. On the other hand, TBA reactants increased higher than those of the control groups and were inversely related to their LC50. These results suggest that the protective enzymes and the antioxidants are important factors at defence mechanism in lungs to NO2 and that the intensity of the protective systems in pigmented strains is generally greater than that in albino strains.

Effect of ozone toxicity in the drinking behavior of rats.

To clarify the effects of ozone on behavior, drinking activity was observed continuously in animals exposed to ozone at concentrations of 0.2, 0.4, and 0.8 ppm for 1 wk. Drinking decreased considerably on the first day after onset of exposure. On the first day the suppression rate was calculated to be 28.1%, 69.5%, and 93.1%, for the 0.2 ppm, 0.4 ppm, and 0.8 ppm group, respectively. The suppression of drinking and recovery were dependent on the concentration of ozone.

Effects of nitrate and nitrite, chemical intermediates of inhaled nitrogen dioxide, on membrane components of red blood cells of rats

Rat blood was incubated at 37 degrees C for 60 min with either NaNO3 or NaNO2 to examine the relationship between the decrease in the hexose content and Ca2+,Mg2+-ATPase activity of red cell membranes, and NO3- and NO2-. The hexose content decreased depending on the NaNO2 concentration up to 100 microM reaching 76% (p less than 0.05) of the control value. NaNO3 had little effect on the hexose content. On the other hand, the Ca2+,Mg2+-ATPase activity decreased depending on the NaNO3 concentration up to 200 microM, where the activity reached 75% (p less than 0.01) of the control value. The effect of NaNO2 on this activity was smaller than that of NaNO3. The sialic acid content and the Na+,K+-ATPase activity did not show significant alterations by incubation with NaNO2 and NaNO3 at below 100 microM. To examine the in vivo effects of NO2- and NO3-, 50 mM NaNO3 was intravenously injected into rats five times at hourly intervals (dose: 1.0 ml/kg body weight), and blood was collected 1 hr after the last injection. The activities of Ca2+,Mg2+- and Na+,K+-ATPases of red cell membranes were decreased to 68% (p less than 0.05) and 80% of the control value, respectively. Reduction by injection of 50 mM NaNO2 was smaller than that by 50 mM NaNO3. The results show that the hexose content and the Ca2+,Mg2+-ATPase activity of red cell membranes were decreased by NO-x that increased in the blood during short-term exposure of rats to NO2.

EFFECTS OF DIESEL EXHAUST PARTICLES ON BLOOD PRESSURE IN RATS

The effects of diesel exhaust particles (DEP) on pulmonary functions and consequent diseases are well known, but there have been few reports concerning involvement of the cardiovascular system. In order to assess a direct action of DEP on cardiac tissue, the effects on blood pressure of intravenous administration of 12 or 120 mg/kg DEP to anesthetized rats were studied for a 15-min period. DEP (120 mg/kg) significantly lowered blood pressure for 25 s with no signs of arrhythmia or mortality, a phenomenon seen in guinea pigs. After 25 s blood pressure gradually returned to control levels and was maintained for 15 min. The 12-mg/kg DEP concentration did not markedly affect rat blood pressure. Pretreatment with atropine (24 mg/kg) blocked the DEP-induced fall in blood pressure, while pretreatment with propranolol (48 mg/kg) proved ineffective against DEP, suggesting involvement of the parasympathetic system. Data show that the rat is less sensitive to DEP-induced effects on blood pressure and may be a poor model to reflect cardiovascular changes.

Stimulation to the Trigeminal Afferent Nerve of the Nose by Formaldehyde, Acrolein, and Acetaldehyde Gases

AbstractThis study was performed to elucidate the effect of formaldehyde (HCHO), acrolein (CH2CHCHO), and acetaldehyde (CH3CHO) gases on the nasal sensory system in the rat. For this purpose, the afferent activity was recorded from the ethmoidal nerve, one branch of the trigeminal nerve, during delivery of these gases (0.32–4.7 ppm HCHO, 0.78–7.2 ppm CH2CHCHO, 134–2232 ppm CH3CHO) into the upper airway at a flow rate of 200 ml/min. All compounds stimulated nerve activity when they and control gas were alternately applied into the nose. The concentration-response relationships, which were represented by log-log coordinates, showed that a 50% increase in nerve activity was found at 1.8, 1.2, and 908 ppm for HCHO, CH2CHCHO, and CH3CHO, respectively.These results indicated that formaldehyde and acrolein can stimulate the nasal sensory system at concentrations less than I ppm, while such stimulation is much weaker with acetaldehyde. These stimulatory effects on the nasal passage will be associated with some re...

Reflex cardiopulmonary responses by stimulation to type J receptors in rats exposed to NO2.

To examine the role of the vagal pathway on the cardiopulmonary functions in NO2-exposed rats, phenyl diguanide, which stimulates type J receptors in the lungs, was injected to control and exposed rats at a constant dose. Based on a statistical test, a decrease in the heart rate (HR) after the injection was observed in the groups exposed to 20 ppm NO2 for 1.5 h and 3h, and 10 ppm for 24 h. On the other hand, an increase in respiratory rate (RR) was observed in the groups exposed to 10 ppm for 3 h and 4 ppm for 1 wk. No change in HR and RR was found in the group exposed to 0.4 ppm for 4 wk. These results suggest that the augmentation of the reflex cardiopulmonary responses due to stimulation to the type J receptors was produced by exposures with a higher concentration of NO2.

Changes of gaseous exchange in the lung of mice acutely exposed to nitrogen dioxide.

To clarify the acute effects of NO2 on gaseous exchange in the lung of mice, O2 and CO2 concentrations in respiratory gas, respiratory rate (RR), arterial blood pH, PaCO2, PaO2, lung wet weight and lung water content were examined using the head-enclosed method. The results of the present study indicate that in mice exposed to 5 ppm NO2 for 24 h the gaseous exchange in the lung and metabolic rate of O2 and CO2 in the body are accelerated, whereas in mice exposed to 10 ppm and 20 ppm NO2 the gaseous exchange in the lung is inhibited to change the gaseous metabolism.

Reevaluation of arrhythmias and alterations of the autonomic nervous activity induced by T-2 toxin through telemetric measurements in unrestrained rats

This study was conducted to clarify and reevaluate the cardiac and autonomic nervous effects of T-2 toxin, which had been previously examined by several acute experiments, in unrestrained and conscious rats implanted with telemetric transmitters. Two groups of rats were given two subcutaneous injections of 0.1 and 0.5 mg/kg of T-2 toxin with an interval of 3 days. Two other groups of rat were pre-implanted with osmotic minipumps by which atropine (20 mg/kg/day) or propranolol (100 mg/kg/day) was continuously administered preceding subcutaneous injection of T-2 toxin (0.5 mg/kg). The present study demonstrated that T-2 toxin caused marked arrhythmias, such as second-degree atrioventricular (AV) block, sinus bradycardia, supraventricular extrasystole, and ventricular extrasystole, which were accompanied by a significant increase in heart rate and a significant decrease in total power and low- and high-frequency power of heart rate variability, during 3 days of observation after the toxin administration. However, the occurrence of arrhythmia with conduction disturbance such as second-degree atrioventricular blocks was markedly diminished by pretreatment with atropine, while the occurrence of ventricular extrasystole was augmented by atropine. The present study with the telemetric measurement elucidated and confirmed that T-2 toxin produced significant cardiac dysfunctions involving disturbance of the conduction pathway influenced by the autonomic nervous activity and also possible direct effects on cardiac myocytes.