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The aim of this study was to examine the changes in autonomic control of the heart associated with classical appetitive conditioning in rats. We trained rats to learn that a movement into a test chamber was followed by delivery of reward (contextual conditioning) and performed power spectral analysis of heart rate variability from electrocardiograms recorded using the telemetry system. We investigated the sympathovagal balance of autonomic regulation of the heart in response to not only the conditioned stimulus (the movement into the test chamber), but also the unconditioned stimulus (reward), and compared the results of these two kinds of emotional states; it might be considered that "the reward-expecting state" is evoked by the conditioned stimulus and "the reward-receiving state" is evoked by the unconditioned stimulus in rats. The reward-expecting state resulted in a significant increase in both low frequency (LF) power and high frequency (HF) power with no change in heart rate (HR) and LF/HF ratio, indicating that both sympathetic and parasympathetic activity increased with no change in sympathovagal balance. The reward-receiving state resulted in a significant increase in HR and a significant decrease in LF power, HF power, and LF/HF ratio, indicating that both sympathetic and parasympathetic activity decreased with predominance in the parasympathetic activity. These results suggest that the method performed in our present study might be useful for distinguishing between two different emotional states evoked by classical appetitive conditioning in rats.

The time courses of changes in cardiovascular and autonomic nervous functions during acclimatization to hypoxia were studied in conscious Sprague-Dawley rats. The animals were kept under a 12:12-h light-dark cycle and exposed to hypoxia (1 atm, 10% O2). Implanted telemetry transmitters were used to record blood pressure (BP). Changes in heart rate (HR) and BP were monitored over a 21-day period, and variations before and during hypoxia were analyzed using the wavelet transform method. The HR, high-frequency power of HR variability (HR-HF) and low-frequency power of BP variability (BP-LF) were all significantly increased after 1 h of hypoxia, whereas the LF/HF ratio of HR variability did not change. After this initial increase, both HR and the BP-LF were found to decrease. On the first day of hypoxia, HR and BP-LF values were significantly lower than those of the control rats, whereas the HR-HF was higher. Subsequently, these values altered so that they were similar to the control after 14 days of hypoxia. In addition, the amplitude of diurnal variation in HR was reduced during hypoxia. These results suggest that a sequence of dynamic interactions between sympathetic and parasympathetic nervous activities might have important roles in the regulation of cardiovascular function during acclimatization to hypoxia.

This study investigated the effects of pair housing on diurnal rhythms of heart rate and autonomic nervous activity in miniature swine. For this purpose, six adult Gottingen miniature swine were initially housed individually in an animal cage. Then, two of each swine were housed in a large cage together for 3 weeks. After that swine were separated into individual cages again. During this experimental procedure, electrocardiogram (ECG) was recorded with a Holter ECG recorder. Autonomic nervous activity was evaluated by power spectral analysis of heart rate variability. Heart rate and autonomic nervous activity clearly showed a diurnal rhythm in miniature swine housed in individual cages. When two swine were housed together, heart rate was significantly increased throughout the day and diurnal rhythm disappeared. Although these changes gradually recovered to basal levels, these parameters had not completely returned to basal levels even after 2 weeks. Heart rate was still higher than the initial level just after swine were re-housed in their own individual cages. Heart rate and autonomic nervous activity returned to basal levels about 2 weeks after re-housing. Further, heart rate in some swine decreased below their initial levels. These results suggest that it takes miniature swine at least 2 weeks to adapt to different circumstances. Furthermore, the power spectral analysis of heart rate variability can be used as a useful method in a study for answering controversial issues related to stress response.

We investigated the characteristics of autonomic nervous function in Zucker-fatty and Zucker-lean rats. For this purpose, a long-term electrocardiogram (ECG) was recorded from conscious and unrestrained rats using a telemetry system, and the autonomic nervous function was investigated by power spectral analysis of heart rate variability (HRV). Although heart rate (HR) in Zucker-fatty rats was lower than that in Zucker-lean rats throughout 24 h, apparent diurnal variation in HR was observed in both strains and HR during the dark period was significantly higher than that in light period. Diurnal variation in locomotor activity (LA) in Zucker-fatty rats was also observed, but LA was lower than that in Zucker lean rats, especially during the dark period. There were no significant differences, however, in high-frequency (HF) power, low-frequency (LF) power, and the LF/HF ratio between Zucker-fatty and Zucker-lean rats. The circadian rhythm of these parameters was mostly preserved in both strains of rats. Moreover, the effect of autonomic blockades on HRV was nearly the same in Zucker-fatty and Zucker-lean rats. These results suggest that the autonomic nervous function of insulin-resistant Zucker-fatty rats remain normal, from the aspect of power spectral analysis of HRV.

Objective—To determine the effects of immersion in warm springwater (38° to 40°C) on autonomic nervous activity in horses. Animals—10 male Thoroughbreds. Procedure—Electrocardiograms were recorded from horses for 15 minutes during a warm springwater bath after being recorded for 15 minutes during stall rest. Variations in heart rate (HR) were evaluated from the power spectrum in terms of low frequency (LF, 0.01 to 0.07 Hz) power and high frequency (HF, 0.07 to 0.6 Hz) power as indices of autonomic nervous activity. Results—Mean (±SE) HR during stall rest and immersion in warm springwater was 31.1 ± 1.7 and 30.3 ± 1.0 beat/min, respectively. No significant difference was found between the HR recorded during stall rest and that recorded during immersion in warm springwater. The HF power significantly increased from 1,361 ± 466 milliseconds2 during stall rest to 2,344 ± 720 milliseconds2 during immersion in warm springwater. The LF power during stall rest and immersion in warm springwater was 3,847 ± 663 and 5,120 ± 1,094 milliseconds2, respectively, and were not significantly different from each other. Similarly, the LF:HF ratio did not change during immersion in warm springwater. The frequency of second-degree atrioventricular block, which was observed in 2 horses, increased during immersion in warm springwater, compared with during stall rest. Conclusions and Clinical Relevance—Increases in HF power indicates that the parasympathetic nervous activity in horses increases during immersion in warm springwater. Thus, immersion in warm springwater may provide a means of relaxation for horses. ( Am J Vet Res 2003;64:1482–1485)

The present study assessed the effects of bovine milk-derived lactoferrin (bLf) on distress activities induced by maternal separation in 5- to 18-day-old rat pups. The rat pups were injected with BSA (100 mg/kg, i.p.; control) or bLf (100 mg/kg, i.p.) 30 min before the behavioral test. Distress activity was estimated by means of recording body movements or ultrasonic vocalizations (USVs). After 5 min of maternal separation, bLf significantly (P

Adult rats emit 22 kHz ultrasonic vocalizations (USVs) in response to aversive stimuli, and these sounds are suggested to have communicative information among conspecifics. It is conceivable that social environment during development of rats has relevance to the emission of 22 kHz USVs. To examine the effects of social environment after weaning on production of stress-induced USVs, we compared the amount of emission of USVs among three groups of rats reared under different conditions after weaning. One group of rats was housed individually, and the other two groups were housed in pairs, in which social hierarchy of the pair was determined by social dominance-subordination relationships. The USVs were induced by acute mild somatic stimuli on the back and neck. Individually reared rats emitted much fewer USVs than pair-reared rats. In addition, socially subordinate rats emitted more USVs compared with socially dominant ones. These results suggest that not only social interaction but also the status in social hierarchy may play an important role in the process of the development of USVs induced by somatic stimuli.

Objective—To determine the effects of initial handling and training on autonomic nervous functions in young Thoroughbreds. Animals—63 healthy Thoroughbreds. Procedure—All horses were trained to be handled and initially ridden in September of the yearling year and then trained until the following April by conventional training regimens. To obtain the heart rate (HR), electrocardiograms were recorded in the stable before initial handling and training and following 7 months of training; variations in HR were then evaluated from the power spectrum in terms of the low frequency (LF; 0.01 to 0.07 Hz) power and high frequency (HF; 0.07 to 0.6 Hz) power as indices of autonomic nervous activity. To evaluate the fitness, the V200 (velocity at HR of 200 beat/min), which is reflective of the aerobic capacity of the horse, was measured. Results—Mean (± SE) resting HR decreased significantly from 41.5 ± 0.8 to 38.7 ± 0.4 beat/min following 7 months of training. The LF power of horses increased significantly from 1,037 ± 128 milliseconds2 in September of the yearling year to 2,944 ± 223 milliseconds2 in the following April. Similarly, the HF power increased significantly from 326 ± 30 milliseconds2 to 576 ± 39 milliseconds2 at the corresponding time points. The V200 increased significantly following training. Conclusions and Clinical Relevance—Increases in LF and HF powers indicate that parasympathetic nervous activity increases in horses by 7 months of training. The decrease in resting HR may be dependent on the training-induced increase of parasympathetic nervous activity in Thoroughbreds. (Am J Vet Res 2002;63:1488–1491)

Mechanisms underlying the Ca2+-activated K+ channel (K(Ca)) blockers-induced oscillatory contractions were investigated in guinea pig tracheal smooth muscle. The mean oscillatory frequencies induced by charybdotoxin (ChTX; 100 nM) and iberiotoxin (IbTX; 100 nM) were 9.8+/-0.8 (counts/h) and 8.0+/-1.3 (counts/h), respectively. Apamin (1 microM ), a blocker of SK(Ca), induced no contraction in guinea pig trachea and did not affect ChTX-induced oscillatory contractions. In Ca2+ free solution, no ChTX-induced contraction was observed. Nifedipine (100 nM), a blocker of voltage-dependent Ca2+ channels, and SK&F 96365 (10 microM), a blocker of capacitative Ca2+ entry, completely abolished ChTX-induced oscillatory contractions. Ryanodine (1 microM) decreased the amplitude, but increased the frequency of the oscillatory contractions. Thapsigargin (1 microM) changed contractions from the oscillatory type to the sustained type. Moreover, the protein kinase C (PKC) inhibitor, bisindolylamaleimide I (1 microM), decreased the amplitude and frequency, but PKC activator, phorbol 12-myristate 13-acetate (1 microM), increased the frequency of oscillatory contractions. These results suggest that K(Ca) inhibitors-induced oscillatory contractions are initiated by Ca2+ influx through L-type voltage-dependent Ca2+ channels. The ryanodine-sensitive calcium release channels in the sarcoplasmic reticulum may play an important role in maintaining the oscillatory contractions. Moreover, PKC activity modulates these oscillatory contractions.

We established characteristics of power spectral analysis of heart rate variability, and assessed the diurnal variations of autonomic nervous function in guinea pigs. For this purpose, an electrocardiogram (ECG) was recorded for 24 hr from conscious and unrestrained guinea pigs using a telemetry system. There were two major spectral components, at low frequency (LF) and high frequency (HF) bands, in the power spectrum of HR variability. On the basis of these data, we defined two frequency bands of interest: LF (0.07-0.7 Hz) and HF (0.7-3.0 Hz). The power of LF was higher than that of HF in the normal guinea pigs. Atropine significantly reduced power at HF. Propranolol also significantly reduced power at LF. Furthermore, the decrease in the parasympathetic mechanism produced by atropine was reflected in a slight increase in the LF/HF ratio. The LF/HF ratio appeared to follow the reductions of sympathetic activity produced by propranolol. Autonomic blockade studies indicated that the HF component reflected parasympathetic activity and the LF/HF ratio seemed to be a convenient index of autonomic balance. Nocturnal patterns, in which the values of heart rate in the dark phase (20:00-06:00) were higher than those in the light phase (06:00-20:00), were observed. However, the HF, LF and the LF/HF ratio showed no daily pattern. These results suggest that the autonomic nervous function in guinea pigs has no clear circadian rhythmicity. Therefore, this information may be useful for future studies concerning the autonomic nervous function in this species.

Diurnal fluctuations of heart rate (HR), body temperature (BT) and locomotor activity (LA) in the unanaesthetized and unrestrained house musk shrew (Suncus murinus) were studied using a telemetry system. Six adult male shrews (Jic:SUN) weighing 60-70 g were used in the present study. They were housed under conditions of 24 C and a 12/12-hr light-dark cycle. HR, BT and LA were recorded over 10 days, following the post-implantation period (10 days or more) of the telemetric transmitter. A clear nocturnal rhythm of LA was shown, while intermittent and short-term LA were shown during the light period. The mean HR was 323.5 +/- 8.8 bpm in the light period and 354.3 +/- 5.2 bpm in the dark period, and the fluctuation of HR showed a nocturnal pattern. A nocturnal pattern was also observed in BT fluctuation, and all animals lowered their body temperature from 35-37 C to approximately 30 C or below, mostly during the light period. The fall of body temperature progressed over 2-3 hr, and then rose to the baseline temperature rapidly within approximately 30 min. While the body temperature fell, HR markedly decreased to approximately 100 bpm. These results suggest that the shrew has unique physiological properties in maintaining metabolic balance which are anticipated to be caused by the dramatic alteration of the autonomic nervous function.

Cough elicitation and major physiological factors influencing cough occurrence were investigated in congenitally bronchial-hypersensitive (BHS) and -hyposensitive (BHR) guinea pigs exposed to citric acid (0.3 M) aerosol for 10 min. The number of cough in BHS was significantly larger than in BHR, while the latency to cough in BHS was significantly shorter than in BHR. Pretreatment with atropine (0.2%), lidocaine (2%) or salbutamol (0.1%) aerosol and desensitization of C-fibers with capsaicin (100 mg/kg) decreased the cough numbers in both BHS and BHR. The salbutamol, atropine and capsaicin pretreatments prolonged the cough latency in BHS, but only salbutamol prolonged the latency in BHR. After salbutamol pretreatment all BHR guinea pigs exhibited cough, while 66.7% of BHS guinea pigs exhibited it. Vagal blocking by atropine suppressed coughing in both BHS and BHR. Only a small number (33.3%) of BHR guinea pigs and no BHR guinea pigs exhibited a cough response after capsaicin and lidocaine pretreatment whereas many BHS guinea pigs still produced cough after such pretreatment. The present study demonstrated that the cough responsiveness to citric acid aerosol was significantly higher in BHS than in BHR. It was revealed that airway smooth muscle contraction and functional and/or morphological development of airway nervous receptors, especially C-fiber endings, contributed to aggravation of coughing in BHS.

An autolysate of bonito bowels was treated with ultrafiltration, loose RO concentration, ion-exchange chromatography, and reverse phase chromatography to increase its potency to inhibit angiotensin I-converting enzyme (ACE) activity by 16-fold. Oral administration of the partially purified autolysate decreased the systolic blood pressure of spontaneously hypertensive rats (SHR) in a dose-dependent manner at the doses of 1 g peptides/kg or higher. The relationship between the antihypertensive activity (in vivo) of the partially purified preparation and its ACE inhibitory activity (in vitro) in comparison with previously reported ACE inhibitory peptides is discussed.

The expression balance of M2 and M3 muscarinic receptor subtypes on the pathogenesis of airway hyperresponsiveness was investigated by using two congenitally related strains of guinea pigs, bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR). CCh-induced airway responses in vivo and in vitro were investigated by comparing the effects of muscarinic receptor subtype antagonists, and the relative amounts of M2 and M3 muscarinic receptor mRNA in tracheal smooth muscle and lung tissue were investigated. After treatment with muscarinic receptor subtype antagonists, the ventilatory mechanics (VT, Raw, and Cdyn) of response to CCh aerosol inhalation were measured by the bodyplethysmograph method. The effects of these antagonists on CCh-induced tracheal smooth muscle contraction were also investigated. The effects of M2 muscarinic receptor blockade were less but the effects of M3 muscarinic receptors blockade on the airway contractile responses were greater in BHS than in BHR. In M3 muscarinic receptor blockades, CCh-induced tracheal contractions in BHS were significantly greater than those in BHR. In tracheal smooth muscle from BHS, the relative amount of M2 muscarinic receptors mRNA was less but that of M3 muscarinic receptor mRNA was more than those in BHR. These results suggest that the high ACh level as a consequence of dysfunction of M2 muscarinic autoreceptors and the excessive effect of M3 muscarinic receptors on the airway smooth muscle may play an important role in the pathogenesis of airway hyperresponsiveness.

This study was designed to assess the usefulness of young farm pigs as an experimental model for hypercholesterolemia. In order to test this, we investigated both serologic and electrocardiographic effects of atherogenic diet. Four-week-old pigs were fed an atherogenic diet for 8 weeks. No arrhythmia was observed on ECG in all animals. There were no significant difference between control and atherogenic diet group on the values of ECG parameters. However, plasma lipids values of atherogenic diet group were significantly (p less than 0.05) higher than those of control diet group. Thus, hypercholesterolemia was induced in young farm pigs by feeding atherogenic diet in a relatively short time. This fact suggests that young farm pigs may be an useful model for further studies of the effect of hypercholesterolemia on cardiovascular function and the early pathogenesis of atherosclerosis.

Summary We studied the influence of training on autonomic nervous function in the horse. For this purpose, Holter electrocardiogram (ECG) was recorded before and after training from 24 Thoroughbred horses (2-year-olds) and autonomic nervous function was evaluated by the power spectral analysis of heart rate (HR) variability. We obtained HR, low-frequency (LF) power, high-frequency (HF) power, and LF/HF ratio from recording. We set LF at 0.01–0.07 Hz and HF at 0.07–0.6 Hz. The HF power is thought to reflect primarily parasympathetic nervous function. Both the sympathetic and parasympathetic nervous systems have been shown to contribute to the LF power. The LF/HF ratio is considered as an index of the cardiac sympathovagal balance. Second degree atrioventricular blocks were found in the ECG of 3 and 5 horses before and after the training period, respectively. Ventricular premature depolarisations were detected in a horse after the training period. Heart rate decreased at night The lowest HR values had a tendency to appear in the early morning. Both the LF and HF power tended to be higher at night However, the LF/HF ratio was almost the same throughout the day. The HR was significantly decreased by training. Although the LF power and LF/HF ratio were significantly increased, the HF power was not changed by training. These results suggest that parasympathetic nervous activity may be fully activated even before training in this species.

Responses of nasal receptors to capsaicin and water were studied from afferent recordings of the posterior nasal nerve (PNN) in 12 anesthetized dogs. Out of 12 non-respiration-modulated nasal receptors, 7 responded only to capsaicin, 3 responded to both water and capsaicin, and 2 to neither of them. All the fibers showed a rapid adaptation to mechanical probing of the nasal mucosa. These results indicate that the presence of sensory receptors responding to capsaicin and water are involved in PNN afferents of the dog.

Tail blood flow (TBF) in the rat markedly increases during sympathetic withdrawal such as hyperthermia or lumbar sympathetic blockade. However, a long-term alteration of TBF after chronic sympathetic denervation is not well understood. In the present study, TBF following lumbar sympathectomy (LSX) was observed to ascertain whether subsequent changes in TBF occur in the absence of the sympathetic nervous activity in the rat tail. Assessed by recording tail and rectal temperature, the LSX immediately caused an increase in TBF. TBF was gradually decreased along with time and returned to the sham operated (SO) control level within 4 days. About a week after the surgery, a rapid increase in TBF in response to whole body heating was almost abolished in denervated animals. Neither hexamethonium (20 mg/kg, i.v.) for ganglion blockade nor intra-arterial infusion of alpha-receptor antagonist, phentolamine (10, 100 microg) produced vasodilation in LSX animals. Nitroprusside, a donor of nitric oxide, produced an increase in TBF in both LSX and SO animals. These results indicate that the tail vasculature after LSX constricts with capability to be vasodilated independent of sympathetic reinnervation. Quantification of the tail vascular mRNA expression by reverse transcriptase-polymerase chain reaction showed less endothelial nitric oxide synthetase in LSX group than that in SO group whereas endothelin-1 was not significantly different in both groups. It is suggested that functional changes in tail vascular endothelium takes at least a part in the reduction in TBF after LSX.

Morphological and immunohistochemical features of the abdominal mesotheliomas that were developed by inoculation of 3 cell lines (MeET-4, -5 and -6) established from spontaneous abdominal mesotheliomas in male F344 rats. Although the original tumors of three cell lines showed signs of epithelioid growth with a predominantly simple papillary pattern, transplanted tumors revealed a variety of morphologic features including epithelioid with glandular structures, sarcomatous, and a mixture of these components. All tumor cells of transplanted tumors were positive for alpha-smooth muscle actin (ASMA) but almost negative for desmin as were epithelioid cells of the original tumors, and the cell lines were positive for desmin but not for ASMA. These results suggested that mesothelioma in the F344 rat had the potential for wide spectrum differentiation under in vitro conditions. The microenvironmental factors obtained in vivo can modify their potential ability and their morphological aspects. These factors may be related to tumor cell reexpression of ASMA of tumor cells that were masked under in vitro culture conditions.

The characteristics of airway responsiveness to acetylcholine (ACh) in congenitally bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs were clarified in vivo and in vitro. We measured the change in ventilatory mechanics in response to ACh inhalation by means of the bodyplethysmograph and the contractile responses of isolated trachea to ACh and carbachol (CCh). Further, muscarinic receptor subtypes involved these responses were identified. The basal values for ventilatory mechanics in BHS were not significantly different from those in BHR. Respiratory resistance to ACh was progressively increased in a time- and dose-dependent manner in BHS. The contractile responses of tracheal smooth muscle to ACh in BHS were significantly greater than those in BHR, but CCh-induced responses in BHS and BHR were similar. ACh- and CCh-induced contractions were mediated via M3 receptors. These results suggested that the falling-down of BHS in response to ACh inhalation was caused by the strong constriction of the airway and the reduction in ventilation. Moreover, the airway hyperresponsiveness to ACh in BHS might be partly dependent on the change in acetylcholinesterase activity.

We investigated the endothelin production and endothelin receptor activity of pericardial mesothelial cells obtained from spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. The pericardial mesothelial cells were maintained in vitro and the production of endothelin-1 by these cells was evaluated by using a sensitive sandwich-type enzyme immunoassay for endothelin-1 and big endothelin-1. Endothelin receptor subtypes were pharmacologically analyzed by measuring the changes of intracellular Ca2+ concentration ([Ca2+]i) in pericardial mesothelial cells. Mesothelial cells from both strains produced more immunoreactive endothelin-1 than big endothelin-1. The production of immunoreactive endothelin-1 progressively increased in a culture time-dependent manner. The amount of immunoreactive endothelin-1 detected after 72 h in pericardial mesothelial cells of SHR was significantly (P0.05) higher than that in the cells of WKY rats (SHR: 196.7 +/- 19.1 pg/10(6) cells; WKY: 122.7 +/- 10.6 pg/10(6) cells). Endothelin-1 and endothelin-3 induced elevation of [Ca2+]i in pericardial mesothelial cells. The selective agonist of the endothelin ETB receptor, sarafotoxin S6c, also induced elevation of [Ca2+]i. The endothelin- and sarafotoxin S6c-induced elevations of [Ca2+]i in pericardial mesothelial cells from SHR were greater than those in mesothelial cells from WKY rats. The endothelin ETB receptor antagonist, IRL 1038 ([Cys11,Cys15]endothelin-1-(11-21)), significantly inhibited the endothelin-1- and endothelin-3-induced changes in [Ca2+]i. The endothelin ETA receptor antagonist, FR 1393171 ((R)2-[(R)-2-[(S)-2-[[1-(hexahydro-1H-azepinyl)]carbonyl]ammino -4-methylpentanoyl]amino-3-[3-(1-methyl-1H-indoyl)]propio nyl]amino-3-(2-pyridyl)propionic acid), did not affect these changes. From these results, pericardial mesothelial cells from both SHR and WKY rats shared the ability to produce endothelin-1 spontaneously in culture, although consistently greater production was detected in cultures of SHR origin. Moreover, pericardial mesothelial cells of SHR origin may have increased numbers of endothelin ETB receptors and/or a more active signal transduction system compared with those of WKY rats. These results suggest that endothelin-1 may play an important role in the pericardium in an autocrine and/or paracrine fashion.

Electrolyte abnormalities have become an increasingly important cause of arrhythmias owing to the widespread use of high-potency diuretics. Hypokalemia is one of the common complications of diuretic use. Although some studies of hypokalemia induced by furosemide as well as of potassium-deficient diets in the rat have been reported, the electrocardiographic (ECG) changes during hypokalemia in the rat are poorly understood. This study was designed to examine such changes. For this purpose, hypokalemia was induced by furosemide administration, and the diagnostic criteria for ECG manifestations of hypokalemia were determined. During hypokalemia, conduction in most parts of the heart was suppressed to an extent depending on plasma potassium concentration. Prolongation of the QT interval was also observed, which agrees with findings in humans and dogs. Furthermore, prolonged durations of the P wave and QRS complex were observed during hypokalemia in the rat. The extent of alteration of the PR interval induced by hypokalemia was less significant than that of P wave and QRS complex durations. These results suggest that the excitabilities of the myocardium in the atria and ventricles may be affected by extracellular potassium level rather than by the atrioventricular conduction system in the rat. Wave amplitude, except that of the P wave, was decreased by severe hypokalemia. These changes were not dependent on the plasma potassium concentration. Typical T wave changes observed with hypokalemia in humans and dogs did not occur in the rat. The ECG manifestations of acute hypokalemia in the rat did not include the typical T wave changes seen in species with ST-segment type ECGs; however, other ECG parameter changes occurring with hypokalemia were qualitatively similar to those in other species. These results may be useful for testing the toxicity of potassium-depleting drugs in the rat.

Airway hyper-responsiveness is known as an important pathogenesis of asthma. In the present study, the airway responsiveness to aerosolized and injected histamine in congenitally bronchial-hypersensitive (BHS) and bronchial-hyposensitive (BHR) guinea pigs was investigated. In addition, the role of the vagal reflex in histamine-induced airway contraction was evaluated by vagal blocking with atropine inhalation or bilateral vagotomy. A significantly higher bronchoconstrictive reaction, i.e., a decrease in tidal volume (VT) and an increase in respiratory resistance (Rrs), to histamine-inhalation was observed in BHS than in BHR. A noticeably lower reduction in VT was noted after atropine pretreatment for both BHS and BHR, whereas an increase in Rrs was inhibited only in BHS. The intravenous injection of histamine caused a noticeable bronchoconstrictive reaction in both BHS and BHR with a dose-dependent relationship, but no significant differences were observed and the bilateral vagotomy failed to induce any difference between the two animal groups. These results demonstrated that the airway responsiveness to histamine is considerably different in BHS from that in BHR, but the difference is largely dependent on the route of administration of histamine. The important role of the vagal reflex on the elicitation of airway contraction was elucidated in both animal groups, and it appeared that the BHS possessed relatively higher dependency on the vagal reflex mechanism than the BHR.

This study has demonstrated the power spectral analysis of heart rate variability in a horse with atrial fibrillation. A large peak in the high frequency (HF) area of the power spectrum appeared in the horse. Hourly heart rate, the low frequency (LF) power, the HF power, and LF/HF ratio were almost constant during the recording period. The values of HF and LF power in the horse with atrial fibrillation were much larger than those in normal horses. The normalized unit of HF (HF n.u.) was much larger than that of LF (LF n.u.). Furthermore, the LF/HF ratio was very small in the horse. These results suggest that the ventricular rhythm has a respiratory related periodicity in the horse with atrial fibrillation and the predominant parasympathetic activity may modulate the intrinsic behavior of the atrioventricular node during atrial fibrillation.

Three mesothelioma cell lines (MeET-4, MeET-5, and MeET-6) established from ascitic fluid of F344 rats with spontaneous abdominal mesothelioma have been maintained through at least 60 passages on the DMEM with 10% FBS. Two of original tumours consisted of epithelioid cells growing in a papillary pattern, while one (original tumour of MeET-5) had sarcomatous areas composed of spindle-shaped tumour cells. The cell line originating from MeET-5 showed a constantly beiphasic growth pattern during the repetitive subcloning, while the other two lines retained a monophasic growth pattern. Although the growth pattern was different, the tumour cells in all three lines were positive for vimentin and keratin and ultrastructurally showed an abundant distribution of glycogen granules in the cytoplasm and numerous long microvilli on all surface. The modal chromosome number of cell lines varied from 41 to 71, and abnormal chromosomes were frequently seen. All cell lines established formed colonies on semi-solid medium and could be successfully transplanted, growing tumour masses in syngeneic rats and thus indicating their malignant nature. Cell lines grew even on a medium with a low concentration of FBS. The evidence suggests that they may produce growth factors that enable them to survive unfavourable medium conditions.

We have studied the autonomic nervous function in voles ( Microtus arvalis) and mice. For this purpose, ECGs were recorded from conscious and unrestrained voles and mice using radiotelemetry and the autonomic nervous function was investigated by the power spectral analysis of heart rate variability. Heart rate in voles was lower than mice and the coefficient of variance was larger in voles. In the power spectra of voles and mice, there were two major spectral components with the high frequency (HF) peak generally appearing between 2.0 and 4.0 Hz, and the low frequency (LF) peak appearing below 0.6 Hz. On the basis of this data, we set the two frequency bands as LF (0.1-1.0 Hz) and HF (1.0-5.0 Hz) to evaluate autonomic nervous function. The LF and HF powers were larger in voles than mice. The LF/HF ratio was thought to provide a convenient index of autonomic nervous balance and was smaller in voles than mice. The LF powers in both species were reduced by atropine, but propranolol reduced the LF power only in mice. The HF power was reduced by atropine only in voles. The intrinsic heart rate produced by a double blockade with atropine and propranolol in voles was almost the same as control levels, but in mice was lower than controls. The ratio of the LF and HF powers by a double blockade were almost the same as those of the administration of atropine in voles, but nearer to propranolol in mice. These results suggested that the parasympathetic nervous function was predominant in voles, but the sympathetic one was predominant in mice.

The authors studied power spectral analysis of heart rate variability in the rat, hypothesizing that the quantitative information provided by this analysis reflects the interaction between sympathetic and parasympathetic regulatory activities. For this purpose, an electrocardiogram was recorded from conscious and unrestrained Wistar rats (Nippon, Shizuoka) (12–16 weeks old) by a telemetry system and analyzed by a power spectrum. Because it was thought that the electrocardiogram recorded by the telemetry system could provide more reliable data to assess autonomic nervous activity than the tethering system, the telemetry recording system was used. There were two major spectral components in the power spectrum at low frequency (LF) (0.6 Hz) and high frequency (HF) (∼1.4 Hz). On the basis of these data, the authors defined two frequency bands of interest: LF (0.04–1.0 Hz) and HF (1.0–3.0 Hz). The power of LF was higher than that of HF in the normal rat. Atropine (2 mg/kg intraperitoneally) significantly reduced both HF and LF power. Propranolol (4 mg/kg intraperitoneally) also significantly reduced LF power; however, it had no significant effect on HF power. Thus, this study in the rat confirmed earlier observations in the conscious dog and human. Furthermore, the decrease in the parasympathetic mechanism produced by atropine was reflected by a slight increase in the LF/HF ratio. The LF/HF ratio appeared to follow the reductions of sympathetic activity produced by propranolol. From these results, the LF/HF ratio seemed to be a convenient index of parasympathetic and sympathetic interactions in the rat. Therefore, power spectral analysis of heart rate variability may provide a very powerful noninvasive technique for assessing autonomic nervous activity in the rat.

1. Peptides C111 (Gly-Val-Tyr-Pro-His-Lys) and C112 (Ile-Arg-Pro-Val-Gln), extracted from the autolysis product of bonito liver and intestine, have been shown to inhibit angiotensin converting enzyme (ACE) activity in vitro with IC50s of 1.6 microM and 1.4 microM, respectively. We examined the effects of oral administration of these peptides on blood pressure. 2. Oral administration of these peptides (500 mg kg-1 body weight each) inhibited the pressor effect of intravenously administered angiotensin I in Sprague-Dawley rats. 3. In spontaneously hypertensive rats, oral administration of these peptides (100-200 mg kg-1 body weight) showed depressor effects. 4. These results suggest that the peptides, C111 and C112, are orally effective ACE inhibitors with hypotensive effect.

To investigate the effects of repeated atropine injection on heart rate (HR) variability in resting Thoroughbred horses, two microg/ kg of atropine as parasympathetic nervous blockade was injected intravenously every 6 min to a total of 8 microg/kg after intravenous administration of 0.2 mg/kg of propranolol as sympathetic nervous blockade. We recorded electrocardiograms and obtained the HR, then evaluated variation in HR from the power spectrum in terms of low frequency (LF, 0.01-0.07 Hz) power and high frequency (HF, 0.07-0.6 Hz) power. Administration of atropine decreased parasympathetic nervous activity in a dose-dependent manner, affecting first the LF power, then the HF power and finally HR. These responses may provide valuable information for evaluating autonomic nervous activity in Thoroughbred horses.

Electrolyte abnormalities have become an increasingly important cause of arrhythmias. Although the electrocardiographic (ECG) changes under hyperkalemia in the rat are poorly understood, it is conceivable that excess plasma potassium may also alter the cardiac excitations in the rat. Further, effects of hyperkalemia on ECG in the rat may differ from other species that have ST-segment and longer QT intervals in ECG. The present study was designed to determine the diagnostic criteria for ECG manifestations to various levels of plasma potassium concentration. For this purpose, hyperkalemia was induced by nephrectomy with and without infusions. Because it was difficult to produce various levels of plasma potassium concentration by only nephrectomy, we used two kinds of infusions to obtain especially moderate levels of nephrectomy-induced hyperkalemia. ECGs were recorded 24, 36, and 48 hours after nephrectomy. Plasma potassium concentration and number of abnormal ECGs were increased time-dependently. Increased T wave amplitude was present with mild hyperkalemia. The typical T wave change observed with so-called sinoventricular conduction levels of potassium concentration in species with long QT intervals did not occur in the rat. PR interval and QRS duration became slightly shorter within moderate hyperkalemia. P wave disappeared in most rats at potassium levels above 8.0 mEq/l. In advanced hyperkalemia (plasma potassium concentration above 7.5 mEq/l), conduction in all parts of the heart was suppressed. Moreover, sinoventricular conduction appeared. Thus, the diagnostic criteria for ECG manifestations to various levels of plasma potassium concentration in the rat were demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated coronary atherosclerosis is the limiting factor for long-term survival of cardiac transplant recipients, but its pathogenesis is poorly understood. Morphologic and ultrastructural changes in suitable models may help explain the underlying mechanisms. In this study, early (3, 7, 14, and 21 days) and late (42 days) ultrastructural changes of the coronary artery were characterized in rabbit cardiac allografts. Thirty-four New Zealand white male rabbits (3.0-4.0 kg) served as donors and recipients. All recipients received cyclosporine (10 mg/kg/day i.m.) as immunosuppressant. In order to increase the normally very low cholesterol levels in rabbits, both the donor and recipient animals were fed a 0.5% cholesterol diet. Recipient animals were sacrificed between 3 days and 6 weeks after transplantation. The specimens from both donor and recipient were examined by transmission electron microscopy, immunohistochemistry, and morphometry. Our data indicate that intimal thickening was initiated with smooth muscle cell migration within 1 week after transplantation, and occurrence of macrophage-derived foam cells and vacuolized smooth muscle cells 3 weeks after transplantation. These changes occurred in the presence of an ultrastructurally intact endothelium. Platelets were only seldom seen adhering to the endothelium. In contrast, lymphocytes and monocytes were frequently found adhering to the endothelium at 2 and 3 weeks posttransplantation. From 3 weeks posttransplantation, lymphocytes were seen only occasionally in the intima but not in the media. This study suggests that early events elicit a change in the smooth muscle cells in the media to the secretory phenotype that migrates to the intima and proliferate. Lymphocyte and monocyte adhesion to the endothelium may enhance smooth muscle migration and proliferation. The large macrophage involvement may relate to the high serum cholesterol levels induced by the cholesterol diet. All these changes occurred in the presence of a structurally normal endothelium and without apparent platelet involvement.

Pleural fibrosis may complicate several types of non-exudative pleural injury. Although the pathogenesis of such lesions is poorly understood, it is conceivable that mesothelial cells may recruit fibroblasts to sites of pleural damage. In order to test this possibility, conditioned medium from cultured rat mesothelial cells was tested for chemoattractant activity towards RL-87 rat lung fibroblasts. For this purpose, rat pleural or pericardial mesothelial cells were maintained in vitro for 6 to 96 h. Conditioned medium from each source was obtained at defined culture times and tested for chemotactic activity in a 48-well microchemotaxis assembly. A progressive, time-dependent increase in fibroblast chemoattractant activity was detected in both pleural and pericardial mesothelial cell conditioned medium samples. This effect was maximal in 96-h cultures. Checkerboard analysis revealed that the conditioned medium was truly chemotactic for lung fibroblasts. Characterization of the chemoattractant demonstrated that it was a nondialyzable (greater than 16 kD), thermolabile (100 degrees C for 15 min), acid-stable (pH 2.5), trypsin-sensitive, and pepsin-sensitive protein. The chemotaxin was shown to be fibronectin, since activity was abolished, in a dose-dependent manner, by treatment with anti-rat fibronectin antiserum as well as by passage through a gelatin agarose affinity column. This product consisted of two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis of apparent molecular masses 250 and 220 kD. The secretion of a mesothelial cell-derived fibroblast chemoattractant may play a role in the response of the pleura to injury and in the pathogenesis of pleural fibrosis.

The changes with growth in the intrinsic cardiovascular functions of piglets between the ages of 2 and 12 weeks were investigated by recording simultaneously the heart rate, femoral arterial pressure, right and left intraventricular pressure, left intraventricular dP/dt, aortic flow and stroke volume before and after autonomic blockade under anesthesia with halothane. The values in cardiovascular function increased with body weight through the growing stage examined in this study, regardless of autonomic blockade. The intrinsic cardiovascular function of piglets during the growth process was regulated sympathetically in all the parameters except for stroke volume, which might be regulated autonomically through the Frank-Starling mechanism rather than autonomic nervous system.

Immunoreactive endothelin-1 (ET-1) and big-endothelin-1 (big-ET-1) were detected in conditioned medium of cultured rat pleural mesothelial cells by using sensitive sandwich-type enzyme immunoassays. The amount of both ET-1 and big-ET-1 increased time-dependently. In both instances, maximal amount was detectable in conditioned medium obtained after 72 h in culture (ET-1: 117.1 ± 30.1 pg/106 cells; big-ET-1: 2.4 ± 2.1 pg/106 cells). Fetal calf serum markedly stimulated the production of both ET-1 and big-ET-1.

Alterations of the heart rate with and without autonomic blockade were traced through the growing period in rats and pigs. The heart rates following the atropine and/or propranolol administration were measured to estimate the autonomic nervous tone. The heart rate per body weight was calculated to make a comparison between rats and piglets. The heart rate in rats under autonomic blockade (a combined injection of atropine and propranolol) increased progressively during 2 to 4 weeks of age and thereafter decreased gradually with advancing age. On the other hand, the heart rate in piglets under the same treatment decreased gradually with age tracing a similar changing pattern as of the control heart rate. The parasympathetic tone of rats was low at 2 weeks of age and became higher during 2 to 4 weeks of age, whereas that of piglets at 2 weeks of age was at almost the same high level as other weeks of age. The sympathetic tone of piglets as well as rats was highest at 2 weeks of age. In piglets, the net autonomic tone, expressed as a sum of the sympathetic and the parasympathetic tones, was maintained at the sympathetic side through the experimental period. Although the net autonomic tone of rats was also in the sympathetic side at 2 weeks of age, it inverted to the parasympathetic side later on.