No abstract

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.

The administration of certain quinolone antibiotics has been associated with a prolongation of the QT interval on electrocardiogram, and in rare cases ventricular arrhythmias such as torsades de pointes. In this in vivo study using a rabbit arrhythmia model, we assessed the proarrhythmic effects and changes in the QT interval elicited by the administration of NM394 (UFX), an active metabolite of the new quinolone antibiotic prulifloxacin, and three representative quinolones, sparfloxacin (SPFX), gatifloxacin (GFLX) and levofloxacin (LVFX). Chloralose-anesthetized rabbits were co-administered a continuous infusion of methoxamine (15 microg/kg/min) together with NaOH (vehicle, 0.2 mol/L), SPFX (2, 3, 4 mg/kg/min), GFLX (4 mg/kg/min), LVFX (4 mg/kg/min) or UFX (4 mg/kg/min) via the ear vein, and then the effects on electrocardiogram were examined. SPFX and GFLX both prolonged the QT and QTc intervals. GFLX also induced premature ventricular contractions in all 6 rabbits that received it, and subsequently it induced torsades de pointes (TdP) in 3 of the 6 rabbits. SPFX infused at the dose of 4 mg/ kg/min induced conduction blocks without inducing TdP, whereas that infused at the lower dose of 3 mg/ kg/min induced both conduction blocks and TdP. The infusions with LVFX and UFX did not elicit remarkable prolongations in the QT interval, and none of the animals infused with the agents developed arrhythmia. These findings suggested that LVFX and UFX were less potent than SPFX and GFLX in prolonging the QT interval and inducing life-threatening arrhythmias.

Abstract:We studied the characteristics of the rhythmicity of heart rate (HR), body temperature (BT), and locomotor activity (LA) in conscious and unrestrained guinea pigs using a telemetry system. HR and/or LA in some guinea pigs clearly showed circadian rhythms, but in others there were no significant daily patterns; BT did not show significant daily rhythms. These results suggest that guinea pigs might have different individual characteristics of rhythmicity, and we should, therefore, be careful when using guinea pigs in chrono-biomedical research. We believe that the results of this study may be useful for future biomedical studies using guinea pigs.

Many epidemiological studies have shown that polyphenols can reduce the risk of mortality from cardiovascular diseases. This study tested the hypothesis that cacao liquor polyphenols have the properties to restore the cardiovascular and autonomic nervous function in an animal model of familial hypercholesterolaemia. Male Kurosawa and Kusanagihypercholesterolaemic rabbits were housed in individual cages in a room where a 12-hr light:dark cycle (lights-on at 8:00 and lights-off at 20:00) was maintained. At 3 months of age, they were divided into two groups (standard diet and cacao liquor polyphenol) and the animals received 100 g of the respective diets per day and were provided with tap water ad libitum . Heart rate and blood pressure were measured by a telemetry system. To clarify the autonomic nervous function, power spectral analysis of heart rate variability, baroreflex sensitivity and autonomic nervous tone were measured. After 6 months of dietary administration of cacao liquor polyphenols, heart rate and blood pressure were lowered but plasma lipid concentrations were unchanged. The area of atherosclerotic lesions in the aorta in the cacao liquor polyphenol group was significantly smaller than that in the standard diet group. The high-frequency power of heart rate variability in the rabbits in the standard diet group was significantly decreased with ageing, but that in the cacao liquor polyphenol group was not different between short-term and long-term treatment. Moreover, cacao liquor polyphenols preserved parasympathetic nervous tone, although that in the standard diet group was significantly decreased with ageing. We conclude that cacao liquor polyphenols may play an important role to protect cardiovascular and autonomic nervous functions.