Hemodynamic and thermoregulatory effects of xylazine-ketamine mixture persist even after the anesthetic stage in rats / Efeitos hemodinâmicos e termorregulatórios da mistura cetamina-xilasina persistem mesmo após o período anestésico em ratos

The xylazine-ketamine mixture (KX) is an anesthetic approach commonly administered to assess cardiovascular function in rodents. This study aimed to examine if the cardiovascular and thermoregulatory effects of KX could persist after the anesthetic state ceased in rats. Male Wistar rats were anesthetized with K (50mg/kg) X (10mg/kg) through the intra-peritoneal route. Hemodynamic and thermoregulatory repercussions were evaluated in animals in awake state, during an anesthetic depth and after complete recovery of anesthetized state. KX was efficient to significantly induce deep anesthesia in all rats after 10min. A complete recovery of anesthetized state was observed only after 210min. Compared with preanesthetic state and control animals that received no drug, KX induced a significant reduction of systolic and diastolic blood pressure at 10min. Hypotension was more prominent at 150min. The heart rate was also significantly reduced after 10 min of KX and the highest magnitude of bradycardia was observed at 30min. In addition, rectal temperature was markedly decreased at 30min of KX and the higher reduction occurred at 150min. The hemodynamic and thermoregulatory effects of KX were maintained even after complete anesthetic recovery.

Objetivou-se com este estudo avaliar a persistência dos efeitos cardiovasculares e termorregulatórios da associação cetamina e xilasina (CX) mesmo após o período anestésico em ratos. Ratos Wistar machos foram anestesiados com cetamina 50mg/kg e xilasina 10mg/kg, por via intra-peritoneal. As repercussões hemodinâmica e termorregulatória foram avaliadas com os animais acordados, durante o período anestésico e após recuperação completa da anestesia. A CX foi eficiente em induzir significante regime anestésico em todos os ratos após 10min. A recuperação completa do estado de anestesia foi observada somente após 210min. Comparado com o estado pré-anestésico e com animais controles, que não receberam anestesia, a CX induziu significativa redução das pressões sistólica e diastólica aos 10min. A hipotensão foi mais evidente aos 150min após CX. A frequência cardíaca também foi significativamente reduzida com 10min de CX e a bradicardia foi mais acentuada aos 30min. A temperatura retal foi reduzida aos 30min, sendo mais acentuada após 150min de anestesia. Os efeitos hemodinâmicos e termorregulatórios da CX persistem mesmo após completa recuperação anestésica.

Determination of myocardial infarction size in rats by echocardiography and tetrazolium staining: correlation, agreements, and simplifications

Triphenyltetrazolium chloride (TTC) staining and echocardiography (ECHO) are methods used to determine experimental myocardial infarction (MI) size, whose practical applicability should be expanded. Our objectives were to analyze the accuracy of ECHO in determining infarction size in rats during the first days following coronary occlusion and to test whether a simplified single measurement by TTC correctly indicates MI size, as determined by the average value for multiple slices. Infarction was induced in female Wistar rats by coronary artery occlusion and MI size analysis was performed after the acute (7th day) and chronic periods (after 4 weeks) by ECHO matched with TTC. ECHO and TTC showed similar values of MI size ( percent of left ventricle perimeter) in acute (ECHO: 33 ± 11, TTC: 35 ± 14) and chronic (ECHO: 38 ± 14, TTC: 39 ± 13 periods), and also presented an excellent correlation (r = 0.92, P < 0.001). Although measurements from different heart planes showed discrepancies, a single measurement acquired from the mid-ventricular level by TTC was a good estimate of MI size calculated by the average of multiple planes, with minimal disagreement (Bland-Altman test with mean ratio bias of 0.99 ± 0.07) and close to an ideal correlation (r = 0.99, P < 0.001). In the present study, ECHO was confirmed as a useful method for the determination of MI size even in the acute phase. Also, the single measure of a mid-ventricular section proposed as a simplification of the TTC method is a satisfactory prediction of average MI extension.

Rats with high left ventricular end-diastolic pressure can be identified by Doppler echocardiography one week after myocardial infarction

The severity of left ventricular (LV) dysfunction in rats with myocardial infarction (MI) varies widely. Because homogeneity in baseline parameters is essential for experimental investigations, a study was conducted to establish whether Doppler echocardiography (DE) could accurately identify animals with high LV end-diastolic pressure as a marker of LV dysfunction soon after MI. Direct measurements of LV end-diastolic pressure were made and DE was performed simultaneously 1 week after surgically induced MI (N = 16) or sham-operation (N = 17) in female Wistar rats (200 to 250 g). The ratio of peak early (E) to late (A) diastolic LV filling velocities and the ratio of E velocity to peak early (Em) diastolic myocardial velocity were the best predictors of high LV end-diastolic pressure (>12 mmHg) soon after MI. Cut-off values of 1.77 for the E/A ratio (P = 0.001) identified rats with elevated LV end-diastolic pressure with 90 percent sensitivity and 80 percent specificity. Cut-off values of 20.4 for the E/Em ratio (P = 0.0001) identified rats with elevated LV end-diastolic pressure with 81.8 percent sensitivity and 80 percent specificity. Moreover, E/A and E/Em ratios were the only echocardiographic parameters independently associated with LV end-diastolic pressure in multiple linear regression analysis. Therefore, DE identifies rats with high LV end-diastolic pressure soon after MI. These findings have implications for using serial DE in animal selection and in the assessment of their response to experimental therapies.

Incidence of heart failure in infarcted rats that die spontaneously

The present study reports for the first time the incidence of congestive heart failure (CHF) in previously infarcted rats that died spontaneously. Previously, pulmonary (PWC) and hepatic (HWC) water contents were determined in normal rats: 14 control animals were evaluated immediately after sacrifice, 8 placed in a refrigerator for 24 h, and 10 left at room temperature for 24 h. In the infarcted group, 9 rats died before (acute) and 28 died 48 h after (chronic) myocardial infarction. Thirteen chronic animals were submitted only to autopsy (N = 13), whereas PWC and HWC were also determined in the others (N = 15). Seven rats survived 48 h and died during anesthesia. Notably, PWC differed in normal rats: ambient (75.7 ± 1.3 percent) < control (77.5 ± 0.7 percent) < refrigerator (79.1 ± 1.4 percent) and there were no differences with respect to HWC. No clinical signs of CHF (dyspnea, lethargy or foot edema) were observed in infarcted rats before death. PWC was elevated in all chronic and anesthetized rats. HWC was increased in 48 percent of chronic and in all anesthetized rats. Our data showed that PWC needs to be evaluated before 24 h post mortem and that CHF is the rule in chronic infarcted rats suffering natural death. The congestive syndrome cannot be diagnosed correctly in rats by clinical signs alone, as previously proposed.

A routine electrocardiogram cannot be used to determine the size of myocardial infarction in the rat

Nine lead electrocardiograms of non-infarcted (N = 61) and infarcted (N = 71) female Wistar rats (200-250 g) were analyzed in order to distinguish left ventricle myocardial infarction (MI) larger than 40 percent (LMI) from MI smaller than 40 percent (SMI). MI larger than 40 percent clearly caused a deviation of AQRS and AT from normal values of 270-360 degrees to 90-270 degrees. Infarcted rats showed Q wave in D1 larger than 1 mm with 94 percent sensitivity and 100 percent specificity. The sum of QRS positivity in V1, V2 and V6 lower than 10 mm identified MI with 82 percent sensitivity and 100 percent specificity. The data showed that MI can be easily and reliably diagnosed by electrocardiogram in the rat. However, contradicting what is frequently believed, when specificity and sensitivity were analyzed focusing on MI size, none of these current electrocardiographic indices of MI size adequately discriminates LMI from SMI.