Core temperature circadian rhythm across aging in Spontaneously Hypertensive Rats.

The purpose of this study was to evaluate the circadian rhythm of core temperature (Tcore) across aging in Spontaneously Hypertensive Rats (SHR) with comparison to the two rat strains often used as their normotensive control animals, namely, Wistar (WIS) and Wistar Kyoto (WKY). METHODS: WIS, WKY and SHR rats were subdivided into three different groups according their age: WIS16, WIS48, WIS72, WKY16, WKY48, WKY72, SHR16, SHR48 and SHR72 weeks-old. Body mass and blood pressure were periodically measured along the experiments. All animal group had their circadian rhythm of Tcore evaluated over three consecutive days (72 h) by telemetry using an implanted temperature sensor. The Tcore circadian rhythm was averaged in 1-h blocks and analyzed using the cosinor method. RESULTS: Sixteen-week-old SHR (SHR16) presented higher Tcore than WIS16 (from 06am to 06pm) and WKY16 (from 07am to 06pm). Both normotensive groups exhibited increases in Tcore during circadian rhythm with aging. The cosinor analysis showed no differences between strains and ages for the acrophase. An age effect on the SHR strain (SHR16 < SHR72) was observed regarding the amplitude. SHR16 had higher values regarding MESOR compared to WIS16 and WKY16. In addition, WIS72 and WKY72 showed higher values than WIS16 and WKY16, respectively. Finally, no differences were observed in the strength rhythm analysis. CONCLUSIONS: SHR presented impaired thermoregulatory control at only 16 weeks of age when showing a higher body temperature during the activity phase, while other circadian rhythm parameters showed no differences across aging. Therefore, in taking our results as a whole we can conclude that WIS and WKY are appropriate Wistar strains to be used as normotensive controls for SHR.

Meniscal allograft transplantation in rabbit.

This study evaluated the technique for meniscal allograft transplantation using allografts preserved in glycerin 98% in rabbits. Euthanasia was performed at 70 days to compare the transplanted (TM1 to TM16) versus the contralateral meniscus (OM1 to OM16). Sixteen menisci, 8 transplanted and 8 contralateral, were submitted to gross examination, histomorphometric analysis for identification and quantification of cellular type, and for quantification and distribution of collagen fibers. A revascularization study was conducted in all of the other samples. Lengths of the OM varied from 0.9 to 1.0 cm and two TM were smaller. All TM were completely attached to the synovial membrane, except for one case that presented partial fixation. Both, TM and OM had similar amounts of chondrocytes, fibroblasts and fibrocytes, and at the horns, chondrocytes were predominant. The collagen fibers in TM were well organized throughout the body, and disorganized at the horns. These fibers in OM were organized. The amounts of collagen type I and III, and the vascularization of the perimeniscal tissue and of the edge were similar in OM and TM. These results demonstrated graft integration and thus this transplantation technique and preservation method may be recommended.

Acute and chronic observations of complete atrioventricular block in rats.

The mechanisms of production, and gross, microscopic and electrocardiograhic findings of surgically-induced complete heart block (CHB) in the adult rat are presented. This is an effective in vivo model for establishing alternative methods to electronic pacemakers and for providing detailed information aimed at replacement, reduction and refinement of the technique. Sternal thoracotomy was employed to identify the epicardial fat pad by the aortic root, used as a landmark for cauterization of the atrioventricular (AV) node. Stable CHB was produced in 60 rats with a 70% survival rate. The best survival rate was observed in 8-week-old animals weighing 221 ± 27.6 g. Heart rate before cauterization was 387 ± 55 bpm, reduced after cauterization to 126 ± 40 bpm in the survival and to 65 ± 19 bpm in the non-survival groups. At 30 days findings were: elevated left ventricular end-diastolic pressure (21 ± 5.4 mmHg, P < 0.05); maximal rate of rise of left ventricular pressure (LVP) during isovolumetric contraction (2192 ± 235 mmHg/s, P < 0.05); maximal rate of decrease of LVP (-1658 ± 191 mmHg/s, P < 0.05); isovolumetric relaxation constant (5.7 ± 0.8 ms, P < 0.05) with wet-to-dry lung-weight ratio (78.1 ± 0.4, P < 0.05); heart weight/body weight (0.6 ± 0.1, P < 0.05); heart volume (1.8 ± 0.3 mL, P < 0.05); longitudinal diameter (20.2 ± 1.91 mm, P < 0.05); and transversal diameter (17.0 ± 1.4 mm, P < 0.05) with supported dilated cardiomyopathy which culminated in chronic heart failure. CHB hearts had increased preload and replacement of myofibrils by collagen. CHB was achieved reproducibly by cauterization of the rat AV node and/or His bundle. This led to electrophysiological, hemodynamic, and structural remodeling, and could be useful in long-term cardiac remodeling assessments and potential therapy development.