The myogenic response in uremic hypertension.

BACKGROUND: The constriction of resistance arteries in response to an increase in transmural pressure, the myogenic response, is thought to be an important determinant of peripheral vascular resistance and therefore of arterial blood pressure. Since raised peripheral resistance is known to occur in uremic hypertension, abnormal myogenic constriction might be responsible. We sought to assess the myogenic response of resistance arteries from the subtotal nephrectomy rat model of uremic hypertension. METHODS: Uremic Wistar-Kyoto (WKYU) rats, and sham-operated normotensive (WKYC) and spontaneously hypertensive (SHRC) controls were studied in parallel. Skeletal muscle arteries were mounted on a pressure myograph and allowed to develop myogenic constriction. The active internal diameter was measured at increasing lumen pressures from 20 to 200 mm Hg. Vascular smooth muscle then was relaxed in a calcium free solution containing nitroprusside, and the passive internal diameter measured at the same pressure steps. The ratio of active to passive diameter at any given pressure was used to assess the myogenic response. RESULTS: Myogenic constriction was not increased in either WKYU or SHRC compared to WKYC at pressures up to 180 mm Hg. CONCLUSIONS: Increased myogenic tone is not the cause of uremic hypertension.

Factor analysis can be a useful standard setting tool in a high stakes OSCE assessment.

BACKGROUND: No method of standard setting for objective structured clinical examinations (OSCEs) is perfect. Using scores aggregated across stations risks allowing students who are incompetent in some core skills to pass an examination, which may not be acceptable for high stakes assessments. AIM: To assess the feasibility of using a factor analysis of station scores in a high stakes OSCE to derive measures of underlying competencies. METHODS: A 12-station OSCE was administered to all 192 students in the penultimate undergraduate year at the University of Aberdeen Medical School. Analysis of the correlation table of station scores was used to exclude stations performing unreliably. Factor analysis of the remaining station scores was carried out to characterise the underlying competencies being assessed. Factor scores were used to derive pass/fail cut-off scores for the examination. RESULTS: Four stations were identified as having unpredicted variations in station scores. Analysis of the content of these stations allowed the underlying problems with the station designs to be isolated. Factor analysis of the remaining 8 stations revealed 3 main underlying factors, accounting for 53% of the total variance in scores. These were labelled "examination skills", "communication skills" and "history taking skills". CONCLUSION: Factor analysis is a useful tool for characterising and quantifying the skills that are assessed in an OSCE. Standard setting procedures can be used to calculate cut-off scores for each underlying factor.

Cardiac troponin T and creatine kinase MB content in skeletal muscle of the uremic rat.

BACKGROUND: The assertion that creatine kinase MB (CK-MB) and the developmental isoforms of cardiac troponin T (cTnT) are expressed by skeletal muscle in some clinical settings is an extrapolation from nonuremic rodent studies. We studied the content of CK-MB and cTnT in skeletal muscle of the renal-insufficient rat. METHODS: Skeletal muscles (gastrocnemius) were collected from both five-sixths nephrectomized rats (n = 11) and sham-operated controls (n = 11). cTnT content was analyzed by Elecsys (Roche), immunoblotting, and immunohistochemistry with antibodies M7 and M11-7 (Roche). CK isoenzymes were analyzed electrophoretically. RESULTS: Trace concentrations of cTnT were detected in some of the skeletal muscle samples [controls (3 of 11) and uremic rats (1 of 11)] at concentrations <0.01% of that detected in heart. By contrast, positive staining appeared in both groups with M11-7 by immunoblotting and immunohistochemistry. No immunoreactivity was detected in skeletal muscle using M7 in the immunoblot format, although immunoreactivity was detected by immunohistochemistry in all samples. The median percentages of CK-MB were 6.0% and 4.1% for the skeletal muscle from control and uremic rats, respectively. CONCLUSION: The detection of cTnT and CK-MB in skeletal muscle does not differ for uremic rats compared with sham-operated controls. cTnT isoforms detected by qualitative methods are not detected with the cTnT immunoassay. Observations with rodents should not necessarily be extrapolated to humans.

Calpain is activated in experimental uremia: is calpain a mediator of uremia-induced myocardial injury?

BACKGROUND: The cysteine proteases calpain and caspase-3 are known mediators of cell death. The aim of this study was to assess their contribution to the tissue damage found in experimental uremia. METHODS: Calpain and caspase-3 activities were measured in the hearts of rats that were sham-operated (control), sham-operated and spontaneously hypertensive (SHR), and those rendered uremic by 5/6 nephrectomy (uremic). In an in vitro study, heart myoblasts (Girardi) were incubated with human serum from healthy subjects (control serum conditioned media, CSCM) or uremic patients (uremic serum conditioned media, USCM), in the presence and absence of calpain and caspase-3 inhibitors. After 48 hours the activity of calpain and caspase-3 was measured, and cell injury determined by DNA fragmentation (ELISA) and lactate dehydrogenase (LDH) release. An in situ assay was designed to study how USCM affects calpain activity over time. RESULTS: In the in vivo study, mean calpain activities were almost identical in the control and SHR groups, but calpain and caspase-3 activities were much elevated in the uremic group (P < 0.01 and 0.001 respectively vs. control). The SHR group had significantly higher mean arterial blood pressure (P < 0.001 vs. control, 0.01 vs. uremic). In the in vitro study calpain activity and DNA fragmentation were markedly higher in USCM treated cells compared to CSCM (both P<0.05). Both were reduced in USCM cells containing calpain inhibitors (E64d, calpastatin, or PD 150606). LDH release was raised also in USCM treated cultures (P < 0.05), which only the E64d treatment could significantly reduce (P < 0.02). Caspase-3 activities were similar in USCM and CSCM groups. The in situ assay showed significant increases in calpain activity in USCM treated cells compared to CSCM after just 3.5 hours (P<0.01). CONCLUSIONS: In vivo results suggest that the increases in calpain and caspase-3 activity in uremic rat hearts were primarily due to uremia and not to hypertension. In vitro data demonstrate that uremia-induced cell injury can be attenuated by calpain inhibition. Therefore, it is likely that calpain is a mediator of uremia-induced myocardial injury.