Validity and Reproducibility of an Incremental Sit-To-Stand Exercise Test for Evaluating Anaerobic Threshold in Young,Healthy Individuals

Sit-to-stand exercise (STS) is a common activity of daily living. The objectives of the present study were: 1) to assess the validity of aerobic fitness measurements based on anaerobic thresholds (ATs), during incremental sit-to-stand exercise (ISTS) with and without arm support compared with an incremental cycle-ergometer (CE) test; and 2) to examine the reproducibility of the AT measured during the ISTSs. Twenty-six healthy individuals randomly performed the ISTS and CE test. Oxygen uptakes at the AT (AT-VO₂) and heart rate at the AT (AT-HR) were determined during the ISTSs and CE test, and repeated-measures analyses of variance and Tukey’s post-hoc test were used to evaluate the differences between these variables. Pearson correlation coefficients were used to assess the strength of the relationship between AT-VO₂ and AT-HR during the ISTSs and CE test. Data analysis yielded the following correlations: AT-VO₂ during the ISTS with arm support and the CE test, r = 0.77 (p < 0.05); AT-VO₂ during the ISTS without arm support and the CE test, r = 0.70 (p < 0.05); AT-HR during the ISTS with arm support and the CE test, r = 0.80 (p < 0.05); and AT-HR during the ISTS without arm support and the CE test, r = 0.66 (p < 0.05). The AT-VO₂ values during the ISTS with arm support (18.5 ± 1.9 mL·min^-1·kg^-1) and the CE test (18.4 ± 1.8 mL·min^-1·kg^-1) were significantly higher than those during the ISTS without arm support (16.6 ± 1.8 mL·min^-1·kg^-1; p < 0.05). The AT-HR values during the ISTS with arm support (126 ± 10 bpm) and the CE test (126 ± 13 bpm) were significantly higher than those during the ISTS without arm support (119 ± 9 bpm; p < 0.05). The ISTS with arm support may provide a cardiopulmonary function load equivalent to the CE test; therefore, it is a potentially valid test for evaluating AT-VO2 and AT-HR in healthy, young adults.

Key points

• The ISTS is a simple test that varies only according to the frequency of standing up, and requires only a small space and a chair.
• The ISTS with arm support is valid and reproducible, and is a safe test for evaluating AT in healthy young adults.
• For evaluating the AT, the ISTS may serve as a valid alternative to conventional CPX, using either a cycle ergometer or treadmill, in cases where the latter methods are difficult to implement.

Key words: Sit-to-stand, cycle ergometer, anaerobic threshold, correlations, reproducibility, validity     

Comparison of the point-by-point versus catheter dragging technique for curative radiofrequency ablation of atrial fibrillation

Background: The relationship between the applied techniques and clinical outcomes after radiofrequency (RF) ablation of atrial fibrillation (AF) remains unclear. We compared the results of ablation by RF delivered via a point‐by‐point versus catheter dragging technique for the treatment of AF. Methods: This study included 66 patients with drug‐refractory AF who underwent circumferential pulmonary vein (PV) ablation. A point‐by‐point technique was used in 35 (53%) patients (Group I), and catheter dragging technique in the remaining 31 (47%) patients (Group II). If AF persisted or remained inducible after the PV isolation, additional ablation of complex fractionated atrial electrograms and linear ablation were performed. Results: Significantly, fewer RF applications were delivered in Group II than in Group I. The total RF energy duration delivered was comparable between the two groups (P = 0.55). However, the total energy of RF deliveries was significantly greater in Group II than in Group I (P = 0.02). Despite a longer fluoroscopic exposure time (P = 0.01), the total procedural duration was significantly shorter in Group II than in Group I (P = 0.005). Within 3 months after a single ablation procedure, 24 patients (69%) in Group I versus 13 patients (42%) in Group II had ≥1 recurrence(s) of atrial tachyarrhythmias (P = 0.03). A multivariate analysis showed that a point‐by‐point ablation was the only independent predictor of early atrial tachyarrhythmia recurrences. Conclusions: The catheter dragging technique for ablation of AF was associated with a lower early recurrence rate of atrial tachyarrhythmias than the point‐by‐point technique. (PACE 2011; 15–22)     

AU-1 from Agavaceae plants causes transient increase in p21/Cip1 expression in renal adenocarcinoma ACHN cells in an miR-34-dependent manner

Here, we show that AU-1, spirostanol saponin isolated from Agavaceae plants, causes a transient increase in cyclin-dependent kinase inhibitor (CDKI) p21/Cip1 through the upregulation of miRNAs, miR-34 and miR-21. AU-1 stimulated p21/Cip1 expression without exerting cytotoxicity against different types of carcinoma cell lines. In renal adenocarcinoma ACHN cells, AU-1 transiently elevated the expression level of p21/Cip1 protein without marked increases in p21/Cip1 mRNA levels. Rapid and transient increases in miR-34 and miR-21, both of which are known to upregulate p21/Cip1, were observed in AU-1-treated cells. Inhibitor for miR-34 and for miR-21 significantly blocked the AU-1-caused increase in p21/Cip1, indicating that elevation of p21/Cip1 protein by AU-1 is dependent on these microRNAs. We further clarified that NAD-dependent deacetylase SIRT1, a direct target of miR-34, is decreased by the treatment with AU-1. Furthermore, we found that SIRT1-knockdown increases p21/Cip1 protein levels in an miR-21-dependent manner. On the other hand, ectopic expression of p21/Cip1 resulted in the lowered expression of miR-34 and miR-21, suggesting that reciprocal regulation exists between p21/Cip1 and these miRNAs. We propose that the following feedback network composed of miR-34/SIRT1/miR-21/p21 is triggered by the treatment with AU-1: in cells treated with AU-1, transient elevation of miR-34 leads to the downregulation of SIRT1, thereby miR-21 is freed from SIRT1-dependent suppression. Then, elevated miR-21 upregulates p21/Cip1 protein, followed by the suppression of miR-34 expression.     

Thrombin stimulates the production of immunoreactive endothelin-1 in cultured human umbilical vein endothelial cells

The present study was designed to examine the effect of thrombin on endothelin production by cultured human umbilical vein endothelial cells (HUVEC) by radioimmunoassay. Cultured HUVEC released immunoreactive endothelin-1 (ir-endothelin-1) into the medium in a time-dependent manner. This release was inhibited completely by 10 micrograms/mL cycloheximide and is, therefore, directly related to de novo protein synthesis. Further endothelin release was stimulated by the addition of thrombin to the culture medium. Thrombin-induced ir-endothelin-1 release also was inhibited completely by 10 micrograms/mL cycloheximide. These results suggest that HUVEC in culture produce ir-endothelin-1 slowly, but continuously, and that this production is stimulated by thrombin.     

Pharmacological characterization of the voltage-dependent calcium channel of pancreatic B-cell

Pharmacological characteristics of the voltage-dependent calcium channel (VDCC) of the pancreatic B-cell were studied using omega-conotoxin (omega CgTX) and dihydropyridine (DHP) calcium channel blockers. High glucose and potassium (K+) depolarization were employed as the stimulant of insulin release. omega CgTX (greater than 50 nM), a blocker of neural, but not muscular, Ca2+ channels, partially blocked (27%) the second, but not the first, phase of glucose-induced insulin release without a significant effect on K+ depolarization-induced insulin release. The DHP Ca2+ channel blocker nifedipine inhibited both phases of glucose-induced insulin release (ED50 = 200 nM) and completely abolished both phases of response at 10 microM. In contrast, the DHP Ca2+ channel blocker only partially suppressed (75% at 10 microM) K+ depolarization-induced insulin release with an ED50 of 100 nM. We conclude that pancreatic B-cell possesses at least two classes of VDCCs; one is DHP sensitive, and the other DHP insensitive. Partial suppression of the second phase of glucose-induced insulin release by a high concentration of omega CgTX may be due to its toxic effect on the secretory machinery other than VDCC.     

C-type natriuretic peptide inhibits thrombin- and angiotensin II-stimulated endothelin release via cyclic guanosine 3',5'-monophosphate.

We examined the inhibitory effect of porcine C-type natriuretic peptide (CNP) on endothelin-1 secretion stimulated by thrombin and angiotensin II (Ang II) in cultured porcine endothelial cells. The results were compared with the effects of atrial (ANP) and brain (BNP) natriuretic peptides. Thrombin and Ang II produced a concentration-dependent stimulation of immunoreactive endothelin-1 secretion, and porcine CNP-22 potently inhibited this stimulated secretion in a concentration-dependent manner. CNP-22 had a stronger inhibitory effect than either porcine ANP(1-28) or porcine BNP-26. In addition, CNP potently increased the cellular level of cyclic guanosine 3',5'-monophosphate (GMP), with the inhibition of immunoreactive endothelin-1 secretion in response to thrombin and Ang II being paralleled by the increase in the cyclic GMP level. The increase of cyclic GMP produced by CNP was also greater than that due to porcine ANP(1-28) or porcine BNP-26. The immunoreactive endothelin-1 in the culture medium had two components on high-performance liquid chromatography; the major one corresponded to endothelin-1 (1-21) and the minor one to big endothelin-1 (porcine 1-39). Treatment with CNP did not affect this profile. Our results suggest that CNP probably inhibits the endothelin-1 secretion stimulated by thrombin and Ang II through a cyclic GMP-dependent process. The increase of cyclic GMP levels and the inhibition of immunoreactive endothelin-1 secretion produced by CNP appear to be greater than those produced by ANP or BNP.