Reduced susceptibility to ventricular tachyarrhythmias in rats selectively bred for high aerobic capacity

Reperfusion after a brief period of cardiac ischemia can lead to potentially lethal arrhythmias. Human epidemiological studies and experimental work with animals indicate that regular physical activity is associated with reductions in cardiovascular disease (CVD) risk factors and sudden cardiac death. Similarly, artificial selection of rats for high aerobic treadmill-running capacity (high-capacity runners; HCR) has been shown to reduce CVD risk factors relative to rats selected as low-capacity runners (LCR). Therefore, we tested the hypothesis that HCR, relative to LCR rats, would be less susceptible to ischemia-reperfusion-mediated ventricular tachyarrhythmias. To test this hypothesis, we measured the susceptibility to ventricular tachyarrhythmias produced by 3 min of occlusion and reperfusion of the left main coronary artery in conscious LCR and HCR rats. Results document a significantly lower incidence of ventricular tachyarrhythmias in HCR (3 of 11, 27.3%) relative to LCR (6 of 7, 85.6%) rats. The decreased susceptibility to tachyarrhythmias in HCR rats was associated with a reduced cardiac metabolic demand during ischemia (lower rate-pressure product and ST segment elevation) as well as a wider range for the autonomic control of heart rate. The HCR and LCR represent a unique substrate for evaluation of the mechanisms underlying ischemia-mediated cardiac arrhythmogenesis.     

Effects of sequential biventricular pacing during acute right ventricular pressure overload

Temporary sequential biventricular pacing (BiVP) is a promising treatment for postoperative cardiac dysfunction, but the mechanism for improvement in right ventricular (RV) dysfunction is not understood. In the present study, cardiac output (CO) was optimized by sequential BiVP in six anesthetized, open-chest pigs during control and acute RV pressure overload (RVPO). Ventricular contractility was assessed by the maximum rate of increase of ventricular pressure (dP/dt(max)). Mechanical interventricular synchrony was measured by the area of the normalized RV-left ventricular (LV) pressure diagram (A(PP)). Positive A(PP) indicates RV pressure preceding LV pressure, whereas zero indicates complete synchrony. In the control state, CO was maximized with nearly simultaneous stimulation of the RV and LV, which increased RV (P = 0.006) and LV dP/dt(max) (P = 0.002). During RVPO, CO was maximized with RV-first pacing, which increased RV dP/dt(max) (P = 0.007), but did not affect LV dP/dt(max), and decreased the left-to-right, end-diastolic pressure gradient (P = 0.023). Percent increase of RV dP/dt(max) was greater than LV dP/dt(max) (P = 0.014). There were no increases in end-diastolic pressure to account for increases in dP/dt(max). In control and RVPO, RV dP/dt(max) was linearly related to A(PP) (r = 0.779, P < 0.001). The relation of CO to A(PP) was curvilinear, with a peak in CO with positive A(PP) in the control state (P = 0.004) and with A(PP) approaching zero during RVPO (P = 0.001). These observations imply that, in our model, BiVP optimization improves CO by augmenting RV contractility. This is mediated by changes in mechanical interventricular synchrony. Afterload increases during RVPO exaggerate this effect, making CO critically dependent on simultaneous pressure generation in the RV and LV, with support of RV contractility by transmission of LV pressure across the interventricular septum.     

Biphasic regulation by bile acids of dermal fibroblast proliferation through regulation of cAMP production and COX-2 expression level

We have previously reported that the bile acids chenodeoxycholate (CDCA) and ursodeoxycholate (UDCA) decreased PGE1-induced cAMP production in a time- and dose-dependent manner not only in hepatocytes but also in nonhepatic cells, including dermal fibroblasts. In the present study, we investigated the physiological relevance of this cAMP modulatory action of bile acids. PGE1 induced cAMP production in a time- and dose-dependent manner. Moreover, PGE1 (1 µM), forskolin (1–10 µM), and the membrane-permeable cAMP analog CPT-cAMP (0.1–10 µM) decreased dermal fibroblast proliferation in a dose-dependent manner with a maximum inhibition of 80%. CDCA alone had no significant effect on cell proliferation at a concentration up to 25 µM. However, CDCA significantly reduced PGE1-induced cAMP production by 80–90% with an EC₅₀ of 20 µM. Furthermore, at concentrations 25 µM, CDCA significantly attenuated the PGE-1-induced decreased cell proliferation. However, at concentrations of 50 µM and above, while still able to almost completely inhibit PGE-1-induced cAMP production, CDCA, at least in part through an increased cyclooxygenase-2 (COX-2) expression level and PGE2 synthesis, produced a direct and significant decrease in cell proliferation. Indeed, the CDCA effect was partially blocked by 50–70% by both indomethacin and dexamethasone. In addition, overexpression of COX-2 cDNA wild type resulted in an increased efficacy of CDCA to block cell proliferation. The effects of CDCA on both cAMP production and cell proliferation were similar to those of UDCA and under the same conditions cholate had no effect. Results of the present study underline pathophysiological consequences of cholestatic hepatobiliary disorders, in which cells outside of the enterohepatic circulation can be exposed to elevated bile acid concentrations. Under these conditions, low bile acid concentrations can attenuate the negative hormonal control on cell proliferation, resulting in the stimulation of cell growth, while at high concentrations these bile acids provide for a profound and prolonged inhibition of cell proliferation. chenodeoxycholic acid; cyclic adenosine monophosphate     

Initiation of remote microvascular preconditioning requires K(ATP) channel activity

The purpose of this study was to investigate vascular preconditioning of individual microvascular networks. Prior work shows that exposure of downstream arterioles to specific agonists preconditions upstream arterioles so that they exhibit an altered local vasoactive response [remote microvascular preconditioning (RMP)]. We hypothesized that mitochondrial ATP-sensitive K+ (K(ATP)) channels were involved in stimulation of RMP. Arteriolar diameter (approximately 15 microm) was observed approximately 1,000 microm upstream of the remote exposure site in the cheek pouch of pentobarbital sodium-anesthetized (70 mg/kg) male hamsters (n = 104); all agonists were applied via micropipette. RMP was initiated by application of pinacidil (Pin), diazoxide (DZ), sodium nitroprusside (SNP), or bradykinin (BK) to the downstream vessel. After 15 min, RMP was apparent at the upstream observation site from testing of local vasoactive responses to L-arginine. Pin, DZ, SNP, and BK each stimulated RMP. To evaluate a specific role for mitochondrial K(ATP) channels in this response, 5-hydroxydecanoate was applied (via a 2nd pipette) during downstream stimulation with agonist. 5-Hydroxydecanoate blocked RMP initiated by Pin, DZ, or SNP, suggesting that mitochondrial K(ATP) channels are involved before SNP signal transduction. To verify this, we applied N(omega)-nitro-L-arginine during DZ or SNP stimulation. RMP was blocked during SNP, but not during DZ, stimulation. Thus stimulation of the RMP response requires mitochondrial K(ATP) channel activity after stimulation by nitric oxide donors.     

Osteoblast-conditioned media influence the expression of E-selectin on bone-derived vascular endothelial cells

Breast cancer cells frequently metastasize to the ends of long bones, ribs and vertebrae, structures which contain a rich microvasculature that is closely juxtaposed to metabolically active trabecular bone surfaces. This study focuses on the effects of osteoblast secretions on the surface presentation of adhesive proteins on skeletal vascular endothelial cells. Vascular endothelial cells were isolated from trabecular bone regions of the long bones of 7-week-old Swiss Webster mice and also from the central marrow cavity where trabecular bone is absent. Both types of endothelial cells were placed in culture for 7 days, then exposed 24 h to conditioned media from MC3T3-E1 osteoblasts. Conditioned medium (CM) from two different stages of osteoblast development were tested: (1) from immature MC3T3-E1 cells cultured for 5-7 days and (2) from mature MC3T3-E1 cells cultured for 28-30 days. The immature osteoblasts were in a stage of rapid proliferation; the mature osteoblasts formed a matrix that mineralized. Following exposure to the conditioned media, the vascular cells were exposed to anti-P-selectin, anti-E-selectin, anti-ICAM-1, and anti-VCAM-1 to detect the corresponding adhesive proteins on their surfaces. Breast cancer cells are known to bind to these adhesive proteins. Of the four proteins evaluated, E-selectin was consistently found on more cell surfaces (approximately 30%) of bone-derived vascular endothelial cells (BVECs) when exposed to the immature CM whereas vascular endothelial cells from marrow (MVECs) did not show this response to either immature CM or mature CM. These studies suggest that the BVEC blood vessels near immature bone cells express more surface adhesive protein that could enhance entrapment and extravasation of breast cancer cells. Once cancer cells have undergone extravasation into marrow adjacent to bone, they could be readily attracted to nearby bone surfaces.     

Endometrial and endocervical secretion: the search for histochemical differentiation

OBJECTIVE: To determine the ideal histochemical stain to differentiate between non-neoplastic and neoplastic endocervix and endometrium. STUDY DESIGN: A total of 90 cases representing nonneoplastic cervix, non-neoplastic endometrium, endocervical adenocarcinoma and endometrial adenocarcinoma were stained with toluidine blue (TB); methylene blue (MB); mucicarmine (MUC); periodic acid-Schiff before and after diastase digestion (PAS, PAS-D); Alcian blue, pH 2.5 (AB); and periodic acid-Schiff after Alcian blue, pH 2.5 (PAB). Cases were blinded and randomly divided between two pathologists for evaluation of the staining and the staining distribution of the glandular epithelium by means of a 36-color scheme. RESULTS: The majority of non-neoplastic endocervix samples stained blue with MB (57%), fuchsia with MUC (70%), magenta with PAS (77%) and PAS-D (73%) and dark turquoise with AB (70%). The majority of non-neoplastic endometrium samples stained slate blue with TB (60%) and pink with PAS-D (53.3%). There is statistical difference (p < 0.05) in the color of the epithelium and secretions between the non-neoplastic cervix and endometrium. The malignant glands of endocervical origin could be differentiated significantly (p = 0.043) from non-neoplastic endocervical epithelium by MUC. The epithelium of the non-neoplastic endometrium is significantly differentiated from malignant endometrium using TB (p = 0.015) and MB (p = 0.038). Endocervical carcinoma could be significantly differentiated from endometrial carcinoma by MB. The staining in endocervical adenocarcinoma and endometrial carcinoma was predominantly present in both apical and cytoplasmic locations compared to their non-neoplastic counterparts (endocervix, p = 0.003; endometrium, p = 0.049). CONCLUSION: This study showed that a panel of histochemical stains could differentiate glandular cells of endocervical epithelium from endometrium.     

The non-typeable Haemophilus influenzae Sap transporter provides a mechanism of antimicrobial peptide resistance and SapD-dependent potassium acquisition

We have shown that non-typeable Haemophilus influenzae (NTHI) resists killing by antimicrobial peptides (APs). A mutant defective in expression of the sap (sensitivity to antimicrobial peptides) gene cluster product SapA is sensitive to killing by APs and is significantly attenuated in its ability to survive in a chinchilla model of otitis media compared with the parent strain. In NTHI, SapA is believed to function as the periplasmic solute binding protein of an ABC transporter. Here, we demonstrated that recombinant chinchilla beta defensin-1 specifically interacted with recombinant SapA and that AP exposure increased expression of the sap operon. We further demonstrated that the putative Sap transporter ATPase protein, SapD, was required for AP resistance as well as potassium uptake in NTHI strain 86-028NP. Loss of SapD additionally abrogated NTHI survival in vivo. Complementation of the sapD mutation restored the ability to grow in potassium-limited medium, resistance to AP-mediated killing and survival in vivo. Collectively, these data support a mechanism of Sap system-mediated resistance to APs that depends on Sap-dependent transport of APs and a Sap-dependent restoration of potassium homeostasis. Thus, NTHI required a functional Sap system to mediate bacterial survival and pathogenesis in vivo.     

Gustatory processing: a dynamic systems approach

Recent gustatory studies have provided a growing body of evidence that taste processing is dynamic and distributed, and the taste system too complex to be adequately described by traditional feed-forward models of taste coding. Current research demonstrates that neuronal responses throughout the gustatory neuroaxis are broad, variable and temporally structured, as a result of the fact that the taste network is extensive and heavily interconnected, containing modulatory pathways, many of which are reciprocal. Multimodal influences (e.g. olfactory and somatosensory) and effects of internal state (e.g. attention and expectation), shown in both behavioral and neuronal responses to taste stimuli, add further complexity to neural taste responses. Future gustatory research should extend to more brain regions, incorporate more connections, and analyze behaviors and neuronal responses in both time- and state-dependent manners.     

Network frailty and the geometry of herd immunity

The spread of infectious disease through communities depends fundamentally on the underlying patterns of contacts between individuals. Generally, the more contacts one individual has, the more vulnerable they are to infection during an epidemic. Thus, outbreaks disproportionately impact the most highly connected demographics. Epidemics can then lead, through immunization or removal of individuals, to sparser networks that are more resistant to future transmission of a given disease. Using several classes of contact networks-Poisson, scale-free and small-world-we characterize the structural evolution of a network due to an epidemic in terms of frailty (the degree to which highly connected individuals are more vulnerable to infection) and interference (the extent to which the epidemic cuts off connectivity among the susceptible population that remains following an epidemic). The evolution of the susceptible network over the course of an epidemic differs among the classes of networks; frailty, relative to interference, accounts for an increasing component of network evolution on networks with greater variance in contacts. The result is that immunization due to prior epidemics can provide greater community protection than random vaccination on networks with heterogeneous contact patterns, while the reverse is true for highly structured populations.