Ischemic preconditioning depends on age and gender.

UNLABELLED: The goal of this study was to determine if an ischemic preconditioning (IPC) protocol improved post-ischemic functional recovery of female mouse hearts. A previous study found that IPC did not occur in hearts from 10-week-old females. We studied Langendorff-perfused hearts from both 10- and 18-week-old mice (males and females). Hearts were subjected to 45 min ischemia and 45 reperfusion (I/R); IPC involved pretreatment with 3 min ischemia. We measured hemodynamics, infarct size and levels of the phosphorylated prosurvival kinase Akt (p-Akt). Similar to a previous study, for 10- week-old mice we found that the IPC protocol appreciably improved recovery of LV developed pressure (LVDP) for hearts from males but not females. However, for 18-week-old mice we found that the IPC protocol doubled the recovery of LVDP for both males and females. For both ages, hearts from females had greater recovery of LVDP and higher levels of p-Akt compared to males. CONCLUSIONS: These findings are consistent with growing evidence that preconditioning induced by ischemia or other interventions can occur in hearts from females. However, for hearts from females, preconditioning depends on age. Moreover, consistent with previous studies, hearts from females have greater inherent resistance to ischemic injury, possibly involving increased signaling via p-Akt.

[Biocompatibility of the acetate in the dialysis fluid]. / Biocompatibilità dell'acetato contenuto nel bagno di dialisi.

PURPOSE: Dialytic vasculopathy is a major morbidity and mortality risk factor in patients undergoing chronic dialysis treatment. Among the pathogenetic factors some are related to the uremic condition, others are due to biocompatible reactions to dialytic materials. Endothelial cells (EC) are the target of the mediators released during bioincompatible reactions, and the related effects could be considered the initial event eliciting the vasculopathy pathogenesis. Among the others, we focused our attention on the role played in this process by the inducible isoform of nitric oxide (NO) synthase (iNOS). In previous studies we demonstrated that bioincompatible membranes, as well as acetate-containing dialysis buffers stimulate iNOS gene expression and activity in endothelial cells in culture. In this study, we planned to evaluate the potential role of a new dialysis buffer in which acetate has been substituted with HCl as a stabilizer. METHODS: ECs were incubated for 12 h at 37 degrees C with different dialysis buffers: acetate (Acet), standard bicarbonate (Bic), acetate-free buffer (AF) and HCl-bicarbonate (BicHCl). We evaluated in reverse transcriptase polymerase chain reaction (RT-PCR) the gene transcription for iNOS, the NOS activity (as the production of H3 citrulline from H3 arginine by ionic exchange chromatography), EC proliferative (H3 thymidine incorporation) and pro-apoptotic rate (TUNEL analysis) and the nuclear translocation of the transcriptional factor NF-kappaB (EMSA). RESULTS: Acetate, even in the low concentration present in Bic was able to induce a significant iNOS gene transcription (results expressed as relative units and referred to basal values: Acet 1.9 +/- 0.01 fold increase, p<0.01; Bic 1.45 +/- 0.03 p<0.05; BicHCl 1.24 +/- 0.01; AF 1.17 +/- 0.02) and translation. Acetate at concentrations both of 3 mmoL and 38 mmoL (present in the bicarbonate buffer) significantly increased the enzymatic NOS activity vs unconditioned ECs: Acet 3.46 +/- 0.3, p<0.0005; Bic 1.69 +/- 0.2, p<0.005; BicHCl 1.24 +/- 0.15; AF 1.17 +/- 0.05. The EC proliferative index was significantly depressed by acetate containing dialysis buffers (unconditioned ECs 100%, Acet 38 +/- 15%, p<0.01; Bic 65 +/- 6%, p<0.05; AF 87 +/- 8%; BicHCl 75 +/- 6%). The percentage of apoptotic ECs was significantly increased by buffers contain-ing Acet vs BicHCl and AF. Finally, acetate at the concentrations present in Acet and Bic activated and promoted the nuclear translocation of the transcriptional factor NF-kappaB in ECs (p<0.01 vs unconditioned cells). CONCLUSIONS: The acetate-free dialysis buffers have better biocompatibility and potentially down-modulate the flogistic and sclerotic processes responsible for dialytic vasculopathy.

Effects of the adenylyl cyclase inhibitor SQ22536 on iloprost-induced vasorelaxation and cyclic AMP elevation in isolated guinea-pig aorta.

The stable prostacyclin analogue, iloprost relaxes a variety of blood vessels and increases cyclic AMP, although the relationship between adenosine 3': 5'-cyclic monophosphate (cyclic AMP) and vasorelaxation remains unclear. We therefore investigated the effect of the adenylyl cyclase inhibitor, 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ22536) on iloprost-mediated relaxation and cyclic AMP elevation in endothelium-denuded aortic strips. Iloprost (1-1000 nM) caused a concentration-dependent inhibition of phenylephrine (1-6 microM) contractions, the responses being unaffected by pre-incubation with SQ22536 (100 microM) for 30 min. In other experiments 60 nM iloprost caused a 64% inhibition of phenylephrine contractions concomitant with a 3 fold rise in cyclic AMP. SQ22536 completely abolished the iloprost-induced elevation in cyclic AMP while having no significant effect on relaxation. Our results therefore strongly suggest that cyclic AMP-independent pathways are responsible for the vasorelaxant effects of iloprost in guinea-pig aorta.

Evidence that Ca2+-activated K+ channels play a major role in mediating the vascular effects of iloprost and cicaprost.

The role of K+ channels in mediating vasorelaxation induced by two prostacyclin analogues was investigated in guinea-pig aorta. Iloprost caused substantial relaxation of tissues contracted with phenylephrine or 25 mM K+ but not 60 mM K+. In endothelial-denuded tissues, maximal relaxations to iloprost, cicaprost or isoprenaline were inhibited by approximately 40-50% with tetraethylammonium or iberiotoxin, both blockers of large conductance Ca2+-activated K+ (BKCa) channels. In contrast, the response to forskolin, an activator of adenylate cyclase was marginally inhibited by tetraethylammonium. The K(ATP) channel blocker, glibenclamide significantly augmented the response to iloprost but not cicaprost. These effects were largely inhibited by the EP1 receptor antagonist, 8-chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid 2-[1-oxo-3(4-pyridinyl)propyl]hydrazide, monohydrochloride (SC-51089) and partially by indomethacin, suggesting that iloprost relaxation is counterbalanced by activation of EP1 receptors, in part through a constrictor prostaglandin. We conclude that BKCa channels play an important role in mediating the effects of iloprost and cicaprost and raises the possibility that cyclic AMP-independent pathways might be involved.

Abnormal activation of K+ channels underlies relaxation to bacterial lipopolysaccharide in rat aorta.

We have examined the role of K+ channels in mediating vasorelaxation produced by bacterial lipopolysaccharide (LPS) in endothelial-denuded strips of rat aorta precontracted with phenylephrine (1 microM). Salmonella typhosa LPS (0.1 microgram/ml) caused significant relaxation of tension which peaked at approximately 4hr. The K+ channel blocker, tetraethylammonium chloride (TEA; 10 mM), fully reversed these relaxations whether applied before or after long term exposure to LPS. L-arginine, the substrate for nitric oxide synthase, caused large relaxations in tissues incubated with LPS that were markedly inhibited by TEA. In contrast, TEA or L-arginine had little effect on phenylephrine contractions in control tissues. Furthermore, the inducible nitric oxide synthase inhibitor, aminoguanidine (0.4 mM), reversed the effects of LPS and blocked responses to TEA. These results suggest that activation of K+ channels, possibly Ca-activated K+ channels, through induction of the nitric oxide synthase pathway, may well be responsible for endotoxin-mediated hyporeactivity to vasoconstrictor agents in vascular smooth muscle.