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We examined the effects of pharmacological alteration of Ca2+ sources on mechanical and energetic properties of paired-pulse ("bigeminic") contractions. The fraction of heat release that is related to pressure development and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricles. The heat released by regular and bigeminic contractions showed two brief pressure-independent components (H1 and H2) and a pressure-dependent component (H3). We used the ratio of active heat (Ha') to pressure-time integral (PtI) and the ratio of H3 to PtI to estimate the energetic cost of muscle contraction (overall economy) and pressure maintenance (contractile economy), respectively. Neither of these ratios was affected by stimulation pattern. Caffeine (an inhibitor of sarcoplasmic reticulum function) significantly decreased mechanical responses and increased the energetic cost of contraction (delta = 101 +/- 12.6%). Verapamil (an L-type Ca2+ channel blocker) decreased pressure maintenance of extrasystolic (delta = 43.4 +/- 3.7%) and postextrasystolic (delta = 37.5 +/- 3.5%) contractions without affecting postextrasystolic potentiation, suggesting that a verapamil-insensitive fraction is responsible for potentiation. The verapamil-insensitive fraction was further studied in the presence of lithium (45 mM) and KB-R7943 (5 microM), inhibitors of the Na+/Ca2+ exchanger. Both agents decreased all mechanical responses, including postextrasystolic potentiation (delta = 67.3 +/- 3.3%), without altering overall or contractile economies, suggesting an association of the verapamil-insensitive Ca2+ fraction to the sarcolemmal Na+/Ca2+ exchanger. The effect of the inhibitors of the Na+/Ca2+ exchanger on potentiation suggests an increased participation of extracellular Ca2+ (and, thus, a redistribution of the relative participation of the Ca2+ pools) during bigeminic contractions in rat myocardium.

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The role of calcium influx on energy expenditure during cardiac contraction was studied. For this purpose, the described ability of lithium and KB-R 7943 (KBR) to diminish Ca entry through Na-Ca exchanger (Ponce-Hornos & Langer, J Mol Cell Cardiol 1980, 12, 1367, Satoh et al., Circulation 2000, 101, 1441) were used. In isolated contractions (contractions elicited after at least 5 min of rest) LiCl 45 mmol L(-1) decreased pressure developed and pressure-time integral from 42.3 +/- 2.7 and 14.5 +/- 1.2 to 32.1 +/- 3.4 mN mm(-2) and 8.3 +/- 0.9 mN mm(-2) s, respectively. A similar effect was observed in regular contractions (at 0.16 Hz stimulation). The presence of KBR (5 micromol L(-1)) in the perfusate induced a slight but not significant decrease in pressure developed and pressure-time integral in steady-state contractions. As it was previously described, the heat involved in a heart muscle contraction can be decomposed into several components (H1, H2, H3 and H4), but only one (H3) was associated with force generation. While H3 decreased with lithium in both types of contractions, H3/PtI ratio remained unaltered, indicating that the economy for pressure maintenance was unaffected. To further investigate the role of Ca entry on force development, a condition in which the contraction is mainly dependent on extracellular calcium was studied. An 'extra' stimulus applied 200 ms after the regular one in a muscle stimulated at 0.16 Hz induces a contraction with this characteristic (Marengo et al., Am J Physiol 1999, 276, H309). Lithium induced a strong decrease in pressure-time integral and H3 associated with this contraction (43 and 45%, respectively) with no change in H3/PtI ratio. Lithium also reduced (53%) an energy component (H2) associated with Ca cycling. The use of KBR showed qualitatively similar results [i.e. a 33% reduction in pressure-time integral associated with the extrasystole (ES) with no changes in H3/PtI ratio and a 30% reduction in the H2 component]. Li and KBR effects appear to be additive and in the presence of 45 mmol L(-1) Li and 5 micromol L(-1) KBR the extrasystole was abolished in 77%. Lithium and KBR effects particularly for the extrasystole can be explained through the inhibition of Ca entry via Na-Ca exchange giving support to the participation of the Na-Ca exchanger in the Ca influx from the extracellular space. In addition, the results also suggest the possibility of an effect of Li on an additional Ca sensitive locus (different than the Na-Ca exchanger). In this connection, in isolated contractions lithium decreased the energy release fraction related to mitochondrial processes (H4) increasing the economy of the overall cardiac contraction.

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This paper shows the most important germs that are responsible for exit-site and tunnel infections in CAPD patients, and the possible action to care for them. Prevention of PD catheter infection begins with good surgical practice in catheter implantation and includes appropriate preoperative patient preparation. Some of the operative protocols for dialytic methods used in our unit are shown.

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Continuous Ambulatory Peritoneal Dialysis (CAPD) patients may have non infectious abdominal complications that affect the survival of their dialysis treatment. It is important to document the origin of leakages and hernias, causes of catheter malfunction or haemoperitoneum. Therapeutic options will depend on investigations and include catheter removal or replacement, surgical intervention or eventual transfer to automated peritoneal dialysis (APD). In this paper we report our experience of the technical implementation of Peritoneography and Peritoneum Computed Tomography.

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Cholesterol levels in plasma and different tissues were determined in Sprague-Dawley male rats, on standard and cholesterol-cholic acid enriched diets, after short term treatment with the absorbable hypolipidemic agents, clofibrate, WY-14,643 and Pirinixil (BR 931). The objective of the study was to evaluate the mode of action of these drugs in decreasing plasma cholesterol, be it by increased tissue mobilization, or by redistribution from plasma to tissues. After one or two weeks on a standard diet, none of the three agents significantly affected total body cholesterol stores. In spite of the liver enlargement induced by all three, in no case was total liver cholesterol significantly raised. Only clofibrate significantly increased colonic cholesterol concentrations. On a cholesterol-cholic acid regimen, some cholesterol mobilization was noted with all three drugs. However, only Pirinixil significantly reduced total liver cholesterol as well as the estimated total body cholesterol. A parallel effect of diet and drugs on plasma and body cholesterol pools is not constantly observed. In the examined rat model, clofibrate and two chemically unrelated compounds with a probably similar mechanism of action, markedly reduce plasma cholesterol levels while not affecting or decreasing total body cholesterol stores.

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The effect of a new anti-inflammatory agent, 2-phenyl-4-p-chlorophenyl-thiazol-5-ylacetic acid (BR 700) on the development of cover slip granuloma was studied. The drug decreased macrophage emigration and delayed some characteristic processes of the mononuclear cells.

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The anticatabolic action of 2-formyl-17a-methylandrosta-1,4-diene-11a,17beta-diol-3-one (formebolone) was demonstrated by assessing the nitrogen elimination in the urine of castrated rats treated with dexamethasone-21-phosphate. The absence of a virilizing action is duly pointed out.

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