Canadian Journal of Physiology and Pharmacology

Exercise is a powerful therapy for preventing the onset of and slowing the progression of cardiovascular disease. Increased shear stress during exercise improves vascular homeostasis by both decreasing reactive oxygen species and increasing nitric oxide bioavailability in the endothelium. While these observations are well accepted as they apply to individuals at risk for cardiovascular disease, less is known about how exercise, especially intense exercise, affects vascular function in healthy individuals. This review highlights examples of how vascular function can paradoxically be impaired in otherwise healthy individuals by extreme levels of exercise, with a focus on the causative role that reactive oxygen species play in this impairment.

The possible relationship of the atractyloside-sensitive adenine nucleotide translocase activity, oxidative phosphorylation, and the recovery of ventricular contractility following reperfusion of the ischemic isolated rat heart was studied. Five minutes of total global ischemia without reperfusion produced a significant depression in adenine nucleotide translocase in subsarcolemmal mitochondria (SLM), whereas a minimum of 10 min ischemia was required to observe a significant depression in interfibrillar mitochondria (IFM). Increasing durations of ischemia resulted in a progressively larger depression in translocase activity, with a maximum depression of approximately 75% seen in both populations following 20 min ischemia. In contrast, oxidative phosphorylation was totally unaffected in either mitochondrial population following up to 20 min of ischemia. We assessed whether translocase activity or oxidative phosphorylation were related to contractile recovery in hearts reperfused following various durations of ischemia. In SLM, translocase activity was further depressed following reperfusion compared with pre-reperfusion ischemic values, whereas with IFM only reperfusion following 5 min ischemia produced a further depression in translocase values. Oxidative phosphorylation rates of SLM and IFM were significantly depressed following reperfusion of ischemic hearts, although SLM exhibited a generally higher sensitivity in this regard. In reperfused hearts, an overall significant relationship was found between oxidative phosphorylation rate and adenine translocase activity as well as between translocase activity and post-reperfusion contractile recovery. These data show that ischemia can produce a significant depression in translocase activity in the absence of any change in oxidative phosphorylation. The results also suggest that the depression in mitochondrial ADP/ATP translocase and subsequent inhibition of oxidative phosphorylation in the reperfused heart may represent one of the important contributory mechanisms involved in cardiac failure and injury during acute ischemia and reperfusion.Key words: myocardial ischemia, myocardial reperfusion, mitochondria, oxidative phosphorylation, adenine nucleotide translocase.

Ischemia–reperfusion (I/R) injury after a liver transplant is a major cause of severe complications that lead to graft dysfunction. Fucoidan, a complex of sulfated polysaccharides derived from marine brown algae, demonstrated antiapoptotic as well as potential anti-inflammatory properties in previous studies. Fucoidan has also shown protective effects on I/R-injured kidney and heart. However, whether fucoidan can attenuate hepatic I/R injury has not been examined. To clarify the role of fucoidan in hepatic I/R injury, Sprague–Dawley rats were subjected to sham operation or ischemia followed by reperfusion with treatment of saline or fucoidan (50, 100, or 200 mg·(kg body mass)⁻¹·d⁻¹). The fucoidan-treated group showed decreased levels of alanine aminotransferase and aspartate aminotransferase compared with the control group. Myeloperoxidase and malondialdehyde activities and mRNA levels of CD11b in the fucoidan-treated group were significantly decreased. Hepatocellular swelling/necrosis, sinusoidal/vascular congestion, and inflammatory cell infiltration were also attenuated in the fucoidan group. The expression of TNF-α, IL-6, IL-1β, CXCL-10, VCAM-1, and ICAM-1 were markedly decreased in the samples from the fucoidan-treated group. Fucoidan largely prevented activation of the inflammatory signaling pathway, compared with the control group. In summary, fucoidan can protect the liver from I/R injury through suppressing activation of the inflammatory signaling pathway, as well as the expression of inflammatory mediators, and inflammatory cell infiltration.

The nature and mechanisms of septohippocampal transmission have been elucidated by taking advantage of an in situ preparation in experiments with Sprague–Dawley rats under urethane. Both extracellular field potentials and intracellular recordings were made in CA1–3 regions of the hippocampus; and the hippocampal commissure and medial septum stimulated to evoke synaptic activity. Using muscarinic and nicotinic agonists and antagonists it was shown that both acetylcholine and medial septal activity can increase the excitability of pyramidal cells, mainly through muscarinic receptors. The effect of septal stimulation was enhanced by local application of physostigmine and reduced by intraventricular injections of hemicholinium. It was also shown that acetylcholine, when applied in the stratum pyramidale, can reduce the voltage and conductance changes observed during evoked inhibitory postsynaptic potentials (IPSP) without affecting the action of γ-aminobutyric acid on membrane conductance and voltage. It is therefore proposed that acetylcholine can reduce evoked IPSPs through presynaptic inhibition. Evidence is also presented that medial septal stimulation can reduce the efficacy of evoked IPSPs. These observations provide further support for the existence of a cholinergic septohippocampal pathway.

The actions of a series of 15 Ca²⁺ channel antagonists including D-6(X), nifedipine, and diltiazem were examined against K⁺ depolarization and muscarinic receptor induced responses in guinea pig bladder smooth muscle. Responses of bladder are very dependent upon extracellular Ca²⁺ and sensitive to the Ca²⁺ channel antagonists, the tonic component more than the phasic component of response. Regardless of stimulant, K⁺ or methylfurmethide (MF), or component of response, the same rank order of antagonist activities is expressed, suggestive of a single structure–activity relationship and the existence of a single category of binding site which may, however, exist in several affinity states. High affinity binding of [³H]nitrendipine (K_D = 1.1 × 10⁻¹⁰ M) occurs in bladder membranes, and similar high affinity binding was found in microsomal preparations from other smooth muscles including guinea pig and rat lung, rat vas deferens, uterus, and stomach. [³H]nitrendipine binding in the bladder was sensitive to displacement by other 1,4-dihydropyridines, paralleling their pharmacologic activities and showing excellent agreement with binding data previously obtained for guinea pig ileal smooth muscle. Comparison of pharmacologic data for inhibition of K⁺- and MF-induced responses by a common series of Ca²⁺ channel antagonists in bladder and ileum revealed excellent correlations. Neither pharmacologic nor binding studies suggest significant differences in Ca²⁺ channel antagonist properties in smooth muscle from bladder and intestine.

An understanding of the physiological and behavioral determinants of resting energy requirements is important to nutritional considerations in females. We examined the influence of endurance training and self-reported dietary restraint on resting metabolic rate and fasting plasma hormones in 44 nonobese females characterized for body composition, maximal aerobic power [Formula: see text], and daily energy intake. To examine the association of metabolic rate and dietary restraint with hormonal status, fasting plasma levels of insulin, glucose, and thyroid hormones (total and free fractions of thyroxine and triiodothyronine) were determined. In univariate analysis, resting metabolic rate (kcal∙min⁻¹) was positively related to [Formula: see text] (L∙min⁻¹) (r = 0.54; p < 0.01). This relationship, however, was partially dependent on body size, since fat-free mass was also related to resting metabolic rate (r = 0.42; p < 0.01) and [Formula: see text] (L∙min⁻¹) (r = 0.75; p < 0.01). After controlling for fat-free weight using partial correlation analysis, the relation between RMR and [Formula: see text] was weaker but still significant (partial r = 0.38; p < 0.05). On the other hand, high levels of dietary restraint were associated with higher levels of body fat (r = 0.31; p < 0.05) and a lower resting metabolic rate (r = −0.29; p = 0.07). These associations persisted after control for differences in fat-free mass. Total energy intake as well as total and free levels of triiodothyronine were not related to resting metabolic rate or level of dietary restraint. Our results suggest that the level of endurance training (i.e., [Formula: see text]) and dietary restraint, independent of differences in fat-free mass, contribute to individual variation in resting metabolic rate of nonobese females. These findings appear to be unrelated to fasting plasma concentrations of thyroid hormones. Whereas high levels of endurance training are associated with increased energy requirements at rest, higher levels of dietary restraint are associated with a lower resting metabolic rate and possibly a propensity to gain body fat.Key words: endurance training, dietary restraint, resting metabolic rate, females, energy intake.

MK-0591 (3-[1-(4-chlorobenzyl)-3-(t-butylthio)-5-(quinolin-2-yl-methoxy)-indol-2-yl]-2,2-dimethyl propanoic acid, previously L-686,708) is a potent inhibitor of leukotriene (LT) biosynthesis in intact human and elicited rat polymorphonuclear leukocytes (PMNLs) (IC₅₀ values 3.1 and 6.1 nM, respectively) and in human, squirrel monkey, and rat whole blood (IC₅₀ values 510, 69, and 9 nM, respectively). MK-0591 had no effect on rat 5-lipoxygenase. MK-0591 has a high affinity for 5-lipoxygenase activating protein (FLAP) as evidenced by an IC₅₀ value of 1.6 nM in a FLAP binding assay and inhibition of the photoaffinity labelling of FLAP by two different photoaffinity ligands. Inhibition of activation of 5-lipoxygenase was shown through inhibition of the translocation of the enzyme from the cytosol to the membrane in human PMNLs. MK-0591 was a potent inhibitor of LT biosynthesis in vivo, first, following ex vivo challenge of blood obtained from treated rats and squirrel monkeys, second, in a rat pleurisy model, and, third, as monitored by inhibition of the urinary excretion of LTE₄ in antigen-challenged allergic sheep. Inhibition of antigen-induced bronchoconstriction by MK-0591 was observed in inbred rats pretreated with methysergide, Ascaris-challenged squirrel monkeys, and Ascaris-challenged sheep (early and late phase response). These results indicate that MK-0591 is a potent inhibitor of LT biosynthesis both in vitro and in vivo indicating that the compound will be suitable for assessing the role of leukotrienes in pathological situations.Key words: leukotriene, 5-lipoxygenase, leukotriene inhibitor, bronchoconstriction, inflammation, 5-lipoxygenase activating protein.

An investigation was made of the effects of bathing media low in divalent cations on rapid axonal transport in the sciatic nerve of the amphibian Xenopus laevis. The anterograde transport of a pulse of [³⁵S]methionine proteins was observed using a multiple proportional counter as the detector. Organelles undergoing anterograde and retrograde transport were detected by light microscopy. The structure of nerve fibres was examined by light and electron microscopy. There was no significant difference in the anterograde transport of proteins in nerves bathed in normal medium (NM) containing millimolar Ca²⁺ and Mg²⁺ and in those bathed in calcium-free medium (CaFM) containing Mg²⁺. The anterograde transport of labelled proteins continued at a normal velocity in nerves bathed in divalent cation free medium (DCFM) for at least 14 h. DCFM did cause some alterations in protein transport: the ratio of the plateau (following pulse passage) to the peak radioactivity was increased, the pulse amplitude decreased more rapidly, and the label continued to arrive at the distal end of the nerve for >16 h. Anterograde and retrograde organelle transport continued normally for periods of [Formula: see text] in fibres bathed in DCFM. All myelinated fibres became distorted within 4 h in DCFM. Similar distortion was rare in fibres bathed in CaFM. The results indicate that axonal transport in Xenopus is largely independent of lowered concentrations of divalent cations in the bathing medium. Those alterations in axonal transport that were produced by DCFM may have been secondary to morphological changes in the nerve fibres.

The release of acetylcholine (ACh) by rat cerebral cortex slices, with and without electrical stimulation, and the effect of ethanol (EtOH) on this release were examined during the acquisition and loss of EtOH tolerance in vivo. ACh was measured by pyrolytic monodemethylation and gas–liquid chromatography. Electrical stimulation of control slices in medium containing diisopropyl phosphofluoridate (1.26 μM) and atropine (0.3 μM) increased ACh release by 88 ± 12%. Addition of 0.11 M EtOH to the medium had negligible effect on ACh release from unstimulated slices, but reduced the effect of stimulation to 51 ± 10%. After chronic treatment with EtOH by gavage or in a liquid diet, rats became tolerant to EtOH in vivo as shown by reduced impairment on the moving belt test. Slices from tolerant rats showed increased release of ACh in response to electrical stimulation and less inhibition of this response by added EtOH. The changes had disappeared by 2 weeks after cessation of EtOH treatment.Similar findings were obtained by measurement of release of [¹⁴C]ACh from slices preloaded with [¹⁴C]choline, except that electrical stimulation in the absence of EtOH appeared to cause a smaller increase in slices from chronic EtOH animals than from controls. This may reflect differences in isotope dilution. Release of [³H]norepinephrine was less affected by EtOH than that of ACh. The findings suggest that tolerance to EtOH is accompanied by increased ACh release by cortical neurones, as well as decreased direct inhibitory effect of EtOH on this, but do not permit any conclusion about the relative importance of such changes in various parts of the brain.

Calcium flux responses mediated by voltage-dependent calcium channels have been studied in transverse tubule membrane vesicles from rabbit skeletal muscle. Vesicles were loaded with ⁴⁵Ca²⁺, and membrane potentials were generated by establishing potassium gradients across the membrane in the presence of valinomycin. After the membranes were polarized to an estimated −80 mV to approximate the resting state of the cell, a significant ⁴⁵Ca²⁺ efflux occurred upon subsequent depolarization to −60 mV. The efflux response was modulated by activators and inhibitors of slow, dihydropyridine-sensitive calcium channels, being inhibited by inorganic calcium channel blockers, verapamil, nifedipine, and (−)-SDZ 202 – 791 and potentiated by the dihydropyridine agonists (±)-Bay K8644 and (+)-SDZ 202 – 791. These results demonstrate that calcium channels in transverse tubule membranes can open to mediate calcium flux in the same range of membrane potential as the late afterpotentials that occur during tetanic contractions of intact muscle fibres.Key words: Ca²⁺ channels, dihydropyridines, skeletal muscle (rabbit), ⁴⁵Ca²⁺ flux, late afterpotentials.