Canadian journal of physiology and pharmacology
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Can. J. Physiol. Pharmacol. · May 2000
Acute effects of methoxamine on left ventricular-arterial coupling in streptozotocin-diabetic rats: a pressure-volume analysis.
We determined the acute effects of methoxamine, a specific alpha1-selective adrenoceptor agonist, on the left ventricular-arterial coupling in streptozotocin (STZ)-diabetic rats, using the end-systolic pressure-stroke volume relationships. Rats given STZ 65 mg x kg(-1) iv (n = 8) were compared with untreated age-matched controls (n = 8). A high-fidelity pressure sensor and an electromagnetic flow probe measured left ventricular (LV) pressure and ascending aortic flow, respectively. ⋯ Methoxamine administration to STZ-diabetic rats significantly increased LV end-systolic elastance E(LV,ES), from 513 +/- 30 to 602 +/- 38 mmHg x mL(-1), and effective arterial elastance Ea, from 296 +/- 20 to 371 +/- 28 mmHg x mL(-1), but did not change optimal afterload Q(load). We conclude that diabetes worsens not only the contractile function of the left ventricle, but also the matching condition for the left ventricular-arterial coupling. In STZ-diabetic rats, administration of methoxamine improves the contractile status of the ventricle and arteries, but not the optimality of energy transmission from the left ventricle to the arterial system.
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Can. J. Physiol. Pharmacol. · Oct 1999
Comparative StudyFunctional comparison of the human isolated femoral artery, internal mammary artery, gastroepiploic artery, and saphenous vein.
Human femoral, internal mammary, and gastroepiploic arteries and saphenous veins are used as bypass grafts for coronary surgery or for reconstruction in arterial occlusive disease. We have characterized the contractile responses of these vessels to various agents that are liberated during cardiac or vascular surgery. In organ baths, U46619 (a stable thromboxane A2 mimetic), norepinephrine, endothelin-1, angiotensin II, and KCl caused concentration-dependent contractions in all vessels tested. ⋯ In conclusion, thromboxane A2 appears to be the most potent endogenous constricting agent on different human vascular beds. Our second finding is that saphenous veins are more sensitive to contract to leukotriene C4 and endothelin-1 than arteries. These properties may influence early and (or) long-term vein graft patency.
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Can. J. Physiol. Pharmacol. · Dec 1998
Body fluid volume status and the renal response to atrial natriuretic peptide in rats.
The effect of altering the volumes of different body fluid compartments on the renal response to atrial natriuretic peptide (ANP) was studied in anesthetized rats before and during administration of the peptide at 170 ng/min. Four different groups were used. In the first (De), reduction of total body water content was induced by 48 h water deprivation. ⋯ According to the study design, the two nonresponding groups had, respectively, a decreased or a normal intracellular compartment, and a decreased or increased plasma volume. The common feature of both nonresponding groups was a decreased interstitial fluid compartment, whereas the two responding groups had normal or increased interstitial volume. We suggest, therefore, that a replete interstitial fluid compartment is essential for the renal response to ANP.
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Can. J. Physiol. Pharmacol. · Sep 1998
Modulation of GABA(A) receptor function by neuroactive steroids: evidence for heterogeneity of steroid sensitivity of recombinant GABA(A) receptor isoforms.
Neuroactive steroids are potent, selective allosteric modulators of gamma-aminobutyric acid type A (GABA(A)) receptor function in the central nervous system, and may serve as endogenous anxiolytic and analgesic agents. In order to study the influence of subunit subtypes of the GABA(A) receptor on modulation of receptor function by neuroactive steroids, we expressed human recombinant GABA(A) receptors in Xenopus oocytes. GABA-activated membrane current, and the modulatory effects of the endogenous neurosteroid 5alpha-pregnan-3alpha-ol-20-one (allopregnanolone) and the synthetic steroid anesthetic 5alpha-pregnan-3alpha-ol-11,20-dione (alphaxalone) were measured using two-electrode voltage-clamp recording techniques. ⋯ Epipregnanolone had a greater efficacy as a blocker at the alpha1beta2gamma2L receptor isoform compared with the alpha1beta1gamma2L receptor isoform, and also produced a greater degree of block of potentiation caused by allopregnanolone compared with alphaxalone. Our results support the hypothesis that the heteromeric assembly of different GABA(A) receptor isoforms containing different subunit subtypes results in multiple steroid recognition sites on GABA(A) receptors, which in turn produces distinctly different modulatory interactions between neuroactive steroids acting at the GABA(A) receptor. The alpha and gamma subunit subtypes may have the greatest influence on allopregnanolone modulation of GABA(A) receptor function, whereas the beta and gamma subunit subtypes appear to be most important for the modulatory effects of alphaxalone.
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Can. J. Physiol. Pharmacol. · May 1998
ReviewPhysical exercise as a human model of limited inflammatory response.
An inflammatory response represents a fundamental series of humoral and cellular reaction cascades in response to infection, tissue injury, and related insults. An excessive response is commonly seen under the pathological conditions of trauma, sepsis, and burns. It is becoming increasingly evident that most, if not all, of the distinguishing features of a classical inflammatory response are detectable in an exercising individual, namely mobilization and activation of granulocytes, lymphocytes, and monocytes; release of inflammatory factors and soluble mediators; involvement of active phase reactants; and activation of the complement and other reactive humoral cascade systems. ⋯ Unlike the exaggerated and sometimes uncontrollable inflammatory response in septic and trauma patients resulting in morbidity and mortality, strenuous and severe exercise normally elicits an inflammatory response of a subclinical nature to facilitate the repairing process for site-specific tissue damage. Regardless of the inciting event, for example trauma, infection, or exercise, and given an appropriate triggering signal, a remarkably similar sequence of inflammatory reactions can be reproduced in the affected host. Therefore, physical exercise and training represent an acceptable and good model for the study of limited inflammatory responses in humans.