bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium and contractions of isolated smooth muscle cells from rat myometrium
Authors: Kyozuka M. , Crankshaw J. , Berezin I. , Collins S. M. , Daniel E. E.
Published: April 2011

Smooth muscle cells were isolated from estrogenized rat myometrium by collagenase digestion. Electron microscopic examination and measurement of cell lengths by image-splitting micrometry were carried out after fixation with acrolein. Mean lengths of cells before and after isolation were 81.7 and 66.9 μm, respectively. Responses of cells were compared with contractions of isolated strips recorded isometrically. Effects of carbachol and KCl were examined in 2 mM Ca, 2 mM Ca + 4 mM EGTA, and 2 mM Ca + 10−8 M nitrendipine solution. Carbachol and KCl produced concentration-dependent shortening of isolated cells maximal at 30 s after addition. The concentrations of carbachol required to produce shortenings were about 100-fold less than those required to produce isometric contractions; but no major difference was observed in the concentration dependence of cell shortening and isometric contraction produced by potassium-induced depolarization. In 2 mM Ca solution, there was a phasic response, followed by a tonic response such that more than 50% of maximum cell shortening was maintained for 10 min. However, in 2 mM Ca + 4 mM EGTA or 10−8 M nitrendipine, the tonic contraction was abolished and cells rapidly relaxed after 30 s. If carbachol was added to cells after varying times in the EGTA-containing solution, the ability to initiate a contraction declined exponentially with a half-time of 160 s. Effects of depolarization by KCl were examined in 2 mM Ca plus nitrendipine and 2 mM Ca + 4 mM EGTA solution. Shortening occurred in 2 mM Ca solution by depolarization but not if nitrendipine was added. Though shortening was not observed in 2 mM Ca + 4 mM EGTA solution by KCl, subsequent addition of carbachol induced shortening. These results suggested that there was an intracellular Ca store site from which Ca was released by carbachol and which was not affected by depolarization in the absence of external Ca. No evidence was obtained that the contraction persists in Ca2+-free medium in isolated cells, which is in agreement with previous findings in small muscle strips in which only a similar transient response was obtained.
An endogenous peptide that stimulates lanthanum-resistant calcium uptake in vascular tissue
Authors: McCumbee William D. , Johnson Peter , Kasvinsky Peter J. , Wright Gary L.
Published: April 2011

A recent report has described the preparation of an extract from hemolyzed erythrocytes that has a stimulatory effect on lanthanum-resistant calcium uptake by vascular tissue in vitro and a hypertensive effect when injected into normotensive rats. The compound having a stimulatory effect on calcium uptake was further fractionated by molecular sieve and ion exchange chromatography, precipitation with CaCl2, high voltage paper electrophoresis, and high performance liquid chromatography (HPLC). HPLC yielded only a single fraction containing biological activity. This fraction was ninhydrin positive and acid labile. The amino acid composition was as follows: Asp/Asn (1.41), Ser (1.02), Glu/Gln (1.00), and Gly (2.00). Based on the assumption that the compound contains a single glutamic acid or glutamine residue, concentration–response data indicated that only nanomolar amounts of material were necessary to achieve significant stimulation. There was a marked increase in stimulatory activity of the resolubilized compound following calcium precipitation. The compound became inactive or showed a reduction in activity after being applied to a cation exchange column to remove calcium. Subsequent reprecipitation with CaCl2 and resolubilization restored the lost activity. Thus, we conclude that the compound is a small, acidic, calcium-dependent peptide that is extremely potent in stimulating lanthanum-resistant calcium uptake in vascular tissue.
Atrial peptides and the renal response to hypervolemia in nephrotic rats
Authors: Keeler R. , Feuchuk D. , Wilson N.
Published: April 2011

Immunoreactive atrial natriuretic peptide (iANP) levels in plasma of edematous rats with an experimental nephrotic syndrome produced by the injection of puromycin aminonucleoside (PAN) were not different from those in untreated rats. To test the ability of nephrotic rats to secrete iANP in response to a volume stress, the rats were subjected to 20% expansion of their estimated blood volumes using blood from donor rats. PAN-treated rats had very small natriuretic and diuretic responses compared with untreated rats; however, there was no difference in the secretory response of iANP, which increased approximately threefold in each group. There were highly significant correlations between changes in plasma iANP and changes in right atrial pressure in both normal and nephrotic rats. Nephrotic rats that were infused with synthetic ANP showed only a very small natriuretic and diuretic response compared with normal rats, and no change in glomerular filtration rate. The hypotensive response was still present, however. Urine concentration in nephrotic rats was much lower than in controls and was not increased by exogenous arginine vasopressin. It is concluded that the absence of a normal natriuretic and diuretic response to hypervolemia in PAN-treated rats is not caused by a failure to secrete ANP but might be a result of an intrarenal defect that makes their kidneys unresponsive.
Role of atrial natriuretic peptide and urinary cGMP in the natriuretic and diuretic response to central hypervolemia in normal human subjects
Authors: Leung W. M. , Logan A. G. , Campbell P. J. , Debowski T. E. , Bull S. B. , Wong P. Y. , Blendis L. M. , Skorecki K. L.
Published: April 2011

The response of plasma atrial natriuretic peptide (ANP) and urinary cGMP excretion to central hypervolemia induced by water immersion was assessed twice in five healthy male subjects, once while immersed in water to the neck for 3 h and again on a control day. Plasma ANP and urinary cGMP were measured by radioimmunoassay. Compared with the control day, overall change in plasma ANP on the immersion day was significant (p < 0.05). In response to water immersion, plasma ANP increased from a base-line level of 13.2 ± 3.1 (mean ± SEM) to 24.2 ± 5.5 pg/mL by 0.5 h of immersion and was sustained at that level throughout the immersion period. Plasma ANP returned to the base-line level at 1 h postimmersion. Urinary cGMP excretion increased significantly by 1 h of immersion and was sustained at that level throughout water immersion and 1 h postimmersion (p < 0.05). During water immersion urine flow, urinary sodium and potassium excretion, free water clearance, and osmolar clearance increased while plasma renin activity, serum aldosterone, and blood pressure fell; all changes were significant (p < 0.05). Creatinine clearance and hematocrit did not show any significant changes. These data suggest that an increase in plasma ANP may contribute to the natriuretic and diuretic response to central hypervolemia, and that the measurement of urinary cGMP may be a valuable marker of ANP biological responsiveness.
Multiple actions of cadmium on transmitter release at the mouse neuromuscular junction
Authors: Guan Y.-Y. , Quastel D. M. J. , Saint D. A.
Published: April 2011

The action of cadmium ions on transmitter release was studied at the neuromuscular junction in mouse diaphragm. In the presence of raised K+, Cd2+ caused a parallel shift to the right of the graph of transmitter release rate (frequency of miniature end-plate potentials, fmepp) versus log [Ca2+], with no change in maximum or slope, indicating a competitive mode of action of Cd2+. The apparent dissociation constant for Cd2+ was 3 μM. In calcium-free solutions containing 15 mM K+, Cd2+ caused a rise in the fmepp, which subsequently slowly declined despite the continued presence of Cd2+. The rise in fmepp caused by Cd2+ could be interrupted, but not reversed, by washing out the Cd2+ with EDTA. Exposure of the preparation to 100 μM Cd2+ for 15 min or more resulted in a raised fmepp that persisted despite the removal of Cd2+ and exposure to 200 μM EDTA. Following such treatment, the graph of fmepp versus log [Ca2+] continued to be shifted to the right. The interaction of Ca2+ with the residual effect of Cd2+ indicates that Cd2+, in addition to its action to block Ca2+ entry into the terminal, may act as a competitor and perhaps as a partial agonist at intracellular sites that normally bind Ca2+ and govern transmitter release. If this is the case, then it must be supposed that, in raised K+, quantal release of transmitter represents intermittent intense activation of release sites with local high levels of Ca2+ rather than continuous low level activation.
Effect of short-term administration of vasopressin on arterial pressure and norepinephrine turnover in Long–Evans rats
Authors: Kline R. L. , Chow K.-Y. , Mercer P. F.
Published: April 2011

Vasopressin (AVP) in acute experiments has been shown to influence cardiovascular reflexes, but the effect of a more prolonged administration of AVP on the sympathetic nervous system has not been investigated. Long–Evans rats were treated for 7 days with AVP (Pitressin tannate in oil, with single daily doses of 100 or 500 mU∙100 g−1, s.c.) to determine whether AVP alters norepinephrine (NE) turnover in kidney, intestine, or skeletal muscle. Control rats were given equal doses of peanut oil daily. NE turnover was determined by measuring the decline in tissue levels of NE for 8 h after inhibition of tyrosine hydroxylase with α-methyl-p-tyrosine (300 mg∙kg−1, i.p. every 4 h). Measurements of water intake, urine output, and urine osmolality showed that chronic administration of the high dose, but not the low dose, of AVP produced maintained increases in urine osmolality and decreases in water intake and urine output. Body weight, plasma osmolality, plasma electrolytes, and hematocrit were not significantly altered by AVP treatment, but mean arterial pressure was elevated significantly (control, 105 ± 3 mmHg versus AVP, 119 ± 4 mmHg, p < 0.05) (1 mmHg = 133.3 Pa) in the high dose group. Plasma renin activity was decreased slightly, but significantly in rats treated with the high dose of AVP. Compared with results in control animals, there were no statistically significant changes in NE turnover after chronic administration of either the low or the high dose of AVP. The results indicate that administration of AVP for 7 days to rats in normal fluid balance does not result in a decrease in NE turnover in peripheral organs.
Effect of exercise training on insulin binding and glucose metabolism in mouse soleus muscle
Authors: Tan M. H. , Bonen A.
Published: April 2011

Training stimulates glucose uptake and metabolism by muscles independent of a rise in serum glucose. Whether this increased insulin action is associated with enhanced insulin binding in muscles is unknown. We studied the effect of 6 weeks of treadmill running on insulin binding, uptake of 2-deoxy-D-glucose, glycolysis, and glycogenesis by the soleus muscle of Swiss Webster mice. Training was progressively increased. The in vitro studies using intact soleus preparations were done 48 h after the last exercise bout. Training increased insulin binding, insulin-stimulated uptake of 2-deoxy-D-glucose, and glycogenesis but not glycolysis in the soleus. Our data suggest that the enhanced glucose uptake and metabolism in muscles induced by exercise training are associated with an increase in insulin binding.
Alteration of pial vessel responses to blood pressure changes in rats after hypoxia
Authors: Ong B. Y. , Kettler J. J. , Bose D.
Published: April 2011

Previous studies in newborn lamb have shown impairment of cerebral blood flow autoregulation after hypoxia followed by reoxygenation. The present study was done to see if such a phenomenon existed in the adult rat and if it could be demonstrated at the level of the pial arterioles. Using an open cranial window preparation, we assessed the changes in pial vessel diameter during blood pressure alterations induced by hemorrhage and reinfusion of blood, before and after 30 s of hypoxia, in 15 male Sprague–Dawley rats. Mean diameters of pial arteries in the study group of rats were 128 ± 54 μm before hypoxia and 141 ± 61 μm after normoxia following hypoxia. The corresponding diameters in rats serving as time controls were 136 ± 52 and 138 ± 52 μm. Slopes of pial vessel diameters as a function of mean arterial blood pressures descreased significantly (p < 0.05) after hypoxia from −0.86 ± 0.45 to 0.03 ± 0.66 (mean ± SD). In the control rats not subjected to hypoxia, the slopes remained unchanged over a similar time period (−0.60 ± 0.16 and −0.42 ± 0.19). The negative slopes indicate that pial vessels dilate during hypotension and constrict during hypertension. Such vascular responses may play a role in autoregulation of cerebral blood flow. We found that a relatively brief period of hypoxia can cause a long-lasting impairment of vascular responses even after restoration of normoxia. These findings are consistent with a previous report of persistent impairment of cerebral blood flow autoregulation after a brief period of hypoxia.
Ileal resection and dietary content of sucrose influence the intestinal uptake of monosaccharides
Authors: Thomson A. B. R.
Published: April 2011

The intestinal uptake of 0.5 and 40 mM glucose, galactose, and 3-O-methyl glucose (3-O-MG) was examined in vitro in rabbits fed a high (HS) or a low (LS) sucrose diet. In animals with an intact intestinal tract, the jejunal uptake of 0.5 mM 3-O-MG was unaffected by the dietary content of sucrose, whereas the uptake of 40 mM 3-O-MG was lower in LS than HS. The uptake of 40 mM galactose was higher in LS than HS and the uptake of 0.5 mM galactose was similar in HS and LS, whereas the uptake of 0.5 mM but not 40 mM glucose was lower in LS than HS. In animals subjected 6 weeks previously to an ileal resection, the adaptive changes in the jejunal uptake of the hexoses in response to alterations in the dietary content of sucrose differed from the changes observed in rabbits with an intact intestinal tract. For example, feeding HS to ileal resected animals was associated with increased jejunal uptake of 40 mM galactose, decreased uptake of 40 mM glucose, and unchanged uptake of 40 mM 3-O-MG; whereas in control animals with an intact intestinal tract, feeding HS resulted in increased uptake of 40 mM 3-O-MG, decreased uptake of 40 mM galactose, and no change in the uptake of 40 mM glucose. A similar adaptive pattern was noted in the jejunum and ileum for the effect of dietary sucrose on the uptake of 0.5 and 40 mM glucose. Thus, (1) the intestinal uptake of these sugars is responsive to dietary changes in the level of sucrose; (2) the variable effects of sucrose and ileal resection on the uptake of these sugars suggest that there is more than one hexose carrier; and (3) dietary sucrose levels exert a positive feedback effect on the uptake of low luminal concentrations of glucose and a negative feedback effect on the uptake of high luminal concentrations of glucose; this latter effect becomes apparent only when the potential reserve absorptive capacity of the ileum becomes lost following ileal resection.
Effects of β-adrenergic agonist infusions on myometrial activity and plasma prostaglandin levels in the nonpregnant sheep
Authors: Lye S. J. , Christopher P. , Casper R. F.
Published: April 2011

Recent studies have reported that β-adrenergic agonists stimulate the production of stimulatory prostaglandins (PGs) by intrauterine tissues in vitro. These drugs are used clinically to inhibit uterine contractions; consequently an increase in stimulatory PGs in vivo might have potentially adverse effects. We have, therefore, investigated whether β-adrenergic agonists increase plasma PG concentrations in vivo. Samples of peripheral (aorta) and uterine venous enriched (vena cava) blood from nonpregnant sheep were collected at 15-min intervals for 1 h before, 3 h during, and 1 h postinfusion of either (a) the β-adrenergic agonist isoproterenol (Isop) at a dose of 0.16 μg∙kg−1 min−1; (b) Isop at a dose of 0.08 μg∙kg−1∙min−1; or (c) saline, 1 mL/h via a jugular vein catheter. The sheep were also equipped with intrauterine recording balloons to record intrauterine pressure and myometrial electromyographic (EMG) electrodes to measure EMG activity. Infusion of Isop at 0.16 μg∙kg−1∙min−1 produced a significant initial inhibition of uterine activity, although contractions returned (within 60 min) despite continued administration of Isop. Plasma PGE2 (but not PGF2α or 13,14-dihydro-15-keto-PGF2α (PGFM)) concentrations were significantly elevated during the Isop infusion. Administration of Isop at 0.08 μg∙kg−1∙min−1 produced no effects on uterine contractile activity but was associated with a significant elevation in plasma PGE2 (but not PGF2α or PGFM) concentrations. No changes in plasma PGE2, PGF2α, or PGFM occurred during saline infusion. The data suggest that β-adrenergic agonist infusion is associated with a differential increase in plasma PG levels in vivo, but that this effect is probably not related to the failure of Isop (0.16 μg∙kg−1∙min−1) to maintain inhibition of myometrial contractions.
The role of biotransformation–detoxication in acetone-, 2-butanone-, and 2-hexanone-potentiated chloroform-induced hepatotoxicity
Authors: Hewitt L. Arthur , Valiquette Céline , Plaa Gabriel L.
Published: April 2011

The hepatotoxicity of chloroform (CHCl3) is thought to require biotransformation, by the polysubstrate monooxygenase system (P-450), to a reactive intermediate(s). Therefore, the potentiation of CHCl3-induced hepatotoxicity, which occurs following exposure to certain ketones, may hypothetically be explained by a reduced capacity of the cell to form glutathione conjugates (detoxicate the intermediate) and (or) by an increased rate of reactive intermediate(s) generation secondary to a modification of the P-450 system. To test these hypotheses, liver damage, as indicated by elevation in plasma alanine aminotransferase and ornithine carbamyl transferase activities, was modulated in male Sprague-Dawley rats by varying the time interval (10, 18, 24, 48, 72, 96 h) between acetone, 2-butanone, or 2-hexanone (15 mmol/kg, p.o.) pretreatment and CHCl3 (0.5 mL/kg, p.o.) administration. These data were compared with hepatic glutathione and with various parameters of the polysubstrate monooxygenase system: cytochrome P-450, cytochrome c reductase, cytochrome b5, and microsomal binding of 14CHCl3-derived radiolabel. Reduced detoxication capacity does not appear to be involved as hepatic glutathione levels were not reduced. Globally, a relationship between modifications to the polysubstrate monooxygenase system and potentiation of CHCl3-induced hepatotoxicity appears to exist. The rank order of each ketone's ability to modify P-450 parameters was the same in most instances as that based on peak ability to potentiate CHCl3-induced hepatotoxicity: 2-hexanone > 2-butanone ≥ acetone. Therefore, these results suggest that a general relationship exists between the ketone-induced potentiation of CHCl3-induced hepatotoxicity and increased CHCl3 reactive metabolite generation. However, other factors may also contribute to the phenomenon.
L-Dopa metabolism in genetically hypertensive mice: effect of pargyline
Authors: Buu Nguyen T. , Duhaime Johanne , Racz Karoly , Kuchel Otto , Schlager Gunther
Published: April 2011

This study on the role of the sympathetic nervous system in the development of hypertension involves the measurement of dopamine and norepinephrine accumulation in various tissues of the hypertensive and random-bred normotensive strains of mice at basal levels, and following a pargyline–L-dopa treatment. Under such a treatment, designed to suppress the homeostatic action of monoamine oxidase and to better expose the relationship between dopamine and norepinephrine, the brain and heart of the hypertensive mice accumulated more dopamine than the normotensive mice. There was a significantly lower norepinephrine accumulation in the heart of the hypertensive mice in spite of comparable dopamine-β-hydroxylase activity in this tissue between the two strains of mice. Under the pargyline–L-dopa treatment, the brain and heart of the older mice in both hypertensive and normotensive strains accumulated significantly (p < 0.05) more dopamine than those of their younger counterparts, while their norepinephrine accumulation remained unchanged. The results demonstrated different patterns of response of dopamine and norepinephrine in the development of hypertension.
Mechanism of contractile action of barium ion on rat aortic smooth muscle
Authors: Ebeigbe Anthony B. , Aloamaka C. Peter
Published: April 2011

The mechanism of Ba2+-induced contraction has been examined in helical strips of Ca2+-depleted, 60 mM K+-depolarized rat aortae. The concentration–response curves to Ca2+ or Ba2+ were significantly potentiated by exposure to 3 × 10−8 M Bay K 8644 (a Ca2+ channel agonist) in the order Ca2+ > Ba2+, suggesting an action of Ba2+ ions through potential-sensitive membrane Ca2+ channels. Exposure of strips to background concentration of Ca2+ (0.05 mM) enhanced the contractile responses to Ba2+, whereas background exposure to Ba2+ (0.1 mM) attenuated Ca2+ responses. Repeated stimulation with Ba2+ resulted in tachyphylaxis, contrary to the result when Ca2+ was used. The results suggest that Ba2+ ions enter rat aortic smooth muscle cells through Ca2+ channels and mobilize a noradrenaline-insensitive intracellular Ca2+ pool. Ba2+ may also cause a desensitization of some intracellular process.
In vitro and in vivo characterization of 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-isothiocyano)phenyl-l,4-dihydropyridine as a Ca2+ channel antagonist
Authors: Gengo P. , Su C. M. , Yousif F. B. , Triggle D. J.
Published: April 2011

The actions of 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-isothiocyano)phenyl-1,4-dihydropyridine(o-NCS-DHP), a nifedipine analog bearing a reactive group, have been characterized in vitro by pharmacological and radioligand binding techniques in a number of smooth muscles and in vivo by blood pressure and radioligand binding. o-NCS-DHP exhibits persistent, but slowly reversible, antagonism in guinea pig ileal longitudinal smooth muscle, guinea pig bladder, taenia coli, rat portal vein, and rat tail artery to receptor responses (muscarinic and α-adrenoceptor) and K+ depolarization initiated responses. Duration of response was significantly longer than that of equivalent concentrations of nifedipine. In many tissues a component of antagonism produced by o-NCS-DHP was not reversed by repeated washing over the duration of the experiment (up to 2 or 7 h). A comparison of the actions of o-NCS-DHP and its isomers m-NCS-DHP and p-NCS-DHP revealed the former to be significantly longer lasting in rat tail artery against K+ depolarization induced responses. A similar profile was exhibited when the Ca2+ channel activator Bay K 8644 was employed as the stimulant, but the antagonism produced by all three compounds was fully reversed with sufficiently prolonged washing. In vivo administration of o-NCS-DHP (5–25 mg/kg) produced a persistent reduction of [3H]nitrendipine binding in rat brain, gut, and heart characterized as Bmax, but not KD, changes. No effects on [3H]dihydroalprenolol or [3H]quinuclidinyl benzilate binding were detected. Binding site recoveries were characterized by t½ values of 35–50 h, and these were significantly prolonged to 91–107 h in animals treated with cycloheximide. Recovery of [3H]nitrendipine binding sites correlated with blood pressure restoration in spontaneously hypertensive rats. These data suggest that o-NCS-DHP possesses both reversible and irreversible actions. The reversible actions are unusually persistent compared with nifedipine and other 1,4-dihydropyridine analogs. This persistent, but reversible component, may be accompanied by an irreversible action particularly at the higher concentrations employed in the in vivo experiments.
Disulfiram is a potent inhibitor of rat 5-lipoxygenase activity
Authors: Choo Lancelot Y. , Riendeau Denis
Published: April 2011

The effect of disulfiram on the 5-lipoxygenase activity from rat polymorphonuclear leukocyte cell-free lysates was determined and compared with that of other thiocarbamoyl and aryl disulfides. Disulfiram was a potent inhibitor of the soluble 5-lipoxygenase causing 50% inhibition at submicromolar concentrations (0.4–0.7 μM). The inhibition by disulfiram was similar to that of bis(diisopropylthiocarbamoyl) disulfide with both compounds being about 100-fold more potent as inhibitors than the structurally related bis(4-methyl-1-homopiperazinylthiocarbonyl) disulfide analog. The potency of 5-lipoxygenase inhibition by disulfiram was comparable to that of diphenyldisulfide (IC50 = 0.2–0.4 μM), in the same range or better than most typically used inhibitors. However, the degree of inhibition by disulfiram was more sensitive to thiols than that of diphenyldisulfide, as shown by the selective protection against disulfiram inhibition by low concentrations of thiols. Diethyldithiocarbamate, the reduction product of disulfiram, was a less potent inhibitor of the 5-lipoxygenase activity, causing only a partial inhibition (40–60%) over a wide range of concentrations (2–30 μM). The results demonstrate that disulfiram is a potent inhibitor of 5-lipoxygenase in vitro and provide the basis for further investigations on the effect of the drug on leukotriene biosynthesis inhibition and its contribution to the ethanol–disulfiram reaction. They also indicate that disulfiram represents a sensitive reagent to characterize the thiol requirement of the 5-lipoxygenase reaction.
Bradykinin stimulates a rise in cytosolic calcium in renal glomerular mesangial cells via a pertussis toxin insensitive pathway
Authors: Kremer S. , Harper P. , Hegele R. , Skorecki K.
Published: April 2011

Bradykinin elicits a complex response in the renal glomerulus which includes a reduction in the glomerular capillary ultrafiltration coefficient. To elucidate the biochemical mechanism of this response, we investigated calcium signalling in rat renal glomerular mesangial cells in culture using the calcium-sensitive fluorescent dye, Indo-1. Bradykinin was found to cause a concentration-dependent transient rise in cytosolic free calcium followed by a sustained slower secondary rise. The bradykinin response persisted with acute removal of extracellular calcium using EGTA, indicating that calcium entry from outside the cell did not mediate this primary response. Prolonged exposure to EGTA, which reduced intracellular stores, eliminated the calcium response to bradykinin but not to vasopressin, indicating differential sensitivity to intracellular calcium stores of these two hormonal responses. In agreement, prior stimulation with vasopressin significantly attenuated the response to bradykinin, but the converse did not occur. Aluminum fluoride and pertussis toxin were used to investigate the possible involvement of a guanyl nucleotide regulatory protein in signal transduction. Aluminum fluoride induced a transient rise in cytosolic calcium that was abrogated by prior exposure of the cells to pertussis toxin. This demonstrates the effectiveness of pertussis toxin and the presence of a calcium-signalling pathway susceptible to pertussis toxin in these cells. In contrast, the responses to bradykinin and vasopressin were unaffected by pertussis toxin. We conclude that bradykinin stimulates release of calcium from intracellular stores in glomerular mesangial cells via a pertussis toxin insensitive pathway. This mesangial response provides a direct biochemical basis for the bradykinin-induced fall in glomerular capillary ultrafiltration coefficient which has been observed in vivo.
Neural stimulation of gluconeogenesis in isolated pyruvate-perfused rat kidneys
Authors: Baines Andrew DeWitt , Drangova Rosa , Ho Patrick
Published: April 2011

To estimate peritubular norepinephrine concentration during renal nerve stimulation, we compared gluconeogenic responses in isolated pyruvate-perfused rat kidneys with electrical nerve stimulation and exogenous norepinephrine. During 2 and 4 Hz stimulation, venous norepinephrine was 1.7 ± 0.4 and 2.7 ± 0.9 nmol/L, respectively. Intra-arterial norepinephrine infusion of 60 pmol/min for 20 min (an amount corresponding to that released during 4 Hz stimulation) resulted in venous norepinephrine levels of 3.6 ± 0.6 nmol/L. Electrical stimuli (1, 2, and 4 Hz) sustained increases in vascular resistance of 2, 5, and 11% during 20 min of stimulation, while the norepinephrine infusion increased resistance gradually by 8% and a bolus (12.5 nmol/L) transiently increased resistance by 2%. All electrical and norepinephrine interventions, except 1 Hz, decreased fractional Cl excretion. Decreased glomerular filtration rate was observed only during 4 Hz stimulation. Gluconeogenesis transiently increased during stimulation at 2 or 4 Hz (12% (p = 0.056) and 15% (p = 0.028)). The 5% increase in gluconeogenesis during norepinephrine infusion did not differ from the increase during 4 Hz stimulation (p = 0.45). An exogenous norepinephrine bolus (12.5 nmol/L) increased gluconeogenesis 60% for 15 min, four times more than the response to 4 Hz nerve stimulation (p = 0.012). Therefore, we conclude that nerve stimulation sufficient to produce sustained vasoconstriction and antinatriuresis raised norepinephrine concentration less than 12 nmol/L on the peritubular surface of the S1 proximal tubule, thus accounting for the small gluconeogenic response.
Effects of a κ-receptor agonist, U-50,488H, on the release of endogenous brain dopamine
Authors: Clow Daniel W. , Jhamandas Khem
Published: April 2011

The potential interaction between κ-opiate receptors and dopamine activity was examined in this study by monitoring the effect of U-50,488H on the release of endogenous dopamine from rat striatal slices in both the absence and presence of 10 μM nomifensine, a potent dopamine uptake inhibitor. Basal dopamine release was increased 10-fold in the presence of nomifensine, and the normally steady base line was observed to increase gradually under these conditions. U-50,488H, a potent κ-agonist, enhanced the spontaneous release of dopamine, but only at relatively high concentrations (40.0 μM) and only in the absence of nomifensine. Likewise, nomifensine and U-50,488H (40.0 μM) each significantly inhibited the synaptosomal uptake of [3H]dopamine. As with basal release, nomifensine markedly enhanced the potassium-evoked release of dopamine, and this evoked release was significantly attenuated by U-50,488H (0.4 and 40.0 μM) in both the absence and presence of nomifensine. This opiate-mediated inhibition of evoked dopamine release was antagonized in a time-dependent manner by the putative κ-antagonist, WIN 44,441-3, suggesting that striatal κ-receptor activation modulates dopamine release.
Energy cost and metabolic regulation during intermittent and continuous tetanic contractions in human skeletal muscle
Authors: Spriet Lawrence L. , Soderlund Karin , Hultman Eric
Published: April 2011

Muscle ATP turnover, glycogenolytic, and glycolytic rates were estimated to compare the energy cost and glycolytic regulation of 102.4 s of continuous and intermittent stimulation. Quadriceps femoris muscles of male subjects were stimulated at 20 Hz for one continuous contraction (n = 6) or a series of 64 contractions (1.6 s on, 1.6 s off; n = 6). Leg blood flow was occluded and muscle biopsies were obtained at rest and following 51.2 and 102.4 s of contraction time in both conditions. Isometric force production by the activated knee extensors decreased to 55% of initial contraction force with intermittent and 80% of initial contraction force with continuous stimulation following 51.2 s of contraction time. Corresponding ATP turnover rates were 4.49 ± 0.39 and 3.80 ± 0.44 mmol∙kg dry muscle−1∙s−1.When normalized for tension production the respective energy costs of intermittent and continuous contractions were 3.66 ± 0.47 and 2.64 ± 0.36 mmol ATP∙kg−1∙100 N−1.Glycogenolytic rates were identical during the first 51.2 s of stimulation but glycolysis was higher in the intermittent group (1.05 ± 0.10 vs. 0.86 ± 0.11 mmol∙kg−1∙s−1). We suggest that the increased ATP utilization of intermittent contractions is associated with enhanced Ca2+-transport ATPase activity during relaxation and enhanced actomyosin ATPase activity during the early portion of each contraction. Glycolytic rate is dependent on ATP demand and regulated by allosteric modulators of phosphofructokinase and pyruvate kinase which are released or consumed in the reactions associated with contraction.
Glucose and lactate turnover and gluconeogenesis in chronic metabolic acidosis and alkalosis in normal and diabetic dogs
Authors: Hetenyi Jr. G. , Paradis H. , Kucharczyk J.
Published: April 2011

The turnover rate of glucose, the irreversible disposal rate of lactate, and the rate of gluconeogenesis from lactate were calculated by tracer methods in four normal and four alloxan-diabetic dogs under control conditions as well as in chronic, stable metabolic acidosis and alkalosis. Acidosis was produced by feeding dogs 0.8–1 g∙kg−1∙day−1 NH4Clover 1 week, alkalosis was produced by feeding dogs a chloride-free diet and injections of furosemide. Mean plasma pH in the three states were 7.28 ± 0.013, 7.40 ± 0.024, and 7.51 ± 0.015 in normal dogs, and 7.22 ± 0.025,7.42 ± 0.009, and 7.49 ± 0.002 in the diabetic dogs. Respective mean plasma bicarbonate levels were 14.6 ± 0.88, 22.0 ± 0.80, and 32.4 ± 1.88 mequiv. in normal dogs, and 12.3 ± 1.30, 22.6 ± 0.66, and 35.0 ± 1.14 mequiv. in diabetic animals. In normal dogs shifts in acid–base balance had no effect on the level of plasma glucose or the turnover rate of glucose. In diabetic dogs plasma glucose level was significantly elevated by alkalosis. Plasma lactate was positively correlated with plasma pH(r = 0.69, p < 0.01) and was in general higher in diabetic than in normal animals. The increment in concentration was due to a decreased clearance of lactate from the plasma. The irreversible disposal rate was not changed by the acid–base status. Whereas a larger fraction of lactate removed from the plasma appeared in glucose in diabetic animals, this fraction was not changed significantly by shifts in the acid–base status. The glycemic response to i.v. injected 0.05 U/kg insulin was not appreciably altered by the shifts in acid–base status in either normal or diabetic dogs. Stable metabolic acidosis and alkalosis of moderate degree has little effect on glucose and lactate kinetics and gluconeogenesis from lactate in either normal or diabetic dogs.
Time course of adaptation to hypoxia in newborn rats
Authors: Piazza Tiziana , Lauzon Anne Marie , Mortola Jacopo P.
Published: April 2011

In newborn rats after a few minutes of hypoxia, ventilation is similar to the normoxic value. Nevertheless, after a few days in hypoxia, newborn rats have a sustained hyperventilation. In this study we examined the time course of the newborn rat's adaptation to hypoxia. Measurements of body size, hematocrit, lung and heart mass, and breathing pattern have been performed on newborn rats exposed to hypoxia (10% O2) for different time intervals from 4 to 60 h (hypoxic, H), and on same-age rats growing in air (controls, C). Ventilation measured by flow plethysmography was increased in H rats above the C value from about 8 h; this was due to a higher breathing rate and, from 24 h, also to a larger tidal volume. During the early hours of hypoxia, oxygen consumption measured manometrically was about 50% of C, while after 3 days in hypoxia it was almost like the C value. These observations indicate that the lack of sustained hyperventilation, characteristic of the newborn's acute exposure to hypoxia, is an immediate but transient phenomenon that is resolved after a few hours, and suggest a tight link between metabolic and ventilatory hypoxic responses. Body weight of H rats was less than in C, owing to an immediate decrease below the prehypoxic value. Dry heart and lung weight changed in proportion with the rest of the body during the first 36–48 h of hypoxia, then they increased disproportionately more. Hence, these temporal changes suggest that the large heart and lung weight – body weight ratios of the chronic hypoxic animals result from their smaller body mass and the stimulated growth of cardiac and pulmonary tissues.
Distribution of atrial natriuretic factor-like immunoreactivity in the brain of the frog Rana ridibunda
Authors: Netchitaïlo P. , Feuilloley M. , Lihrmann I. , Leboulenger F. , Gutkowska J. , Cantin M. , Pelletier G. , Vaudry H.
Published: April 2011

The localization of atrial natriuretic factor (ANF)-like immunoreactivity in the central nervous system of the frog Rana ridibunda was examined by the indirect immunofluorescence technique, using an antiserum against synthetic ANF (Arg101-Tyr126). Immunoreactive cell bodies were principally found in the dorsal and medial pallium, the medial septal nucleus, the ventrolateral and anteroventral areas of the thalamus, the lateral forebrain bundle, the posterolateral thalamic nuclei, the preoptic nucleus, the dorsal infundibular nucleus, and the anteroventral tegmentum nucleus of the mesencephalon. Numerous cell bodies and a very dense fiber bundle were visualized in the interpeduncular nucleus. All the areas mentioned above contained a high density of immunoreactive fibers. In addition, the amygdala, the infundibular nucleus, the median eminence, and most of the areas of the mesencephalon contained a moderate number of ANF-positive nerve processes. In the frog pituitary, fibers and nerve terminals were found in the peripheral zone of the neural lobe. The intermediate and anterior lobes of the frog pituitary were totally devoid of ANF immunoreactivity. These results indicate that ANF-like material is widely distributed in the frog brain and that ANF may be involved in various brain functions including neuroendocrine regulations.
Immunoglobulin E mediated membrane conductance changes in rat basophilic leukemia cells
Authors: Barajas-López Carlos , Huizinga Jan D.
Published: April 2011

Electrophysiological effects of anaphylactic stimulation of rat basophilic leukemia cells (RBL-2H3) were studied using conventional microelectrodes. Stimulation of passively sensitized cells by anti-immunoglobulin E resulted in hyperpolarization followed by depolarization. These changes in membrane polarization were associated with a decrease in input membrane resistance. No effect of anaphylactic stimulation was seen in Ca2+-free solution or when Ca2+ influx was blocked by Co2+, but it was mimicked by the Ca2+ ionophore A-23187. This suggests that the changes in ionic conductances were associated with calcium influx. These results support the hypothesis that membrane conductance changes are involved in the stimulus-secretion process of the RBL-2H3 cells.
Potential misconceptions arising from the application of enzyme kinetic equations to ligand–receptor systems at equilibrium
Authors: Tomlinson George
Published: April 2011

The interactions of ligands with their receptors and the modulation of those interactions by other ligands are commonly described in the (verbal and mathematical) language of enzymology. While this analogy is appropriate in that velocity–substrate concentration curves and ligand–receptor binding isotherms often conform to similar rectangular hyperbolic relationships, the mathematical and conceptual similarities between the two systems strictly apply only to the simplest cases (absence or presence of a pure competitive inhibitor). To conclude that other classic forms of enzyme inhibition (uncompetitive, noncompetitive, mixed) have their exact mechanistic counterparts in "receptorology" can be misleading if due consideration is not given to the differences between the two types of system (steady-state versus equilibrium). In this communication, it is shown that relating receptor binding mechanisms to enzymological models results in Scatchard plots that are markedly different in appearance from the equivalent Eadie plots displaying enzyme kinetic data for all cases other than those in the absence of inhibitor or in the presence of a purely competitive inhibitor. It follows that receptor binding systems, which do produce inhibition patterns similar to those indicative of uncompetitive, noncompetitive, or mixed inhibition of an enzyme system, must do so through mechanisms that are different from those that produce these effects on enzymes. Consequently, terms such as uncompetitive or noncompetitive inhibition have different meanings when applied to receptors as compared with enzymes.
Prolactin, LH, and estradiol-17β in utilization of lipoprotein substrate by porcine granulosa cells in vitro
Authors: Rajkumar K. , Klingshorn P. , Chedrese P. J. , Murphy B. D.
Published: April 2011

Porcine granulosa cells cultured under serum free conditions responded by increased progesterone secretion to the addition of the leuteotropic hormones, LH, prolactin, and estradiol. Provision of extracellular substrate for steroidogenesis in the form of porcine high density lipoprotein or low density lipoprotein enhanced progesterone accumulation by granulosa cell cultures. Estradiol, LH, and prolactin all greatly increased progesterone accumulation in the presence of either high or low density lipoproteins. Increases in progesterone accumulation following addition of prolactin or LH in combination with estradiol suggested the presence of a synergistic interaction among leuteotropins. Pre-exposure of granulosa cell cultures to estradiol increased the subsequent stimulatory effect of prolactin on lipoprotein utilization. It is concluded that all three leuteotropins function to enhance and may interact in the utilization of extracellular lipoprotein substrate for progesterone synthesis.
Vascular reactivity to norepinephrine in rats with cirrhosis of the liver
Authors: Villamediana Luis M. , Dieguez Godofredo , Santos Juan C. , García-Villalón Angel L. , Caramelo Carlos , López-Novoa José M.
Published: April 2011

Vascular reactivity to norepinephrine was studied in rats with early cirrhosis of the liver and in control rats. Cirrhotic rats showed water and sodium retention but not ascites. Studies were performed in whole animals, isolated hindquarters, and isolated femoral arteries. Plasma catecholamine levels were measured by radioenzymoassay and their urinary metabolites by gas–liquid chromatography. Plasma norepinephrine was 331 ± 49 pg/mL (mean ± SEM) in control rats and 371 ± 66 pg/mL in cirrhotic animals (p > 0.05). No differences in plasma epinephrine or dopamine were observed. Urinary excretion of catecholamine metabolites was increased in cirrhotic rats. These data suggest a moderate activation of the sympathetic nervous system. In basal conditions, cirrhotic rats showed lower mean arterial pressure than controls (101 ± 4 vs. 116 ± 4 mmHg (1 mmHg = 133.3 Pa); p < 0.01). However, perfused hindlimb resistance was similar in cirrhotic and in control animals. In the whole animal and in the perfused hindquarter, the contractile response to norepinephrine was similar for control and for cirrhotic rats. The contractile response to norepinephrine exhibited by isolated femoral arteries was similar in those from cirrhotic and control rats. This indicates that the peripheral vascular bed has a well-maintained ability to constrict in response to norepinephrine, suggesting that circulatory abnormalities in early experimental cirrhosis are not caused by refractoriness of the vascular smooth muscle to norepinephrine.
Renal actions of atrial natriuretic peptide on the postischemic kidney
Authors: Akabane Satoshi , Imanishi Masahito , Matsushima Yohkazu , Kawamura Minoru , Kuramochi Morio , Ito Keiichi , Omae Teruo
Published: April 2011

The objective of this study was to evaluate the renal actions of atrial natriuretic peptide (ANP) in the unilateral postischemic kidney of anesthetized dogs with a severe reduction in glomerular filtration rate. The dose of atrial natriuretic peptide (50 ng∙kg−1∙min−1) we gave did not alter the mean systemic arterial pressure, renal blood flow, and glomerular filtration rate in the normal kidney, as determined in foregoing studies. ANP was infused into the intrarenal artery continuously for 60 min after the release from 45 min of complete renal artery occlusion. In the vehicle-infused group, the glomerular filtration rate fell dramatically (6% of control), the renal blood flow decreased (60% of control), and the mean systemic arterial pressure tended to increase (136% of control). The urine flow rate and urinary excretion of sodium decreased significantly (25 and 25%, respectively) at 30 min after reflow in the postischemic period. Continuous renal artery infusion of ANP resulted in a marked increase in urine flow rate (246% of control) and the urinary excretion of sodium (286% of control). The administration of ANP led to an improvement in renal blood flow (99% of control) and glomerular filtration rate (40% of control), and attenuated the rise in mean systemic arterial pressure (109% of control), compared with findings in the vehicle-infused group. Plasma renin activity and prostaglandin E2 concentration in the renal venous blood were elevated after the release from complete renal artery occlusion in both groups. These results indicate that the vascular effects of ANP on the postischemic kidney were enhanced and that the peptide maintained the natriuretic effect.
The action of agonists and antagonists at the histamine H1 receptor and receptor protection studies in guinea pig ileum
Authors: Cook D. A. , Yong M. S. , Ramji K. , Vollrath B.
Published: April 2011

We have examined the ability of histamine and the competitive reversible antihistamines to protect the histamine H1 receptor against alkylation with the 2-haloalkylamines, phenoxybenzamine and SY-14. In isolated guinea pig ileum these irreversible antagonists produce a parallel shift in the dose–response curve to histamine with retention of the maximum response if they are used at concentrations less than about 10−6 M. Treatment with these 2-haloalkylamines in the presence of a high concentration of histamine did not alter the blocking activity. Thus histamine appears to be unable to protect its own receptor against irreversible blockade. The competitive reversible antagonists, on the other hand, did provide effective protection against irreversible blockade. It is likely that the competitive reversible H1 receptor antagonists have at least some part of their attachment site in common with irreversible antagonists of the 2-haloalkylamine type, while the inability of histamine to provide self-protection suggests that its primary attachment site is different from that of the antagonists.
Stimulation of rapidly adapting pulmonary stretch receptors by pulmonary lymphatic obstruction in dogs
Authors: Ravi K. , Teo K. K. , Kappagoda C. T.
Published: April 2011

The effects of pulmonary lymphatic obstruction and pulmonary venous congestion on the activities of slowly adapting receptors (SAR) and rapidly adapting receptors (RAR) of the airways were examined in anaesthetized, artificially ventilated dogs. In 11 out of 12 RAR (12 dogs) examined, pulmonary lymphatic obstruction for a period of 20 min produced a sustained significant increase in activity without a significant change in peak airway pressure and dynamic compliance. The activity remained significantly elevated even after the pulmonary lymphatic obstruction was released. This stimulus was without effect on the SAR (n = 5 dogs). Pulmonary venous congestion alone increased the RAR activity (n = 7 dogs) significantly without producing significant changes in airway mechanics. Lymphatic obstruction, when superimposed upon congestion, did not produce a further significant increase in activity. In four dogs the effect of pulmonary venous congestion (left atrial pressure increased from 7.6 ± 1.7 to 16.3 ± 2.7 mmHg) (1 mmHg = 133.3 Pa) on pulmonary lymphatic flow was examined. The procedure caused a significant increase in lymph flow. These results suggest that in the dog, the RAR activity is influenced by changes in the pulmonary extra vascular space.