bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of the antiandrogen hydroxyflutamide on progesterone secretion by preovulatory rat follicles in vivo and in vitro
Authors: Chandrasekhar Yallampalli , Armstrong David T.
Published: April 2011

Serum and ovarian progesterone levels and in vitro production of progesterone by preovulatory follicles were measured on proestrus in pregnant mare's serum gonadotropin (PMSG) primed immature rats in which the luteinizing hormone (LH) surge and ovulation were blocked by administration of the antiandrogen hydroxyflutamide. Serum progesterone levels observed at 12:00 on proestrus were significantly elevated, twofold above those observed in vehicle-treated controls, by in vivo administration of 5 mg hydroxyflutamide 4 h earlier. In control rats, proestrous progesterone did not increase until 16:00, in parallel with rising LH levels of the LH surge. No LH surge occurred in the hydroxyflutamide-treated rats, ovulation was blocked, and serum progesterone declined throughout the afternoon of proestrus, from the elevated levels present at 12:00. Administration of human chorionic gonadotropin (hCG) at 11:00 advanced the elevation of serum progesterone by 2 h in vehicle-treated controls and prevented the decline in progesterone levels in hydroxyfiutamide-treated rats. The patterns of change in ovarian tissue concentrations with time and treatment were essentially similar to those observed for serum progesterone. In in vitro experiments, progesterone secretion during 24 h culture of preovulatory follicles obtained on PMSG-induced proestrus was significantly increased, sixfold, by addition to the culture media of 370 μM but not of 37 μM hydroxyflutamide. Testosterone (50 nM) and hCG (20 mIU/mL) caused 26- and 14-fold increases, respectively, in progesterone secretion by cultured follicles. Hydroxyflutamide significantly reduced the stimulatory effect of testosterone but not of hCG on progesterone secretion in vitro. These results suggest that the antiandrogen hydroxyflutamide stimulates progesterone secretion, both in vivo and in vitro, through an initial androgen-agonistic action, before its antagonistic action is expressed. Its androgen-antagonistic action is responsible for its ability to inhibit testosterone-induced progesterone secretion in vitro. Its failure to reduce hCG-stimulated progesterone secretion in vivo and in vitro indicates that the latter stimulation is exerted independently of, and not as a consequence of, androgen action. The decrease in serum progesterone levels on the afternoon of proestrus therefore appears to be a consequence rather than a cause of the absence of an LH surge in the hydroxyflutamide-treated rats. It is concluded that the inhibitory effect of hydroxyflutamide on the preovulatory LH surge and ovulation is due not to inhibition of progesterone secretion at the ovarian level but most likely to neuroendocrine site(s) of action of the inhibitor.Key words: antiandrogen, hydroxyflutamide, progesterone, luteinizing hormone, ovulation, human chorionic gonadotropin.
Observations on the renal processing and sorting of prorenin
Authors: Hsueh Willa A. , Do Yung S. , Wang Pou-Hsiung
Published: April 2011

Human prorenin is the biosynthetic precursor of renin. In general, prorenin is enzymatically inactive until it is converted to renin. The kidney is the major source of renin in the circulation, and is also an important source of circulating prorenin. The mechanisms of prorenin sorting and processing to renin in the juxtaglomerular cell may be a determinant of renal renin production. Therefore, our studies have focused on renal enzymes involved in "limited proteolysis" of prorenin to renin and on the morphology of prorenin sorting in the human juxtaglomerular cell.Key words: renin, processing, cell, sorting.
Activation and measurement of plasma prorenin in the rat
Authors: Ioannou P. , Loh A. Y. , Osmond D. H.
Published: April 2011

Prorenin determination in rat plasma has been problematic from the outset. Consequently, its existence is questioned by some and its quantity by others, making it difficult for knowledge to advance as to its function relative to the renin system. The present study examines major variables in the determination of rat plasma prorenin and renin, notably different prorenin activation protocols involving blood samples obtained under various conditions from animals under different anesthetics. We found that a trypsin activation step with 5 mg/mL plasma, 60 min at 23 °C, followed by a PRA step of 10 min at 37 °C, resulted in the highest prorenin estimates, up to approximately 400 ng∙mL−1∙h−1 in terms of angiotensin I, as compared with published values of 0–190, based on other protocols. These estimates were obtained despite considerable destruction of angiotensinogen (renin substrate) by trypsin. Cryoactivation of prorenin was much less effective than in human plasma but, when followed by trypsin, it facilitated greater activation than with trypsin alone. Comparable fresh and fresh-frozen plasmas had similar prorenin–renin values, but lower values were observed in plasmas that had been repeatedly frozen and thawed. Conscious rats and those anesthetized with Inactin or ether had higher renins and prorenins than those anesthetized with methoxyflurane or halothane. Rats with kidneys in place during blood collection had higher renins (but not prorenins) than those whose kidneys were clamped off, suggesting that last-minute renin release during blood collection had occurred. We conclude that (i) trypsin generates increased renin, or renin-like, activity in plasma, suggesting activation of a precursor; (ii) on this basis, high prorenin levels exist in normal rat plasma; (iii) renin and prorenin levels are variously influenced by different anesthetics and blood handling procedures; (iv) variation in prorenin levels suggests that it is a dynamic (functional?) component of the renin system; (v) prorenin measurements are heavily influenced by methodological variations during the trypsin step or the subsequent PRA step; (vi) using standardized methodology, the rat can serve as a model for investigating the function of prorenin in normotension and hypertension.Key words: tryptic activation, angiotensinogen, adrenalectomy, anesthesia.
Investigation of human and rat inactive renin in plasma and kidney
Authors: Jindra Jr. A. , Bultas J. , Ort J. , Kvetnansky R.
Published: April 2011

Under an initial interval of immobilization stress in rats, reciprocal changes of plasma active and inactive renin were observed, suggesting activation of circulating inactive renin. Molecular weight (MW) studies revealed that this activation might proceed via a MW shift from inactive renin with MW of 50 000 to active renin of MW 43 000. In a later interval of stress, under stimulated renin secretion, a lower MW form (38 000) of active renin was released into the circulation. This MW is close to that of active renin (39 000) found in rat kidney renin granules. In renin granules, equilibrated in fractions of 1.6 and 1.7 mol/L sucrose in discontinuous density gradient, trypsin-activatable renin activity formed 36 and 16% of total activity, respectively. In humans, under acute bicycle exercise, a lower MW form (39 000) of active renin was released into the circulation, while the content of inactive renin with MW in the range of 51 000–58 000 and at 47 000 did not substantially change. There was a slight decrease in circulating inactive renin passing through the kidney. The data suggest that, at least in rats, in vivo pathways for activation of inactive renin might exist, other than that proceeding before secretion from renin granules. Under the conditions of increased renin secretion, a lower MW form of active renin is mainly released into the circulation in both rats and humans.Key words: active renin, inactive renin, renal veins, renin granules, stress.
Effect of prostaglandin inhibition by indomethacin on plasma active and inactive renin concentration in men
Authors: Lijnen P. , Staessen J. , Fagard R. , Amery A.
Published: April 2011

The effect of inhibition of prostaglandin synthesis by indomethacin on active renin and on acid-activable inactive renin was studied in nine healthy, sodium-replete men, both at rest and exercise. These volunteers were investigated after pretreatment with placebo or indomethacin, 150 mg daily for 3 days. Indomethacin induced a decrease in active (p = 0.004), total (p < 0.001), and inactive (p = 0.02) renin at rest recumbent on average by 42, 19, and 8%, respectively, and at rest sitting on average by 45, 15, and 3%, respectively. Inhibition of prostaglandins with indomethacin reduced (p < 0.001) active and total renin at each level of work load but not (p = 0.32) inactive renin. However, the exercise-induced stimulation (p < 0.05) of active and total renin still occur during indomethacin. Indomethacin reduced (p < 0.001) at rest sitting and at maximal exercise the plasma concentrations of immunoreactive prostaglandins E2 by 50 and 54%, respectively, prostaglandin F2α by 36 and 39%, respectively, and 13,14-dihydro-15-keto-prostaglandin Fα by 38 and 60%, respectively. The urinary excretion of immunoreactive prostaglandin E2 and F2α was also reduced.Key words: indomethacin, prorenin, active renin, prostaglandins.
Plasma active and acid-activatable renin during the development of one-kidney, one-clip and two-kidney, one-clip hypertension in the rabbit
Authors: Noble A. R. , Richards H. K.
Published: April 2011

Systolic blood pressure in the central ear artery of eight rabbits increased by 21 mmHg (1 mmHg = 133.32 Pa) over 40 days following renal artery clipping and contralateral nephrectomy (one-kidney, one-clip). Plasma active and acid-activatable (pH 2.8) renin did not change significantly. Similar data were obtained from a group of 12 rabbits following renal artery clipping alone (two-kidney, one-clip) except that blood pressure in this group increased for 26 days but then declined until 40 days. Two animals with one-kidney, one-clip hypertension and three rabbits with two-kidney, one-clip hypertension had large increases in plasma active and inactive renin levels, which followed a more exaggerated rise in blood pressure than in the previous two groups. Forty days after unilateral renal artery clipping, the unclipped kidney was removed in 10 animals with two-kidney, one-clip hypertension. A further increase in blood pressure (+29%) occurred in seven of the animals but no change in plasma active or inactive renin. Results were compared with two groups of control animals, a unilateral nephrectomy group and a laparotomy group. None of the surgical procedures used produced a consistent pattern of change in the relative amounts of active and inactive renin in plasma. No marked changes in sodium, potassium, or water balance occurred in any group of animals.Key words: renovascular hypertension, renin, inactive renin, prorenin, rabbit.
Active and inactive renin in human forearm of hypertensive patients
Authors: Taddei Stefano , Favilla Stefania , Salvetti Antonio
Published: April 2011

Although many in vitro and animal studies indicate the existence of a local renin–angiotensin system, data regarding its physiological role are quite controversial, and moreover, evidence suggesting inactive and active renin release from vascular tissue in vivo is lacking both in animal and humans. The aim of our study was to evaluate whether β-adrenoceptor stimulation, a well-known stimulus to renin production, through isoproterenol might cause local renin production from vessels of the forearm of hypertensive patients. Drugs were infused into the brachial artery at systemically ineffective rates, while forearm blood flow (FBF, venous plethysmography), mean intra-arterial pressure, and heart rate were monitored throughout. Active and inactive vessel renin production was measured by calculating venous-arterial (V-A) differences by simultaneous sampling from brachial artery and an ipsilateral deep vein. Active renin (PRA) and total renin (Sepharose bound trypsin activation) were measured by radioimmunoassay while inactive renin was calculated as the difference between total and active renin. V-A differences were corrected for FBF to calculate renin extraction or production. In a group of 10 patients, isoproterenol, which was infused at increasing cumulative rates (0.03, 0.1, 0.3 μg∙100 mL−1 forearm tissue∙min−1 for 5 min each), caused a dose-dependent increment in FBF that was blunted by intra-arterial propranolol (n = 5) pretreatment (10 μg∙100 mL−1 forearm tissue∙min−1 for 10 min). β-Adrenoceptor stimulation caused a dose-dependent outflow of both active and inactive renin, an effect antagonized by propranolol. In conclusion, our data represent the first evidence in humans of tissue active and inactive renin production in the forearm vascular bed.Key words: tissue renin, active renin, inactive renin, isoproterenol.
Effects of tetanic stimulation on monosynaptic and dorsal root reflexes in kittens
Authors: Bawa Parveen
Published: April 2011

The effects of tetanic stimulation of peripheral afferents were examined on monosynaptic reflexes and dorsal root reflexes in kittens of various ages. Concomitantly recorded monosynaptic and dorsal root reflexes resulting from the stimulation of muscle nerves showed similar post-tetanic changes, namely, predominantly post-tetanic depression in neonates and post-tetanic potentiation in older kittens or adults. However, the changes in post-tetanic responses expressed as a percentage of control in dorsal root reflexes were much smaller than those in monosynaptic reflexes. When dorsal root reflexes originating from muscle and cutaneous afferents were compared, dorsal root reflexes from the latter behaved quite differently. For all ages, post-tetanic effects on dorsal root reflexes arising from cutaneous afferents were either insignificant or very small. The possible mechanisms underlying differences in post-tetanic effects from muscle and cutaneous afferents in adults and neonates are discussed.Key words: cat, kitten, development, dorsal root reflex, monosynaptic reflex, spinal cord, post-tetanic potentiation.
A north-temperate migratory bird: a model for the fate of lipids during exercise of long duration
Authors: Savard Roland , Ramenofsky Marilyn , Greenwood M. R. C.
Published: April 2011

Changes in deposition and the utilization of lipids during one night of migratory activity (nocturnal physical activity) were investigated in dark-eyed Juncos (Junco hyemalis) held in large outdoor aviaries. During vernal migration (May), captive Juncos were sampled at the beginning and conclusion of one night of nocturnal restlessness. Comparisons of variables were drawn with control samples collected from birds in March. Measurements included body weight, fat stored in subcutaneous depots (adiposity), adipose and muscle lipoprotein lipase activity, and fat cell lipolysis. During the migratory period, body weight and adiposity were increased over levels measured in the March birds (p < 0.01). On the other hand, neither body weight nor adiposity were significantly altered as a result of nocturnal physical activity and no significant changes were observed in adipose lipoprotein lipase activity. Fat cell lipolysis was lower at the beginning than at the end of nocturnal physical activity while, the opposite was observed for muscle lipoprotein lipase activity (p < 0.05). These results suggest that the amount of work of one night of nocturnal physical activity modifies both muscle lipoprotein lipase activity and fat cell lipolysis in an interrelated fashion. This phenomenon could act to direct a steady supply of fatty acids to the site of energy utilization, i.e., flight muscles.Key words: lipoprotein lipase, fat cell lipolysis, exercise, lipids.
Failure of oxygen radical scavengers to modify fatigue in electrically stimulated muscle
Authors: Shrier Ian , Hussain Sabah , Magder Sheldon
Published: April 2011

We used in situ gastrocnemius muscle of anaesthetized dogs to test the hypothesis that O2 radical production during muscle contraction contributes to fatigue. Muscle tension was measured with a force transducer and blood flow was monitored with an electromagnetic flow probe. Muscle contractions were produced by stimulating the nerve for 15 min at 20 Hz, 12 trains/min, and a duty cycle of 0.25. Three groups of seven animals were given an infusion of 0.2 mL∙min−1 of either saline, low-dose oxygen radical scavengers (250 IU∙mL−1 superoxide dismutase, 640 IU∙mL−1 polyethylene glycol (PEG)-catalase, 0.25 mg∙mL−1 deferoxamine, and 0.1 mg∙mL−1 oxypurinol), or high-dose oxygen radical scavengers (3300 IU∙mL−1 uperoxide dismutase, 6600 IU∙mL−1 PEG-catalase, 2.5 mg∙mL−1 deferoxamine, and 0.1 mg∙mL−1 oxypurinol). Blood flow and vascular resistance of the gastrocnemius muscle during stimulation did not differ among groups. After 15 min of stimulation, the developed tension (represented as a percentage of initial tension developed) was 66 ± 7% in the saline treated group, 70 ± 6% in the low-dose group, and 70 ± 4% in the high-dose group. The change in tension during recovery was not significant in the control or low-dose groups. However, there was partial recovery in the high-dose group. In conclusion, in this preparation, oxygen radical scavengers did not delay the development of decreased muscle tension.Key words: muscle fatigue, oxygen free radicals, resistance, flow.
Atrial dynamics and release of atrial natriuretic factor in vivo
Authors: Ledsome J. R. , King K. A.
Published: April 2011

In anaesthetized rabbits blood volume was altered by infusion and withdrawal of donor blood over the range of +60 to −40% of the blood volume. Right and left atrial pressures were measured and it was shown that sonomicrometry allowed adequate measurement of phasic changes in atrial dimensions. Plasma immunoreactive atrial natriuretic peptide concentration changed in a nonlinear fashion with changes in blood volume, and was linearly related to both peak systolic and peak diastolic right and left atrial wall stress. It was not possible to make the distinction between distension (diastolic stress) or tension (systolic stress) as the major determinant of ANF release in response to changes in blood volume.Key words: atrial dimensions, sonomicrometry, atrial compliance, atrial wall stress, blood volume, rabbit.
Studies of ANF processing and secretion using a primary cardiocyte culture model
Authors: Glembotski Christopher C. , Irons Christopher E. , Sprenkle Amy B. , Sei Catherine A.
Published: April 2011

In contrast to most other endocrine peptides ANF is stored in the heart as part of a larger prohormone, often called pro-ANF, yet is found in the circulation as a 28 amino acid peptide, called ANF. It has been shown that the conversion of the 126 amino acid pro-ANF to ANF occurs in the heart. This paper summarizes studies from our laboratory that have used a primary neonatal rat heart cell culture system to investigate the location and mechanism of this relatively unusual processing event. We have found that in culture the maintenance of the cells in a glucocorticoid-containing serum-free medium is required to observe processing as occurs in vivo. The cells contain the prohormone while ANF accumulates in the medium. Various experiments with protease inhibitors, pulse-chase biosynthetic labeling, incubation of cells with ANF-related peptides, and enrichment of cultures for myocytes have resulted in our conclusion that the processing of pro-ANF takes place most likely within the cardiac myocyte just prior to, but in concert with secretion. We have expanded on the use of this processing-competent atrial myocyte culture system to investigate mechanisms of stimulated ANF secretion. It has been shown that the activation of several phospholipase C-coupled receptors (e.g., α1-adrenergic and endothelin receptors) produces a robust release of ANF, but only in cultures that have been maintained under appropriate conditions. Further, it is apparent that the phenylephrine- or endothelin-mediated release of ANF depends in part on influx of extracellular calcium (Ca2+o), while the remaining component of stimulated release may depend on mobilization of intracellular calcium. It also appears that these agonists produce an initial phase of stimulated release, occurring within the first 5 min of agonist exposure, independent of Ca2+o, and a sustained phase that persists as long as the agonists remain on the cells, and depends on the presence of Ca2+o and thus calcium influx. Taken together our studies indicate that the hormonal environment may be an important factor directing the development of differentiated endocrine functions by atrial myocytes and may be involved in the regulation of ANF expression, biosynthesis, and secretion.Key words: atrial myocytes, processing, secretion, myocardial cells, calcium dependence.
Effects of small C-ANF receptor ligands on plasma levels of atrial natriuretic factor, blood pressure, and renal function in the rat
Authors: Okolicany Juraj , McEnroe Glenn A. , Gregory Lisa C. , Lewicki John A. , Maack Thomas
Published: April 2011

In this article, after a very brief review on ANF receptors, we report our study on the effects of small C-ANF receptor ligands in the rat. Two small ligands were synthesized: 2-napthoxyacetyl-isonipecotyl-rANF 11–15-NH2 (5 aa), containing 5 amino acids; and Ala7-rANF 8–17-NH2 (10 aa), containing 10 amino acids from the ring structure of ANF 1–28. After control periods, 5 aa or 10 aa were infused i.v. at a dose of 10 μg∙min−1∙kg−1 body weight for 70 min in anesthetized rats, followed by a 60-min recovery period. The 5 aa and 10 aa peptides significantly and reversibly increased plasma levels of endogenous immunoreactive ANF by 106 ± 29 and 52 ± 24 pg/mL, respectively. Infusion of the 5 aa peptide significantly decreased mean arterial blood pressure from 113 ± 1 to 100 ± 3 mmHg (1 mmHg = 133.32 Pa) and increased glomerular filtration rate from 1.6 ± 0.2 to 2.3 ± 0.2 mL/min, sodium excretion from 0.6 ± 0.3 to 3.4 ± 0.4 μmol/min, and potassium excretion from 0.5 ± 0.2 to 1.2 ± 0.2 μmol/min. Similar results were obtained with the 10 aa peptide. The effects of both peptides on blood pressure and sodium excretion persisted throughout the recovery period. The results confirm and extend previous observations showing that C-ANF receptors mediate the removal of ANF from the circulation. The shortening of the minimal peptide length necessary to bind to C-ANF receptors markedly enhances the possibility of developing orally active C-ANF receptor ligands for the treatment of cardiovascular and renal diseases.Key words: C-ANF receptors, linear atrial peptides, glomerular filtration rate, natriuresis, kaliuresis.
Autoradiography of atrial natriuretic peptide (ANP) receptors in the rat brain
Authors: Saavedra Juan M. , Kurihara Masaki
Published: April 2011

Quantitative autodradiography was used to localize and characterize atrial natriuretic peptide (ANP) receptors in the rat brain and to study their regulation. Peptide receptors are selectively located to circumventricular organs outside the blood brain barrier, such as the subfornical organ, and to brain areas involved in fluid and cardiovascular regulation. Dehydration, either by water deprivation of normal rats, or chronic dehydration present in homozygous Brattleboro rats lacking vasopressin, results in large increases in ANP binding in receptor number in the subfornical organ. In the deoxycorticosterone acetate (DOCA)–salt hypertensive model, only salt treatment, but not DOCA alone or the combination of DOCA–salt, increased the ANP receptor number in the subfornical organ and the choroid plexus. Both young and adult genetically hypertensive rats have a greatly decreased ANP receptor number in the subfornical organ and the choroid plexus. Selective displacement with an inactive analog lacking the disulfide bond (ANP 111–126) suggests that genetically hypertensive rats may lack C (clearance) atrial natriuretic peptide receptors. Our results implicate brain atrial natriuretic peptide receptors in the central response to alterations in fluid regulation and blood pressure.Key words: quantitative autoradiography, fluid regulation, atriopeptins, genetic hypertension, atrial natriuretic peptide binding sites.
Developing essential hypertension: a syndrome involving ANF deficiency?
Authors: Weidmann P. , Ferrari P. , Allemann Y. , Ferrier C. , Shaw S. G.
Published: April 2011

The pathogenesis of essential hypertension may possibly involve a deficiency in, or a decreased response to, endogenous vasodilator and natriuretic factor(s). Searching for hereditary or familial defects, it is plausible to evaluate blood pressure (BP) regulating factors in (yet) normotensive offspring of hypertensive parents (OHyp), some of whom are in fact in a stage of prehypertension. Studies by our group demonstrated that compared with healthy offspring of normotensive parents, OHyp have plasma atrial natriuretic (ANF) factor levels that are unaltered on a low salt intake but often fail to increase normally in response to a high salt intake. Plasma levels of cyclic GMP, the presumed second messenger of ANF, also may tend to be decreased in certain OHyp. On the other hand, renal excretory responses of cyclic GMP and electrolytes to ANF infused in "physiological" dose were unchanged in some OHyp tested so far. In borderline to moderate, uncomplicated essential hypertension, plasma ANF levels are often "normal." This may be inappropriately low relative to the existing BP, although the relationship of circulating ANF to atrial pressures in essential hypertension remains to be clarified. A conversion to higher plasma ANF values may occur with cardiac complications such as left ventricular hypertrophy, enlargement, dysfunction, or overt heart failure. Acute or short-term elevation of circulating ANF within the physiological and pathophysiological range by ANF infusion produces an exaggerated natriuresis and lowers BP in essential hypertensive patients. We postulate a syndrome of ANF deficiency, characterized by an impaired response of circulating ANF to high salt intake and by low cyclic GMP levels in certain yet normotensive offspring of essential hypertensive parents and by inappropriately "normal" plasma ANF in some patients with uncomplicated essential hypertension. At the stage of prehypertension, a disturbance in the ANF – cyclic GMP pathway may be expressed primarily at the circulatory rather than at the renal level. Hypertension-prone humans also tend to have an exaggerated vascular reactivity to norepinephrine. Whether the two disturbances may be interrelated is presently unknown. Both defects may potentially predispose to the development of essential hypertension. Relative ANF deficiency, an enhanced natriuretic response to ANF, and a sustained antihypertensive effect of infused ANF may represent a rational basis for treatment of essential hypertension with agents that activate the ANF system.Key words: offspring of hypertensive parents, essential hypertension, ANF, ANF deficiency syndrome, cyclic GMP, blood pressure regulation, vascular reactivity, renal function.
Graham W. Mainwood (1929–1990)
Authors: Biro George P. , Parry David J.
Published: April 2011

Canada's biomedical research community was deeply saddened by the untimely death of Graham Mainwood on June 10, 1990, after a brief but courageous battle with cancer.A native of Birmingham, U.K., Graham joined the Physiology Department at the fledgling Faculty of Medicine at the University of Ottawa in 1955. Since then, he has been a tireless force in building the reputation of the Department and of the Faculty. He became well known beyond Canada's borders for his studies on the electrophysiology and energetics of muscle and the mechanism of fatigue. His work on the effects of lactate flux and the role of changes in intracellular pH in muscle fatigue (e.g., Mainwood and Worsley-Brown 1975; Mainwood and Cechetto 1982; Renaud, Allard, and Mainwood 1986) is still cited in virtually every paper in this area. These studies, together with an ongoing interest in cardiac muscle, formed a natural platform from which he moved into the area of the elucidation of muscle metabolism by means of magnetic resonance spectroscopy–work he was actively pursuing up to the time of his death. Indeed, he had taken early retirement to be able to spend more time at the bench at the National Research Council of Canada. Three of the papers in this special issue arise from this work.All of us have been greatly touched by his sparkling intellect and generous helpfulness. We felt that the most appropriate way to recognize Graham's contributions to science and to our personal scientific development was to dedicate to his memory a special issue of the Journal which he served with distinction as a member of the Editorial Board for many years.
Kinetic studies on the biological activity of calmodulin in canine heart and liver during endotoxin shock
Authors: Clark B. Ruth , Liu Maw-Shung
Published: April 2011

Effects of endotoxin administration on the biological activity of calmodulin isolated from canine heart and liver were studied. Calmodulin was isolated and purified to homogeneity. The biological activity of calmodulin was determined by its ability to activate Ca2+-dependent phosphodiesterase. Results obtained 4 h after endotoxin administration show that the Vmax and A0.5 for calmodulin, the Vmax and Km for cAMP, and the Vmax and the Hill coefficient for Ca2+ were unchanged, while the S0.5 for Ca2+ for the activation of phosphodiesterase were significantly increased in the heart. The kinetic parameters as described above were not significantly altered in the liver. These data indicate that the biological activity of calmodulin is inhibited in the heart during endotoxin shock and that the nature of inhibition is associated with a mechanism involving a decrease in the affinity (1/S0.5) towards Ca2+ binding. Since calmodulin plays an important role in the regulation of cardiac function through calmodulin-dependent calcium transport systems, our findings may have a pathophysiological significance in contributing to the understanding of myocardial dysfunction in endotoxin shock.Key words: endotoxin shock, calmodulin biological activity, phosphodiesterase, heart, liver.
Influences of anabolic androgens on cardiac growth and metabolism in the rat
Authors: Kinson Gordon A. , Layberry R. A. , Hébert Barbara
Published: April 2011

Testosterone, and to a lesser degree methandrostenolone, was shown to influence cardiac growth in immature male rats by affecting protein synthesis and degradation. The nature of cardiac responses to androgen appear to depend on the prevailing experimental conditions. Protein synthesis was inhibited in the castrate rat and was stimulated by subsequent treatment with androgen. Under conditions of induced overgrowth of the ventricles, androgens gave rise to an attenuation of the effects of aortic constriction on ventricular mass and blood pressure involving smaller changes in protein synthesis and proteolysis. Concentrations of testosterone receptors in ventricular cytosol further indicated that the myocardium is more sensitive to androgen action during the prepubertal phase of the life-span. Changes in amount and properties of the receptors showed them to be functional and responsive to castration, aortic constriction, and administration of the androgens. The androgens affected cardiac protein balance by stimulating the incorporation of radiolabelled amino acid into protein in vivo. They also appeared to influence proteolytic processes involving lysosomal hydrolase activities, but their actions were either stimulatory or inhibitory depending on the internal environment. The heart is a target organ for several hormones including androgen, and our findings fortify the notion that hormone action needs to be investigated alone and in association with other endocrines.Key words: cardiac ventricle, testosterone, anabolic steroid, rat, protein, growth receptor, lysosome.
Peptide YY induces nerve-mediated responses in the guinea pig intestine
Authors: Krantis A. , Harding R. K.
Published: April 2011

The actions of peptide YY (PYY) were studied in longitudinal organ-bath preparations of the guinea pig intestine. PYY induced concentration-dependent (10−9 – 5 × 10−8 M) relaxations of tissue from the duodenum, jejunum, ileum, and colon. These responses were unaffected by adrenergic blockade and atropine treatment but could be prevented by tetrodotoxin. The pharmacology of PYY actions in segments of the small and large intestine indicated the involvement of intrinsic nonadrenergic, noncholinergic inhibitory neurones in the relaxation response to this peptide. All tissues could be made tachyphylactic to PYY without affecting their ability to respond to the direct acting muscle relaxants ATP or papaverine. Moreover, nicotinic ganglion stimulated relaxations and cholinergic nerve-mediated contractions were also unaffected. These results show applied PYY to have potent neurogenic actions in the guinea pig intestine with some similarities to PYY actions in the rat intestine.Key words: intestine, guinea pig, peptide YY, relaxations.
In vivo diffusion–perfusion magnetic resonance imaging of acute cerebral ischemia
Authors: Kucharczyk John , Mintorovitch Jan , Asgari Haleh , Tsuura Mitsuharu , Moseley Michael
Published: April 2011

We compared the anatomic extent and severity of ischemic brain injury shown on diffusion-weighted magnetic resonance (MR) images, with cerebral tissue perfusion deficits demonstrated by a nonionic intravascular T2*-shortening magnetic susceptibility contrast agent used in conjunction with standard T2-weighted spin-echo and gradient-echo echo-planar images. Diffusion-weighted images displayed increased signal intensity in the vascular territory of the middle cerebral artery 25–40 min after permanent occlusion, whereas T2-weighted images without contrast were negative or equivocal for at least 2–3 h after stroke was induced. Contrast-enhanced T2-weighted and echo-planar images revealed perfusion deficits that were spatially closely related to the anatomic regions of ischemic tissue injury. These data indicate that diffusion-weighted MR images are very sensitive to early onset pathophysiologic changes induced by acute cerebral ischemia. Combined sequential diffusion–perfusion imaging enables noninvasive in vivo examination of the relationship between hypoperfusion and evolving ischemic brain injury.Key words: in vivo, diffusion, perfusion, acute cerebral ischemia, magnetic resonance imaging.
Spatial relationship between cardiac mast cells and coronary capillaries in neonatal rats with cardiomegaly
Authors: Rakusan K. , Campbell S. E.
Published: April 2011

Density of cardiac mast cells and their localization with respect to coronary capillaries was studied in two experimental situations. First, cardiac hypertrophy produced by aortic constriction in 5-day-old rats was studied. Left ventricular weight increased more than twofold in this experimental situation, while the increases in total capillary length and total number of cardiac mast cells were much smaller, resulting in decreased densities of both tissue components. In the second series of experiments, localization of cardiac mast cells at two distinct portions of coronary capillaries was studied in normal hearts of adult rats. Differential histochemical staining enabled us to distinguish between the portions of capillaries close to arterioles and portions on the venular side. The number of mast cells close to arteriolar portions of coronary capillaries was significantly higher than one would expect in the case of their even distribution along the capillary wall. The relationship between the mast cells and formation of new capillaries is discussed.Key words: angiogenesis, microcirculation, capillary net, cardiac hypertrophy.
The effects of isotonic contractions on the rate of fatigue development and the resting membrane potential in the sartorius muscle of the frog, Rana pipiens
Authors: Renaud Jean Marc , Kong Melvin
Published: April 2011

The goal of this study was to characterize how isotonic contractions affect the rate of fatigue development. Muscle bundles dissected from frog sartorius muscles were stimulated with 100-ms long train of pulses (0.5 ms, 6 V, 140 Hz). To measure the effect of the isotonic contractions, isometric tetanus were elicited at regular time intervals during the stimulation to fatigue. In general, isotonic contractions caused a faster decrease in tetanic force than isometric contractions. The difference in tetanic force between an isotonic and isometric fatigue increased gradually over a 20-min period to 7.9 and 13.5% at 0.04 and 0.1 trains/s (TPS), respectively. At 0.2, 0.5, and 1.0 TPS, the decrease in tetanic force was also faster during an isotonic fatigue, which resulted in an initial difference in tetanic force between the two types of fatigue. The difference did not exceed 18.5% and did not persist throughout the stimulation period; i.e., the difference disappeared before the end of the fatigue stimulation. The half-relaxation time was prolonged during fatigue development, and the prolongation was greater during an isotonic fatigue, except at 0.04 TPS. The increases in the half-relaxation time at 0.2, 0.5, and 1.0 TPS were followed by a decrease, and the decreases were especially pronounced during an isotonic fatigue at 0.5 and 1.0 TPS. The results showed for the first time that isotonic contractions cause a faster rate of fatigue development in frog sartorius muscles, and this effect depends on the frequency of stimulation.Key words: muscle, fatigue, force, shortening, resting potential.
α1-Adrenergic stimulation increases the Vmax of isolated myocardial papillary muscles
Authors: Li Kai , Rouleau Jean L.
Published: April 2011

α-Adrenergic agonists have been shown to increase the tension developed by myocardial muscle. However, their effects on the maximum velocity of unloaded muscle shortening (Vmax) have not been rigorously examined. In this study, the contractile effects of the α-adrenergic agonist phenylephrine were examined in the presence of propranolol in papillary muscles of two species, the dog and the rabbit. In rabbit papillary muscles studied at physiological calcium concentrations (1.25 mM), phenylephrine increased all indices of contractility (Vmax, tension, and maximum rate of tension developed (dT/dt)) starting at 10−8 M. The percent increase in Vmax (121 ± 8%) was less than that of tension (188 ± 20%, p < 0.05) and dT/dt (262 ± 35%, p < 0.01). These findings occurred at both 29 and 35 °C and were inhibited by adding 10−5 M prazosin. Increasing extracellular calcium concentration from 1.25 to 15 mM caused changes in twitch configuration that were significantly different from those of phenylephrine. Calcium increased all indices of contractility more than did phenylephrine. This was particularly true for dT/dt (502 ± 82 vs. 262 ± 35% for phenylephrine, p < 0.01). Nonetheless, the ratio of increase in tension to increase in Vmax under both experimental conditions was similar (the increase in Vmax was 64% of that of tension with phenylephrine and 69% with increased calcium). At 1.25 mM calcium, the increase in contractility caused by phenylephrine was much smaller in dog myocardium as compared with rabbit myocardium. Rather, the effects of phenylephrine on dog myocardium studied at 1.25 mM calcium resembled that of rabbit myocardium studied at 15 mM calcium. We conclude that (i) α1-adrenergic receptor stimulation increases all indices of contractility at a similar threshold concentration but increases Vmax relatively less; (ii) despite markedly different effects on the intensity of the cytosolic calcium transient and twitch configuration characteristics, the increase in Vmax relative to tension caused by phenylephrine is similar to that caused by increasing extracellular calcium concentration; (iii) species differences in myocardial contractile response to α1-adrenergic stimulation exist, and that some of these differences can be abolished by altering extracellular calcium.Key words: α1-adrenergic, Vmax, contractility, calcium.
Gender differences and time course of castration-induced changes in porphyrins, indoles, and proteins in the Harderian glands of the Syrian hamster
Authors: Buzzell Gerald R. , Menendez-Pelaez Armando , Chlumecky Vera , Reiter Russel J.
Published: April 2011

Sexual differences and the effects of orchidectomy were determined for porphyrin and melatonin concentrations and for the activities of the enzymes N-acetyltransferase and hydroxyindole-O-methyltransferase, which synthesize melatonin from serotonin, in the Harderian glands of the Syrian hamster. Porphyrin concentrations in intact males were about 1/400th those of intact females. Castration for 1 week increased male Harderian porphyrin concentrations 10-fold; by 3 weeks, castrated male porphyrin levels were 140 times those of control values. N-Acetyltransferase activity in intact male Harderian glands was about 4 times that of females. Castration led to a drop in N-acety transferase activity to female levels within 2 weeks. Hydroxyindole-O-methyltransferase activity was 7 times higher in females than in males and castration had no effect on male Harderian hydroxyindole-O-methyltransferase activity. Neither gender nor castration influenced Harderian melatonin concentrations. Soluble proteins in Harderian glands from male and female hamsters and from male hamsters castrated for 1 and 4 weeks were examined by sodium docecyl sulfate – polyacrylamide gel electrophoresis. The gel profiles revealed several differences among the protein distribution in male and female gland lysates. Orchidectomy led to a female protein pattern within 4 weeks.Key words: hamsters, Harderian glands, sexual dimorphism, hydroxyindole-O-methyltransferase, melatonin, N-acetyl-transferase, porphyrins, proteins, SDS-PAGE.
A limited rote for leukotrienes and platelet-activating factor in food protein induced jejunal smooth muscle contraction in sensitized rats
Authors: Scott R. B. , Maric M.
Published: April 2011

To determine whether the release of newly formed mediators such as the peptidoleukotrienes and platelet-activating factor might modulate the food protein induced jejunal smooth muscle contraction observed in sensitized rats, Hooded–Lister rats were sensitized by injection of ovalbumin (10 μg i.p.) and controls were sham sensitized with saline. Fourteen days later the contractility of longitudinally (n = 9) and circularly (n = 9) oriented jejunal segments (mucosa intact) were examined in standard tissue baths in response to antigen, leukotrienes, and platelet-activating factor alone and in the presence of a specific leukotriene receptor antagonist (MK-571), a 5-lipoxygenase inhibitor (L651,392), and a platelet-activating factor receptor antagonist (WEB 2086). Although the responses of control and sensitized tissues to stretch and 10−4 M bethanechol were similar, only sensitized tissues contracted in response to antigen (1 mg/mL). MK-571 (10−5 M) reduced or significantly inhibited the contractile response of sensitized longitudinally and circularly oriented tissues to 10−7 M leukotrienes C4, D4, or E4, but neither L651,392 (10−4 M) nor MK-571 (10−5 M) significantly reduced the contractile response of sensitized tissues to antigen challenge. WEB 2086 (10−4 M) significantly (p < 0.01) reduced the contractile response of sensitized longitudinally and circularly oriented tissues to 10−7 M platelet-activating factor but did not significantly alter the response to antigen in longitudinally (45% of control, p = 0.14) or circularly (118% of control, ns) oriented jejunal smooth muscle. In this model leukotrienes and platelet-activating factor play an insignificant role in modulating food protein induced jejunal smooth muscle contraction in intestinal anaphylaxis.Key words: leukotrienes, platelet-activating factor, smooth muscle, anaphylaxis, food allergy.
Role of the sympathetic innervation in the cold-induced activation of 5′-deiodinase in brown adipose tissue of the Djungarian hamster
Authors: Meywirth Anette , Redlin Uwe , Steinlechner Stephan , Heldmaier Gerhard , Reiter Russel J.
Published: April 2011

The importance of the sympathetic innervation in the regulation of 5′-deiodinase activity in the interscapular brown adipose tissue (BAT) of the Djungarian hamster was studied. Interscapular BAT of Djungarian hamsters was either unilaterally or bilaterally denervated, and thereafter the animals were maintained at thermoneutral temperature or exposed to 0 °C for 24 h. Denervation reduced the norepinephrine content to 2–10% of the level in the control groups. Unilateral denervation was as effective as bilateral denervation in depressing the norepinephrine content of the interscapular BAT. Cold exposure for 24 h resulted in a pronounced 5′-deiodinase activation. Denervation reduced, but did not completely prevent, the cold-induced increase in 5′-deiodinase activity. The basal level of 5′-deiodinase activity at thermoneutral temperature was not reduced by denervation. We conclude that cold-induced activation of BAT 5′-deiodinase primarily depends on the intact sympathetic innervation.Key words: nonshivering thermogenesis, brown fat, 5′-deiodinase, Phodopus sungorus.
Involvement of K+-channel opening in endothelin-1 induced suppression of spontaneous contractions in the guinea pig taenia coli
Authors: Usune Sadaharu , Katsuragi Takeshi , Furukawa Tatsuo
Published: April 2011

Effects of porcine–human endothelin-1 on mechanical as well as electrical activities and on intracellular free Ca2+ levels in the guinea pig taenia coli were compared with those of nifedipine, a voltage-dependent Ca2+ channel blocker. Endothelin-1 (0.1–100 nM) caused a concentration-dependent suppression of spontaneous contractions but did not significantly affect the sustained contraction evoked by 40 mM KCl. However, nifedipine (0.1–100 nM) inhibited both types of contractions in a concentration-dependent manner. In electrophysiological studies, endothelin-1 (30 nM) or nifedipine (30 nM) eliminated spontaneous spike discharges. Endothelin-1 produced hyperpolarization, while nifedipine did not change the resting membrane potential. The endothelin-1 induced suppression of spontaneous contractions was dose-dependently antagonized by apamin (0.01–10 nM), an inhibitor of a small conductance Ca2+-dependent K+ channel, and D-tubocurarine (10–100 μM), an inhibitor of Ca2+-dependent K+ channel, but was unaffected by 4-aminopyridine (0.01–1 mM), an inhibitor of a voltage-dependent K+ channel. In the study with fura 2 excited at 340 nm, endothelin-1 abolished, from the tissue, the fluorescence signals that were coupled with spontaneous contraction. It is suggested that the inhibitory action of endothelin-1 on spontaneous contraction may be caused by hyperpolarization of the membrane that reduces the spontaneous generation of spike discharge coupled normally to an increase in the intracellular free Ca2+ levels in the guinea pig taenia coli. The hyperpolarization may be caused by activating apamin-sensitive Ca2+-dependent K+ channels.Key words: guinea pig taenia coli, endothelin-1, membrane potential, apamin, 4-aminopyridine.
Skeletal Muscle Metabolism Symposium
Authors: Bonen Arend
Published: April 2011

Living organisms move freely within their environment. It is a biological marvel that the mobility demands, ranging from postural maintenance to rapid bursts of movement, either at play or for survival, are performed by just one type of organ, namely skeletal muscle. To cope with these wide ranges of demands, exquisitely sensitive and complexly regulated biochemical pathways have evolved to support skeletal muscle energetics. A. V. Hill's challenge to biochemists led to the confirmation of a long-held belief that ATP provides the chemical energy for muscle contraction. However, the reservoir of ATP in muscle is extremely small, and without the continuous synthesis of ATP, muscle contractility would cease in only a few seconds. Therefore, the regulation of substrate metabolism in muscle has been of considerable interest to muscle physiologists and biochemists. In this symposium, five scientists provide a comprehensive review of different aspects of the regulation of skeletal muscle metabolism during increased contractile activity, from work in their laboratories.I would like to thank the Natural Sciences and Engineering Research Council of Canada for its financial support of this symposium.