bluuebunny/crossref_metadata_2025 huggingface dataset:
The relationship between ischaemic conduction failure and conduction velocity in cat myelinated axons
Authors: Fern R , Harrison PJ
Published: December 2014

Unitary action potentials have been recorded from cat spinal root filaments following electrical stimulation of hindlimb peripheral nerves. Potentials were monitored both before the ischaemia which follows the onset of cardiac arrest. The relationship between time to conduction failure (survival time) and initial conduction velocity was determined for 164 nerve fibres. This revealed that during ischaemia, slow myelinated axons tend to fail before fast myelinated axons. The average survival time was 24.6 min (range 11–39 min). The results are discussed in terms of (i) the possible mechanisms underlying ischaemic conduction block, (ii) their clinical implications for the role of ischaemia in peripheral neuropathies, and (iii) using ischaemia as an experimental technique to produce a differential nerve block.
Changes in human and rat uterine phosphoethanolamine and taurine with pregnancy and parturition
Authors: Phoenix J , Wray S
Published: December 2014

Phosphoethanolamine and taurine have been identified in uterine extracts from rat and, for the first time, human tissue. The concentration of phosphoethanolamine [PEtn] determined by HPLC and 31P NMR spectroscopy, increased markedly (40%) within the first 6‐12 h following parturition in rats, suggesting a role in involution. It appears that changes in [PEtn] account for the changes in the NMR phosphomonoester peak previously reported. A significant fall in [PEtn] was found in the human myometrium with pregnancy. Taurine was found in high concentrations in the rat and human uterus but decreased with pregnancy. The possible functional significance of these changes is discussed.
The relationship between blood flow and diameter in the iliac artery of the anaesthetized dog: the role of endothelium‐derived relaxing factor and shear stress
Authors: Snow HM , McAuliffe SJ , Moors JA , Brownlie R
Published: December 2014

The quantitative relationship between, increase in blood flow and arterial diameter was determined in an anaesthetized dog preparation (pentobarbitone, induction 30 mg kg‐1 i.v., maintenance 3 mg kg‐1 i.v. every 30 min). Changes in external iliac artery diameter were measured using piezoelectric ultrasound transducers capable of measuring diameters within the range of 2–20 mm with a resolution of +/− 0.005 mm. The diameter of the artery was measured at two sites, at one of which the endothelium was damaged using a balloon angioplasty catheter. Increases in blood flow were brought about by a combination of vasodilatation and cardiac stimulation (intra‐arterial administration of acetylcholine, downstream to the sites of diameter measurement, and electrical stimulation of the left ansa subclavia), thereby preventing large changes in blood pressure. The effects of both transient and maintained increases in blood flow on mean arterial diameter in the section of artery with intact endothelium were measured. Transient increases in mean flow from 147 +/− 0.21 to 611 +/− 80.0 ml min‐1 caused increases in diameter of 0.12 +/− 0.02 mm from a control of 5.42 +/− 0.19 mm. The mean delay between maximum flow and maximum diameter was 24.51 +/− 1.1 s and the half‐time for the return to control diameter was 82.0 +/− 9.6 s, compared with 12.1 +/− 1.5 s for the return to control flow. Maintained (3‐4 min) increases in mean blood flow (from 104.7 +/− 15.1 to 694.7 +/− 135.1 ml min‐1) produced larger increases in diameter of 0.48 +/− 0.30 mm from a control diameter of 4.89 +/− 0.12 mm. These changes in diameter were abolished by N omega‐nitro‐L‐arginine methyl ester (L‐NAME. 10‐100 mg kg‐1 i.v.). In the section of artery with damaged endothelium, changes in diameter were relatively small and associated with small changes in blood pressure. This effect of a nearly 7‐fold increase in flow on arterial diameter is dependent upon the integrity of the endothelium and the release of endothelium‐derived relaxing factor and causes a 29% reduction in calculated boundary wall shear stress.
Sodium and chloride transport across the rumen epithelium of cattle in vitro: effect of short‐chain fatty acids and amiloride
Authors: Diernaes L , Sehested J , Moller PD , Skadhauge E
Published: December 2014

Isolated mucosal sheets of cattle rumen were studied in vitro in Ussing chambers using a computer‐controlled voltage clamp. Unidirectional fluxes of Na+ and Cl‐ were measured in standard (short‐chain fatty acid (SCFA)‐free) or SCFA‐containing Ringer solution under zero voltage clamp conditions. Net NaCl absorption was observed under zero voltage clamp conditions, was stimulated by SCFAs and was not reduced by 1 mmol l‐1 amiloride, although short‐circuit current was significantly reduced by this concentration of the blocker. A constant coupling ratio of Na+ and Cl‐ absorption was observed.
Activation of the vasopressin‐sensitive water permeability pathway in the toad bladder by N‐ethyl maleimide
Authors: Marples D , Bourguet J , Taylor A
Published: December 2014

Vasopressin stimulates transepithelial water flow in the toad urinary bladder. We report here that N‐ethyl maleimide (NEM) (0.1 mM) produces a similar increase in osmotic water flow when applied to the mucosal surface of the tissue. NEM‐induced water flow is sensitive to inhibitors of hormone‐induced water flow, including serosal acidification, or exposure to quinidine or cytoskeleton‐disruptive drugs. NEM‐induced water flow is additive with that induced by a submaximal, but not a maximal, dose of vasopressin. The response to mucosal NEM is not reversed on removal of the reagent, but established NEM‐induced water flow can be inhibited by serosal acidification or quinidine. Like vasopressin, mucosal NEM induces the appearance of fusion profiles and intramembranous particle aggregates (putative water channels) in the apical plasma membrane of the granular cells, and the incidence of particle aggregates correlates with water flow. NEM does not cause an increase in intracellular cAMP. Our data suggest that NEM stimulates transepithelial water flow by irreversibly activating cellular mechanisms normally triggered by vasopressin, hence causing the insertion of water channels.
Differentiation of the peripherally mediated from the centrally mediated influences of adenosine in the rat during systemic hypoxia
Authors: Thomas T , Elnazir BK , Marshall JM
Published: December 2014

In two groups of Saffan‐anaesthetized, spontaneously breathing rats we have attempted to identify the peripheral influences of adenosine in mediating the responses evoked by hypoxia by using an adenosine receptor antagonist, 8‐sulphophenyltheophylline (8‐SPT, 20 mg kg‐1 i.v., Group 1) and adenosine deaminase (ADA, 500 units in 0.04 ml infused into the tail artery for 10 min, Group 2); neither of these drugs crosses the blood‐brain barrier. Recordings were made of respiration, heart rate, arterial pressure, blood flow and vascular conductance in the femoral artery, with ankle ligated (FBF and FVC, respectively) and in the carotid artery with all branches except the internal carotid ligated (CBF and CVC, respectively, Group 1 only) in order to indicate responses in skeletal muscle and cerebral vasculature. Hypoxia (breathing 8 or 10% O2 for 10 min) evoked an increase followed by a secondary decrease in respiration, tachycardia followed by secondary bradycardia, a fall in arterial pressure, an increase in FVC and CVC and an increase, followed by a decrease, in CBF. Neither 8‐SPT nor ADA had any significant effect on the secondary decrease in respiration. The secondary bradycardia was unaffected by 8‐SPT, but abolished by ADA. Both drugs reduced the fall in arterial pressure and the increase in FVC; 8‐SPT had no significant effect on the increase in CVC, but CBF no longer fell with arterial pressure. We propose that adenosine contributes to the hypoxia‐induced fall in arterial pressure by causing vasodilatation in skeletal muscle and possibly by causing bradycardia by a direct action on the heart; other evidence suggests that adenosine contributes to the secondary decrease in respiration by acting on central respiratory neurones. The possibility that the fall in arterial pressure and the secondary falls in CBF, respiration and heart rate, can become interdependent in a positive feedback manner is discussed.
Micropuncture and cannulation studies of fluid composition and transport in the ductuli efferentes testis of the rat: comparisons with the homologous metanephric proximal tubule
Authors: Clulow J , Jones RC , Hansen LA
Published: December 2014

Luminal fluids were collected in vivo by micropuncture and cannulation from the rete testis, efferent ducts and ductus epididymidis of the rat to determine the composition of efferent duct fluids and the rates of reabsorption of water and solutes by the efferent ducts. The concentration of spermatozoa increased by a factor of about 25 from 2.42 x 10(4) microliters‐1 in the fluid from the rete testis to 6.00 x 10(5) microliters‐1 in fluid at the end of the efferent ducts, indicating that 96.2% of the fluid leaving the testis is reabsorbed from the lumen of the efferent ducts. Most of this reabsorption (70.9% or 33.4 microliters h‐1) occurs in the region between the rete testis and the middle of the coni vasculosi, with only 25.1% (11.8 microliters h‐1) occurring between the coni and the beginning of the ductus epididymidis. However, reabsorption across the epithelium occurs at about the same rate in both regions, with the proximal region reabsorbing 17.2 microliters cm‐2 h‐1 (70.9% of fluid entering the region) and the distal region reabsorbing 12.2 microliters cm‐2 h‐1 (86.1% of fluid entering the region). Consequently, the fluid reabsorption rate for the whole efferent duct system (15.6 microliters cm‐2 h‐1) is similar to the values for individual regions. The principal solutes in luminal fluids from the efferent ducts are Na+ (137‐144 mM) and Cl‐ (113‐130 mM). The estimated sum contribution of Na+, Cl‐ and K+ to the osmotic pressure of luminal fluids was approximately 80% at each site sampled in the efferent ducts. The osmotic pressure of luminal fluid samples (301‐307 mosmol kg‐1) did not vary significantly along the ducts or differ significantly from that of blood plasma. The results demonstrate that there is a net reabsorption in the efferent ducts of nearly all the testicular output of water and inorganic electrolytes, and most of the protein, and that, in comparison, the ductus epididymidis is a negligible site of net fluid reabsorption. The results indicate that the ductus epididymidis, rather than the efferent ducts, is the site of accumulation of high concentrations of specific organic compounds like inositol. The efferent ducts are similar to the homologous proximal tubules of the metanephric kidney in that the luminal electrolyte composition (principal solutes Na+ and Cl‐) and osmotic pressure remain relatively stable and that fluid reabsorption is close to isotonic and occurs at the same rate as the reabsorption of Na+.
Defensive reflexes of the respiratory system in anaesthetized rabbits during high frequency jet ventilation
Authors: Javorka K , Kulisek V , Calkovska A
Published: December 2014

The defensive airway reflexes during high frequency jet ventilation (HFJV) were studied in anaesthetized, non‐vagotomized (n = 16) and vagotomized (n = 11) rabbits. The animals were ventilated by a high frequency jet ventilator. Sneezing and coughing were evoked by mechanical stimulation of the airways. During HFJV spontaneous breathing was inhibited only in the non‐vagotomized rabbits. Mechanical stimulation of the airways during HFJV evoked sneezing and coughing, in which the inspiratory component was inhibited. This inhibition occurred not only in defensive reflexes evoked from the regions with increased pressure (trachea, bronchi), but also from the nose. Vagotomy diminished but did not fully eliminate the changes in sneezing accompanying HFJV. The intensity of maximum expiratory efforts was not significantly affected by HFJV in both subgroups.
Effects of hyposmotic shock on taurine transport in isolated trout hepatocytes
Authors: Michel F , Fossat B , Porthe-Nibelle J , Lahlou B , Saint-Marc P
Published: December 2014

Isolated trout hepatocytes exposed to hypotonic medium undergo a regulatory volume decrease (RVD) that occurs via two separate routes, K(+)‐Cl‐ cotransport and amino acid release, the ion efflux accounting for 70% of the total osmolyte loss. Taurine, glutamine and glutamic acid are the most important and represent 73% of the total amino acid content (53 mmol (l cell water)‐1). The osmolarity‐sensitive release of amino acids was studied using [3H]taurine. Kinetic studies indicated two components for taurine influx: a linear Na(+)‐independent transport and a saturable Na(+)‐dependent system with a Michaelis‐Menten constant (Km) of 122 microM and a maximum velocity (Vmax) of 31.2 pmol (mg protein)‐1 min‐1. This second way of uptake was also chloride dependent and indicated an apparent coupling ratio Na+:Cl‐:taurine of 2:1:1. The latter component and the taurine efflux were stimulated during RVD, leading to intracellular amino acid loss. Taurine efflux activation during volume recovery was transient and also dependent on the presence of both Na+ and Cl‐ in the extracellular medium. Furthermore, taurine release and RVD were slowed down when Ca2+ was omitted from the medium. These results suggested two distinct and complementary mechanisms for volume regulation in trout hepatocytes during hypotonic conditions.
The mechanism of relaxation in response to magnesium by the aorta of pregnant rats with salt‐induced hypertension
Authors: Aloamaka CP , Ezimokhai M , Osman NA , Morrison J
Published: December 2014

The study examined the effect of salt‐induced hypertension on vascular relaxation in response to magnesium sulphate during pregnancy. Pregnant Wistar rats were fed for 6 weeks on a diet containing 0.3% (control) and 8.0% (test) sodium chloride. Aortic rings were then removed and contracted with 10(‐7) M phenylephrine or 30 mM potassium chloride. High salt intake increased the systolic blood pressure of the rats and increased the relaxation of phenylephrine‐contracted intact rings in response to magnesium sulphate. Neither endothelium removal nor treatment with 10(‐6) M indomethacin altered the relaxation of rings from the two groups of rats, when contracted with potassium chloride. Both processes significantly (P < 0.05) and similarly decreased the sensitivity and the maximal relaxation of rings from test rats contracted with phenylephrine; the relaxation of rings from the control rats was not altered. The results suggest that the relaxation of isolated rat aortic rings contracted with phenylephrine is enhanced in pregnant rats with salt‐induced hypertension. The mechanism involved in this enhancement is dependent on the vascular endothelium and receptor activation, and is indomethacin sensitive.
Composition and viscosity of interstitial fluid of rabbits
Authors: Zurovsky Y , Mitchell G , Hattingh J
Published: December 2014

Open‐ended plastic tubes were used as capsules for obtaining interstitial fluid from rabbits. The capsule was a 2.5 cm long plastic tube with an inner diameter of 6 mm. Three small incisions were made in the dorsal mid‐line of the anaesthetized rabbit; two capsules were inserted into each incision. A sample of capsular fluid was obtained 6 weeks later by inserting a hypodermic needle through the skin. The volume of fluid obtained from the capsule was sufficient for the analysis of total protein, albumin, albumin:globulin ratio, colloid osmotic pressure and the fluid viscosity. Despite the significantly lower total protein, albumin, globulin and colloid pressure of intracapsular fluid compared with plasma, the intracapsular fluid was found to have a greater viscosity. It is our opinion that the increased viscosity of the intracapsular fluid is due to the presence of a high molecular weight substance other than albumin and globulin, possibly hyaluronan.
Force responses to controlled stretches of electrically stimulated human muscle‐tendon complex
Authors: Cook CS , McDonagh MJ
Published: December 2014

Human first dorsal interosseus muscle was tetanized using percutaneous electrical stimulation. During the tetanus the muscle was subjected to constant velocity stretches. The stretch produced an enhancement of muscular force of up to 80% during the stretch. The size of the enhancement was dependent on both the amplitude and the velocity of the stretch. During an isometric hold phase after the stretch, the force decayed quickly for the first 100 ms and thereafter much more slowly, reaching a level 30% higher than the isometric force without pre‐stretch. The force during this hold phase was dependent on amplitude of stretch but was independent of stretch velocity. The interaction of tendon elasticity and muscle fibre mechanics in producing these responses is discussed. Implications for normal human movements are also explored.
The endothelial and non‐endothelial mechanism responsible for attenuated vasoconstriction in cirrhotic rats
Authors: Van Obbergh L , Leonard V , Chen H , Xu D , Blaise G
Published: December 2014

The pathogenesis of the vasodilatation associated with liver cirrhosis is not fully understood, but it has recently been postulated that it may be related to an increase in nitric oxide production. The aim of this study was to compare the response of isolated aortic rings from normal and cirrhotic rats to two vasoconstrictors, phenylephrine and U46619, a thromboxane analogue. Biliary cirrhosis was induced by ligation of the common bile duct; a sham operation was performed in control animals. Five weeks later, the aorta was removed and dissected into rings for study in organ chambers. Concentration‐response curves were obtained for the two vasoconstrictors from rings with intact endothelium and from rings denuded of endothelium. We found that the vasoconstriction produced by phenylephrine was decreased in cirrhotic vessels both with and without endothelium, but the response to U46619 was not modified by cirrhosis. Concentration‐response curves for phenylephrine were also obtained from rings in which the synthesis of nitric oxide and prostaglandins was inhibited by NG‐monomethyl‐L‐arginine and indomethacin, respectively. Nitric oxide synthase inhibition restored normal contractility of the rings with and without endothelium. This beneficial effect was not observed when cyclo‐oxygenase activity was blocked with indomethacin. This study suggests that cirrhotic vessels are hyporeactive to vasoconstrictors and that this effect is mediated through increased nitric oxide production. The improvement observed after inhibition of the nitric oxide pathway in denuded rings led us to suggest that cirrhosis also induces nitric oxide synthase in smooth muscle cells, as previously observed by others in septic animals.
A micropuncture study of the renal response to haemorrhage in rats: assessment of the role of vasopressin
Authors: Shirley DG , Walter SJ
Published: December 2014

The acute effects of haemorrhage (15 ml (kg body wt)‐1) on renal function at whole‐kidney and single‐nephron levels were studied in Inactin‐anaesthetized rats. In order to assess the role of vasopressin in mediating the haemodynamic effects, responses in untreated Long‐Evans rats were compared with those in Brattleboro rats (which lack circulating vasopressin) and in Long‐Evans rats treated with a V1 receptor antagonist. In time‐control animals, there were no significant changes in mean arterial pressure (MAP), excretion rates, glomerular filtration rate (GFR), superficial‐nephron GFR (SNGFR) or fluid reabsorption in the superficial proximal tubules during the course of the experiment. Following haemorrhage, the immediate reduction in MAP was followed in each group by partial recovery for 30 min; thereafter, MAP was stable. In untreated Long‐Evans rats, haemorrhage was followed by a 26% reduction in GFR (P < 0.001, measured 60‐150 min post‐haemorrhage) and a larger reduction (45%, P < 0.001) in SNGFR, so that the SNGFR/GFR ratio fell significantly ((27.9 +/− 1.9) x 10(−6), control period; (20.2 +/− 2.2) x 10(−6) post‐haemorrhage, P < 0.01). Slightly greater reductions in GFR and SNGFR were seen in Brattleboro rats and V1 antagonist‐treated Long‐Evans rats, which corresponded to slightly greater haemorrhage‐induced reductions in blood pressure in these groups; the falls in the SNGFR/GFR ratio were similar to that in untreated Long‐Evans rats. In all three groups of bled rats, fractional reabsorption by the proximal convoluted tubule increased slightly 30–60 min after haemorrhage, but during the subsequent period (60–150 min) returned to values indistinguishable from those during the control period. The results suggest that the renal haemodynamic changes that follow moderate haemorrhage include a preferential reduction in the GFR of superficial nephrons. Vasopressin appears to play no role in this response. Increases in fractional reabsorption in the proximal tubules are seen only during the immediate post‐haemorrhage period.
The effects of pregnancy and parturition on the substance P content of the rat uterus: uterine growth is accompanied by hypertrophy of its afferent innervation
Authors: Amira S , Morrison JF , Rayfield KM
Published: December 2014

The afferent innervation of the uterus might be expected to grow during pregnancy as the size of the uterus increases. Substance P‐like immunoreactivity (SPLI) has been measured as a means of monitoring the changes in the afferent innervation of the urogenital tract of rats during pregnancy and following parturition. The great growth of uterine tissue during pregnancy causes an overall decrease in SPLI concentrations during pregnancy, but it has been found that the amount of SPLI present per uterine horn increases nearly 3‐fold by the end of pregnancy. This increase is greater in uterine horns that contain more fetuses, suggesting that the SPLI innervation expands to a greater extent in uterine horns that undergo greater degrees of hypertrophy. There is a significant correlation between SPLI content and the number or total weight of fetuses throughout the latter two‐thirds of pregnancy. There is a fall in SPLI content of uterine horns following parturition, but not to a statistically significant degree, and this may be related to the release of the peptide during parturition.
Effect of calcitonin, elevated calcium and extracellular matrices on superoxide anion production by rat osteoclasts
Authors: Datta HK , Manning P , Rathod H , McNeil CJ
Published: December 2014

The electrochemical determination of superoxide anion generation by isolated mammalian osteoclasts was carried out by employing cytochrome c, immobilized at a surface‐modified gold electrode. Osteoclasts cultured on bone generated 15‐fold more superoxide anions than cells plated on plastic. Superoxide anion production by osteoclasts cultured on bone was almost completely abolished by salmon calcitonin, and partially abolished following exposure to elevated extracellular calcium. We therefore conclude that osteoclast activity is influenced substantially by the extracellular matrix.
Regional differences in the contractile and intracellular Ca2+ responses of the guinea‐pig vas deferens to neurotransmitters and excess K+
Authors: Kato K , Tsutsui I , Furuya K , Ozaki T , Yamagishi S
Published: December 2014

The contractile responses to various concentrations of noradrenaline (NA), adenosine triphosphate (ATP), acetylcholine (ACh) and excess external K+ in the epididymal, middle and prostatic portions of the guinea‐pig vas deferens were investigated by measuring the isotonic contraction, and the intracellular Ca2+ concentration ([Ca2+]i) using fura‐2 fluorescence. In the epididymal portion, the contractions evoked by each of these agonists were biphasic, comprising a transient followed by a tonic phase. In the middle portion, NA and ACh evoked biphasic contractions, whereas the ATP‐induced contraction was an almost monophasic transient. In contrast, in the prostatic portion, only transient contractions were evoked by ACh and ATP, while the NA‐induced contraction was oscillatory. The responses to each of the neurotransmitters in the three portions were not affected by pretreatment with TTX. The maximal responses of tonic contraction in response to each of the neurotransmitters were largest in the epididymal portion, decreased in the middle and were almost absent in the prostatic portion. These regional differences in the contractile properties of the vas deferens were also evident upon stimulation with excess external K+. As with the contractile responses, regional differences in the [Ca2+]i increases were observed during exposure to all the stimulants. It is suggested that the regional differences in the contractile responses of the vas deferens to various neurotransmitters and excess external K+ may involve variation in the mechanisms of Ca2+ homeostasis and in the sensitivity of the contractile apparatus to intracellular Ca2+ ions.
Cardiovascular responses to heat stress in late gestation fetal sheep
Authors: Walker DW , Hale  , Fawcett AA , Pratt NM
Published: December 2014

Heat stress during pregnancy in sheep is associated with respiratory alkalosis in both the mother and fetus, and, if prolonged, fetal growth is retarded. In seven pregnant sheep at 130‐137 days gestation we used 15 microns diameter radioactive microspheres to determine the effect of raising the environmental temperature from 20 to 43 degrees C for 8 h on uteroplacental blood flows and the distribution of cardiac output in the ewe and fetus. Fetal cardiac output increased slightly from 47.0 +/‐ 3.2 (mean +/‐ S.E.M.) to 54.0 +/‐ 3.6 ml min‐1 (100 g tissue)‐1, fetal arterial pressure and heart rate were unchanged, and total vascular conductance in the fetus increased significantly from 12397 +/‐ 1111 to 14732 +/‐ 1569 ml min‐1 kg‐1 mmHg‐1 (P < 0.01). Tissue blood flows (in ml min‐1 (100 g)‐1) increased significantly (P < 0.05) in the fetal body (e.g. nasal mucosa, torso and foreleg skin, adrenal, thyroid and thymus glands, brown and omental fats, heart, urinary bladder and carcass) and the fetal brain (e.g. cerebellum, cerebral grey matter, cervical spinal cord and pituitary gland). These regional vasodilatations occurred despite a significant fall (P < 0.01) in fetal arterial O2 saturation (55.2 +/‐ 1.8 vs. 38.6 +/‐ 2.4%), PO2 (18.1 +/‐ 0.7 vs. 13.5 +/‐ 0.8 mmHg) and PCO2 (51.0 +/‐ 1.8 vs. 36.1 +/‐ 2.3 mmHg); under normothermic conditions hypoxia is associated with peripheral vasoconstriction. Because hypocapnia would also be expected to cause cerebral vasoconstriction it is suggested that during hyperthermia, hypoxia‐ and hypocapnia‐induced vasoconstrictions are reduced by the release of vasodilator substances, or a decrease of sympathoadrenal effector responses. Blood flow to the fetal and maternal sides of the placenta did not change during the heat stress, suggesting that perfusion‐dependent transfer of heat from fetus to mother across the placenta does not increase under hyperthermic conditions.
Impact of gestational age on the catecholamine responses of the fetal sheep adrenal to cholinergic stimulation in vitro
Authors: Butler TG , Simonetta G , Roberts ML , McMillen IC
Published: December 2014

We have used the retrograde perfused adrenal preparation to investigate the catecholamine responses of the fetal sheep adrenal to increasing doses of acetylcholine (ACh) and excess potassium. Adrenal glands were collected from fetal sheep between 84 and 99 days gestation (before innervation; n = 7), between 103 and 113 days gestation (during innervation; n = 8) and between 137 and 144 days (after innervation; n = 9). Whilst the basal output of noradrenaline (NA) did not change between 84 and 144 days gestation, there was a significant increase in the adrenal output of adrenaline (Adr) between 84 and 144 days. The NA response to submaximal doses of ACh (10‐10(3) microM) was significantly greater (P < 0.05) between 84 and 99 days gestation (mean NA response: 49.6 +/‐ 11.4 nmol/(30 min)) than after 137 days gestation (mean NA response: 27.3 +/‐ 8.3 nmol/(30 min)). Similarly, when the NA response to 10‐10(3) microM ACh was expressed as a proportion of the maximal NA response to 10(4) microM ACh, the proportional NA response was greater at 84‐99 days (48.9 +/‐ 11.3% of maximal) than at 137‐144 days gestation (27.2 +/‐ 8.3%). The adrenal NA and Adr responses to 10(3) microM ACh between 84 and 137 days were reduced by up to 99% after the addition of hexamethonium. It appears, therefore, that the fetal adrenal is responsive to ACh before the development of innervation of the gland. There is also a decrease in sensitivity of the NA‐secreting cells to submaximal doses of ACh as gestation progresses, which is not associated with a decrease in the size of the releasable pool of NA in the fetal adrenal. We speculate, therefore, that innervation of the fetal adrenal may be associated with an increase in the excitation threshold of the NA cells to nicotinic stimulation.
Intracellular pH regulation in chicken enterocytes: the importance of extracellular pH
Authors: Peral MJ , Calonge ML , Ilundain AA
Published: December 2014

The present work reports the effect of pHo on pHi and Na(+)‐H+ exchanger activity. Intracellular pH tended to follow pHo, but the proton distribution across the cell membrane is not at electrochemical equilibrium. Removal of external Na+ acidified the cells by both reversing the direction of the Na(+)‐H+ exchanger and hyperpolarizing the cell membrane potential. The relationship between pHo and the rate of Na(+)‐dependent proton efflux following an acid load suggests that external protons interact with the Na(+)‐H+ exchanger at a single site with an apparent pK (‐log of the dissociation constant) of 7.22. The results demonstrate that maintenance of pHo in the physiological range is essential for maintenance of normal cell pH and that the activity of the Na(+)‐H+ exchanger involved in pHi regulation is affected by external protons. The results also suggest that, at least at low pHo, some intracellular mechanism is involved in pHi regulation.
Biphasic L‐arginine uptake by the isolated guinea‐pig heart
Authors: Kostic MM , Rosic GL , Segal MB , Rosic MA
Published: December 2014

L‐Arginine is the physiological substrate for the formation of nitric oxide (NO) and accounts for the biological activity of endothelium‐derived relaxing factor. We have studied L‐arginine transport in the heart using a rapid dual‐isotope dilution technique. The time course of L‐[3H]arginine uptake (extraction) by the isolated perfused guinea‐pig heart was found to occur in two phases. The first phase reached a plateau in 6.6 +/− 0.6 s and lasted 8.8 +/− 0.7 s, whereas the second phase developed a plateau after 16.3 +/− 0.8 s. The first phase of maximal uptake (Umax,1) accounted for 13.4 +/− 1.4% of the total uptake and the second (Umax,2) for 32.3 +/− 1.8%. The two phases of uptake were inhibited by unlabelled L‐arginine in a dose‐dependent manner, which suggests that both phases are carrier mediated. The degree of inhibition of Umax,1 and Umax,2 by unlabelled L‐arginine was not significantly different. Studies of the kinetics of uptake of these processes revealed an apparent Km,1 of 183 +/− 10 microM with a Vmax,1 of 50 +/− 10 nmol min‐1 g‐1 for the first phase and Km,2 of 167 +/− 14 microM with a Vmax,2 of 93 +/− 13 nmol min‐1 g‐1 for the second phase of uptake. These results suggest a similar affinity for the receptors of both transport systems, but with different values for Vmax (P < 0.05). In contrast, 1 mM unlabelled D‐arginine had no effect on either the first or second phase of uptake of L‐[3H]arginine by the heart, which suggests that these processes are stereospecific. In the presence of the L‐stereoisomer of nitro‐arginine‐mono‐methyl ester (L‐NAME), a potent inhibitor of NO synthesis, the Umax,1 was inhibited by about 60% while Umax,2 was inhibited by only 20%, which suggests that there is a difference in the effect of L‐NAME on the two phases of L‐arginine uptake. The first phase most probably represents uptake into the capillary wall, i.e. endothelium and smooth muscle, while the second phase represents entry into the extra‐endothelial compartment, i.e. the cardiac myocytes and fibroblasts.
Effect of an aldose reductase inhibitor, SNK‐860, on deficits in the electroretinogram of diabetic rats
Authors: Hotta N , Koh N , Sakakibara F , Nakamura J , Hamada Y , Naruse K , Sasaki H , Mizuno K , Matsubara A , Kakuta H , et al.
Published: December 2014

To determine the effect of an aldose reductase inhibitor, SNK‐860, on the worsening of the electroretinogram (ERG) during a diabetic state, rats with streptozotocin‐induced diabetes were administered SNK‐860 (1 or 4 mg kg‐1 orally) daily for 4 weeks. The effectiveness of SNK‐860 in prolonging the peak latencies of oscillatory potentials in the b‐wave of the electroretinogram of diabetic rats varied between these different waveform components (designated O1, O2 and O3). SNK‐860 (4 mg kg‐1 day‐1) either completely or partially prevented the prolonged peak latencies at O1 and sigma(O1 + O2 + O3). The drug failed to shorten the latency of the O2 and O3 components, and produced only a modest reduction in retinal levels of sorbitol and fructose, with no increase in myo‐inositol. There was a significant correlation between the state of the ERG (components O1 and sigma(O1 + O2 + O3)) and the retinal levels of sorbitol and fructose (P < 0.01), but not of myo‐inositol. It is concluded that a better understanding of the mechanism by which SNK‐860 acts may provide new insight into the pathogenesis of hyperglycaemic retinal dysfunction and help to establish effective therapy for diabetic retinopathy.
The role of adenosine receptors in the rostral ventrolateral medulla in the cardiovascular response to defence area stimulation in the rat
Authors: Thomas T , Spyer KM
Published: December 2014

The effects of microinjections of adenosine and an adenosine receptor antagonist into the rostral ventrolateral medulla (RVLM) on the cardiovascular changes associated with the defence reaction were investigated in anaesthetized rats. Responses to electrical and chemical stimulation in RVLM were determined in alpha‐chloralose‐anaesthetized, paralysed and artificially ventilated rats. Microinjections of adenosine (10 nM) and the adenosine receptor antagonist 8‐sulphophenyl‐theophylline (8‐SPT; 0.12 microM) were made into the RVLM and their effects on arterial pressure (ABP), heart rate (HR) and skeletal muscle blood flow determined. Microinjections of adenosine into the RVLM evoked either an increase or a decrease in ABP, with variable effects on HR. These actions of adenosine were blocked by prior injection of 8‐SPT at the same site. Histological analysis showed that adenosine evoked an increase in arterial pressure when injected into rostral areas of the RVLM, and a depressor response when injected into caudal regions. Furthermore, microinjections of adenosine into the RVLM augmented the increase in ABP evoked by electrical stimulation of the hypothalamic defence area (HDA). Whilst microinjection of 8‐SPT into RVLM had no effect on the baseline levels of the variables measured, it reduced the HDA‐evoked increase in ABP. From these results we propose that adenosine modulates the cardiovascular changes evoked upon stimulation of the HDA via an action on sympatho‐excitatory neurones within the rostral ventrolateral medulla.
Luminal capsaicin inhibits fluid secretion induced by enterotoxin E. coli STa, but not by carbachol, in vivo in rat small and large intestine
Authors: Nzegwu HC , Levin RJ
Published: December 2014

The enterotoxin E. coli STa induced fluid secretion in the rat jejunum, ileum and proximal colon in vivo that was greatly inhibited by the co‐presence of luminal capsaicin, which is a specific neural toxin of afferent C fibres. The same dose of capsaicin had no effect on the fluid secretion activated by carbachol in the jejunum, ileum and proximal colon. Afferent C fibres appear to be involved in the activation by STa of fluid secretion in the rat intestine in vivo.
The induction of c‐fos and c‐jun in the stretched latissimus dorsi muscle of the rabbit: responses to duration, degree and re‐application of the stretch stimulus
Authors: Dawes NJ , Cox VM , Park KS , Nga H , Goldspink DF
Published: December 2014

The mRNA levels of the proto‐oncogenes c‐fos and c‐jun were measured in the rabbit latissimus dorsi (LD) muscle in response to the application of various stretch regimes in vivo. It was shown that it was necessary for the stretch to be applied continuously over 1 h in order to achieve full induction of c‐fos and c‐jun mRNA at 1 h. In addition, a correlation was demonstrated between the degree of stretch imposed on the LD and the induced levels of c‐fos and c‐jun mRNA. Moreover, a second induction of these genes occurred when the LD was subjected to a second stretch stimulus. The magnitude and time course of the second response depended on the precise timing of the second stimulus in relation to the initial induction.
The cellular physiology of articular cartilage
Authors: Hall AC , Horwitz ER , Wilkins RJ
Published: December 2014

The cells of articular cartilage, or chondrocytes, live in an unusual and constantly changing physicochemical environment. They receive poorly understood signals during the loading of the tissue and produce, through a balance between macromolecular synthesis and degradation, a mechanically resilient extracellular matrix. Matrix turnover is influenced by changes to the intracellular composition (cell volume, pH and ionic content) of chondrocytes, and there are suggestions that this is altered in the disease process of osteoarthrosis. However, there is little information on the fundamental aspects of articular cartilage cellular physiology, which is essential if the factors controlling cartilage integrity in health and disease are to be understood. The present short review focuses on some of the membrane transporters of chondrocytes involved in volume regulation, electrophysiology and the regulation of intracellular pH.
The relationship between the intracellular Ca2+ transient and the isometric twitch force in frog muscle fibres
Authors: Sun YB , Lou F , Edman KA
Published: December 2014

The calcium‐sensitive fluorescent indicator fluo‐3 was used to monitor the intracellular free calcium concentration ([Ca2+]i) during isometric twitches in twenty‐nine single muscle fibres from the anterior tibialis muscle of Rana temporaria (sarcomere length, 2.2 microns; 2‐4 degrees C). The transient change in [Ca2+]i in response to a single stimulus was very brief. The time to peak and the duration of the Ca2+ signal, measured at 50% of the peak amplitude, were 8.3 +/‐ 0.2 and 22.1 +/‐ 1.4 ms (mean +/‐ S.E.M., n = 29), respectively. The mean peak amplitude of the Ca2+ transient was 3.2 +/‐ 0.1 microM, ranging from 2.46 to 3.92 microM among the different fibres. The isometric force started to rise 2.5 ms before [Ca2+]i reached its maximum value. When peak twitch force was attained, [Ca2+]i had already declined to approximately 10% of its maximum value. The peak force produced during a twitch was closely related to the decay phase of the Ca2+ transient, a slower decay of [Ca2+]i being associated with a greater amplitude of the twitch. The amplitude and duration of the Ca2+ transient varied in a systematic way relative to one another in different fibres, in that a greater amplitude was associated with a more rapid decay of the Ca2+ transient. NO3‐ and Zn2+ added to the external medium greatly enhanced the peak twitch force without markedly affecting the amplitude of the Ca2+ transient. However, both agents delayed the decay of [Ca2+]i. It is concluded that the decay phase of the Ca2+ transient is a more important determinant of the mechanical response during an isometric twitch than is the peak amplitude of the transient.
Transepithelial fluid shift generated by osmolarity gradients in unstimulated perfused rat submandibular glands
Authors: Nakahari T , Yoshida H , Imai Y
Published: December 2014

The effects of osmotic gradients on transepithelial water movements were examined in unstimulated perfused submandibular glands of the rat. Osmotic gradients were applied transepithelially by adding sucrose to or removing it from the perfusate. An infusion of hypotonic perfusate shifted fluid from the interstitium to the lumen (luminal fluid shift) transiently, whereas an infusion of hypertonic perfusate shifted fluid from the lumen to the interstitium (interstitial fluid shift) transiently. The amount of fluid shifted from lumen to interstitium increased as the luminal fluid osmolarity was raised or as the perfusate osmolarity was reduced. Thus, fluid movements across the salivary epithelium were shown to be simply dependent on the osmolarity difference between lumen and interstitium. To estimate the effective pore radius of the epithelium, non‐electrolyte solutions (urea, dimethylurea, diethylurea, mannitol, sucrose and maltotriose) were also used as luminal solutions. The results from non‐electrolyte experiments showed that the effective pore radius of the passage for non‐electrolytes was slightly larger than 0.38 nm. Solutes smaller than mannitol were less effective in opposing the interstitial fluid shift, and the value of effective pore radius in this report was similar to that of the secretory water pathway that has been measured in solvent drag studies (0.4 0.45 nm). These findings suggest that the passage for non‐electrolytes may be water transport pathway in salivary epithelium.
The influence of age on the assessment of motor unit activation in a human hand muscle
Authors: Spiegel KM , Stratton J , Burke  , Glendinning DS , Enoka RM
Published: December 2014

Two indices of motor unit recruitment, the ramp‐force and repetitive‐discharge thresholds, were compared in the first dorsal interosseus muscle of ten young and twelve elderly subjects. The purpose was to determine the effect of age on the relationship between the two recruitment thresholds and the spike‐triggered average force of motor units. Each subject performed three tasks requiring isometric abduction of the left index finger: a maximum voluntary contraction (MVC), a ramp‐and‐hold contraction, and a repetitive‐discharge task. The elderly subjects used coactivation of the antagonist muscle (second palmar interosseus) more frequently than the young subjects during the ramp‐and‐hold contraction. Many elderly subjects expressed difficulty with the controlled ramp‐down phase of the ramp‐and‐hold contraction and preferred a coactivation strategy to a derecruitment strategy for this task. There were no differences due to age or gender in the ramp‐force thresholds between the various groups. However, the normalized repetitive‐discharge threshold was significantly less for the younger subjects and for the male subjects. Nonetheless, the two recruitment thresholds were able to predict the spike‐triggered average force with similar success for both the young and the elderly subjects. These data suggest that the recruitment threshold of a motor unit in first dorsal interosseus was characterized equally well by either the ramp‐force or repetitive‐discharge measurement for both young and elderly subjects but that coactivation was used more frequently by the elderly subjects during the ramp‐and‐hold task.
The effect of H‐wave therapy upon conduction in the human superficial radial nerve in vivo
Authors: McDowell BC , Lowe AS , Walsh DM , Baxter GD , Allen JM
Published: December 2014

This study was designed to investigate the putative neurophysiological effects of so‐called 'H‐wave therapy' (HWT), a form of electrical stimulation, upon conduction latencies in the human superficial radial nerve. Antidromic compound action potentials were recorded from the superficial radial nerve in the dominant forearms of thirty‐two healthy human volunteers, who were randomly assigned to a control or one. of three HWT groups (2, 16 or 60 Hz). HWT was applied under double‐blind conditions for three consecutive 5 min periods. Action potentials were recorded pre‐HWT and immediately after each period of stimulation, i.e. at 5, 10 and 15 min. Analysis of results showed significant increases in negative and positive peak latencies in the 16 Hz and, to a greater extent, in the 60 Hz groups when compared with controls. No changes in conduction latency were observed in the low frequency 2 Hz group. The results of this study demonstrate that HWT applied at frequencies of 16 and 60 Hz may produce a direct, localized effect upon conduction in underlying peripheral nerves.
Possible role of calcium release from the sarcoplasmic reticulum in pacemaking in guinea‐pig sino‐atrial node
Authors: Rigg L , Terrar DA
Published: December 2014

Ryanodine and cyclopiazonic acid were used to alter the ability of the sarcoplasmic reticulum (SR) to store calcium. Interventions of this kind significantly reduced the rate of spontaneous beating of guinea‐pig sino‐atrial node preparations. In addition, both of these drugs decreased the rate of rise and modified other characteristics of the action potentials recorded from this region. It is proposed that calcium released from the SR plays an important, previously unrecognized, role in pacemaking in the sino‐atrial node, possibly through regulation of sarcolemmal ionic currents.
Appearance of the capillary endothelial glycocalyx in chronically stimulated rat skeletal muscles in relation to angiogenesis
Authors: Brown MD , Egginton S , Hudlicka O , Zhou AL
Published: December 2014

The endothelial glycocalyx layer of capillaries was stained with Ruthenium Red and examined by transmission electron microscopy in rat extensor hallucis proprius muscles after 2 or 4 days of indirect electrical stimulation via implanted electrodes. The layer appeared continuous on the luminal surface of 63% capillaries in control muscles and absent 13%. This situation was reversed in muscles stimulated for 2 or 4 days, with a continuous layer in 12 and 10% of capillaries and no glycocalyx in 44 and 58%, respectively. The greater disruption of the endothelial luminal glycocalyx in capillaries from stimulated muscles suggests that flow‐related shear forces on endothelial cells could be important signals for initiation of angiogenesis in actively contracting skeletal muscle.
Non‐adrenergic, non‐cholinergic influences on parotid acinar degranulation in response to stimulation of the parasympathetic innervation in the anaesthetized rat
Authors: Ekstrom J , Asztely A , Tobin G
Published: December 2014

In pentobarbitione‐anaesthetized rats the parasympathetic auriculotemporal nerve of the parotid gland was continuously stimulated at supramaximal voltage and at maximal frequency (40 Hz) for salivary secretion. The animals were pretreated with phentolamine and propranolol (2 mg kg‐1 i.p. of each) and, in some groups, additionally with atropine (2 mg kg‐1 i.p.). Morphometric assessment at the light microscopic level (x 100) showed that the numerical density of parotid acinar secretory granules (per 100 microns2 acinar epithelial cytoplasm) was reduced by 30 and 39% after 40 and 80 min, respectively, of stimulation in non‐atropinized animals and by 30 and 27% in atropinized animals. The numerical density of acinar granules was not influenced by pretreatment with the protein synthesis inhibitor cycloheximide. The results suggest that most of the parasympathetic nerve‐induced degranulation in the absence of muscarinic receptor blockade can be attributed to the action of non‐adrenergic, non‐cholinergic mechanisms.