bluuebunny/crossref_metadata_2025 huggingface dataset:
IS THERE CIRCADIAN VARIATION IN VILLUS HEIGHT IN RAT SMALL INTESTINE?
Authors: Gardner Michael L. G. , Steele Deborah L.
Published: December 2014

Measurements of villus height, crypt depth and mucosal thickness were made for each of duodenum, jejunum and ileum of rat small intestine from animals on both unrestricted and restricted feeding regimes. Contrary to a previous report, there was no evidence for consistent or synchronized diurnal variation in villus height at any region of small intestine on any of the feeding regimes. Likewise, no diurnal variation was seen in crypt depth or mucosal thickness. Variation in villus cell numbers, therefore, cannot account for previously reported diurnal variation in absorptive and digestive activities in rat small intestine. The present results support the hypothesis that the stimulus for exfoliation is probably cell recruitment and migration up the villi.
THE EFFECT OF AN INTRAVENOUS INFUSION OF ALDOSTERONE UPON MAGNESIUM METABOLISM IN THE SHEEP
Authors: Charlton Judith A. , Armstrong D. G.
Published: December 2014

The concentration of Mg, Na and K in the rumen and plasma of each of four sheep has been studied while test solutions were infused into their jugular veins for 8 h. The experiment was designed as a 4 x 4 Latin square with: treatment 1: diet only; treatment 2: diet +5% dextrose infusion; treatment 3: diet +5% dextrose infusion containing aldosterone; treatment 4: diet +5% dextrose infusion containing aldosterone and potassium canrenoate (a specific inhibitor of the action of aldosterone). Rumen and blood samples were collected every hour during the 8 h treatment period and for the subsequent 4 h. Rumen volume and outflow rate were estimated using an intra‐ruminal infusion of [14C]Cr‐EDTA throughout the collection period. The aldosterone infusion significantly (P 〈 0·001) increased the concentration of Mg in the rumen while rumen volume and outflow rate remained unchanged. Plasma concentrations of Mg and K were significantly (P 〈 0·001 and P 〈 0·05, respectively) lower during the aldosterone infusion while plasma Na concentrations did not vary significantly. The results are discussed in relation to hypomagnesaemic tetany.
EFFECT OF AGE ON VOLUNTARY FORCE AND CROSS‐SECTIONAL AREA OF HUMAN ADDUCTOR POLLICIS MUSCLE
Authors: Bruce S. A. , Newton D. , Woledge R. C.
Published: December 2014

Muscle weakness accompanies ageing but its causes are still uncertain. We report maximum voluntary force measurements of adductor pollicis muscle, normalized for cross‐sectional area, in twenty‐three elderly subjects. Normalized force was lower in the elderly compared with a group of fifty‐five young adult subjects by 27±4 % (S.E.M.). This shows that atrophy alone is not the cause of the weakness of old age.
EFFECTS OF TETRODOTOXIN AND MONENSIN ON THE NORADRENALINE OUTPUT INDUCED BY OUABAIN FROM THE GUINEA‐PIG VAS DEFERENS IN THE PRESENCE OF VARIOUS DIVALENT CATIONS
Authors: Nakazato Yoshikazu , Ito Shigeo , Ohga Akira
Published: December 2014

The importance of Na+ in the ouabain‐induced increase in noradrenaline output from adrenergic nerve terminals of the guinea‐pig vas deferens was investigated during incubation in standard Krebs solution and Sr2+‐ and Ba2+−substituted Krebs solutions. Ouabain (10−4 M) caused a gradual increase in noradrenaline output regardless of the type of divalent cation used. The rate of development of the ouabain‐induced noradrenaline output and the maximum amount released depended on the divalent cation present (Ba2+ 〉 Sr2+ 〉 Ca2+). The magnitude of the ouabain‐induced response depended on the concentration of extracellular Na+. The sensitivity of the ouabain‐induced response to a change in Na+ concentration depended on the divalent cation present (Ca2+ 〉 Sr2+ 〉 Ba2+). Tetrodotoxin (1·6 x 10−6 M) delayed the onset, whereas monensin (10−5 M) hastened it. The maximum level of the ouabain‐induced response was attenuated by monensin in all the incubation solutions. These results suggest that Na+ entry into adrenergic nerve terminals through tetrodotoxin‐sensitive mechanisms is crucial for the increase in noradrenaline output due to ouabain when extracellular Ca2+ is replaced with Sr2+ or Ba2+.
THE PEPTIDE RELEASE INHIBITOR, OCTREOTIDE (SMS 201–995), PREVENTS THE HAEMODYNAMIC CHANGES FOLLOWING FOOD INGESTION IN NORMAL HUMAN SUBJECTS
Authors: Kooner J. S. , Peart W. S. , Mathias C. J.
Published: December 2014

We have determined the haemodynamic responses to a balanced liquid meal in eight normal subjects, before and after administration of the somatostatin analogue, Octreotide (SMS 201‐995), which inhibits the release of gastrointestinal peptides. In the absence of Octreotide ingestion of the meal caused a marked increase in superior mesenteric artery (SMA) blood flow. Blood pressure was maintained, presumably by a compensatory rise in cardiac output and forearm vascular resistance. After Octreotide there was a fall in SMA blood flow alone, with no further changes after food ingestion. We conclude that Octreotide prevents the haemodynamic changes following food ingestion, probably by inhibiting the release of those gastrointestinal peptides that induce splanchnic vasodilatation.
INTERACTIONS BETWEEN INTRACELLULAR pH AND CALCIUM IN‐SINGLE MOUSE NEUROBLASTOMA (N2A) AND RAT PHEOCHROMOCYTOMA CELLS (PC12)
Authors: Dickens Claire J. , Gillespie J. I. , Greenwell J. R.
Published: December 2014

Intracellular pH (pHi) was measured at the tips of extending neurites and in the corresponding cell bodies of single cultured mouse neuroblastoma (N2A) and rat pheochromocytoma cells (PC12) using the fluorescent dye 2,3‐di‐cyanohydroquinone (DCH). It was observed that pHi at the tip of an extending neurite was consistently 0·2‐0·3 pH units higher than pHi in the cell body. Experiments performed on whole cells to establish the types of cellular mechanism which could be responsible for such regional differences demonstrate the presence of Na+‐H+ exchange and Cl−‐HCO3− exchange in these cells. Since regional variations in Cai2+ have been reported between neurites and the cell body, experiments were performed to examine the possible interactions between pHi and Cai2+. Intracellular calcium was measured using the fluorescent Ca2+‐sensitive dye Indo‐1. An increase in pHi, on application of NH4Cl, resulted in a transient elevation of Cai2+. On subsequent acidification, on removal of NH4Cl, there was a further transient increase in Cai2+. These changes in Cai2+ were also present in solutions with low calcium suggesting that Cai2+ is mobilized from within the cell. The results are discussed in terms of possible mechanisms whereby the extension and retraction of cell processes could be influenced by Cai2+ and modulated by pHi.
THE EFFECT OF ANAESTHESIA AND STANDARD CLEARANCE PROCEDURES ON RENAL FUNCTION IN THE RAT
Authors: Walter S. J. , Zewde T. , Shirley D. G.
Published: December 2014

Renal function was assessed in unrestrained conscious rats during either their active period (i.e. the hours of darkness) or their inactive period. On the following day, measurements were repeated after Inactin anaesthesia and preparation for clearance studies. In rats anaesthetized during their active period, preparation for clearance studies had no effect on inulin clearance (used as a measure of glomerular filtration rate), lithium clearance (used as an estimate of endproximal fluid delivery) or fractional lithium excretion. In rats anaesthetized during their inactive period, the same procedures resulted in increases in all three variables, to reach values indistinguishable from those in animals studied during their active period. In both groups of rats there were increases in the fractional reabsorption of sodium and water in the distal nephron and in the urinary excretion of potassium. It is concluded that in anaesthetized rats prepared for clearance studies, rates of glomerular filtration and proximal tubular reabsorption (as indicated by lithium clearance) are similar to those in conscious animals during their active period.
SOMATOSTATIN AND ITS ANALOGUE (D‐Trp8,D‐Cys14‐SOMATOSTATIN DO NOT MODIFY INTESTINAL ABSORPTION IN VIVO OF CARBOHYDRATES IN HAMSTER INTESTINE, BUT THEY DO MODIFY SOME DISACCHARIDASES
Authors: MartíNez-Sapiña J. , Vieytes M. R. , Taboada M. C.
Published: December 2014

Somatostatin is a widely distributed hormone localized in the central nervous system, pancreas and gastrointestinal tract. We have investigated the possible influence of somatostatin and a synthetic analogue, (D‐Trp8,D‐Cys14)‐somatostatin, on the intestinal absorption ‘in vivo’ of D(+)‐glucose and D(+)‐galactose and also the effect on disaccharidase intestinal activities in hamster. Somatostatin, or its analogue, (12 µg/100 g body wt) was administered intraperitoneally 4 or 14 h prior to experiments. The results are compared to control animals. Animals treated with somatostatin and the synthetic analogue showed that there were no significant difference from control animals with respect to intestinal absorption of carbohydrates. Somatostatin produced inhibition of brush‐border lactase activity in females only, whereas brush‐border sucrase was increased 14 h after treatment in males and females, and brush‐border maltase was inhibited in females only 4 h after hormone administration.
FACTORS DETERMINING GASTkOINTESTINAL TRANSIT TIME OF SEVERAL MARKERS IN THE DOMESTIC FOWL
Authors: Vergara P. , Ferrando C. , Jiménez M. , Fernández E. , Goñalons E.
Published: December 2014

The aim of this study was to find out how marker characteristics could affect digestive transit time in Gallus gallus. One soluble marker, Cr‐EDTA, and two insoluble markers, Cr2O3 and chromium‐mordanted plant cells of two sizes, were used. Three‐to six‐week‐old chickens were killed in series after the oral administration of the markers at intervals of 0, 0·5, 1, 2, 3, 5, 7, and 9 h. The amount of chromium in each digestive segment was determined by atomic absorption. There were some differences in the initial distribution of markers: whereas almost the total amount of the chromium‐mordanted rice husk of the largest size was found in the crop at time 0, less than half of the Cr‐EDTA was found. Marker emptying out of the crop was fast and not related to either the type or size. In contrast, the emptying rate of the gizzard depended on marker particle size. As far as the caeca were concerned, the ileocaecal junction allowed the passage of soluble Cr‐EDTA whereas solid markers were impeded (Cr2O3) or not allowed to pass through at all (vegetable fibre of any size). It can be concluded that marker selection is of major importance to transit time studies in chickens, since its characteristics can determine transit time in an absolute way.
FATIGUE OF ISOLATED MOUSE MUSCLE DUE TO ISOMETRIC TETANI AND TETANI WITH HIGH POWER OUTPUT
Authors: Cummins Michelle E. , Soomal Rabinder S. , Curtin N. A.
Published: December 2014

The fatiguing effect of a series of isometric tetani and of tetani with shortening and maximum power output were compared using soleus and extensor digitorum longus muscle of mouse. Mean force in test isometric tetani after the series was reduced by up to 35 % compared with pre‐series controls. Tetani with shortening were always more fatiguing than isometric tetani.
Possible lymphocyte effects on lactase expression by mouse jejunal enterocytes
Authors: Savidge TC , Smith MW , Kilshaw PJ
Published: December 2014

Jejunal intraepithelial lymphocyte numbers fall and lactase activity increases during early infection with the intestinal parasite Nematospiroides dubius. Both these variables later return to values found in control mice. These results support the view that local immune reactions, suppressed by the presence of N. dubius, normally inhibit lactase expression by mouse enterocytes.
Fluid absorption from the rumen during rehydration in sheep
Authors: Dahlborn K , Holtenius K
Published: December 2014

Water movements across the rumen wall were studied during rehydration in four fistulated sheep. The animals were dehydrated for 48 h which increased total plasma protein, plasma osmolality, plasma Na+, arginine vasopressin and plasma renin activity. Two series of experiments were performed: Expt I with no food available during rehydration, and Expt II where the animals were fed hay. On the rehydration day, a fluid marker (cobalt‐EDTA) was administered into the rumen. To avoid water outflow from the rumen a stopper was inserted into the reticulo‐omasal orifice. When the animals were provided with water they immediately drank 9 l. The water offered contained the same marker concentration (Co2+) as in the rumen liquid. In Expt I, Co2+ concentration increased after drinking, and remained elevated until the stopper was removed. The highest value was obtained after 20 min, and this corresponded to at least a 11 water absorption in individual animals. In Expt II, the sheep immediately started to eat following drinking and the inflow of saliva caused a dilution of the marker. Plasma osmolality and Na+ concentration decreased in both experiments indicating that water absorption occurred in both experiments. Removal of the stopper did not cause any significant changes in the parameters measured. Vasopressin concentration fell immediately on the sight of water, and then continued to decrease. It is concluded that in the sheep, voluntary drinking is followed by an immediate and substantial absorption of water from the rumen.
Effect of electrical field stimulation on muscle strips from chicken crop
Authors: Denac M , Kumin G , Scharrer E
Published: December 2014

The effect of electrical field stimulation (EFS) on smooth muscle strips from the chicken crop was investigated. The EFS (5 Hz, 2 ms, 400 mA; 10 Hz, 2 ms, 400 mA; 5 Hz, 2 ms, 500 mA; 10 Hz, 2 ms, 500 mA) produced contractions in all preparations. Atropine (10(−5) mol l−1) diminished muscle contraction in response to EFS. Tetrodotoxin (5 X 10(−6) mol l−1) fully suppressed the contractile responses to EFS. A serotonin antagonist (methysergide, 10(−4) mol l−1) did not alter contractions elicited by EFS. Propranolol (10(−5) mol l−1) led to an increase of contractions induced by EFS. Noradrenaline (10(−6)−10(−4) mol l−1) reduced acetylcholine‐induced (1.1 X 10(−6) mol l−1) contraction of the crop smooth muscle strips. Propranolol (10(−5) mol l−1) abolished noradrenaline‐induced relaxation almost fully. Tetrodotoxin (5 X 10(−6) mol l−1) did not change the relaxing effect of noradrenaline. These results suggested that the responses of crop smooth muscle to EFS involve excitatory cholinergic and non‐cholinergic (probably peptidergic) as well as inhibitory adrenergic nerves.
Autonomic and somatic responses evoked by stimulation of the cerebellar uvula in the conscious rabbit
Authors: Bradley DJ , Ghelarducci B , La Noce A , Spyer KM
Published: December 2014

The present study has investigated the effects of electrical stimulation of the cerebellar posterior cortex in the conscious rabbit. Stimulation of lobule IX (the uvula) elicited an increase in mean arterial blood pressure and heart rate, accompanied by EEG desynchronization, pupillary dilatation and a specific motor reaction, consisting of pricking of the ears, neck stiffening and running movements. Stimulation of lobule VIII was ineffective in evoking equivalent responses. The administration of barbiturates reversed the cardiovascular response to uvula stimulation, producing a fall in mean arterial pressure. The characteristics of the pattern of responses obtained, together with the anatomical and electrophysical observations provided in the preceding paper (Bradley, Ghelarducci, La Noce, Paton, Spyer & Withington‐Wray, 1990), suggest a possible involvement of uvula cortex in the expression of the alerting reaction in the rabbit.
The secretion of organic acids and bases by the ovine fetal kidney
Authors: Elbourne I , Lumbers ER , Hill KJ
Published: December 2014

Excretion of organic acids and bases was studied in twelve fetal sheep aged 120‐140 days. There was no significant plasma protein binding of the organic anion, p‐aminohippurate (PAH), nor of the organic cation, [14C]tetraethylammonium (TEA). There was a significant amount of acetyl‐PAH (20 +/‐ 3%) in fetal urine but none could be detected in fetal plasma. The fractional excretion of unconjugated PAH was less than one, i.e. there was net reabsorption of 31.7 +/‐ 3.9% of the filtered load of unconjugated PAH. Since there was no acetyl‐PAH in fetal plasma it is concluded that all acetyl‐PAH in fetal urine occurred as a result of metabolism of PAH and secretion of the metabolite into the tubular lumen. The rate of excretion of acetyl‐PAH in fetal urine varied from 0 to 14.0 micrograms min‐1. Thus unconjugated PAH is filtered and there is net reabsorption; in addition, PAH is metabolized and enters the urine via tubular mechanisms. The fractional excretion of PAH was unaffected by I.V. administration of penicillin either acutely or chronically. The clearance of [14C]TEA was significantly greater than the glomerular filtration rate (GFR). The mean fractional excretion of [14C]TEA was 5.4 +/‐ 0.17. Thus 80.7 +/‐ 0.63% of the excreted TEA was secreted. The clearance of TEA was related to body weight (P less than 0.001) but the fractional excretion of TEA declined with gestation age, probably because GFR increased at a greater rate than the rate at which the secretory pathways increase their activity. It is concluded that those pathways that excrete organic anions like PAH into the urine mature much later (probably after birth) than those pathways responsible for the tubular secretion of organic bases.
Histamine‐evoked amylase secretion is associated with small changes in calcium mobilization in isolated guinea‐pig pancreas
Authors: Salido G , Lennard R , Singh J , Pariente JA
Published: December 2014

An investigation was made of the effect of histamine on amylase secretion and calcium mobilization in isolated guinea‐pig pancreatic segments. The effect of acetylcholine (ACh) was also examined for comparison. Histamine evoked a dose‐dependent increase in amylase output from superfused segments. It had small transient effects on both 45Ca influx and efflux, and elevated cytosolic free Ca2+ concentration in acini. The equivalent dose of ACh evoked a greater amylase output and greater changes in Ca2+ mobilization. The results suggest that histamine may have a physiological role in exocrine secretion of the guinea‐pig pancreas but is less potent than ACh.
The responses of superior laryngeal nerve afferent fibres to laryngeal airway CO2 concentration in the anaesthetized cat
Authors: Bradford A , Nolan P , McKeogh D , Bannon C , O'Regan RG
Published: December 2014

In anaesthetized cats, the isolated, in situ, larynx was subjected to a simulated respiratory cycle and the responses of fifty‐six superior laryngeal nerve (SLN) afferent fibres to respiration‐related stimuli were examined during changes in the fractional CO2 concentration of the laryngeal airway (Faw, CO2). Sensory SLN fibres which displayed low rates of discharge when the larynx was unventilated (quiescent fibres) and which responded to negative laryngeal airway pressure were excited by elevations in Faw, CO2 whereas quiescent fibres responsive to positive laryngeal pressure were inhibited by the same procedure. We propose that changes in airway CO2 levels may play a role in maintaining upper airway patency, especially during sleep.
Secretory agonists stimulate a rise in intracellular cyclic AMP but not Ca2+ and inositol phosphates in cultured rat epididymal epithelium
Authors: Wong PY , Huang SJ
Published: December 2014

Primary monolayer cultures of rat epididymal cells have been shown to secrete chloride and bicarbonate when stimulated with beta‐adrenergic agents, humoral agents and vasoactive peptides. The intracellular messengers mediating the secretory response are unknown. In this study intracellular AMP, Ca2+ and inositol phosphates were measured in epididymal monolayers at rest and upon stimulation with various secretory agonists. Adrenaline, forskolin, lysylbradykinin, prostaglandin, endothelin, angiotensin II, antidiuretic hormone and vasoactive intestinal peptide at concentrations that stimulate anion secretion caused a rise in intracellular cyclic AMP. The increase in cyclic AMP by adrenaline was blocked by propranolol but not by phentolamine. Studies of the concentration‐effect relationships showed that for adrenaline and endothelin the EC50 for stimulation of cyclic AMP was higher than that for stimulation of anion secretion. None of these agonists affects intracellular Ca2+ concentration and inositol phosphate contents in epididymal monolayers. Ca2+ ionophores A21387, ionomycin and erythrosin B (with irradiation with white light), at concentrations that stimulate anion secretion, also stimulated a rise in intracellular cyclic AMP and concomitantly increased intracellular Ca2+. The increase in cyclic AMP was dependent on extracellular Ca2+. It is not known whether the secretory response to Ca2+ ionophores was mediated by an increase in cell Ca2+ per se, or cyclic AMP. However, it can be concluded that cyclic AMP is the second messenger which mediates the secretory responses to physiological stimuli.
The effects of K+ channel blockers on ovine parotid secretion depend on the mode of stimulation
Authors: Wright RD , Blair-West
Published: December 2014

The vascularly isolated parotid glands of sheep were submaximally stimulated for 4 min by nerve stimulation, or by infusion of acetylcholine (ACh) or bethanechol directly into the artery supplying the gland. The three modes of stimulation caused almost equal increases in the rate of salivary flow, initial losses of K+ and phosphate from the gland and total glandular deficits of K+ and phosphate. Concurrent arterial infusion of the K+ channel blocker tetraethylammonium (TEA), at 1.5‐3.3 mM in blood, almost abolished these responses to bethanechol but did not alter the responses to nerve stimulation or ACh. The responses to bethanechol were restored by increasing the concentration fourfold. Concurrent arterial infusion of 4‐aminopyridine (4‐AP), at 0.1‐2.3 mM in blood, partially inhibited the increase in salivary flow due to bethanechol but not the response to nerve stimulation or ACh. The specificity and competitive nature of the action of TEA and 4‐AP on responses to direct muscarinic stimulation by bethanechol are consistent with blockade of K+ channels in secretory end‐piece cells. The failure of TEA and 4‐AP to inhibit responses to nerve stimulation and ACh may be due to the blocking agents potentiating the release of neurotransmitter ACh. It is also possible that nerve stimulation and ACh may cause the release of a co‐transmitter which bethanechol does not.
K+ (Rb+) transport by a mammary secretory cell apical membrane fraction isolated from goats' milk
Authors: Smith KM , McNeillie SA , Shennan DB
Published: December 2014

The transport of K+ (Rb+) by cell fragments isolated from goats' milk, which are believed to be pieces of mammary epithelial cell cytoplasm encapsulated by apical membrane, has been studied. K+ (Rb+) accumulation was time dependent and was virtually abolished by 0.1% Triton X‐100 which indicates that K+ (Rb+) uptake is into a membrane‐limited space rather than by binding. Replacing medium Cl‐ with SCN‐ increased whereas gluconate replacement of Cl‐ decreased K+ (Rb+) influx suggesting that uptake is sensitive to changes in membrane potential. Na+, K+, Li+ and Rb+ ions added to the incubation medium reduced the rate of K+ (Rb+) accumulation. K+ (Rb+) uptake was markedly reduced by both barium ions and quinine; the inhibitory effects were not additive suggesting they are acting at a single locus. Increasing the pH of the medium stimulated the Ba2(+)‐sensitive component of K+ (Rb+) influx. The results show that the transport properties of the goats' milk membrane fraction used here are similar to the apical aspect of the intact mammary epithelium. Therefore this membrane preparation may be a good source and model to study mammary secretory cell apical membrane ion transport.
Interactions between K+ and beta 2‐adrenoreceptors in determining muscle vasodilatation induced in the rat by systemic hypoxia
Authors: Mian R , Marshall JM , Kumar P
Published: December 2014

In spontaneously breathing anaesthetized rats, both moderate and severe hypoxia caused increases in [K+] in venous efflux from hindlimb muscle, from 4.3 to 4.6 and from 3.8 to 4.4 mM respectively; the increases were accentuated to 5.2 and 5.7 mM after beta 2‐receptor blockade with I.V. sotalol. Sotalol also potentiated the vasodilatation evoked in hindlimb muscle by moderate hypoxia, but reduced that evoked by severe hypoxia. We propose that K+ released from muscle during hypoxia contributed to the local vasodilatation. Further, we suggest that this effect was enhanced in moderate hypoxia by blockade of the beta 2‐mediated uptake mechanism for K+ in skeletal muscle, but outweighed in severe hypoxia by blockade of the beta 2‐mediated dilator action of circulating catecholamines on vascular muscle.
Effect of lithium on the intracellular potassium concentration in sheep heart Purkinje fibres
Authors: Gow IF , Ellis D
Published: December 2014

Simultaneous measurements were made of the intracellular activities of potassium and lithium in sheep heart Purkinje fibres using ion‐sensitive microelectrodes. On exposure of the fibres to lithium, the intracellular activity of lithium rose, with an equivalent decrease in the level of intracellular potassium.
The action of strophanthidin on calcium‐activated current and contraction in single guinea‐pig ventricular myocytes
Authors: White E , Terrar DA
Published: December 2014

Calcium‐activated tail current was used as a qualitative indicator of changes in [Ca]i in order to investigate the mechanism of strophanthidin‐induced inotropy in single guinea‐pig ventricular myocytes. Action potentials were interrupted (by application of a voltage clamp to ‐40 mV) in order to evoke Ca‐activated current. Exposure to 10 microM‐strophanthidin for 2 min resulted in an increase in contractions associated with complete action potentials and in an increase in Ca‐activated current. Strophanthidin appeared not to substantially modify the time course of the envelope of tail currents (recorded by interrupting action potentials at different durations), which is thought to reflect the time course of the systolic [Ca]i transient. Exposure to 1 microM‐ryanodine slowed the development of the Ca‐activated current envelopes and abolished the above effects of strophanthidin. Exposure to strophanthidin led to reduction in Ca current in a majority of cells (measured by a voltage‐clamp step from ‐40 to 0 mV). These results are consistent with the hypothesis that in single guinea‐pig ventricular myocytes strophanthidin causes an increased loading of ryanodine‐sensitive intracellular stores of Ca, possibly through reduced extrusion of Ca from the cell by Na‐Ca exchange during the action potential plateau.
Stimulation of ovine placental transport of calcium and magnesium by mid‐molecule fragments of human parathyroid hormone‐related protein
Authors: Care AD , Abbas SK , Pickard DW , Barri M , Drinkhill M , Findlay JB , White IR , Caple IW
Published: December 2014

Perfusion in situ of the placenta of intact or previously parathyroidectomized fetal lambs has been used to assess the ability of three mid‐molecule fragments of the human parathyroid hormone‐related protein (PTHrP) molecule to stimulate the placental transport of calcium and magnesium. PTHrP(67‐86 amide) was most effective but some activity was also shown by PTHrP(75‐86 amide) and by PTHrP (75‐84) in decreasing order. This placental action of PTHrP(67‐86 amide) was rapid and could be observed using the placenta from an intact fetus, whereas it was necessary to use the placenta from a previously parathyroidectomized fetus to demonstrate stimulation of placental calcium transport by PTHrP(1‐84). PTHrP(67‐86 amide) may resemble the molecule that activates the placental calcium pump.
Plasma noradrenaline levels and thermogenic responses to injected noradrenaline in the conscious rat
Authors: Macdonald IA , Siyamak AY
Published: December 2014

The changes in metabolic rate (MR) and plasma noradrenaline (NA) were studied in rats injected with NA either subcutaneously (S.C.) or intravenously (I.V.). Injection of NA (400 micrograms kg‐1 S.C.) raised the MR by 54.0 +/‐ 10.2% above baseline and the levels of plasma NA were higher in right atrial venous plasma (147.0 +/‐ 6.6 nmol l‐1) than in arterial plasma (54.4 +/‐ 6.6 nmol l‐1) 90 min after the injection. There was no significant increase in MR in response to the infusion of 0.4 microgram NA min‐1 kg‐1 but significant responses occurred (P less than 0.01) with infusion of 1.5, 3.0, 4.0 and 8.0 micrograms min‐1 kg‐1. The maximum increase in MR was 90.3 +/‐ 7.4% during the 3.0 micrograms min‐1 kg‐1 infusion. The arterial plasma NA levels were directly proportional to the NA infusion rate, 18.0 +/‐ 8.3, 72.4 +/‐ 14.3, 159.5 +/‐ 28.4, 222.3 +/‐ 62.1 and 590.0 +/‐ 172.1 nmol l‐1 for the 0.4, 1.5, 3.0, 4.0 and 8.0 micrograms min‐1 kg‐1 infusion respectively. This study shows that high plasma levels of NA are needed to induce thermogenesis when NA is administered either S.C. or I.V.
The role of platelets in the reflex tachypnoeic response to miliary pulmonary embolism in anaesthetized rabbits
Authors: Armstrong DJ , Miller SA
Published: December 2014

Experiments were performed upon twenty‐eight male Californian rabbits anaesthetized with sodium pentobarbitone and breathing room air. Successive injections of glass bead emboli (diameter 125 microns) caused an increase in respiratory rate, and decreases in tidal volume (tachypnoeic response) and platelet count. The tachypnoeic response was not observed in rabbits that had been rendered thrombocytopaenic by platelet antiserum. Induction of thrombocytopaenia by antiserum was accompanied by tachypnoea which was not significantly different (P greater than 0.05) from the response to emboli. The tachypnoeic response to antiserum, like that to emboli, was prevented by bilateral cervical vagotomy. Pre‐treatment with aspirin (5 mg/kg), which inhibits the platelet‐release reaction, also prevented the tachypnoeic response to both emboli and antiserum, although it did not prevent the fall in platelet count which following injection of antiserum. These data support the hypothesis that the post‐embolic reflex tachypnoea is platelet dependent and may be secondary to the platelet‐release reaction.
Reflex co‐ordination of corporal and antral contractions in the conscious dog
Authors: Rudge L , Grundy D , Hutson D , Scratcherd T , Kerrigan D
Published: December 2014

This study characterizes the role of extrinsic nerves in the co‐ordination of corporal and antral contractions in the dog. Fasting motor activity was recorded in conscious dogs with stomachs previously divided into separate corporal and antral pouches. Both corpus and antrum showed synchronized phases of activity and quiescence recognizable as migrating motor complexes (MMCs, duration 81.2 +/‐ 9.6 min, n = 4). Moreover, individual contractions were temporally linked such that corpus contractions, occurring at 76 +/‐ 4 s intervals, were each followed by a burst of one to three antral contractions at a frequency of 4‐5 min‐1. The mean latency between the onset of individual contractions in the corpus and antrum was 10.9 +/‐ 2.6 s (n = 4). Denervation of the antral pouch in two additional dogs did not affect the MMC cycle (mean durations 106.6 and 82.1 min) and the onset of activity in the corpus and antrum was generally co‐ordinated but less precise. However, individual antral contractions were no longer linked to corporal contractions, occurring randomly throughout the corpus contraction cycle. This was associated with a lower contraction frequency in the denervated antral pouches than in the corpus (0.3 +/‐ 0.1 min‐1 compared to 0.6 +/‐ 0.08 min‐1). It is proposed that a vagal reflex, excited by corporal tension receptors, provides phasic excitation facilitating the generation of antral contractions. Such a reflex is likely to reinforce the myogenic mechanisms which occur in the intact stomach and thus plays a role in co‐ordinating gastric peristalsis.
A sodium‐activated potassium current in intact ventricular myocytes isolated from the guinea‐pig heart
Authors: Rodrigo GC , Chapman RA
Published: December 2014

A current generated by the Na‐activated K channel has been identified in whole cell currents recorded from isolated guinea‐pig ventricular myocytes. A partial activation of this current can be achieved near to the physiological range of intracellular sodium concentration [( Na+]i) when it contributes significantly to the global outward current. The decline of the Na‐activated K current, the lengthening of the action potential duration and the recovery of [Na+]i occur with a similar time course during recovery from Na loading.
High‐energy phosphates and fatigue during repeated dynamic contractions of rat muscle
Authors: de Haan A
Published: December 2014

Reductions in work output during repeated contractions of rat medial gastrocnemius muscles (37 degrees C) were compared with changes in muscle metabolite concentrations. Three different exercise protocols were used in which the total number of stimuli and the length excursion were the same. The muscles performed a series of either 10, 25 or 40 repeated contractions at velocities of 20, 50 and 80 mm/s for groups A, B and C, respectively. In group A work output decreased steadily to 66% of the output in the first contraction. In groups B and C work output decreased to less than 10% of the first contraction. Changes in phosphocreatine and lactate concentrations were similar for all groups. However, very low ATP concentrations (approximately 35% of the resting value) were observed in groups B and C, compared with approximately 65% in group A. Inosine 5'‐monophosphate (IMP) production was 9.9 mumol/g dry wt in group A and approximately 18 mumol/g dry wt in groups B and C. The results suggest fatigue does not depend on changes in intracellular inorganic phosphate and pH but possibly on changes in nucleotide metabolism.
Role of vagal afferent C fibres in the bradycardiac response to an increase in arterial blood pressure in ferrets
Authors: Bowser-Riley F , Cornish M , Kidd C , Zheng F
Published: December 2014

The effects on baroreceptor reflexes of bilateral application of the C fibre neurotoxin, capsaicin, to the cervical vagi have been investigated in decerebrate ferrets. Baroreflex sensitivity was estimated from the relationship between cardiac interval and systolic blood pressure following I.V. infusion of phenylephrine. Control responses to phenylephrine were fitted by two linear slopes with an initial shallow slope, a, followed by a steeper slope, b. Capsaicin abolished slope b and the resulting relationship was best fitted by a single regression with a slope not significantly different from that of the control response a. This suggests that a significant proportion of the baroreflex response induced by phenylephrine is mediated by cardiopulmonary receptors attached to vagal afferent C fibres.
Effect of feeding on the diurnal rhythm of plasma cortisol and adrenocorticotrophic hormone concentrations in the pregnant ewe and sheep fetus
Authors: Simonetta G , Walker DW , McMillen IC
Published: December 2014

The effects of two different feeding regimes on the 24 h profiles of maternal and fetal plasma cortisol and adrenocorticotrophic hormone (ACTH) concentrations were studied in eight pregnant ewes between 123 and 144 days of gestation. Once daily‐fed ewes (n = 4) received 1 kg of lucerne‐chaff at 11.00 h, and multi‐fed ewes (n = 4) received 100‐200 g of lucerne‐chaff at 09.00, 11.00 and 13.00 h and then 150 g until 09.00 h the following day. There were significant differences between the two feeding groups in the 24 h profile of maternal plasma osmolality; once daily feeding at 11.00 h was associated with a peak in maternal plasma osmolality at 15.00 h whereas maternal plasma osmolality reached plateau levels at around 17.00 h in the multi‐fed group. There were also differences between the two feeding groups in the 24 h profiles of maternal and fetal plasma glucose. Maternal and fetal plasma glucose reached peak concentrations at 19.00 h in the once daily‐fed ewes in contrast to the multi‐fed group, where a plateau in maternal and fetal plasma glucose was reached between 19.00 h and 09.00 h the following day. A significant diurnal variation in the plasma concentrations of cortisol was present in the once daily‐fed ewes from 123 days gestation and in their fetuses after, but not before, 135 days gestation. Plasma cortisol peaked at 11.00 h in the ewes and at 13.00 h in the fetuses of this group. In the once daily‐fed group there was also a significant diurnal variation in maternal and fetal plasma ACTH; plasma ACTH concentrations were highest at 11.00 h in the ewes aged between 123 and 144 days and in fetuses after 135 days gestation. In the multi‐fed group, whilst ACTH was highest at 09.00 h in the ewes and at 13.00 h in the fetuses, there was no significant diurnal variation in the plasma concentrations of cortisol in the ewes or fetuses of this group at any stage between 123 and 144 days gestation.
Endogenous transmembrane electrical gradients associated with human placental microvillous membrane vesicles
Authors: Shennan DB , Reid D
Published: December 2014

Experiments were designed to test for the presence of an endogenous (i.e. Donnan) electrical potential in human placental microvillous membrane vesicles. Vesicles were capable of passively accumulating K+ (86Rb+) above unity in a manner which was influenced by both pH and ionic strength of the medium. It appears that the transmembrane electrical potential is generated by the presence of fixed negative charges associated with the vesicle interior.
An olfactory‐parotid salivary reflex in humans?
Authors: Lee VM , Linden RW
Published: December 2014

It is commonly stated that smell elicits a parotid salivary reflex in humans. However, this assumption seems to be supported only by experiments in which either a lemon or an irritating odour has been used as the primary stimulus. In this study six pleasant odours, chocolate, vanilla, peppermint, beef, tomato and lemon, were administered to ten subjects. Air was passed through a solution of the stimulant and the resultant odour was administered to the subject via a face mask. Unilateral parotid saliva was collected via a Lashley cup and salivary flow was measured using an instantaneous flowmeter sensitive to flows as low as 0.008 ml min‐1. Citric acid, lemon juice, chocolate and distilled water were also delivered to the subjects at increasing concentrations. At low concentrations none of these stimuli significantly increased the parotid salivary flow above resting levels. However, an increase in salivary flow was seen when lemon juice or odourless citric acid was sniffed or delivered to the subject at high concentrations, causing irritation in the nasal cavity and/or the back of the throat. Our results suggest that there is no true olfactory‐parotid salivary reflex in humans, and that acidic stimuli can cause irritation with a concomitant increase in the salivary flow.
The effect of distension of the urinary bladder on coronary blood flow in anesthetized dogs
Authors: Cevese A , Drinkhill M , Mary DA , Patel P , Schena F , Vacca G
Published: December 2014

To determine whether distension of the urinary bladder reflexly affects coronary blood flow, experiments were performed in eleven dogs anaesthetized with sodium pentobarbitone. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution at a steady intravesical pressure. Arterial blood pressure was prevented from changing by a pressurized reservoir of warm Ringer solution connected to the femoral arteries. Coronary blood flow was measured with an electromagnetic flowmeter positioned around the origin of the left circumflex coronary artery. When the reflex increase in heart rate was prevented by atrial pacing in seven dogs, distension of the urinary bladder always caused a decrease in mean coronary blood flow. Similar results were obtained in all eleven dogs after administration of propranolol. The decrease in mean coronary blood flow was significantly reduced by atropine or bilateral cervical vagotomy, and was abolished by bretylium tosylate. The results showed that distension of the urinary bladder reflexly decreased mean coronary blood flow, a response involving efferent cardiac vagal and sympathetic pathways.
Components of transmembrane potassium (86Rb+) flux during evoked tension development in dog saphenous vein: contribution of the Na(+)‐K+ pump
Authors: Powis DA
Published: December 2014

The relationship between the concurrent increase in net K+ efflux and isometric tension development has been studied in perifused dog saphenous vein strips using 86Rb+ as a marker for K+. Noradrenaline, acting through alpha‐adrenoceptors, or depolarization induced by raised extracellular K+ (in the presence of an alpha‐adrenoceptor antagonist) increased both 86Rb+ efflux and isometric tension. However, even with a high concentration of K+ (120 mmol l–1) the evoked changes in 86Rb+ efflux and tension were small compared with those produced by noradrenaline. There was a linear relationship between 86Rb+ efflux and tension maintained throughout the time course of each evoked response. This linear relationship was the same for each response evoked throughout the concentration range of noradrenaline (1–100 mumol l–1) or K+ (30–120 mmol l–1) used. Substitution of extracellular Ca2+ by Ba2+ did not alter either basal tension or 86Rb+ efflux; nor did it alter either the magnitude of noradrenaline‐evoked changes in 86Rb+ efflux or tension, or the slope of the relationship between the two seen with Ca2+. The cardioactive steroid, acetylstrophanthidin, altered the evoked response to exogenous noradrenaline and to K+ depolarization in that there was now a significant increase in 86Rb+ efflux relative to tension, although the linear relationship between the two was maintained. In the nominal absence of extracellular Ca2+ the increase in 86Rb+ efflux produced by exogenous noradrenaline was maintained but the evoked increased in tension was reduced. The data shows for dog saphenous vein: (a) that gross evoked 86Rb+ efflux is attenuated by an active backflux mediated by the sodium‐potassium pump and (b) that 86Rb+ efflux can occur through a membrane potential‐activated pathway and through an independent alpha‐adrenoceptor‐activated pathway but although the linear relationship between 86Rb+ efflux and tension can be best explained by their co‐dependence upon Ca2+, the present experiments provide no objective evidence for an internal calcium‐activated pathway.
Osmotic‐hypertensive opening of the blood‐brain barrier in rats does not necessarily provide access for potassium to cerebral interstitial fluid
Authors: Somjen GG , Segal MB , Herreras O
Published: December 2014

The blood‐brain barrier was breached in urethane anaesthetized rats by infusing hypertonic mannitol or NaCl at high rate under high pressure into one internal carotid artery. Opening of the blood‐brain barrier was confirmed by staining of the perfused hemisphere by intravenous Evans Blue dye. Orthodromic‐evoked potentials in CAl region of hippocampus were transiently extinguished, and the extracellular potential in hippocampus and neocortex shifted in the positive direction during hypertonic infusion. After the hypertonic infusion, the permeability of the barrier to K+ was tested by infusing into the internal carotid artery artificial cerebrospinal fluid in which K+ replaced most of the Na+, raising the concentration of K+ in the blood plasma in the superior sagittal sinus to 13‐17 mM. Extracellular potential and interstitial potassium concentration ([K+]O) in hippocampus and neocortex, and evoked potentials in hippocampus, remained unchanged during prolonged infusion of high K+, unless and until spreading depression occurred. After a wave of spreading depression, [K+]O returned to baseline in spite of continued high K+ infusion. We conclude that [K+]O in brain tissue is effectively regulated even when colloidal dye can penetrate the blood‐brain barrier, but excess K+ may have entered the cerebral interstitial space in scattered patches outside the region sensed by the ion‐selective microelectrodes, triggering spreading depression.
Studies on the ionic selectivity of the GABA‐operated chloride channel on the somatic muscle bag cells of the parasitic nematode Ascaris suum
Authors: Parri HR , Holden-Dye L , Walker RJ
Published: December 2014

The reversal potential for the GABA‐elicited hyperpolarization (EGABA) of the muscle bag cells of the parasite nematode Ascaris suum is near to the equilibrium potential for chloride ions (ECl) indicating that this is a chloride‐mediated event. The value of EGABA in the presence of different anions indicates the selectivity sequence of the GABA‐operated chloride channel as SCN‐ greater than Br‐, I‐ greater than ClO3‐, NO3‐, Cl‐ greater than C2H5COO‐ greater than CH3COO‐, HCOO‐, OHCH2CH2SO3H‐, CH3SO4‐, BrO3‐, SO4(2‐). The cut‐off point in terms of relative hydrated size for permeation is between ClO3‐ and BrO3‐ suggesting that the diameter of the channel is between 0.29 and 0.33 nm. The selectivity sequence of the resting membrane chloride channels was indicated by the degree of muscle cell hyperpolarization upon addition of the anion to the bathing medium and was SCN‐ greater than NO3‐ greater than I‐, Br‐, greater than ClO3‐ greater than Cl‐. These sequences are consistent with the anions interacting with a cationic site of low field strength at the selectivity determining portion of the channel for both the GABA‐operated and the resting chloride channel.
5‐Hydroxytryptamine induces electrogenic secretion and simultaneously activates a modulating inhibitory neural circuit in rat small intestine in vitro
Authors: Beesley A , Levin RJ
Published: December 2014

5‐Hydroxytryptamine (5‐HT) induces electrogenic secretion across rat jejunum and ileum in vitro expressed as an increase in the short‐circuit current. Enhancement of this secretory response by previous serosal addition of atropine (1 microM), hexamethonium (0.2 microM) or yohimbine (0.2 microM), especially in the ileum, indicated that 5‐HT simultaneously activates an anti‐secretory, inhibitory, enteric, neural, cholinergic‐adrenergic pathway (ENCAP). A similar inhibitory ENCAP activated by 5‐HT has previously been characterized in rat colon in vitro.
Effect of short‐chain fatty acids on calcium absorption by the rat colon
Authors: Lutz T , Scharrer E
Published: December 2014

An in vivo luminal perfusion technique was used to investigate whether short‐chain fatty acids influence the absorption of Ca by the rat colon. Na and water absorption were also determined. In the distal colon, acetate and butyrate caused a significant increase in Ca absorption, while the absorption of Na and water were not affected. In the proximal colon, butyrate did not influence Ca absorption, but significantly enhanced Na and water absorption. These results are in part consistent with the presence of a Ca‐H exchanger in the apical membrane of the distal colon mediating Ca uptake into the epithelial cell.