bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of central adenosine on brainstem blood flow in fetal sheep
Authors: Bissonnette JM , Hohimer AR , Knopp SJ
Published: December 2014

The effect of the adenosine analogue R‐N6‐(phenylisopropyl)adenosine (R‐PIA) on blood flow to the medulla and pons was examined in unanaesthetized fetal sheep. Microspheres labelled with isotopes were used to determine blood flow before and after instillation of 0.2 or 0.5 microgram R‐PIA into the cerebrospinal fluid of the fourth ventricle. Blood flow to the medulla, which had a mean value (+/− S.E.M.) of 285 +/− 41 ml min‐1 (100 g)‐1 during the control period, was not changed by the central instillation of R‐PIA. Blood flow to the pons was also not affected. These data indicate that central adenosine, which depresses respiratory drive in fetal sheep, acts by mechanisms independent of removal of carbon dioxide from the brainstem.
Properties of an identified dopamine‐containing neurone in culture from the snail Helisoma
Authors: Harris SJ , Cottrell GA
Published: December 2014

The giant neurone in the left pedal ganglion of the snail Helisoma trivolvis is homologous with the giant dopaminergic neurone of Planorbis corneus, because the neurones have a very similar location and morphology, and react similarly with glyoxylic acid to produce an intense blue fluorescence, indicating the presence of dopamine. Each of these neurones is therefore referred to as a giant dopaminergic neurone, or GDN. Conditions for the extension of neurites and formation of chemical junctions in culture have been determined for the H. trivolvis GDN, and compared with other neurones from this species. The pattern of neurites that extended from the neurone was indistinguishable from that of another identified aminergic neurone, the large serotonergic neurone (LSN), but differed markedly from many other central neurones. However, the type of substrate also greatly affected the pattern of the neurites observed. Some of the electrical properties of the GDN in culture differed from those recorded in situ: peak spike amplitude was increased, spike half‐width reduced and the firing pattern of the neurone was altered. However, the resting membrane potential was very similar. The GDN formed chemical and electrical junctions in culture. The chemical junctions formed were of the same type as those found in situ. They formed rapidly, within 18 h after plating, but were not stable and were lost within 48 h, to be replaced by a non‐rectifying electrical junction. A chemical junction may form in either direction between the GDN and the LSN, but only rarely did such junctions allow transmission in both directions, as observed in situ. Experiments in which neurones were plated out at different times suggested that the direction of formation of the chemical junction was not dependent on the degree or state of neurite extension.
Influence of stretch on excitation threshold of single frog ventricular cells
Authors: Tung L , Zou S
Published: December 2014

The excitation threshold of enzymatically dissociated single frog ventricular myocytes was measured as a function of cell length or sarcomere length. Field stimulation with 3 ms duration rectangular current pulses was applied via two platinum wire electrodes oriented either parallel or perpendicular to the long axis of the cell. Excitation threshold was measured as the amplitude of applied current, with an error of less than 1%. Single cells were held isometrically by two glass pipettes and wrapped around an optical fibre, which was used to control cell length. Sarcomere length was measured using video microscopy and a phase‐locked loop system. Changes in cell length and sarcomere length were induced by mechanical stretch and release of the whole cell. The excitation threshold decreased with increasing resting length (preload), and increased with decrease of the cell length back to its original length, regardless of the orientation of the electric field. The measured change in excitation threshold with stretch was of the order of 1%/% strain. These results suggest that stretch affects the excitation threshold of cardiac cells by factors other than simple shape changes in the cell, perhaps through the activity of mechanosensitive ionic channels.
Renal, endocrine and vascular effects of atrial natriuretic peptide in a novel vasopressin‐deficient genetically hypertensive strain of rat
Authors: al-Barazanji KA , Balment RJ
Published: December 2014

In the absence of the potentially confounding influence of vasopressin in hypertension, the effects of atrial natriuretic peptide (ANP) on arterial blood pressure and renal handling of water and sodium were assessed from comparison of responses to intravenous ANP infusion in anaesthetized vasopressin‐deficient New Zealand genetically hypertensive (DI/H) rats and their normotensive substrain (DI/N). After 320 min of hypotonic saline infusion, plasma ANP concentration was significantly higher in DI/H compared with DI/N rats. ANP administration increased circulating ANP concentration in both groups. Plasma angiotensin II concentration was higher in DI/H than in DI/N rats; infusion of ANP raised circulating angiotensin II in both groups though this achieved statistical significance only in DI/N rats. Plasma aldosterone concentrations were initially similar in normotensive and hypertensive animals and, in both, were reduced markedly by I.V. ANP infusion. Administration of ANP produced sustained hypotension in both groups. However, the hypotensive effect of ANP was more pronounced in DI/H compared with DI/N rats. Heart rate was initially similar in the two groups, and infusion of ANP produced no detectable change. By comparison with animals maintained on hormone‐free infusate, urine flow increased markedly over the 80 min period of ANP infusion in both groups, by 142% in DI/H rats and 127% in DI/N rats. ANP administration produced a natriuresis in both groups but the increase in Na+ excretion was much greater in DI/H (342%) than in DI/N (139%) rats. It appears from the current study that vasopressin‐deficient hypertensive rats are more sensitive to ANP with regard to effects on blood pressure and renal excretion than their vasopressin‐deficient normotensive substrain. These differences may, in part, reflect adjustments to long‐term elevation in blood pressure and in plasma ANP concentration in hypertension and, in part, rely on the associated disturbances in related endocrine systems.
The effects of attentional factors on an inhibitory jaw reflex in man
Authors: Cadden SW , Newton JP
Published: December 2014

Electromyographic recordings (EMGs) were made from the active masseter muscle, of the inhibitory reflex evoked by application of electrical stimuli to the skin of the upper lip in fifteen human subjects. In control sequences, the reflex had a mean latency of 42 +/‐ 1.1 ms and a mean duration of 45 +/‐ 2.1 ms. The magnitude of the reflex (measured by integration of the EMG) was reduced (by 18 +/‐ 7.0%, n = 11; P < 0.05, Student's t test) while the subjects concentrated on a visual feedback signal in order to maintain a steady level of EMG activity. It was further reduced (by 25 +/‐ 3.6%, n = 10; P < 0.001, Student's t test) when the subjects additionally undertook mental calculations (the 17‐times table). These effects were predominantly in the later parts of the responses. They occurred regardless of whether the baseline activity in the masseter muscle was inadvertently raised or lowered during the conditioning procedures. It is concluded that attentional factors can modulate jaw reflexes in man by exerting an influence on the reflex pathway at a point prior to the motoneurones. The underlying mechanism may involve the activation of descending inhibitory pathways and/or a facilitation of mechanisms underlying excitatory responses in jaw closing muscles.
The measurement of permeability in single rat venules using the red cell microperfusion technique
Authors: Kendall S , Michel CC
Published: December 2014

The red cell microperfusion‐micro‐occlusion technique has been used to measure fluid filtration and reabsorption (Jv/A) at known microvascular pressures (Pc) in single mesenteric venules of anaesthetized rats. The relation between Jv/A and Pc is linear over the range of Pc from 15 to 50 cmH2O and its slope is the hydraulic permeability, Lp. Reproducible estimates of Lp can be made in the same venule in separate microperfusions. The value of Pc at Jv/A = 0 varies linearly with perfusate oncotic pressure and is the effective oncotic pressure of the perfusate, sigma delta pi, when the hydrostatic pressure in the pericapillary fluid is zero. The mean value for Lp (+/− S.E.M.) in forty venules was 2.43 (+/− 0.2) x 10(‐7) cm s‐1 cmH2O‐1. Two potential errors of the micro‐occlusion technique (vessel distensibility and marker red cell size) were investigated. It was found that the effects of vessel distensibility had little effect on red cell movements at times later than 2 s after a step change in Pc. Red cell size had a potentially large effect on estimates of the absolute values of Lp. Cooling the mesenteric tissues from 37 to 7 degrees C reduced Lp in proportion to the change in the reciprocal of water viscosity with temperature. Rat venular permeability was shown to be sensitive to histamine, with Lp increasing and sigma delta pi falling in a concentration‐dependent fashion with histamine concentrations of 1.6 x 10(‐5) to 3.3 x 10(‐4) mol l‐1 in the perfusate.
Chloride current activated by hypotonicity in cultured human astrocytoma cells
Authors: Bakhramov A , Fenech C , Bolton TB
Published: December 2014

Cultured astrocytoma cells were voltage clamped with pipettes where [Ca2+] in the pipette was buffered to 10(‐7) M with 10 mM 1,2‐bis(O‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA) and membrane currents recorded. In isotonic solution predominantly K+ currents were evoked by depolarizing or hyperpolarizing commands and 4,4'‐diisothiocyanatostilbene‐2,2'‐disulphonic acid (DIDS; 1 mM) had little effect on inward and outward currents evoked by voltage steps to negative and positive potentials. If the osmolarity of the bathing solution was reduced from 280 to 200 mosmol l‐1, a large current developed, which rectified outwardly and reversed close to the equilibrium potential for chloride ions, ECl. Upon stepping to potentials positive to about +30 mV in hypotonic solution, this outward current inactivated over 2‐3 s; this decline was greater with N‐methyl‐D‐glucamine chloride (NMDG‐Cl) in the pipette than when KCl or sodium glutamate was present. Holding at various positive potentials inactivated the current, with half‐inactivation occurring around +50 mV. The current reactivated over 2‐3 s at potentials negative to about +30 mV. The current evoked by hypotonic solution was inhibited by various putative chloride channel blockers with the order of potency DIDS > SITS (4‐acetamido‐4'‐isothiocyanatostilbene‐2,2'‐disulphonic acid) approximately NPPB (5‐nitro‐2‐(3‐phenylpropylamino)‐benzoic acid) > niflumic acid > 9‐AC (anthracene 9‐carboxylic acid). The currents inhibited by these compounds reversed close to the calculated ECl. It is concluded that hypotonic solution evokes a large anionic current in these cultured astrocytoma cells largely carried by chloride ions. This current is absent in isotonic solution, when currents are carried mainly by potassium ions. It is likely that the current elicited by hypotonic solution is part of the mechanisms regulating astrocyte volume in vivo.
Contractile activation and measurements of intracellular Ca2+ concentration in cane toad twitch fibres in the presence of 2,3‐butanedione monoxime
Authors: Lyster DJ , Stephenson DG
Published: December 2014

The effects of 2,3‐butanedione monoxime (BDM, 0.5‐20 mM) on Ca(2+)‐activated force in skinned muscle fibres, and force and Ca2+ responses in aequorin‐injected intact fibres from the iliofibularis muscle of the cane toad Bufo marinus were investigated. Peak twitch force responses progressively decreased to 3% of the control response with increasing [BDM] up to 20 mM. Peak twitch aequorin light responses decreased to 65% of the control response in 10 mM BDM, but increased again to control values in 20 mM BDM. The duration of the twitch aequorin light response increased by up to 60% above 5 mM BDM. Tetanic (170 Hz) force and aequorin light responses reversibly decreased in a dose‐dependent fashion to about 50% of the control response in 10 mM BDM. Failure of tetanic (170 Hz) stimulation was observed in the presence of 20 mM BDM. Intracellular [Ca2+] could be modified by changing the frequency of tetanic stimulation in the presence of BDM, permitting a study of the dependence of isometric force on intracellular [Ca2+] at different concentrations of BDM. In 10 mM BDM, the rate of force development in intact fibres was slower by a factor of two at saturating [Ca2+], and was up to one order of magnitude slower at non‐saturating [Ca2+], when compared with control responses. At a similar intracellular [Ca2+] steady‐state isometric force was reduced to about 85 and 50% of the control responses in 2 and 10 mM BDM, respectively. The effect of BDM on maximum Ca2+‐activated force in skinned fibres paralleled the decrease in tetanic (170 Hz) force observed in intact fibres. The rate of force development in skinned fibres decreased with an increase in [BDM] at constant [Ca2+], and the sensitivity of the contractile apparatus to Ca2+ was shifted to a higher [Ca2+] by BDM. The results suggest that BDM reduces contractility in cane toad iliofibularis muscle by direct inhibition of the contractile apparatus, and reduction of the release of activator Ca2+ from the sarcoplasmic reticulum. Furthermore, BDM may be a useful tool to help study the relationship between force and [Ca2+] in intact muscle fibres.
Sympathoadrenal and other endocrine and metabolic responses to hypoglycaemia in the fetal foal during late gestation
Authors: Silver M , Fowden AL
Published: December 2014

In the present study, ten insulin challenge tests were carried out on nine chronically catheterized fetal foals between 253 and 314 days gestation (term > 320 days). Changes in fetal plasma concentrations of glucose, catecholamines, cortisol, ACTH, free fatty acid (FFA) and lactate were measured before and after a bolus dose of insulin (0.5‐2.0 u/kg I.V.). Fetal blood gases, pH, haemoglobin levels and heart rate were measured throughout the 2‐3h experimental period. The fetuses fell into two distinct groups on the basis of proximity to delivery and basal plasma cortisol and catecholamine levels. Those within 2‐10 days of delivery after 300 days (group 2, number of experiments (n) = 4) had plasma cortisol and noradrenaline concentrations which were significantly higher (P < 0.05) than the corresponding values in fetuses sampled earlier in gestation or at least 2 weeks before foaling (group 1, n = 6). Although insulin administration resulted in a 50% fall in plasma glucose in all animals, group 2 showed significantly greater increases in plasma noradrenaline than group 1. In neither group were there detectable changes in plasma adrenaline. In group 2, increases in plasma cortisol were seen following insulin, whereas no cortisol changes were observed in group 1, despite rises in plasma ACTH. Insulin administration also led to acidosis and increases in heart rate and plasma lactate and FFA levels in all fetuses studied. However, only group 2 became consistently hypoxic during the insulin challenge. No significant changes in plasma glucose or any of the other parameters were observed in the fetuses after saline administration (n = 5). These findings suggest that hypoglycaemia activates the sympathoadrenal system in the fetal foal from 75% of gestation but has relatively little effect on the fetal pituitary‐adrenocortical axis until much closer to term.
Cyclo‐oxygenase mediation of endotoxin‐induced fever, anterior and posterior pituitary hormone release, and hypothalamic c‐Fos expression in the prepubertal pig
Authors: Parrott RF , Vellucci SV , Goode JA , Lloyd DM , Forsling ML
Published: December 2014

Prepubertal pigs (n = 8) treated with bacterial endotoxin (20 micrograms lipopolysaccharide; LPS) exhibited a sustained (4 h) hyperthermia, increased plasma concentrations of cortisol, prolactin, growth hormone and vasopressin, but no change in adrenaline or noradrenaline levels was observed. All these effects were prevented or attenuated when the animals were pretreated intravenously with the cyclo‐oxygenase inhibitor indomethacin (IND; 2 mg/kg). Similarly, in pigs (n = 3 per treatment) given IND, LPS or IND + LPS, parallel changes in the neuronal expression of c‐Fos were observed in hypothalamic regions concerned with thermoregulation, neurohypophysial secretion, and the control of pituitary‐adrenocortical function. The stimulatory action of LPS in the median preoptic, supraoptic and paraventricular nuclei was prevented by IND, whereas IND given alone was without effect. These findings suggest that inducible cyclo‐oxygenase pathways are responsible for the febrile and neuroendocrine effects of endotoxin in this species.
The effect of mechanical loading on the response of rat ventricular myocytes to acidosis
Authors: Hongo K , White E , Orchard CH
Published: December 2014

The effect of mechanical loading on the negative inotropic effect of acidosis in isolated rat ventricular myocytes was investigated. The mechanical loading of the myocytes was changed by attaching carbon fibres to the ends of the cell. To monitor intracellular Ca2+ and Na+ concentrations, cells were loaded with fluorescent dyes (fura‐2 for Ca2+ and SBFI for Na+) using the acetoxymethyl (AM) esters. Mechanical loading reduced cell shortening by 73.0 +/‐ 3.5% (mean +/‐ S.E.M., n = 16) and abbreviated the time course of contraction. CO2‐induced acidosis caused a rapid decrease in contraction followed by a slow partial recovery. The percentage changes in contraction were not significantly different in mechanically loaded and unloaded conditions. Mechanical loading had little effect on the time course of contraction during acidosis. Changes in intracellular Ca2+ and Na+ concentrations during acidosis were unaffected by mechanical loading. The mechanical loading conditions of a region of the heart can be modified by ischaemia and the subsequent acidosis. Our results suggest that the response of cardiac muscle to acidosis is not markedly modified by such changes in mechanical loading.
Selective transport of microparticles across Peyer's patch follicle‐associated M cells from mice and rats
Authors: Smith MW , Thomas NW , Jenkins PG , Miller NG , Cremaschi D , Porta C
Published: December 2014

M cells are specialized structures in the Peyer's patch follicle‐associated epithelium capable of taking up bacteria, viruses and other pathogens for later presentation to the gut‐associated lymphoid tissue. The present work studies how coating microspheres with different proteins affects their ability to be taken up by M cells under near physiological conditions in vivo. The later appearance of microspheres in intestinal lymph has also been measured by flow cytometry. The protein preparations used in these experiments included bovine serum albumin (bSA), human immunoglobulin G (hIgG), secretory immunoglobulin A (hIgA), bovine growth hormone (bGH) and bGH complexed with an IgG antibody raised against bGH (bGH‐Ab). Selectivity in binding of these microspheres to M cells, determined by confocal microscopy, was bGH < bSA < hIgG (mice) and bGH < bGH‐Ab (rats and mice). A similar selectivity was seen for microsphere entry into M cells (bGH < bSA < hIgG; bGH < bGH‐Ab). The appearance of protein‐coated microspheres in rat mesenteric lymph showed a similar selectivity to that found for binding and entry into M cells (bGH < bGH‐Ab). This latter selectivity was also found for hIgA‐coated microspheres (bSA < hIgA). Preservation of transport selectivity throughout transcytosis highlights the unique importance of the M cell surface as being the primary site determining which type of antigen can be presented subsequently to the gut immune system. The possibility that this is a transient or phasic property of the M cell surface and that this could have physiological relevance is also discussed.
The role of the endothelium in hypoxic pulmonary vasoconstriction
Authors: Ward JP , Robertson TP
Published: December 2014

The precise mechanisms underlying hypoxic pulmonary vasoconstriction (HPV) are still elusive. The recent discovery of K+ channels that are depressed by hypoxia in pulmonary vascular smooth muscle has provided a potential signal transduction mechanism for linking a reduction in Po2 to Ca2+ entry, but there are many reports suggesting that sustained HPV depends on the presence of the endothelium. Many endothelium‐derived vasoactive factors have been investigated as possible mediators of HPV, including endothelium‐derived relaxing factor (EDRF‐NO), leukotrienes, prostanoids and endothelin, yet none have been found to be indispensable for HPV. They do, however, act as powerful modulators of the response to hypoxia. HPV is probably multifactorial in origin, as exemplified by the biphasic response to hypoxia seen in isolated pulmonary arteries over 40 min. The first phase is of rapid onset but transient, endothelium independent and partly related to Ca2+ release from intracellular stores. The second phase is slowly developing but sustained, dependent on the endothelium and associated with a stable elevation of cytosolic Ca2+. Since tension continues to rise while intracellular [Ca2+] remains constant, this implies Ca2+ sensitization of the contractile apparatus. This is independent of protein kinase C or pH. It is proposed that HPV depends upon both smooth muscle and endothelium resident mechanisms. Inhibition of K+ channels causes an elevation of cytosolic Ca2+, which may not be sufficient to generate substantive contraction on its own. However, release from the endothelium of an as yet unidentified mediator increases Ca2+ sensitivity of the contractile apparatus, and sustained contraction ensues.
Ca(2+)‐activated Cl‐ and K+ channels and their modulation by endothelin‐1 in rat pulmonary arterial smooth muscle cells
Authors: Salter KJ , Turner JL , Albarwani S , Clapp LH , Kozlowski RZ
Published: December 2014

Using the patch‐clamp recording technique, we observed that endothelin‐1 (ET‐1; 0.8‐16 nM) enhanced a voltage‐activated outward current (Iout) and induced periodic oscillations of inward current in smooth muscle cells isolated from small pulmonary arteries (200‐400 microns in diameter). Anion substitution experiments revealed that the ET‐1‐induced inward current was carried by Cl‐ ions. Application of bosentan (10 microM; and ETA and ETB receptor antagonist) and FR 139317 (1‐10 microM; a selective ETA receptor antagonist) prevented initiation of inward currents or enhancement of Iout by ET‐1. The ETB receptor agonist tetra‐Ala‐endothelin‐1 (1‐20 nM) failed to evoke these responses. Caffeine (10 mM) induced a single transient inward current and prevented any further activation of inward current, or enhancement of Iout, by subsequent application of 16 nM ET‐1, suggesting that these currents were mediated by Ca2+ release from internal stores. Rapid intracellular release of Ca2+ by photolysis of nitr‐5 activated an inward Cl‐ current and increased the magnitude of Iout. These results demonstrate the existence of Ca(2+)‐activated Cl‐ and K+ channels in pulmonary arterial smooth muscle. The physiological role of these channels is at present uncertain, although their activation may be involved in the contractile responses of pulmonary arterial smooth muscle to ET‐1.
Opposing effects of oxidants and antioxidants on K+ channel activity and tone in rat vascular tissue
Authors: Reeve HL , Weir EK , Nelson DP , Peterson DA , Archer SL
Published: December 2014

K+ channels regulate tone in both the systemic and pulmonary circulations. K+ channel inhibition leads to membrane depolarization, Ca2+ influx and vasoconstriction; K+ channel activation leads to hyperpolarization and vasodilatation. The sulfhydryl oxidant diamide opens K+ channels in pulmonary smooth muscle and acts as a potent vasodilator in perfused lungs. We examined the hypothesis that antioxidants cause constriction and oxidants cause relaxation through their effects on K+ channels in vascular smooth muscle. The oxidant diamide (380 microM and 3.8 mM) inhibited the reduction of cytochrome C by ferrous sulphate in vitro whilst the antioxidants co‐enzyme Q10 (770 microM) and duroquinone (700 microM) increased the rate of reduction. Both antioxidants caused dose‐dependent constriction of endothelium‐intact and ‐denuded rat pulmonary artery and aortic rings. This constriction could be reversed by 1 microM diamide. Co‐enzyme Q10 and duroquinone (both at 100 microM) partially inhibited (approximately 30%) whole‐cell K+ channel currents and depolarized membranes of isolated pulmonary artery smooth muscle cell recorded using the amphotericin‐perforated‐patch‐clamp technique. Diamide (100 microM) increased whole‐cell K+ channel currents and hyperpolarized the membrane. The data suggest that oxidants and antioxidants may modulate vascular tone via an effect on K+ channels.
Redox agents as a link between hypoxia and the responses of ionic channels in rabbit pulmonary vascular smooth muscle
Authors: Park MK , Lee SH , Ho WK , Earm YE
Published: December 2014

Ca(2+)‐activated K+ currents (IK(Ca)) and voltage‐dependent Ca(2+)‐insensitive K+ currents (IK(V)) were recorded using the patch clamp technique to study the pulmonary (PASMC) and ear arterial smooth muscle cells (EASMC) of the rabbit and the possible regulatory mechanisms related to hypoxia. When a hypoxic solution (1 mM Na2S2O4, gassed with 100% N2) was superfused, the activity of Ca(2+)‐activated K+ channels (KCa channels) recorded at a pipette potential of ‐70 mV in cell‐attached mode was decreased to 49 +/‐ 7% in PASMC, whereas EASMC KCa channels did not respond to hypoxia. In inside‐out patches (bathed symmetrically in 150 mM KCl), reducing agents such as dithiothreitol (DTT; 5 mM), reduced glutathione (GSH; 5 mM) and NADH (2 mM) decreased KCa channel activity in PASMC, but they did not affect the EASMC KCa channel. However, oxidizing agents such as 5,5'‐dithio‐bis(2‐nitrobenzoic acid) (DTNB; 1 mM), oxidized GSH (GSSG; 5 mM) and NAD (2 mM) increased KCa channel activity in both PASMC and EASMC. In the whole‐cell configuration, using a pipette solution containing a high concentration of 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid (BAPTA; 10 mM), PASMC IK(V) were activated by depolarizing step pulses to voltages more positive than ‐30 mV (holding potential, ‐80 mV). IK(V) was increased by application of a membrane‐permeable oxidizing agent, 2,2'‐dithio‐bis(5‐nitropyridine) (DTBNP; 200 microM), whereas it was decreased by application of DTT (5 mM). From these results, it could be suggested that hypoxic pulmonary vasoconstriction is attributable, at least in part, to a change of cellular redox state, which decreases outward K+ currents. This hypothesis is further supported by the observation that the basal redox state of EASMC KCa channels is more reduced than that of PASMC KCa channels. The distinct responses to hypoxia of pulmonary and systemic arterial smooth muscle could be explained by this difference.
Development of the normal and hypertensive pulmonary vasculature
Authors: Haworth SG
Published: December 2014

Normal adaptation to extra‐uterine life consists of an immediate increase in endothelial and smooth muscle cell (SMC) surface: volume ratio as the cells ‘spread’ in the vessel wall. Lumen diameter increases and resistance falls. Changes in SMC shape are associated with a transient depolymerization of contractile and cytoskeletal filaments. The four SMC phenotypes identified in the vessel wall rapidly show postnatal changes in the types of filament proteins and contractile‐associated proteins, indicating that the term ‘differentiation’ means little at this age. At birth, all SMCs have a predominantly synthetic phenotype. Endothelium‐dependent relaxation is relatively poor despite abundant nitric oxide synthase. SMCs are relatively insensitive to nitric oxide despite a high basal generation and a stimulated increase in cGMP generation. By contrast, the relaxation in response to ATP‐sensitive potassium (KATP) channel activation is present at birth, the response being similar to that seen in the adult. Neonatal pulmonary hypertension, due to either congenital heart disease or experimental chronic hypobaric hypoxia (51 kPa) is associated with abnormal structural remodelling. In experimental pulmonary hypertension, the normal maturation of endothelium‐dependent and ‐independent relaxation via soluble guanylate cyclase is delayed in newborns and the established responses are inhibited in older animals. The relaxant response to KATP channel activation is preserved. Thus, adaptation to extra‐uterine life consists of a rapid sequence of integrated morphological and functional changes, which is disturbed by the presence of pulmonary hypertension. The pattern of recovery from a pulmonary hypertensive insult is determined by the age at exposure and type and duration of the insult.
Cold‐induced changes in circulating levels of catecholamines and thyroid hormones are modulated by energy intake in newborn pigs
Authors: Herpin P , Berthon D , Bertin R , De Marco F , Dauncey MJ , Le Dividich J
Published: December 2014

Newborn pigs were kept at a low ambient temperature from 6 until 54 h of age and supplied with a limited (LI, 415 g (kg body weight)‐1) or a high (HI, 655 g (kg body weight)‐1) intake of milk. At the end of the treatment, both groups had similar deep body temperatures and metabolic rates. However, plasma adrenaline and noradrenaline levels were, respectively, 5.8‐ and 3.0‐fold lower (P < 0.01) in HI than LI piglets, whereas plasma 3,5,3'‐triiodothyronine (T3) was 1.5‐fold higher (P < 0.01) in HI piglets. It is concluded that the hormonal control of cold‐induced thermogenesis is modulated by energy intake, with catecholamines and thyroid hormones acting in a closely related and complementary manner.
The effect of raised hydrostatic pressure on heart rate variability during breath holding in man
Authors: Byrne DE , Bowser‐Riley F , Kidd C
Published: December 2014

Changes in cardiac interval (difference between two consecutive R waves of the ECG) during an expiratory breath hold (16 s) were examined in four divers during a saturation dive to 450 msw (metres of seawater). At 450 msw, breath hold caused a progressive shortening of cardiac interval that was significantly different from the changes seen at surface. The cause and significance of this shortening is unknown, but it might serve to maintain normal cardiovascular dynamics under hyperbaric conditions.
Epidermal growth factor stimulates the restitution of rat gastric mucosa in vitro
Authors: Miller CA , Debas HT
Published: December 2014

Epidermal growth factor (EGF) is mitogenic to gastric mucosal cells, protects against gastric mucosal injury induced by ulcerogenic agents, and stimulates cell migration in many systems. Restitution, the rapid re‐establishment of mucosal integrity following damage, involves epithelial cell migration and can be monitored by measuring the transmucosal potential difference (PD) of tissue mounted in an Ussing chamber. The role of EGF in restitution is poorly characterized. To assess the effect of exogenous EGF on restitution, samples of rat gastric mucosa were mounted in an Ussing chamber with a solution of 10 nM EGF bathing either the mucosal or serosal surface. Matched control tissues from the same animals were untreated. Mucosal damage was induced by exposure of tissues to hyperosmolar sodium chloride. Restitution following injury was monitored by measuring the recovery of transmucosal PD, which reflects the degree of mucosal integrity. Undamaged mucosa maintained a PD of approximately ‐30 mV for several hours (mucosa negative with respect to serosa). Mucosal exposure to 1.2 M NaCl for 2 min reduced the PD to near 0 mV. Thereafter, the PD returned in approximately 60 min to plateau at a value representing maximal recovery. Tissues mucosally treated with 10 nM EGF recovered following damage to a maximum of 60.2 +/− 5.1% of pre‐exposure PD, while matched controls recovered to only 46.2 +/− 5.8%, a significant difference. Tissues serosally treated with EGF recovered to 61.0 +/− 3.2% and matched controls recovered to 51.1 +/− 2.9%, also a significant difference. These results suggest that both serosally and mucosally applied EGF stimulates the restitution of rat gastric mucosa in vitro.
Effects of a temperature increase on oxygen consumption of yellow freshwater eels exposed to high hydrostatic pressure
Authors: Sebert P , Simon B , Barthelemy L
Published: December 2014

Oxygen consumption was measured in yellow freshwater eels, Anguilla anguilla, during exposure to a hydrostatic pressure (HP) of 101 atmosphere absolute (ATA) for 3 h, either with or without a 5 degrees C increase in water temperature. It was found that concomitant increases in temperature and pressure resulted in an increase in oxygen consumption that was lower than when pressure alone was increased. When eels were acclimated to HP for 21 days and then submitted to a temperature increase of 5 degrees C, this induced a significant increase in oxygen consumption but only during the first hour. It is therefore concluded that raising the water temperature during the first hours under pressure could counterbalance the pressure effects on membrane fluidity in a thermodynamic manner and thus help shallow‐water fish acclimate to high pressure. In contrast, when acclimation processes are ended, the temperature effect disappears within 1 h.
The effects of relaxin on the response of intramammary pressure and mammary blood flow to exogenous oxytocin in the goat
Authors: Peaker M , Fleet IR , Davis AJ , Taylor E
Published: December 2014

Lactating goats were given relaxin (50 micrograms) by close‐arterial infusion into one mammary gland. The increase in intramammary pressure and in mammary blood flow elicited by exogenous oxytocin i.v. was attenuated by relaxin in goats during pregnancy and early lactation but not in a group studied during the oestrous cycle. Intramammary pressure in both mammary glands was affected at the dose of relaxin used. It is concluded that a change in responsiveness of the mammary myoepithelium to oxytocin is one possible effect of relaxin, acting directly or indirectly, circulating systemically during pregnancy and produced locally by the mammary gland at the onset of and during lactation.
Cerebral microvascular permeability and CSF pH in anaesthetized rats
Authors: Wolff CB , Sarker MH , Fraser PA
Published: December 2014

The idea that the blood‐brain barrier (BBB) may be made slightly permeable by an acid load on the brain side was tested in single pial venular capillaries of anaesthetized young rats. The fluorescent dye, Lucifer Yellow (457 Da), was used as a fluid‐phase marker to measure permeability in the presence of a free radical scavenger. Tight microvessels were unresponsive to pH changes of 0.3‐0.5 units. Vessels that were permeable showed small, significant increases in permeability with decreasing pH (2.19 +/− 0.562 x 10(‐6) cm s‐1 (pH unit)‐1). This effect increased with increasing permeability.
The role of circulating catecholamines in the depletion of parotid acinar granules in conscious rats in the cold
Authors: Asztely A , Tobin G , Ekstrom J
Published: December 2014

The possibility that circulating catecholamines might affect parotid gland function during feeding (over a period of 80 min) and cold stress (2–4 degree C) was investigated in rats that had been fasted for 30 h. In the first set of experiments, in which the glands had been sympathectomized by removing both superior cervical ganglia 10–12 days previously, there was a substantial reduction in the density of acinar secretory granules (42% compared with non‐fed animals in the cold) and in the total glandular amylase activity (54%). However, similar, or even greater, losses were recorded in rats subjected to additional bilateral adrenal medullectomy and pretreatment with atropine and alpha‐ and beta‐adrenoceptor blockers. The losses were therefore attributed to activation of parasympathetic non‐adrenergic, non‐cholinergic mechanisms. In a second set of experiments, employing only morphometric assessment, the parasympathetic auriculotemporal nerve was cut on one side in addition to bilateral sympathectomy and, as a further precaution, the animal was atropinized. It was then found that there was a loss of 17% of granules in the parasympathectomized plus sympathectomized gland, but not the contralateral gland, of non‐fed cold‐exposed rats compared with non‐fed animals kept at room temperature. When rats were fed as well as exposed to cold the number of granules in parasympathectomized plus sympathectomized glands fell by 46% compared with similar non‐fed animals in the cold and by 55% compared with those at room temperature. After adrenal medullectomy, cold exposure alone had no effect on the granular density of parasympathectomized plus sympathectomized glands but, when combined with feeding, granular loss amounted to 30%. Pretreatment with a combination of alpha‐ and beta‐adrenoceptor blocking agents abolished this effect. Thus circulating catecholamines liberated not only from the adrenal medulla but also from other sources (extraglandular adrenergic nerve terminals and extra‐adrenal chromaffin tissue) are able to induce losses in the number of acinar granules in the parasympathectomized plus sympathectomized glands. However, a high degree of sensitization of the parotid acinar cells may be required to allow the response to become manifest.
Hepatic branch vagotomy enhances feeding in response to centrally elicited glucose deprivation in rats
Authors: Rossi R , Meissner A , Del Prete E , Scharrer E
Published: December 2014

Intracerebroventricular (I.C.V.) administration of 2‐deoxy‐D‐glucose (2‐DG) produces glucose deprivation‐induced (‘glucoprivic’) feeding and sympathoadrenal activation. To find out whether peripheral mechanisms modulate centrally elicited glucoprivic feeding the effect of hepatic branch vagotomy (HBV) compared with sham vagotomy (SV) on the feeding response to I.C.V.‐injected 2‐DG (1.2 or 2.4 mg per rat) was tested in rats fed a fat‐enriched diet (18% fat). 2‐DG was injected into the lateral ventricle 1 h after after dark onset, at light onset or 6 h after light onset of the 12 h light‐12 h dark cycle. Apart from one (1.2 mg 2‐DG injected 1 h after dark onset) out of six experiments, HBV enhanced glucoprivic feeding. This finding is consistent with the assumption that centrally elicited glucoprivic feeding is antagonized by peripheral stimuli signalled to the brain through the hepatic vagus branch.
Continuous versus single drainage of milk from the bovine mammary gland during a 24 hour period
Authors: Stelwagen K , Knight CH , Farr VC , Davis SR , Prosser CG , McFadden TB
Published: December 2014

Five primiparous and five multiparous cows were used to determine if mammary cisternal storage of milk during a 24 h period of milk accumulation limited milk secretion. In addition, we investigated if there is a parity effect for the capacity of the mammary cisternal compartment to hold a 24 h accumulation of milk secretion, and studied the movement of milk from the alveolar compartment into the cisternal compartment. All cows were fitted with catheters in all teats in order to collect cisternal and alveolar milk fractions separately. For a 24 h period of milk accumulation, the milk was drained once (after 24 h) from one side of the udder (OD), and continuously from the other side of the udder (CD). There was no significant parity effect for cisternal, alveolar and total milk volumes at 24 h. Therefore, data from primi‐ and multiparous cows were pooled for subsequent analyses. Cisternal milk volume from CD glands was higher than that from OD glands (P < 0.01), indicating that cisternal storage of milk in the mammary gland may be limiting to milk secretion during 24 h milking intervals. Alveolar volumes did not differ between OD and CD, but, as a result of the higher cisternal milk volume, total milk volume was highest in the CD glands (P = 0.05). Movement of milk from the alveolar into the cisternal compartment was intermittent. Moreover, analyses of the slopes of individual milk accumulation profiles of the first 6 h of accumulation revealed that the cisternal compartment starts filling immediately following milking, although the rate of filling is relatively low until 7–8 h postmilking.
The Wellcome Prize Lecture. Genetic imprinting: the battle of the sexes rages on
Authors: Reik W
Published: December 2014

Genomic imprinting in mammals is an important genetic mechanism by which genes are expressed or repressed depending on which parent they have been inherited from. Some properties of the imprinting mechanism are already established; notably, some of the effects of imprinting on mammalian development can be explained by the phenotypic effects of a number of specific imprinted genes, which include major fetal growth factors. An evolutionary explanation of imprinting has also been suggested. Some of the molecular mechanisms of imprinting are known, and these include the modification of DNA and chromosomes in the form of DNA methylation and possibly heritable chromatin structures. Loss of imprinting or altered imprinting is implicated in a large number of genetic diseases and cancers. Many important issues remain to be resolved; these include the precise molecular mechanisms and, in particular, the nature of the primary imprints that are inherited from the parental gametes, and the genes that control the imprinting process. Isolation of the majority of imprinted genes and the elucidation of their phenotypic effects and physiology are major goals for the future. These studies will provide important insights into human genetics, and will connect evolutionary understanding with physiology, genetic disease and human behaviour.
Haemodynamic and metabolic responses of the lower limb after high intensity exercise in humans
Authors: Hussain ST , Smith RE , Medbak S , Wood RF , Whipp BJ
Published: December 2014

This study assessed blood flow in the common femoral, superficial femoral and profunda femoris arteries, the effects of vasodilator metabolites and changes in blood pressure and pulse during recovery after high intensity exercise (Wingate test). Mean common femoral artery flow increased sevenfold in response to the exercise. The subsequent decline in mean common femoral artery flow was mono‐exponential with a mean time constant of 19 min. The post‐exercise increase in profunda femoris artery flow (ninefold) was significantly greater than the superficial femoral artery flow (fourfold, P < 0.05). Systolic blood pressure and heart rate decreased monotonically throughout recovery. In contrast, diastolic blood pressure showed a significant fall below baseline at 3 min (P < 0.05) with a return to baseline at 60 min. The greatest drop below baseline (approximately 20 mmHg) occurred around 7 min. Lactate reached a maximum of 13.6 +/− 2.3 mmol ‐1 at 8 min (P < 0.05) and was still significantly above baseline at 60 min. pH remained below 7.2 until 20 min of recovery. The results demonstrate that following high intensity exercise, blood flow to the limbs appears to be controlled by complex interactions of various vaso‐active metabolites, each contributing proportionally more at different times during recovery.
The effects of sodium‐calcium exchange inhibitors on protein loss associated with the calcium paradox of the isolated Langendorff perfused guinea‐pig heart
Authors: Chatamra KR , Chapman RA
Published: December 2014

The damage done to Langendorff perfused guinea‐pig hearts by initiation of a calcium paradox, as assessed by the loss of myoglobin, is significantly reduced if inhibitors of Na(+)−Ca2+ exchange (Mn2+, Ni2+, bepridil and dodecylamine) are present when Ca2+ is repleted. This protection is not, to any major extent, due to secondary effects of these agents on the L‐type Ca2+ channels, because more specific inhibitors of the Ca2+ channels are much less effective. These results suggest that the principal route for Ca2+ entry during the calcium paradox is Na(+)−Ca2+ exchange.
Microdialysis of a non‐NMDA receptor antagonist into the L7 dorsal horn attenuates the pressor response to static muscle contraction but not passive stretch in cats
Authors: Hand GA , Ordway GA , Wilson LB
Published: December 2014

Mean arterial pressure (MAP) and heart rate (HR) were measured during static contraction or passive stretch of the triceps surae muscle of chloralose‐anaesthetized cats. MAP and HR increased by 46 +/− 5 mmHg and 17 +/− 3 beats min‐1, respectively, during a 1 min contraction. Passive stretch of the same muscle for 1 min reflexly increased MAP and HR by 40 +/− 7 mmHg and 14 +/− 3 beats min‐1, respectively. Microdialysis of 2 mM 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNX), a non‐NMDA receptor antagonist, into the dorsal horn at the L7 spinal level attenuated the reflex pressor response to static contraction (2 h of dialysis: delta MAP = 23 +/− 5 mmHg, delta HR = 8 +/− 2 beats min‐1). By contrast, there was no attenuation of the pressor response to passive stretch at 2 h of CNQX perfusion. However, the simultaneous microdialysis of 2 mM CNQX into the L6 and S1 levels blunted the pressor and tachycardic responses to contraction and stretch. These data show that the reflex pressor response to static muscle contraction is partly mediated by activation of non‐NMDA receptors at the level of afferent fibre entry into the dorsal horn and through collateral pathways. Further, it appears that the afferent pathways within the dorsal horn for the signal transduction arising from static muscle contraction and passive stretch of the hindlimb are dissimilar.
The use of coloured dye‐extraction microspheres to measure blood flow in rabbit skeletal muscle: a validation study with special emphasis on repeated measurements
Authors: Degens H , Craven AJ , Jarvis JC , Salmons S
Published: December 2014

We evaluated the use of coloured dye‐extraction microspheres for measuring blood flow in the skeletal muscle of anaesthetized rabbits. Spheres were injected into the left atrium after sternotomy or lateral thoracotomy, or into the left ventricle via the left carotid artery. Both routes of administration produced adequate mixing of microspheres with the blood. In general, the values of flow obtained from spheres of different colour were well correlated. Resting flows were difficult to measure, owing to the low number of spheres and the correspondingly low absorption of the samples. Occlusion of the capillary bed by trapped spheres was less than 10% in both tibialis anterior and extensor digitorum longus muscles after injection of a total of 15 x 10(6) spheres. Injection via the left ventricle, a closed‐chest procedure, gave a more stable preparation than injections via the left atrium. However, in both cases there was a progressive decline in hyperaemic muscle blood flow during a series of injections. These results indicate that it is possible to use this technique to measure skeletal muscle blood flow in the rabbit, but that it is difficult to exploit the advantages of sequential microsphere injection in this species.