bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of the expression of laminin in the spinal cord of the frog during development and regeneration
Authors: Gordon-Weeks PR , Golding JP , Clarke JD , Tonge D
Published: December 2014

In the present experiments, we have used an affinity‐purified polyclonal antibody to laminin to determine the time course of expression of laminin in the central nervous system (CNS) of Rana temporaria tadpoles during normal development and during restoration of the dorsal columns of the spinal cord. Immunoblotting analysis indicated that in the peripheral nervous system (PNS) of adult frogs the antibody recognized proteins of molecular weights 350–400 and 205–220 kDa, corresponding to the A and B chains respectively of mammalian laminin. Immunohistochemistry with our antibody suggested that laminin was absent from the tadpole spinal cord, and did not appear even in the basal lamina of the blood vessels within the spinal cord until after metamorphosis. Furthermore, there was no evidence of laminin expression in the dorsal columns after hemisection of the spinal cord. However, throughout development laminin was present in basal lamina outside the CNS, in particular in the pial membranes, and in the basal lamina of blood vessels and sheath cells in the dorsal and ventral roots. Electron microscopy showed that the blood vessels of CNS capillaries had basal laminae throughout development that was morphologically indistinguishable from that seen in peripheral vessels.
The role of cholecystokinin in inhibition of gastric emptying by peptone in the rat
Authors: Forster ER , Dockray GJ
Published: December 2014

It is clear that the intestinal hormone cholecystokinin (CCK) inhibits gastric emptying, but doubts remain about the physiological significance of this action. Evaluation of the apparently conflicting data is complicated by the fact that little is known of the duration of action of CCK‐releasing meals in delaying emptying. We have studied this issue by following the emptying of the second of two successive liquid test meals instilled into the stomach in conscious gastric fistula rats. Prior administration of peptone, but not saline, delayed the emptying of subsequently administered saline and delayed still further the emptying of subsequently administered peptone. The action of isotonic peptone lasted about 10 min from the initial instillation into the stomach. Radioimmunoassay of plasma CCK indicated a significant increase 5 min after intragastric peptone, and a still further rise occurred 5 min after administration of the second of two consecutive peptone meals; 21 min after the first meal, plasma CCK had returned to basal levels. Intravenous infusion of CCK in a dose that matched the inhibition of gastric emptying caused by peptone gave plasma concentrations about 35% higher than those seen 5 min after the second of two consecutive peptone meals. It is concluded that a liquid test meal of peptone delays gastric emptying in part through release of CCK and that the response lasts 10 min or less. The relatively short duration of action of endogenous CCK released by a single protein‐rich meal in the rat should be kept in mind in interpreting the significance of studies on the physiology of CCK.
Effect of cortisol on blood pressure and vascular reactivity in the ovine fetus
Authors: Tangalakis K , Lumbers ER , Moritz KM , Towstoless MK , Wintour EM
Published: December 2014

The aim of this study was to investigate the cardiovascular effects of exogenous cortisol in fetal sheep, (a) between 100 and 120 days of gestation when cortisol production is minimal and (b) after 130 days when endogenous plasma cortisol starts to rise. Chronically cannulated ovine fetuses (103–120 days, n = 9; 130–137 days, n = 7), received sequentially a 24 h infusion of vehicle (0.9% sodium chloride) and a 24 h infusion of cortisol at 100 micrograms/h. Blood pressure and heart rate changes to bolus injections each of angiotensin II and noradrenaline (0.2, 0.5, 1.0, 2.0 micrograms) were measured before and after the saline and cortisol infusions. Fetuses in each age group, served as additional controls receiving 48 h saline infusions. In both immature and mature age groups, the cortisol infusion increased basal fetal blood cortisol concentrations by 33.7 and 35.4 nmol/l respectively. In the immature group, cortisol, but not saline, caused significant 14.3 and 15.3% increases in basal systolic and diastolic pressures respectively. Basal blood pressure was higher in the mature group, but did not increase further despite the increase in cortisol levels. Furthermore, vascular responsiveness to angiotensin II but not to noradrenaline was significantly enhanced following the cortisol infusion, at both ages. Fetal heart rate did not change following the cortisol infusion. Exogenous cortisol contributes to the regulation of fetal blood pressure in the immature fetus, when other mechanisms have not developed. Cortisol might achieve this, in part, by enhancing vascular sensitivity to angiotensin II.
The protective effect of damaging eccentric exercise against repeated bouts of exercise in the mouse tibialis anterior muscle
Authors: Sacco P , Jones DA
Published: December 2014

Using a damaging eccentric exercise regime of the mouse tibialis anterior (TA) muscle we have investigated the extent and time course of protection afforded by one bout of exercise against damage resulting from a second bout of activity. Maximal force and fibre morphology were preserved if the exercise was repeated within 21 days, but by 84 days muscles once again became susceptible to damage. Low‐frequency force loss had a shorter time course of protection against repeated exercise, lasting less than 21 days. The results provide evidence for different mechanisms contributing to the development of muscle damage following eccentric exercise and provide a basis for characterizing the adaptive response of muscle to damaging exercise.
Differences between sheep excreting sodium predominantly in their urine or in their faeces: the effect of changes in sodium intake
Authors: Michell AR , Moss P
Published: December 2014

Sheep receiving a total of about 31 mmol day‐1 (0.5 mmol kg‐1) of sodium were classified according to the predominant route of sodium excretion; urinary (U) or faecal (F). U sheep had a greater water turnover than F sheep; their intake was 41% higher and they produced 133% more urine but there was little difference in faecal water loss. Most faecal sodium was readily exchangeable with water in both groups. When sodium intake was reduced by 80% (to 6 mmol day‐1; 0.1 mmol kg‐1), the reduction in total sodium excretion was equally effective in F sheep and U sheep after 48 h and after 2 weeks the overall losses of sodium were smaller in F sheep. On sodium intakes close to requirement (0.1 mmol kg‐1 or less) the majority of the sheep excreted most of their sodium in faeces and did so on intakes up to 0.5 mmol kg‐1 day‐1. Excess dietary sodium is mainly excreted renally. When sodium intake is increased abruptly (by 20 mmol day‐1, 0.3 mmol kg‐1), total sodium excretion only increases gradually but after about 3 days it ‘overshoots’ as in humans.
The effects of Na(+)‐K(+)‐Cl‐ co‐transport and Cl(‐)‐HCO3‐exchange blockade on the membrane potential and intracellular chloride levels of rat arterial smooth muscle, in vitro
Authors: Davis JP
Published: December 2014

Membrane potential and intracellular chloride levels have been measured simultaneously in vascular smooth muscle from the femoral artery of the rat, in vitro, using double‐barrelled chloride‐sensitive microelectrodes. These values are compared in the presence and absence of bicarbonate, and inhibitors of Cl(‐)‐HCO3‐ exchange and Na(+)‐K(+)‐Cl‐ co‐transport. Both DIDS and bumetanide caused a hyperpolarization of membrane potential (Em) and a fall in [Cl‐]i, in the presence of extracellular HCO3‐. The effects of bumetanide were reversible, but those of DIDS were not. The effect of both agents were additive. The results demonstrate that both Cl(‐)‐HCO3‐ exchange and Na(+)‐K(+)‐Cl‐ co‐transport accumulate intracellular chloride in this preparation, and it is suggested that this may allow the modulation of membrane potential (and hence excitability) of smooth muscle.
Influence of extracellular bicarbonate on the short‐circuit current and intracellular free calcium of human cultured sweat duct cells
Authors: Pedersen PS
Published: December 2014

Transepithelial short‐circuit current (Iscc) and intracellular free Ca2+ (Ca2+i) was studied in monolayers of cultured human sweat duct cells (CSDCs) in the presence or absence of HCO3‐ (and CO2) in the bathing solutions. Addition of HCO3‐ (and CO2) increased the control Iscc by more than 50%. The effect of HCO3‐ (and CO2) on Iscc was confined to the serosal bath. The HCO3‐ (and CO2) effect was also studied during stimulation with the cholinergic agonist methacholine (MCh), which in CSDC induces a complex response consisting of an initial Iscc and Ca2+i spike, which is independent of extracellular Ca2+, followed by regular Iscc and Ca2+i oscillations, which are absent during Ca(2+)‐free bathing conditions. The sustained Iscc and Ca2+i oscillations, but not the initial Iscc and Ca2+i spike were abolished by the removal of extracellular HCO3‐ (and CO2). It is concluded that the Ca2+ influx and the Iscc in CSDCs are critically influenced by the presence of extracellular HCO3‐ (and CO2) in the bathing solutions.
Rapid stimulatory effect of bradykinin on glucose transport across the brush‐border and basolateral membranes of rat jejunal enterocytes
Authors: Sharp PA , Debnam ES
Published: December 2014

Bradykinin has been shown to stimulate sugar uptake by intact intestine, but the cellular locus of this action is unknown. In this study on rat we show that bradykinin (10(‐7) M) stimulates both sodium‐dependent glucose uptake at the brush‐border membrane and carrier‐mediated movement across the basolateral membrane of upper villus enterocytes. These results suggest a role for bradykinin in the local control of glucose transport though the mechanisms underlying these effects have still to be elucidated.
Some aspects of the use of laser Doppler flow meters for recording tissue blood flow
Authors: Vongsavan N , Matthews B
Published: December 2014

Laser Doppler flow meters are used to provide continuous records of blood flow in tissues. An account is given of their principles of operation and of the differences between two of the commercially available instruments: the Periflux model PF3 and the Moor blood flow monitor model MBF3D. The Periflux tended to have higher noise levels and to drift more than the Moor. The principal disadvantage of these instruments is that they cannot be calibrated in absolute units of blood flow. It is suggested that the method of standardization adopted for the Periflux be used with other machines, based on the signal produced by the Brownian motion of a 0.5% suspension of 0.48 micron diameter polystyrene microspheres at 20 degrees C. The signal representing zero flow in a tissue can be obtained by recording with the same light intensity from a stationary reflector. In model systems the instruments are linear with red cell volume fractions up to only 1%, which is below that likely to be encountered in many tissues. The effects of ambient light and the origin of movement artifacts are also considered.
Localized neural control of blood flow in the posterior region of the knee joint in anaesthetized rabbits
Authors: Ferrell WR , Khoshbaten A , Angerson WJ , Najafipour H
Published: December 2014

Radiolabelled microspheres were used to measure blood flow of structures in and around the rabbit knee joint and to determine the effect of electrical stimulation of the posterior articular nerve (PAN) supplying the knee. Surgical exposure of the posterior aspect of the knee joint ‘capsule’ and section of PAN resulted in an increase in flow restricted to this region. Electrical stimulation produced frequency‐dependent reductions of blood flow in the posterior region, but no alterations occurred in the anterior region or in any other surrounding structures, suggesting that the neural supply is specific to the posterior joint capsule.
Enterocytes on rat jejunal villi but not in the crypts posses m3 mRNA for the M3 muscarinic receptor localized by in situ hybridization
Authors: Przyborski SA , Levin RJ
Published: December 2014

Localization of m3 mRNA, for the expression of the M3 muscarinic receptor, along the crypt‐villus axis, was undertaken in rat jejunum by in situ hybridization. While enterocytes on the lower two‐thirds of the villi showed the presence of m3 mRNA it was absent in the crypt enterocytes. This indicates that the final locus of muscarinically activated jejunal secretion is mediated by the M3 receptor on the enterocytes of the villi and not via the crypt cells.
The use of midbrain stimulation to identify the discharges of static and dynamic fusimotor neurones during reflex jaw movements in the anaesthetized cat
Authors: Donga R , Taylor A , Juch PJ
Published: December 2014

In anaesthetized cats, it was possible to enhance the dynamic sensitivity to stretch of jaw muscle spindle primary afferents by electrical stimulation in the midbrain. This effect was taken to be due to excitation of dynamic fusimotor neurones and was used to identify fusimotor fibres as static or dynamic in recordings from the masseter nerve. During reflex movements, some fusimotor fibres fired tonically, while others were markedly modulated with increases in firing corresponding approximately to muscle shortening. The modulated group had a significantly higher mean resting firing frequency than the tonic group. Midbrain stimulation at points shown to produce dynamic effects on muscle spindle primary afferents increased the discharge frequency of the tonic fusimotor units, but did not significantly affect the modulated fusimotor units. We conclude that the fusimotor fibres in the masseter nerve which fire tonically during reflex jaw movements are probably of the dynamic type, while those which show strongly modulated increases in firing are probably static.
Structural and functional characterization of striated ducts isolated from the rabbit mandibular salivary gland
Authors: Evans RL , Lau KR , Case RM
Published: December 2014

Ductal elements within salivary glands are responsible for modifying the electrolyte composition of primary saliva secreted by the acini. To study the mechanism and regulation of the transport processes involved requires a suitable preparation of functional ducts. To this end we have isolated intralobular ducts from rabbit mandibular salivary glands using the technique of tissue dissociation and microdissection. Light and electron microscopy demonstrated that the ducts corresponded ultrastructurally to striated intralobular ducts of the intact gland. Ducts could be maintained in tissue culture on polycarbonate filter rafts for up to 36 h, during which time the ends of the ducts did not usually seal. The overall resting content of ductal adenosine 3',5'‐cyclic monophosphate (cyclic AMP) was 16.0 +/− 3.0 fmol mm‐1 and increased dose dependently in response to stimulation with the beta‐adrenoceptor agonist isoprenaline (10(−9)−10(−4) M; concentration required to produce a half‐maximal response, K0.5 = 2.1 x 10(−6) M). The response to isoprenaline was blocked by the antagonist propranolol. Intracellular cyclic AMP content was also raised by the adenylate cyclase activator forskolin and by prostaglandin E2. Acetylcholine (3 x 10(−8)−10(−5) M) caused a dose‐dependent and maintained rise in [Ca2+]i (K0.5 = 2.5 x 10(−7) M). This increase in [Ca2+]i could be reversed by the muscarinic antagonist atropine and appeared to result from a combination of mobilization of intracellular Ca2+ stores and entry of Ca2+ from the extracellular fluid. Noradrenaline induced only a very small, mainly transient rise in [Ca2+]i while phenylephrine failed to increase [Ca2+]i at all. Vasoactive intestinal peptide (5 x 10(−7) M) also produced a marginal, maintained rise in [Ca2+]i. Substance P, bombesin, isoprenaline, and prostaglandin E2 did not elevate [Ca2+]i. Application of the calcium ionophore ionomycin induced a substantial maintained rise in [Ca2+]i. Taken together, these results indicate that isolated and cultured striated ducts (i) possess intact beta‐adrenoceptors coupled to adenylate cyclase, putative receptors for prostaglandin E2 and muscarinic receptors, and (ii) represent a viable preparation for the study of the transport mechanisms involved in the ductal modification of salivary fluid composition.
Acute and chronic effects of pancreatic glucagon on sugar transport across the brush‐border and basolateral membranes of rat jejunal enterocytes
Authors: Debnam ES , Sharp PA
Published: December 2014

Preparations of isolated rat jejunal enterocyte and brush‐border and basolateral membrane vesicles have been used to study the effects of a 15 min exposure of upper and mid‐villus enterocytes to pancreatic glucagon on the initial, unidirectional phlorhizin‐sensitive (brush border) transport of galactose and phlorhizin‐insensitive (basolateral) movement of the sugar. These acute effects of glucagon have been compared with responses following treatment of animals for 1 or 3 days with the hormone. Incubation of cells with glucagon significantly stimulated phlorhizin‐sensitive uptake by 42 and 64% for upper and mid‐villus cells, respectively. Glucagon, however, was without effect on phlorhizin‐insensitive galactose uptake. This differential action of the hormone at the two cellular loci was confirmed by uptake data obtained using purified brush‐border and basolateral membrane vesicles prepared from isolated cells. In contrast to the acute challenge with glucagon, treatment of animals for 3 days with the hormone significantly increased both phlorizin‐sensitive (upper villus +31%, mid‐villus +74%) and phlorizin‐insensitive (upper villus +42%, mid‐villus +53%) galactose uptake. Glucagon exposure of exposure of isolated cells from 3 days treated animals was without further effect on galactose uptake at the two membrane loci. These data represent the first evidence for a direct action of pancreatic glucagon on enterocyte sugar transport. Thus the hormone is likely to be important in the physiological control of sugar absorption in addition to its possible role in the modulation of transport during starvation and diabetes mellitus, conditions characterized by hyperglucanonaemia and enhanced intestinal sugar transport.
The actions of caffeine and 2,3‐butanedione monoxime on calcium transients in human vascular smooth muscle
Authors: Otun H , Gillespie JI , Greenwell  , Dunlop W
Published: December 2014

Ca2+ mobilization by membrane depolarization or histamine application, was measured in isolated human uterine artery smooth muscle cells. Nifedipine, a Ca2+ channel blocker, was found to inhibit the depolarization‐induced increase in [Ca2+]i but not the histamine‐induced increase. This suggests the presence of functional voltage‐dependent Ca2+ channels and agonist‐induced mobilization of Ca2+ via a different mechanism. Caffeine inhibited both the depolarization‐ and histamine‐induced increases in intracellular calcium. The mechanisms of inhibition do not involve cAMP and point to a complex action of caffeine at multiple sites. The dephosphorylating agent 2,3‐butanedione monoxime (BDM) was found to block voltage‐dependent Ca2+ changes but not agonist‐induced changes suggesting a role for phosphorylation in the regulation of the Ca2+ channels in these cells.
Administration of 3,5,3'‐triiodothyronine induces a rapid increase in enterocyte lactase‐phlorizin hydrolase activity of young pigs on a low energy intake
Authors: Tivey DR , Morovat A , Dauncey MJ
Published: December 2014

The rapid increase in plasma concentration of 3,5,3'‐triiodothyronine (T3) which occurs after feeding may invoke changes in lactase‐phlorizin hydrolase (LPH) activity of the small intestine. This hypothesis has been tested in 6‐week‐old pigs living at thermal neutrality (26 degrees C) on a low level of energy intake. Littermate pairs were infused with either saline or T3 at 30 min intervals over a 6 h period, 18‐24 h after the last meal. The activity of LPH in mucosal homogenates increased significantly in test compared with control animals (P < 0.05; T3 37% > saline). This was a specific effect on LPH since there was no effect of T3 on the activity of sucrase‐isomaltase. Further, it could not be attributed to changes in intestinal morphology since there were no differences in crypt depth, villus height or villus area between the two groups. Enzyme‐cytochemical analysis indicated that administration of T3 increases LPH activity at all points along the villus axis, whereas there is no effect on alpha‐glucosidase (combined sucrase‐isomaltase and maltase) activities. These results indicate that there is unlikely to be a simple causal relation between the immediate increase in plasma T3 after feeding and the initial decline in LPH activity observed previously in young pigs living in a cold environment. By contrast, the subsequent increase in LPH activity could be under the direct control of the food‐induced increase in plasma T3 concentration, and the present results suggest a potential role for T3 as an important short‐term homeostatic regulator of LPH in the small intestine.
Motor units within the normal rat medial gastrocnemius
Authors: Einsiedel LJ , Luff AR
Published: December 2014

The contractile properties, fatiguability and axonal conduction velocity were determined for 118 motor units in the medial gastrocnemius of eighteen rats. Fast‐twitch and slow‐twitch units could be categorized on the basis of the 'sag' test. For the purposes of statistical comparison the fast‐twitch units were classified on the basis of their fatiguability as fast‐fatiguable (FF), fast intermediate (FI) and fast fatigue‐resistant (FR). As such, FR units tended to have a longer isometric twitch time course than other fast‐twitch units. On the basis of peak tetanic force FF units were largest (mean 341 +/− 120 mN) followed by FI (145 +/− 85 mN), FR (87.3 +/− 38) and slow units (40.4 +/− 11.0 mN). There were no differences in motor axonal conduction velocity. Although units were categorized, it is clear that for all characteristics investigated the fast‐twitch units exist as a continuum. Some of the largest FF units (peak force 350‐500 mN) failed to maintain force with high‐frequency stimulation (300 Hz) and this was associated with a failure of the EMG signal.
Stretch‐activation of rat cardiac myocytes
Authors: Craelius W
Published: December 2014

Mechanically activated ion channels (MACs) in rat ventricular myocytes were activated by stretching membrane patches attached to microelectrodes. Charge injection from MACs, consisting mainly of inward K+, was sometimes of sufficient magnitude (0.2 pC) during brief (50 ms) periods, to trigger action currents. Action currents were shown to be extracellular records of action potentials. These results demonstrate the activation of myocytes by injection of approximately 4 pA from a few MACs in a membrane patch.
Hypothalamic‐evoked effects in cat nucleus tractus solitarius facilitating chemoreceptor reflexes
Authors: Silva-Carvalho L , Dawid-Milner MS , Goldsmith GE , Spyer KM
Published: December 2014

In anaesthetized cats intracellular recordings in the nucleus tractus solitarius (NTS) have been used to identify neurones receiving inputs from the carotid sinus nerve (SN), the aortic nerve and hypothalamic defence area (HDA). In forty‐four neurones activated by SN stimulation HDA activation evoked an IPSP in fourteen (32%) and an EPSP in eight (11%). Those neurones receiving an HDA‐evoked IPSP, and tested for reflex inputs, responded only to baroreceptor activation. Neurones receiving HDA‐evoked EPSPs responded only to chemoreceptor activation. In three neurones unaffected by SN stimulation, short latency inputs from HDA were observed, suggesting direct monosynaptic inputs.
Transport of tricarballylate by intestinal brush‐border membrane vesicles from steers
Authors: Wolffram S , Zimmermann W , Scharrer E
Published: December 2014

Tricarballylic acid is a non‐metabolizable rumen bacterial fermentation product of the naturally occurring tricarboxylic acid trans‐aconitic acid. The aim of the present study was to investigate intestinal absorption of tricarballylate using brush‐border membrane vesicles (BBMVs) isolated from the proximal jejunum of steers by a Ca2+ precipitation method with subsequent differential centrifugation. Transport of tricarballylate was investigated indirectly (influence of tricarballylate on the uptake of 14C‐labelled citrate) as well as directly (uptake of 3H‐labelled tricarballylate). Citrate as well as tricarballylate uptake (at a concentration of 0.05 mmol l‐1) was strongly stimulated by an inwardly directed initial Na+ gradient. Furthermore, transport of both tricarboxylates under Na+ gradient conditions was clearly enhanced by lowering the extravesicular pH from 7.8 to 5.6. The imposition of an inwardly directed H+ gradient (pH(out)/pH(in) = 5.6/7.8) further enhanced the intravesicular accumulation of citrate as well as of tricarballylate compared with pH(out)/pH(in) = 5.6/5.6. Unequivocal evidence for a common transport site for tricarballylate and citrate was obtained from ‘cis‐inhibition’ and ‘trans‐stimulation’ of Na(+)‐dependent citrate uptake by tricarballylate. In further experiments the influence of different substances on the uptake of 3H‐labelled tricarballylate was evaluated. Unlabelled tricarballylate, citrate, succinate as well as trans‐ and cis‐aconitate significantly inhibited the accumulation of 3H‐labelled tricarballylate by BBMVs. Tricarballylate uptake as a function of the tricarballylate concentration revealed a Na(+)‐dependent saturable component (apparent kinetic parameters: maximal transport capacity (Vmax) = 119 pmol (mg protein)‐1 (3s)−1; affinity constant (Km) = 0.097 mmol l‐1) and a Na(+)‐independent diffusional component (diffusion constant: 169 nl (mg protein)‐1 (3s)−1). It is concluded that tricarballylate and citrate are transported across the intestinal brush‐border membrane by a common, Na(+)‐dependent transport mechanism. The stimulatory influence of a low extravesicular pH most probably indicates that the protonated forms of tricarboxylates are better transported than the trivalent species.
Neural modulation of bovine mesenteric lymph node contraction
Authors: Hughes GA , Allen JM
Published: December 2014

Spontaneous isometric contractions and field‐evoked responses were recorded in vitro from strips of bovine mesenteric lymph node capsule. Field stimulation (0.3 ms pulses, 60 V nominal, 2 min trains) at frequencies > or = 2 Hz evoked a frequency‐dependent increase in baseline tension which was maximum at frequencies > or = 16 Hz. Evoked contractions were significantly reduced (P = 0.02) by the neurotoxin tetrodotoxin (10(−6) M) although they were unaffected by the alpha‐adrenoceptor antagonists phentolamine, rauwolscine and prazosin (3 x 10(−6) M). Similarly, responses were unaffected by the beta‐adrenoceptor antagonist propranolol (10(−6) M), the cholinergic antagonist atropine (10(−6) M) or the uptake blocker cocaine (10(−6) M). Field‐evoked contraction was also unaffected by a 30 min exposure to alpha,beta‐methylene ATP (10(−6) M). The results suggest that bovine lymph node capsular smooth muscle is innervated by excitatory nerves which are non‐adrenergic, non‐cholinergic and non‐purinergic in nature.
Insulin and intestinal epithelial cell proliferation
Authors: Goodlad RA , Lee CY , Gilbey SG , Ghatei MA , Bloom SR
Published: December 2014

The effects of modification of the levels of endogenous plasma insulin on intestinal epithelial cell proliferation were investigated in rats maintained by total parenteral nutrition (TPN) using either a TPN diet that was high in glucose, or a low glucose (hypocaloric) TPN diet and in orally fed rats (normal and sham operated). The rats were put on their respective treatments for 7 days and were then injected with vincristine sulphate to arrest cells as they entered metaphase. Intestinal tissue was fixed for the determination of crypt cell production rate (CCPR) and blood plasma was taken for hormone radioimmunoassay. Sham operation had no effect on either plasma hormone levels or on CCPR. The standard TPN diet was associated with significantly reduced levels of gastrin, peptide YY and enteroglucagon. Gastrin and PYY were further reduced by the hypocaloric diet. However, plasma insulin was much increased in the TPN but not in the hypocaloric group. Small intestinal CCPR was reduced in the TPN groups, but no difference was observed between the standard and the low calorie TPN diets. The lack of difference in CCPR between the two TPN diets despite the massive elevation of plasma insulin strongly suggests that insulin does not have a substantial role in the control of gastrointestinal epithelial cell renewal.
Sound stimulation increases the cerebral glucose:oxygen quotient in the fetal sheep
Authors: Chao CR , Glenford PG , Karibo EJ , Salha SD
Published: December 2014

We sought to determine the cerebral metabolic fate of glucose during sound stimulation in near‐term fetal sheep. Blood oxygen content was significantly decreased by 6‐7% during sound stimulation. The cerebral glucose:oxygen quotient increased from 0.88 +/− 0.08 to 1.13 +/− 0.12 (mean +/− S.E.M., P < 0.01). This is consistent with the phenomenon of stimulated glycolysis which has been shown to increase brain lactate concentration in other models.
Degree of breast emptying explains changes in the fat content, but not fatty acid composition, of human milk
Authors: Daly SE , Di Rosso A , Owens RA , Hartmann PE
Published: December 2014

We compared within and between breastfeed changes in milk fat to short‐term rates of milk synthesis and degree of breast emptying (measured using the Computerized Breast Measurement system) over two 24 h periods for five lactating mothers. The fat content (f) of fore and hind milk samples increased more steeply as the breast was progressively emptied by the infant (degree of emptying, d, range 0‐1; f = 21.59 + 9.38d + 70.99d2; P < 0.0001; r2 = 0.68; n = 154). For the nine individual breasts, between 41‐95% of the variance of the fat content of milk was explained by degree of breast emptying. We argue that this relationship explains differences in the circadian rhythm of the fat content of milk and allows the accurate calculation of the average fat content of milk consumed by infants (37‐66 g/l for the nine individual breasts). The fatty acid composition of the fore and hind milk samples was determined for four of the mothers. We observed within and between breastfeed variability in the relative proportions of the seven major fatty acids of milk fat and these changes are discussed with reference to the control of fat synthesis in the human mammary gland.
Evidence for an age‐dependent decrease in the immunoreactive prolactin‐containing terminals of the median eminence of male rats
Authors: Siaud P , Barbanel G , Givalois L , Reymond MJ , Balmefrezol M , Assenmacher I
Published: December 2014

Labelling patterns of immunoreactive prolactin (IR‐PRL)‐containing and tyrosine hydroxylase (TH)‐containing nerve terminals of the median eminence (ME) were compared in young adult (aged 3 months) and old (aged 24 months) male Wistar rats. In the young rats, IR‐PRL‐ and TH‐immunostained fibres extended throughout the external most layer of the ME. In the old rats, a significant decrease in the intensity of labelling of IR‐PRL terminals was observed in this layer, with a slight reduction in the extent of labelling. As far as TH terminals were concerned, no difference could be detected between young and old animals.
Hyaluronan reduces fluid escape rate from rabbit knee joints disparately from its effect on fluidity
Authors: McDonald JN , Levick
Published: December 2014

The effect of hyaluronan, the major viscous component of synovial fluid, on trans‐synovial flow was measured in rabbit knees. Hyaluronan reduced fluid escape rate by up to 45%. This was much less than the reduction in intra‐articular fluidity (1/viscosity). Electron micrographs supported the view that hyaluronan might be partially reflected by synovium, creating a molecular filtercake at the surface.
Reduction in the contraction and intracellular calcium transient of single rat ventricular myocytes by gadolinium and the attenuation of these effects by extracellular NaH2PO4
Authors: Ward H , White E
Published: December 2014

Gadolinium (Gd3+) is the most commonly used blocker of stretch‐activated channels (SACs). The actions of Gd3+ in unstretched adult heart were investigated by observing its effects on the contraction and intracellular calcium transient of single rat ventricular myocytes. We found that Gd3+ caused a profound reduction in both these parameters at doses typically used to block SACs. However, the actions of Gd3+ were severely attenuated by the presence of 0.33 mM NaH2PO4, which possibly chelates the Gd3+ ion.
Role of prostaglandins in regulation of blood flow and modulation of sympathetic vasoconstriction in normal and acutely inflamed rabbit knee joints
Authors: Najafipour H , Ferrell WR
Published: December 2014

Experiments were performed to investigate, in the normal and acutely inflamed rabbit knee joint, the role of prostaglandins in the regulation of joint blood flow, measured by laser Doppler flowmetry, as well as their modulation of sympathetic vasoconstriction. Close intra‐arterial injection of prostaglandin E2 (PGE2) produced a dose‐dependent vasodilatation in control joints, but the responses in inflamed joints were much smaller. Close intra‐arterial infusion of indomethacin significantly increased the responses of the control joints to PGE2, but had no effect on the responsiveness of the inflamed joints. Nerve‐mediated vasoconstrictor responses did not change significantly with close intra‐arterial infusion of indomethacin, either in control or in inflamed joints. Indomethacin infusions decreased basal joint blood flow in the control joint significantly more than in the inflamed joint. The systemic blood pressure was elevated slightly only in the control group. The results of this study show that although prostaglandins have a role to play in regulation of basal blood flow in both normal and acutely inflamed rabbit knee joints, they do not appear to play a significant role in modulation of sympathetic vasoconstrictor responses. Prostaglandin E2 receptors are functional in normal knee joint blood vessels, but they may be disabled by the process of inflammation.
The effect of chronic sodium depletion on renal function in conscious rats
Authors: Shirley DG , Skinner J
Published: December 2014

In order to investigate the effect of chronic sodium depletion on renal proximal tubular reabsorption, studies were performed in conscious, unrestrained Brattleboro rats. Since these animals lack circulating vasopressin, fractional water reabsorption in the distal nephron can be assumed to be constant and changes in urine flow rate should therefore reflect changes in end‐proximal fluid delivery. Sodium depletion was induced by placing rats on a low‐sodium diet (4 mmol Na (kg dry wt)‐1) and administering frusemide (40 mg (kg body wt)‐1) by gavage on the first 2 days. Extracellular volume, measured after 7‐9 days, was reduced by 19% (P < 0.02) as compared with that of rats maintained on a control diet. Urine flow rate, measured during days 4‐7 of the low‐sodium diet, was significantly lower than that of control rats (142 +/− 8 vs. 168 +/− 5 ml day‐1, P < 0.01). Since renal papillary interstitial fluid osmolality was found to be reduced in the sodium‐depleted rats (693 +/− 38 vs. 812 +/− 36 mosmol (kg H2O)‐1, P < 0.05), it is unlikely that water reabsorption from sites beyond the proximal tubule had increased. The observed reduction in urine flow rate therefore strongly suggests a reduction in end‐proximal fluid delivery. In the second part of the study, a single group of Brattleboro rats was used, in which osmotic minipumps were implanted in the peritoneal cavity for continuous infusion of [14C]inulin. After recovery from the operation, the rats were maintained on a control diet for 6 days (pre‐control period), then subjected to sodium depletion (low‐sodium diet for 6 days, frusemide administration on the first 2 days), and finally returned to the control diet for 6 days, with access to 0.46 M NaCl solution on the first 2 days, in order to restore sodium balance (post‐control period). On the final 2 days of each phase, urine flow rate and [14C]inulin clearance (= glomerular filtration rate, GFR) were measured. Urine flow rates during the pre‐control, sodium depletion and post‐control periods were 169 +/− 7, 132 +/− 8 (P < 0.001) and 176 +/− 8 microliters min‐1, respectively; corresponding values for fractional water excretion were 7.0 +/− 0.3, 6.0 +/− 0.5 (P < 0.01) and 7.4 +/− 0.4%. Only a small reduction GFR, of borderline statistical significance, was observed during sodium depletion.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of low phosphate intake on bone and mineral metabolism and microbial protein synthesis in lambs
Authors: Scott D , Robins SP , Nicol P , Chen XB , Buchan W
Published: December 2014

Growing lambs were fed diets either low or adequate in phosphorus and their effects on Ca and P retention, bone formation and resorption and on ruminal microbial protein synthesis were measured. Plasma osteocalcin was used as an indicator of bone formation rate. Levels in plasma were lower in lambs fed the low P diet and were associated with a fall in plasma P concentration and reduced Ca and P retention. Low P intake had no effect on microbial protein synthesis or on bone resorption determined using urinary pyridinoline and deoxypyridinoline as markers. These results suggest that lack of mineral, rather than reduced ruminal microbial protein synthesis, is the main factor contributing to the reduction in bone formation rate seen in lambs fed low P diets.
The role of cyclic AMP in the control of sugar transport across the brush‐border and basolateral membranes of rat jejunal enterocytes
Authors: Sharp PA , Debnam ES
Published: December 2014

Although the involvement of the adenylate cyclase system with glucose transport in the small intestine is poorly understood, there is increasing evidence that cyclic AMP stimulates sugar uptake. In order to study further the effects of cyclic AMP on this process, we have measured glucose accumulation by brush‐border and basolateral membrane vesicles prepared from villus enterocytes following exposure of these cells to cyclic AMP and theophylline. Brush‐border vesicles derived from enterocytes incubated with cyclic AMP and theophylline accumulated significantly more glucose over a wide range of sugar concentrations, suggesting a change in maximum velocity of the transport system. Glucose uptake by basolateral vesicles was increased at low, but not at high sugar concentrations. Incubation of isolated enterocytes with pancreatic glucagon at concentrations known to stimulate sugar transport by these cells significantly increased enterocyte levels of cyclic AMP. Treatment with glucagon or cyclic AMP resulted in significant hyperpolarization of the potential difference across the brush‐border membrane, an important driving force for Na(+)‐sugar cotransport. The response to glucagon and cyclic AMP appears to be caused by a decrease in Na+ permeability of the mucosal membrane. Taken together, these results suggest that cyclic AMP is a mediator of the actions of glucagon on enterocytes and provide further evidence for a role of cyclic AMP in the modulation of sugar transport across the intestinal enterocyte.
Calcium store depletion in dimethyl BAPTA‐loaded human platelets increases protein tyrosine phosphorylation in the absence of a rise in cytosolic calcium
Authors: Sargeant P , Farndale RW , Sage SO
Published: December 2014

The endomembrane Ca(2+)‐ATPase inhibitor, thapsigargin, was used to deplete the intracellular Ca2+ stores of fura‐2‐loaded human platelets. In control cells, thapsigargin evoked a rise in cytosolic [Ca2+] and a substantial increase in protein tyrosine phosphorylation. Thapsigargin also evoked an increase in tyrosine phosphorylation in cells co‐loaded with fura‐2 and the Ca2+ chelator dimethyl BAPTA, such that the rise in cytosolic [Ca2+] was abolished. These data support the existence of a tyrosine phosphatase regulated by the Ca2+ content of the intracellular store, a requirement of the putative model for reciprocal control of Ca2+ entry by cytosolic and store [Ca2+] via protein tyrosine phosphorylation.
Local versus peripheral blood administration of cholecystokinin‐8 and secretin on pancreatic secretion in calves
Authors: Zabielski R , Onaga T , Mineo H , Pierzynowski SG , Kato S
Published: December 2014

The effects of local and peripheral administration of cholecystokinin‐8 (CCK‐8) and secretin on the interdigestive pancreatic secretion were examined in conscious preruminating calves. Six calves were surgically fitted with a pancreatic catheter and duodenal cannula, duodenal electrodes and strain gauges, and cooling devices on the cervical vagi. Local intra‐arterial (I.A.) infusions were made into the duodenal branch of the right gastroepiploic artery, and peripheral infusions (I.V.) into the external jugular vein. CCK‐8 and secretin were infused I.A. and I.V. for 5 min (0, 10, 30 and 100 pmol (kg body weight)‐1) during the asecretory phase of the pancreatic interdigestive cycle. CCK‐8 and secretin at 100 pmol kg‐1 were administered concomitant with reversible cold vagal blockade. Local infusion of CCK‐8 without vagal blockade resulted in a significantly faster and stronger pancreatic response than the respective peripheral infusion, although CCK in peripheral blood plasma was paradoxically only minimally increased after I.A. CCK‐8 in comparison with a marked increase after I.V. CCK‐8. Vagal blockade noticeably decreased the pancreatic response for I.A. CCK‐8, but not for I.V. CCK‐8. Secretin produced similar pancreatic responses after I.V. and I.A. administration, but the plasma secretin concentration in peripheral blood was markedly lower after I.A. than after I.V. infusions. Cold vagal blockade uniformly reduced the stimulatory effect of I.A. and I.V. secretin infusion on the exocrine pancreas. In calves, CCK‐8 apparently stimulates the exocrine pancreas by two different mechanisms: by a direct effect that is vagally independent as well as by an indirect effect in the duodenum that is vagally dependent. The indirect effect of secretin in the duodenum is less clear, but both direct and indirect effects of secretin depend on vagal integrity.
The use of sinusoidal and ramp stretch stimuli in characterizing fusimotor effects on cat muscle spindles
Authors: Rodgers JF , Durbaba R , Taylor A , Fowle AJ
Published: December 2014

Comparisons were made between the results of testing muscle spindle primary afferents with low‐frequency, large‐amplitude sine waves of muscle stretch and with repeating ramp‐and‐hold stretches. Three different situations were explored, namely, activation with succinylcholine (SCh), generation of various fusimotor outflow patterns by brainstem stimulation and fusimotor activation by stimulation of single ventral root gamma‐axons. With ramp‐and‐hold stretches the effects of bag1 fibre contraction were thought to be generally better represented by increases in the dynamic response to stretch (delta DD) than by increases in dynamic index. The equivalent effect on the sine wave response was an increase in the magnitude of the fitted sine (delta Mag). Static effects were best measured by increases in the initial frequency for ramps (delta IF) and by increases in the fitted centre frequency (delta CF) for sines. There was good agreement between sine and ramp testing in the case of SCh effects, but much less consistency during brainstem stimulation. Sine wave testing can be regarded as less efficient than ramp testing in distinguishing between static and dynamic actions because dynamic fusimotor stimulation causes equal rises in CF and Mag, but fourfold larger rises in DD than in IF. Ramp responses with combined dynamic and static fusimotor stimulation showed increases of both IF and DD as expected, but whilst sine wave responses always showed increase in CF, they often showed no increase in Mag. Comparisons of the effects of SCh, central stimulation and fusimotor stimulation showed that it is important to recognize the different effects of chain and bag2 intrafusal fibre activation as components of static fusimotor excitation. Stimulation of driving static axons (chain activation) raised the IF and CF often with 1:1 or 1:2 driving during the shortened phase of ramps and sines. However, the stretch response in both cases was either unchanged or reduced. Stimulation of a non‐driving static fusimotor axon (bag2 activation) caused a marked rise in CF for sine waves and a fall in Mag, but a modest increase in ramp stretch sensitivity (DD) with no increase in dynamic index. A way is described for measuring flattening of sine wave responses as a possible way of detecting chain fibre activation. The consequences of these findings are discussed in relation to previous reports of the use of sine wave testing for assessing fusimotor mechanisms.
Evidence for preservation of epithelial function in cryopreserved porcine and human bronchi
Authors: Vacciana A , Ebeigbe AB , Hasse J , Swoboda L , Muller-Schweinitzer E
Published: December 2014

Porcine and human bronchi have been investigated in vitro without or after storage at ‐196 degrees C in Krebs‐Henseleit solution containing 2.0 M dimethyl sulphoxide and 0.1 M sucrose as cryoprotectants. In bronchi from both species maximal post‐thaw contractile responses to acetylcholine (ACh) were reduced by about 25‐30% compared to unfrozen bronchi. To assess the viability of bronchi and endothelium‐denuded rat aortic strips, was employed. The release of an epithelium‐derived inhibitory factor (EpDIF) was induced by ACh and assessed in terms of concentration‐dependent relaxation of the endothelium‐denuded rat aortae. Following removal of bronchial epithelium, ACh failed to elicit any relaxation of rat aorta. With cryopreserved bronchi from both pig and human about 5 and 30 times higher concentrations of ACh, respectively, were required to elicit the same relaxant response as with unfrozen bronchi. The results suggest that after the freezing‐thawing process both smooth muscle and epithelial function is largely preserved and provide support for the use of cryopreservation for storage of airway preparations for pharmacological studies.