bluuebunny/crossref_metadata_2025 huggingface dataset:
The struggle to maintain hydration and osmoregulation in animals experiencing severe dehydration and rapid rehydration: the story of ruminants
Authors: Silanikove N
Published: December 2014

Ruminants in tropical and desert areas routinely experience cycles of severe dehydration and rapid rehydration. These animals can withstand severe dehydration (18‐40% of initial body weight), which exceeds considerably the capacity of most monogastric mammals. This capacity is related to their ability to use, during the course of dehydration, their large water reservoir in the rumen, which contributes 50‐70% of the total water loss. As rumen fluid is in approximate isotonicity with systemic fluid, the utilization of gut water during the course of dehydration involves a considerable load of sodium and potassium. Consequently, the effectiveness of utilization of rumen fluid during dehydration depends on the capacity of the kidney to ‘desalt’ the water absorbed from the gut and on maintenance of salivary flow to the rumen. Following rehydration, ruminants can imbibe their entire water deficit in one drinking and the entire amount ingested is first retained in the rumen. The rumen volume at this stage may exceed the extracellular fluid volume and the sudden drop in rumen osmolality creates a huge osmotic gradient (200‐300 mosmol kg‐1) between the rumen and systemic fluid. Ruminant animals are confronted at this stage by two opposing tasks, each of them of vital importance: (i) the need to prevent the osmotic hazard leading to water intoxication; and (ii) the need to retain the ingested water, so that it is not missing for the next dehydration cycle. The most prevalent view until recently was a theory which attributes an osmotic protective mechanism to the rumen wall. However, such a capacity has not yet been demonstrated and is challenged by contradictory observations that large amounts of water are absorbed from the rumen following rehydration. The view that is most consistent with available information is that gustatory‐alimentary and hepatoportal signals regarding the presence of large amounts of water in the rumen and the absorption of water from the gut activate a range of homeostatic responses involved in fluid and sodium restitution. The efferent elements, presumably activated by the CNS, include: a dramatic increase in secretion of hypotonic saliva and, reciprocally, a dramatic drop in urine flow. The enhanced saliva secretion recycles a considerable portion of the water absorbed from the gut back to the rumen, which allows effective retention of water while avoiding the danger of osmotic threat to the red blood cells. The enhanced saliva secretion also drains large amounts of sodium and bicarbonate from the blood. Accompanying responses are marked retention of sodium and carbonic acid in the kidney.(ABSTRACT TRUNCATED AT 400 WORDS)
Post‐crucial period effects of visual experience and deprivation on the guinea‐pig superior collicular map of auditory space
Authors: Withington DJ , Binns KE , Keating MJ , Thornton SK , Ingham NJ
Published: December 2014

There were two primary aims of this study. First, to observe if the map of auditory space in the superior colliculus (SC) of the guinea‐pig could recover after periods of normal visual experience following visual deprivation during the crucial period. Second, to determine whether any degradation of the space map was observed when the animal was visually deprived for different lengths of time after the crucial period. Animals deprived of visual experience during the crucial period and then allowed normal experience did show a limited ability to construct a SC auditory space map. Whereas visual deprivation following normal auditory and visual experience during the crucial period caused a profound degradation, of both spatial tuning and topography, of auditory receptive fields in the SC. Additional data indicate that the SC auditory space map remains vulnerable to visual deprivation until at least 100 days after birth.
Plasticity in the superior collicular auditory space map of adult guinea‐pigs
Authors: Withington DJ , Binns KE , Ingham NJ , Thornton SK
Published: December 2014

In the guinea‐pig the development and maintenance of the superior collicular (SC) auditory space map requires both auditory and visual experience. This paper reports the results of experiments in which adult animals (of different ages) were dark‐reared for 4 weeks to define the extent of the period of susceptibility to visual deprivation of the SC auditory map. Dark‐rearing for 4 weeks from 100, 150 or 200 days after birth caused degradation of spatial tuning and topography of multi‐unit auditory responses in the SC. In contrast, animals reared in the dark from 250 days after birth showed spatially tuned auditory responses similar to those seen in normal animals. These data suggest that the SC auditory space map in the adult guinea‐pig remains susceptible to visual deprivation up to 200 days after birth.
Blockade of intrafusal neuromuscular junctions of cat muscle spindles with gallamine
Authors: Yamamoto T , Morgan DL , Gregory JE , Proske U
Published: December 2014

This is a report on the resistance to block of the motor terminals on intrafusal fibres of cat soleus muscle spindles using the drug gallamine triethiodide (Flaxedil). To minimize diffusion barriers and to permit accurate measurements of time courses, rather slow rates of gallamine infusion were used (0.15 mg min‐1). The main finding made was that after gallamine infusion, when extrafusal tension had dropped to half, all dynamic fusimotor effects and eight of twenty static effects had fallen to 40% or less of their control value. The remaining static effects persisted at 60‐80% of their control value. Where fusimotor fibres were stimulated together with one or two skeletomotor fibres, the influence of the skeletomotor axons was significant only after spindle biasing had fallen to low levels. When gallamine infusion was stopped extrafusal tension returned to control levels within 20‐75 min, depending on the length of the block, while fusimotor responses did not fully recover within the recording period of up to 150 min. The combination for some fusimotor responses of an early fall and a late recovery when compared with extrafusal tension, suggested a greater sensitivity of these endings to the drug. A comparison of spindle responses to the drug succinyl choline (SCh) and to fusimotor stimulation in the presence of gallamine showed that SCh responses were rapidly reduced by gallamine and had a long recovery time course, as were some fusimotor responses. From this it is argued that fusimotor effects with a high sensitivity to gallamine blockade were associated with nuclear bag fibre contractions and the more resistant effects with nuclear chain fibre contraction. It is generally believed that intrafusal neuromuscular junctions are more resistant to neuromuscular blockers than extrafusal junctions. The present experiments provide evidence to the contrary for some intrafusal junctions. Since muscle relaxants are often used in general anaesthesia it is interesting to speculate about the recovery of function of proprioceptive reflexes and of kinaesthesia during the immediate post‐anaesthetic period, in view of the large difference in recovery time for transmission at intrafusal and extrafusal junctions.
Dimensional analysis of osteoclastic bone resorption and the measurement of biologically active calcitonin
Authors: Zaidi M , Bax BE , Shankar VS , Moonga BS , Simon B , Alam AS , Gaines Das RE , Pazianas M , Huang CL
Published: December 2014

Calcitonin inhibits bone resorption through a direct action on the osteoclast. We report a quantitative analysis of bone resorption by disaggregated rat osteoclasts. We then used our findings to develop a formal bioassay for calcitonin. Osteoclasts were mechanically disaggregated from neonatal rat long bones and dispersed at low densities on slices of devitalized bovine cortical bone. The resulting areas of bone excavation were quantified to micrometric precision by scanning electron microscopy together with computer‐assisted image analysis. These findings were correlated with the volumes of bone resorption in the same slices measured by confocal scanning microscopy for the first time. The total planar areas of bone resorption per slice correlated linearly (r = 0.78) with the confocal microscopic measurements of total volume resorbed, provided that volume was expressed to its two‐thirds power. The latter transformation resulted in representations of the determined areas ([length]2) and volumes ([length]3) which were dimensionally consistent. These findings thus demonstrate that osteoclastic bone excavations show a consistent relationship between area and volume and that assessments of the area of excavations accordingly provide an empirical representation of the volume of bone resorbed. Furthermore, in view of the skewed nature of the distributions of area measurements, we assessed the effect of transforming the response variable to derive a metameter, (planar area of resorption)1/2. Such transformed data points, which expressed the data in the dimensions of [length], were more normally distributed than the raw data points and had more stable variances over a wider concentration range. We accordingly determined relative potencies using parallel line analyses on the transformed data. The latter offered a consistent correlation to the volume measurements when these were also converted to dimensions of [length] (r = 0.805). It was confirmed that the inhibition of bone resorption by calcitonins from various species, namely, pig, salmon and eel, was quantitatively dependent upon concentration of the respective peptides. The resulting assay was also found to be sufficiently sensitive to measure picomolar peptide concentrations with a precision, lambda (standard deviation/slope), ranging between 0.3 and 0.8. Finally, we identified factors affecting assay precision and sensitivity.
The regulation of membrane 125I‐ and 86Rb+ permeability in a virally transformed cell line (NCL‐SG3) derived from the human sweat gland epithelium
Authors: Wilson SM , Whiteford ML , Bovell DL , Pediani JD , Ko WH , Smith GL , Lee CM , Elder HY
Published: December 2014

We have explored the factors that may regulate membrane permeability in a cell line (NCL‐SG3) derived from the human sweat gland epithelium. Ionomycin increased the rate of 125I‐efflux from preloaded cells and this action appeared to be due to an increase in intracellular free calcium ([Ca2+]i). The ionomycin‐evoked increase in 125I‐ efflux was reduced in cells that were exposed either to barium or to valinomycin in the presence of a high concentration of external potassium. It thus appears that a fraction of the ionomycin‐evoked increase in 125I‐ efflux is due to the activation of potassium channels and experiments using 86Rb+ also suggested that ionomycin increased the rate of potassium efflux, an effect which was totally abolished by barium. Blockade of Na(+)‐K(+)‐2Cl‐ cotransport and of Cl‐ ‐HCO3‐ exchange reduced the basal rate of 125I‐ efflux and the ionomycin‐evoked increase in 125I‐efflux from control cells and from cells depolarized by valinomycin. These transport systems thus contribute to anion efflux, although [Ca2+]i‐dependent chloride channels also appear to be present. Acetylcholine increases [Ca2+]i in the secretory cells of human sweat glands, but this neurotransmitter did not increase [Ca2+]i in NCL‐SG3 cells and so membrane permeability was not under cholinergic control. Adrenaline did not increase [Ca2+]i, but this hormone did evoke cyclic‐3',5'‐adenosine monophosphate (cyclic AMP) production. However, membrane permeability was not under adrenergic control, as the cells did not appear to express functional, cyclic AMP‐dependent anion channels. This may be because they were not fully differentiated under the culture conditions. ATP consistently evoked a dose‐dependent increase in anion efflux that appeared to be mediated by [Ca2+]i. The increase in [Ca2+]i was initiated by the release of calcium from a limited internal store and was subsequently sustained by calcium influx. UTP and ADP also increased [Ca2+]i, whereas adenosine, AMP and alpha,beta‐methylene ATP were without effect. These data thus suggest that a subclass of type 2 purine receptor, which is functionally coupled to phosphoinositidase C, is present in these cells.
The effect of immobilization on the recovery of rabbit soleus muscle from tenotomy: modulation by chronic electrical stimulation
Authors: Barry JA , Cotter MA , Cameron NE , Pattullo MC
Published: December 2014

The effect of unilateral Achilles' tendon section on the soleus muscle of rabbits was examined after 2 and 4 weeks of unsutured recovery. Immobilization of the limb during recovery was also investigated. Following tendon section the limb was immobilized with an ankle angle of 90 deg, and final experiments were performed either after 2 weeks, or after the splints were removed and a further 2 weeks recovery allowed. Remobilized recovery was either allowed to occur naturally or with chronic low‐frequency electrical stimulation of the soleus nerve. Achilles' tendon section resulted in very little change in the morphological profile of the soleus, but a marked decrease in tension production. Two weeks following tenotomy, tetanic tension was reduced to 50% of normal; this reduction persisted for the following 2 weeks of recovery. Imposition of immobilization after tendon section produced gross degeneration of the soleus. The fibres that remained had a mean fibre area of 20% of control values and displayed an immature staining pattern. This was accompanied by a reduction in tension production to less than 5% of normal and a marked speeding of contraction. Two weeks of passive recovery following splint removal slowed contraction and improved both the morphological profile and tension production of the soleus. Application of stimulation during this time restored contraction times to normal, reflecting the return to normal fibre‐type proportions of this group, and improved the morphological profile and tension production beyond that of the unstimulated group. Thus immobilization worsened considerably the alterations occurring in the morphological and physiological properties of the soleus following Achilles' tendon section. Upon remobilization, chronic stimulation accelerated recovery of both parameters.
Fluid hypersecretion induced by enterotoxin STa in nutritionally deprived rats: jejunal and ileal dynamics in vivo
Authors: Nzegwu HC , Levin RJ
Published: December 2014

The effect of luminal enterotoxin Escherichia coliSTa on fluid transport across the jejunum and ileum of fed, starved (72 h) and chronically undernourished (50% control food intake for 21 days) rats was assessed in vivo using a gravimetric technique. Dose‐response curves for net fluid secretion (stimulated‐basal (30 min)‐1) activated by 5,50 and 500 ng ml‐1 STa were obtained for jejuna and ilea from fed, starved and chronically undernourished rats. Compared to the fed rats, both dietary deprivations showed enhanced net fluid secretion at 500 ng ml‐1, but only the jejunum from chronically undernourished rats showed significantly enhanced secretion at 5 and 50 ng ml‐1. Net fluid secretory responses to a standard dose of STa (500 ng ml‐1) were monitored in the jejuna and ilea of fed, starved and chronically undernourished rats at 30, 60, 90 and 120 min. The pattern in jejuna and ilea from fed rats was very different; the jejunal secretion over 30 min was transient, but ileal secretion increased continuously to a maximum at 120 min. In both jejunum and ileum from starved rats, the secretory response to STa at 30 min was significantly greater than that in fed rats and subsequently remained near this level. In the jejunum from chronically undernourished rats, the net fluid secreted in response to STa was greatly enhanced at 30 and 60 min, but not at 90 min. The ileal response was significantly greater than that in the fed rats at 30 and 120 min. Luminal procaine (10 mM) selectively increased fluid absorptive tone in the jejunum from fed rats, reduced STa‐induced fluid secretion in the ileum from undernourished rats, but had no effect on STa in the jejunum from undernourished rats or in the jejunum or ileum from starved rats. Luminal 8‐bromo‐cyclic GMP (1 mM) had no effect on basal absorptive tone in the jejunum of fed or chronically undernourished rats, but enhanced the secretory tone of jejunum from starved rats. In the ileum, however, while 8‐bromo‐cyclic GMP enhanced secretory tone in the fed and starved conditions, it still had no action in the chronically undernourished state. The enhanced fluid secretion observed in the jejunum and ileum of the starved and undernourished rats compared to the fed rats supports previous in vitro findings of an increased electrogenic secretion induced by STa in these dietary deprivations. The fluid hypersecretion could be a cause of the increased severity of diarrhoea often observed in undernourished and starved humans.
The effect of high concentrations of inspired oxygen on middle cerebral artery blood velocity measured by transcranial Doppler
Authors: Bew SA , Field LM , Droste DW , Razis P
Published: December 2014

The effects of high concentrations of inspired oxygen on cerebrovascular haemodynamics were studied in healthy human volunteers using transcranial Doppler measurements of middle cerebral artery blood velocity. If the end‐tidal carbon dioxide level was kept constant, the measured blood velocity and the calculated Pulsatility Index showed no significant change when subjects were breathing 21, 40, 75 or 100% oxygen.
Hypoxia activates a potassium current in isolated smooth muscle cells from large pulmonary arteries of the rabbit
Authors: Bonnet P , Vandier C , Cheliakine C , Garnier D
Published: December 2014

Severe hypoxia (< 10 mmHg) induced relaxation of precontracted rings obtained from large diameter (3–4 mm) pulmonary arteries of the rabbit but had no effect upon their basal tone nor upon the length of enzymatically isolated smooth muscle cells. In isolated smooth muscle cells severe hypoxia increased a voltage‐gated K+ current. The magnitude of this response depended upon the degree of intracellular Ca2+ buffering, being abolished by 10 mM EGTA. The hypoxic response of K+ currents demonstrates a direct effect of hypoxia on pulmonary artery smooth muscle cells via a modulation of potassium channel activity.
Laminin mediates the restitution of rat gastric mucosa in vitro
Authors: Miller MA , Bunnett NW , Debas HT
Published: December 2014

Restitution, the rapid re‐establishment of mucosal integrity following damage, involves cell migration and can be monitored by measuring transmucosal potential difference of tissue mounted in an Ussing chamber. The involvement of extracellular matrix proteins and matrix receptors was examined in the restitution of rat gastric mucosa. Undamaged mucosa maintained a potential difference of ‐32.7 +/− 2.2 mV for several hours. Mucosal exposure to 0.6 M NaCl for 1 min reduced this to −3.3 +/− 1.4 mV in 2‐3 min. Thereafter, the potential difference returned in 60 min to plateau at ‐28.9 +/− 1.3 mV (88.5 +/− 3.6% of pre‐exposure). Tissues mucosally treated with 1:100 anti‐laminin antiserum maximally recovered following damage to 65.6 +/− 6.6% of pre‐exposure potential difference (PD), while those treated with 1:100 anti‐collagen IV or anti‐fibronectin antisera recovered to 88.8 +/− 9.7% and 86.3 +/− 3.2%, respectively. Only the anti‐laminin result was significantly different from controls. The anti‐laminin effect was abolished by pre‐incubation of the anti‐laminin antiserum with purified rat laminin, suggesting that the effect was laminin specific. In experiments involving matrix protein receptors, tissues treated with alpha‐lactalbumin, a protein altering the substrate specificity of cell surface laminin receptor/enzyme beta‐1,4‐galactosyltransferase, maximally recovered following damage to only 49.3 +/− 7.7% of pre‐exposure PD, which was significantly different from controls, while those treated with anti‐beta 1 integrin recovered to 85.0 +/− 9.7%. Our data suggest that laminin is involved in mediation of gastric mucosal restitution, possibly via beta‐1,4‐galactosyltransferase.
The effect of frusemide on oxytocin‐induced contractions of the rat myometrium
Authors: Mozhayeva MG , Bagrov YaYu , Ostretsova IB , Gillespie JI
Published: December 2014

Oxytocin‐induced contractions of isolated strips of oestradiol‐treated rat myometrium were found to be affected by exposure to the diuretic frusemide. At a concentration of 20 microM. frusemide transiently increased the force of contraction over a period of approximately 10 min. After this time there was a progressive fall in contractile force. At a higher concentration of 200 microM, only the progressive fall in force was seen until contractions were completely abolished. Frusemide has been reported to increase the activity of cAMP‐phosphodiesterase in tissue extracts from oestradiol‐treated rat myometrium. Therefore, the changes in contraction due to exposure to frusemide may be a reflection of the changes in intracellular cAMP resulting from a stimulation of cAMP‐phosphodiesterase activity. In support of this idea, addition of dibutyryl cAMP was found to partially restore contractions after frusemide treatment. These data suggest that frusemide may be a useful tool in the manipulation of tissue cAMP levels in order to determine the different roles of cAMP in the oestradiol‐treated rat myometrium.
The intracortical neuronal connectivity subserving focal epileptiform activity in rat neocortex
Authors: Holmes O
Published: December 2014

In the anaesthetized rat, regions of the somatosensory cortex have been subpially isolated, leaving intact the cortical blood supply and the connectivity via the white matter. Application of penicillin or strychnine into layer IV of intact cortex resulted in enhancement of amplitude and prolongation of evoked potentials together with the appearance of spontaneous epileptiform discharges. Within a partially isolated region of cortex, spontaneous and evoked potentials occurred as in normal cortex, but application of convulsant drug resulted in no changes in evoked potentials and in no spontaneous spiking. With incisions for which the surface profile measured 0.9 x 0.9 mm, full‐depth isolation resulted in interruption of the propensity for epilepsy, whereas half‐depth incisions left epileptic manifestations unimpaired. With the surface profile measuring 0.5 x 0.5 mm, half‐depth isolation was sufficient to prevent epileptic activity. Results from isolated regions of various geometries and sizes indicated that the ability of cortical neurones to generate epileptic activity depends on the amount of connectivity with surrounding cortex. The propensity of cortex to become epileptic is thus a mass action effect and the 'epileptic neuronal aggregate' is operationally different from anatomically based modular organizations such as thalamo‐cortical or cortico‐cortical columns. In the small barrel field of the somatosensory cortex, partial isolations that prevented the appearance of spontaneous epileptiform spiking contained many barrels, indicating that a single thalamo‐cortical module contains insufficient inherent lateral connectivity to support epileptiform activity. Theoretical considerations indicated that the excitability of a neurone depends both on its monosynaptic connections with other neurones and on the connectivity of these latter with neurones further afield. The interruption of epileptiform activity by partial isolation could be mimicked by a computer model in which connectivity was mediated via short synaptic paths. The model exhibited self‐sustaining synchronized neural activity that could be prevented by interruption solely of polysynaptic paths.
Calcium currents and contraction in frog atrial trabeculae
Authors: Badaoui A , Leoty C
Published: December 2014

The properties of two types of calcium current (ICa(T) and ICa(L)) and their relationship with contraction were studied in isolated frog atrial trabeculae using the double mannitol gap technique. In Ringer solution containing TTX the calcium currents observed are similar to the ICa(T) and ICa(L) found in single frog atrial cells. The results obtained by using inorganic calcium channel blockers have shown that the phasic contraction appears only when ICa(T) and ICa(L) are simultaneously present. It is proposed that ICa(T) loads the sarcoplasmic reticulum (SR) while ICa(L) triggers Ca2+ release from the SR.
Interaction between secretin and nerve‐mediated amylase secretion in the isolated exocrine rat pancreas
Authors: Wisdom DM , Camello PJ , Salido GM , Singh J
Published: December 2014

This study investigates the effects of the gut peptide, secretin, on nerve‐mediated and acetylcholine‐evoked amylase secretion and calcium (Ca2+) and magnesium (Mg2+) mobilization in the in vitro rat pancreas. Both electrical field stimulation (EFS; 50 V, 20 Hz, 1 ms) and acetylcholine (ACh; 10(−6) M) caused marked increases in amylase output in isolated pancreatic segments. These responses were inhibited by atropine (10(−5) M). Secretin (10(−10) and 10(−8) M) evoked only a small increase in amylase secretion, which was unaffected by atropine. Combining either EFS or ACh with secretin resulted in an attenuation in amylase output compared with the response obtained with either EFS or ACh alone. In a Mg(2+)‐free medium, secretin failed to inhibit the amylase output evoked by EFS. When forskolin (10(−5) M) was combined with EFS there was a marked potentiation of amylase output. In fura‐2‐loaded acinar cells, ACh (10(−6) M) elevated cytosolic free Ca2+ concentration ([Ca2+]i). Secretin alone had no detectable effect on [Ca2+]i compared with basal values, but it attenuated the ACh‐induced elevation of [Ca2+]i. Both EFS and ACh elicited 45Ca2+ influx, whereas secretin had no significant effect. In the presence of secretin the EFS‐ and ACh‐induced 45Ca2+ influx was reduced compared with responses obtained with either EFS or ACh alone. EFS caused a net efflux of Mg2+, whereas secretin alone evoked a net uptake of Mg2+ in pancreatic segments. Combining secretin with EFS resulted in a net uptake of Mg2+. In mag‐fura‐2‐loaded acini ACh (10(−5) M) stimulated an initial transient rise in cytosolic free Mg2+ concentration ([Mg2+]i) followed by a sustained decrease in [Mg2+]i. Stimulation of acinar cells with secretin (10(−8) M) resulted in an elevation in [Mg2+]i compared with the resting level. When ACh (10(−5) M) was combined with secretin there was an initial increase in [Mg2+]i followed by a marked decrease to the pre‐secretin‐stimulated value. The results indicate that secretin may control nerve‐mediated and ACh‐evoked secretory responses in the rat pancreas, possibly by an interaction between cellular Ca2+ and Mg2+.
Assessment of thermoregulatory and postprandial thermogenesis over the first 24 hours after birth in pigs
Authors: Herpin P , Le Dividich J , Berthon D , Hulin JC
Published: December 2014

Heat production was continuously measured from birth to 24 h after birth in pigs tube‐fed 14 g kg‐1 of colostrum or water (sham‐fed animals) at hourly intervals, and maintained at thermoneutrality (34 degrees C) or in moderate cold (24 degrees C). Results indicate that colostrum was necessary to initiate and sustain the postnatal rise in metabolic rate observed at 34 degrees C. It provided about 75% of the energy required for heat production at 24 degrees C. Heat production was increased by 74% in the cold and decreased by 30% during starvation. In both cases, maintenance of the energy balance was achieved with a compensatory drop in body temperature. At 34 degrees C, variations in postmeal heat production represented 12% of the total 24 h energy expenditure and were almost equally due to the thermogenic effect of colostrum and to confounding factors, including physical activity. In the cold, calculated postmeal thermogenesis accounted only for 3% of 24 h energy expenditure and for 9% of the extra heat produced in the cold. Our results highlight the main role of colostral energy in the energy metabolism of the newborn pig in a typical birth environment (24 degrees C) and in thermoneutral conditions (34 degrees C). Thermoneutral postmeal thermogenesis is low and its contribution to the extra heat produced in the cold very limited.
Haemodynamic responses to hypotensive haemorrhage in conscious sheep with emphasis on renal and femoral blood flow
Authors: Gunnarsson U , Hjelmqvist H , Rundgren M
Published: December 2014

Haemodynamic responses to slow (0.7 ml kg‐1 min‐1) haemorrhage were investigated in eight adult conscious sheep, fitted with permanent ultrasonic flow probes around the renal and femoral artery. The haemorrhage was continued until the mean systemic arterial pressure (MSAP) suddenly dropped to about 50 mmHg. The spontaneous recovery was followed for 60 min and then the blood was retransfused. A distinct fall in MSAP was obtained after 14.5 +/− 0.9 ml blood (kg body weight)‐1 (24% of the estimated blood volume) had been removed, but the interindividual differences were rather large (range, 10.2‐18.1 ml kg‐1). Therefore, the haemodynamic responses during haemorrhage were related to the total bleeding volume and not to time or volume per kilogram body weight. Before 90% of the total haemorrhage volume had been removed, the MSAP decreased gradually, reaching statistical significance at 80% (P < 0.05). At end of bleeding the cardiac output (CO) had fallen from a pre‐haemorrhage level of 4.7 +/− 0.2 to 2.9 +/− 0.2 1 min‐1. Although the femoral blood flow (FBF) was largely unaffected by the haemorrhage, and thus increased as a fraction of CO, the total systemic vascular resistance was markedly increased during the post‐haemorrhage period, indicating a longer lasting elevation of vascular resistance in other vascular beds. In spite of a concomitant marginal decrease in renal blood flow (RBF), the renal vascular resistance (RVR) was unchanged until 90% total haemorrhage had occurred. At the same time as blood pressure fell, RBF decreased markedly, concomitant with a transient increase in RVR, which was followed by a decrease towards basal levels.(ABSTRACT TRUNCATED AT 250 WORDS)
The nature of increased blood‐cerebrospinal fluid barrier exchange during CO2 inhalation in newborn and adult rats
Authors: Habgood MD
Published: December 2014

Exposure of newborn (2‐day‐old) and adult rats to increasing levels of inspired carbon dioxide (5‐15% CO2) resulted in increased steady‐state cerebrospinal fluid/plasma ratios for a wide range of different‐sized, lipid‐insoluble permeability markers (molecular radius ranged from 0.43 nm for L‐glucose to 5.3 nm for immunoglobulin G). In control animals breathing room air and animals exposed to an elevated level of inspired CO2, steady‐state CSF/plasma ratios for all permeability markers were proportional to their free diffusion coefficient. Steady‐state CSF/plasma ratios in newborn animals were significantly higher than in adult animals, and at all ages the ratios for animals exposed to CO2 were higher than the ratios in control animals. In contrast to the increased steady‐state CSF/plasma ratios in animals exposed to elevated levels of inspired CO2, there was no significant difference in short‐term (10 min after i.v. injection) CSF/plasma ratios for [14C]L‐glucose between 10‐ to 20‐day‐old control rats and rats of similar age exposed to 10% inspired CO2. Steady‐state experiments confirmed that CSF/plasma ratios for [14C]L‐glucose in 20‐day‐old rats exposed to 10% inspired CO2 were raised significantly (twice those measured in control animals breathing room air). The lack of effect of raised CO2 on short‐term CSF/plasma ratios indicates that the significant increases in steady‐state CSF/plasma ratios, in animals exposed to elevated levels of inspired CO2, are not due to a general increase in the permeability of the blood‐CSF or blood‐brain barriers; they are likely to be accounted for by CO2‐induced reductions in the rate of CSF secretion.
Glibenclamide, a blocker of ATP‐sensitive potassium channels, reverses endotoxin‐induced hypotension in pig
Authors: Vanelli G , Hussain SN , Aguggini G
Published: December 2014

In anaesthetized, mechanically ventilated, indomethacin‐treated pigs, we infused E. coli endotoxin (LPS, 20 micrograms kg‐1 h‐1, i.v.). After 150 min of endotoxaemia, 10 mg kg‐1 glibenclamide (an ATP‐sensitive K+ channel antagonist) was administered i.v. over 5 min. Vascular variables were recorded before (control), after 150 min of endotoxaemia and 5, 15 and 30 min after glibenclamide infusion. Glibenclamide transiently (within 5 min) increased systemic arterial pressure, reduced by LPS administration, without an effect on cardiac output. Our data indicate that ATP‐sensitive K+ channels may play a partial role in the vascular changes due to endotoxaemia.
The effect of experimental hypertension on retinal vascular autoregulation in humans: a mechanism for the progression of diabetic retinopathy
Authors: Rassam SM , Patel V , Kohner EM
Published: December 2014

Since the retinal vessels have no sympathetic innervation, blood flow in response to raised blood pressure is dependent on autoregulation. To determine the effect of hypertension on retinal haemodynamics and the autoregulatory capacity of the retinal circulation under conditions of normoglycaemia and hyperglycaemia, retinal blood flow was measured before and after raising the systemic blood pressure in ten normal control subjects, ten diabetic subjects with blood glucose < 10 mmol l‐1 and ten diabetic subjects with blood glucose > 15 mmol l‐1. A controlled rise in systemic blood pressure was achieved using an intravenous infusion of tyramine. Retinal volume flow was determined from red cell velocity using laser Doppler velocimetry and from retinal vessel diameter measurements using digital image analysis of fundus photographs. With a 40% increase in mean arterial blood pressure (MAP), there was a significant increase in retinal blood flow of 32.9 +/− 7.1% in non‐diabetic controls. In diabetics at the low blood glucose level, the increase in retinal blood flow was significant at 30% increase in MAP (23.6 +/− 8.7%, P = 0.032) and at 40% increase (49.9 +/− 12.03%, P = 0.004). Diabetics with high blood glucose failed to autoregulate at any of the increased levels of MAP (15% increase, 27.0 +/− 11.1%; 30% increase, 66.9 +/− 19.8%; and 40% increase, 101.9 +/− 21.4%; P < 0.022). The coefficients of autoregulation showed that in non‐diabetic controls, retinal vascular autoregulation broke down with increases in MAP of between 30 and 40%. In diabetic subjects, it broke down between 15 and 30% in normoglycaemia and at less than 15% in hyperglycaemia. This study demonstrates an impairment in retinal vascular autoregulation in response to raised systemic blood pressure in diabetic subjects, more so at an elevated blood glucose level, thus providing a mechanism for the detrimental effect of hypertension on diabetic retinopathy.
Skeletal muscle buffer value, fibre type distribution and high intensity exercise performance in man
Authors: Mannion AF , Jakeman PM , Willan PL
Published: December 2014

Interrelationships between quadriceps femoris muscle buffer value (beta), fibre type distribution, and lactate concentration and pH following short‐term high intensity exercise were examined in eighteen young healthy human volunteers. Muscle biopsy samples were taken from the lateral portion of the quadriceps femoris muscle at rest and after fatiguing dynamic or isometric exercise. Isometric exercise required the maintenance of 60% quadriceps maximum voluntary contraction, and dynamic exercise, the performance of a modified Wingate Test. The muscle buffer value displayed a positive, but non‐significant correlation with the relative area of the muscle occupied by type II fibres (r = 0.42, P = 0.09). An elevated beta was associated with a lesser decrement in muscle pH during intensive exercise but did not permit the accumulation of a higher muscle lactate concentration or allow for an enhanced dynamic or isometric exercise performance. A superior performance during dynamic exercise was associated with a high concentration of muscle lactate and a low muscle pH post‐exercise; in turn, each of these factors was positively dependent on the relative area of the muscle occupied by type II fibres. The converse was found for isometric exercise, where there was a tendency for an enhanced performance to be associated with a low muscle lactate and high muscle pH post‐exercise. No significant relationship between the relative type II fibre area and isometric performance capacity could be established. It was concluded that the muscle buffer value is not a major limiting factor to the performance of high intensity exercise, suggesting that the involvement of intramuscular acidosis in the development of fatigue may be indirect. The most important determinant of high intensity exercise capacity appears to be the proportional area of the muscle occupied by type II fibres, where a high value provides for a superior dynamic but inferior isometric exercise performance.
Glutamate‐immunoreactivity in identified vagal afferent terminals of the cat: a study combining horseradish peroxidase tracing and postembedding electron microscopic immunogold staining
Authors: Saha S , Batten TF , McWilliam PN
Published: December 2014

Using electron microscopic immunohistochemistry we have shown that strong glutamate‐immunoreactivity (glutamate‐ir) is present in neuronal cell bodies of the nodose ganglion, axons in the tractus solitarius and afferent terminals in the nucleus tractus solitarii. Vagal afferent fibres were specifically labelled by transganglionic retrograde transport of horseradish peroxidase (HRP). Fifty‐seven per cent of the HRP‐labelled terminals in the dorsomedial medulla were found to contain a high level of glutamate‐ir, suggesting that a population of vagal afferent fibres uses glutamate as a neurotransmitter substance. There were no apparent ultrastructural differences between glutamate‐ir and non‐glutamate‐ir vagal afferent terminals, both classes mainly containing rounded vesicles and forming asymmetric synapses. However, some difference in their preference for postsynaptic target was noted. The great majority (83%) of non‐glutamate‐ir vagal afferent terminals made axodendritic synapses, but only just over half (57%) of the glutamate‐ir vagal terminals made synaptic contact with dendrites. Approximately 13% of the HRP‐labelled terminals were found to make synaptic contact with HRP‐labelled dendrites or soma of motoneurones of the dorsal vagal motor nucleus, confirming the existence of monosynaptic connections between vagal afferent fibres and vagal motoneurones.
The effect of NG‐nitro‐L‐arginine methyl ester upon hindlimb blood flow responses to muscle contraction in the anaesthetized cat
Authors: Poucher SM
Published: December 2014

The aim of the present experiment was to investigate the relative contribution of nitric oxide produced in endothelial cells to functional and reactive hyperaemia in the hindlimb of anaesthetized cats. Cats (2.5‐3.4 kg) were anaesthetized with alphadalone‐alphalaxone, and breathed spontaneously following tracheotomy. Left hindlimb blood flow was measured with a flow probe and hyperaemia responses were monitored following 10 s occlusion of the left external iliac artery and during 20 min stimulation of the sciatic and femoral nerves at 3 Hz. This was repeated following nitric oxide synthase inhibition with NG‐nitro‐L‐arginine methyl ester (L‐NAME, 100 mg kg‐1, I.V.). Following L‐NAME administration, baseline hindlimb blood flow and arterial blood pressure were restored by infusion of sodium nitroprusside (range, 0.3‐2.25 micrograms kg‐1 min‐1, I.V.). Following arterial occlusion, L‐NAME reduced the peak reactive hyperaemia (6.5 +/‐ 0.8 vs. 4.5 +/‐ 1.0 ml min‐1 kg‐1, P < 0.05) and blood flow repayment (9.9 +/‐ 2.3 vs. 6.1 +/‐ 2.6 ml, P < 0.05) responses. In contrast, the total functional hyperaemia response during hindlimb contraction was not altered (264.7 +/‐ 68.2 vs. 264.4 +/‐ 62.8 ml kg‐1, n.s.). The results of the study suggest that the production of nitric oxide from endothelial cells does not contribute to functional hyperaemia in contracting skeletal muscle, but plays a large role in reactive hyperaemia. The results imply that flow‐dependent dilatation of feed arteries is mediated by NO in reactive hyperaemia.
Depression of ventilation by dopamine in cats: effects of bilateral cervical sympathetic and vagal trunk section
Authors: Wypych B , Szereda‐Przestaszewska M
Published: December 2014

The contribution of sympathetic and vagal inputs to ventilatory depression induced by dopamine was studied in eighteen anaesthetized, spontaneously breathing, normoxic cats. Breathing was via a tracheostomy. Dopamine (20 micrograms (kg body wt)‐1) was injected intravenously in the intact animal, then after section of the cervical sympathetic trunks, and finally after midcervical vagotomy. Dopamine, injected as a bolus, induced depression of ventilation, affecting predominantly the volume component of the breathing pattern at all experimental stages. The extent of volume reduction was larger and different from that in intact animals following section of sympathetic (P < 0.05) and vagal trunks (P < 0.01). The respiratory cycle was significantly prolonged (P < 0.01) prior to vagotomy, due entirely to the increase in the expiratory time (TE). Bilateral section of the carotid sinus nerves performed in six cats virtually abolished postdopamine ventilatory depression.
Haemodynamic responses to an angiotensin II receptor antagonist (GR 117289) in maternal and fetal sheep
Authors: Forhead AJ , Fowden AL , Silver M , Hughes P , Broughton‐Pipkin F , Sutherland MF
Published: December 2014

An AT1‐specific angiotensin II receptor antagonist (GR117289; 1 mg/kg I.V. bolus) was administered daily to ten chronically catheterized, normotensive ewes during late pregnancy (from 126 +/‐ 1 days) until parturition (139 +/‐ 1 days); five control animals received an equivalent volume of vehicle solution. Following drug administration, mean maternal blood pressure decreased from 87 +/‐ 1 mmHg to a minimum of 79 +/‐ 1 mmHg at 0.5 h (P < 0.05; n = 10) and remained low for 4‐6 h without any concomitant change in fetal blood pressure or maternal and fetal heart rates. In animals fitted with flow probes, uterine blood flow decreased from 443 +/‐ 21 to 363 +/‐ 27 ml/min at 0.5 h post‐drug (P < 0.05; n = 6); this change was positively correlated with the reduction in maternal blood pressure. The mean decrements in uterine and umbilical blood flows measured by steady‐state infusion of tritiated water were ‐611 +/‐ 171 ml/min at 4‐6 h (P < 0.05; n = 5) and ‐71 +/‐ 19 ml/min at 0.5‐1 h (P < 0.05; n = 5), respectively. Significant reductions (P < 0.05; n = 10) in fetal arterial oxygen tension (‐1.6 +/‐ 0.4 mmHg), saturation (‐6.6 +/‐ 1.6%) and content (‐0.3 +/‐ 0.1 mumol/ml) were evident at 0.5 h post‐drug and were maintained for 6‐12 h. Umbilical oxygen delivery decreased at 0.5‐1 h following drug administration (P < 0.01; n = 5), but was unaccompanied by any significant change in fetal oxygen consumption. Chronic decreases in daily fetal pH and blood oxygen content occurred in GR117289‐treated ewes. There were no significant differences in gestational length or neonatal outcome between vehicle‐ and GR117289‐treated groups of ewes with single fetuses.
Influences of secretory activities in rat submandibular glands on tissue kallikrein circulating in the blood
Authors: Garrett  , Chao J , Proctor GB , Wang C , Zhang XS , Chan KM , Shori DK
Published: December 2014

Changes in serum levels of rat tissue kallikrein (rK1) in venous blood were measured, using a newly developed radioimmunoassay, before and after autonomic nerve stimulations of submandibular salivary secretion. rK1 secreted into saliva under these conditions was measured by radioimmunoassay and by enzymic activity assay, using the fluorogenic peptide substrate D‐Val‐Leu‐Arg‐7‐amino‐4‐trifluoromethylcoumarin (AFC). Following an overnight fast, serum rK1 concentration was 30‐40 ng ml‐1. Unilateral electrical stimulation of the submandibular sympathetic nerve supply (at 50 Hz in bursts of 1 s every 10 s for 60 min) evoked a small flow of saliva with a very high rK1 concentration, resulting in a large output of rK1 of 2104.4 +/− 603.5 micrograms (n = 6). Such stimulation caused a large degranulation of granular duct cells and a corresponding reduction in glandular rK1 content. Unilateral electrical stimulation of the parasympathetic nerve supply (at 5 Hz continuously for 60 min) evoked a copious flow of saliva with a very low rK1 concentration, resulting in a low output of rK1 (18.1 +/− 4.9 micrograms; n = 6). Despite these large differences in salivary outputs of rK1, serum concentrations of rK1 were increased similarly following either sympathetic or parasympathetic stimulation by 48 and 46%, respectively. If the submandibular duct was briefly obstructed during sympathetic stimulation, inducing leakage and glandular oedema, then serum rK1 increased greatly (40‐fold); a similar increase to that seen by others in previous studies without deliberate obstruction. Four days after bilateral submandibular‐sublingual sialadenectomy serum rK1 concentration was reduced by approximately 50%. The results indicate that submandibular glands normally contribute to circulating levels of rK1 in rats, but this contribution is independent of the amounts of rK1 secreted into saliva by sympathetically induced exocytosis, and is likely to arise from basal vesicular transport. However, if glandular leakage occurs during sympathetic stimulation of submandibular secretion this then causes increases in the circulating levels of rK1 that correlate with the large amounts being secreted into saliva.
Interactions between oxoglutarate oxidation and acid secretion in isolated rabbit gastric glands
Authors: Chacin J , Hernandez I
Published: December 2014

The effects of gastric secretagogues, and other agents that modify H+,K(+)‐ATPase activity and cell calcium concentration, on the rate of oxoglutarate oxidation were investigated in isolated gastric glands. Oxoglutarate was oxidized in a dose‐dependent manner by gastric glands, with an apparent Km for oxoglutarate of 3.9 +/‐ 0.5 mM. Oxoglutarate progressively inhibited the rate of glucose oxidation. In the presence of 0.5 mM oxoglutarate plus 10 mM glucose, the latter substrate was preferentially oxidized and contributed most to oxygen uptake. With 10 mM oxoglutarate plus 10 mM glucose, the rate of glucose oxidation was greatly inhibited and oxoglutarate oxidation accounted for most of the oxygen consumption. Acid secretion (aminopyrine accumulation) was significantly increased by 0.1 mM histamine in glands oxidizing 10 mM oxoglutarate, although this stimulation was significantly lower than that observed in the presence of 0.5 mM oxoglutarate plus 10 mM glucose. Omeprazole, an inhibitor of the H+,K(+)‐ATPase, significantly reduced the oxidation of oxoglutarate, whereas NH4+, an activator of the enzyme, stimulated the oxidation of a submaximal dose of oxoglutarate. Carbachol at 0.1 mM significantly increased the rate of oxidation of non‐saturating concentrations of oxoglutarate. The calcium ionophore ionomycin at 10 microM produced a similar effect. Chelation of intracellular calcium by BAPTA AM caused a significant inhibition of oxoglutarate oxidation. The results provide further evidence that changes in the ATP:ADP ratio resulting from activation of the H+,K(+)‐ATPase, and calcium ions are involved in the mechanisms of activation of oxidative metabolism in the parietal cell.