bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbonic anhydrase in the normal rat stomach and duodenum and after treatment with omeprazole and ranitidine
Authors: LÖNNERHOLM G. , KNUTSON L. , WISTRAND P. J. , FLEMSTRÖM G.
Published: December 2008

A low pH in the lumen of the stomach and duodenum stimulates gastroduodenal mucosal secretion of bicarbonate, particularly in the duodenum. Long‐term deprivation of this acid stimulus might affect the ability of the mucosa to secrete bicarbonate, with a consequent decrease in mucosal protection against the acid. This could occur by ‘down‐regulation’ of carbonic anhydrase (CA) activity in the bicarbonate‐transporting cells. Levels of CA activity and amounts of CA isoenzymes in rat gastric and duodenal mucosa were determined by biochemical assay and histochemical and immunohisto‐chemical staining. Control animals and animals pre‐treated for 4–6 weeks with the histamine Ha‐receptor antagonist ranitidine (600 mg kg‐1 daily) or the H+,K+‐ATPase inhibitor omeprazole (28 mg kg‐1 daily) were examined. Both drugs are potent inhibitors of gastric secretion of acid. Both gastric and duodenal mucosal total CA activity and the distribution of isoenzymes were very similar in control animals and animals treated with these drugs. In the stomach, CA II was found in the surface epithelial and parietal cells. In the duodenum both CA I and CA II were observed. The staining for CA I was restricted to a small number of villus cells which looked like ordinary duodenal enterocytes. CA II in the duodenum was found in all villus cells, except the goblet cells. The staining decreased gradually from the top to the bottom of the villi and was absent in the crypts. Duodenal bicarbonate secretion is dependent on mucosal CA activity, and the distribution of CA II thus suggests that this alkaline secretion is of villous rather than cryptal origin.
Failure to deduce a peptide inhibitor of Na,K‐ATPase from the gene coding for the catalytic α‐subunit of Na,K‐ATPase
Authors: LUNDGREN O. , HAGLIND E. , MÅRDH S.
Published: December 2008

It has been proposed (Bost et al. 1985, Blalock & Bost 1986, Smith et al. 1987) that the DNA strand opposite the one coding, for example, for a hormone or a neurotransmitter codes for its receptor protein. This proposal was tested with regard to the possibility of deducing a peptide inhibitor of Na,K‐ATPase from the known gene of the catalytic α‐subunit of the enzyme. Three such peptides, deduced from presumed extracellular domains of the catalytic α‐subunit, were tested in vitro and in vivo with regard to their effects on Na,K‐ATPase activity. No effect on the enzyme could be demonstrated.
α2‐Aclrenoceptor agonist‐mediated inhibition of [3H]noradrenaline release from rat hippocampus is reduced by 4‐aminopyridine, but that caused by an adenosine analogue or co‐conotoxin is not
Authors: HU P.‐S. , FREDHOLM B. B.
Published: December 2008

The inhibitory effect of an adenosine analogue, R‐PIA, and an α2‐adrenoceptor agonist, UK 14,304, on [3H]NA efflux from field‐stimulated rat hippocampal slices was examined. The effect of 0.1 μm UK 14,304 was mimicked by 30 nM w‐conotoxin and by 10 μM cadmium chloride, inhibitors of N‐ and L‐type Ca2+ channels. R‐PIA (1 μM) had no effect per se, but caused a clear‐cut inhibition after blockade of the pre‐synaptic α2‐receptor by yohimbine.

4‐Aminopyridine (4‐AP) caused a dose‐dependent increase in evoked transmitter release. At 30 μM 4‐AP did not affect the actions of ω‐conotoxin or cadmium chloride. The pre‐synaptic effect of R‐PIA was similarly unaffected by 30 μM 4‐AP. The presynaptic effect of UK 14,304 was virtually abolished by 4‐AP (30 μM). The effect of UK 14,304 (0.1 μM) could be partly restored by reducing the Ca2+ concentration during treatment with 4‐AP (22% inhibition compared to 42% with normal Ca2+). The magnitude of increase in evoked [3H]NA efflux by yohimbine (1 μM) was decreased by 4‐AP in a concentration‐dependent manner from 142% increase in controls to 21 % at 100 μM 4‐AP.

The present results indicate that NA release is reduced by somewhat different mechanisms by pre‐synaptic α2‐ and adenosine Aj‐receptors. Furthermore, the results indicate that pre‐synaptic Arreceptors on hippocampal NA neurons do not primarily regulate 4‐AP‐dependent potassium channels, but they might act directly on a Ca2+ conductance.
Bistable firing properties of soleus motor units in unrestrained rats
Authors: EKEN T. , KIEHN O.
Published: December 2008

EMG recordings from single motor units in the soleus muscle were performed in alert unrestrained rats. A cuff electrode around the tibial nerve and subcutaneously placed electrodes in the foot permitted stimulation of afferent fibres. The movements of the rat and the simultaneous EMG activity were displayed together on a video monitor.

Most motor units were tonically active for extended periods during quiet standing. During tonic discharge, maintained shifts between stable low (8–12 Hz; quartiles) and high (16–22.8 Hz) frequency ranges were initiated by short‐lasting synaptic excitation of the motoneuron pool by stimulation of la afferents, or inhibition by stimulation of skin afferents. The shifts were not related to gross limb movements. This phenomenon is referred to as a bistable firing pattern. Bistable firing also occurred spontaneously during quiet standing. Typically the firing frequency shifted between a low (9–12.5 Hz) and a high (20–24.5 H) mode. During recordings of simultaneous activity in two units, spontaneous and stimulus‐induced frequency jumps causing maintained changes in firing frequency were regularly seen to occur in one unit, while the frequency in the second unit was unchanged or only phasically influenced.

These results demonstrate for the first time a bistable firing pattern during postural activity in the intact animal. The firing pattern closely resembles the bistable behaviour described in spinal motoneurons in reduced preparations, where it is due to the presence of a plateau potential. This suggests that the bistable firing is unexplained by plateau potentials also in the intact animal.
Effects of atrial natriuretic peptide (ANP) on jejunal net fluid absorption in the rat
Authors: PETTERSSON A. , JÖNSSON C.‐O.
Published: December 2008

The role of atrial natriuretic peptide (ANP) on jejunal net fluid transport was studied in intact rats as well as in rats subjected to a perivascular denervation of the intestinal segment. In rats with intact nerves, an acute volume expansion with 5% albumin (10% of estimated blood volume) decreased jejunal net fluid absorption by approximately 70% compared to control animals not subjected to volume expansion. After a perivascular denervation of the intestinal segment, the acute volume expansion reversed net fluid absorption into a net fluid secretion. In order to reduce the volume expansion‐induced endogenous release of ANP, one group of rats was subjected to a right atrial appendectomy 7 days prior to the experiments. In these animals, the intestinal response to the same 10% volume load was blunted compared to controls. Administration of rat α‐ANP (99–126; 5 μg kg‐li.v.) induced effects similar to those of volume expansion both in rats with intact perivascular nerves as well as in denervated animals. Volume expansion increased mean arterial pressure (MAP) as well as central venous pressure and decreased heart rate (HR) in all groups. When exogenous ANP was administered, a fall in MAP was seen, while HR remained unchanged.

In conclusion, these data strongly indicate a physiological role for ANP in jejunal fluid transfer in response to acute volume expansion.
Substance P and vasoactive intestinal peptide influence polyamine metabolism in salivary glands of the rat
Authors: EKSTRÖUM J. , NILSSON B.‐O. , ROSENGREN E.
Published: December 2008

In parotid, sublingual and submaxillary glands stimulated by continuous intravenous infusion of the neuropeptides substance P or vasoactive intestinal peptide at various doses for 3 h, the concentrations of the polyamines putrescine, spermidine, spermine and N1‐acetylspermidine as well as the activity of ornithine decarboxylase were determined. This enzyme catalyses the synthesis of putrescine and is the key enzyme in polyamine formation. Vasoactive intestinal peptide induced the most marked effects, and the most conspicuous findings were made in the sublingual glands, where the ornithine decarboxylase activity was found to have increased more than 100‐fold, accompanied by an increased level of putrescine in those glands which were removed immediately after the end of the infusion. When, instead, the glands were removed 5 h after the end of the infusion there was no longer any increase in the activity of ornithine decarboxylase or in putrescine concentration, but now spermidine and spermine were found to be increased. Interestingly, the parasympathetic non‐adrenergic, non‐cholinergic regulation of polyamine metabolism in the major salivary glands of the rat is most predominant in the sublingual glands.
Mechanism of isotonic water transport in glands
Authors: USSING H. H. , ESKESEN K.
Published: December 2008

Since water and electrolytes pass cell membranes via separate channels, there can be no interactions in the membranes, and osmotic interactions between water and solutes can be expressed as the product of solute flux, frictional coefficient of solute, and length of pathway. It becomes clear that isotonic transport via a cell is impossible. In glands, where cation‐selective junctions impede anion flux between the cells, isotonic water transport is only possible if sodium, after having passed the junction, is reabsorbed in the acinus and returned to the serosal side. Thus it can be recycled via the cation‐selective junction and exert its drag on water more than once. This hypothesis was tested on frog skin glands. Skins were mounted in flux chambers with identical Ringer solutions on both sides. Na channels of the principal cells were closed with amiloride in the outside solution, and secretion stimulated with noradrenaline in the inside solution. Influx and efflux of Na, K and Br (used as tracer for CI) were measured on paired half‐skins during the constant‐secretion phase. Flux ratios for both Na and K were higher than expected for electrodiffusion, indicating outgoing solvent drag. Flux ratios for K were much higher than those for Na. This is in agreement with the concept that Na is reabsorbed in the acinus and K is not.

Two independent expressions for the degree of sodium recycling are developed. Under all experimental conditions these expressions give values for the recycling which are in good agreement.
Initial plasma disappearance and distribution volume of [131l]albumin and [125l]fibrinogen in man
Authors: BENT‐HANSEN L.
Published: December 2008

The simultaneous plasma disappearance curves of albumin and fibrinogen were recorded in eight normal subjects from 10 to 60 min following intravenous injection. Additional samples were taken at 3, 4, 5, 6 and 7 min. The initial distribution volume (IDV) of albumin calculated by semilogarithmic extrapolation to zero time was 5.56% (range 3.73–8.53) larger than that of fibrinogen, denoting an initial high‐rate function of albumin efflux extending from zero to about 10 min after tracer injection. The following slower phase of the albumin curve from 10 to 60 min was found to be similar to the so‐called transcapillary escape rate (TER) of single‐tracer experiments. By introducing the value Cp(o) (i.e. the estimated curve height at t= 0, from the injected amount of albumin tracer divided by the IDVf), the entire initial part of the albumin curves was analysed. From this analysis the mean value of 0.0135+ 0.0038 min1 was determined for initial slope, corresponding to a whole‐body unidirectional albumin efflux [j(0)] of 0.0572 + 0.0160 ml 100 g‐1 min‐1. The result is about 16 times higher than normal estimates of total lymphatic albumin return, indicating a huge backflux of interstitial albumin at the whole‐body capillary level. Both phases of efflux seem to reflect uptake in a variety of peripheral tissues, and the hypothesis that the second phase (TER) expresses the initial slope of albumin escape into non‐liver tissues is not substantiated. Based on the difference in IDV of the tracers demonstrated, the uncritical use of albumin as a plasma volume marker is not justified.
Excitatory amino acids and cerebrovascular tone
Authors: HARDEBO J. E. , WIELOCH T. , KÄHRSTRÖM J.
Published: December 2008

Levels of excitatory amino acids in the brain extracellular fluid compartment rise during pathological conditions in the brain such as ischaemia, anoxia and epilepsy. One such amino acid, glutamate, is present in sensory nerve fibres innervating, for example, cerebral vessels. Enhanced levels of circulating glutamate and aspartate are found in migraine sufferers. The present study examined whether excitatory amino acids, in concentrations found in the brain extracellular fluid compartment during pathological conditions, exert a direct effect on cerebrovascular tone. As tested in flow‐regulating pial arteries from rat, cat and man, no such constrictive or dilatory effect was obtained.
Transport pathways for Na+ and Br‐ (CI‐) in noradrenaline‐stimulated frog skin (Rana temporaria)
Authors: ESKESEN K. , USSING H. H.
Published: December 2008

Transport pathways for Na+ and Br‐ across noradrenaline‐stimulated frog skin, in which the sodium channels in the apical membrane had been blocked with amiloride, were examined by pre‐steady‐state flux ratio experiments.

 To analyse the experiments, equations are derived from which the fluxes through two parallel pathways can be determined if these differ with respect to the flux ratio as well as the mean passage time for the ion in question.

 The fluxes of Na+ and Cl‐ were followed over a period of 3 h and it was found that about 1 h after addition of noradrenaline time‐invariant fluxes could be achieved. In that period inward and outward tracer fluxes of Na+ and Br‐ (used as a substitute for Cl‐) were followed during the build‐up of isotope in the tissue until steady‐state fluxes were attained.

 The experiments showed that when the Na channels of the capital cells are blocked the glands provide the major pathway for sodium transport across the skin. The efflux of Br‐ can be separated into two components. A fast one through the mitochondria‐rich cells, which is the pathway for passive anion fluxes, and a slower one through the glands. No influx through the slow transport pathway could be detected. In some skins exchange of Br‐ through the mitochondria‐rich cells is revealed. An anion exchange mechanism also appears to be present in the basolateral membrane of the gland cells.
Density and functioning of human lymphocytic β‐adrenergic receptors during prolonged physical exercise
Authors: MÄKI T.
Published: December 2008

In order to study the regulation of β‐adrenergic receptor number and function in response to prolonged physical effort, lymphocytic β‐adrenoceptor density (determined by (‐)[125I]iodocyanopindolol binding), lymphocytic basal and isoproterenol‐stimulated cyclic AMP (cAMP) production and concentrations of plasma catecholamines were measured before and during 3 h running exercise in eight healthy volunteers. A significant (P < 0.01) increase of the lymphocytic β‐adrenoceptor density from 45±4 to 81 ± 9 fmol mg‐1protein (mean ± SEM) took place during the first hour of exercise. As the exercise was continued for up to 2.1–3 h, the receptor densities did not change significantly any more and remained elevated (72 ± 9 fmol mg‐1protein) in comparison to the resting levels (P < 0.02). The isoproterenol‐stimulated cAMP production of the lymphocytes increased during the first hour of running from 190 ± 36 to 269 ± 56 pmol mg‐1protein (P < 0.01) and returned to the resting level at the end of the exercise (182 ± 38 pmol mg‐1protein). The mean levels of plasma catecholamines increased ˜ sixfold during the first hour of exercise and remained elevated until the end of the running. This study demonstrates that the β‐adrenergic receptor system is activated in lymphocytes during prolonged aerobic physical exercise. This activated state becomes, however, attenuated within 2–3 h of exercise as indicated by a diminishing ability of β‐adrenoceptors to mediate catecholamine‐induced cAMP production.
Functional development of the visual system in normal and protein‐deprived rats. VIM. Post‐natal development of optic nerve axons
Authors: CONRADI N. G. , SJÖUSTRÖUM A. , RYDENHAG B.
Published: December 2008

Protein deprivation results in a persistent impairment of transmission of impulses from the specific cortical projection within the visual cortex. In order to evaluate changes in subcortical structures during pre‐weaning development, a study was made on number, calibre and myelination of optic nerve axons in control (C) and protein‐deprived (PD) rats 5, 12, 20 and 30 days of age. Protein deprivation was induced by giving rat mothers a diet containing 7% protein by weight (control diet 14%, during gestation and lactation. The cross‐sectional area of the nerve was measured on a digitizer. Between 3000 and 4000 axons collected from 7–13 field areas sampled by a random, systematic procedure from a cross‐shaped area of the nerve were counted and measured. Between 5 and 12 days after birth, the number of axons was reduced by 50% in C rats. The total number of optic nerve axons was not significantly different in PD compared to C rats, indicating that protein deprivation does not affect the formation or naturally occurring nerve cell death of retinal ganglion cells. At all ages examined there were significant reductions in the number of axons larger than 0.52μm as well as the number of myelinated axons. The rates of growth/maturation and myelination of axons in C rats and PD rats suggested that the reductions seen in PD rats up to 20 days of age may represent a developmental delay of approximately 4 days. At 30 days, a delay or a distortion of development may be present. The retarded development of optic nerve axons is discussed in relation to delays, distortions and deficits during visual system maturation in protein‐deprived rats.
Functional development of the visual system in normal and protein‐deprived rats. IX. Visual evoked response in young rats
Authors: SJÖUSTRÖUM A. , CONRADI N. G.
Published: December 2008

Changes in latencies of the visual evoked response (VER) during early post‐natal development were examined in protein‐deprived (PD) rats. The evoked response to light‐flash stimulation was recorded in the dorsal lateral geniculate nucleus (dLGN) and on the surface of the visual cortex. In control rats, latencies of the cortical VER decreased rapidly up to 20 days and slowly thereafter. In PD rats, the latencies of the cortical VER were increased by 10–15 ms at 17 days; the developmental decrease was delayed by approximately 3 days. After 20 days, PD rats also went into a phase with slow decrease of the latencies, and the onset latency of the cortical VER was still increased by some 10 ms at 26/27 days. At this age, PD rats showed an increase in the latencies of the VER in the dLGN which was of similar magnitude to that in the cortical VER, indicating that alterations were more marked in the peripheral parts of the visual system at this stage of development. The findings are in agreement with previous studies indicating that there is a delay of visual system development in PD rats before 20 days. A maturational event which turns rapid into slow development at approximately 20 days in both C and PD rats turns this delay into a distortion of development. The delays and distortions of visual system development may be one causative factor for the functional deficit present in the visual cortex of adult PD rats.
Resynthesis of glycogen in different muscle fibre types after prolonged exhaustive exercise in man
Authors: VØLLESTAD N. K. , RLOM P. C. S. , GRØNNERBD O.
Published: December 2008

The rate of glycogen resynthesis was examined in different muscle fibre types after prolonged exhaustive exercise. Six subjects exercised to exhaustion at 75% of Vo2 max, and muscle hiopsies were taken after 0, 90 and 180 niin of recovery. Glucose drinks (1.4, 0.7 and 0.7 g kg‐1 body wt) were taken at time 0, 60 and 120 min. Photometric determination of periodic acid‐Schiff stain intensity revealed a 65% faster rate of glycogen resynthesis in type IIA and IIAB as compared to type I fibres during the first 90 min. Thereafter no differences between the various fibre types were detected. No digerences in the rate of glycogen resynthesis were observed between the subgroups of type II muscle fibres. These results suggest that there was a slower acceleration of glycogen resynthesis in type I compared to type II fibres. In all fibre types a positive relationship between rate of synthesis and glycogen concentration was observed. It is suggested that the size of the glycogen molecule and hence the number of available terminal glucospl units is a major determinant of rate of resynthesis.
Differential release of coexisting neurotransmitters: frequency dependence of the efflux of substance P, thyrotropin releasing hormone and [3H]serotonin from tissue slices of rat ventral spinal cord
Authors: IVERFELDT K. , SERFÖZÖ P. , ARNESTO L. DIAZ , BARTFAI T.
Published: December 2008

In few systems has the release of coexisting classical and peptide neurotransmitters been studied. Here the release of substance P‐like immunoreactivity (SP‐LI), thyrotropin releasing hormone‐like immunoreactivity (TRH‐LI) and [3H]serotonin ([3H]5‐HT) from tissue slices of rat ventral spinal cord was investigated in a superfusion system. The slices were stimulated electrically with field stimulation (900 pulses, 2 ms duration, 36 V) at frequencies between 0.25 Hz and 40 Hz. The evoked fractional release of SP‐LI increased significantly from 0.46 to 1.24% of the total tissue store when the frequency of stimulation was changed from 3 to 10 Hz, while the evoked fractional release of TRH‐LI increased significantly from 0.28 to 0.71% of the total tissue store with increasing frequency of stimulation between 0.5 and 3 Hz. The evoked fractional release of [3H]5‐HT did not show any significant change when the frequency of stimulation was changed in the frequency range of 0.25–40 Hz but remained between 5.6 and 7.2% of the total tissue store. It appears that at frequencies lower than 0.5–1 Hz these 5‐HT/SP/TRH neurons may function predominantly as serotonergic neurons. At 3 Hz stimulation with 900 pulses the extracellular Ca2+ concentration required for half‐maximal release of [3H]5‐HT was 1.2 mmol 1‐‐1, while for half‐maximal release of SP‐LI significantly higher concentrations of Ca2+ (4.2 mmol 1‐‐1) would be required. The results demonstrate that the coexisting neurotransmitters substance P, thyrotropin releasing hormone and [3H]serotonin show different dependence on frequency of stimulation for the electrically evoked in‐vitro release and suggest that the mechanism of release of these coexisting neurotransmitters is at least partly different.
Regional cerebral blood flow in acute hypertension induced by adrenaline, noradrenaline and phenylephrine in the conscious rat
Authors: SOKRAB T.‐E. O. , JOHANSSON B. B.
Published: December 2008

Hypertension was induced in conscious rats by intravenous infusion of phenylephrine (3, 6 or 12 μg kg‐1min‐1), noradrenaline (3 μg min‐1) or adrenaline (3 μg kg‐1min‐1). Local cerebral blood flow was measured autoradiographically in 24 defined brain structures using [14C]iodoantipyrine as the diffusible tracer. The mean arterial pressure induced by adrenaline, noradrenaline and the two higher doses of phenylephrine was 158–168 mmHg with no significant differences between the groups. Only adrenaline significantly increased local cerebral blood flow in nine of the 24 structures studied. The smaller capacity for autoregulation after adrenaline compared with other drugs might be related to a β‐adrenoreceptor‐stimulating effect.
Heterogeneous blood flow distribution within single skeletal muscles in the rabbit: role of vasomotion, sympathetic nerve activity and effect of vasodilation
Authors: IVERSEN P. O. , NICOLAYSEN G.
Published: December 2008

A major heterogeneous distribution of blood flow has been described on a non‐microvascular level within single skeletal muscles at rest and during exercise hyperaemia both in the dog and in the rabbit.

Thde heterogeneity in blood flow distribution could bhd composed of both a steady‐state region‐to‐region variability (spatial) and a time‐dependent variability (temporal) in blood flow to each region. In the present study we estimated their relative contributions to the variations in blood flow within the muscles. Furthermore, we determined whether sympathetic nerve activity contributed to and whether pharmacologically induced vasodilation affected the heterogeneous blood flow pattern.

Regional blood flow measurements were based on microsphere infusions into anaesthetized rabbits. Blood flow was determined under both resting conditions and during exercise hyperaemia in regions weighing 0.25 g each within hind leg muscles.

Thde coefficient of variation for the spatial variability wahd twice that of the temporal one: 0.32 and 0.16 (mean) respectively. Neither stimulation of the sympathetic nerves, sympathectomy nor vasodilation affected the heterogeneity in blood flow. When exercise hyperaemia was induced, blood flow increased in all regions so that a positive (P l 0.05) correlation was present between resting and exercising blood flow values in the individual regions.

Although regional variation in vascularization could explain the observations during exercise hyperaemia, we have at present no fully satisfying explanation for the observed regional heterogeneity in blood flow.
Oestrogen‐induced changes in muscarinic receptor density and contractile responses in the female rabbit urinary bladder
Authors: BATRA S. , ANDERSSON K.‐E.
Published: December 2008

Mature ovariectomized rabbits were treated for 1, 4 or 8 weeks with oestrogen, and the effects on contractile responses and on muscarinic receptor density in the isolated urinary bladder were studied. Oestrogen treatment caused a significant increase in the weight of the bladders. The responses to K+(124 mm) were depressed, but not the maximum responses to carbachol. The frequency‐response curve to electrical stimulation was shifted to the right after 4 and 8 weeks of treatment, but the maximum response was not reduced. There was also a (non‐significant) shift to the right of the carbachol concentration‐response curve. Pre‐treatment with scopolamine revealed a significant reduction of the non‐cholinergic response to electrical stimulation after oestrogen treatment compared to controls. Binding of [3H]quinuclidinyl benzilate (QNB) was saturable and of high affinity. There were no changes in apparent dissociation constant after oestrogen treatment. However, the muscarinic receptor density decreased already after I week of treatment and was only 10% of the control after 4 weeks. It is concluded that oestrogen treatment causes a down‐regulation of muscarinic receptors in the rabbit urinary bladder, but the consequences for contractile activation through muscarinic receptors seem to be small.
Aldosterone secretion during acute metabolic and respiratory alkalosis in the goat
Authors: AUGUSTINSSON O. , JÓNASSON H. , JUNKERGÅRD J.
Published: December 2008

Received 6 March 1989, accepted 20 April 1989. ISSN 0001–6772. Department of Physiology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden.

Mhdtabolic and respiratory alkalosis were produced in goathd with the primary aim of studying possible influence of a reduced blood hydrogen ion concentration on aldosterone secretion.

Metabolic alkalosis was induced by I h i. v. infusion of hypertonic tris(hydroxy‐methyl)aminomethane (THAM) solution. The infusion was associated with a significant reduction in plasma aldosterone concentration (PA). It occurred in the absence of a detectable fall in plasma K or obvious change in plasma renin activity, but simultaneously with a moderate increase in plasma cortisol concentration and a significant reduction of plasma Na concentration. It suggests that changes of the primary aldosterone regulators were not the cause of the fall in PA, but leaves open the possibility that either the decreased blood hydrogen ion concentration as such or THAM‐induced blood hypertonicity reduced the aldosterone secretion.

Thde respiratory alkalosis was due to heat polypnoea elicitehd by 2 h exposure of the goats to 45°C. Here, no obvious change in PA was observed during the alkalotic period, which, however, was associated with a rise in plasma K. Increased K stimulation may therefore have masked a possible inhibitory influence of the alkalosis upon the aldosterone secretion.
Low oxygen cost of carbonic anhydrase‐dependent sodium reabsorption in the dog kidney
Authors: ØSTENSEN J. , STOKKE E. S. , HARTMANN A. , WENSELL K. , KIIL F.
Published: December 2008

To examine the oxygen requirement of carbonic anhydrase‐dependent sodium reabsorption in the proximal tubule, 18 anaesthctized dogs were studied under conditions of saturated distal NaCl reabsorption; the latter was accomplished by volume expansion (all groups) combined with infusion of loop diuretics (groups 1 and 3). Acetazolamide reduced HCO3 reabsorption by 602 ± 32 μmol min‐1 (55%, group 1) and hy 777 ± 103 μmol min‐1 (66%, group 2). This was accompanied with a reduction in sodium reahsorption and oxygen consumption in a molar ΔNa/ΔO2 ratio of ahout 45 in both groups of dogs. The ΔHCO3/ΔO2 ratio averaged 16 ± 1, which was not significantly different from the theoretical value of 18 expectcd for transcellular sodium transport by Na+, K+‐ATPasc. Mannitol (group 3) reduced NaCl rcabsorption by 37 ± 2% without affecting NaHCO3 reabsorption or oxygen consumption significantly. We conclude that carbonic anhydrase‐dependent NaCI reahsorption in the proximal tuhules is passive, and that NaHCO3 reahsorption is the only important active sodium transport which is sensitive to inhibition of carbonic anhydrase.,
Renal denervation does not prevent dehydration‐induced natriuresis in sheep
Authors: PARK R. G. , CLEVERS J. , McKINLEY M. J. , RUNDGREN M.
Published: December 2008

Normal sheep or sheep in which the renal nerves had been extirpated were deprived of water for 2 days in order to determine whether changes in renal nerve activity contribute to natriuresis during water deprivation. Both groups of sheep showed a considerable natriuresis throughout the period of water deprivation and increases in plasma osmolality and plasma Na concentration. Renal denervation, as indicated by the absence of catecholamine fluoresence in kidney sections, was extensive.

Phdevious experiments have suggested cerebral involvemenhd in the induction of dehydration‐induced natriuresis. The present results indicate that the efferent pathway mediating this cerebral influence on renal sodium excretion does not involve the renal nerves, suggesting a hormonal mechanism as the likely pathway.,
The enhancement of carbachol‐induced salivary secretion by VIP and CGRP in rat parotid gland is mimicked by forskolin
Authors: LARSSON O. , OLGART L.
Published: December 2008

Low doses of vasoactive intestinal polypeptide (VIP) and calcitonin gene‐related peptide (CGRP) have been shown to augment the salivary volume secretion evoked by muscarinic receptor agonists or substance P (SP) in rat parotid gland. Since VIP and CGRP are known to activate adenylate cyclase, we have studied whether forskolin, which directly activates this enzyme, can mimic the effects of these peptides on salivary secretion from the parotid gland in anaesthetized (Inactin 0.5 g kg‐1 i. p.) rats. We have also studied the effect of the secretagogues and peptides on glandular blood flow as revealed by the laser Doppler technique.

Crbachol (5 nmol kg‐1) and SP (185 pmol kghd‐1) injected i. v. caused a transient increase in parotid blood flow and a decrease in systematic blood pressure concomitant with a salivary secretion of 3.3 ± 0.3 mg(n= 22) and 18.7 ± 1.9 mg(n= 25) respectively. VIP (150 pmol kg‐1) and CGRP (25 pmol kg‐1) also caused a transient increase in glandular blood flow concomitant with a decrease in systemic blood pressure, but no salivary secretion. The glandular blood flow increased by 166 ± 5% and 43 ± 11% for VIP and CGRP respectively. When carbachol was given 20 s after the injection of VIP or CGRP, the secretory response was increased by about 250% and 60% respectively. The adenylate cyclase stimulator forskolin (2.5 pmol kg‐1) produced the same type of response regarding blood flow and systemic blood pressure as VIP and CGRP and potentiated the salivary secretion evoked by carbachol (5 nmol kg‐) by about 100%.

Since forskolin can mimic VIP in potentiating salivary secretion, the ability of this peptide to induce CAMP formation in the gland cells may contribute importantly to the stimulation of salivary secretion.,
Neural and biomechanical differences between men and young boys during a variety of motor tasks
Authors: MORITANI T. , ODDSSON L. , THORSTENSSON A. , ÅSTRAND P.‐O.
Published: December 2008

The adaptation in activation patterns of the ankle extensor muscles to different functional demands a‐as studied in adult men (n = 10) and 9‐year‐old boys (n= 10). The relative magnitude of the activation of the slow soleus (SOL) and the relatively fist medial gastrocnemius (MG) muscle was measured during various postures and hopping tasks on a force plate. In addition, the myo‐electric activity was quantificd in three different phases of the stretchbshortening cycles during hopping. Major differences between boys and adults were observed in the postul‐al tasks, where the boys appeared to utilize the MG to a relatively larger extent. During maximal height hopping there was a clearly larger potentiation of the MG activity in the adults, particularly in the eccentric phase. On the other hand, there were striking similarities between boqs and adults aith respect to the degree of pre‐activation of both muscles during the different hopping regimes as Hell as potentiation of muscle activity during the concentric phase ot maximal height hopping. Thus, sonic aspects of the selectivc ncural control of the ankle extenson muscles appear to be manifested in pre‐pubertal boys. However, the data also indicate that other factors, such as utilization of stored elastic energy in the muscles and stretch reflex potentiation, will still continue to develop from the age of nine.
Hypothalamic inhibition of duodenal alkaline secretion via a sympatho‐adrenergic mechanism in the rat
Authors: FÄNDRIKS L. , JONSON C. , LISANDER B.
Published: December 2008

Experiments were performed on rats anaesthetized with chloralose. A duodenal segment was perfused with recirculating isotonic saline, and alkalinization of this perfusate (HCO‐3secretion) was measured by continuous pH‐stat titration. Stereotaxic electric unipolar stimulations were performed in the perifornical region of the hypothalamus. Stimulation points eliciting an increased arterial pressure were stimulated for a period of 15 min. Duodenal HCO‐3secretion decreased in 19 out of 25 experiments and increased in four out of 25 experiments. Inhibitory responses to hypothalamic stimulation were blocked either by thoracic epidural anaesthesia or by the adrenolytic agent guanethidine, suggesting a spinal pathway to the duodenum, presumably in the thoracic splanchnic nerves, and involvement of adrenergic neurons.
Effects of pre‐junctional a‐receptor blockade on vascular neuro‐effector characteristics in rats on high sodium intake
Authors: SJÖRLOM‐WIDFELDT N. , NILSSON H. , GUSTAFSSON H. , ELY D. L. , FOLKOW R.
Published: December 2008

Various in‐vitro studies have indicated a direct attenuating effect of sodium on the affinity of adrenergic α2‐receptors. It has been suggested that ingested sodium in this way might increase blood pressure by reducing the activity of central α2‐receptors and therebl‐ increasing sympathetic discharge. However, such an effect of sodium would also impair the function of peripheral α2‐receptors. In the present study ne have therefore investigated the effect of high sodium intake on the a,‐receptor‐mediated inhibition of the vascular neurogenic response.

Male Wistar rats were given 2% NaCl in their drinking water from 4 to 9 weeks of age. Another group receiving plain tap water served as controls. Segments of small branches from the mesenteric artery were mounted in a myograph. Responses to transmural nerve stimulation were determined before and after α2‐receptor blockade with either yohimbine or idazoxan.

The response to a continuous nerve stimulation that elicited 30% of maximal contraction was increased 2–3 times after addition of either idazoxan (0.1 μm) or yohimbine (0.3 μm), with no significant difference between sodium‐treated and control rats; if anything the enhancement was slightly greater in the sodium‐treated group. Also, responses to intermittent burst stimulation were increased from 30 to about 80% of maximal response in both rat groups.

The results thus indicate that high sodium intake does not affect the inhibitory influence of pre‐junctional α2‐receptors on the vascular neurogenic response.
Electrophysiological characteristics of the Necturus proximal duodenal mucosa: effects of ion substitutions
Authors: BRIDÉN S.
Published: December 2008

Voltage‐sensitive glass micro‐electrodes were used to determine the electrical characteristics of Necturus proximal duodenal epithelium. Some comparative experiments with amiloride were performed with gastric antrum. The apical and the basolateral cell membrane potential differences in duodenum averaged ‐32 mV and ‐34 mV (cell negative) respectively. The transepithelial potential difference was ‐2 mV (lumen negative). The EMF across the apical cell membrane was ‐29 mV and that across the basolateral cell membrane ‐39 mV. The transepithelial resistance (R1) of 63 Ω cm2 and the paracellular pathway resistance (Rs) of 8o Ω cm2 are of magnitudes similar to that previously reported for more distal amphibian small intestine. The apical and basolateral cell membrane resistances, however, were lower than those reported for distal small intestine. Ion permeabilities for Na+, K+ and Cl‐ across the apical cell membrane were calculated from ion substitution experiments. The permeability sequence across the apical cell membrane was PK:Pcl:PNa 3.02:1.31:1.00. Luminal amiloride (10‐4 M) was without significant effect, further indicating a low duodenal membrane conductance for Na+. The low conductances for K+, Na+ and Cl‐ suggest that the major ion transport modes across the apical duodenal cell membrane are electroneutral in nature. In contrast, amiloride caused a marked increase in the transmembrane potentials in the antrum.
Characterization of the actions of botulinum neurotoxin type E at the rat neuromuscular junction
Authors: MOLGÓ J. , DASGUPTA B. R. , THESLEFF S.
Published: December 2008

Botulinum neurotoxin (BoTx) serotype E blocks spontaneous and evoked quanta! release of acetylcholine at the rat neuromuscular junction. Increasing extracellular Ca2+ to 8 mmol l‐1 or substituting Ca2+ with La3+ (0.1 and 1.0 mmol l‐1) or depolarizing the nerve terminals by 20 mmol l‐1 K+ markedly increases miniature end‐plate potential frequency in normal muscle, but in BoTx‐E poisoned preparations none of these ions, with the exception of 1 mmol l‐1 La3+, was able to restore spontaneous quantal transmitter release to levels recorded at unpoisoned junctions. In absolute values the enhancement with La3+ was much less than that reported at normal junctions.

Nerve stimulation in the presence of 3,4–diaminopyridine (10–20 μmol l‐1) and high calcium (8 mmol l‐1) evoked multiquantal end‐plate potentials and muscle twitches. We conclude that the neuromuscular block produced by BoTx serotype E is similar to that previously described for BoTx serotype A but differs from that produced by BoTx serotypes B, D and F in not causing desynchronization of nerve impulse‐evoked transmitter release. 3,4–Diaminopyridine might be useful in the treatment of poisoning by BoTx serotype E since it markedly enhanced synchronous transmitter release from poisoned motor nerve terminals.
Influence of mild sodium depletion upon peripheral and centrally mediated effects of intravenous angiotensin II in the goat
Authors: JUNKERGÅRD J.
Published: December 2008

Previous evidence for cerebral sodium/angiotensin interaction concerning centrally mediated effects of angiotensin II (All) provided the incitement to compare in goats effects of i. v. All during sodium repletion (SR) with those obtained during mild sodium depeletion (SD). The experiments were performed in the euhydrated as well as hyperhydrated animals, and All was infused for 10 min at 40 pmol kg‐1 min‐1. It was confirmed that SD is associated with elevated plasma aldosterone concentration (PA) and (as regards aldosterone secretion) a sensitization of the adrenal cortex. In contrast to PA, the plasma Cortisol (PC) response to i. v. All was significantly reduced during SD, apparently due to diminished cerebral sensitivity to circulating AIL A similar SD‐associated attenuation was observed during euhydration as regards release of arginine vasopressin (AVP) in response to i. v. All, and during hyperhydration as regards the antidiuretic effect of the octapeptide. It was confirmed that the pressor effect of i. v. All becomes markedly reduced during SD. However, in spite of this, the associated bradycardia remained the same during SR and SD, suggesting that SD also attenuated the centrally mediated chronotropic effect of All.
Water intake and changes in plasma and CSF composition in response to acute administration of hypertonic NaCI and water deprivation in sheep
Authors: RUNDGREN M. , JONASSON H. , HJELMQVIST H.
Published: December 2008

Water intake and changes in plasma and cerebrospinal fluid (CSF) composition were measured in response to intracerebroventricular (i. e.v.) and intracarotid infusions of hypertonic NaCI solutions and after 48 h of water deprivation in sheep. Significant interindividual differences in dipsogenic sensitivity to i. e.v. NaCI were found, whereas no such differences were observed in response to intracarotid infusion of hypertonic NaCI. In the more sensitive animals, the increase in CSF [Na] at initiation of drinking during i. e.v. infusion did not differ significantly from the increase in plasma [Na] seen at the thirst threshold during intracarotid infusion of 1 M NaCI. The thirst‐eliciting infusions of hypertonic NaCI into the carotid arteries were associated with a small, significant, increase in CSF [Na], which however did not differ from that caused by an i. e. v. non‐dipsogenic ‘control’ infusion of a slightly hypertonic (0.154 M) NaCI solution. Water deprivation for 48 h induced increases in CSF and plasma [Na] similar to those observed at the onset of drinking in response to i. e.v. and intracarotid infusions of hypertonic NaCI. However, the dehydrated animals drank about four times the amount of water consumed in response to the separate treatments with hypertonic NaCI.

It is concluded that significant interindividual differences in dipsogenic sensitivity to osmotic stimuli are present in sheep, and that these differences may not necessarily be simultaneously expressed on both sides of the blood‐brain barrier.

The thirst‐eliciting effect of intravascular infusion of hypertonic NaCI may be induced without concomitant increase in CSF [Na] and/or osmolality.

A simultaneous increase in CSF and plasma [Na] and/or osmolality is suggested to contribute to the conspicuous water consumption seen in response to dehydration compared to that caused by acute administration of hypertonic NaCl.
Differences in cardiorespiratory responses during and after arm crank and cycle exercise
Authors: LOUHEVAARA V. , SOVIJÄRVI A. , ILMARINEN J. , TERÄSLINNA P.
Published: December 2008

The differences in cardiorespiratory responses were examined during and after intermittent progressive maximal arm‐crank and cycle exercise. Arm‐crank exercise was performed in a standing position using no torso restraints to maximize the amount of active skeletal muscle mass. Recovery was followed for 16 min. In the tests a variety of ventilatory gas exchange variables, heart rate, the blood pressure, and the arm venous blood lactate concentration were measured in 21 untrained healthy men aged 24–45 years. At equal submaximal external workloads for arm cranking and cycling (50 and 100 W) the respiratory frequency, tidal volume, pulmonary ventilation, oxygen uptake, carbon dioxide output, the respiratory exchange ratio, heart rate, the arm venous blood lactate concentration, and the ventilatory equivalent for oxygen were higher (P < 0.001) during arm cranking than cycling. The maximal workload for arm cranking was 44% lower than that for cycling (155 ±37 vs 277 ± 39 W, P < 0.001) associated with significantly (P < 0.001) lower maximal tidal volume (‐20 %), oxygen uptake (‐22 %), carbon dioxide output (‐28%), systolic blood pressure (‐17%) and oxygen pulse (‐22%) but a higher ventilatory equivalent for carbon dioxide (+ 22%) and arm venous blood lactate concentration (+ 37%). However, these responses after arm‐crank and cycle exercises behaved almost similarly during recovery. The high cardiorespiratory stress induced by arm work should be taken into account when the work stress and work‐rest regimens in actual manual tasks are assessed, and when arm work is used for clinical testing, and in physiotherapy particularly for patients with heart or pulmonary diseases.
Hypothalamic LHRH concentration decreases in intact but increases in castrated rats in constant light
Authors: PORKKA‐HEISKANEN T.
Published: December 2008

In order to evaluate the effects of environmental lighting on the hypothalamic secretion of luteinizing hormone‐releasing hormone (LHRH), intact and castrated male Wistar rats were kept either in periodic (LD) or in constant light (LL) for 1 week, and the hypothalamic LHRH concentration was measured by radioimmunoassay. In the intact rats the LHRH concentration was lower in constant than in periodic light (30 ± 3 vs 61 ± 3 pg mg‐1, P < 0.05), whereas in the castrated rats it was higher (16 ± 2 is 5 ± 1 pg mg‐1, P < 0.05). The intact and castrated rats Receivedmelatonin (50 μg) or saline injections daily at either 09.00 h or 16.00 h in LD and LL for 1 week. In intact or castrated rats the melatonin injections were not able to prevent the change of hypothalamic LHRH in constant light. In castrated rats testosterone (125 or 250 μg) had no effect on the LHRH concentration under either lighting condition. The present results suggest that constant light reduces the synthesis of hypothalamic LHRH in intact rats but increases it in castrated rats. These effects of constant light do not appear to be related to melatonin.