bluuebunny/crossref_metadata_2025 huggingface dataset:
Block of potassium outward currents in the crayfish stretch receptor neurons by 4‐aminopyridine, tetraethylammonium chloride and some other chemical substances
Authors: PURALI N. , RYDQVIST B.
Published: December 2008

The effects of 4‐aminopyridine (4‐AP) and tetraethylammonium (TEA) on the outward potassium currents in the rapidly and slowly adapting stretch receptor neurons (SRNs) of the crayfish (Pacifastacus leniusculus) were studied using a two micro‐electrode voltage‐clamp technique. The leakage current was not affected by either 4‐AP or TEA. External 4‐AP blocked the peak outward current in a dose‐dependent manner (1:1 stoichiometry) with an apparent dissociation constant (Kd) of 2.3 ± 0.2 mm (mean ± SEM) in the slowly and 1.4 ± 0.2 mm in the rapidly adapting SRN, the block being voltage dependent. External application of TEA resulted in a block of the steady state current enhancing the transient characteristics of the current response. The block appeared to deviate from a 1: 1 stoichiometry and the apparent Kd for TEA was 9.6 ± 3.4 mm with a cooperativity factor n= 0.43 ± 0.03 in the slowly adapting SRN and 34.5 ± 9.2 mm and 0.37 ± 0.03 respectively in the rapidly adapting SRN. Low Ca2+, apamin and charybdotoxin, which are known to block Ca2+‐dependent K‐currents, had no effects on the outward current as was also the case with catechol.

It is concluded that the different effects of TEA and 4‐AP on the outward current in the two types of SRNs can be explained by the presence of at least two, probably heteromultimeric, channel populations having similar sensitivity to 4‐AP but different sensitivity to TEA. One channel has a high affinity (Kd= 0.8–1.6 mm) for TEA and the other a low affinity (Kd= 173–213 mm) for TEA. The low‐affinity channel seems to dominate in the slowly adapting SRN while both channels are equally common in the rapidly adapting SRN. Further, the present results do not support the existence of a macroscopic Ca2+‐dependent K+ current in the SRNs.
Protein kinase C activity in rat renal proximal tubule cells
Authors: MENDEZ C. F. , HANSSON A. , SKOGLUND G. , INGELMAN‐SUNDBERG M. , APERIA A.
Published: December 2008

The presence of protein kinase C (PKC) in proximal tubule cells of the rat kidney is established by means of immunodetection and by the demonstration of calcium‐and phospholipid‐dependent, staurosporine‐inhibitable histone phosphorylation. The calcium‐dependence of renal PKC is described. Maximal activation of the enzyme (178.2 and 258.8 pmol P1 mg‐1 min‐1 for cytosol and membrane respectively) was achieved with 5 μM of Ca2+. Phorbol 12,13 dibutyrate (PDBu) translocated PKC from cytosol to membrane in a dose‐ and time‐dependent fashion, while 4α‐phorbol 12,13‐didecanoate produced no significant effect on translocation. Cytosolic PKC activity was compared in immature and mature tissues (10‐ and 40‐day‐old kidneys). Basal activity was found to be significantly higher (P < 0.05) in immature cells (272.8 vs. 157.5 pmol P, mg‐1 min‐1). PDBu at 10‐6 M for 15 min reduced immunoreactivity in the soluble fraction of both groups, which was accompanied by a significant decrease in kinase activity. We speculate that the high PKC activity in the infant kidney plays a role in cell growth.
Polyamines in nerve terminals and secretory granules isolated from neurohypophyses
Authors: KRØIGAARD M. , THAMS P. , THORN N. A.
Published: December 2008

In isolated nerve terminals from ox neurohypophyses the following concentrations of polyamines [pmol (μg protein)‐1 (mean ± SEM)] were found: spermine: 2.07 ± 0.14 (n = 3), spermidine: 0.22 ± 0.01 (n = 4), putrescine: 0.20 ± 0.01 (n = 4).

In secretory granules isolated from the same tissue, the concentrations were: spermine: 0.57 ± 0.02 (n = 3), spermidine: 0.07 ± 0.04 (n = 3), putrescine: 0.13 ± 0.04 (n = 3).

After incubation of isolated nerve terminals with the polyamines, they were taken up as a function of time and concentration, approaching saturation at high concentrations.

The kinetic parameters of their synthesizing enzyme, ornithine decarboxylase, in ox neurohypophyseal nerve terminals (apparent Km 0.75 mm and Vmax 22.5 pmol mg protein‐1 h‐1) were comparable to those previously found in cerebral cortex of rats.

When isolated, hemilobes from rat neurohypophyses were incubated in a medium which contained spermidine (5 mM), and were stimulated by 56 mrs K+, release of vasopressin was smaller than in control experiments. However, after removal of spermidine and after restimulation, 50 min after initial stimulation, the release was significantly elevated.

It is suggested that polyamines may take part in modulation of vasopressin release.
Neuro‐effector characteristics of sweat glands in the human hand activated by irregular stimuli
Authors: KUNIMOTO M. , KIRNÖ K. , ELAM M. , KARLSSON T. , WALLIN B. G.
Published: December 2008

Intraneural electrical stimulation of cutaneous fascicles in the median nerve was performed in 24 normal subjects and the effects on sweating within the innervation zone were monitored as changes of skin resistance and water vapour partial pressure (wvpp). The aims were: (1) to investigate the response variability between repeated stimulation sequences in the same skin site and between different sites and (2) to compare quantitative effects of regular and irregular stimulation on skin resistance and wvpp. Regional axillary anaesthesia of the brachial plexus eliminated spontaneous and reflex sympathetic activity.

With repeated irregular stimulation sequences skin resistance responses from the same skin site varied only slightly between trials. Differences between response curves from two skin sites in the same subject or from different subjects were also small but significantly greater (P < 0.01) than differences between responses to repeated stimulation in the same site.

Irregular stimulation with average frequencies of 0.49 Hz and 3.51 Hz gave greater resistance responses than if the same number of stimuli were delivered regularly (P < 0.01). The difference was most pronounced at 0.49 Hz.

At an average frequency of 0.49 Hz the stimulation usually evoked no changes of wvpp whereas an average frequency of 3.51 Hz caused an increase of wvpp which was greater with irregular than with regular stimulation in all subjects.

We conclude that: (1) sweat responses to sudomotor nerve traffic vary slightly due to local factors in the skin or the terminal nerve endings and (2) irregular sudomotor nerve traffic evokes more sweat than if the same impulses occur regularly.
Effect of branched‐chain amino acid supplementation on the exercise‐induced change in aromatic amino acid concentration in human muscle
Authors: BLOMSTRAND E. , NEWSHOLME E. A.
Published: December 2008

A mixture of the three branched‐chain amino acids (BCAAs) was supplied to subjects during two types of sustained intense exercise, a 30 km cross‐country race and a full marathon, and the effect on plasma and muscle concentrations of aromatic and BCCAs was studied. When BCAAs (7.5–12 g) were taken during exercise, the plasma and muscle (vastus lateralis) concentration of these amino acids increased, while in the placebo groups the concentration of BCAAs decreased in the plasma and remained unchanged in the muscle. In the placebo group, both types of exercise caused a 20–40% increase in the muscle concentration of the aromatic amino acids, tyrosine and phenylalanine, and the plasma concentration of these amino acids was increased after the marathon. Since tyrosine and phenylalanine are neither taken up nor metabolized by skeletal muscle, the increases in their concentrations in muscle might indicate net protein degradation during exercise. However, when the subjects were supplied with BCAAs during exercise, the increases in tyrosine and phenylalanine concentrations in both muscle and plasma were prevented. These results suggest that an intake of BCAAs during exercise can prevent or decrease the net rate of protein degradation caused by heavy exercise.
Large capillary fluid permeability in skeletal muscle and skin of man as a basis for rapid beneficial fluid transfer between tissue and blood
Authors: LÄNNE T. , EDFELDT H. , QUITTENBAUM S. , LUNDVALL J.
Published: December 2008

Our previous studies strongly indicate that the capillary filtration coefficient (CFC) in skeletal muscle and skin of man is much larger than previously believed, or about 0.050 ml min‐1 100 ml‐1 mmHg‐1. The hypothesis that this large capillary fluid permeability is a factor of primary importance for plasma volume control was approached. Experimental hypovolaemia induced by lower body negative pressure (Lbnp of 70–95 cmH2O) was associated with a rapid net fluid gain from the studied upper arm into the circulation of 0.17 ml min‐1 100 ml‐1 tissue. The transcapillary driving force for this fluid transfer, probably caused by adrenergic adjustment of vascular resistance, with a decline of capillary pressure, was relatively small, or 1.7 mmHg on average. CFC was instead very high during LBNP, increasing from a control value of 0.054±0.004 (SE) to no less than 0.097±0.007 ml min‐1 100 ml‐1 mmHg‐1, probably reflecting an increased number of effectively perfused capillaries. It is suggested that the large capillary fluid permeability in skeletal muscle and skin of man, with large tissue mass and fluid reservoir, may be of great functional importance for plasma volume control after blood loss and also in other (patho)physiological situations. As demonstrated, it can thus permit rapid transfer of large fluid volumes into the circulation and, perhaps of special importance, with only small transcapillary driving force (capillary pressure decline). If capillary permeability were to be more limited, reasonably rapid fluid transfer instead might have required pronounced and, for tissue nutrition, necessarily undue adjustments of vascular resistance in order to cause more marked decline in capillary pressure.
Evidence for long‐term fluctuations in regional blood flow within the rabbit left ventricle
Authors: IVERSEN P.O.
Published: December 2008

The regional distribution of coronary perfusion within the left ventricle is markedly heterogenous. The perfusion pattern is composed of both spatial and temporal variations in perfusion among single myocardial samples. Previous investigators have mostly studied short‐term (< 1 min) temporal variability. The aim of this study was to quantify long‐term fluctuations in perfusion to single samples within the rabbit left ventricle.

Coronary perfusion was estimated from the deposition of microspheres in myocardial samples (range 32–96 mg). Two batches of microspheres were infused either simultaneously or sequentially over specified periods of time. The paired values for regional perfusion were compared and Kendalls correlation coefficient (T) calculated. The assumption being that the lower T, the higher degree of temporal perfusion variability was present.

The T for paired values of regional myocardial perfusion based on two sequential infusions lasting either 10 s, 5, 10 or 30 min, averaged 0.40, 0.55, 0.80 and 0.80, respectively. No difference was detected between awake and anaesthetized animals. The T for two simultaneous infusions averaged 0.95 irrespective of the duration of the infusion, indicating negligible methodological error. The coefficient of variation for spatial perfusion heterogeneity ranged from 0.3 to 0.4 irrespective of the infusion duration.

The findings suggest that regional coronary vasomotion is characterized by a wide range of cycle times, some of which have cycle times of more than 30‐min duration. Although part of the regional perfusion heterogeneity was due to long‐term fluctuations in perfusion, temporal variations with cycle times less than 5 and 10 min, respectively, were more prominent.
Pain‐induced inhibition of gastric motility is mediated by adrenergic and vagal non‐adrenergic reflexes in the rat
Authors: BOJÖ L. , CASSUTO J. , NELLGÅRD P.
Published: December 2008

Painful stimuli have been shown to inhibit gastric motility in animal experiments and delay gastric emptying in humans. The aim of the present study was to investigate in detail mechanisms involved in pain‐induced gastric inhibition.

Pain stimulation by exerting pressure on a testicle induced a prompt gastric relaxation which lasted throughout the period of stimulation. Pain‐induced gastric relaxation was significantly reduced by the selective α‐1 blocker, prazosin, and by the non‐selective β‐blocker, propranolol. Similarly pain‐induced inhibition of gastric tone was significantly reduced by bilateral cervical vagotomy. In contrast, gastric relaxation following pain stimulation was significantly potentiated by the selective adrenergic α‐2 blocker, yohimbine. Combined administration of prazosin and propranol followed by bilateral cervical vagotomy abolished gastric relaxation in response to pain stimulation.

In conclusion, gastric relaxation in response to painful stimulation was found to be reflex‐mediated via sympathetic neurons acting on α‐1 and β receptors and possibly also via vagal non‐adrenergic fibres. Pain‐induced inhibition of gastric tone was significantly increased by yohimbine. It is suggested that yohimbine by blocking presynaptic inhibitory receptors on adrenergic neurons facilitates the release of noradrenaline in response to pain stimulation.
Effects of autonomic reflexes on tooth pulp blood flow in man
Authors: AARS H. , GAZELIUS B. , EDWALL L. , OLGART L.
Published: December 2008

In 15 subjects, laser‐Doppler flowmetry (LDF) was used to investigate whether the nervous control of pulpal blood flow (PBF) is affected by three tests known to excite the sympathetic nervous system. For comparison, skin blood flow was similarly recorded. Dynamic exercise (bicycle ergometer, 5 min, 90–100 W) in eight subjects was accompanied by a rise in PBF. PBF was increased by the cold pressor test (2 min) in eight subjects, while in five the flow decreased or remained unaffected. The isometric hand grip (2 min, 30% MVC) and the subsequent muscle ischaemia (2 min) led to a rise in PBF in two subjects and a fall in four. Following unilateral anaesthesia of the mandibular nerve, PBF in five subjects became unresponsive to dynamic exercise or the cold pressor test, indicating pressure autoregulation. All three tests triggered increases in mean arterial pressure (MAP) and heart rate (HR). Skin blood flow usually increased in response to the tests, but could also decrease, and often changed in a direction opposite to that of PBF. It is concluded that the circulation of blood in the human tooth is affected by evoked changes in autonomic nerve activity, involving activation of both vasodilator and vasoconstrictor nerves to vessels serving the tooth.
The role of purinergic neurotransmission in various cardiovascular reflexes
Authors: TARASOVA O. S. , RODIONOV I. M.
Published: December 2008

In urethane‐anaesthetized rats the effects of α‐adrenoceptor antagonists and desensitization of P2‐purinoceptors with α,β‐methylene ATP on the pressor reflex responses were investigated. Pressor responses were elicited by electrical stimulation of the central end of the sciatic nerve, by asphyxia and by occlusion of the common carotid artery. Responses to sciatic nerve stimulation and to asphyxia, but not those to carotid artery occlusion were entirely suppressed by dihydroergotamine and phentolamine. Under the action of dihydroergotamine the sinocarotid reflex decreased by over 70% in 40% of the experiments. In 60% of experiments the response was only slightly reduced or even augmented, but it was entirely inhibited by subsequent desensitization with α,β‐methylene ATP.

The magnitude of response to sciatic nerve stimulation was almost unaffected by α,β‐imethylene ATP, while the response to carotid occlusion was decreased by 40–50%. The recovery of purinoceptor sensitivity to α,β‐methylene ATP was accompanied by restoration of the sinocarotid reflex.

It is suggested that purinergic neurotransmission plays a considerable role in the pressor sinocarotid reflex, while in the pressor response to stimulation of somatic afferents its role is negligible.
Regulation of glomerular angiotensin II receptor densities in renovascular hypertension: response to reduced sympathetic and vasopressin influence
Authors: SAHLGREN B. , EKLÖF A‐CH. , APERIA A.
Published: December 2008

The regulation of the density of angiotensin II receptors in renal glomeruli in response to changes in salt intake is altered in Sprague‐Dawley rats with renovascular hypertension due to aortic constriction, and in hypertensive salt‐sensitive Dahl rats (Sahlgren 1989, Sahlgren & Aperia 1989). This study examines the modulatory role of sympathetic activity and arginine‐vasopressin on angiotensin II receptors in hypertensive Sprague‐Dawley rats with aortic constriction as well as in normotensive control rats. Denervation of the left kidney caused a 50% increase in the glomerular angiotensin II receptor density in the denervated kidney in both hypertensive rats and normotensive controls. An even more marked increase in glomerular receptor density occurred in both hypertensive rats and controls after blocking the sympathetic nervous system with guanethidine. To block the effects of arginine‐vasopressin we used a blocker of the V1‐receptors (predominant in vessels) and found an approximately 100% increase in the glomerular receptor density of angiotensin II in rats with aortic constriction. There was no reduction in blood pressure. Thus, on the receptor level the renin‐angiotensin system is markedly influenced by the activity of other major pressor systems.
A technique for studies of the contractile apparatus in single human muscle fibre segments obtained by percutaneous biopsy
Authors: LARSSON L. , SALVIATI G.
Published: December 2008

Human muscle samples were obtained with the percutaneous biopsy technique. The samples were membrane‐hyperpermeabilized (skinned) using a chemical or freeze‐drying technique. Short single fibre segments were dissected from the sample, transferred to an experimental chamber, connected to a force transducer and manipulator, and exposed to temperature‐controlled solutions. The force generating‐capacity, the sensitivity of the contractile apparatus to calcium and the caffeine threshold for calcium release from the sarcoplasmic reticulum could be studied in the short muscle fibre segments obtained from man with the percutaneous muscle biopsy technique. The average length of the fibre segments between the connectors was 0.44±0.21 mm. Thus, detailed studies of the contractile machinery can be made on human skinned muscle fibres with only minimal discomfort to the patient or subject during biopsy, which should be useful in studies of neuromuscular disease, muscle plasticity or in applied physiology.
NMDA‐receptor blockers but not NBQX, an AMPA‐receptor antagonist, inhibit spreading depression in the rat brain
Authors: NELLGÅRD B. , WIELOCH T.
Published: December 2008

The effect of different glutamate‐receptor antagonists on the induction of cortical spreading depression of Leao and of cortical anoxic membrane depolarization were investigated in the anaesthetized rat. Spreading depression (SD), elicited by mechanical stimulation of the cortical surface, was inhibited by the non‐competitive N‐methyl‐d‐aspartate (NMDA)‐receptor blocker, (±)‐5‐methyl‐10,11‐dihydro‐SH‐dibenzo(a, d)‐cyclo‐hepten‐5,10‐imine maleate (dizocilpine or MK‐801), (0. 30 μmol kg‐1 (0. 10 mg kg ‐1)), and the competitive NMDA‐receptor antagonists; cis‐4‐phosphonomethyl‐2‐piperidine carboxylate (CGS 19755), (3.36 μmol kg‐1 (0.75 mg kg‐1)), d‐(E)‐2‐amino‐4‐methyl‐5‐phosphono‐3‐pentenoic acid (CGP 40116), (1.20 μmol kg‐1 (0.25 mg kg‐1)) and its carboxylester CGP 43487, (6.30 μmol kg‐1 (1.50 mg kg‐1)). The α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepripriate (AMPA)‐receptor blocker, 2,3‐dihydroxy‐6‐nitro‐7‐sulfamoyl‐benzo(F) quinoxaline (NBQX), administered as an intravenous dose of 29.76 and 89.29 μmol kg‐1 (10 & 30 mg kg‐1), which is sufficient to block seizures and protect against ischaemic brain damage, did not inhibit spreading depression. None of the drugs utilized inhibited the anoxic membrane depolarization. The data demonstrate that NMDA‐receptor activation is essential for the initiation and propagation of spreading depression, while activation of AMPA‐receptors is not obligatory. The observed initiation and propagation of SD, during AMPA‐receptor blockade, suggest that activation of voltage‐operated ion channels may contribute to release the magnesium block of the NMDA‐receptor operated channel and to the initiation of SD.
Activation of sympathetic nerves exerts an inhibitory influence on afferent nerve‐induced vasodilation unrelated to vasoconstriction in rat dental pulp
Authors: KEREZOUDIS N. P. , FUNATO A. , EDWALL L. , OLGART L.
Published: December 2008

In order to elucidate a possible influence of the sympathetic nervous system on afferent nerve function, rat mandibular incisors were electrically stimulated and blood flow changes monitored in the incisor pulp of untreated and sympathectomized animals by a laser Doppler flowmeter. Monopolar electrical stimulation of the tooth (200 μA, 5 ms, 40 Hz, 1 s) in normal animals resulted in a transient reduction in pulpal blood flow (PBF) (16%, reduction,n= 10) followed by a small but long‐lasting increase (11% increase). After administration of phenoxybenzamine or phentolamine (3 mg kg‐1, i.v.) the initial dip in PRF was reduced by 59% (P <0.001) while the subsequent increase was enhanced by 185% (P <0.001). Similarly, infusion of prazosin (50μg kg‐1, i.v.) and idazoxan (0.5 mg kg‐1i.v.) significantly enhanced the increase in PBF by 118 and by 79%, respectively. In chronically sympathectomized animals the increase in PBF was 250% larger than that seen in untreated animals (P <0.001). This increase in PBF was not further enhanced after α‐adrenergic blockade. Acute resection of the superior cervical sympathetic ganglion, also resulted in some enhancement (by 56%) of the stimulation‐induced increase in PBF (P <0.01,n =6). The increase in PBF was unaffected by infusion of timolol (150 μgkg‐1) and atropine (1 mg kg‐1) but was totally abolished by intravenous pre‐treatment with capsaicin (1–3 mg kg‐1). The present results suggest that activation of sympathetic nerves exerts inhibitory effects on the afferent nerve‐induced vasodilation in the rat incisor pulp unrelated to sympathetic vasoconstriction.
Local forearm and whole‐body respiratory quotient in humans after an oral glucose load: methodological problems
Authors: SIMONSEN L. , BÜLOW J. , MADSEN J. , HERMANSEN F. , ASTRUP A.
Published: December 2008

The effects of an oral glucose load of 75 g on the local forearm and whole‐body energy thermogenesis were measured in normal subjects during the 4 h after the glucose intake. Simultaneous assessment of substrate metabolism in the forearm was performed.

Energy expenditure (EE) increased after the glucose load and had not returned to baseline level at the end of the experiment. Whole‐body respiratory quotient (RQ) was, on average, 0.80 (SD 0.05) in the baseline condition and increased to a maximum of 0.91 (0.03) and then decreased to baseline level at the end of the experiment. The local forearm oxygen uptake increased 30 min after the glucose intake and remained elevated during the rest of the experiment. The carbon dioxide output from the forearm did not increase before 90 min after the glucose load. Consequently the local forearm RQ decreased significantly from a baseline value of 0.86 (0.17) to 0.63 (0.17) 30 min after the glucose load (P < 0.05). Ninety min after the glucose load RQ increased to a maximum level at 0.95 (0.22) and decreased then gradually to baseline level.

The experiments emphasize several methodological problems in the measurement of local forearm RQ The whole‐body RQ and local forearm RQ are not significantly different in the fasting state. The finding of a decrease in local forearm RQ below 0.70 30 min after the glucose load probably indicates a non‐steady state in the carbon dioxide exchange. Thus, indirect calorimetry cannot be applied locally during short time periods.
Regulation of glycogen synthase in human muscle during isometric contraction and recovery
Authors: YAN Z. , SPENCER M. K. , BECHTEL P. J. , KATZ A.
Published: December 2008

Six subjects performed isometric contraction (66% maximal force) to fatigue with the knee extensor muscles. Biopsies were taken from the quadriceps femoris muscle at rest, at fatigue and 1 min after termination of contraction. In three of the subjects recovery from contraction occurred in the presence of an intact circulation (non‐occluded, NON) to the thigh, whereas in the other three the circulation during recovery was occluded (OCC). Glycogen synthase fractional activity (GSF) decreased in all subjects from (mean±SE) 0.53 ± 0.06 at rest to 0.37 ± 0.04 at fatigue (P < 0.001). In the OCC group GSF returned to the pre‐exercise value within 1 min after termination of contraction (0.59 ± 0.07 at rest vs. 0.57 ± 0.04 at 1 min post‐exercise), whereas in the NON group GSF increased to a higher extent (0.48 ± 0.09 at rest vs. 0.70 ± 0.06 at 1 min post‐exercise). The increase in GSF during the 1‐min recovery was almost three‐fold higher in the NON group (0.15 ± 0.02 vs. 0.38 ± 0.03). Cyclic AMP‐dependent protein kinase (CAMP‐PK) (assayed at 0/100 μm and 0.2/100 μm cAMP) did not change at fatigue or during recovery in either group. Glycogen synthase phosphatase (GSP) increased at fatigue by ˜ 30% (P < 0.05 vs. rest). It is concluded that isometric contraction mediated inactivation of GS (i.e. phosphorylation of GS) is due to activation of a protein kinase(s) but not cAMP‐PK. The rapid activation of GS in the NON group demonstrates that a humoral factor(s), possibly insulin and/or oxygen, is responsible for this phenomenon.
Changes in the ovarian intermediate filament desmin during the luteal phase of the adult pseudopregnant rat
Authors: SELSTAM G. , NILSSON I. , MATTSSON M.‐O.
Published: December 2008

The occurrence of the intermediate filament desmin in ovary and corpus luteum of pseudopregnant rats was studied using Western blot analysis and immunohisto‐chemistry. The luteal phase was induced by mating with vasectomized male rats and ovaries were studied after 6, 11 and 19 days. The findings from the Western blot analysis showed that desmin was present in the corpus luteum. Immunohistochemical localization of desmin showed two types of localization in the corpus luteum. The arteries around the corpus luteum, as well as arteries elsewhere in the ovary, had a high content of desmin in their muscle layer. Dispersed in the corpus luteum was an immunohistochemical staining of desmin that was localized mainly adjacent to the luteal cells. In the other part of the ovary a weak staining was registered in the theca layer, no staining in the granulosa layer and a streaky staining in the hilar region of the ovary.

Desmin filaments are found in muscle cells of all types, including vascular smooth muscle cells. Probably, all desmin in the ovary is localized to smooth muscle cells with the possible exception of the corpus luteum where very few muscle cells have been identified. Localization to other vascular cells as endothelial is possible. In this study we found an increase in desmin content in the corpus luteum after day 6. If desmin is related to vascular resistance, our finding is consistent with the decrease in blood flow that occurs after day 6.
Association of breathing movements to the variability of heart rate and blood pressure in foetal lambs
Authors: METSÄLÄ T. , SIIMES A. , ANTILA K. , VÄLIMÄKI I.
Published: December 2008

Heart rate (HR) variability and arterial blood pressure (BP) variability were analysed as functions of foetal breathing movements (FBMs) by means of power spectral analysis in seven foetal lambs during the third trimester of gestation. No evidence of FBM‐related changes, either in mean HR, mean systolic or diastolic arterial pressures, were found. Mean arterial pulse pressure, HR variability, and BP variability increased during FBMs. The increase in BP variability occurred at frequencies higher than 0.35 Hz, i.e. those of FBMs. The increase in HR variability occurred at 0.07‐1.0 Hz, i.e. at every frequency band except the lowest one. Thus, the increase in HR variability was not frequency‐specifically related to FBMs. During FBMs the periodic variability of HR at frequencies > 0.35 Hz was only 10% of total HR variability. We suggest that the FBM‐related changes of BP variability may be mediated by direct peripheral, hydraulic mechanisms. HR changes involve autonomic control systems: the vagal component of baroreflex seems to be relatively insensitive, whereas the very slow vasomotor component of HR variability is dominant.
Gross efficiency of muscular work during step exercise at ‐15°C and 21 °C
Authors: OKSA J. , RINTAMÄKI H. , HASSI J. , RISSANEN S.
Published: December 2008

In an effort to assess the effect of ambient temperature on the gross efficiency (Effg) of step exercise 12 subjects performed a modified step test either at —15 °C or 21°C ascending to three different heights (corresponding to light, moderate and heavy work), for 20 min each with a frequency of 18 steps min‐1. Heart rate (HR), rectal temperature, skin temperatures and heat flux from skin were continuously measured. Oxygen consumption was measured during the last 5 min of each step height and perceptions of thermal sensation were recorded. The results indicate that, while using conventional clothing adequate in these temperatures, Effg is altered in a contradictory manner. At —15°C Effg increased with increasing work load, whereas at 21°C it decreased when the work load increased. The highest Effg (heavy work at —15°C and light work at 21°C) values are reflected as rather similar rectal temperatures (37.4–37.7°C) and identical mean skin temperatures (32.8 °C) as well as the same (slightly warm) thermal sensation of the legs. At — 15 °C the lowest Effg in light work was probably hue to the need to warm up the muscles. At 21°C, on the contrary, the activation of heat dissipation systems was probably responsible for the lowest Effg in heavy work.
Relationship between blood buffering properties, erythrocyte pH and water content, in gray seals (Halichoerus grypus)
Authors: BOUTILIER R. G. , NIKINMAA M. , TUFTS B. L.
Published: December 2008

The separated plasma of gray seals (Halichoerus grypus) has an unusually high non‐bicarbonate buffering capacity (βNB = d[HCO‐3]/dpH = — 21 Slykes; Slyke = mmol 1‐1 pH unit‐1). To examine whether this represents a trait of mammalian carnivora, or is related instead to deep diving, we examined blood from dog and killer whale, respectively. The bTnb of separated plasma of dog was typically low (— 4 to — 8 Slykes), as in other mammals, whereas that of the whale (—13.5 Slykes), while significantly higher than dog, was not nearly as high as in seal. As one would theoretically predict of a blood system with exceptionally high extracellular buffering and functional anion exchange across the erythrocyte membrane, there was little difference in the buffer slope between true plasma and whole blood of seal. This appears to be a novel pattern of CO2 carriage in mammals. Erythrocyte ion concentrations were similar to other mammalian carnivora, with intracellular sodium concentration being high and potassium low. The red cell water content was unaffected by changes in oxygen saturation and tended to decrease when extracellular pH decreased below 7.4. Apart from the comparatively elevated Bohr factor, —0.518 as a function of extracellular pH and —0.550 as a function of red blood cell pH, the blood oxygen binding properties were similar to terrestrial mammals of similar size.
Selective brain cooling in resting and exercising Norwegian reindeer (Rangifer tarandus tarandus)
Authors: KUHNEN G. , MERCER J. B.
Published: December 2008

The threshold body core temperature for selective brain cooling (SBC) as well as the slope of brain cooling were determined in three Norwegian reindeer (Rangifer tarandus tarandus) during rest and during exercise. Brain temperature was measured in the hypothalamus (Thypo) and blood temperature (Tblood) was measured either in the right carotid artery or in a few cases in the right atrium of the heart. During rest the animals were subjected to ramp‐like increases of Tblood by means of a thermostatically controlled water circulated heat exchanger (HE) introduced into the rumen via a chronically implanted rumen cannula. During exercise the animals ran on a treadmill at a speed of between 5.5–8.0 km hr‐1 and a slope of 13.5° for periods of 30–60 min. The elevation of Tblood during both rest and exercise resulted in significant amounts of SBC. The mean threshold for SBC (Thypo= Tblood) during rest was 38.7°C. The threshold for SBC was elevated significantly to 39.5°C during exercise. The mean slope of SBC (increase of SBC per degree increase of Tblood) was 0.82 both during rest and exercise.
Charge density of renal interstitium
Authors: ÖJTEG G. , WOLGAST M.
Published: December 2008

The charge density of renal interstitium was analysed from the volume of distribution of negative native albumin as compared with neutralized albumin, labelled with 125I and 131 I, respectively. The experiments were conducted by infusing the two probes intravenously at a rate which kept the plasma concentrations stable. The concentration in renal hilar lymph, Clymph(t), will then obey the function Clymph(t) = Clymph(tx) (1‐exp—Kt), where Clymph(tx) is the steady state Concentration and K the time constant for passage of the tracer through the renal interstitium ‐ the former is dependent on the permeability of the peritubular capillary membrane, whereas the time constant is inversely related to the interstitial distribution volume of the tracers. The lymph‐to‐plasma concentration ratio (L/P‐ratio) of negative, native albumin was found to be lower than that of neutralized albumin, a finding suggesting that the peritubular capillary membrane is negatively charged. Regarding the interstitium, it was calculated from the respective time constants, K, that the interstitium/lymph concentration ratio of negative native albumin was 0.96 ± 0.06 of that of neutralized albumin. This suggests the presence of negative fixed charges repelling negative native albumin. However, since the calculated charge density of — 1.8 ± 1.2 mEq 1‐‐1 was not significantly different from zero, it is concluded that the renal interstitium is uncharged. This does not, however, rule out the possibility that, for example, negative groups are fixed to the interstitial matrix, merely that the average fixed charge density of renal interstitial fluid is negligible.
Intravenous saline infusion in rat increases hyaluronan efflux in intestinal lymph by increasing lymph flow
Authors: ØSTGAARD G. , REED R. K.
Published: December 2008

The output of hyaluronan in mesenteric lymph was studied in anaesthetized rats to allow estimation of the turnover rate. The duodenum/jejunum contained 45 ,μg of this glycosaminoglycan per g wet tissue weight. In fasted rats the concentration of hyaluronan in postnodal lymph averaged 15 μg ml‐1 and the mean efflux was 2.1 μg h‐1, corresponding to a daily removal of 10% of the intestinal hyaluronan content. An intravenously injected bolus of 0.9% saline 4 ml 100 g‐1 followed by an infusion of the same amount per hour increased the hyaluronan concentration in lymph transiently to 22 μg ml‐1. During the 8‐h i.v. infusion the hyaluronan output remained five times above control due to the high lymph flow. Water and hyaluronan content of the small intestine remained unaltered despite the saline load, the maintained tissue level of hyaluronan suggests an increased rate of synthesis.
Energy turnover and lactate dehydrogenase activity in detrusor smooth muscle from rats with streptozotocin‐induced diabetes
Authors: ARNER A. , MALMQVIST U. , ÖSTERMAN Å. , UVELIUS B.
Published: December 2008

Force generation and tissue glucose metabolism were measured in the urinary bladder smooth muscle from rats with streptozotocin‐induced diabetes (7–8 wk duration). Bladder wet wt was almost 4–fold higher in the diabetic animals compared with the untreated controls. Morphological analysis showed that the growth was associated with hypertrophy of the smooth muscle component in the bladder wall. Force generation of isolated bladder strip preparations was measured in vitro at different ambient oxygen tensions. Activation of intramural nerves, with electrical field stimulation, induced contractions that were unaffected by reduction of oxygen tension down to Po2 100 mmHg for both control and diabetic muscle strips. At zero Po2 force was reduced by approximately 10–20% in both groups. High‐K+ solution induced ‘tonic’ contractions that were slightly more inhibited by lowering Po2. At intermediate Po2 (between 100 and 20 mmHg) the diabetic muscle gave slightly higher force. At zero Po2 no significant difference could be detected between strips from control and diabetic animals. Oxygen consumption and lactate production in the preparations were determined at a Po2 of 290 mmHg and related to the volume of smooth muscle. At zero Po2 lactate formation increased 3‐ to 4‐fold. The metabolic tension cost was lower at zero Po2 No differences in basal and contraction related metabolic rates could be detected between the two groups under normoxic and anoxic conditions. The maximal activity of lactate dehydrogenase (LDH) determined in tissue sampIes was about 2‐fold higher in the diabetic bladder muscle. This increased enzymatic activity could thus not be correlated with any altered metabolic properties of the smooth muscle in the urinary bladder from diabetic rats.
Nervous regulation of the tone of the retractor penis muscle in the goat
Authors: SJöSTRAND N. O. , BECKETT S. D. , KLINGE E.
Published: December 2008

The nervous control of the retractor penis muscle (rp) was investigated in the anaesthetized goat. Also, isolated field stimulated strips of the muscle were studied. The noradrenaline (NA) and acetylcholine (ACh) content of the rp was determined, and histochemistry for adrenergic and acetylcholinesterase (AChE) positive nerves was performed. The muscle exhibited spontaneous activity that persisted after section of all nerves. There was, however, also a tendency of the activity to follow the general vasomotor tone, which disappeared after section of the sympathetic chains. The excitatory adrenergic nerves which innervate the muscle come from the sympathetic chains and run along the pudendal, the hypogastric and the pelvic nerves. The rp has a dense network of adrenergic fibres and is very sensitive to excitatory adrenergic stimulation. It has a fairly large NA content, which is higher in old goats (5.95 ± 0.42 μgg‐1) than in young goats (2.87 ± 0.78 μg g‐1). Inhibitory non‐adrenergic non‐cholinergic (NANC) innervation reaches it via the pelvic and the hypogastric nerves. The maximum inhibitory response is reached at low frequencies (2–4 Hz). Cholinergic prejunctional inhibition of the excitatory response to sympathetic chain stimulation was effected by simultaneous stimulation of the hypogastric nerves.In vitroexperiments confirmed the presence of endogenous cholinergic muscarinic suppression of the excitatory adrenergic neurotransmission. Significant amounts of ACh (0.81 7 plusmn; 0.18 μg g‐1) are present in the muscle, and it contains strongly AChE positive nerve fibres and nerve cell bodies. It is concluded that the goat rp is innervated by sympathetic adrenergic excitatory nerves and parasympathetic NANC inhibitory nerves. It further has a direct sympathetic inhibitory NANC innervation, and an indirect inhibitory cholinergic innervation which at least in part is sympathetic.
Atrial natriuretic factor (ANF) does not affect ion transport in human intestine but does in porcine intestine
Authors: GROTMOL T. , RøDNES J. T. , BUANES T. , CHRISTENSEN G. , LANDSVERK T.
Published: December 2008

The aim of this study was to test whether atrial natriuretic factor (ANF) exerts any effect on human intestinal ion transport, and the porcine intestine was used as a positive control of ANF's effects. Tissues from human proximal (n = 6) and distal (n = 6) colons, and from distal ileum (n = 6) were mounted in Ussing chambers, and short circuit current (Isc) was measured subsequent to serosal application of ANF (10‐‐6 m), 8–Br‐cyclic guanosine monophosphate (8–Br‐cGMP) (10‐‐4 m), and theophylline (10‐‐2 m). ANF did not affect Isc whereas 8–Br‐cGMP increased Isc by 28 (8–53), 16 (3–36), and 16 (5–41) μA cm‐2 in the distal colon (DC), proximal colon (PC) and distal ileum (DI), respectively. Likewise, transepithelial potential difference (PD) became more negative by 5.0 (0.6–8.9), 2.5 (0.4–4.0) and 0.9 (0.3–2.3) mV in DC, PC, and DI, respectively, subsequent to addition of 8–Br‐cGMP. Isc and PD were further increased by theophylline. Additional radio‐isotope flux studies in human colon revealed that ANF did not affect electroneutral sodium and chloride transport either. For comparison, ANF (10‐‐6 m) was administered to large intestinal tissues from young pigs in which ANF induced a significant increase in Isc which was comparable to the 8–Br‐cGMP response in humans. The porcine Isc response was partly inhibited by chloride‐free solution on the serosal side, by serosal application of bumetanide (10‐‐4 m) and BaCl2 (10‐‐3 m), and mucosal application of the chloride‐channel blocker diphenylamine‐2–carboxylate (DPC) (10‐‐3 m). Mucosal amiloride (10‐‐5 m) pre‐treatment reduced baseline Isc but did not affect the porcine intestinal Isc response to ANF. In vitro radio‐autography demonstrated specific binding sites for ANF in porcine distal colon, whereas no apparent labelling was observed in human distal colon. These findings suggest that the lack of effect of ANF on sodium and chloride transport in human distal ileum and colon is probably due to lack of ANF receptors. In the porcine intestine, however, the IS0 response induced by ANF seems to involve stimulation of electrogenic chloride secretion, whereas electrogenic sodium absorption seems unaffected.
The high‐force region of the force‐velocity relation in frog skinned muscle fibres
Authors: Lou F. , Sun Y.‐B.
Published: December 2008

The force‐velocity relation has been studied during calcium‐induced contracture of chemically skinned fibres from the semitendinosus muscle of Rana temporaria with special interest focused on the high‐load region. The force‐velocity curve was hyperbolic at low and intermediate loads but departed below the hyperbola as the load exceeded about 80% of the isometric force (Po). The force intercept (P*o) of the hyperbola derived from force‐velocity data truncated at 0.78 Po was higher than Po (P*o /Po = 1.14±0.04). At submaximum Ca2+ concentration, where the isometric force of the fibre was 65–75% of the maximum value, the force‐velocity data still departed below the hyperbola at high loads (Po /Po = 1.09±0.04). The departure of the force‐velocity data from the hyperbola at high force was also found at high ionic strength (250 mM), but not at low ionic strength (150 mM) (Po /Po = 1.09±0.03 and 0.98±0.03, respectively). The force‐velocity relations derived under different experimental conditions could be fitted well by a modified version of Hill's (1938) hyperbolic equation (Edman 1988) using similar numerical values of k1 and k2 in the latter equation. The results indicate that the force‐velocity relation in skinned muscle fibres is biphasic, and that the two curvatures, as in intact muscle fibres, are closely related to one another. Furthermore the evidence supports the hypothesis that the altered shape of the force‐velocity relation at high loads is not related to the force level per se but rather to the speed of shortening of the contractile system (Edman 1992).
Mechanisms for hypothermia‐induced increase in contractile force studied by mechanical restitution and post‐rest contractions in guinea‐pig papillary muscle
Authors: BJØRNSTAD H. , TANDE P. M. , REFSUM H.
Published: December 2008

Lowering myocardial temperature increases contractile force, presumably by increasing intracellular calcium content. To study the mechanisms behind this, we compared the effects of some known inotropic interventions with hypothermia on mechanical restitution and post‐rest contractile force in isolated guinea‐pig papillary muscles. In four groups (n = 6 per group), the effects of: (1) reducing the ability for Na/Ca exchange to extrude Ca2+ (a) by increasing [Na+]1 with ouabain or (b) by increasing [Ca2+]o; and (2) activation of calcium channels with Bay‐K 8644, were compared with lowering temperature from 37 to 27 °C. Normally (at 37 °C and 2 mm CaCl2), mechanical restitution could be described by a rapid recovery phase with a time constant between 180 and 220 ms, followed by a slowly decaying phase with a time constant between 5000 and 8000 ms and post‐rest contractions (1–10 min rest) were markedly depressed compared to steady‐state contractions. Steady‐state developed force was markedly increased at 27 °C, after 1 μm ouabain, 6 mm CaCl2 or 0.1 μM Bay‐K 8644. At 27 °C the rapid recovery phase of restitution was delayed while the slowly decaying phase was not affected. Ouabain and increased [Ca2+]o caused elevation of the slowly decaying phase of restitution and markedly attenuated the post‐rest depression of developed force, which may be attributed to a reduced diastolic extrusion of Ca2+ via the Na/Ca exchanger. Hypothermia and Bay‐K 8644 on the other hand, augmented this post‐rest depression. Hence, this study suggests that increased Ca2+ influx due to delayed inactivation of calcium channels may account for the increased developed force during hypothermia rather than reduced diastolic extrusion of Ca2+ via the Na/Ca exchanger.
Effects of metabolic inhibition on cytoplasmic calcium and contraction in smooth muscle of rat portal vein
Authors: SWÄRD K. , JOSEFSSON M. , LYDRUP M.‐L. , HELLSTRAND P.
Published: December 2008

Contractions in the rat portal vein, evoked by spontaneous action potentials or depolarizing high‐K+solution, are rapidly and reversibly inhibited by hypoxia or respiratory blockade. Intracellular free calcium ([Ca2+]i) was measured using Fura‐2 to evaluate the effects of metabolic blockade on excitation–contraction coupling. Spontaneous contractions were associated with transient increases in [Ca2+]i. During exposure to cyanide (0.2–0.4 mm) or 2,4‐dinitrophenol (30μm) the duration and amplitude of the Ca2+transients were decreased, leading to a decreased mean time integral of the individual [Ca2+]itransient, and corresponding decrease in the duration and amplitude of the contraction. Basal [Ca2+]iwas increased in the presence of the metabolic inhibitors. High‐K+(40 mM) contractions caused a sustained increase in [Ca2+]i, which was not inhibited by exposure to cyanide, although the amplitude of the associated contraction was greatly reduced. Together with the earlier demonstration of decreased 20 kD myosin light chain phosphorylation under these conditions, this indicates that the activation of contraction is influenced by metabolism via the energy dependence of the light chain phosphorylation reaction. Thus at least three steps in the excitation–contraction sequence are influenced by inhibition of oxidative metabolism: membrane excitation, light chain phosphorylation, and the cross‐bridge cycle. This provides mechanisms for a high degree of metabolic sensitivity of vascular tone, of importance for the adaptation of blood flow to tissue metabolic demands.