bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of adenosine receptors in bone. Studies on the effect of adenosine analogues on cyclic AMP formation and bone resorption in cultured mouse calvaria
Authors: LERNER U. H. , SAHLBERG K. , FREDHOLM B. B.
Published: December 2008

The effect of different adenosine analogues on cyclic AMP (cAMP) formation and bone resorption in cultured mouse calvarial bones was investigated. 5′‐N‐ethylcarboxamidoadenosine (NECA),r‐N6‐phenylisopropyl‐adenosine (PIA),N6‐cyclohexyl‐adenosine (CHA) and 2‐chloroadenosine all stimulated cyclic AMP formation with a threshold close totμmol l‐1; NECA was the most potent agonist. Theophylline (10, 100μmol l‐1) inhibited the cAMP accumulation induced by NECA and 2‐chloroadenosine (30 and 300μmol l‐1), dose dependently. There was no inhibition of cAMP formation by PIA and CHA in forskolin‐treated bone tissue. SQ 22, 536 and 2′,5′‐dideoxyadenosine (100μmol l‐1) both inhibited rolipram‐stimulated cAMP formation. Cyclic AMP accumulation in isolated osteoblast‐like cells from neonatal mouse calvarial bones was stimulated by NECA (10 and 100μmol l‐1) and 2‐chloroadenosine (100μmol l‐1). 2‐chloroadenosine (10 and 30μmol l‐1), but not NECA, PIA nor CHA, caused a dose‐dependent stimulation of45Ca release in both 48‐ and 120‐h culture. The effect of 2‐chloroadenosine on45Ca release could not be antagonized by theophylline. Neither NECA, PIA, CHA nor 2‐chloroadenosine could affect PTH‐stimulated45Ca release in short term cultures (6, 24 h). By contrast, stimulation of cAMP formation by forskolin or dibutyryl cAMP caused a rapid (6 h) inhibition of PTH‐stimulated bone resorption. The results demonstrate functional A2and P‐site receptors in mouse calvaria and osteoblast‐like cells, but no A1‐receptor was detected. These adenosine receptors regulate cAMP, but are not intimately linked to bone resorption. The calcium mobilization induced by 2‐chloroadenosine appears to be unrelated to adenosine receptors.
Endotoxin‐induced prostaglandin (PGF2α) biosynthesis, fever and miosis in dexamethasonetreated goats
Authors: JÓNASSON H. , AUGUSTINSSON O. , KINDAHL H.
Published: December 2008

Prostaglandin‐releasing, adrenocortical, febrile and miotic responses to endotoxin (ET) (E. coil lipopolysaccharide; 0.25 μg kg‐1) were studied in goats with and without prolonged dexamethasone influence. The i.v. injection of ET induced a three‐fold peak elevation in plasma 15‐ketodihydro‐PGF2α at 1.5 h post‐injection, that is, between the first and second phase of the temperature elevation. During the latter phase, the plasma concentration of this primary PGF2α metabolite gradually returned to basal level, which implies that the second phase of ET fever is not PG dependent. The PG response exhibited a similar pattern, but was less pronounced in the dexamethasone‐ET experiments, where the duration of maximum temperature elevation and of the miosis became shortened by about 20 min, and the typical biphasic pattern of ET fever was no longer seen. The ET‐induced rise in plasma aldosterone concentration was completely blocked by dexamethasone. The corresponding rise in plasma cortisol concentration was prevented for 2 h, but was later only partially inhibited in spite of the repeated dexamethasone treatment.
A new method for continuous recording of oviductal pressure variations in unrestrained gilts
Authors: HENRIKSSON A. , GUSTAVSSON A. , EINARSSON S.
Published: December 2008

A new method using two intraluminally placed ultra‐miniature pressure sensors placed in the same isthmus of the oviduct has been developed for continuous monitoring of oviductal pressure variations during the oestrous cycle in unrestrained gilts. Each test animal was followed for 48 h during which recordings were made at frequent intervals. By using two points of registration, directions of pressure waves could be determined. This technique allows for the determinaton of the base pressure in the oviduct and how it varies during the oestrous cycle. Effects of different stimuli and the effect of narcosis on oviductal activity can also be directly studied.
Motoneuronal innervation and mechanical properties of extraocular muscles in the catfish, (Ictalurus punctatus)
Authors: LENNERSTRAND G. , BAKER R.
Published: December 2008

Mechanical characteristics and electrical activity were studied in the extraocular muscles of the catfish, Ictalurus punctatus. The contractile properties were determined by stimulation of the individual muscle nerve branches to lateral and medial rectii and the superior and inferior oblique muscles. The speed of contraction was higher than in most other fish muscle, with a twitch contraction time of about 12 ms and a tetanus fusion frequency of 150–170 Hz in all four eye muscles. The fatigue resistance was also high. These properties were the same in fully innervated and partially innervated muscle, largely irrespective of what part of the muscle that was activated. Although different fibre types are known to exist in fish extraocular muscle, it was not possible to obtain functional separation of the mechanical force profile even in the lateral rectus with two distinct motoneuronal innervations. We suggest that polyneuronal innervation of the muscle fibres produces the mechanical responses. Since EMG activity during spontaneous eye movements was similar in the global and the orbital parts of the muscle, all types of fibres in fish extraocular muscle are probably recruited for all types of eye movements.
Increase of insulin and decrease of glucagon levels in response to total and fractionated weaning in sows
Authors: ERIKSSON M. , EINARSSON S. , KUNAVONGKRIT A. , UVNAS‐MOBERG K.
Published: December 2008

The effect of weaning on plasma levels of insulin and glucagon as well as on plasma glucose levels was studied in sows after final weaning (all the piglets removed in week 5 of lactation) and fractionated weaning (7 out of 12 piglets removed in week 3 of lactation). Insulin levels rose from 24 ± 6 to 106 ± 22 μU ml‐1 4 days after final weaning and from i i ± 1 to 128 ± 20 μU ml‐1 7 days after fractionated weaning. Glucagon levels fell from 60 ± 20 and 42 ± 8 to 35 ± to and 24 ± 5 pM in the two groups, respectively. Plasma glucose levels increased from 4.5 ± 0.5 to 7.2 ± 1.2 mm after fractionated weaning and remained unchanged after final weaning. One possible mechanism that can explain this pronounced insulin increase and decrease of glucagon is the elevation of plasma glucose, since milk is no longer emptied from the mammary gland and since insulin resistance occurs after weaning in rats. Another possible explanation could be a decreased number of insulin receptors in the mammary gland, since prolactin which is known to increase insulin receptors is decreased in weaned rats.
Mechanism of osmotic diuresis studied by infusion of NaHCO3 and mannitol in dogs
Authors: OSTENSEN J. , BUGGE J. F. , STOKKE E. S. , LANGBERG H. , KIIL F.
Published: December 2008

To examine whether mannitol and NaHCO3 are equally potent inhibitors of proximal tubular fluid reabsorption, experiments were performed in to anaesthetized volume‐expanded dogs during continuous infusion of ethacrynic acid. At plasma pH 7.5, a rise in plasma osmolality of 40 mosmol kg‐1 reduced the remaining tubular fluid reabsorption in five dogs by 14 ± 3% during NaHCO3 infusion and by 28 ± 1% during mannitol infusion. Bicarbonate reabsorption increased by 25 ± 5% during NaHCO3 infusion and decreased by 14 ± 1% during mannitol infusion. At equal rates of bicarbonate reabsorption the inhibitory effects on tubular fluid and NaCl reabsorption were slightly less during mannitol than during NaHCO3 infusion. In five other dogs studied at constant plasma concentration of sodium, changes in bicarbonate reabsorption were avoided by raising plasma pH to 7.7 during NaHCO3 infusion and by reducing plasma pH to 7.4 during mannitol infusion. Tubular fluid reabsorption was reduced 32 ± 4% by NaHCO3 and 34 ± 4% by mannitol infusion, indicating equal inhibitory effects. The mechanism may be that the osmotic force for paracellular reabsorption of water and NaCl across the tight junction is equally reduced by equiosmolal increments in the NaHCO3 and mannitol concentration of the proximal tubular fluid.
Adaptation‐related changes in the spatial and temporal summation of frog retinal ganglion cells
Authors: DONNER K.
Published: December 2008

The spatial and temporal summation of light by the receptive field centre of frog retinal ganglion cells were studied by extracellular recording in the eyecup preparation. The purpose was to quantify how summation changes with the state of light and dark adaptation and to clarify whether changes are due to the transition between rod and cone vision. Spatial summation was found to decrease by 30–50% as the cell was light‐adapted to a threshold some 4 log units above the dark‐adapted one. Temporal summation for threshold responses fell as the power –0.17 of the intensity of an adapting steady background. Neither change was bound to the rod‐cone transition but occurred in the ranges of both receptor types; at equal sensitivities the summation of both receptor systems was matched.
Transient expression of insulin‐like growth factor I immunoreactivity in skeletal muscle cells during postnatal development in the rat
Authors: JENNISCHE E. , OLIVECRONA H.
Published: December 2008

The immunohistochemical expression of insulin‐like growth factor I (IGF‐I; somatomedin C) was investigated in hindlimb skeletal muscle of rats during postnatal development. IGF‐I immunoreactivity could be demonstrated in satellite fibres and myotubes 1, 2 and 3 days after birth, while no IGF‐I immunoreactivity could be demonstrated in the more mature primary fibres. Five days after birth only scattered cells showed IGF‐I immunoreactivity and io days after birth no specific IGF‐I immunoreactivity could be demonstrated in muscle cells, i.e. the adult pattern was established. It is concluded that IGF‐I immunoreactivity is expressed during a limited period of postnatal skeletal muscle maturation in rats. IGF‐I is probably synthesized by IGF‐I immunoreactive muscle cells and contributes to the differentiation/maturation process by autocrine and/or paracrine mechanisms.
Neuropeptide Y (NPY) induced inhibition of preganglionic nerve stimulation evoked release of adrenalin and noradrenaline in the pithed rat
Authors: DAHLÖF P. , PERSSON K. , LUNDBERG J. M. , DAHLÖF C.
Published: December 2008

NPY, a peptide with 36 amino acid residues, is co‐stored together with noradrenaline (NA) in cardiac and sympathetic perivascular nerves as well as with adrenalin (A) in adrenal chromaffin cells. NPY is released together with NA from sympathetic nerves and with A from the adrenal glands and appears to be involved in the control of sympathetic neurotransmission.

The aim of the present study was to analyse the effect of NPY on the preganglionic nerve stimulation (PNS) evoked increases in plasma A and NA concentrations in pithed rats. In the first part of the study (I) only one PSN period (2 Hz for 45 s) was performed in each rat and the control group was compared to the NPY treated group. In the second part of the study (II) two PNS periods (1 Hz for 45 s) were performed in each rat, which either received saline or NPY before the second PNS. Thus, interindividual changes between the responses to the first and second PNS in control and NPY rats could be compared.

In both study I and II, systemic infusion of NPY (2 μg kg‐1 min1 i.v.) significantly reduced the PNS‐induced increase in plasma A by 26% and 42%, respectively (P < 0.05). However, the increase in plasma NA elicited by PNS was significantly reduced only in study II by 23% (P < 0.05). Infusion of NPY did not affect basal heart rate in either of the studies, but significantly increased basal blood pressure by about 10 mmHg. The blood pressure responses to PNS were significantly greater in NPY treated rats.

It is concluded that PNS‐evoked release of A and NA is under inhibitory control of NPY. The inhibition of NA release from the sympathetic nerve terminals is most probably due to a prejunctional site of action, whereas the reduced secretion of A could be due to a local effect of NPY in the adrenal medulla,. The negative influence of NPY on A and NA release appears to be compensated for by the additional facilitatory action of NPY on the postjunctioned responses to these catecholamines.
Studies on terminal differentiation of rat renal proximal tubular cells in culture: ouabain‐sensitive K and NA transport
Authors: LARSSON S. H. , APERIA A. , LECHENE C.
Published: December 2008

We have studied the ontogeny of Na‐K ATPase‐mediated Na and K transport in rat renal proximal tubular cells using electron probe analysis. The cells were cultured from kidneys of 10‐day‐old, young (Y), and 40‐day‐old, adult (A) rats. Before an experiment cells were Na‐loaded and K‐dcpleted by incubation in K‐free medium. The maximum rate of ouabain‐sensitive Na and K transport was measured after reactivating the Na‐K pump by transferring the cells from K‐free medium to medium containing 5 mM K. In cells cultured for 2 days, ouabain‐sensitive Na and K net initial transport rates were significantly higher in A than in Y cells. Between 2 and 4 days in culture there was a significant decrease in ouabain‐sensitive Na and K transport rates in both Y and A cells. From 2 to 4 days of culture there was, in Y but not in A cells, a significant decrease in K/Na ratio. The decrease in K/Na ratio was due to a significant increase in Na content. After incubation in K‐free medium, net intracellular solute accumulation was observed in A and Y cells cultured for 4 days but not in A and Y cells cultured for 2 days.

In conclusion, maximal Na‐ and K‐pump‐mediated transport increases during terminal differentiation. This increase can be measured in cells cultured for 2 days. With longer time in culture, Na K pump activity decreases and the difference between A and Y cells is not measurable. We had previously observed that net Na and K permeabilities decrease from 2 to 4 days in culture in A but not in Y cells. In Y cells cultured for 4 days, a decrease in pump activity without a change in Na and K permeability causes an increase in intracellular Na content.
Carbonic anhydrase isoenzymes in the caecum and colon of normal and germ‐free rats
Authors: LÖNNERHOLM G. , MIDTVEDT T. , SCHENHOLM M. , WISTRAND P. J.
Published: December 2008

Histochemical and immunocytochemical methods were used to study the presence of carbonic anhydrase (CA) isoenzymes in the caecum and colon of normal and germ‐free rats. Very high enzyme activity was demonstrated by histochemistry in the caecum and proximal colon of normal rats, while the activity decreased in the distal colon. Very strong immunostaining for the isoenzyme CA I was found in the cytoplasm of surface cells and upper gland cells in the caecum and colon of normal rats. In the distal colon the staining was less intense with a marked cell‐to‐cell variation. Ca II was found in the apical (luminal) cell region of the surface epithelium in all regions. Ca III was possibly present in small amounts, but this could not be judged with certainty. There was no difference in carbonic anhydrase between normal and germ‐free rats (except for less staining of the mucosal capillaries in germ‐free animals). Therefore, our data give no support to the hypothesis that CA I participates in the absorption of microbial fermentation products. The location of CA II in the apical cell region suggests a role for this isoenzyme in regulation of the microclimate close to the epithelial cells.
Acidosis, hypoxia and stress hormone release in response to one‐minute inhalation of 80% CO2 in swine
Authors: FORSLID A. , AUGUSTINSSON O.
Published: December 2008

The study pertains to a series of investigations on the effects of CO2 inhalation as used for pre‐slaughter anaesthesia in swine.

Acid/base parameters, blood oxygen tension, plasma Na, K, Ca and stress hormone concentrations were monitored in Yorkshire swine before, during, and for 10 min after the animals were descended for 1 min into 80% CO2 in air.

Severe respiratory acidosis (Paco2˜ 50 kPa, arterial pH ˜ 6.6) and hypoxia (Pao2˜ 4 kPa) had developed after 45 s of the CO2 inhalation. The corresponding changes in venous blood were less drastic (PvCO2˜ 17 kPa, pH 7.1, Pvo2˜ 4 kPa). Readjustment to PaCO2˜ 11 kPa, arterial pH 7.2, and Pao2˜ 13 kPa had occurred at 1 min post CO2. Four minutes later the respiratory acidosis had become converted into metabolic acidosis subjected to partial respiratory compensation (arterial pH 7.3 in the presence of moderate hypocapnia and hyperoxaemia). The cause of this metabolic acidosis (present also at 10 min post CO2) was apparently hypoxia‐induced anaerobic metabolism (= lactic acid production). Apparently due to hydrogen ion transport into the cells in exchange for other cations, hyperkalaemia (K˜ 6.6 mmol 1‐l), and a 7 mmol 1‐1 increase in plasma Na had developed at 1.5 min later. The CO2 inhalation did not change the total plasma Ca significantly.

The transport of the swine from the stable to the immediate pre‐experimental situation induced a 3‐fold increase in plasma Cortisol concentration (PC, to ˜ 130 mmol 1‐1). No further increase in PC occurred in response to the CO2 inhalation. It indicates that no additional emotional strain was imposed upon the animals during the CO2 exposure. Another possibility is that a maximal secretion of Cortisol was here reached already before the descent into the CO2.

The transport procedure caused only minor increases in plasma adrenalin (A) and noradrenaline (NA). However, during the CO2 exposure plasma A and NA exhibited 15‐ and 50‐fold rises, respectively (to 3.5 and 22 mmol l‐1, respectively). The main cause of the A/NA elevation seems to have been the severe respiratory acidosis.
Baroreflex control of jejunal blood flow and fluid transport in cats; effects of yohimbine, an α.‐adrenergic antagonist
Authors: SJÖVALL H. , BUTCHER P. , HEMLIN M.
Published: December 2008

The aim of the study was to test the hypothesis that baroreceptor unloading increases jejunal fluid absorption rate via an α2‐adrenergic effect on electrogenic active transport. In 13 chloralose‐anaesthetized cats, the carotid sinus baroreceptors were isolated and perfused with arterial blood, and we studied the effects of a graded decrease in carotid sinus pressure on intestinal vascular resistance, net fluid absorption rate and the potential difference between the intestinal lumen and the peritoneal cavity (PD). Experiments were performed in seven control animals and in six animals pretreated with yohimbine, an α2‐adrenergic antagonist, at a dose of 0.1 mg kg‐I i.v. Yohimbine per se had no significant effects on systemic arterial pressure, intestinal vascular resistance, net fluid absorption rate or PD. In the control animals, baroreceptor unloading induced an increase in systemic arterial pressure, intestinal vascular resistance and net fluid absorption rate, and a decrease in the PD. Yohimbine pretreatment did not significantly affect the systemic blood pressure response to baroreceptor unloading, but abolished the effect on intestinal vascular resistance and PD. After yohimbine treatment, decreases in carotid sinus pressure still enhanced net fluid absorption rate, but this response was observed in a higher range of carotid sinus pressures than in control animals. We conclude that (1) a major component of the increase in jejunal absorption rate during baroreceptor unloading is due to a non‐electrogenic mechanism, which may be either active or passive; (2) this component of the response is not blocked by yohimbine at a dose sufficient for an effect on presynaptic α2‐receptors; (3) the absorptive response to baroreceptor unloading is not a phenomenon secondary to the concomitant jejunal vasoconstriction.
Catecholamines (CA) and adenosine triphosphate (ATP) are separately stored in bovine adrenal medulla, both in ionic linkage to granule sites, andnot asa non‐diffusible CA‐ATP‐protein complex*
Authors: UVNÄS B. , ÄBORG C.‐H.
Published: December 2008

On superfusion of chromaffin granules from bovine adrenals with isotonic sodium and potassium salts, catecholamines and ATP were released in parallel and both in accordance with ion exchange kinetics. An artificial model was prepared by mixing a cationic (IRC‐50) and an anionic (IR‐4B) ion exchanger with COO and NH+3groups, respectively, as binding sites. This mixed ion exchanger showed in its storage and release of CA+and ATP‐striking similarities to the chromaffin granules. Within the pH range given for the interior of the granules ‐ 5.5–6 ‐ the artificial model even stored and released CA+and ATP‐within the same molar ratio as observed for the granules. We hypothesize that the chromaffin granule matrix in its storage and release functions operates as an amphoteric ion exchanger with COO‐and NH+3, groups as the binding sites.
Seasonal, menstrual and circadian secretions of melatonin, gonadotropins and prolactin in women
Authors: KIVELÄ A. , KAUPPILA A. , YLÖSTALO P. , VAKKURI O. , LEPPÄLUOTO J.
Published: December 2008

In order to evaluate the role of the pineal gland in human reproduction, day‐ and nighttime concentrations of serum melatonin, FSH, LH and prolactin were measured by radioimmunoassays on various days of the menstrual cycle during summer (average daylight 22 h) and winter (daylight 5 h) in healthy females (n= 12) from northern Finland (65o N). A multifactorial analysis of variance showed that, in addition to the well‐established increases of gonadotropins at midcycle and melatonin and prolactin at night, there was a significant effect of season on the serum levels of melatonin and LH. Night‐time serum melatonin levels on cycle days 2 and 10 were 27% and 49% (P < 0.05 and < 0.01) higher in winter than in summer. Night‐time serum LH levels at midcycle were 76% (P < 0.05) higher in summer than in winter. There were no significant effects of season on the serum levels of FSH, prolactin, day‐time melatonin or LH outside the mid‐cycle. Neither were there any significant effects of the day of the menstrual cycle on the serum melatonin levels. It is possible that in winter the high levels of melatonin in the follicular phase have an inhibitory effect on the serum LH levels. In summer the melatonin levels are lower and perhaps less inhibitory on the secretion of LH, resulting in the stimulation of the reproductive competence in human females.
Haematocrit distribution in rabbit tenuissimus muscle
Authors: LEY K. , LINDBOM L. , ARFORS K.‐E.
Published: December 2008

Low values of mean capillary haematocrit have been reported in many tissues including skeletal muscle. The present study was undertaken to analyse haematocrit distribution in the transverse and terminal arterioles, capillaries and venules of the rabbit tenuissimus muscle preparation. Tube haematocrit, i.e. the volume fraction of red cells, in muscle capillaries (n= 85) was found to be 39% of systematic haematocrit Hsys. In part, this haematocrit reduction is due to the Fahraeus effect. Corresponding capillary discharge haematocrit HD was 56% of Hsys. Tenuissimus muscle capillaries are fed by terminal arterioles originating from transverse arterioles. The latter extend into and supply adjacent connective tissue septa in addition to the muscle tissue proper. In transverse arterioles leaving the muscle to enter the connective tissue, HD was found to be 127% of Hsys (n= 18), and in collecting venules at the muscle edge HD was 129% of Hsys (n= 18). These findings indicate that the connective tissue microcirculation represents a functional red‐cell shunt in resting tenuissimus muscle. Since only about 20% of the inflow to the preparation passes through the connective tissue, this shunting is not sufficient to satisfy conservation of red‐cell mass. In addition, it is likely that the observed low capillary haematocrit is in part due to a positive correlation between blood‐flow velocity and HD in capillaries originating from individual terminal arterioles. This phenomenon is called the network Fahraeus effect.
Blood flow, histomorphology and elemental composition of the canine femur after physical training or immobilization
Authors: JURVELIN J. , LAHTINEN T. , KIVIRANTA I. , ARNALA I. , LAPPALAINEN R. , TAMMI M. , HELMINEN H. J.
Published: December 2008

Effects of long‐term physical training (treadmill running 4 km/day for 15 weeks) and immobilization (casting of the limb for 11 weeks) on the blood flow, bone marrow uptake of radio‐colloid, histomorphology as well as elemental composition of the proximal canine femur were investigated. In the runners both bone marrow and mean bone perfusions measured with a 133Xe washout method were increased by 53.5% (P < 0.05) and 54.1 % (P < 0.05), respectively, as compared with the age‐matched controls. Bone marrow uptake of [99mTcjtincolloid and volumetric fractions of trabecular bone and bone marrow were not significantly altered after training or immobilization. The amount of zinc measured by atomic absorption spectrophotometry was, however, significantly higher (P < 0.01) after immobilization as compared with the controls. Consequently, long‐term physical training is suggested to stimulate bone metabolism by enhancing its blood perfusion even in the resting state, whereas the increase of zinc content was considered to be linked to the obvious bone resorption caused by immobilization.
IGF‐I immunoreactivity is expressed by regenerating renal tubular cells after ischaemic injury in the rat
Authors: ANDERSSON G. , JENNISCHE E.
Published: December 2008

The immunohistochemical expression of the trophic peptide insulin‐like growth factor I (IGF‐I; somatomedin C) was investigated in the post‐ischaemic regenerating rat kidney. The part of the nephron most severely injured by the ischaemic insult was the pars rectae or S3 region of the proximal tubules. In this part of the nephron no specific IGF‐I immunoreactivity could be demonstrated under control conditions. Three days after injury, however, low regenerating tubular cells expressing IGF‐I immunoreactivity could be demonstrated invading the damaged region. Five and 7 days post‐ischaemia some of the regenerating cells showed IGF‐I immunoreactivity while adjacent and similar‐looking cells did not. In parallel with an increasing differentiation of the regenerating cells the IGF‐I immunoreactivity vanished. Fourteen days after the injury the S3 cells had regained their normal morphology, and by this time the IGF‐I immunoreactivity had returned to a normal undetectable level. It is concluded that there is a transient increase in the expression of IGF‐I mainly confined to the early phase of post‐ischaemic rat kidney regeneration. It is proposed that IGF‐I exerts its trophic role by paracrine mechanisms.
Temperature‐dependent interaction between vasoconstrictor and vasodilator mechanisms in human skin
Authors: OBERLE J. , ELAM M. , KARLSSON T. , WALLIN B. GUNNAR
Published: December 2008

The putative influence of the thermoregulatory state on skin blood‐flow responses to various stimuli was studied in 17 healthy subjects exposed to different ambient temperatures. Skin blood flow was monitored by laser Doppler flowmeters and photoelectrical pulse plethysmographs. Stimuli included painful intraneural electrical stimulation (INS) in the median nerve at the wrist, mental stress, arousal stimuli and deep breaths. Intraneural electrical stimulation and mental stress were accompanied by virtually identical changes in skin blood flow, warm subjects responding with cutaneous vasoconstriction whereas cold subjects responded with vasodilatation. Similar but less pronounced responses were obtained with arousal stimuli and single deep breaths. The data indicate that the thermoregulatory state profoundly influences the extent and direction of various cutaneous vasomotor reflex responses. Furthermore, there were differences between responses in hands and feet, suggesting a spatial organization of vasomotor control.
Peak torque and OBLA running capacity in male orienteers
Authors: JOHANSSON C. , LORENTZON R. , RASMUSON S. , REIZ S. , HAGGMARK S. , NYMAN H. , FUGL‐MEYER A. R.
Published: December 2008

The isokinetic (30, 60, 120 and 1800 s‐1) peak torque of m. quadriceps femoris and m. triceps surae, and the running velocity at the onset of blood lactate accumulation (V0BLa) were determined at three different occasions (November, April and September) during a year in 15 male elite orienteers. The amount and type of training for each individual was also registered.

At the first test (November) there was no significant intra‐individual correlation between peak torque of m. quadriceps and m. triceps surae. A negative correlation was found between V0BLA and peak torque of m. quadriceps at the lower velocities of angular motion, but not at the higher. The peak torque of m. triceps surae increased during the training period and decreased during the competition period back to the original level. Over the whole year the peak torque of m. quadriceps increased while no changes could be demonstrated within the two periods of the study. The running velocity at the onset of blood lactate accumulation increased during both training and competition periods. The changes in V0BLawere negatively associated with the changes in peak torque of m. quadriceps at 1800 s‐1 during the training period. During the competition period the changes in VOBLA were, for the majority of the orienteers, negatively correlated to the ratio of quality: quantity running, i.e. to a high content of forest running.
Parabronchial oxygen extraction in ducks during selective cooling of the spinal cord
Authors: JOHANNESEN H. , BECH C.
Published: December 2008

Pekin ducks Anas platyrhynchos were chronically equipped with thermodes in the vertebral canal. Metabolic heat production, parabronchial oxygen extraction, vertebral canal temperature and body temperature were measured simultaneously before and during spinal cooling, at ambient temperatures ranging from 6 to 25 oC. Lowering vertebral canal temperature from 41.4 ± 0.2 °C to 35.9 ± 0.6 °C gave a mean increase in metabolic heat production of 1.54 ± 0.26 W kg‐1. Even though the spinal cooling had a clear metabolic effect, there was no concomitant change in parabronchial oxygen extraction. It is concluded that the thermosensitive structures residing in the spinal cord are not involved in the regulation of parabronchial gas exchange. The increase in parabronchial oxygen extraction, which is reported during cold exposure in birds, may therefore be induced by thermal inputs from peripheral thermoreceptors.
Acid in proximal and distal duodenum inhibits, but hyperosmolal solution does not inhibit pentagastrin‐stimulated acid secretion in chronic gastric fistula rats
Authors: WALLIN C. , NYLANDER G. , EMÅS S.
Published: December 2008

In chronic gastric fistula (GF) rats, hyperosmolal 0.20 M HC1 infused into a duodenal loop anastomosed to the jejunum (Roux‐en‐Y) produced a greater inhibition of the maximal acid response to pentagastrin than HC1 or 1200 mosmol kg‐1 solution of polyethylene glycol (PEG) alone, suggesting that HC1 and hyperosmolal solution inhibit secretion by different mechanisms. In the present study on chronic GF rats with Thirty‐Vella loops of the proximal or distal duodenum (bile and pancreatic ducts transplanted to the jejunum), perfusion of the proximal or distal loop with 0.20 M HC1 significantly inhibited the maximal acid response to pentagastrin, but perfusion with hyperosmolal PEG solution did not alter the response. The results suggest different anatomical sites for the inhibitory mechanisms, sensitive to acid and hyperosmolal solution.
Characterization of the glucose‐induced lowering of sodium in mouse pancreatic β‐cells
Authors: WESSLÉN N. , HELLMAN B.
Published: December 2008

The mechanisms for glucose regulation of the sodium content of the pancreatic β‐cells were examined using aggregates of cells prepared from ob/ob‐mice of a local colony. Exposure to glucose rapidly resulted in a protracted lowering of the sodium content as estimated with integrating flame photometry. Sodium became decreased after addition of 1 mmol 1‐1 glucose, and this effect was maximal with 5 mmol I‐1 of the sugar. The effects of low glucose concentrations on the sodium content could not be mimicked by the poorly metabolized 3‐o‐methyl‐D‐glucose, and it disappeared in the presence of the metabolic inhibitor antimycin A. The significance of the Na/K pump for maintaining low sodium was illustrated by a substantial increase of the element in the presence of ouabain. However, there was no indication that glucose‐induced lowering of sodium reflected activation of this pump when measuring the ouabain‐sensitive uptake of 86Rb+. Neither bumetanide nor the bromo derivatives of cyclic AMP or cyclic GMP modified the glucose action on the sodium content. In evaluating whether the effect of glucose was mimicked by other inhibitors of the K+ permeability it was observed that 100 μmol l‐1 quinine, but not tolbutamide, decreased sodium. It is concluded that the β‐ceIl is exceptional among excitable cells in responding to its natural physiological stimulant (glucose) by reduction of sodium. Acting in this way glucose facilitates the removal of Ca2+ from the cytoplasm.
Site of autoregulatory reactions in the vascular bed of cat skeletal muscle as determined with a new technique for segmental vascular resistance recordings
Authors: BJÖRNBERG J. , GRÄNDE P.‐O. , MASPERS M. , MELLANDER S.
Published: December 2008

An arterial and venous microcannulation technique was developed for circulatory studies in the cat gastrocnemius muscle which, based on detailed morphological and functional observations of the microvascular arrangement, seems to permit continuous recordings of pressure in arterioles (diameter ± 25 μm) and capillary pressure. These variables in combination with measurements of arterial and venous pressure and blood flow provided a means of continuous simultaneous recordings of total as well as segmental resistances in defined sections of the vascular bed, viz. in large arterial vessels (diameter ± 25 μm), arterioles (± 25 μm), and on the venous side. This new technique was applied to a study of the site(s) of autoregulatory reactions along the vascular bed evoked by changes of arterial pressure over the range 50–150 mmHg. The results indicated that active autoregulation mainly occurred within arterioles smaller than about 25 μm. In larger arterial vessels concomitant moderate active smooth muscle adjustments barely balanced out the pressure‐induced passive calibre changes, and the venous vessels did not seem to contribute actively to autoregulation, but exhibited a passive change in postcapillary resistance (Rven). The described pattern of response results in quite effective autoregulation of blood flow and capillary pressure (PC). The observed passive Rven change, via its effect on the pre‐ to postcapillary resistance ratio, seems to explain the fact that autoregulation of Pc can be more efficient than flow autoregulation. The study also provided quantitative data for the level of active intrinsic vascular tone in defined consecutive sections of the muscle vascular bed at normal arterial pressure and for segmental redistributions of tone evoked by pressure alterations.
Baroreflex modulation of sympathetic activity and sympathetic neurotransmitters in humans
Authors: ECKBERG D. L. , REA R. F. , ANDERSSON O. K. , HEDNER T. , PERNOW J. , LUNDBERG J. M. , WALLIN B. G.
Published: December 2008

We raised and lowered arterial pressures with stepwise intravenous infusions of phenylephrine and nitroprusside in ten healthy young men and measured changes of R‐R intervals, post‐ganglionic peroneal nerve muscle sympathetic activity, and antecubital vein plasma noradrenaline and neuropeptide Y concentrations. Respiratory peak‐valley R‐R interval changes declined with arterial pressure reductions, but did not rise with pressure elevations. Sympathetic activity was modulated by respiration over the entire range of pressures and, at each pressure, was more prominent in expiration than inspiration. Levels of muscle sympathetic nerve activity were low during supine rest, were suppressed almost completely during small increases of pressure, and were increased proportionally during pressure reductions. Over a range of average diastolic pressures from 69 to 89 mmHg, antecubital vein plasma noradrenaline levels were related linearly (r= 0.86, P= 0.0001) to muscle sympathetic nerve activity. Neuropeptide Y levels increased proportionally with muscle sympathetic nerve activity during pressure reductions, but did not decline during pressure elevations. Our results suggest that in man, muscle sympathetic outflow is modulated finely by small changes of baroreceptor input, and that during pharmacologically induced changes of arterial pressure, changes of antecubital vein plasma noradrenaline concentrations provide excellent estimates of changes of sympathetic nerve traffic to skeletal muscle.
Plasma pattern of growth hormone regulates sexual differentiation of phosphatidylcholine in rat plasma
Authors: OSCARSSON J. , JANSSON J. ‐O. , EDÉN S.
Published: December 2008

The effects of continuous and intermittent administration of human growth hormone (hGH) in the regulation of plasma phosphatidylcholine fatty acid composition was studied in adult hypophysectomized male and female Sprague‐Dawley rats. Human GH was given for 7 days, either continuously by means of Alzet osmotic minipumps implanted s.c. or intermittently by means of s.c. injections at 12‐h intervals. The ‘masculinizing’ effect of hypophysectomy on the fatty acid composition of plasma phosphatidylcholine in female rats, i.e. an increase in the proportions of palmitic and Iinoleic acids and a decrease in the proportions of stearic and arachidonic acids, was to a large extent reversed by continuous administration of hGH, while intermittent administration had no consistent effect. This effect of continuous hGH administration on the fatty acid composition of phosphatidylcholine was dose‐dependent. A similar effect of continuous administration of hGH was also observed in hypophysectomized male rats. Prolactin had no effect on the fatty acid composition of phosphatidylcholine. Replacement therapy with thyroid hormones and glucocorticoids had a small effect on the proportions of palmitic and stearic acids in plasma phosphatidylcholine. It is concluded that the more continuous secretory pattern of GH in female rats is involved in the sexual differentiation of the fatty acid composition of plasma phosphatidylcholine.
Subcutaneous interstitial fluid colloid osmotic pressure in dehydrated rats
Authors: HEIR S. , WIIG H.
Published: December 2008

We collected interstitial fluid for measurement of colloid osmotic pressure (COPi) of normally hydrated and dehydrated rats with two methods: (I) saline‐soaked nylon‐wicks implanted in vivo for 1 h; and (2) the crossover method, i.e. titration with wicks pre‐loaded with serial dilutions of rat plasma implanted post mortem for 15–20 min. All wicks were implanted in subcutis on the back. Dehydration was induced by injection of 40 mg furosemide followed by 24 h water deprivation. The saline‐soaked wick method gave an average control COPi of 10.8 mmHg, 2–3 mmHg lower than the corresponding pressure obtained with the crossover method. This discrepancy between the methods increased to 10–11 mmHg in dehydrated animals, indicating that the saline‐soaked wick method underestimates COPi even more during dehydration than during control conditions. The mean COPi of 22.8 mmHg (SD = 3.7, n= 9) obtained in dehydrated rats using the crossover method corresponds well with what is to be expected from the reduction in interstitial fluid volume. The present study suggests that the frequently used implantation period for saline‐soaked wicks of 60 min should be prolonged to 90–120 min. It further shows that the rise in COPi is about 3 times more important than the fall in interstitial fluid hydrostatic pressure in restricting mobilization of interstitial fluid during dehydration.
CNS‐induced natriuresis during dopamine receptor blockade. Further support for the existence of, at least, two separate natriuretic hormonal systems
Authors: HANSELL P. , SJÖQUIST M. , FASCHING A. , ISAKSSON B. , KARLSSON M. , ULFENDAHL H. R.
Published: December 2008

Intracerebroventricular (ICV) stimulation with hypertonic sodium chloride solutions has previously shown indications to stimulate the release of a blood‐borne natriuretic factor. Sodium excretion in this situation increases in the order of 10–20 times. Acute isotonic volume expansion has shown to be a potent stimulus for endogenous release of the atrial natriuretic factor (ANF). It has also been demonstrated that the natriuretic response to both volume expansion and exogenously applied ANF can be attenuated by the dopamine receptor blocker haloperidol. The present study was performed to investigate if the natriuretic response to ICV stimulation also could be attenuated with haloperidol, thus indicating similar effector mechanisms as for ANF. A first group of anaesthetized animals was, therefore, pre‐treated with haloperidol (H) and then ICV stimulated (H‐ICV). A second group of animals was subjected to acute isotonic volume expansion (VE, 2% b.w.h.‐1) to evoke the documented ANF release. In a third group of animals pre‐treatment with haloperidol was followed by volume expansion (H‐VE). In the H‐ICV group there was a more than 30‐fold increase in sodium excretion, due to an increase both in urine flow rate (more than sixfold) and in the urinary concentration of sodium (more than fourfold). Potassium excretion increased more than eightfold, urine osmolality was unchanged, and blood pressure increased by 7%. In the VE group sodium excretion increased more than 18‐fold, consequent to large increases in urine flow rate (more than 23‐fold), while the urinary concentration of sodium tended to decrease. Potassium excretion increased more than threefold, urine osmolality decreased by 88%, and blood pressure was unchanged. In the H‐VE group the natriuretic response was only 42% of that in the VE group (sevenfold). Potassium excretion increased more than twofold, while urine osmolality and blood pressure was unaltered. In conclusion, dopamine receptor blockade achieved by haloperidol does not interfere with CNS‐induced natriuresis. However, the natriuretic response to acute isotonic volume expansion (partly ANF‐mediated) is severly attenuated by the haloperidol treatment. These findings are compatible with a suggestion of at least two separate natriuretic hormonal systems.
Adrenocorticotropic hormone in the control of renal tubular hydrogen ion secretion. Balance of non‐metabolizable base in ACTH‐stimulated weanling rats subject to acid or base loading
Authors: KILDEBERG P. , WAMBERG S. , ENGEL K.
Published: December 2008

Groups of weanling rats subject to ACTH‐stimulation (tetracosactrin, 1 mg kg‐1 day‐1) were exposed to heavy oral loads of ammonium chloride (approx. 21 mmol kg‐1 day‐1) or sodium bicarbonate (approx. 40 mmol kg‐1 day‐1) for 8 days. During loading with sodium bicarbonate, the animals maintained a normal positive external (whole body) balance of non‐metabolizable base (NB), excess NB being excreted quantitatively in the urine, whereas loading with ammonium chloride caused a fall in the mean balance of NB from a reference value of 12.1 mmol per 8 days to about zero. However, in the two groups the concentration in plasma of NB rose from the reference value (41 mmol l‐1) to the same level (57 and 59 mmol l‐1, respectively; P > 0.5) despite extreme differences in rates of gastrointestinal NB absorption, despite a significant rise in the rate of endogenous sulphuric acid production and despite the presence of ample chloride in diet and urine. These results indicate that ACTH determines the extracellular concentration of NB at which exchange of NB takes place by influencing, directly or indirectly, the relative rates of renal tubular H+ secretion and CI‐ reabsorption at any given rate of tubular reabsorption of Na+. Some cybernetic considerations of the disturbance are presented.
Intradental nerve activity and jaw‐opening reflex in response to mechanical deformation of cat teeth
Authors: OLGART L. , GAZELIUS B. , SUNDSTRÖM F.
Published: December 2008

Mechanical stress was applied to canine teeth in anaesthetized cats to excite intradental A‐fibres and to produce digastric muscle EMG responses. Activity in the intradental sensory units was recorded by two electrodes,‐ one inserted in a dentinal cavity, the other in contact with the gingival sulcus. A pneumatically driven piston was used to cause a mechanical stress (10–150 N) on the stabilized tooth crown for 30 s, with instantaneous onset and release. Application of a load of 30 N produced a momentary burst of impulses in 2 of 12 teeth; 8 out of 10 teeth responded when 150 N was used. Digastric EMG responses were obtained at and above 60 N. Removal of the coronal pulp or cooling of the tooth crown with ethyl chloride abolished this reflex, whereas percussion of the tooth still produced a digastric response. Our results suggest that load‐induced deformation of teeth activates intradental sensory mechanisms and a reflex withdrawal reaction unrelated to periodontal stimulation.
The sympathetic innervation of the internal anal sphincter and rectum in the cat
Authors: CARLSTEDT A. , FASTH S. , HULTÉN L. , NORDGREN S.
Published: December 2008

The distribution of the sympathetic innervation to the internal anal sphincter (IAS) and rectum and the occurrence of different types of adrenergic receptors in the two organs were investigated in anaesthetized cats. Anal pressure and rectal motility were recorded by a manometric and a volumetric method respectively. Division of both the hypogastric nerves (HGN) and the lumbar colonic nerves (LCN) reduced the anal pressure by 46 ± 6% of the resting pressure (40.9 ± 6.4 mmHg) and consistently increased rectal motility. Efferent electrical stimulation of the HGN as well as the LCN elicited a contraction in the anus and the rectum, which, at maximal stimulation, caused the anal pressure to reach a similar level to that recorded before division of these nerves. After injection of phentolamine the anal contraction was abolished, whereas the rectal contraction was either abolished or converted to a β‐adrenergic relaxation. Propranolol caused increased rectal contraction in response to stimulation of the HGN and the LCN, whereas the anal contraction was unaffected. The results imply that the sympathetic nerves exert a tonic excitatory effect on the IAS and a dual effect on the rectum in the cat. The results also indicate that sympathetic fibres to the IAS are conveyed in both the HGN and the LCN. Inhibitory β‐adrenergic receptors seem to be of minor importance in regulating anal pressure.
Effects of voluntary physical exercise on cardiac function and energetics in spontaneously hypertensive rats
Authors: FRIBERG P. , HOFFMANN P. , NORDLANDER M. , THOREN P.
Published: December 2008

The influence of voluntary physical exercise in running wheels on myocardial function, cardiac oxygen utilization and cardiovascular response to emotional stress was analysed in the spontaneously hypertensive rat. After 6 weeks of exercise, a significant increase in resting cardiac output was found, which was due to an elevation of stroke volume. However, voluntary training for 12 weeks had no effect on resting blood pressure or on the blood‐pressure response to mental stress. Cardiac function was also examined in vitro. At a low aortic diastolic pressure, it was markedly augmented in trained spontaneously hypertensive rats. At high aortic diastolic pressure, maximal cardiac function was similar in the two groups. Myocardial oxygen consumption (μmol min‐1 g‐1) for a given level of external work was reduced in trained, compared with non‐exercised control spontaneously hypertensive rats. Chronic physical exercise thus greatly improved myocardial function at a subnormal perfusion pressure, suggesting better nutritional supply to the myocardium, probably created by an increased capillary surface area.