bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of pre‐stretch on mechanical efficiency of human skeletal muscle
Authors: BOSCO C. , MONTANARI G. , TARKKAI I. , LATTERI F. , COZZI M. , IACHELLI G. , FAINA M. , COLLI R. , MONTE A. DAL , LA ROSA M. , RIBACCHI R. , GIOVENALI P. , CORTILI G. , SAIBENESS F.
Published: December 2008

The mechanical efficiency of positive work was studied in six subjects performing three different types of exercises. On the first occasion the subjects ran on a motor‐driven treadmill at 3.33 m s‐1;the second and the third exercises consisted of performing rhythmical vertical jumps for 1 min both in rebound (RJ) and no‐rebound (NRJ) conditions. The mechanical efficiency calculated in NRJ, which reflects only the conversion of biochemical energy into mechanical work, was found to be lower than the corresponding observation in RJ, 17.2 vs. 27.8% (P < 0.001), respectively. These differences could not be explained by only the storage and recoil of elastic energy occurring in RJ compared with NRJ. The calculated extra work delivered ‘free’ was greater than the potential elastic energy which could be stored within the leg extensor muscles (187 vs. 124 J for each jump, P < 0.05). It is likely that other factors might be responsible for the extra work found in NRJ. It was suggested that the difference in the length of time to perform positive work between a simple shortening contraction and a stretch‐shortening muscular activity could be also responsible for the enhanced efficiency observed in RJ. This suggestion was supported by the high relationship (P < 0.001) found between the time to perform positive work and the mechanical efficiency measured in jumping and estimated during running.
Responses to antidromic trigeminal nerve stimulation, substance P, NKA, CGRP and capsaicin in the rat eye
Authors: ANDERSSON SVEN E.
Published: December 2008

In the rat eye, intracameral injections of substance P in doses of 10–30 pmol caused a maximal long‐lasting miosis and a leakage of plasma proteins into the aqueous humor, indicating a breakdown of the blood‐aqueous barrier. Neurokinin A seemed equipotent to SP, but calcitonin‐gene‐related peptide (CGRP) (17 pmol) caused neither moisis nor protein leakage into the aqueous humor. The same result was obtained when CGRP was administered intravenously. Intracameral injection of capsaicin caused only a transient moisis which could not be repeated with further injections, even though the pupillary sphincter was still able to react to exogenous SP.

Antidromic electrical stimulation of the trigeminal nerve caused plasma extravasation in the skin and a breakdown of the blood‐aqueous barrier with an increased protein content in the aqueous humor. The stimulation did not affect the pupil size. The results indicate that in rat eyes SP and NKA are miotics, but the amounts that can be released from sensory nerve endings are too small to cause persistent miosis. These peptides are more likely to play a role in the neurogenic breakdown of the blood‐aqueous barrier. CGRP at the same dose affects neither the pupillary sphincter muscle nor the barrier.
Suckling increases insulin and glucagon levels in peripheral venous blood of lactating dogs
Authors: ERIKSSON M. , LINDÉN A. , UVNÄS‐MOBERG K.
Published: December 2008

The aim of the present investigation was to study changes in insulin, glucagon and plasma glucose levels in response to suckling in lactating dogs. Blood samples were drawn from a peripheral vein during suckling in weeks 1 and 3 of lactation in 10 lactating beagles. Insulin‐ and glucagon‐like immunoreactivity (below referred to as insulin and glucagon) were determined by radio‐immunoassay, and plasma glucose levels by the glucose oxidase method. Insulin and glucagon levels rose following onset of suckling. However, only the rises recorded in week 3 of lactation were statistically significant. Plasma glucose levels were not affected. The mechansim by which suckling influences the levels of insulin and glucagon is not known. However, the release of both hormones is under vagal control and it is possible that touching of the teats reflexly elicits a vagally mediated release of these hormones. Alternatively, since oxytocin stimulates the secretion of insulin and glucagon, the effects might be secondary to the oxytocin released by suckling. The physiological function of the suckling‐related release of insulin may be to stimulate milk production. Furthermore, since glucagon is also released, each suckling period may be accompanied by a transfer of glucose to the mammary glands from other maternal stores.
Noradrenaline spillover during exercise in active versus resting skeletal muscle in man
Authors: SAVARD G. , STRANGE S. , KIENS B. , RICHTER E. A. , CHRISTENSEN N. J. , SALTIN B.
Published: December 2008

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one‐legged knee‐extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for to min at each of 50% and too% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (Nae) or of adrenalin (Ae) is required: Naewas measured by repeating the experiment under constant [3H]NA infusion following a 40‐min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this tissue.
Effect of insulin‐like growth factor‐I on metabolism in bovine mesenteric arteries
Authors: BORNFELDT K. E. , ARNQVIST H.J.
Published: December 2008

The effect of insulin‐like growth factor‐I (IGF‐I) on glucose accumulation, amino acid uptake and incorporation of amino acid into protein was studied in arterial smooth muscle. Accumulation of [14C]glucose, uptake of [14C]α‐aminoisobutyric acid (AIB) and incorporation of [14C]phenylalanine into protein were measured in intima‐media preparations of bovine mesenteric arteries (BMA) incubated with IGF‐I for 2, 4 or 6 h. IGF‐I (2.2 nmol l‐1) increased the accumulation of glucose into BMA after 4 h (P= 0.0079) and 6 h incubation (P= 0.0027) and in a concentration of 22 nmol l‐1also after 2 h (P= 0.015). The uptake of AIB and the incorporation of phenylalanine were increased after 4 h incubation with 2.2 nmol l‐1IGF‐I (P= 0.0045 andP= 0.026, respectively). The effects of IGF‐I on all of the metabolic parameters were dependent on incubation time and concentration of IGF‐I. Concentration‐effect curves were determined for the effect of IGF‐I and also for insulin on glucose accumulation in BMA incubated for 6 h. The concentration‐effect relationships for IGF‐I and insulin were very similar with pD2values of 7.6±0.2 (EC50= 27 nmol l‐1) and 7.5±0.2 (EC50= 34 nmol l‐1), respectively. No additive effect of IGF‐I and insulin in supra‐physiological concentrations (1.0μmol l‐1) could be demonstrated. These results show that IGF‐I has metabolic effects which are similar to the effects of insulin in vascular smooth muscle and suggest that IGF‐I may be of importance for the metabolism in vascular smooth muscle.
Gastrointestinal regulatory peptides during oxytocin infusion in post‐term pregnancies
Authors: HOLST N. , JENSSEN T.G. , BURHOL P. G. , JORDE R.
Published: December 2008

The plasma concentrations of the gastrointestinal regulatory peptides vasoactive intestinal polypeptide (VIP), insulin, secretin, somatostatin, motilin, pancreatic polypeptide (PP) and gastric inhibitory polypeptide (GIP), as well as blood glucose, were measured in eight healthy women before, during and after oxytocin infusion in post‐term pregnancies. Plasma VIP increased significantly (P < 0.01) during oxytocin infusion. Plasma secretin showed a significant (P < 0.05) decrease during oxytocin infusion. Plasma somatostatin remained unchanged during oxytocin infusion, but thereafter a significant (P < 0.05) increase occurred. Both plasma motilin and plasma PP showed a non‐significant increase during oxytocin infusion with sustained levels thereafter. No changes were found for plasma insulin, GIP and blood glucose.
Is serotonin involved in the ovulatory process of the rat ovary perfused in vitro?
Authors: SCHMIDT G. , KANNISTO P. , OWMAN C. , SJÖBERG N.‐O.
Published: December 2008

The presence of 5‐HT (serotonin) in ovarian tissue and its varying concentrations during the oestrous cycle suggests that it takes part in ovarian function and in the ovulatory process as one of several mediators of the inflammatory‐type reaction preceding follicular rupture. With the aid of a recirculating perfusion model, in which the central stimulatory action of 5‐HT was avoided, its direct ovarian effect on ovulation was studied using immature, pregnant, mare serum gonadotrophin (PMSG)‐treated rats. Four out of five ovaries ovulated after the addition of 5‐HT to the perfusion medium, though the ovulation rate (0.8 per ovary) did not reach the order of magnitude seen after luteinizing hormone (LH) stimulation (5.4 per ovary). The selective 5‐HT2receptor antagonist, ketanserin, did not signficantly reduce the 5‐HT induced ovulations. The nonselective 5‐HT receptor antagonist, methysergide, blocked the 5‐HT induced ovulations, and moreover, reduced the LH‐stimulated ovulations. The calcium entry blocker, nifedipine, had no effect on either 5‐HT or LH induction ovulations.
Key enzymes of myocardial energy metabolism in patients with valvular heart disease: relation to left ventricular function
Authors: SYLVÉN C. , JANSSON E. , BÖÖK K.
Published: December 2008

Endomyocardial biopsies were taken from the apex of the left ventricle in 15 patients operated on for aortic valve disease or ischaemic heart disease and from papillary muscles in six patients operated on for mitral valve disease. Activities of cardiac phosphofructokinase (PFK), total lactate dehydrogenase (LD), its isoenzyme LDD aspartate aminotransferase (ASAT), total creatine kinase (CK), its isoenzyme MB, citrate synthase (CS) and myoglobin content (MYO) were related to the angiographically determined left ventricular function. Activities of total LD, PFK and PFK/CS ratio were lower in patients with decreased, than in those with normal, left ventricular function. Myoglobin content and activities of CS and ASAT were not related to left ventricular function. It is suggested that depressed left ventricular contractility is associated with a decreased glycolytic capacity while the oxidative capacity is mainly unaltered.
Hormonal influence on utero‐ovarian blood flow distribution in the mid‐luteal pseudopregnant rat
Authors: GÅFVELS M. , OLOFSSON J. , NORJAVAARA E. , SELSTAM G.
Published: December 2008

Uterine and ovarian blood flows and ovarian fractional perfusion were measured in adult rats anaesthetized with sodium pentobarbital i.p. on day 6 of pseudopregnancy, by using radioactive microspheres. Fifty i.u. human chorionic gonadotropin (hCG) was found to increase the fractional perfusion of the ovary, and this was at least partially accomplished at the expense of the uterine blood flow, since this was reduced. Noradrenaline (NA) infusion (2 nmol min‐1) reduced ovarian as well as uterine blood flow acutely. After 20 min of NA infusion (2 nmol min‐1), however, ovarian blood flow and fractional perfusion were increased, while no significant effect was seen for uterine blood flow. Antidiuretic hormone (ADH) in a 20‐min infusion (1 nmol min‐1) markedly reduced ovarian and uterine blood flows.
Increased calcium response to ADP in blood platelets from women during ovulation compared with menstruation: cytoplasmic calcium measured with the fura‐2 technique
Authors: PEDERSEN O. S. , REICHELT K. L.
Published: December 2008

Blood platelets from women showed increased sensitivity to adenosine diphosphate (ADP) during ovulation compared with menstruation. The increased sensitivity was registered as an increase in cytoplasmic calcium response measured with the fluorescent indicator fura‐2. Agonist dose‐response studies revealed an increased maximal response, but the dose that gave half maximal response was unchanged. This indicates an increased mobility of calcium, without changed affinity to receptor(s).
Correlation between single nephron glomerular filtration rate and filtration area in superficial glomeruli of developing rats
Authors: LARSSON L. , CELSI G. , MAUNSBACH A. B.
Published: December 2008

Single nephron glomerular filtration rate (SNGFR) was correlated to the area of the glomerular basement membrane (GBM) determined by stereological techniques in rats between 20 and 40 days of age. Single nephron glomerular filtration rate increased 8.4 times in parallel with a twofold increase in GBM area. The much greater postnatal increase in SNGFR than in GBM area demonstrates that the increase in GBM area cannot account for the entire increase in SNGFR. Instead a combination of other factors influencing SNGFR most likely determines the largest part of the increase in SNGFR during this period. Thus, the drop in vascular resistance known to occur during maturation will increase the renal blood flow and may cause the filtration process to turn from a state of filtration equilibrium to or close to disequilibrium, thereby increasing GFR. Additional increase in GFR may be due to an increased net driving force for filtration and/or changed hydraulic permeability.
Neuropeptide Y and peptide YY inhibit adenylate cyclase activity in the rat striatum
Authors: WESTLIND‐DANIELSSON A. , ANDELL S. , ABENS J. , BARTFAI T.
Published: December 2008

The equilibrium binding of [3H]propionyl neuropeptide Y ([3H]pNPY) to receptors in a crude synaptic membrane preparation from the rat striatum was influenced by GTP, which caused an apparent loss of high‐affinity binding sites for [3H]pNPY. In the presence of GTP (10‐5 M), NPY and peptide YY (PYY) inhibited basal and forskolin‐stimulated adenylate cyclase activity in a concentration‐dependent manner in a cell‐free preparation from rat striatum. The IC50 values for NPY and PYY were 1 times 10 8 M and 1.4 × 10‐8 M respectively. The inhibitory action of NPY (10‐6 M) or of PYY (10‐6 M) was additive to that of acetylcholine (10‐4 M). The two peptides together also showed additivity (P < 0.05) in inhibiting adenylate cyclase.
Measurement of colloid osmotic pressure in submicrolitre samples
Authors: WIIG H. , HALLELAND E. G. , FJÆRTOFT M. , AUKLAND K.
Published: December 2008

A colloid osmometer for submicrolitre samples was constructed from solid poly‐methylmetacrylate and acrylnitrilmethylmetacrylate blocks, exposing a 0.85 mm diameter area of a Diaflo PM‐30 ultrafiltration membrane. The unknown sample, contained in a 1‐μl glass micropipette, was applied to the membrane by suction, providing minimal exposure to air. The lower limit for successful application was 0.1‐0.2 μl. The accuracy of colloid osmotic pressure (COP) measurement depends strongly on the effective compliance of the pressure transducer. We tested three different systems: (i) A Hewlett‐Packard 1280 ‘medical’ transducer gave acceptable measurements on 1‐μl samples. In smaller samples (0.1‐0.5 μl) COP was underestimated, especially at COP greater than 10 mmHg. The equilibration time was 10–30 min. (ii) As (i), but with air pressure applied to the sample by a servoregulated pump, minimizing fluid transport through the membrane. Accurate measurements on 0.2‐,μl samples were obtained in the course of 2–3 min, but the system required special instrumentation and some operating experience, (iii) An ‘industrial’ transducer, SensoNor AE‐880, with very low compliance, gave accurate measurements in the course of 1–3 min on samples as small as 0.1‐0.2 μl and COP up to 37 mmHg. We recommend system (iii) for samples smaller than 1 μl
Fatigue during dynamic muscle contractions in male sprinters and marathon runners: relationships between performance, electromyographic activity, muscle cross‐sectional area and morphology
Authors: LORENTZON R. , JOHANSSON C. , SJÖSTRÖM M. , FAGERLUND M. , FUGL‐MEYER A. R.
Published: December 2008

Knee extensor fatigue and endurance during repeated maximum isokinetic manoeuvres were studied in five sprinters and five marathon runners, all males. Fatigue and endurance were expressed in terms of output (contractional work, CW) and input (integrated electromyograms, iEMG), and was related to muscle fibre composition of m. vastus lateralis and to cross‐sectional area (CSA) of m. quadriceps.

The initially performed contractional work was positively related to the calculated absolute type II fibre area of m. vastus lateralis, but not to the cross‐sectional area of m. quadriceps. During the first 25 contractions, sprinters fatigued, with a slope of decline in contractional work that was correlated to the absolute type II fibre area, also after correction of performed work for CSA of m. quadriceps. As the electromyographic activity decreased less than the contractional work, a drastic fall in the CW/iEMG ratio was found in the sprinter group. Three out of five sprinters could perform less than 50 knee extensions, due to subjective discomfort in tested thighs. In contrast, all marathon runners could, after a minor similar decline in electromyographic activity and contractional work during the first part of the experiment, maintain a steady‐state endurance level of CW and iEMG throughout the test (200 knee extensions). In conclusion, fatigue during isokinetic maximal knee extensions is closely related to the muscle structure of m. vastus lateralis.
Enterohepatic bile‐acid circulation in the pregnant cat
Authors: RÅDBERG G. , FRIMAN S. , SAMSIOE G. , SVANVIK J.
Published: December 2008

Pregnancy increases the risk of gallstones. The physiological changes responsible for this are not clearly demonstrated. Adjustments in the enterohepatic circulation of bile acids have earlier been studied in pregnancy by methods involving dilution of labelled bile acids. In the present study the bile‐acid circulation was measured with direct drainage methods in pregnant animals and controls. It was found that the total bile‐acid‐pool size was reduced to 65% in the pregnant cat (P< 0.01) and there was a reduced accumulation of bile acids in the gallbladder after fasting 24 h (P< 0.01). Bile‐acid synthesis by the liver was not reduced and the relation between water and bile‐acid secretion by the liver was unchanged. It is concluded that, in the pregnant cat, the bile‐acid‐pool size is reduced due to a decreased accumulation of bile acids in the gallbladder and an increased interdigestive recycling rate of the bile‐acid pool (P< 0.05). One possible explanation for the reduced accumulation of bile acids in the gallbladder is delayed emptying of the stomach, inducing a late refilling of the gallbladder after a meal.
Diffusional transport of albumin from interstitium to blood across small pores in the capillary walls of rat skeletal muscle
Authors: HARALDSSON B.
Published: December 2008

The transport of radiolabelled albumin from tissue to blood was measured with an external detection technique in isolated, maximally vasodilated rat skeletal muscles. Initially, rat hindlimbs were perfused with albumin‐serum solutions containing [99mTc]albumin for at least 2 h, during which time the tracer accumulated interstitially. The accumulated tracer albumin was then washed out over a period of 1 h, using a tracer‐free, otherwise identical, perfusate. The wash‐out curve was multi‐exponential and the last 30‐min period was used to calculate the turnover rate constant (k), which was 7.5 times 10‐4 min1 (± 0.7 times 10‐4, n= 5). Moreover, if albumin was assumed to be distributed homogeneously within the interstitium, with a distribution volume (V1 of 10 ml 100 g‐1, a tissue‐to‐blood clearance of albumin (ClT‐B) of 0.0075 ml min‐1 100 g‐1 could be calculated. By this approach ClT‐B is probably slightly overestimated, but is still only 30 % of the clearance from blood to tissue (ClB‐T), as determined in several previous studies under similar conditions. Thus, transcapillary passage of albumin is highly asymmetrical, being at least three times greater from blood to tissue than in the opposite direction. This is in agreement with the concept of the capillary walls being composed of two populations of functional pores, where macromolecules are transported from blood to tissue mainly by convection through large pores, even at low filtration rates.
The effect of temperature and stimulation scheme on fatigue and recovery in Xenopus muscle fibres
Authors: LÄNNERGREN J. , WESTERBLAD H.
Published: December 2008

The influence of temperature and alternations of the stimulation scheme on fatigue development and recovery has been studied in single toe muscle fibres of Xenopus. Fatigue was in all cases produced by intermittent tetanic stimulation. In the temperature experiments easily fatigued (type 1) and fatigue‐resistant (type 2) fibres were fatigued in successive series at 10.0, 15.0 and 22.5 ±C. Lowering the temperature did not markedly influence the time‐course of fatigue development in either of the fibre types. At 22.5 ±C these fibres usually display post‐contractile depression (PCD), a delayed force suppression, during the recovery period. At the lower temperatures PCD was not observed in type 1 fibres and it was delayed in type 2 fibres. Only type 1 fibres were studied in the altered stimulation scheme experiments. Neither the time‐course of fatigue development nor the recovery process was markedly influenced by an alteration of tetanic stimulus frequency in the range of 40–80 Hz. Increasing the time‐tension area produced before the standard fatigue level (40 % of the original force) was reached, by increasing the initial interval between tetani, caused a more pronounced PCD. From these results it can be concluded that fatigue development and recovery are complex processes which cannot be readily explained by a single mechanism.
Apomorphine and pergolide induce hypothermia by stimulation of dopamine D‐2 receptors
Authors: ÖGREN S. O. , FUXE K.
Published: December 2008

Studies in the male rat have shown that the dopamine D‐2 receptor antagonists sulpiride and eticlopride, produce a dose‐dependent prevention of the hypothermia induced by the D‐1/D‐2 receptor agonist apomorphine and the relatively selective D‐2 agonist pergolide in the rat. In contrast, the D‐1 antagonist SCH 23390 (given by the s.c. and i.p. route of administration) failed to prevent the hypothermic effect induced by both DA agonists, but tended to enhance the hypothermia caused by the two DA agonists. Thus, D‐2 dopamine receptors appear to play a decisive role in the mediation of the hypothermic response of apomorphine and pergolide. There may also exist an interaction between D‐i and D‐2 receptors in the expression of DA‐agonist‐induced hypothermia.
Skeletal muscle glucolysis, glycogenolysis and glycogen phosphorylase during electrical stimulation in man
Authors: REN J. M. , CHASIOTIS D. , BERGSTRÖM M. , HULTMAN E.
Published: December 2008

Phosphorylase activity, glycogenolytic and glucolytic rates were estimated in human quadriceps muscle during electrical stimulation at 20 Hz. Two stimulation periods of 10 s duration were separated by a pause of 60 s. The blood circulation to the leg was intact or occluded during the experiment. ATP turnover rates and force production were of the same order during the two contraction periods both with and without intact blood flow. Also the increase in phosphorylase a activity (from ‐ 30% to ‐ 65%) was the same during the contraction periods. Glycogenolytic and glucolytic rates were however about 30% higher (P < 0.05) during the second contraction compared with the first when circulation was occluded, but similar when the circulation was intact. During the 60 s rest period, the phosphocreatine (PCr) was maintained at a low level and inorganic phosphate (P1) remained increased under occluded circulation while PCr was resynthesized in the rest period with intact circulation. We conclude that the increased glycogenolytic rate observed during the second contraction with occluded blood circulation was due to the high [P1] in the muscle and that the increased glucolytic rate was caused by high [P1] and low [PCr]. In the rest period with anoxia the glycogenolysis was completely inhibited and glucolysis was inhibited by 95 % in spite of the changes in [PCr] and [P1].
Changes in plasma concentrations of aromatic and branched‐chain amino acids during sustained exercise in man and their possible role in fatigue
Authors: BLOMSTRAND E. , CELSING F. , NEWSHOLME E. A.
Published: December 2008

The plasma concentrations of branched‐chain and aromatic amino acids have been measured in two different types of sustained dynamic exercise. Twenty‐two subjects participated in the 1986 Stockholm Marathon and eight subjects took part in an army training programme of approximately 1.5‐h duration. Both types of exercise caused a significant decrease in the plasma concentration of branched‐chain amino acids, while there was no change in the concentration of total (free plus bound to albumin) tryptophan. The plasma concentration of free tryptophan, which was measured in the marathon runners, was found to increase 2.4‐fold during the race. This increase is probably caused by a pronounced elevation in the concentration of plasma free fatty acids during exercise, since these are known to displace tryptophan from albumin. The observed increase in plasma free tryptophan concentration, together with the decrease in plasma concentration of branched‐chain amino acids, gives rise to a marked increase in the plasma concentration ratio of free tryptophan/branched‐chain amino acids. This should lead to an increase in the rate of transport of tryptophan across the blood‐brain barrier and hence to an increase in the rate of synthesis of 5‐hydroxytryptamine (5‐HT) in the brain. An elevated concentration of 5‐HT in specific areas of the brain may be responsible, at least in part, for the development of physical, and/or mental fatigue during prolonged exercise.
Measurements of macula densa cell volume changes in isolated and perfused rabbit cortical thick ascending limb. I. Isosmotic and anisosmotic cell volume changes
Authors: GONZÁLEZ E. , SALOMONSSON M. , MÜLLER‐SUUR C. , PERSSON A. E. G.
Published: December 2008

A method to measure time‐dependent volume changes in macula densa (MD) cells is described. Cell volume is calculated from cell height measurements for which an image‐splitting eyepiece is used. This paper presents the results of experiments designed to investigate the behaviour of the macula densa cells in anisosmotic media, to evaluate the cell volume response to sudden decreases in luminal or peritubular osmolarity and to examine the effect of different luminal NaCl concentrations on the steady‐state isosmotic cell volume and on the regulatory volume response to anisosmotic media. The result showed that induced alteration in macula densa cell volume did not change macula densa surface area, but only cell height. The mean control cell height was 13.3 μm ± 0.4. When MD cells were exposed to a luminal osmolarity of 180 mosM (control 300 mosM) they swelled only to 1.19 ± 0.02 of the control value and with furosemide present to 1.13 ± 0.02 or with low NaCl to 1.13 ± 0.01. While after 5 min of exposure values were 1.15 ± 0.03, 0.99 ± 0.02 and 1.02 ± 0.02, respectively. Addition of furosemide (10‐1 M) to the luminal perfusate (300 mosM) resulted in a rapid decrease in cell height to 0.8 ± 0.02 in relation to control. When furosemide was removed cell volume was restituted (0.98 ± 0.03). When luminal perfusate was replaced by mannitol and (12 mM Na+, 7 mM CI‐) cell volume decreased to 0.83 ± 0.02 of the control value.

The results of this study are in accordance with the view that the macula densa cells have a furosemide‐sensitive NaCl absorption system (cation and chloride co‐transport) across the apical membrane. The basolateral cell membrane have very rapid regulatory mechanisms which maintain the cell volume during reductions in basolateral osmolarity. The transport properties of the macula densa cells are not affected by maximal and supramaximal doses of vasopressin. These findings offer more direct support to the hypothesis that the initiation of the tubuloglomerular feedback response involve furosemide‐inhibitable uptake of sodium and chloride ions into the macula densa cells ‐ where the ions would, subsequently, be absorbed and accumulated inside the juxtaglomerular interstitium.
Sympathetic vascular control of the pig nasal mucosa (2): reserpine‐resistant, non‐adrenergic nervous responses in relation to neuropeptide Y and ATP
Authors: LACROIX J. S. , STJÄRNE P. , ÄNGGÅRD A. , LUNDBERG J. M.
Published: December 2008

The possible occurrence of non‐adrenergic mechanisms in the sympathetic vascular control of the nasal mucosa was studiedin vivousing reserpine‐treated pigs (1 mg kg‐1, i.v., 24 h earlier) in combination with pharmacological blockade of alpha‐adrenoceptors by local phenoxybenzamine (1 mg kg‐1, i.a.) infusion. The nasal mucosal depletion (99%) of the content of noradrenaline (NA) in reserpinized animals was not influenced by preganglionic denervation while the depletion (44%) of neuropeptide Y (NPY) was prevented. Upon stimulation with single shocks, 25% of the arterial blood flow reduction and 47 % of the nasal mucosal volume reduction (reflecting contraction of venous sinusoids) were still present after reserpine as compared with controls. In reserpinized animals, the vascular responses were slow developing and long‐lasting, and about 60% remained at 0.59 Hz and more than 80% at 6.9 Hz. The vascular effects after reserpine were, however, subjected to fatigue, which may explain why phenoxybenzamine treatment still reduced the functional effects in the absence of NA. Local intra‐arterial injections of NA, NPY and the metabolically stable adenosine‐5′‐triphospate analogue alpha, beta‐methylene ATP (mATP) caused reduction in both arterial blood flow and nasal mucosal volume. The C‐terminal fragment of NPY (NPY 13–36) also induced nasal vasoconstriction although with a fivefold lower potency than NPY 1–36. Adenosine‐5′‐triphosphate caused a biphasic vascular effect with vasodilatatory actions at low doses and a short‐lasting vasoconstriction followed by vasodilatation at very high doses (100‐fold higher than the threshold response to mATP). In contrast to the response to NA, the long‐lasting vascular effects of NPY and mATP were resistant to phenoxybenzamine treatment.

In conclusion, although NA is likely to mediate most of the sympathetic vascular responses to low‐frequency stimulation in the pig nasal mucosa, a large resistance and capacitance vessel component upon high‐frequency stimulation seems to be non‐adrenergic and mimicked by NPY rather than ATP.
Serotonergic regulation of canine enteric motility (measured as electrical activity) and absorption: physiologic and morphologic evidence
Authors: BJÖRCK S. , AHLMAN H. , DAHLSTRÖM A. , PHILLIPS S. F. , KELLY K. A.
Published: December 2008

To explore the effect of serotonin (5‐HT) on enteric electrical activity, transit and absorption, four dogs were prepared with 50 cm jejunal and ileal Vella loops. Electrodes for recording enteric electrical activity were attached to the loops and to the main small bowel. After recovery, both loops were perfused with a [14C‐]PEG‐glucose‐electrolyte solution via the proximal stomas, while effluent was collected from the distal stomas and enteric electrical activity was monitored. Control periods were compared with periods when 5‐HT was infused intravenously at a rate of 10 μg kg‐1min‐1for 60 min. Serotonin increased the mean ± SEM% of jejunal and ileal pacesetter potentials with spike potentials from 33 ± 7% and 35 ± 9%, before infusion to 63 ± 4% and 61 ± 5% after infusion (P< 0.05). Serotonin also induced distally‐migrating bursts of spikes in the incontinuity small bowel. The changes were blocked by atropine, but not by ketanserin. Absorption of water, sodium and glucose from the jejunal and ileal loop and transit through the loops was not changed by 5‐HT. At autopsy, all layers of the jejunum and ileum contained varicose nerve fibres with a positive immunoreaction to 5‐HT, while positive nerve cell bodies were largely confined to the submucosa.
Somatostatin inhibits prolactin secretion by multiple mechanisms involving a site of action distal to increased cyclic adenosine 3‘,5’‐monophosphate and elevated cytosolic Ca2+in rat lactotrophs
Authors: BJØRO T. , ØSTBERG B. C. , SAND O. , TORJESEN P. A. , PENMAN E. , GORDELADZE J. O. , IVERSEN J.‐G. , GAUTVIK K. M. , HAUG E.
Published: December 2008

The release of prolactin (PRL) from a clonal cell‐line of anterior pituitary cells (GH4C1) was inhibited by somatostatin (SRIH) in a dose‐dependent manner (ED50nM). The inhibition (20% of control levels) was detectable within 50 s and maximal within 90 s. Thyroliberin (TRH) enhancement of PRL secretion was biphasic. SRIH inhibited both phases equally. Ionomycin in combination with the phorbol ester, TPA, mimics the TRH‐elicited PRL release, and SRIH partly inhibited this effect. SRIH had no effect on TRH‐stimulated formation of inositol trisphosphate, and only small effects on TRH‐activated adenylate cyclase. Vasoactive intestinal peptide (VIP) and forskolin stimulated cAMP formation and PRL release potently. SRIH inhibited both effects of VIP and forskolin, and there was a close correlation between the inhibition of PRL secretion and cAMP accumulation. 8‐Bromo‐cAMP enhanced PRL release, an effect that was also partly reduced by SRIH. The Ca2+channel activator, BAY‐K‐8644 and high extracellular K+increased PRL release, and SRIH caused a partial reduction in the release response to both secretagogues. SRIH lowered [Ca2+]1, and markedly reduced the rise in [Ca2+]1elicited by TRH, VIP and K+. SRIH did not influence the Ca2+spikes recorded in Na+‐free solution, and had no effect on the TRH‐induced membrane potential changes.Ourresults demonstrate that SRIH may inhibit PRL release from GH4C1cells by (1) inhibiting hormone‐sensitive adenylate cyclase, (2) blocking the effect of cAMP and (3) lowering [Ca2+]1. None of these effects is, however, sufficient to explain all the effects of SRIH, suggesting that SRIH also exerts a major action at a step subsequent to cAMP accumulation and [Ca2+]1elevation. Since the GH4C1cells possess one single class of binding sites, this implies that the same SRIH receptor is coupled to several cellular signalling systems.
The effect of splanchnic nerve stimulation and neuropeptide Y on cholera secretion and release of vasoactive intestinal polypeptide in the feline small intestine
Authors: SJÖQVIST A. , FAHRENKRUG J. , JODAL M. , LUNDGREN O.
Published: December 2008

The effect of sympathetic nerve stimulation and intra‐arterial infusion of neuropeptide Y (NPY) on net fluid secretion and release of vasoactive intestinal polypeptide (VIP) was studied in the cat small intestine during a secretion due to cholera toxin. Activation of the splanchnic nerves (4 Hz, 5 ms, 5 V) decreased net fluid secretion to 57 ± 10% of control. Concomitantly, the release of VIP was reduced to less than 50 %. Furthermore, close i.a. infusion of NPY (estimated increase in plasma concentration 75 nmol l‐l) reduced the net fluid secretion and VIP release to 27 ± 5 and 28 ± 4% of the pre‐stimulatory value. The correlation between the decrease in net fluid secretion and reduction in VIP release showed a strong positive correlation (r= 0.83). These results strongly indicate that the antisecretory effect of sympathetic nerve stimulation during cholera diarrhoea is mediated by inhibition of secretory VIP neurons in the intestinal mucosa. A similar mechanism is also proposed for the intravascularly administered NPY.
The cardiovascular effects of deconditioning after endurance training in rats
Authors: KARHUNEN M. K. , RÄMÖ M. P. , KETTUNEN R. , HIRVONEN L.
Published: December 2008

The haemodynamic effects of endurance training and physical deconditioning were studied in anaesthetized rats using aortic and left ventricular pressure recordings and volume measurements by thermodilution method during isoproterenol and CaCl2 loads. The resting stroke volume was significantly larger in the training group (TG I, n= 10) than in the control group (CG I, n= 13). During the CaCl2 infusion stroke index, end‐diastolic and end‐systolic volumes increased in the TG I, but decreased in the CG I. Both isoproterenol and CaCl2 decreased systemic vascular resistance in the TG I, but increased it in the CG I. After a six‐week deconditioning following training period (TG II, n= 10) stroke index, end‐diastolic and end‐systolic volumes decreased during CaCl2 and isoproterenol infusions similarly to the control deconditioning group (CG II, n= 12). These responses differed significantly from those observed in the TG I. Peripheral resistance increased in both the CG II and the TG II. Cardiac hypertrophy observed during training was partly reversed after the deconditioning period. In conclusion, endurance training improves the pumping performance of the rat heart by enhancing the diastolic filling of the left ventricle and decreasing peripheral resistance during inotropic load. Left ventricular contractility is not affected. A six‐week deconditioning period after endurance training returns the haemodynamic changes to sedentery levels.
Effects of adrenal demedullation on stress‐induced hypertension and cardiovascular responses to acute stress
Authors: KNARDAHL S. , SANDERS B. J. , JOHNSON A. K.
Published: December 2008

Because chronic infusions of adrenalin (A) produce hypertension in rats, it has been suggested that A is a mediator of stress‐induced hypertension. In order to test the hypothesis that lowering A will attenuate stress‐induced hypertension, rats who had their adrenal medullae removed (ADM) and sham‐operated controls were subjected to chronic stress. All subjects were offspring of a cross between spontaneously hypertensive and Wistar‐Kyoto rats. Prior to chronic stress, systolic pressures were the same in the two groups. The stress consisted of 60 2‐h sessions of shock‐shock conflict during 18 weeks. After conflict stress, the rats were implanted with arterial catheters and allowed two days to recover. The resting mean arterial pressure (MAP) was 141.2 mmHg in the ADM group and 142.3 mmHg in the Sham group. Cardiovascular responses to acute stress were then examined. The rats were transferred to a test‐box and subjected to pulsed foot shocks (0.5‐s duration, 5‐s intervals) for 5 min. The MAP increase after transfer was 22.3% in the ADM and 4.2% in the Shams (P < 0.001). After termination of the shocks, the MAP was elevated 22.2% above baseline in the ADM and 8.1 % in the Shams (P < 0.02). Five minutes after foot shocks the MAP increase was 21.6% in the ADM and 7.2% in the Shams (P < 0.02). Adrenal demedullation was effective in attenuating plasma A during stress and reduced the plasma noradrenaline response. Therefore, the larger pressor responses of the ADM group seem to result from attenuation of β‐adrenoreceptor‐mediated dilation of skeletal muscle vasculature. If lowering A has a beneficial effect, it may have been offset by attenuation of β‐adrenergic vasodilation.
Regulation of spinal cord blood flow in the rat as measured by quantitative autoradiography
Authors: HOLTZ A. , NYSTROM B. , GERDIN B.
Published: December 2008

Spinal cord blood flow (SCBF) and its response to alterations in blood gases and to systemic hypotension, haemodilution and barbiturate anaesthesia were measured in 47 rats at the level of Th 7–8 by quantitative autoradiography with [14C]iodoantipyrine ([14C]IAP) as tracer. During normocapnia and normoxia the mean SCBF values in the grey and white matter were 94 ± 21 and 17 ± 3mlmin‐1 100 g‐1, respectively. SCBF was highly dependent on PaCO2. Thus in hypercapnic animals (PaCQ2 > 9 kPa) SCBF was increased in grey and white matter to 228 ± 22 and 54 ± 7mlmin‐1 100 g‐1 while during hypocapnia (PaCO2 < 3.9 kPa) it was decreased to 64 ± 14 and 11 ± 2 ml min‐1 100 g‐1, respectively. Mean arterial blood pressure (MABP) was reduced by withdrawal of blood to 80 ± 8 mmHg in a light hypotension group and to 53 ± 11 mmHg in a severe hypotension group, compared with 126 ± 13 mmHg in a control group. There was no significant difference in SCBF between the control group and the hypotension groups, suggesting that autoregulation is maintained down to an MABP of at least 50 mmHg. Normovolemic haemodilution, with a reduction of the haematocrit from 50 ± 2 to 33 ± 3, increased SCBF to 113 ± 9 ml min‐1 100 g‐1 in grey matter and to 21 ± 12 ml min‐1 100 g‐1 in white matter. Thirty minutes after an intraperitoneal injection of pentobarbital at 40 mg kg‐1 body weight, SCBF was not significantly lower than in the control group.
Haemodynamics and plasma ANP (atrial natriuretic peptide) after acute blood volume expansion in normotensive and spontaneously hypertensive rats
Authors: PETTERSSON A. , RICKSTEN S.‐E. , TOWLE A. C. , HEDNER J. , HEDNER T.
Published: December 2008

Atrial natriuretic peptide (ANP) was measured in plasma during acute volume load in conscious, spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto (WKY) rats. During basal conditions immunoreactive ANP were similar in the SHR (630 ± 56 pmoles 1‐1) and the WKY (657 ± 114 pmoles 1‐1) groups. An acute 10% and 20% whole blood volume expansion resulted in a linear increase in immunoreactive plasma ANP in the WKY. In the SHR the increase in plasma ANP was attenuated during the 20% volume load. During the 10% and 20% volume load central venous pressure (CVP), central blood volume (CBV) and cardiac output increased relatively more in the SHR compared with the WKY group. In contrast, the increase in peripheral blood volume (PBV) and decrease in heart rate (HR) was attenuated in the SH rats. In the SHR group there was a shift of the ANP vs. CVP and ANP vs. CBV curves to the right compared with the WKY. We conclude that acute volume loading is a potent stimulus for ANP release in WKY as well as SHR. However, in the SHR, ANP release was blunted in spite of the increased centralization of the volume load in this rat strain. Thus, the decreased reponsiveness of the ANP hormonal system may contribute to the development and maintenance of hypertension in this genetic form of hypertension.
A heterogenous population of α1‐adrenoceptors mediates contraction of the isolated follicle wall from the bovine ovary
Authors: KANNISTO P. , OWMAN CH. , SCHMIDT G. , SJÖBERG N.‐O.
Published: December 2008

Strips from Graafian follicles of bovine ovaries were tested for their contractile responsein vitroin order to characterize the type of post‐junctional α‐adrenoceptor involved. Electrically induced contractions were inhibited concentration‐dependently by the α1‐ antagonist, prazosin. Besides noradrenaline the α1‐ selective agonists, methoxamine and phenylephrine, caused the strips to contract, whereas the α2‐ selective agonists clonidine, oxymetazoline and B‐HT920 were without effect. However, the α1‐ selective antagonist prazosin gave a line with a slope less than unity in the Schild plots with noradrenaline and methoxamine. From results obtained with or without the presence of two classes of neuronal uptake blockers (desipramine and cocaine) it is concluded that the postjunctional α1‐ receptor population is inhomogeneous. The regular appearance of the Schild plot obtained with phenylephrine may be due to involvement also of a component of noradrenaline release by this agonist. The pA2value in the test with phenylephrine was 9.27, with a correspondingkBof 3.81 ± 1.15 times 150‐10M.
Effects of oxygen free radical scavengers, xanthine oxidase inhibition and calcium entry‐blockers on leakage of albumin after ischaemia. An experimental study in rabbit kidneys
Authors: BRATELL S. , FOLMERZ P. , HANSSON R. , JONSSON O. , LUNDSTAM S. , PETTERSSON S. , RIPPE B. , SCHERSTÉN T.
Published: December 2008

The effect of pretreatment with various substances protecting against oxygen free radicals on the leakage of proteins across the vessel walls of rabbit kidneys induced by ischaemia has been studied. The leakage of proteins was estimated from the difference between the 120‐min distribution space of [131I]albumin and the 5‐min distribution space of [125I]albumin, the latter mainly measuring the intravascular volume. Neither SOD (superoxide dismutase), catalase, allopurinol or two different Ca2+ channel blockers (nifedipine, felodipine) could alone reduce the leakage induced by ischaemia. A combined pretreatment with SOD, catalase and nifedipine reduced the leakage in the cortex, and pretreatment with mannitol alone reduced the leakage in the cortex and outer stripe of the medulla. The results indicate that oxygen free radicals are involved in the leakage of proteins across the vessel walls induced by ischaemia, but that other mechanisms are involved as well.
Receptor autoradiograhical evidence of a preferential reduction of binding sites for atrial natriuretic factor in renal papilla of the spontaneously hypertensive rat
Authors: AGNATI L. F. , FUXE K. , HÄRFSTRAND A. , LANG R. E. , UNGER T. , GANTEN D.
Published: December 2008

In the spontaneously hypertensive rat (SHR) as well as in the pathophysiological states with volume retention, high levels of atrial natriuretic factor (ANF) do not produce adequate diuresis and natriuresis. We have investigated the question whether the reduced effectiveness of ANF could be due to a reduction of the ANF binding. Evidence is provided by quantitative autoradiography with [125I]ANF than higher ANF plasma levels in SHRSP compared to normotensive WKY rats are associated with a reduced number of binding sites (25%) in the renal papilla as well as in the subfornical organ (69%). This could contribute to the reduced response of ANF in SHRSP.
Plasma elimination kinetics and renal handling of copper/zinc superoxide dismutase in the rat
Authors: BAYATI A. , KÄLLSKOG Ö. , ODLIND B. , WOLGAST M.
Published: December 2008

The renal handling of bovine and human superoxide dismutase (SOD) was investigated in Sprague—Dawley and Munich—Wistar rats. Under normal physiological conditions the half‐time of the major rapid component of the plasma elimination curve was estimated at 6.0 ± 0.5 min, the volume of distribution at 35.7 ± 3.3 ml kg‐1, i. e. the plasma volume and the corresponding plasma clearance at 4 ml min‐1 kg‐1. After a single intravenous dose, most of the enzyme was distributed to and eliminated by the two kidneys, whereas the non‐renal clearance was low, 0.5 ml min‐1 kg‐1. The single nephron filtration of SOD, as assessed from micropuncture of Bowman's space, was 10.4 ± 1.0 nl min‐1, which was 26 ± 2% of that for inulin. The total elimination of SOD by glomerular filtration would thereby be 2.5 ml min‐1 kg‐1, i. e. the glomerular ultrafiltration process would account for the largest part of the elimination of SOD from circulating plasma. After the dosage of 20 mg kg‐1, about two‐thirds of the injected SOD was excreted as the intact molecule into the urine, whereas one‐third was found to be reabsorbed and metabolized by the proximal tubular epithelial cells. In animals suffering from unilateral post‐ischaemic acute renal failure, the elimination half‐time was 13 ± 1.9 min, a value which increased by 55 ± 5 min after bilateral functional nephrectomy. By contrast, the distribution volume remained essentially unchanged.