bluuebunny/crossref_metadata_2025 huggingface dataset:
Decrease in survival time in β2‐adrenoceptor blocked cats exposed to bleeding
Authors: GUSTAFSSON DAVID , ANDERSSON LARS OLAF , LUNDVALL JAN
Published: December 2008

Our previous investigations have indicated that β2‐adrenergic regulatory mechanisms contribute to important compensatory hemodynamic adjustments in hemorrhage. In the present study an attempt was made to examine, by comparative observations after standardized fatal hemorrhage on cats with intact and ‘selectively’ blocked β2‐adrenoceptors (ICI 118,551), whether such compensatory effects are crucial for survival. On the average, the survival time after bleeding was 686 min in cats with intact and 427 min in cats with blocked β2‐adrenoceptors (p < 0.05), the difference thus approaching 4.5 h. It is suggested that the reduced survival time after β2‐blockade, at least partly, can be ascribed to interference with the circulatory β2‐adrenergic control in hemorrhage aimed at improving tissue perfusion.
Adenosine antagonism and related effects of theophylline derivatives in guinea pig ileum longitudinal muscle
Authors: GUSTAFSSON LARS E.
Published: December 2008

Alkylxanthines, such as theophylline and 8–(p‐sulfo)phenyltheophylline were found to enhance contractile responses to transmural nerve stimulation in guinea pig ileum longitudinal muscle. At higher concentrations, theophylline and the non‐sulfonylated compound 8–phenyltheophylline inhibited contractile responses, an action not observed with the sulfoderivative. Direct muscle responses to electrical stimulation in the presence of tetrodotoxin were markedly inhibited by theophylline but were unaltered by 8–(p‐sulfo)phenyltheophylline. During nerve stimulation acetylcholine release, as measured by gas chromatography‐mass spectrometry, was significantly increased by application of 8–(p‐sulfo)phenyltheophylline. The enhancing action by alkylxanthines is thus due to a prejunctional effect, via increased transmitter release. The enhancing action was most marked with the sulfo‐derivative, which also showed characteristics of truly competitive adenosine antagonism, with slope of unity in Schild plots, when 2‐chloroadenosine was used as agonist. The enhancing action by 8–(p‐sulfo)phenyltheophylline was unaffected by the cyclic AMP phosphodiesterase inhibitor, ZK 62.711, which, however, enhanced the postjunctional inhibitory action of theophylline. It is thus suggested that alkylxanthine derivatives have a prejunctional enhancing action due to adenosine antagonism, and a postjunctional inhibitory action due to cyclic AMP phosphodiesterase inhibition. Furthermore, 8–(p‐sulfo)phenyltheophylline is suggested to be selectively acting on extracellular adenosine receptors, and lacking in phosphodiesterase inhibition, because of negligible intracellular penetration due to its permanent charge in aqueous solution. Purine modulation of neurotransmission is more pronounced in the ileum, than previously understood.
Influence of intravenous saline infusion on the aortic baroreceptor and left atrial B‐type receptor activity in dogs
Authors: HAKUMÄKI MARTTI O. K. , HYÖDYNMAA SIMO J.
Published: December 2008

Influence of i. v. saline infusion on aortic arch pressure, left atrial mean pressure, heart rate, and the time‐related characteristics of aortic arch baroreceptor and left atrial B‐type receptor activities were studied in 20 beagle dogs. Saline infusion induced tachycardia in 10 dogs and bradycardia in 10. Aortic arch and left atrial pressures increased in both HR response groups. The average discharge rate of baroreceptors increased in both HR response groups, while the duration of baroreceptor burst, the number of baroreceptor action potentials/heart cycle and the average burst frequency did not increase significantly in the group that responded with tachycardia but increased significantly in the group that responded with bradycardia. The number of left atrial B‐type action potentials/heart cycle, the average discharge rate and average burst frequency increased in both HR response groups. We conclude that the duration of baroreceptor burst, baroreceptor average burst frequency and the number of baroreceptor impulses/cardiac cycle are the important parameters eliciting baroreceptor reflex to i. v. saline infusion.
Non‐homogeneous blood flow distribution in the rabbit tenuissimus muscle Differential control of total blood flow and capillary perfusion
Authors: LINDBOM LENNART , ARFORS KARL‐E.
Published: December 2008

Structural and functional relationships underlying the blood flow distribution in the rabbit tenuissimus muscle were examined by means of intravital microscopy. A majority of the main feeding arterioles (transverse arterioles) continued into adjacent connective tissue, after giving off branches (terminal arterioles) within the muscle tissue to supply the muscle capillaries. The transverse arterioles thus supplied two vascular areas, although the major part of the arteriolar flow, under normal resting conditions, was distributed to the muscle capillaries—a flow fraction over which the terminal arterioles exerted ultimate control. The fractional distribution of the blood flow between muscle and connective tissue was determined by the relative contributions of the transverse and terminal arterioles to the vascular resistance. These arteriolar segments showed a differential response to an increase in oxygen availability (elevated ambient pO2), resulting in a total reduction of muscle capillary flow, but no concomitant change in the flow to connective tissue. A decrease in perfusion pressure, on the other hand, led to similar flow changes in the muscle and connective tissue circulation, which was attributed to proportionate resistance changes in the transverse and terminal arterioles. Differences between the larger transverse and smaller terminal arterioles in their sensitivity to various stimuli may form a functional basis for a differential control of arteriolar blood supply and capillary perfusion in this muscle.
An evaluation of the metabolic interaction with myogenic vascular reactivity during blood flow autoregulation
Authors: BORGSTRÖM PER , GRÄNDE PER‐OLOF , MELLANDER STEFAN
Published: December 2008

An attempt was made to evaluate the possible metabolic interaction with myogenic vascular reactivity during autoregulation of blood flow in sympathectomized cat skeletal muscle. This was done by studying the extent to which a purely myogenic response, elicited by a standardized 2 s vascular transmural pressure impulse stimulus was altered when mean arterial inflow pressure was varied in the range from 160 down to 40 mmHg. The observations were made during the steady state blood flows encountered at the different pressure levels. The data were corrected for the effects of physical factors inherent in altered basal vascular tone and intravascular pressure with the aid of a mathematical model for purely myogenic responses. The results demonstrated a flow dependent decline in myogenic vascular reactivity during reduction of arterial pressure, even in the range where blood flow was autoregulated quite effectively. This suggested a significant metabolic interaction with myogenic reactivity, an interpretation corroborated by a similar decline in myogenic reactivity found during more defined activation of the vascular metabolic control system by graded light muscle exercise. The fact that a significant metabolic interaction was revealed even at such minute flow changes that occur in the autoregulatory range indicates a high ‘gain’ in the metabolic feedback interacting, directly or indirectly, with myogenic mechanisms in local vascular regulation.
Effect of GM1ganglioside treatment on the recovery of dopaminergic nigro‐striatal neurons after different types of lesion
Authors: TOFFANO G. , AGNATI L. F. , FUXE K. , ALDINIO C. , CONSOLAZIONE A. , VALENTI G. , SAVOINI G.
Published: December 2008

The effect of GM1ganglioside treatment on the recovery of biochemical and behavioral parameters which define the activity of nigro‐striatal dopaminergic systems has been investigated in rats after different types of lesion. GM1favours the recovery of tyrosine‐hydroxylase activity, of the number and affinity of3H‐N‐n‐propyl‐norapomorphine binding sites in the striatum of the lesioned side and reduces the apomorphine‐induced rotational behavior after mechanical (i. e. unilateral hemitransection) but not after chemical (i. e. 6‐OHDA injected in the substantia nigra) lesion. The source of regrowing dopaminergic nerve terminals in the striatum after hemitransection is mainly a response of intact remaining axons of the ipsilateral side. Moreover the contralateral nigro‐striatal systems seems to play, through intrathalamic connections, an important role in regulating the GM1‐induced increase of the tyrosine‐hydroxylase activity.
Incorporation of biogenic amines into phospholipids studied in two‐phase‐system
Authors: LISHAJKO F.
Published: December 2008

Phospholipids (PL) from splenic nerves, splenic nerve granules, adrenal medullary granules and egg yolk were used as binding ligands for studies on uptake of various biogenic amines. Efficient uptake of catecholamine (CA) occurred at low ionic strength (about 2–5 mM) and at pH 6.8‐7.7. This uptake was also a function of the amine concentration in the aqueous medium. At higher ionic strength (e. g. 128 mM K‐phosphate buffer) an uptake still occurred, but to considerably less extent, apparently since the association/dissociation ability of the amines within the PL was a function of cation concentration in the aqueous media. Sucrose‐ and dextrose‐induced increase in the osmolarity of the aqueous medium did not to any appreciable extent reduce the CA uptake. Scatchard plot indicated that only one type of binding sites was engaged when PL from splenic nerves was used. Using PL from splenic nerves the following affinity order was obtained for the amine tested: 5‐HT>TA>DA>NA>IP>A. When PL from medullary granules was used the order was: DA>IP>ANA. No or negligible uptake of Dopa and its metabolites Doma and Dopac occurred. When added to the aqueous medium, the cationic amphiphilic detergent CTAB induced some uptake of Doma and Dopac, but no a Dopa. However, CTAB considerably diminished the uptake of NA and the other amines. On the other hand, ionic (DOC) and anionic (SDS) detergents strongly increased the uptake of NA and other amines into PL. The nonionic Triton X‐100 was without significant effect on uptake of NA. It is suggested that the binding ligands may be present in the dipolar head of the PL molecules, particularly in the lipid phosphate group. The lipid protein may also be partially involved since chromatographic experiments showed that the CA accompanied lipid phosphorus and lipid protein. Electrostatic or complex interaction of CA within the polar head group or in conjunction with lipid protein would constituate an amine storage with efficient association/dissociation capacity.
The intracarotid 133Xenon injection method for measurement of cerebral blood flow (CBF) in rats: evaluation of the effect of bolus volume
Authors: HERTZ M. M. , BARRY D. I. , HEMMINGSEN R. , BOLWIG T. G.
Published: December 2008

It is assumed that the cerebral microcirculation is not perturbed by the intraarterial injection used in determination of cerebral blood flow (CBF) with the intrarterial 133Xenon technique (and in various assessments of blood brain barrier (BBB) permeability). The application of these techniques to the rat, where the injectate is large compared to normal blood flow, places this problem is focus and it has been claimed that since large intracarotid injections increased cerebral venous outflow, the CBF must also increase. We investigated this problem in the rat by means of the intraarterial 133Xenon injection technique, using a saline bolus injected in less than 1 sec and found that CBF was unaltered at bolus volumes between 10 and 100 μl. Furthermore, injection of 100–200 μl saline during washout detection did not change the slope of the semilogarithmic wash‐put curves. It is concluded that in spite of large intracarotid injections the CBF remained constant and that the hemodilution produced by the saline bolus is not sufficient to inflence CBF. Consequently, estimations of CBF yield valid results in the present rat preparation.
Effects of atropine or high frequency burst excitation on the composition of parasympathetic rat parotid saliva
Authors: EKSTRÖM J. , MÅNSSON B. , TOBIN G.
Published: December 2008

In the presence of atropine continuous trains of impulses applied to the auriculo‐temporal nerve at relatively high frequencies evoked a flow of parotid saliva that amounted to 5–10% of that before administration of the muscarinic blocker. The output of total protein, amylase, sodium and potassium decreased markedly. However, in terms of concentration protein and amylase increased, while sodium decreased and potassium was unchanged. When, in the absence of atropine, the continuous mode of stimulation was replaced by bursts of impulses of high frequencies the amount of saliva decreased. However, the concentration of protein, amylase and potassium increased, while the concentration of sodium decreased. The findings are discussed in relation to a possible peptidergic innervation of the secretory elements.,
Neuronal and extraneuronal uptake of L‐3H‐adrenaline and L‐14C‐noradrenaline in the fish spleen
Authors: UNGELL ANNA‐LENA , NILSSON STEFAN
Published: December 2008

The neuronal and extraneuronal uptake of adrenaline and noradrenaline in the isolated perfused spleen of the cod has been studied using radiolabelled amines. The neuronal uptake of adrenaline shows an optimum at 0.5 μg/ml, but is less efficient than for noradrenaline in the concentration range 0.01–2.5 μg/ml. The neuronal uptake of noradrenaline accounts for 60–70% of the total (neuronal plus extraneuronal) uptake in the concentration range 0.01–1.0 μg/ml. At higher concentrations (2.5–5.0 μg/ml) the importance of the extraneuronal uptake increases for both amines, to reach more than 90% of the total uptake at 5.0 μg/ml. The extraneuronal uptake shows equal efficiency for the two amines throughout the concentration range studied. It is concluded that the cod spleen possesses a neuronal uptake mechanism which shows a higher uptake efficiency for noradrenaline than for adrenaline, while the extraneuronal uptake mechanism shows no preference.
Calcitonin‐like immunoreactivity in human milk, longitudinal alterations and divalent cations
Authors: ARVER S. , BUCHT E. , SJÖBERG H.E.
Published: December 2008

The concentration of immunoreactive calcitonin (iCT) in human milk was 10–40 times the serum level. Thus in milk samples collected from 29 mothers within one week and from 46 mothers three months post partum the levels of iCT were respectively 2.46±0.99 ng/ml (mean ± SD) and 0.58±0.08 ng/ml. Eight of the 29 mothers delivered milk at two occasions, 1–2 and 4–6 days after delivery. There was a significant decline of iCT with about 20% during this period. One mother delivered milk for two months. During the first week after delivery the iCT decreased from 1.4 to 0.5 ng/ml and after that the iCT content remained rather constant. The level of ionized calcium (Ca++) was correlated to iCT the first week post partum (r=0.72 p<0.01) but not in milk samples obtained after three months. The concentration of magnesium was weakly correlated to iCT during the first week post partum (r=0.37 p<0.05).There was no correlation between iCT and the total calcium level nor to the concentration of zinc. The high concentration of iCT in milk compared to serum suggests a local production of iCT within the mammary gland or a specific transport and concentration mechanism.
Transcapillary passage of albumin in mammary tumours and in normal lactating mammary glands of the rat
Authors: HARALDSSON B. , REGNER L. , HULTBORN R. , WEISS L. , RIPPE B.
Published: December 2008

A triple‐isotope technique was used to obtain albumin clearances and blood flow in DMBA induced mammary tumours, normal lactating mammary glands and various other tissues of the rat. Albumin clearance was high both in tumours (0.0337 ml/min/100 g) and in lactating mammary glands (0.0414 ml/min/100 g).Albumin extraction (defined as the ratio of clearance over plasma flow) was exceptionally high in tumours (23times10‐4) and lactating glands (18times10‐4) as compared to all other tissues (1‐7times10‐4).This probably reflects an increased capillary permeability to macromolecules and/or a change in the relation between blood flow and available capillary surface area, both in the physiological, hormonally induced gland and in the abnormal neoplasia derived from the same tissue. Increased extravasation of albumin, together with other changes (e. g.impaired lymph formation) may be important factors behind the production of increased tumour interstitial pressure, which tend to reduce nutritional blood flow in tumours.
Normal and homogeneous red blood cell populations over a wide range of hyper‐iso‐hypotonic media
Authors: MELA M. , ESKELINEN S.
Published: December 2008

The volumes of human erythrocytes after rapid and gradual swelling in hypotonic NaCl media were measured using a Coulter Counter ZB at temperatures of +4°C and +20°C together with potassium leakage, the degree of hemolysis and the ‘returning volume’, i. e., the volume in an isotonic solution to which the cells will return from that in a hypotonic solution. The methodological and systematic errors in the volume measurements were corrected by taking into account the shape dependence of the Coulter Counter and the change in cell population during hemolysis, whereafter the measured cell volume values and the comparison between them become more reliable. The curves for cell volume as an inverse function of osmotic pressure appeared to be non‐linear. The slopes were small at first but shoed a rapid increase as the cells approached their maximal volume. The critical hemolytic volume was approx.8% higher at +20°C after both rapid and gradual swelling than at +4°C and approx.4% higher after a gradual swelling as compared with a rapid swelling both at +4°C and +20°C.A decrease in temperature resulted in an increase in the critical osmotic pressure both in rapid and gradual hemolysis, but did not greatly affect the amount of prelytic K+ leakage. The critical osmotic pressure was smaller in gradual hemolysis than in rapid hemolysis and the prelytic K+ leakage was doubled at both +4°C and +20°C.The shifts in osmotic fragility as a function of temperature may be due to differences in the visco‐elastic properties of the cell membrane, but the shifts in osmotic fragility as a function of swelling rate may be connected with differences in potassium leakage and membrane stretch.
How to calculate human muscle fibre areas in biopsy samples—methodological considerations
Authors: BLOMSTRAND EVA , CELSING FREDRIK , FRIDÉN JAN , EKBLOM BJÖRN
Published: December 2008

Cross‐sectional muscle fibre areas (type I, IIA and IIB) were determined in duplicate biopsies from the left vastus lateralis (n=11) and in biopsies from right and left vastus lateralis (n=8).The SD for the difference in means between duplicate biopsies was 510 μm2 for type I, 1020 μm2 for type II A and 860 μm2 for type II B.Expressed as coefficient of variation (CV) these SD constituted 10, 15 and 15%, respectively. The variation in fibre size within a sample was considerably less than the variation between samples on the assumption that at least 15–20 areas of each fibre type were measured per sample. No difference in mean fibre area for type I, IIA and IIB fibres was obtained between the right and left muscle. Several artefacts due to the sampling and preparing procedures are discussed and a method for determining muscle fibre areas in biopsy samples is suggested.
Effects of hyperoxia and hypoxia on dynamic and sustained static performance of the human quadriceps muscle
Authors: EIKEN O. , TESCH P.A.
Published: December 2008

The influence of variations in inspired Po2 on dynamic and static muscle performance of the left quadriceps muscle was studied. Eight subjects performed (1) 60 maximal consecutive dynamic contractions and (2) one sustained exhaustive static contraction at 27% of maximal voluntary contraction (MVC).Breathing mixtures containing 11%, 21% or 99% O2, were administered. Peak torque as an average of the 60 knee exteasions was higher (p<0.01) during hyperoxia (mean ± SE= 104±4 Nm) than during normoxia (98±4 Nm), but did not differ significantly between hypoxia (95±5 Nm) and normoxia. Peak torque of individual extensions declined more rapidly during hypoxia than during normoxia, differing in the final 12 extensions by 11% from normoxic values. Static endurance time was reduced (p<0.02) during hypoxia (152±12 s) as compared to normoxia (189±13 s) and hyperoxia (169±11 s).No significant difference in endurance time was demonstrated between hyperoxia and normoxia. Thus, hypoxia impaired muscle performance in both dynamic and sustained static exercise, whereas acute hyperoxia improved dynamic but not static muscle performance. The results are interpreted in terms of differences in rate of intramuscular H+ accumulation.
The effect of autonomic receptor blockers on the ocular response to topical chemical irritation
Authors: UUSITALO HANNU
Published: December 2008

Topical chemical irritants induce an acute reaction in the eye, consisting of an incresed intraocular pressure (IOP), breakdown of the blood‐aqueous barrier, anterior uveal vasodilation and miosis. In the prsent study these effects were studied in the rabbit eye after topical application of neutral formaldehyde by measuring IOP continuously using electromanometrical equipment. The protein content of the aqueous humour was measured and miosis as well as anterior hyperemia were analyzed. Intravenously injected sodium fluorescein was used to visualize the site of the disruption of the blood‐aqueous barrier in freeze‐dried specimens. Iridectomies were performed to study the mechanisms of hypertension and disruption of the blood‐aqueous barrier. In iridectomized rabbits the acute irritative response was very similar to that of normal eyes. Breakdown of the blood‐aqueous barrier, miosis and anterior hyperemia occurred. However, the increase in IOP was only partially reduced. This indicates that a pupillary block due to the intense miosis plays a minor role in the hypertensive reaction or in the breakdown of the barrier. The effect of three autonomic receptor blocking agents: phentolamine (alpha‐adrenergic antagonist), timolol (beta‐adrenergic antagonist) and biperiden (cholinergic antagonist) on the irritative ocular response caused by formaldehyde was studied. Phentolamine proved to be an efficient inhibitor of the hypertensive reaction. It also effectively prevented the breakdown of the blood‐aqueous barrier. Biperiden inhibited only slightly the increase in IOP caused by formaldehyde. Timolol had no significant effect. None of these three antagonists was able to prevent the miosis or hyperemia. The present findings indicate that a part of the irritative response is mediated by a phentolamine‐sensitive neuronal pathway. This observation is also consistent with the hypothesis that in this kind of response at least two separate pathways are involved.
Dissociation of phosphorylase a activation and contractile activity in rat portal vein
Authors: PAUL RICHARD J. , HELLSTRAND PER
Published: December 2008

Isometric force, glycogen phosphorylase activity and lactate production were measured under conditions known to alter intracellular Ca2+and cAMP to assess the role of these messengers in the coordination of metabolism with contractility in rat portal vein. Total phosphorylase (a+b) activity, was independent of treatment. The activity ratio phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on or high‐K+medium, and 0.57 after 20 min treatment with 10–5M isoproterenol+10‐4M papaverine. Under both of these conditions the muscle was totally relaxed. The phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on extracellular Ca2+, both in normal and depolarizing medium. This suggests a lower Ca2+sensitivity of the contractile than the phosphorylase system under these conditions, known to be associated with raised intracellular cAMP. During spontaneous activity and high‐K+induced contractures phosphorylase activity was increased compared to the relaxed state in Ca2+‐free medium. A high level of phosphorylase activity (0.48) was elicited by the addition of 300 mM sucrose, which induces a contracture in Ca2+‐free medium. Lactate production was in general parallel to phosphorylase activity, except for a relative increase in anoxia. The results suggest that in the intact cell the Ca2+‐mediated linkage of contraction and phosphorylase may be modified by cAMP changing the Ca2+sensitivities of the two systems in opposite directions.
Stimulation of mucosal bicarbonate secretion in rat duodenum in vivo by BW755C
Authors: FLEMSTRÖM GUNNAR , BERGMAN ANITA , BRIDÉN STEFAN
Published: December 2008

Bicarbonate secretion from 12 mm segments of duodenum just distal to the Brunner's gland area was titrated (pH 7.60) in situ in anesthetized rats. Intravenous BW755C (10–20 mg/kg) increased both bicarbonate secretion and the transmucosal electrical potential difference and pretreatment with indomethacin (3 mg/kg intravenously) prevented these effects. Indomethacin also inhibited stimulation of HCO3‐secretion by luminal acid (10 mM HCl) but had no effect on the rise in secretion in response to exogenous (luminal) prostaglandin E2. The results support previous suggestions of a role for endogenous prostaglandins in mediation of the HCO3‐response to acid and are consistent with the recent demonstration that BW755C increased prostaglandin formation in homogenates of rat intestinal mucosa. Stimulation of HCO3‐secretion by BW755C was not enhanced but attenuated by preexposure to luminal acid, suggesting that the latter increases secretion by effects other than mucosal mobilization of arachidonate.
Effects of captopril on arterial blood pressure, plasma renin activity and vasopressin concentration in sodium‐repleted and sodium‐deficient goats: A serial study during pregnancy, lactation and anestrus
Authors: OLSSON K. , FYHRQUIST F. , BENLAMLIH S. , DAHLBORN K.
Published: December 2008

The effects of captopril (intravenous loading dose of 20 mg, 1 h later followed by 10 mg infused during the next h) on arterial blood pressure and plasma renin activity were followed in 4 goats during the last months of pregnancy, during lactation and during anestrus. Experiments were made both when the animals were sodium‐repleted and sodium‐deficient. Furosemide and dietary restriction were used to deprive the animals of sodium. In sodium‐replete animals, captopril caused a more pronounced fall in mean arterial blood pressure and a larger increase in plasma renin activity (PRA) when the animals were pregnant than when they were lactating or in anestrus. During sodiumdeficient conditions the response was similar as during sodium repletion in pregnant goats. In anestral goats, PRA rose in response to captopril, but the blood pressure fall was similar as when the goats were sodium‐replete. In lactating sodium‐deficient goats, captopril caused a marked fall in mean arterial blood pressure concomitant with a 2–3 times higher rise in PRA than during corresponding sodium‐repletion experiments. The respiratory rate was elevated in pregnant animals and increased further during captopril. The plasma vasopressin concentration did not change during captopril‐induced hypotension. If the blood pressure fell ≥10 mmHg the animals became very quiet and occasionally they fell asleep. All goats delivered healthy kids. The fact that the blood pressure fall was marked and consistent in all animals during pregnancy, but less and more variable during anestrus indicates that the activity of the renin‐angiotensin system is of greater importance for blood pressure maintenance during pregnancy than during anestrus. The exaggerated effects in lactating sodium‐deficient animals were probably due to a more efficient salt depletion, these animals losing extra salt via the milk.
Adaptive response of human skeletal muscle to simulated hypergravity condition
Authors: BOSCO C.
Published: December 2008

The mechanical behaviour of leg extensor muscles of five international‐level athletes was evaluated during 13 months training period. Drop jumps, average mechanical power during 15 s continuous jump, and vertical jumps performed with and without extra weights were used to measure explosive power characteristics. The data recorded in vertical jumps was utilized for construction of force‐velocity relationship (F‐V curve). The athletes did not show improvement in any of the variables studied after 12 months of intensive systematic training programme. It was assumed that the subjects already had reached their upper limit of performance. However, after that the athletes underwent a simulated 3 weeks high‐gravity period. The hypergravitational condition was created by wearing a special vest filled with extra loads (11% of BW). The vest was used from morning to evening. No changes in the ordinary training programme were allowed. After the simulated high‐gravity conditioning period significant improvement in almost all the variables studied was observed (P <0.05‐0.001). Vertical jump performance was enhanced from 44.3 to 54.9 cm. The F‐V curve remained stable all year but after hypergravity period shifted markedly to the right. The drastic improvement was attributed to be caused by a fast adaptation to the new functional requirements (1.1 g). Therefore, once the biological adaptation occurred the mechanical behaviour of the athlete's leg extensor muscle was similar to that which could be experienced in a field at low gravity condition (0.9 g). Adaptive response to the hypergravity conditioning was speculated to occur mainly at neurogenic level and less in myogenic component.
Blockade of substance P receptors inhibits non‐nicotinic, non‐adrenergic colonic contractions induced by stimulation of the lumbar sympathetic nerves to the feline large intestine
Authors: FÅNDRIKS L. , JÖNSON C. , DELBRO D.
Published: December 2008

Experiments were performed on chloralosed cats, pretreated with guanethidine and hexamethonium and with ligated adrenals. The motility of an arterially isolated colonic segment was monitored by a volumetric method. Colonic contractions were induced either by electric stimulation of the centrally cut lumbar splanchnic nerves, or by close i.a. injections of acethylcholine (ACh). Close i.a. injections of substance P (SP) were performed in order to test the degree of SP‐receptor blockade. Blockade of colonic SP‐receptors, either by close i.a. administration of large amounts of SP itself or by Spantide, a competitive SP‐receptor antagonist, markedly reduced or abolished the neurally induced colonic contractions, while responses to ACh were unchanged. These results indicate a role for SP, or a closely related peptide, as an intermediate neurotransmitter in the neurally induced colonic responses. Thus, the present study gives support to the hypothesis that non‐nicotinic, non‐adrenergic colonic contractions, in response to electric stimulation of sympathetic nerves, are due to an antidromic activation of sensory neurons with peripheral excitatory collaterals which release SP, in turn activating the colonic smooth muscle, mainly via a muscarinic mechanism.
Studies on the oxygen radical mechanism involved in the small intestinal reperfusion damage
Authors: SCHOENBERG M. H. , FREDHOLM B. B. , HAGLUND U. , JUNG H. , SELLIN D. , YOUNES M. , SCHILDBERG F. W.
Published: December 2008

Characteristic mucosal lesions develop in the small intestine during ischaemia and hypotension. This tissue damage can be further aggravated in the immediate reperfusion phase, presumably secondary to the generation of oxygen free radicals which have been proposed to be generated in this situation through the hypoxanthine‐xanthine oxidase system. This was further investigated in the cat small intestine using a standardized regional intestinal hypotension model in which the effects of allopurinol (a xanthine oxidase inhibitor) were compared to those of an exogenous supply of inosine. The grade of mucosal damage, the nucleotide levels, the concentrations of hypoxanthine, total and oxidized glutathione, and of conjugated dienes were measured in the intestinal tissue. The results indicate that oxygen radicals generated by xanthine oxidase are very important, but not the only significant factor in the small intestinal reperfusion damage.
Effects of fasting and refeeding on the activity of hepatic glucose‐6‐phosphatase in rats
Authors: KHAN A. , LÖW H. , EFENDIĆ S.
Published: December 2008

The activities of glucose‐6‐phosphate hydrolase and glucose‐6‐phosphate translocase were determined in rats fasted for 1–3 days and in animals fasted for one day and then either refed with mixed pellet or given oral or intraperitoneal glucose. The assay was based on the colorimetric measurement of the released inorganic phosphate. Fasting over 24 h significantly increased both the translocase and the hydrolase activity of glucose‐6‐phosphatase. These parameters showed a further increase when rats were fasted for another 24 h. In animals fasted for 24 h and then refed with standardized pellet diet, a progressive fall of enzyme activity was noticed. However, even 72 h of refeeding did not lead to complete normalization. Glucose given orally or intraperitoneally also suppressed the enzyme activity, although the effect was somewhat delayed. As expected, in fasting rats glucose and insulin levels were significantly decreased. Normoglycaemia was established after just 24 h, regardless of refeeding with pellets or with glucose. The former group exhibited hyper‐ and the latter hypo‐insulinaemic pattern. We speculate that augmented activity of hepatic glucose‐6‐phosphatase during fasting stimulates the metabolism of glucose through the glucose cycle and is thereby at least partially responsible for insulin resistance accompanying the fasting state.
Neuropeptide Y may mediate effects of sympathetic nerve stimulations on colonic motility and blood flow in the cat
Authors: HELLSTRÖM PER M. , OLERUP OLLE , TATEMOTO KAZUHIKO
Published: December 2008

The present study investigated sympathetic mechanisms involved in the regulation of colonic motility and blood flow in the cat. Infusion of neuropeptide Y (NPY) close i.a. produced an inhibition of colonic motility and a vasoconstriction of long duration but no post‐infusion vasodilatation. In contrast to NPY, porcine pancreatic polypeptide did not evoke any vascular or motility response. On a molar basis, NPY was 25 times more potent than noradrenaline in producing 50% reduction of the colonic blood flow. These vascular and motility effects of NPY were resistant to guanethidine, phentolamine, phenoxybenzamine and propranolol. Thus, the action of NPY on vascular and colonic smooth muscle did not seem to be mediated via adrenergic receptors. Noradrenaline administered close i.a. produced inhibition of colonic motility, and vasoconstriction followed by a rapid vasodilatation. These effects were completely blocked by combined α‐ and β‐adrenoceptor blockade. Electrical stimulation of the splanchnic and lumbar colonic nerves produced an overall inhibition of colonic motility, and vasoconstriction of the proximal and distal colon, respectively, with a rapid post‐stimulatory vasodilatation. After combined α‐ and β‐adrenoceptor blockade the inhibitory effect of the nerve stimulations on colonic motility partly remained together with a marked vasoconstriction, which was most pronounced upon lumbar colonic nerve stimulation. All vascular effects of sympathetic nerve stimulation were eradicated by guanethidine, which also abolished the inhibitory motility response to splanchnic nerve stimulation. However, lumbar colonic nerve stimulation elicited a colonic contraction, possibly due to stimulation of afferent C‐fibres. The present findings indicate the existence of a sympathetic non‐adrenergic neuronal mechanism mediating vasoconstriction and inhibition of colonic motility in the cat. Thus, NPY may be released from noradrenergic neurons to act on colonic smooth muscle and vessels.
Osmotic properties of the chromogranins and relation to osmotic pressure in catecholamine storage granules
Authors: HELLE K. B. , REED R. K. , PIHL K. E. , SERCK‐HANSSEN G.
Published: December 2008

The soluble proteins (chromogranins) of bovine chromaffin granules have been studied by micro‐osmometry with semi‐permeable membranes (UM2, PM10 and PM30 with cut‐offs > 1, > 10 and > 30 kD, respectively) at I =0.15 and pH 5–8 for protein concentrations up to 20 mg ml‐1. After lysis of chromaffin granules in phosphate buffer pH 6, the released chromogranins behaved as aggregating solutes, consistent with an inconspicuous osmotic pressure contribution from the chromogranins at the protein concentration of the intact granules. Thus, in the presence of phosphate about 90% of the molecules behaved as colloids withMr=30,300 atc =o. After lysis in phosphate‐free buffers the chromogranins behaved as highly non‐ideal solutes in a manner which was incompatible with isotonicity at the protein concentration of the intact granules. About two‐thirds of the molecules in the lysates in Na‐succinate pH 5–6 and K‐acetate pH 6 exhibitedMr= 66,000 and 79,000, respectively. In dilute solutions (<12mg protein ml‐1) and ATP/protein ratios corresponding to those in the intact granules, the UM2 pressures were markedly increased, indicating release of polypeptides withMr2000–3000 from aggregates. CaCl2was without specific effect on the colloid osmotic pressures but reduced the ATP‐dependent increase in pressure, suggesting release of molecules twice the size of those released by ATP alone. A model is presented for the contribution of the chromogranins to osmotic pressure regulation in the bovine adrenomedullary catecholamine‐storing granules.
Activation of glycogen phosphorylase by electrical stimulation of isolated fast‐twitch and slow‐twitch muscles from rat
Authors: CHASIOTIS D. , EDSTRÖM L. , SAHLIN K. , SJÖHOLM H.
Published: December 2008

The influence of muscle contraction, induced by electrical stimulation, on the activity of glycogen phosphorylase, the contents of high‐energy phosphates, hexosemonophosphates and lactate have been studied in isolated extensor digitorum longus (EDL) and soleus muscles from rats. The activity of phosphorylase a + b was about nine times higher in fast twitch muscles (EDL) than in slow‐twitch soleus and remained unchanged during the stimulation. A pronounced increase of phosphorylase a occurred during the stimulation in EDL muscle. Stimulation with a frequency of 50 Hz for 10 s and 2 Hz for 90 s resulted in a 44‐fold and five‐fold increase in phosphorylase a, respectively. In contrast, stimulation of soleus muscle resulted in only a minor increase of phosphorylase a. The rate of glycogenosis increased in both muscles during the stimulation but the increase was four to five times higher in the EDL than in soleus muscle. The content of phosphocreatine (PCr) before stimulation was much higher in EDL than in soleus but similar after the stimulation. This resulted in a three‐ to four‐fold higher release of inorganic phosphate (P1) in EDL than in soleus during contraction. Pi has previously been shown to be present in a limiting amount for the activity of phosphorylase and the increase during contraction is of importance for increasing the glycogenolytic rate. It is concluded that the higher glycogenolytic capacity in fast‐twitch muscles compared to slow‐twitch muscles is due to: (1) higher content of phosphorylase a + b, (2) higher degree of transformation of the enzyme into the a form during contraction, and (3) higher content of PCr, which liberates a large amount of P1 during contraction.
The effect of adrenalin infusion on the regulation of glycogenolysis in human muscle during isometric contraction
Authors: CHASIOTIS D. , HULTMAN E.
Published: December 2008

The regulation of glycogenolysis in human muscle during isometric contraction without and with adrenalin infusion has been investigated. The content of cAMP in muscle increased three‐fold during the infusion. Total glycogen phosphorylase and synthetase activities were unchanged during contraction without and with adrenalin infusion. The fraction of phosphorylase in the a form was in resting muscle 26% and at the end of contraction 24%. During adrenalin infusion phosphorylase a increased to 80%. Contraction during continued infusion resulted in a decrease of phsophorylase a to 42%, despite persistently increased cAMP content in muscle. The activity of synthetase I decreased to about half of the initial value during adrenalin infusion and contraction both without and with the infusion. The rate of glycogenolysis in muscle during contraction was not significantly changed by the infusion. Phosphocreatine (PCr) decreased during the contraction and the decrease was similar without and with adrenalin infusion. The amount of inorganic phosphate (P1) accumulated in muscle during contraction was lower when adrenalin was given due to a greater accumulation of hexosemonophosphates. It is concluded that the rate of glycogenolysis in muscle during contraction without and with adrenalin infusion is a function both of phosphorylase in the form a form and the availability of Pj at the active site of the enzyme.
Seasonal changes in lipogenesis and lipolysis in isolated adipocytes from Svalbard and Norwegian reindeer
Authors: LARSEN TERJE S. , NILSSON NILS Ö. , BLIX ARNOLDUS SCHYTTE
Published: December 2008

Arctic reindeer exhibit marked seasonal changes in fat deposition and mobilization. At intervals throughout the year, therefore, we have measured feed intake of both Svalbard (SR) and Norwegian reindeer (NR) together with the seasonal changes in size, lipogenic and lipolytic capacity of isolated adipocytes from both sub‐species. Feed intake of both NR and SR was maximal in August, but declined thereafter, reaching minimum values in January (NR) and March (SR), 55 and 69% below the August value, respectively. NR and SR adipocyte volume changed in parallel and were reduced to the same extent (69%) from their maximum in August to their minimum in May. Adipocyte lipogenic capacity, measured as acetate incorporation into cellular lipid at saturated acetate concentrations, was lowest in January (NR adipocytes) and March (SR adipocytes), 92 and 90%, respectively, below the maximum values, which were obtained in August. Lipolytic capacity, measured as maximum adrenaline‐stimulated glycerol release, was high in SR adipocytes from March through to October and in NR adipocytes from July through to January. Minimum lipolytic capacity, on the other hand, was found in January (SR adipocytes) and March (NR adipocytes). The present findings may be explained by alterations in lipogenic enzyme activity and in the lipolytic activation system.
Regression analysis of catecholamine utilization in discrete hypothalamic and forebrain regions of the male rat: effects of thyroidectomy
Authors: ANDERSSON KURT , ENEROTH PETER
Published: December 2008

The effects of thyroidectomy (4 weeks) on dopamine (DA) and noradrenaline (NA) turnover rates were determined by means of regression analysis. The disappearance of catecholamine (CA) fluorescence (using quantitative histofluorimetry) after tyrosine hydroxylase inhibition (α‐methyl‐DL‐p‐tyrosine methyl ester) has been investigated in discrete hypothalamic and forebrain DA and NA nerve terminal systems of the male rat. A time‐dependent monophasic CA fluorescence disappearance was observed in all CA nerve terminal systems of the sham‐operated and thyroidectomized rats. In the thyroidectomized rat, DA turnover in the anterior nucleus accumbens and in the medial and lateral palisade zones of the median eminence (ME) was reduced while DA turnover in the posterior nucleus accumbens was increased as compared to control rats. Furthermore, NA turnover was increased in the paraventricular hypothalamic nucleus (PA) and reduced in the dorsomedial hypothalamic nucleus (DM) and in the ‘border zone’ (lateral hypothalmus). Radoimmunoassay of hormones in serum demonstrated marked increases in TSH levels and reduced concentrations of GH, prolactin, corti‐costerone, triiodothyronine and thyroxine. The reduced DA turnover in the external layer of the ME and the increased NA turnover in the PA may indicate an inhibitory dopaminergic mechanism in the ME and a facilitatory noradrenergic mechanism in the PA in the regulation of TSH secretion. These mechanisms seem to interact with thyroid hormones. The reduced NA turnover demonstrated in the DM and in the border zone may be related to the lowering of growth hormone levels and pulsatility caused by thyroidectomy. Finally, the DA nerve terminal systems in the anterior and posterior parts of the nucleus accumbens are differently regulated by changes in the brain‐pituitary‐thyroid axis.
Training‐induced bradycardia in rats on cardioselective and non‐selective beta receptor blockade
Authors: NYLANDER EVA
Published: December 2008

After 12 weeks of treadmill training 10 Sprague‐Dawley rats got a significant bradycardia at exercise of submaximal intensities compared to 10 sedentary controls. Twenty rats were subjected to the same training programme during oral treatment with the cardioselective beta receptor blocker metroprolol (10 rats) or proprnolol (non‐selective, 10 rats). Both treated groups developed a training‐induced bradycardia at submaximal exercise of the same magnitude as the trained untreated group. It is concluded that the stimulation of cardiac beta receptors or the heart rate increase during exercise are not critical for the development of training bradycardia and that in this respect the effects of cardioselective and non‐selective beta receptor blockade were not significantly different.
Blood pressure and heart rate responses to mental stress in spontaneously hypertensive (SHR) and normotensive (WKY) rats on various sodium diets
Authors: ELY D. L. , FRIBERG P. , NILSSON H. , FOLKOW B.
Published: December 2008

Normotensive (WKY) and hypertensive rats (SHR) were, from 5 to 12 weeks of age, given ‘low’ (LNa), ‘control’ and ‘high’ (HNa) Na diets (0.5, 5 and 50 mmol‐100 g‐1 food, respectively, during weekly recordings of body weight, conscious indirect systolic blood pressure (SBP) and heart rate (HR). During the last week, mean arterial pressure (MAP) and HR responses to standardized stress stimuli (air jet) were recorded before and after sequential cardiac nerve blockade. While resting, SBP was about equal in all WKY groups, but it was significantly reduced in SHR‐LNa (152 mmHg versus 174 and 178 mmHg in SHR controls and HNa; P < 0.05). In both LNa groups HR was elevated nearly 25% compared with controls, being in SHR 513 versus 419 bpm (P < 0.01) and in WKY 489 versus 393 bpm (P < 0.01). Cardiac nerve blockade indicated that this HR elevation was about equally due to elevations of sympathetic activity and ‘intrinsic’ pacemaker activity. SHR‐LNa also showed attenuated MAP elevations to acute mental stress. There were, however, no significant differences between groups concerning haematocrit or plasma Na‐K levels. The results suggest that SHR have a greater salt requirement than WKY, as Na restriction to one‐tenth of normal led to a considerable MAP reduction in SHR despite compensatory sympathetic activation, and also to attenuated pressor responses to mental stress. Further, the cardiovascular effects in SHR were much more extensive when on a low‐Na diet than when Na intake was increased tenfold above normal.