bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of TRH and TRH analogues on the central regulation of breathing in the rat
Authors: HEDNER JAN , HEDNER THOMAS , WESSBERG PER , LUNDBERG DAG , JONASON JAN
Published: December 2008

Respiratory activity was studied in rats during light halothane anesthesia. Thyrotropin releasing hormone (TRH) and two TRH analogues: the desamidated form (TRH‐OH) and γ‐butyrolactone‐γ‐carbonyl‐L‐histidyl‐L‐prolraamide citrate (DN 1417) were administered intracerebroventricularly. TRH 0.5‐5 μg induced a marked tachypnoea with a rapid onset and a duration of at least 20 min. DN 1417, a potent analogue of TRH with a very low TSH (thyroid stimulating hormone) releasing activity was more effective in stimulating respiratory frequency, while TRH‐OH, regarded to have neither TSH releasing nor extra hypothalamic effects, at equimolar doses was unable to induce any changes in the respiratory pattern. When TRH was given into the fourth ventricle the dose response curve was slightly shifted to the left. In experiments employing the occluded breath tehnique, P0.1was increased in the same magnitude as the mean inspiratory flow (VT/T1). The results also indicated an increase in the gain of the inflation reflex loop whereas the central bulbopontine setting for T1and TTOTwere not significantly changed. Local injection of TRH into the nucleus tractus solitarii induced a stimulation of respiratory frequency which was slower in onset compared to the response seen after injection into the lateral or fourth ventricles. Concomitantly to the respiratory changes, i. c. v. TRH injection induced a hypocarbia and an alkalosis. No changes in blood pressure or heart rate were seen. The respiratory stimulant effect of TRH could be potentiated by pretreatment with naloxone, methylatropine or a low dose of GABA. Haloperidol or propranolol did not significantly change the respiratory effects of TRH, while reserpine pretreatment seemed to blunt some of the ventilatory effects of TRH. It seems likely that TRH has few direct effects on brain stem neurones involved in the central regulation of respiration, but the main effects seem to be elicited in areas rostral to the brain stem. The respiratory stimulating effect of TRH is unrelated to TSH. Furthermore, other neurotransmitter systems might also be involved in modulation of the respiratory stimulation evoked by TRH.
Characteristics of brachiocephalic and carotid sinus baroreceptors with non‐medullated afferents in rabbit
Authors: YAO T. , THOREN P.
Published: December 2008

The characteristics of brachiocephalic and carotid sinus baroreceptors with non‐medullated afferents have been studied in rabbits. The conduction velocities of 18 non‐medullated fibers arising from the brachiocephalic baroreceptors were 0.4–0.8 m/s (0.59±0.03 m/s, mean ± SE) and their thresholds were 74–104 mmHg (84±2 mmHg). 29 non‐medullated carotid sinus baroreceptor afferents had thresholds ranging from 60 to 125 mmHg (92±3 mmHg). Their conduction velocities were 0.5–1.1 m/s (0.65±0.05 m/s). Blood pressure‐baroreceptor response curves of both the brachiocephalic and the carotid sinus baroreceptors were constructed. As the aortic arch non‐medullated baroreceptor afferents, the brachiocephalic and the carotid sinus baroreceptors with non‐medullated afferents exhibited thresholds about 30 mmHg higher than the medullated ones, considerably lower firing rates, comparatively rapid adaptation and remarkable irregular discharge pattern. It is suggested that the non‐medullated baroreceptor afferents are of little importance for the cardiovascular regulation under normal conditions but are likely to play an important role during a sudden rise in arterial pressure.
Comparison of urinary and plasma catecholamine responses to mental stress
Authors: ÅKERSTEDT TORBJÖRN , GILLBERG MATS , HJEMDAHL PAUL , SIGURDSON KARIN , GUSTAVSSON INGRID , DALESKOG MAUD , POLLARE THOMAS
Published: December 2008

8 subjects were exposed to the Stroop mental performance test in a design with alternating hourly periods of rest and stress. During each period one urine sample and several venous plasma samples were obtained. Heart rate responded rapidly to initiation and termination of the stress exposure with increases and decreases respectively. Both urinary and plasma adrenaline increased significantly during stress. The plasma response was immediate and sustained. Neither urinary, nor plasma noradrenaline were significantly increased by the test. Plasma noradrenaline, however, increased significantly on termination of the exposure to stress. It was suggested that the latter effect may be due to muscle sympathetic nerve activity decreasing during stress and increasing following stress. The sample‐to‐sample variation was more than 20% of the mean for both catecholamines, indicating the need for frequent sampling to reliably reflect plasma levels. The mean intraindividual plasma/urine correlation was r̄=0.70 (p<0.001) for adrenaline and r̄=0.40 (p<0.05) for noradrenaline. When only resting periods were considered, no significant correlations remained, apparently due to a reduced range of variation and accompanying reduced signal‐to‐noise ratio. It is concluded that both urinary and plasma adrenaline may be useful in the evaluation of changes in sympatho‐adrenal activity during stress.
Role of the kidneys in elimination of glucagon, insulin, secretin and somatostatin in the rat
Authors: MUNSHID H. A. EL , HOLST J. J. , LUNDQUIST I. , LUNDQVIST G. , De MUCKADELL O. B. SCHAFFALITZKY , HÄKANSON R.
Published: December 2008

Immunoreactive plasma glucagon and secretin in the rat was elevated 48 hours after nephrectomy and ureteral ligation. Since kidneys obstructed by ureteral ligation were unable to remove glucagon and secretin from the blood, renal handling of glucagon and secretin must include glomerular filtration. Insulin and somatostatin levels were significantly elevated 48 hours after nephrectomy, but not after ureteral ligation, indicating partial uptake from peritubular capillaries.
The effect of heating and central cooling on serum TSH, GH, and norepinephrine in resting normal man
Authors: WEEKE J. , GUNDERSEN H. J. G.
Published: December 2008

The effects of central cooling and exterior heating on serum concentrations of thyrotropin (TSH), growth hormone (GH), and norepinephrine were studied in 10 normal males under resting conditions. Cooling was induced by ingestion of ice while the subjects were immersed in water of a temperature prone to elicit only minor cutaneous thermal reflexes. TSH and thyroid hormones changed neither during cooling nor during heating. Cooling induced a virtually complete suppression of GH‐secretion whereas heating had the opposite effect: pronounced increase, also without previous cooling. Plasma norepinephrine rose by a factor of 2.5 and 1.7 during cooling and heating, respectively. It is concluded that the pituitary‐thyroid system does not take part in short‐term thermoregulation in man–as opposed to the situation in some smaller mammals. The mechanisms and the physiological role of the GH‐responses to cooling and heating are as yet unknown, but the latter stimulus is an advantageous tool in clinical and pathophysiological studies of pituitary function as it is both safe and convenient.
Distribution of different fibre types in human skeletal muscles 2. A study of cross‐sections of whole m. vastus lateralis
Authors: LEXELL JAN , HENRIKSSON‐LARSÉN KARIN , SJÖSTRÖM MICHAEL
Published: December 2008

In order to determine the total number of fibres and the extent to which the relative occurrence of different fibre types varies within m. vastus lateralis, 15 μm thick cross‐sections of whole muscles were prepared. The total number of type 1 and type 2 fibres was determined in every 48th square millimetre of the section, and the results thus obtained were analysed using a computer program allowing an assessment of bivariate data in the form of contour plots. The total number of fibres varied both in proximal to distal direction in the same muscle and between individuals. No obvious correlation existed between the mean fibre area and the muscle cross‐sectional area. The proportion of type 1 fibres in the whole muscle varied between individuals (from 44% to 57%) with a mean value for all five of 52%. The distribution of different fibre types varied within the muscle, mainly as a function of depth, with a predominance to type 2 fibres at the surface and type 1 fibres in deeper regions of the muscle. Thus, the fibre type distribution in m. vastus lateralis is not random. This must be taken into consideration when data on fibre type composition are compared with functional variables.
Ultrasound study of the cranial venous system in the human new‐born infant and the adult
Authors: COWAN FRANCES , THORESEN MARIANNE
Published: December 2008

A pulsed doppler ultrasound technique has been used to measure changes in blood velocities in the superior sagittal sinus, the jugular veins and intracranial and extracranial arteries in 13 neonates, and in the jugular veins and an extracranial artery in 13 adults, during unilateral and bilateral jugular venous compressions. The results have enabled us to determine how the subject under examination functionally uses his cranial venous drainage system in the resting state, and whether or not he can shunt obstructed venous flow through other cranial venous channels. We have found great variability between the subjects. In the resting situation the range of possibilities from total dependence on one jugular vein alone to usage of both jugular veins and the vertebral veins exists. Shunting of blood on jugular compression from either or both jugular veins to the vertebral veins may occur, and contralateral shunting between the jugular veins may be possible in both directions, in one direction or not at all.
On the control of myotomal motoneurones during “fictive swimming” in the lamprey spinal cord in vitro
Authors: RUSSELL DAVID F. , WALLÉN PETER
Published: December 2008

Intracellular recordings have been made from myotomal motoneurones during “fictive swimming” in the in vitro preparation of the lamprey spinal cord, while monitoring the efferent burst activity in the ventral roots. The pattern of rhythmic activity in the motoneurones is described, as well as how synaptic inputs from the premotoneuronal level exert their control of motoneurone activity. (1) All motoneurones investigated displayed rhythmic, symmetric oscillations of their membrane potential during “fictive swimming”. The period of depolarization occurred in phase with the burst discharge in the ventral root containing the motoneurone axon. (2) About one‐third of the cells fired bursts of action potentials during the depolarized phase, while the remaining motoneurones exhibited subthreshold oscillations. (3) Intracellular injection of chloride ions reversed the sign of the hyperpolarized phase, demonstrating phasic active inhibition of the motoneurones during rhythmicity. (4) The depolarized phase was unaffected after chloride injection, showing that the motoneurones also received phasic active excitation. (5) “Pre‐triggered” averaging of the motoneurone recording (using the ventral root spikes from other motoneurones for triggering), revealed that some degree of synchronous excitation of several motoneurones occurred, suggesting common excitation from the same premotor‐interneurones. It is concluded that the rhythmic oscillations of membrane potential in lamprey myotomal motoneurones during “fictive locomotion” depend on phasic excitation alternating with phasic active inhibition. The premotoneuronal mechanism responsible for this control may consist of reciprocally organized groups of excitatory and inhibitory interneurones.
Effect of chronic sympathetic denervation upon the transcapillary filtration rate induced by venous stasis
Authors: HENRIKSEN O. , SEJRSEN P. , PAASKE W. P. , EICKHOFF J. H.
Published: December 2008

The effect of venous pressure elevation upon capillary filtration rate in the limb was studied in 6 chronically sympathectomized patients. Five healthy subjects served as controls. Volume changes of the forearm or calf were recorded by a strain‐gauge plethysmograph. Relative blod flow in subcutaneous and muscle tissue during venous stasis was measured by the local 133Xe washout technique. In the denervated limbs there was a linear relationship between net capillary filtration rate and venous pressure elevation. In the controls a non‐linear relationship was seen as venous pressure elevation of 40 mmHg only caused an increase in net filtration rate of about 66% of that expected from a linear relationship. In the denervated limbs blood flow in muscle and subcutaneous tissue remained constant during venous pressure elevation of more than 30 mmHg whereas in the non‐denervated limbs blood flow decreased by about 50% in both tissues. The results suggest that a local sympathetic veno‐arteriolar (axon) reflex plays a dominant role for the reduced increase in net capillary filtration rate during large increases in venous pressure. The local axon reflex may therefore act as an edema protecting factor.
Electrical and mechanical properties of the Crustacean stretch receptor during Sinusoidal length changes
Authors: JOHANSSON BO , RYDQVIST BO
Published: December 2008

Isolated slowly adapting stretch receptors of the crayfish (Astacus fluviatilis) were exposed to sinusoidal length changes. The mechanical force, the receptor current and the receptor potential were analysed in terms of frequency response (Bode plots) and input/output functions. Within the frequency range investigated (0.3 to 80 Hz) the mechanical force was found to be only slightly dependent on the frequency of the sinusoidal stimuli, the slope of the gain function in the Bode plot being close to zero. Dynamic length‐force curves exhibited a characteristic hysteresis. In potential clamp experiments, the receptor current induced by sinusoidal length changes was dependent on the clamp potential attaining maximal amplitude at a membrane potential of about ‐20 to ‐30 mV for 80 Hz mechanical stimulation. The membrane potential at which the receptor current changed sign (the reversal potential) increased with increasing frequency. In Bode plots of the receptor current the gain was represented by a straight line, having a slope of about 1.2 dB/octave. The phase shift was positive at low frequencies. Bode plots of the receptor potential gain exhibited a characteristic peak in the region of 15 Hz. Below this peak the gain increased with about 1.2 dB/oct, above the peak the gain decreased with about 4.8 dB/oct. There was a small positive phase shift at low frequencies; at high frequencies the phase shift became negative. The impedance of the cell, as calculated from the receptor potentials and the current responses at resting membrane potential, gave Bode plots comparable to a simple resistive‐capacitive filter compatible with the electrical properties of the receptor cell membrane. The cut‐off frequency of this low pass filter decreased with decreasing stretch amplitude. One physiological significance of this finding, is that the performance of the receptor is improved at low levels of stimulation by reducing the bandwidth of the system.
The involvement of intramural nerves in cholera toxin induced intestinal secretion
Authors: CASSUTO JEAN , SIEWERT ANNICA , JODAL MATS , LUNDGREN OVE
Published: December 2008

In previous reports we have suggested that nervous reflexes are involved in the pathophysiology of cholera secretion and that these nervous reflexes involve a cholinergic synapse and a neuron with vasoactive intestinal polypeptide (VIP) as neurotransmitter. These proposals were further analyzed in this study. Tetrodotoxin (TTX) and lidocaine applied on the serosal surface inhibited cholera secretion in segments of rat small intestine. Fluid absorption in control rats was not significantly changed. Hexamethonium given i. v. decreased cholera secretion in the cat. No additional inhibition of cholera secretion was observed after giving TTX close i. a. Furthermore, the intestinal secretion evoked by VIP was not influenced by hexamethonium given i. v. or TTX given close i. a. The present observations support the hypothesis of a role for nervous reflexes in cholera secretion. The results suggest that at least a major part of the proposed nervous reflex(es) in cholera have a cholinergic synapse. Furthermore, the VIP‐ergic neuron is situated “distal” to the cholinergic neuron in the reflex(es) closer to the effector cells.
The Piper rhythm–a phenomenon related to muscle resonance characteristics?
Authors: HAGBARTH K. ‐E. , JESSOP J. , EKLUND G. , WALLIN E. U.
Published: December 2008

The purpose of the present work is to examine the causes of the Piper rhythm, i. e. the tendency towards rhytmical 40–60 Hz grouping of motor unit potentials in steadily contracting human muscles. At weak or moderate contraction strength individual motor units exhibited preferred firing rates which were subharmonically related to the Piper rhythm in the gross EMG. Microelectrode muscle nerve recordings provided no support for the hypothesis that the Piper rhythm is dependent on resonance‐induced rhythmical volleys of afferent spindle impulses causing reflex entrainment of motor impulses. This hypothesis also seems inconsistent with the findings that Piper rhythms of similar frequency appear in muscles with widely different mechanical properties and that the rhythms are about equally prominent in muscles with brisk as in muscles with weak or absent stretch reflexes. The results suggest that the Piper rhythm is dependent on some kind of pace‐maker in the spinal cord or the cerebrum which tends to entrain and synchronize motor impulses.
Lysine deficiency reduces transcription activity and concentration of chromatin proteins reversibly in rat liver
Authors: ÅSTRÖM STEFAN , VON DER DECKEN ALEXANDRA
Published: December 2008

The reversible effect of dietary lysine deficiency was studied in young adult rats. During 6 days on a lysine deficient diet the rats maintained the same body weight. During 2 days of recovery body weight gain was that of the controls. Liver nuclei were isolated, incubated with micrococcus nuclease and chromatin fractionated into a 2000 ×g pellet. 102 000 ×g pellet and supernatant fraction. Chromatin‐bound RNA polymerase I plus III activity decreased by 15% per mg of fractional and nuclear DNA and by 30% per total liver. The corresponding decrease of RNA polymerase II activity was 30% and 40%. Recovery from lysine deficiency was complete after 2 days of refeeding the amino acid. Chromatin proteins of the 102000 ×g pellet were characterized by polyacrylamide gel electrophoresis in sodium dodecylsulfate and by 2‐dimensional gel electrophoresis. Quantitative but no qualitative differences between the proteins of the dietary groups were observed. Relative to DNA the non‐histone proteins decreased in the lysine deficient group by 43% and histones by 10%. It is concluded that RNA synthesis is restored to its original level within 2 days of refeeding lysine after 6 days of lysine deficiency.
Diazepam, a highly effective twitch potentiator in isolated muscle fibres of the frog
Authors: KHAN A. RAUF , EDMAN K. A. P.
Published: December 2008

The contractile effects of diazepam (10–200 μM) were studied on twitch and tetanus responses of isolated fibres of the semitendinosus muscle of Rana temporaria (3.5‐5.0°C). Diazepam (100–200 μM) enhanced the twitch amplitude to 95–100 % of maximum tetanic force and increased the rate of rise of force, the time to peak twitch force and the total duration of the relaxation phase. The maximum tetanic output was unaffected by diazepam but the drug increased the rate of rise of the tetanic force and delayed the onset of force decay after the last stimulus. However, the kinetics of relaxation was unaffected by the drug. Diazepam had no effect on either threshold, submaximum or maximum contracture responses to caffeine and to increased potassium concentration. Diazepam in concentrations producing full twitch potentiation caused only a moderate (ca 30%) increase in action potential duration. The results are in line with the idea that I: diazepam enhances the twitch response by increasing the rate of release of activator calcium without affecting the rate of calcium resequestration and 2: diazepam acts by modulating a mechanism in the excitation‐contraction coupling that responds specifically to membrane excitation.
Age‐dependent alterations in the structurally determined vascular resistance, pre‐ to postglomerular resistance ratio and glomerular filtration capacity in kidneys, as studied in aging normotensive rats and spontaneously hypertensive rats
Authors: GÖTHBERG G. , FOLKOW B.
Published: December 2008

Maximally dilated renal vascular beds of 13‐month‐old NCR and SHR were compared to explore how aging respectively longstanding primary hypertension structurally alters total renal resistance, pre‐/postglomerular resistance ratio and maximal glomerular filtration capacity, as measured per unit kidney weight. According to comparisons of 1.5‐ and 3.5‐month‐old NCR and SHR (Folkow et al. 1977). a structurally increased pre‐/postglomerular resistance ratio rapidly resets the renal “longterm barostat function” in SHR to match the 30–40% pressure rise, thereby increasing total renal resistance 15–20%, while filtration capacity is unaltered so far. In NCR aging to 13 months hardly alters arterial pressure, but increases total renal resistance 10–15%, mainly affecting postglomerular vessels, while filtration capacity is reduced 25%. 13‐month‐old SHR show an additional 15% pressure rise and–relative to agematched NCR–a further 35% reduction of filtration capacity with a 30–35% increase of total renal resistance, which mainly affects the postglomerular vessels as the resistance ratio is now barely above that in NCR. Thus, advancing SHR hypertension seems to start a renal vicious circle, because accentuated reductions of filtration capacity are parallelled by structural postglomerular resistance increases, apparently to maintain GFR by raised filtration pressure which, however, accelerates glomerular deterioration.
Morphine inhibits substance P release from peripheral sensory nerve endings
Authors: BRODIN ERNST , GAZELIUS BERTIL , PANOPOULOS PANAGIOTIS , OLGART LEIF
Published: December 2008

Tissue levels of substance P (SP) were determined by radioimmunoassay in cat dental pulps after unilateral electrical stimulation of the inferior alveolar nerve. Nerve stimulation (10 V, 10 Hz, 5 ms for 3 min) reduced the SP level at the stimulated side by approximately 40%, indicating a release of SP. Stimulation performed after infusion of morphine (0.3 mg/kg/min, i. v.) for 10 min did not reduce the pulpal SP‐level. Naloxone (3 mg/kg. i. v.) administered immediately before the morphine infusion in three experiments. did not influence the effect of morphine on pulpal SP levels after nerve stimulation. This may indicate an action of morphine on a naloxone‐insensitive receptor type. Morphine in the dosage used did not influence the intradental sensory nerve conductivity. The results indicate that morphine is able to inhibit stimulus evoked release of SP from peripheral endings of primary afferent neurons.
Diastolic properties of the hypertrophied left ventricle in spontaneously hypertensive rats
Authors: LUNDIN S. , FRIBERG P. , RICKSTEN S.‐E.
Published: December 2008

The influence of myocardial hypertrophy on left ventricular volume compliance was studied in vitro in isolated hearts of 4 and 19 month old spontaneously hypertensive rats (SHR) and normotensive Wistar‐Kyoto rats (WKY). In both SHR groups diastolic volume compliance was similar to that in the controls, despite the presence of left ventricular hypertrophy. This seems to be mainly due to an altered geometric situation, since with increased wall thickness to internal radius ratio (w/ri), which was at hand, the less are outer myocardial layers stretched at a given increase in ventricular volume. This may imply that these layers will only little interfere with luminal distension (and thereby with diastolic volume compliance) in SHR. It was also observed that the progressive increase of ventricular hypertrophy from 4 to 19 months of age did not further increase w/ri in SHR, indicating an increase in overall ventricular size with age. Left ventricular end diastolic pressure (LVEDP) was also measured in conscious 5 week and 4 month old SHR compared with matched controls. LVEDP increased with the development of hypertension and was significantly elevated in 4 month old SHR. This will increase also the average diastolic prestretch of the SHR left ventricle and mobilize the “Starling mechanism” to maintain a normal stroke volume against the increased afterload for the heart in established hypertension. This seems particularly important since the hypertrophic w/ri increase (about 20%) is smaller than the great elevation of mean arterial pressure (40–50%) in SHR.
Impaired medullary circulation in postischemic acute renal failure
Authors: KARLBERG LARS , NORLÉN BO JOHAN , ÖJTEG GÖRAN , WOLGAST MATS
Published: December 2008

Acute renal failure was induced in heparinized rats by clamping the renal artery for 45 min. Ten minutes after recirculation the intrarenal blood flow distribution was measured. For this purpose labelled microspheres were injected together with 86‐Rb chloride. The microspheres were used for determination of cardiac output, total renal and cortical blood flow, and 86‐Rb for calculations of medullary blood flow. Total renal blood flow was reduced from 7.6 to 3.8 mlmin‐1· g‐1 and cortical blood flow was reduced from 11.7 to 7.0 ml · min‐1· g‐1. In the outer stripe of the medulla there was a reduction from 2.5 to 1.4 ml · min‐1· g‐1. In the inner stripe there was a more pronounced reduction from 1.8 to 0.2 ml · min‐1· g‐1 and in the inner zone from 0.8 to 0.1 ml · min‐1· g‐1. The marked reduction in the blood flow to the renal medulla after recirculation is suggestive for a medullary ischemia, which might be responsible for the characteristic dysfunctions in acute renal failure.
Responses of the relaxed and contracted portal vein to imposed stretch and shortening at graded rates
Authors: JOHANSSON BÖRJE
Published: December 2008

Portal veins were subjected to stretch and shortening at rates varying from 0.2 to 47% of initial muscle length/s. The total length change was 33% of initial length which was about 6 mm at the resting preload of 1 mN. Relaxed portal veins (Ca‐free medium) gave curvilinear stress‐strain relations which were practically independent of the rate of the length change and they were similar in their ascending and descending branches (non‐linear parallel elasticity). In contractures produced by K+ or hyperosmolar solution the stress‐strain curves showed pronounced and rate dependent hysteresis. The stretch response in K+ contracture showed initially a steep increase in force in relation to rate of lengthening (dP/dL) up to an apparent break‐point at 2–3% elongation, after which the rise in force was quite independent of the rate of stretch. The break‐point is blunted and shifted to greater length change in portal vein due to large series compliance, but in analogy with interpretations from other types of muscle it may reflect the limit of deformation of attached cross bridges. In hypertonicity contracture dP/dL increased in proportion to rate of stretch. Earlier isotonic quick release experiments showed that the force‐velocity relation of portal vein smooth muscle is markedly different in K+ and hyperosmolality contractures, respectively. Similar differences were found when force‐velocity relations were constructed from the present experiments by plotting active force versus rate of imposed length changes. This indicates that the viscous properties of contracted blood vessels, as revealed in stress‐strain hysteresis, are greatly determined by the force‐velocity characteristics of the smooth muscle actomyosin system. There are, however, certain differences between the force‐velocity curves from isotonic quick release experiments and from the present isovelocity study which remain to be explained.
Effects of sodium fluxes and ouabain on brain‐slice tryptophan transport
Authors: KORPI E. R.
Published: December 2008

Efflux of preloaded [3H]tryptophan from rat cerebral cortex slices has been monitored into superfusion media that were altered in their sodium content. Total replacement of sodium with choline greatly increased the release of tryptophan. This release could be cancelled by re‐introducing sodium into the slices. A brief exposure to ouabain, an efficient inhibitor of Na+, K+‐ATPase activity, only slightly increased tryptophan efflux at the concentration of 0.1 mM, whereas at 1.0 mM it produced a similar effect as the sodium‐free medium. Accordingly, when the slices were superfused in the presence of ouabain and sodium, the change of medium to sodium‐free caused much greater relative enhancement of tryptophan efflux with 0.1 than 1.0 mM ouabain. Tryptophan efflux was modified by changes in sodium fluxes also in slices initially depleted of sodium ions and treated with ouabain. The results suggest that the sodium‐free medium and ouabain have a similar mechanism of action in modifying the tryptophan transport, and that the cation gradients across the cell membranes are more crucial for normal amino acid transport than the functional Na+, K+‐ATPase.
Mechanisms of left ventricular filling during increased preload and inotropy
Authors: THORVALDSON JØRGEN , ILEBEKK ARNFINN , BUGGE‐ASPERHEIM BJØRN , KIIL FREDRIK
Published: December 2008

To examine the factors contributing to left ventricular filling, experiments were performed in anesthetized, open‐chest dogs with intact or mechanically constricted mitral ostium. Stroke volume was raised either by increasing left ventricular end‐diastolic volume (preload) by blood volume expansion or by infusing isoproterenol, a β‐adrenergic agonist. In all experimental settings, stroke volume rose in proportion (r>0.9) to the pressure time product (FTP = integral of the diastolic atrio‐ventricular (A‐V) pressure difference). During saline infusion atrial distention and contraction increased atrial pressure more than ventricular pressure whereas diastolic filling time (DFT) was not lengthened. Peak mitral and peak aortic flow rose almost equally. During isoproterenol infusion at constant heart rate (atrial pacing), the increase in PTP was mainly caused by a longer DFT. When heart rate was allowed to rise, DFT was reduced and the A‐V pressure difference increased because of a greater reduction in ventricular than in atrial pressure in early diastole. Thus, the A‐V pressure difference is generated in different ways by raising preload and inotropy with and without changes in heart rate.
Effects of glucose, insulin and nicotinic acid on adipose tissue blood flow in rats
Authors: MADSEN JOOP , MALCHOW‐MØLLER AXEL
Published: December 2008

Adipose tissue blood flow (ATBF) was examined in rat parametrial fat by the133‐Xe elimination method. Intravenous infusion of glucose to fed rats resulting in blood glucose concentrations of 10–12 mmol × 1‐1caused a significant reduction in ATBF (‐37%). Similar infusions to 48 hour fasted rats had no consistant effect on ATBF. Glucose infusion caused a significant rise in plasma insulin concentrations in both fed and fasted animals, although the average concentration in fasted rats given glucose did not exceed the control value in fed animals. Insulin added to the glucose infusion casued a similar reduction in ATBF in fasted animals as that seen after glucose alone in fed animals (‐38%). Guinea pig anti insulin serum administered intravenously to fed rats elicited an increase in blood glucose concentrations similar to that seen after glucose infusion, but was without effect on ATBF. These results suggest that the effect of glucose on ATBF is secondary to a release of insulin resulting in plasma levels above those found in fed control rats. Infusion of nicotinic acid also reduced ATBF without influencing blood glucose concentration and in spite of insulin concentrations lower than in fed control rats. Since both insulin and nicotinic acid inhibit the formation of c‐AMP in adipocytes, it is hypothesized that both compounds decrease ATBF by decreasing the release of the vasodilator adenosine from the cells.
Substance P fibres in the anterior segment of the rabbit eye
Authors: EHINGER B. , SUNDLER F. , TERVO K. , TERVO T. , TORNQVIST K.
Published: December 2008

Some laboratories have obtained diverging results regarding the presence of substance P fibres in the cornea possibly because different antibodies were used. This has been further investigated by comparing results with several antibodies on identically treated sections from the anterior segment of rabbit eyes. In the uvea all antisera gave identical results showing substance P fibres in the iris and ciliary processes. In the cornea, on the other hand, polyclonal rabbit or guinea‐pig antibodies gave high background fluorescence and no immunofluorescent fibres were detected. In contrast, the background staining was low with the monoclonal antibody so that substance P immunoreactive fibres could be demonstrated subepithelially, intraepithelially and in the corneal stroma.
The influence of varied tonicity of the extracellular medium on the depressant effect of active shortening in vertebrate striated muscle
Authors: EKELUND M.C.
Published: December 2008

The depressant effect of active shortening was studied during isometric twitch contraction in intact single muscle fibres of the frog at varied tonicity of the extracellular medium. The shortening effect was calculated as the difference in peak redeveloped force after a small (control) and a larger (test) release step and was expressed in per cent of the isometric tetanic force. The solutions were made hypertonic by addition of sucrose (relative tonicity 1.22T and 1.44T) and hypotonic by reduction of NaCl (relative tonicity 0.81T and 0.62T). The shortening induced depression decreased from 13.0 ± 1.2% in normal Ringer solution to 7.8 ± 1.3% after immersion of the fibre in 1.22T solution (mean ± SE, n = 7). This reduction of the depressant effect by shortening was less than half the size of that obtained in 1.44T solution. An increased force depression by shortening, from 12.7 ± 1.2% to 17.1 ± 1.5% (mean ± SE, n=7), was obtained when normal Ringer was replaced by 0.81T solution. This enhancement was further augmented in 0.62T solution. Experimental evidence is presented supporting the view that the influence of tonicity on the depressant effect of shortening is not due to tonicity induced changes in fibre width. The effect of varied tonicity on the shortening induced depresison appears to be essentially related to alterations in intracellular ionic strength.
Impulse firing in the slowly adapting stretch receptor neurone of lobster and its numerical simulation
Authors: GESTRELIUS S. , GRAMPP W.
Published: December 2008

A mathematical model of the electrical activity of the slowly adapting lobster stretch receptor neurone is presented. The model is based on constant field and state transition theory and employs measurements of the kinetics of membrane currents in sub‐and near‐threshold voltage regions (Gestrelius, Grampp & Sjölin 1981, Gestrelius & Grampp 1983, Gestrelius, Grampp & Sjölin 1983, Edman, Gestrelius & Grampp 1983). In addition to the classical action potential generating mechanisms (Hodgkin & Huxley 1952) the model also includes the processes of slow Na and K inactivation, ion flux dependent changes of the intracellular Na+ and K+ concentrations, and the activity of an electrogenic Na‐K pump sensitive to intracellular Na+ accumulation. The model is able to correctly simulate recorded action potentials as well as repetitive firing both with respect to stimulus dependence (sensitivity) and time dependence (adaptation) during prolonged electrical stimulation. In the living cell firing adaptation is found to consist of an initial phase with a relatively high, and a later phase with a lower rate of adaptation. From the model properties it can be concluded that the initial phase is mainly caused by the slow Na inactivation, while the later phase is due to a slow Na+ influx dependent pump current activation.
The effects of 5‐hydroxytryptamine on large intestinal motility and blood flow in the cat
Authors: FASTH S. , HEDLUND H. , HULTÉN L. , NORDGREN S. , ÖRESLAND T.
Published: December 2008

The effects of 5‐HT on proximal colonic and rectal motility and total colonic blood flow were studied in anaesthetized cats and compared with those evoked by pelvic nerve stimulation. Vasodilator responses, consistently elicited by low doses (5–10 μg/min close i.a.) and intermediate doses (10–50 μg/min) of 5‐HT were invariably abolished by hexamethonium indicating a nerve mediated response. Simultaneously to the vasodilator response both cholinergic and non‐cholinergic hexamethonium sensitive non‐adrenergic motility responses were evoked in the proximal colon. Furthermore non‐cholinergic, non‐adrenergic inhibitory neurons were excited. In the rectum excitation of such inhibitory neurons was the most consistent finding. The mechanisms behind the nerve mediated vascular and motility responses seem to differ as only the vascular effects were blocked by dihydroergotamine. The nerve mediated responses were in many respects similar to those evoked by pelvic nerve stimulation indicating that 5‐HT exerts its effects on the same instrinsic neurons as the pelvic nerves. At intermediate and high doses (50–100 μg/min) the effects exerted on the instrinsic reflex arcs were modulated by direct effects on the smooth muscle.
The membrane potential of the Japanese quail's oviductal smooth muscle during ovum transport
Authors: ARJAMAA O. , TALO A.
Published: December 2008

Previously it has been shown that in the quail's oviductal smooth muscle there exists coordinated electrical and mechanical activity. It is not known how the contractions are regulated; the oviduct probably functions as a stretch receptor and the mechanical stimulus is produced by the ovum itself. The cellular basis for stretch‐induced contractions is not known. In strips (n = 8) from the magnum, stretches of 50% changed the membrane potential. Compared with the resting length Lo (= 100%), stretches to 150% and 200% significantly (p < 0.001) hyperpolarized the membrane potential. Analyses of variance, however, revealed that at the length 150% both the level of stretch and single experiments differed significantly in relation to the membrane potential: F = 7.1, p < 0.5; F = 14.6, p < 0.01, respectively. At the length 200%, there were highly significant differences between the groups 100% and 200% (F = 36.3, p < 0.001) but the differences could be explained by the highly significant (F = 13.9, p < 0.001) interaction. Membrane potential measured from isolated, intact oviducts (n = 7) which had ovum in the magnum was significantly depolarized by 8–9 mV on the region over the ovum. On the other hand, the membrane potentials were the same in the different segments of the oviduct which did not contain an ovum: 52 mV. It is suggested that at fibre level, the temporal and spatial changes in membrane potential could be the basis for the stretch receptor characteristics of the quail's oviductal smooth muscle which has been concluded to be responsible for ovum transport.
Calmodulin binding to secretory granules isolated from bovine neurohypophyses
Authors: OLSEN S. F. , SLANINOVA J. , TREIMAN M. , SÆRMARK T. , THORN N. A.
Published: December 2008

Secretory granules, isolated from bovine neurohypophyses on isoosmolar Percoll‐sucrose‐EGTA gradients had a calmodulin content of 0.09 ± 0.01 μg/mg protein (SE, n = 6). The distribution of calmodulin on the gradient showed that it did not copurify with the granules. Specific binding sites for calmodulin with a high affinity (Kd = 2.43 ± 0.27 × 10‐9 M (SE, n = 5)) and a maximum binding capacity of 1.3 ± 0.4 pmol/mg protein (SE, n = 5) could be demonstrated when such secretory granules were incubated with 125I‐calmodulin.
Failure of naloxone to reduce the clonidine induced reduction of blood pressure and plasma noradrenaline in patients with essential hypertension
Authors: BRAMNERT MARGARETA , HÖKFELT BERNT
Published: December 2008

Studies in animals and man indicate a functional interaction between the adrenergic and the opiate systems. In the present study the effect of the opiate receptor blocker naloxone on the reduction of blood pressure and plasma noradrenaline induced by the α2‐agonist clonidine was investigated in nine patients with essential hypertension. In a randomised manner the patients received a bolus dose of naloxone (10 μg/kg) or physiological saline followed by a slow infusion of naloxone (5 μg/kg/h) or saline, respectively. Fifteen minutes after the respective bolus dose, clonidine (3 μg/kg) was infused over 10 minutes. Naloxone had no effect on the clonidine induced hypotension and reduction of plasma noradrenaline. Accordingly, there is no evidence that the clonidine induced reduction of blood pressure and plasma noradrenaline involves opiate receptors that can be blocked by naloxone. Plasma adrenaline increased significantly during the early phase of naloxone infusion.
Influence of Ca2+ on the mechanosensitivity of the hair cells in the lateral line organs of Necturus maculosus
Authors: JØRGENSEN FINN
Published: December 2008

The degree of synchronization (DOS) between the afferent spike activity from one stitch of the lateral line of Necturus maculosus (in vivo) and the mechanical stimulation of one neuromast of the same stitch was measured under different circumstances. The DOS was found to be independent of changes in the concentration of monovalent cations (Na+, K+ and choline+) in the bulk solution at high Ca concentration (1 mM). DOS was also independent of the Ca concentration in the range 1 mM‐1 μM in Tris‐HCl buffer, but was markedly reduced at Ca = 10 μM in MOPS‐KOH buffer. The reduced DOS, however, could be restored by addition of 10–20 mM KCl. 5 mM of 4‐aminopyridine did not influence the DOS at high Ca concentration, but completely reduced DOS at Ca = 10 μM. D600 (a methoxy derivative of verapamil) decreased DOS both at high and low Ca concentration.
Effect of apamin on release of vasoactive intestinal polypeptide (VIP) from the cat intestines
Authors: SJÖQVIST ANDERS , FAHRENKRUG JAN , JODAL MATS , LUNDGREN OVE
Published: December 2008

The effect of apamin, a polypeptide from bee venom, on the release of vasoactive intestinal polypeptide (VIP) during active neurogenic vasodilatations in the intestines was studied in vivo in anesthetized cats. Three non‐adrenergic, non‐cholinergic mechanisms were investigated, i. e. the vasodilatations seen upon transmural electrical field stimulation, pelvic nerve activation and stimulation of the intramural nerves with 5‐hydroxytryptamine (5‐HT) infused i. a. Apamin given close i. a.abolished the three vasodilator responses. Concomitantly, the increase of VIP release was also markedly diminished although apamin increased the rate of VIP release seen in the “resting” control period. The results are in agreement with the hypothesis that VIP is the neurotransmitter in the three investigated vasodilator mechanisms
Dynamics of the interventricular septum and free ventricular walls during selective left ventricular volume loading in dogs
Authors: MOLAUG MÅLFRID , GEIRAN ODD , KIIL FREDRIK
Published: December 2008

A previous study suggested that a change in the position of the interventricular septum played an important role in regulating cardiac performance during selective right ventricular volume loading. In the present study the cardiac response to selective left ventricular volume loading induced by a shunt between the subclavian artery and the left atrium was examined in anesthetized open‐chest dogs. Opening the shunt increased left and reduced right ventricular stroke volume, particularly after blood volume expansion. The end‐diastolic transseptal pressure difference increased. Myocardial segment length in the septum and free walls of both ventricles and the distances between the septum and the free walls were measured by an ultrasonic technique. Comparisons at similar left ventricular stroke volume with the shunt open and closed showed that the Frank‐Starling mechanisms of the free wall of the left ventricle and the septum were stimulated less with the shunt open. At similar right ventricular stroke volume the end‐diastolic dimension of the right ventricular free wall was larger with the shunt open. The distance decreased across the right ventricle and increased across the left ventricle when the shunt was open. We conclude that a change in the position of the septum improves left and reduces right ventricular performance during selective left ventricular volume loading.
Effects of PYY and PP on endocrine pancreas
Authors: SZECÓWKA J. , TATEMOTO K. , RAJAMÄKI G. , EFENDIĆ S.
Published: December 2008

Novel intestinal polypeptide YY (PYY) and pancreatic polypeptide (PP) were infused in fed anaesthetized rats. The peptides (10 and 100 pmol/kg · min) were administered during 30 min, alone, together with glucose or together with arginine. Plasma concentrations of glucose, insulin and glucagon were measured. At the dose of 10 pmol/kg · min the peptides had no effect. PP at the dose of 100 pmol/kg · min slightly augmented basal, but had no effect on stimulated insulin and glucagon release. PYY at the dose of 100 pmol/kg · min was without effect on basal insulin and glucagon levels and on glucose‐induced insulin release, but exerted an inhibitory effect on arginine‐induced secretion of both insulin and glucagon. It is unlikely that PYY and PP can affect secretion of insulin and glucagon via blood circulation. The potential capability of high doses of PP to affect insulin and glucagon secretion suggests that this peptide may exert direct (paracrine) effects on the pancreatic A‐and B‐cells
Different effects of types A and B botulinum toxin on transmitter release at the rat neuromuscular junction
Authors: SELLIN L.C. , THESLEFF S. , DASGUPTA B.R.
Published: December 2008

Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either crystalline type A botulinum toxin or purified type B botulinum neurotoxin. At 1, 3, 5 and 7 days after injection, the extensor digitorum longus nerve‐muscle preparation was excised and analyzed in vitro for alterations in spontaneous and nerve stimulus‐evoked quantal transmitter release. Muscles receiving type A toxin were paralyzed up to and including 7 days after injection. Muscles treated with type B toxin, although completely paralyzed at 1 and 3 days, twitched in response to nerve stimulation at 5 and 7 days after injection. Both toxins induced a marked decrease in the frequency of miniature endplate potentials but type A did so to a greater extent. The remaining population of miniature endplate potentials contained a greater frequency of potentials with small or large amplitudes and prolonged rise times compared to normal muscle. These changes were more pronounced with type A toxin than with type B toxin. In the presence of α‐dinitrophenol (1 mM), high frequency, fast‐rising miniature endplate potentials of uniform size reappeared. High K+(20 mM) was less effective in this respect. At 3 days after toxin injection nerve impulse evoked transmitter release was reduced more for type A treated muscles than for type B. However, 3,4‐diaminopyridine, an agent which increases nerve‐evoked transmitter release by increasing Ca2+influx, was more effective in reversing the paralysis in type A than in type B‐treated muscles. In contrast to type A, 3,4‐diaminopyridine induced in type B‐paralyzed muscle asynchronous endplate potentials in response to nerve stimuli and a posttetanic increase in miniature endplate potential frequency. The results show that type B toxin differs from type A, mainly by a shorter duration of action and by being less effectively antagonized by 3,4‐diaminopyridine. These findings have implications for the medical treatment of the two types of botulism