摘要:

Experiments performed at 25°C, pH 7.4, confirmed that the human red blood cell possesses both Na‐independent and Na‐dependent transport systems for neutral amino acids. Further evidence for the existence of a major Na‐independent pathway for the large neutral amino acids (L‐leucine, L‐isoleucine, L‐phenylalanine, L‐valine and L‐methionine), designated the ‘L‐system’, was provided from trans‐acceleration experiments of L‐leucine efflux. Transport via the L‐system with respect to kinetics of substrates and stereospecificity was studied. Experiments on inhibition of transport and on kinetics of Na‐dependence of uptake of L‐alanine and glycine were consistent with Na‐dependent amino acid transport being mediated by two different systems, i. e. an ASC‐system for L‐alanine, L‐serine and L‐cysteine and a Gly‐system for glycine transport. When compared with a ‘high capacity/low affinity’ pattern of kinetics of the L‐system, Na‐dependent uptake of L‐alanine and glycine was found to exhibit ‘low capacity/high affinity’ kinetics. The Na‐dependence of L‐alanine uptake conformed to first order interaction, that of glycine uptake to second order. An effect predominantly on the maximum transport capacity (V12) of the saturable Nadependent uptake route of L‐alanine and glycine, respectively, by a 50

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07149.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Local and remote regulation of subcutaneous blood flow in the forearm and leg was studied during head‐up tilt (30°, 457deg; and 70°) in 7 young healthy subjects. Relative blood flow was estimated by the local133Xe washout technique. Incremental levels of head‐up tilt elicited increasing vascular resistance on arm and leg, respectively. Positive pressure similar to a blood column of the same height was able to prevent a significant part of the vasoconstrictor response on the leg to head‐up tilt. Thus if venous distension is prevented the local veno‐arteriolar reflex is abolished, whereas arteriolar constriction due to centrally elicited reflexes remains unaffected. Subcutaneous blood flow in the extremities are regulated by remote (baroreceptor) as well as local sympathetic reflex mechanisms (veno‐arteriolar reflex); but the relative influence of the local veno‐arteriolar reflex on the increase in total peripheral resistance seems to decrease with increasin

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07150.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Theophylline (theo) induced a marked increase in the short circuit current (SCC) after maximal stimulation by the antidiuretic hormone, arginine vasotocin (AVT). The stimulation amounted to 20–70% of the AVT‐stimulation. Practically no effect was seen on osmotic water flow after maximal AVT‐stimulation. A concentration dependence of the SCC stimulation was found from 0.04 to 4 mM theo, 16 mM inhibited the SCC. The response to theo was independent of the time of preincubation with AVT. The theo induced increase of SCC was accounted for by active sodium transport. Theo did induce an increase in the cyclic AMP level after stimulation with a maximal concentration of AVT, but so did a supramaximal dose of AVT. This indicates that the mechanism, by which theo stimulated the SCC additional to maximal AVT stimulation, is different from that by which AVT works. This effect of theo may be unrelated to cAMP or it may be explained by differences in cellular specificity of theo an

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07151.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Stretch‐shortening cycle refers to the mechanical condition in which store and recoil of elastic energy occur in the skeletal muscle. This leads to a greater work output when compared to a simple shortening contraction. The subjects performed vertical jumps with and without preliminary counter‐movement and with small and large knee angular displacement. The results indicated that those subjects who had more fast twitch (FT) fibers benefited more from the stretching phase performed with high speed and short angular displacement. The amounts of elastic energy stored in this phase were 30 and 26 N × kgBW‐1, respectively, for FT and slow twitch (ST) type subjects. The recoil of elastic energy was proportional to the amount of energy storage. In large amplitude jumps where transient period between stretch and shortening is long the both types of subjects demonstrated similar amount of storage of elastic energy (17 and 16 N × kgBW‐1, respectively). However, the re‐use of this elastic energy was greater in ST group (24%) as compared to the FT group (17%). The results can be interpreted through differences in sarcomere cross‐bridge life times between fast and slow muscle fibers. The slow type muscle may be able to retain the cross‐bridge attachment for a longer period of time and therefore it may utilize elastic energy better in a slow type b

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07152.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The bilateral reflex actions of vagus nerve afferent signals on phrenic efferent activity have been tested by unilateral graded single shock electrical stimulation. An early excitation (latency 3–5 msec) was more prominent in the phrenic nerve contralateral to the stimulated vagus. Spinal cord hemisection at C3eliminated both contralateral and ipsilateral responses: thus, both were mediated via descending tracts in the contralateral cord. A bilaterally symmetrical early inhibition (latency 8–12 msec) followed the early excitation. The electrical thresholds for evoking the early responses and the temperature for blocking these responses during graded vagal cooling were closely similar to the threshold and blocking temperature for pulmonary stretch receptor afferents. Higher stimulus strengths evoked a strong, bilaterally similar, late excitation (latency 12–20 msec) followed by a late inhibition. At very high stimulus strengths a third excitation (latency 25–30 msec) could appear. Sometimes these responses were followed by lowered phrenic activity for the remainder of inspiration. Single shock stimulation of the intact vagus nerve or of the peripheral end of the cut recurrent laryngeal nerve provoked. by the contraction of laryngeal muscles, a strong, short latency (12 msec) inhibition of phrenic activity mediated by superior laryngeal nerve afferents. The implications of these results with respect to the reflex pathways of the different responses and their possible integration in the central respiratory control mechanisms are di

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07153.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

A mathematical model for description of static and dynamic myogenic responses to change of vascular transmural pressure in the arterioles of skeletal muscle was developed for the purpose of elucidating some basic characteristics of the myogenic vascular control system which have proved difficult to reveal by physiological observations alone. The model, which is a refined version of a previous one (Borgström&Grände 1979), is based on a force‐equilibrium in the arteriolar wall, including passive forces related to vascular transmural pressure, wall elasticity, and wall viscosity, an active force related to resting vascular tone, and the active static and dynamic myogenic forces considered to be related to and triggered by wall tension (force) and its rate of change as indicated by our previous results. The effects of biological inertia, of shifts along the length‐tension curve of the smooth muscle, and of pressure induced reactions in the more proximal arterial vessels were taken into account in the present force‐equilibrium equation for the arterioles. Arteriolar wall viscosity was assumed to decrease with increasing rate of wall movement, a behaviour predicted by the model and corroborated by in vitro observations on larger vessels. The model was found capable of faithfully simulating microvascular myogenic responses in cat skeletal muscle in vivo in response to ramp as well as impulse transmural pressure stimuli over the entire biological range from maximum constriction to dilatation. With such characteristics, it can serve as a useful complement to physiological approaches in attempts to define more precisely the mode of operation of the myogenic control system and to reveal inherent complexities of biophysical factors and of interaction of other control mechanisms in microvascular regulation in vivo, as exemplified by presented tests and preliminary

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07154.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The actions elicited by electrical stimulation of the rubrospinal path in NR (nucleus ruber), and by stimulation of the rubro‐bulbospinal path in MesADC (mesencephalic area for dynamic control), were studied with intra‐, juxta‐ or extracellular recordings in lumbar γ‐motoneurones of cats anaesthetized with chloralose. The results were obtained during a series of experiments in which reflex effects from muscle, skin and joint afferents were also investigated. 90 cells tested with stimulation both in NR and in MesADC were classified (cf. Appelberg 1981) as dynamic (influenced from MesADC) or static (not influenced). 84 of these γ‐cells responded to stimulation in the red nucleus. The same response pattern was found for dynamic and static γ‐cells. For flexor cells, excitation was by far predominant while equal numbers of extensor cells showed excitatory and inhibitory effects. The shortest route to both static and dynamic γ‐cells was disynaptic. With stimulation of the rubro‐bulbospinal path, excitatory effects were more than twice as frequent as inhibitory effects. No clearcut difference was seen between extensor and flexor cells. The segmental latency for rubro‐bulbospinally mediated excitatory effects could be measured for only one cell, and it is tentatively suggested that the pathway to this dynamic γ‐motoneurone involves one or two interneurones more than in the rubrospinal pathway. Spontaneous activity was significantly more common among the dynamic cells, but the axonal conduction velocities of dynamic and static cells did not differ. The similarities between rubrospinal effects on α‐motoneurones and both classes of γ‐motoneurones indicate that the rubrospinal tract has the ability to coactivate α‐ and γ‐motoneurones (Granit 1955, 1979). The comparison of the properties of the population of γ‐cells classified as dynamic or static showed marked differences strengthening the reliability of the prev

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07155.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Electrical stimulation (10 V, 0.2 ms) of the chorda‐lingual nerve caused a biphasic vasodilatory response in the cat tongue with an initial phase which was most marked at low frequencies and a maintained phase which increased with frequency. Simultaneously, there was a VIP release as indicated by a marked increased VIP output from the tongue. VIP output increased with time of stimulation and was most pronounced at high frequencies. Atropine abolished the initial phase of vasodilation at low frequencies as well as reduced this phase at medium frequencies. At high frequency stimulation (15 Hz), the vasodilation was still somewhat reduced by atropine but in contrast to the cat submandibular salivary gland, the duration of the vasodilatory response did not increase after atropine. Furthermore, atropine did not increase VIP output from the tongue during nerve stimulation. Hexamethonium completely abolished VIP release as well as most of the vasodilation upon stimulation of the chorda‐lingual nerve. The remaining vasodilation may be due to antidromic stimulation of unmyelinated trigeminal sensory neurons, since it was present when using high threshold stimulation parameters (10 V, 5 ms). Local intra‐arterial infusion of acetylcholine or VIP caused a marked vasodilation of the tongue. Also substance P infusion induced a vasodilatory response. The response to acetylcholine was atropine sensitive, while the effects of VIP and substance P were atropine‐resistant. Combined infusions of VIP and acetylcholine had an additive effect on vasodilation. In conclusion, the present data suggest that low threshold chorda‐lingual nerve stimulation induced a release of both acetylcholine and VIP from postganglionic neurons in the tongue. The contribution by these two agents in the vasodilatory response may then depend upon time and frequency of stimulation. In contrast to the VIP nerves in the submandibular gland, no evidence suggests that VIP release from vascular nerves in the tongue is affected by atropine. High threshold stimulation also induces antidromic vasodilation possibly mediated via substance

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07156.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Electrical stimulation of the cat cervical sympathetic trunk caused submandibular salivary secretion and vasoconstriction simultaneously with a contraction of the nictitating membrane. Following α‐ and β‐adrenoceptor blockade by phentolamine or phenoxybenzamine combined with propranolol, the salivary response and the nictitating membrane contraction upon sympathetic stimulation were almost abolished. A considerable vasoconstrictor response (up to 40% of control) however still remained in the submandibular gland. This yasoconstriction, which persisted after α‐adrenoceptor blockade, was rather slow in onset and had a long duration without any poststimulatory hyperemia. Local intra‐arterial infusions of noradrenaline caused submandibular vasoconstriction, salivary secretion and nictitating membrane contraction. The blood flow response to exogenous noradrenaline did, however, not mimic the effects of sympathetic nerve stimulation with regard to vascular escape. Whereas the vascular escape after nerve stimulation was followed by a prolonged vasoconstriction with a gradual decline, the escape after noradrenaline infusions was accompanied by a normalization of blood flow. Local intra‐arterial infusions of pancreatic polypeptide (PP)‐related peptides caused a slowly developing vasoconstriction with a long duration in the submandibular gland, but no salivary secretion or contraction of the nictitating membrane. The relative molar potencies as vasoconstrictory agents were about PYY: 1, neuropeptide Y (NPY): 5, avian and bovine pancreatic polypeptid 100. The vasoconstrictor effects of PP‐related peptides were resistant to α‐adrenoceptor blockade and present also in sympathectomized animals, suggesting a direct action on vascular smooth muscle. Combined local infusions of noradrenaline and NPY caused a vascular response in the submandibular salivary gland which was similar to that seen upon sympathetic nerve stimulation. PYY and NPY caused increase in systemic arterial blood pressure upon systemic administration which indicates general vasoconstrictor actions. This effect was accompanied by a transient bradycardia which was due to inhibition of sympathetic tone, since it was absent in animals treated with propranolol.In conclusion, the present findings illustrate the differential sensitivity to α‐adrenoceptor antagonists of the submandibular vasoconstriction and salivation as well as smooth muscle contraction of the nictitating membrane induced by sympathetic nerve stimulation. This remaining vasoconstriction may be explained by release of a nonadrenergic, PP‐related transmitter such as NPY which may be present together with noradrenaline in the vascular nerves. Release of an additional vasoconstrictory factor may also account for the finding that infusions of noradrenaline do not mimic the vascular effects of sympathetic n

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07157.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The effects of α‐,β‐ or α+β‐adrenergic blockade on arterial plasma concentrations of insulin, glucagon and somatostatin in response to splanchnic nerve stimulation were studied in anesthetized cats. In control experiments splanchnic nerve stimulation caused a marked rise in plasma glucose and glucagon concentrations and a marked fall in insulin but somatostatin was unaffected. Pretreatment with phentolamine significantly increased basal plasma insulin concentration but the response pattern to splanchnic nerve stimulation was not altered. Propranolol attenuated both the glucose and insulin responses. Combined α‐and β‐blockade abolished the hyperglycemia and hypoinsulinemia induced by splanchnic nerve stimulation, whereas the rise in plasma glucagon was not affected. It is concluded that insulin release from the pancreas and glucose release from the liver is controlled by adrenergic mechanisms whereas pancreatic glucagon and somatostatin secretion is relatively insensitive to splanchnic nerve stim

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1982.tb07158.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY