摘要:

It is suggested that the glomerular capillary membrane constitutes a flexible gel, where negative charges fixed to the matrix of the membrane account for the maintenance of its integrity. In this model, the hydrostatic pressure throughout the membrane is assumed to equal the glomerular capillary pressure,Pglom, of 56.7 mmHg. On the plasma side of the membrane, the charge‐induced electro‐osmotic pressure therefore has to balance the colloid osmotic pressure of glomerular plasma, and on its Bowman's space side, it has to balance the pressure drop,Pglom‐PBow, across this interphase. Using micropuncture technique, the glomerular plasma colloid osmotic pressure of 20.6 mmHg was found to require a charge density of 24.8 mEq L‐1and the pressure drop at the Bowman's space side of 56.7‐12.2=44.5 mmHg a density of 36.6 mEq L‐1. The transmembranous electric potential difference was estimated at ‐1.1 mV, a potential which, in a negatively charge membrane, will also constitute the net driving force for the fluid transfer; this force will be close to, but not identical with, that calculated as conventional from the Starling forces of, in the present case, 23.9 mmHg. In the present analysis the distribution of charges in the fluid of the pore resulting from charged groups fixed to the rim of the pore is al

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.552307000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

In our gel model applied to the glomerulus, maintenance of membrane integrity is assumed to be preserved not by rigid elements but by the electro‐osmotic and balancing hydrostatic pressure offered by negative, fixed charges such that the membrane is able to withstand the external colloid osmotic and hydrostatic forces. In a previous study we used micropuncture data to estimate the charge densities required to fulfil this assumption. In the present study the validity of the model was examined from the transport of neutral and negative charged myoglobin as derived from their concentrations in renal venous blood. In order to determine the size of the pores, or rather meshes in the network, the venous concentration of [51Cr]EDTA was also analysed. Based on the ratio between EDTA and neutral myoglobin of 1.08±0.010 (mean±SE,n=9), the equivalent pore radius was calculated to be ∼40 Å. The ratio of neutral to negative myoglobin in the two series performed was found to be 0.96±0.018 (n=8) and 0.97±0.05 (n=7), figures which were the same as ratio of 0.97 predicted on theoretical grounds. It is concluded that the experimental data support the hypotheses, although they may also be adapted to the transport in a homogeneously charged membrane; the charge density in this case was estimated at 2.3 mEq L‐1. Assuming that the membrane constitutes a network with quadratic meshes, each fibre would seem to carry binding sites ∼80 Å apart and where, in between these binding sites, each fibre was calculated to carry three charges such that the mesh will thus be surrounded

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.553306000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Stimulation of the afferent renal nerves in the anaesthetized rabbit by acute reduction in renal perfusion pressure results in a neurally mediated, reflex increase in hindlimb vascular resistance. To determine whether exogenous angiotensin II moderates the reflex, the kidneys of anaesthetized rabbits were vascularly isolated and renal blood flow was occluded acutely, following intrarenal administration of vehicle (0.9% saline) or angiotensin II (0.5 ng), and the hindlimb vascular response was measured. Occlusion of renal blood flow resulted in similar, significant increases in femoral perfusion pressure of 39.7±7.1 mmHg after vehicle and 21.3±8.9 mmHg (P<0.05,n=6) after angiotensin II. The viability of the preparation following repeated episodes of renal blood flow occlusion was tested by a series of three rapid (2–3 min delay) occlusions and three delayed (30 min delay) occlusions. Femoral perfusion pressure rose by 43.1±10.7 mmHg (rapid,P<0.05,n=11) and 64.4±12.3 mmHg (delayed,P<0.05,n= 5) on the first occasion. On the second occasion, the rapid occlusion did not result in a significant increase in femoral perfusion pressure (29.1±8.1 mmHg), but the delayed group did (54.6±22.4 mmHg,P<0.05). On the third occasion, neither group showed a significant change (20.9±16.3 and 30.8±13.5 mmHg). These data suggest that exogenous angiotensin II does not moderate the afferent renal nerve reflex. The decline in hindlimb response following rapid serial occlusion may be attributed to a diminution of an intermediary substance(s) at the nerve rece

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.562312000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The α1‐adrenoceptor subtypes mediating contraction of rabbit prostate and hypogastric artery were pharmacologically characterized using an isolated organ bath technique. The prostate had the same sensitivity to the contractile action of methoxamine and phenylephrine, whereas the hypogastric artery was five times less sensitive to the action of methoxamine in comparison with phenylephrine. Clonidine elicited contraction in the hypogastric artery but not in the prostate. BMY7378 was about 70‐fold more potent to antagonize the phenylephrine‐induced contraction in the hypogastric artery (pA28.14) than in the prostate (pA26.28), and 5‐methyl‐urapidil was about three‐fold more potent on prostrate than on hypogastric artery. The potency of different α1‐adrenoceptor antagonists tested in the rabbit prostate was significantly correlated with their binding affinity for the expressed recombinant α1A‐, but not α1B‐ or α1D‐, adrenoceptor subtype, whereas, the potency of the α1‐adrenoceptor antagonists tested in the rabbit hypogastric artery was better correlated with the defined α1D‐adrenoceptor. Chloroethylclonidine produced a 10‐fold rightward shift in the phenylephrine concentration–response curve in the hypogastric artery but only had a weak effect in the prostate. The results indicate that significant heterogeneity exists among α1‐adrenoceptor in the rabbit hypogastric artery (α1D‐adrenocep

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.565310000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of 17β‐oestradiol on the force responses to KCl and noradrenaline were investigated in rings of the rat tail artery. Incubation with 10 μm17β‐oestradiol for 100–295 min reduced the force amplitude after 5 min in high‐K+(140 mm) to 10% of the control value. The inhibitory effect of the steroid was unaffected by the NO‐synthase inhibitorl‐NAME. Rings activated by an intermediate degree of depolarization (60 mmK+) were less affected by the steroid (58% of control force). The sustained force response to 1 μmnoradrenaline was reduced in the presence of 17β‐oestradiol to 60% of control value. Lower concentrations of 17β‐oestradiol (0.1 and 1 μm) were without acute effects on force development. However, long‐term effects of 17β‐oestradiol on vessel reactivity were found at these low concentrations. Rings were cultured for 3–7 days in the absence or in the presence of the steroid before they were stimulated with agonists. Cultured rings developed an increased sensitivity to noradrenaline compared with freshly prepared ones. Cocaine (30 μm) shifted the noradrenaline concentration–response curve to the left in freshly prepared rings while it had no effect in cultured ones, indicating that the increased sensitivity to noradrenaline in cultured rings depends on loss of noradrenaline uptake. Rings cultured for 7 days in the presence of 0.1 μm17β‐oestradiol developed a more pronounced supersensitivity to noradrenaline (EC50for noradrenaline was 0.13±0.03 μmin steroid exposed rings vs. 0.38±0.09 μmin control rings). Thus, prolonged treatment with 17β‐oestradiol results in a potentiation of noradrenaline evoked force, in

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.567308000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Gastrointestinal, hepatic, and hindleg oxidation of3H‐labelled oleic acid and14C‐labelled glucose based on arterial‐venous differences in3H2O and14CO2were studied before and after an intravenous injection of 24 IU of growth hormone in 10 piglets. Hepatic oleic acid oxidation increased transiently while gastrointestinal oleic acid oxidation decreased correspondingly, maintaining a constant splanchnic oleic acid oxidation. Administration of a growth hormone led to a transient, parallel decrease in both hepatic and gastrointestinal glucose oxidation. We conclude that, in contrast to the growth hormone effect on splanchnic glucose oxidation, growth hormone effect on splanchnic fat oxidation appears to be organ spe

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.550315000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The interaction between morphine and three antagonists of theN‐methyl‐d‐aspartate (NMDA) receptor, MK‐801 (non‐competitive channel blocker), dextromethorphan (clinically available non‐competitive antagonist) and CGS19755 (competitive receptor antagonist), was examined in rats with the hot plate test. The NMDA antagonists were administered intraperitoneally and none of them caused antinociception at doses that did not produce motor deficits (0.1 mg kg‐1MK‐801, 30 mg kg‐1dextromethorphan and 5 mg kg‐1CGS19755). However, pretreatment with the NMDA antagonists at these doses 30 min prior to subcutaneous injection of 5 mg kg‐1morphine significantly potentiated the antinociceptive effect of morphine, with strongest effect observed with dextromethorphan. It is suggested that blockade of NMDA receptors enhances the antinociceptive effect of morphine and NMDA antagonists may improve the analgesic efficacy of m

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.566309000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

In the inner ear, the Reissner's membrane separates the scala vestibuli from the scala media and is thus of importance for maintaining a positive endocochlear potential. The motion of the membrane is thought to be driven by the vibrations of the underlying hearing organ caused by a hydromechanical coupling between the structures. Since the Reissner's membrane is relatively easily accessible in the cochlea its vibratory response has been used as a measure of the micromechanical behaviour of the hearing organ. To determine whether this indirect measure revealed the true characteristics of the hearing organ, experiments were performed using laser heterodyne interferometry in anin vitropreparation of the guinea‐pig temporal bone. Interferometric measurements at the Reissner's membrane and at the surface of the hearing organ directly beneath made it possible to compare the mechanical tuning characteristics of both structures. It was found that the mechanical response characteristics of the Reissner's membrane differed considerably from the hearing organ. The tuning frequency was different and only minor changes in the maximal vibration amplitude were seen when measuring at different radial locations. However, the shape of the response curve changed with location. The Reissner's membrane response appeared to be affected by the mechanical vibrations originating both at the middle ear ossicles and at the hearing organ. It is concluded that the Reissner's membrane response is a poor indicator of cochlear mechanics and that investigations of cochlear micromechanics should be performed directly at the level of the hearing orga

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.563313000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of perchlorate (6–40 mm) on contractile properties and depolarization–contraction coupling of diaphragm have been tested in muscle fibre bundles from 8 to 12‐week‐oldmdxand control mice. Twitch contractile properties were affected by perchlorate to a similar extent inmdxand control muscles. In the absence of perchlorate, voltage‐dependent parameters of both activation and inactivation were similar inmdxand control muscles. In bothmdxand control muscles, perchlorate induced a shift of activation and inactivation curves toward more negative potentials. However,mdxdiaphragm fibres were less sensitive to perchlorate in the low range of concentrations (6–12 mm). These results are unlikely to be due to a possible effect of the lack of dystrophin on the excitation–contraction coupling voltage sensor or ryanodine receptor. However, necrosis and regeneration occur inmdxmouse diaphragm and it is postulated that the presence of a high proportion of not fully mature fibres could contribute to the reduced sensitivity ofmdxdiaphragm fibres t

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.526290000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.546314000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY