摘要:

To examine to what extent the reabsorbate concentrations, calculated as the flux ratios between solutes and water, represent the fluid composition in the lateral intercellular space (LIS) in the proximal tubules, reabsorption was stimulated by elevatingPco2from 5 to 13 kPa before and during infusion of mannitol to a plasma concentration of 70 mM in volume‐expanded dogs receiving ethacrynic acid. The reabsorbate concentration of NaHCO3increased by 50 Mmduring mannitol infusion. The real concentration of NaHCO3in LIS could not, however, be elevated by this amount, since the driving forces for fluid reabsorption then would have increased during osmotic diuresis due to diffusion of mannitol into LIS from plasma. A model analysis of diffusion in LIS showed that transcellular transport can only lead to trivial increases of LIS concentrations compared to plasma, whereas diffusion across tight junctions can increase LIS concentrations by several mM. NaCl diffusion and coupled transcellular water transport map therefore represent a significant contribution to total bicarbonate‐dependent NaCl and water reabsorption in the proximal tubu

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08736.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

To compare the osmotic inhibitory effects of NaCl and NaHCO3on proximal tubular fluid reabsorption, plasma osmolality was raised by 40 mosmol kg‐1H2O by infusing hypertonic NaCl and NaHCO3in volume‐expanded dogs receiving ethacrynic acid. In five dogs studied at constant plasma pH 7.5, both NaCl and NaHCO3reduced water reahsorption by 29 ± 2%. However, NaCl infusion reduced hicarbonate rcabsorption by 31 ± 2%, whereas bicarbonate reabsorption remained unchanged during NaHCO3infusion. In six dogs, bicarbonate reabsorption was kept constant during NaCl and NaHCO3infusion by adjustments of plasma pH. At similar glomerular filtration rates (42.4 ± 2.9 ml min‐1), water reabsorption was 28.7 ± 1.7 ml min‐1in the control period, 29.4 ± ‐2.5 ml min‐1during hypertonic NaCl infusion and 20.6 ± 1.2 ml min‐1during hypertonic NaHCO3infusion. Therefore, NaCl did not reduce proximal tubular water reabsorption by a direct osmotic effect. By calculating the regression coefficient for the relationship between measured chloride reabsorption and maximal convective chloride flux, the effective reflection coefficient for NaCl averaged 0.11 ± 0.01. The combination of a low reflection coefficient and high permeability may explain why hypertonic NaCl is not

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08737.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

To examine the oxygen requirement of carbonic anhydrase‐dependent sodium reabsorption in the proximal tubule, 18 anaesthctized dogs were studied under conditions of saturated distal NaCl reabsorption; the latter was accomplished by volume expansion (all groups) combined with infusion of loop diuretics (groups 1 and 3). Acetazolamide reduced HCO3reabsorption by 602 ± 32 μmol min‐1(55%, group 1) and hy 777 ± 103 μmol min‐1(66%, group 2). This was accompanied with a reduction in sodium reahsorption and oxygen consumption in a molar ΔNa/ΔO2ratio of ahout 45 in both groups of dogs. The ΔHCO3/ΔO2ratio averaged 16 ± 1, which was not significantly different from the theoretical value of 18 expectcd for transcellular sodium transport by Na+, K+‐ATPasc. Mannitol (group 3) reduced NaCl rcabsorption by 37 ± 2% without affecting NaHCO3reabsorption or oxygen consumption significantly. We conclude that carbonic anhydrase‐dependent NaCI reahsorption in the proximal tuhules is passive, and that NaHCO3reahsorption is the only important active sodium transport which is sensitive to inhibition of

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08738.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Normal sheep or sheep in which the renal nerves had been extirpated were deprived of water for 2 days in order to determine whether changes in renal nerve activity contribute to natriuresis during water deprivation. Both groups of sheep showed a considerable natriuresis throughout the period of water deprivation and increases in plasma osmolality and plasma Na concentration. Renal denervation, as indicated by the absence of catecholamine fluoresence in kidney sections, was extensive.Phdevious experiments have suggested cerebral involvemenhd in the induction of dehydration‐induced natriuresis. The present results indicate that the efferent pathway mediating this cerebral influence on renal sodium excretion does not involve the renal nerves, suggesting a hormonal mechanism as the likely pathway

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08739.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The possible existence of a countercurrent exchanger (multiplier) in the intestinal villi of suckling swine was investigated with three different methods:1Comparing venous appearance of oxygen and red cells ihd the mesenteric vein after close i. a. injection of a blood sample equilibrated with pure oxygen and containing methaemoglobinaemic red cells.2Determining sodium (μg) over protein (mg) ratios along villi.3Estimating tissue osmolality in the villus tissue frohd measurements of freezing‐point depression.It was observed that oxygen appeared earlier than red cells in the mesenteric vein after i. a. injection. Furthermore, both the chemical measurements of sodium/protein ratios in the villi and the estimations of tissue osmolality indicate that there exists a gradient of osmolalities along the villus length, the villus tip being hyperosmolar as compared to the villus base. We conclude that a countercurrent exchanger (multiplier) exists in the villi of suckling swine. Its possible pathophysiological significance is discusse

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08740.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The effects of the Cl‐channel blocker, NPPB (5‐nitro‐2‐(3‐phenylpropylamino)‐benzoate), on the transport of Na+and Cl‐in the descending colon of the rat were studied in the Ussing chamber. In control tissue, NPPB administered at the mucosal side of the epithelium increased the short‐circuit current (Isc) and inhibited the unidirectional mucosa‐to‐serosa fluxes of Na+and CI‐. In HCO‐3‐‐or Cl‐‐free media or in the presence of SITS (4‐acetamido‐4′‐isothiocyanato‐stilbene‐2,2′‐disulphonic acid), this increase inIsccaused by mucosal NPPB was not observed. The serosal administration of NPPB was without effect.Mhdcosal NPPB (10‐‐4mol l‐1hd decreased the forskolin‐induced increase inIscby only about 60%. However, the activation of the serosa‐to‐mucosa flux of Cl‐caused by forskolin was inhibited completely. NPPB decreased the mucosa‐to‐serosa fluxes of Na+and Cl‐reduced additionally by forskolin. Serosal NPPB decreasedIscandJNasm, but had no effect onJNasmorJNasm. In HCO‐3‐free buffer the increase inIscinduced by forskolin was inhibited completely by NPPB.The inhibition of Cl‐secretion by NPPB fits well with the capacity of the drug to block Cl‐channels. For the inhibition of neutral NaCl absorption two sites of action are discussed: an interaction with the Cl‐/HCO‐3exchange

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08741.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Ekblad, E. B. M. 1989. Omeprazole: inhibitohd of both acid formation and translocation in gastric mucosa.Acra Physiol Scand137, 223–230. Received 15 March 1989, accepted 2 June 1989. ISSN 0001–6772. Cardiovascular Research Institute, University of California, San Francisco, and Nephrology, Veterans Administration Medical Center, San Francisco, CA, USA.Omeprazole, believed to inhibit H+, K+‐ATPase, was used to study acid secretion dynamics in isolated gastric mucosa. Tissue was mounted in a chamber and continuously supplied with both fresh nutrient and secretory solution (flow‐through). Acid secretion was monitored on and recorded by a pH‐stat microprocessor set‐up. In spontaneously secreting mucosa the continuous presence of omeprazole causes a monotonic decline in secretion rate to a new lower steady state. The relationship between the inhibited steady‐state acid secretion rate and omeprazole concentration is expressed by the sum of two hyperbolic functions withK1s differing by a factor of more than 100. When omeprazole is removed, the secretion rate always recovers. The amount of acid suppressed depends uniquely on omeprazole exposure: it is proportional to the exposure at low exposure and disproportionate (logarithmic) at high exposure. The index of conservation declines with omeprazole exposure, i. e. the inhibition by omeprazole ranges from conservative (no net loss of acid) to non‐conservative (net loss of acid). Dithiothreitol causes the inhibition by omeprazole to be conservative (index of conservation = 0) at even higher omeprazole exposure. The index of conservation was introduced to allow for numerical evaluation of both inhibitory and stimulatory effects regardless of the magnitude of the effect. It is concluded that omeprazole acts at two different sites, possibly with inhibition by sulphoxide derivatives on the formation step and sulphide derivatives on the tran

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08742.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Low doses of vasoactive intestinal polypeptide (VIP) and calcitonin gene‐related peptide (CGRP) have been shown to augment the salivary volume secretion evoked by muscarinic receptor agonists or substance P (SP) in rat parotid gland. Since VIP and CGRP are known to activate adenylate cyclase, we have studied whether forskolin, which directly activates this enzyme, can mimic the effects of these peptides on salivary secretion from the parotid gland in anaesthetized (Inactin 0.5 g kg‐1i. p.) rats. We have also studied the effect of the secretagogues and peptides on glandular blood flow as revealed by the laser Doppler technique.Crbachol (5 nmol kg‐1) and SP (185 pmol kghd‐1) injected i. v. caused a transient increase in parotid blood flow and a decrease in systematic blood pressure concomitant with a salivary secretion of 3.3 ± 0.3 mg(n= 22) and 18.7 ± 1.9 mg(n= 25) respectively. VIP (150 pmol kg‐1) and CGRP (25 pmol kg‐1) also caused a transient increase in glandular blood flow concomitant with a decrease in systemic blood pressure, but no salivary secretion. The glandular blood flow increased by 166 ± 5% and 43 ± 11% for VIP and CGRP respectively. When carbachol was given 20 s after the injection of VIP or CGRP, the secretory response was increased by about 250% and 60% respectively. The adenylate cyclase stimulator forskolin (2.5 pmol kg‐1) produced the same type of response regarding blood flow and systemic blood pressure as VIP and CGRP and potentiated the salivary secretion evoked by carbachol (5 nmol kg‐) by about 100%.Since forskolin can mimic VIP in potentiating salivary secretion, the ability of this peptide to induce CAMP formation in the gland cells may contribute importantly to the stimulation of

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08743.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Ohlsson, L.&Lindström, Phd 1989. Growth hormone‐releasing factor induces a biphasic modulation of K+permeability in perfused cultured rat somatotrophs.Acta Physiol Scand137, 237–241. Received 22 May 1989, accepted 16 June 1989. ISSN 0001–6772. Department of Histology and Cell Biology, University of Umeå, Sweden.Growth hormone‐releasing factor (GKF) induced a biphasic response in86Rb outflow in rat somatotrophs. An early inhibition was observed at all GRF concentrations tested, 1 pm‐10 nm, and this was followed by a later increase. The increase in86Rb outflow rate came earlier at high GRF concentrations and GRF had a dose‐related effect on the magnitude of the increase. The effects of GRF on86Kb outflow were observed also in the absence of extracellular calcium. Peak growth hormone release preceded peak86Rb outflow rate. The timing of the effects of GRF on potassium outflow is consistent with the hypothesis that reduced potassium outflow is involved in somatotroph depolarization leading to increased exocytosis, followed by a later increase in potassium outflow leading to re

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08744.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Centrally administered neuropeptide Y has been shown to produce sedation manifested by a suppression of locomotor activity and a synchronizing effect on the EEG pattern in normal rats. It has been suggested that this sedative effect of NPY is largely due to a facilitation of the α2‐adrenergic transmission line. In the spontaneously hypertensive (SH) rat, the NPY‐induced up‐regulation of α2‐adrenoceptors observed in normal rats is absent, and NPY produces a desynchronization of the EEG. In the present study, we have therefore examined the effects of NPY on locomotor activity of SH rats and of inbred controls of the Wistar‐Kyoto (WKy) strain, in both morning and evening sessions. In morning sessions, NPY (0.2–5.0 nmol intracerebroventricularly, i. c.v.) increased locomotor activity of SH rats in a dosc‐related manner. WKy rats were largelj inactiveper se, and no effects of NPY could be detected. In evening sessions, when spontaneous activity is high, NPY (1.0 nmol i. c.v.) still increased the activity of the SH rats. In WKy rats, an activity suppression similar to that previously reported for normal Sprague‐Dawley rats was seen. The present results indicate that the sedative action of NPY in different rats strains correlates with the ability of the peptide to up‐regulate α2

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1989.tb08745.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY