| 1. |
- Lundberg, Lars, et al.
(författare)
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Intraneural electrical stimulation of cutaneous nociceptive fibres in humans : effects of different pulse patterns on magnitude of pain
- 1992
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Ingår i: Acta Physiologica Scandinavica. - : Wiley-Blackwell. - 0001-6772 .- 1365-201X. ; 146:1, s. 41-48
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Tidskriftsartikel (refereegranskat)abstract
- A study was performed to elucidate how different impulse frequencies and impulse patterns in cutaneous nociceptive fibres influence the subjective magnitude of pain. Groups of nociceptive Aδ and C fibres were co-activated by electrical intraneural stimulation at constant intensity in cutaneous fascicles of the peroneal nerve in healthy human subjects. The resulting pain sensations were rated on a modified visual analogue scale. Five-second trains were administered randomly at irregular intervals of at least 30 s. Five of the stimulus patterns had regular interpulse intervals, corresponding to frequencies of 1, 2, 4, 10 and 15 Hz, and three other patterns were constructed to mimic to some extent the initially phasic and subsequently slowly adapting discharge patterns which may be encountered in recordings from human nociceptors. The results from these experiments using stimulation frequencies within physiological discharge ranges for human nociceptors indicate that the subjective magnitude of pain increases monotonously as a function of stimulus frequency, and that patterns mimicking nociceptor discharges in response to natural stimuli give rise to greater peak magnitudes of pain than artificial regular patterns with a corresponding number of impulses.
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| 2. |
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| 3. |
- Holm, Lena, et al.
(författare)
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Resetting of the pressure range for blood flow autoregulation in the rat kidney.
- 1990
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 138:3, s. 395-401
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Tidskriftsartikel (refereegranskat)abstract
- Both a myogenic response and the tubuloglomerular feedback control mechanism seem to be involved in autoregulation of glomerular filtration rate (GFR) and renal blood flow (RBF). Earlier experiments have shown that clamping of renal arterial perfusion pressure, below the autoregulatory range, reduces single-nephron GFR, and that this low value is maintained during the first 10-15 min after release of the clamp. It was also found that the tubuloglomerular feedback mechanism in the early declamp phase was strongly activated to reduce GFR. These findings can not be easily understood with the current knowledge of autoregulation, but would suggest a resetting of RBF and GFR autoregulation to a new level. To test this, left renal arterial perfusion pressure was reduced from 100 to 60 mmHg during 20 min with and without angiotensin converting enzyme inhibition (0.5 mg i.v. enalapril). Renal blood flow was measured with laser-Doppler flowmetry. When arterial perfusion pressure was reduced from 100 to 60 mmHg for 20 min, RBF was reduced to 77% of control and remained at this low level during the first minutes of declamp. In this situation there was an autoregulation to a new level. Renal blood flow was then slowly normalized (16.1 min). In the enalapril-treated animals RBF was only reduced to 85% during the 20 min of clamping and returned immediately to the control level at declamp. Thus, these experiments demonstrate that if renal blood flow is decreased by reducing the perfusion pressure below the normal autoregulatory range the pressure range for blood flow autoregulation resets to a lower level and that this change is mediated via the renin-angiotensin system.
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| 4. |
- Holm, Lena, et al.
(författare)
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Stimulation of acid secretion increases the gastric gland luminal pressure in the rat.
- 1992
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Ingår i: Gastroenterology. - 0016-5085 .- 1528-0012. ; 103:6, s. 1797-803
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Tidskriftsartikel (refereegranskat)abstract
- The gastric mucosal gland luminal pressure was measured in vivo with a pressure-sensitive microelectrode technique (servo-null) in anesthetized rats. A microelectrode was inserted into a gland lumen by means of a micromanipulator at an angle of 30 degrees to the mucosal surface. Acid secretion was estimated by measuring the pH in the solution covering the mucosa. During control conditions, when the mucosa was secreting acid spontaneously, gland luminal pressure was 12.3 +/- 1.2 mm Hg. At about 9 minutes after starting pentagastrin administration, the luminal pressure stabilized at 17.2 +/- 1.7 mm Hg. In the rats given impromidine (500 micrograms.kg-1.h-1) luminal pressure gradually increased (during 9-10 minutes) from a control level of 9.0 +/- 1.9 to 17.3 +/- 2.6 mm Hg. During the majority of experiments, the luminal pressure oscillated at 3-7 cycles per minute. The results show that intraluminal pressure increases during stimulated acid secretion, indicating that a resistance to the volume secretion exists in the upper part of the gastric crypts. This hydrostatic pressure may well be the driving force for creating channels for acid and pepsin to cross the mucus layer covering the mucosal surface.
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| 5. |
- Morsing, P, et al.
(författare)
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Renal interstitial pressure and tubuloglomerular feedback control in rats during infusion of atrial natriuretic peptide (ANP).
- 1992
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772 .- 1365-201X. ; 146:3, s. 393-8
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Tidskriftsartikel (refereegranskat)abstract
- Atrial natriuretic peptide (ANP), injected at physiological concentrations, is known to induce both natriuresis and diuresis. It has been suggested by some investigators that these changes result from an increasing glomerular filtration rate (GFR), but others have been unable to demonstrate an increased GFR. The tubuloglomerular feedback (TGF) mechanism is an important regulator of GFR, and the sensitivity of TGF is decreased during ANP administration. Furthermore, resetting of TGF is, in most instances, related to changes in renal interstitial hydrostatic and oncotic pressures. It is also known that ANP may increase capillary permeability which may change renal interstitial pressure. The present study was performed to examine renal interstitial pressures and the TGF mechanism during ANP infusion. In accordance with previous studies, TGF sensitivity was found to be decreased. The tubular flow rate which elicited half the maximal drop in stop-flow pressure (Psf) was increased from 18.5 to 25.7 nl min-1. In contrast, ANP infusion resulted in a decreased interstitial hydrostatic pressure and an increased interstitial oncotic pressure. From previous experiments, such changes in interstitial pressures would be expected to increase TGF sensitivity. The changes in interstitial pressure cannot, therefore, directly explain the resetting of the feedback mechanism. In conclusion, the present paper shows a decreased renal net interstitial pressure after intravenous administration of ANP.
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| 6. |
- Nylander, O, et al.
(författare)
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Exposure of the duodenum to high concentrations of hydrochloric acid. Effects on mucosal permeability, alkaline secretion, and blood flow.
- 1994
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Ingår i: Scandinavian Journal of Gastroenterology. - 0036-5521 .- 1502-7708. ; 29:5, s. 437-44
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Tidskriftsartikel (refereegranskat)abstract
- Proximal duodenum was perfused with HCl for 5 min and the effects on blood-to-lumen clearance of 51Cr-EDTA (ED-Cl), morphology, luminal alkalinization, and blood flow determined in anesthetized rats. The rate of alkalinization was determined by back titration and blood flow assessed by laser Doppler flowmetry or by ultrasonic transit time flowmetry. Perfusion of duodenum with 30, 50 or 100 mM HCl for 5 min increased ED-Cl in a concentration-dependent manner and induced a small increase in alkalinization but had no effect on blood flow. At 55 min after cessation of perfusion with 100 mM HCl ED-Cl was 2.2-fold higher than control whereas the ED-Cl values in animals perfused with 30 or 50 mM HCl were not different from pre-acid control values. 100 mM HCl also induced an increase in 14C-mannitol and 14C-polyethylene glycol 4000 clearance, suggesting that HCl does indeed increase mucosal permeability. The 100 mM HCl-induced rise in mucosal permeability most probably reflects disturbance of mucosal integrity because three of five animals exhibited villous tip damage. The increases in ED-Cl in response to 100 mM HCl were the same in control rats as in rats with the renal pedicles ligated, indicating that the acid susceptibility is not affected by acute functional nephrectomy.
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| 7. |
- Nylander, O, et al.
(författare)
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Vasoactive intestinal polypeptide reduces hydrochloric acid-induced duodenal mucosal permeability.
- 1993
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 264:2 Pt 1, s. G272-9
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Tidskriftsartikel (refereegranskat)abstract
- The duodenum in anesthetized rats was perfused with HCl, and mucosal integrity was assessed by measuring the clearance of 51Cr-labeled EDTA from blood to lumen and/or by morphological examination (lesion score). Duodenal blood flow was determined by laser Doppler flowmetry and luminal alkalinization as well as H+ disappearance by backtitration. Intravenous infusion of vasoactive intestinal polypeptide (VIP; 13.5 micrograms.kg-1.h-1) increased luminal alkalinization threefold and decreased clearance of 51Cr-EDTA by 50%. VIP also decreased arterial blood pressure and induced a small and irregular decrease in duodenal blood flow. Perfusion with 10 mM HCl increased clearance of 51Cr-EDTA 2.1-fold, but the lesion score was not different from that in saline-perfused animals. Perfusion with 20 mM HCl increased clearance of 51Cr-EDTA four-fold and induced a greater lesion score than did 10 mM. Perfusion with either 10 or 20 mM HCl did not affect the duodenal blood flow. VIP reduced the rise in clearance of 51Cr-EDTA in response to 10 mM but not that to 20 mM HCl. Intravenous injection of prazosin (50 micrograms/kg) decreased luminal alkalinization, clearance of 51Cr-EDTA, blood pressure, and duodenal blood flow. In prazosin-pretreated rats, perfusion with 10 mM HCl increased clearance of 51Cr-EDTA 2.6-fold, and the lesion score was greater in this group than in animals infused with VIP. A positive linear correlation was obtained between HCO3- secretion and the mean rate of H+ disappearance.(ABSTRACT TRUNCATED AT 250 WORDS)
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