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- Bentzer, Peter, et al.
(författare)
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Supersensitivity in rat micro-arteries after short-term denervation
- 1997
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Ingår i: Acta Physiologica Scandinavica. - 0001-6772. ; 161:2, s. 125-133
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Tidskriftsartikel (refereegranskat)abstract
- Contractile responses to phenylephrine and high-K+ were investigated in vitro in microvascular preparations from the rat medial plantar artery, a branch from the saphenous artery, obtained after short-term denervation in vivo. Two groups of animals were studied: (1) animals undergoing surgical resection of the saphenous nerve, and (2) animals undergoing surgical resection of both the sciatic and saphenous nerves. The animals were operated on one side only. Microvascular preparations (diameter about 325 microns) were obtained 10 days after surgery. Vessels from the non-operated side served as controls. Immunocytochemistry showed a decreased number of both neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) immunoreactive nerve fibres in vessels after resection of the saphenous nerve only. Resection of both the saphenous and the sciatic nerve caused a complete loss of immunoreactive nerve fibres. Mechanical measurements were performed using a wire myograph. In vessels subjected to resection of the saphenous nerve the sensitivity to phenylephrine was similar to controls. Vessels denervated by resection of both the saphenous and sciatic nerves showed significant increases in phenylephrine and potassium sensitivity. When depolarized in high-K+ solution the denervated vessels showed an increased sensitivity to extracellular Ca2+. The results show that complete short-term denervation of the rat medial plantar artery in vivo causes a pronounced supersensitivity in the vascular smooth muscle. The supersensitivity appears not to be restricted to the sympathetic alpha-receptors but also associated with changes in the cellular excitation-contraction coupling. Such altered reactivity of the vascular smooth muscle may contribute to vascular disturbances observed in vivo after nerve damage or surgical denervation.
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- Högberg, Peter, et al.
(författare)
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Nitrogen isotope fractionation during nitrogen uptake by ectomycorrhizal and non-mycorrhizal Pinus sylvestris
- 1999
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 142:3, s. 569-576
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Tidskriftsartikel (refereegranskat)abstract
- An experiment was performed to find out whether ectomycorrhizal (ECM) fungi alter the nitrogen (N) isotope composition, δ15N, of N during the transport of N from the soil through the fungus into the plant. Non- mycorrhizal seedlings of Pinus sylvestris were compared with seedlings inoculated with either of three ECM fungi, Paxillus involutus, Suillus bovinus and S. variegatus. Plants were raised in sand in pots supplied with a nutrient solution with N given as either NH4+ or NO3−. Fractionation against 15N was observed with both N sources; it decreased with increasing plant N uptake, and was larger when NH4+ was the source. At high ratios of Nuptake/Nsupplied there was no (NO3−), or little (NH4+), fractionation. There seemed to be no difference in fractionation between ECM and non-mycorrhizal plants, but fungal rhizomorphs were sometimes enriched in 15N (up to 5‰ at most) relative to plant material; they were also enriched relative to the N source. However, this enrichment of the fungal material was calculated to cause only a marginal decrease (−0.1‰ in P. involutus) in δ15N of the N passing from the substrate through the fungus to the host, which is explained by the small size of the fungal N pool relative to the total N of the plant, i.e. the high efficiency of transfer. We conclude that the relatively high 15N abundance observed in ECM fungal species should be a function of fungal physiology in the ECM symbiosis, rather than a reflection of the isotopic signature of the N source(s) used. This experiment also shows that the δ15N of plant N is a good approximation of δ15N of the available N source(s), provided that N is limiting growth.
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- Synnerstad, I, et al.
(författare)
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Gastric mucosal smooth muscles may explain oscillations in glandular pressure : role of vasoactive intestinal peptide.
- 1998
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Ingår i: Gastroenterology. - 0016-5085 .- 1528-0012. ; 114:2, s. 284-94
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND & AIMS: Oscillating (3-7 cycles/min) high pressures in gastric glands during acid secretion suggest the existence of rhythmically contracting mucosal muscles. The aim of this study was to study vasoactive intestinal peptide (VIP), an inhibitory neurotransmitter in the gastrointestinal tract, in relation to mucosal muscles, glandular pressure, and blood flow.METHODS: Rat, dog, and human mucosae were examined immunocytochemically for smooth muscle actin and VIP. Glandular pressure was measured using microelectrodes, red blood cell velocity (V[RBC]) was measured using a cross-correlation technique, and blood flow was measured using laser Doppler flowmetry in exposed gastric mucosa of thiobutabarbital sodium-anesthetized rats.RESULTS: Actin immunostaining showed muscle strands arising from muscularis mucosae, extending toward the gastric pits. VIP-immunoreactive nerve fibers were found in close relation to these muscles. VIP, administered intra-arterially close to the stomach (2 microg/kg bolus, followed by 10 microg x kg[-1] x h[-1]), significantly decreased glandular pressure from 18.2 +/- 1.6 to 8.9 +/- 1.6 mm Hg and almost eliminated the pressure oscillations. VIP infusion also abolished the oscillations in V(RBC) and significantly increased blood flow by approximately 35%.CONCLUSIONS: Contracting mucosal muscles may be responsible for oscillations in glandular pressure and possibly also in V(RBC). VIP probably relaxes these muscles.
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