Browsing by Author "Briones, R"
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- ItemA2B adenosine receptor mediates human chorionic vasoconstriction and signals through arachidonic acid cascade(2005) Donoso, MV; López, RL; Miranda, R; Briones, R; Huidobro-Toro, JPBecause adenosine is a vascular tone modulator, we examined the effect of adenosine and congeners in the vascular reactivity of isolated human placental vessels and in perfused cotyledons. We characterized its vasomotor action and tentatively identified the receptor subtypes and their intracellular signaling mechanisms. We recorded isometric tension from the circular layer of chorionic vessel rings maintained under 1.5 g of basal tension or precontracted with KCl. The relative order of potency of adenosine and structural analogs is consistent with the expression of A2B receptors, 5'-(N-ethylcarboxamido) adenosine (NECA) being the most potent. The maximal contraction ranged from 45% to 60% of the KCl standard response, except for an A(2A) receptor agonist that did not exceed 15%. Consistently, NECA was 100-fold more potent than adenosine to raise the perfusion pressure of ex vivo perfused cotyledons. In contrast, a selective A(3) receptor agonist relaxed precontracted rings of chorionic vessels. Whereas a selective A3 receptor antagonist was ineffective to antagonize adenosine-induced contraction, A(2) or A(1) receptor antagonists reduced adenosine-induced vasoconstriction concentration-dependently. Denudation of the endothelial layer reduced adenosine- and NECA-induced contractions by 50-70%. Furthermore, indomethacin reduced adenosine- or NECA-induced contractions concentration-dependently in intact and endothelium-denuded rings. A thromboxane receptor antagonist blocked adenosine- and NECA-induced contractions in intact and endothelium-denuded rings, suggesting the involvement of an arachidonic acid metabolite as the mediator of the vasoconstriction. We propose that adenosine A(2B) receptors mediate the adenosine- induced contraction vasomotor effect in human chorionic vessels and that this involves synthesis of a thromboxane receptor activator or a related prostanoid.
- ItemIndustrial uses and sustainable supply of Quillaja saponaria (Rosaceae) saponins(1999) San Martín, R; Briones, RThe bark of the tree Quillaja saponaria, indigenous to Chile, is one of the major sources of industrially used triterpenoid saponins. For decades quillaja extracts have been used as foaming agents in beverages, emulsifiers in foods, wetting agent in photography, etc. Overexploitation of the bar-h: has caused important ecological damage and a shortage of this resource. However; this can still be remedied by using whole quillaja wood (and not just the bark), for the production of saponins. This uaw material can be obtained in Inr-ge quantities from pruning operations. reducing the need to felt trees. This review covers ecological aspects of quillaja exploitation, as well as a discussion of its novel industrial applications.
- ItemP2Y1 and P2Y2 receptors are coupled to the NO/cGMP pathway to vasodilate the rat arterial mesenteric bed(2002) Buvinic, S; Briones, R; Huidobro-Toro, JP1 To assess the role of nucleotide receptors in endothelial-smooth muscle signalling, changes in perfusion pressure of the rat arterial mesenteric bed, the luminal output of nitric oxide (NO) and guanosine 3',5' cyclic monophosphate (cGMP) accumulation were measured after the perfusion of nucleotides.
- ItemPharmacological identification of P2X1, P2X4 and P2X7 nucleotide receptors in the smooth muscles of human umbilical cord and chorionic blood vessels(2003) Valdecantos, P; Briones, R; Moya, P; Germain, A; Huidobro-Toro, JPTo ascertain the role of extracellular adenosine 5'-triphosphate (ATP) receptors in human placenta circulation, we identified and pharmacologically characterized the P2X receptor population in its superficial vessels. Total RNA was extracted from segments of chorionic and umbilical arteries and veins of terminal placentae delivered by vaginal or Caesarian births. Polymerase chain reaction (PCR), followed by sequencing of the products, identified the presence of P2X 1, 4, 5, 6, and 7 mRNAs in smooth muscle from chorionic and umbilical arteries and veins. Umbilical vessels proximal to the fetus expressed the same population of P2X subtypes, except for the P2X(5), but additionally expressed the P2X(2). Rings of chorionic vessels contracted upon addition of nucleotides and analogs with the following relative rank order of potencies in arteries and veins: alpha,beta-methyleneATP>beta,gamma-methyleneATP>PNP>ATP=diBzATP>2-MeSATP>ADP>AMP; in umbilical vessels alpha,beta-methyleneATP was at least 100-fold more potent than ATP. Nucleotide potency was less than that of PGF(2alpha) or endothelin-2, but had the same magnitude as serotonin. ATP-desensitized receptors evidenced cross desensitization to alpha,beta-methyleneATP, 2-MeSATP and diBzATP, effect not observed when desensitization was elicited by alpha,beta-methyleneATP, confirming the presence of various P2X receptor subtypes in the smooth muscles of these vessels. The vasocontractile efficacy of alpha,beta-methyleneATP was unaltered by endothelium removal, while that of ATP was significantly attenuated and those elicited by 2-MeSATP were blunted, indicating the presence of additional endothelial nucleotide receptors. These results suggest that P2X receptors participate in the humoral regulation of placental blood flow. (C) 2002 Elsevier Science Ltd. All rights reserved.
- ItemQuality control of commercial quillaja (Quillaja saponaria Molina) extracts by reverse phase HPLC(2000) San Martín, R; Briones, RSaponin-rich extracts of the Chilean indigenous tree Quillaja saponaria Molina are widely used as natural foaming agents in foods and beverages, food emulsifiers, photographic emulsions, vaccine adjuvants, etc. However, with the exception of the vaccine industry, saponin concentration is not adequately quantified. Normally, the quality and price of the extracts are determined using simple foam tests. This may not be adequate, since similar foam levels can be obtained by blending quillaja extracts with other low-cost saponin sources (eg Yucca shidigera extracts). Also, many products are diluted with high amounts of carriers, reducing significantly their saponin concentration. To overcome these problems and standardise the qualify of commercial extracts, the use of reverse phase HPLC techniques is explored. It is shown that RP-HPLC yields consistent and repetitive results and can be easily implemented to control the quality of quillaja extracts. Commercial non-refined extracts contain 190-200 g saponins kg(-1) solids, while semi-refined extracts contain 750-800 g saponins kg(-1) solids. Also, extracts derived from quillaja bark (traditional raw material) and whole quillaja wood (novel ecological production method) have similar saponin composition and concentration. (C) 2000 Society of Chemical Industry.
- ItemSimultaneous production of ethanol and kraft pulp from pine (Pinus radiata) using steam explosion(ELSEVIER SCI LTD, 1995) Martin, RS; Perez, C; Briones, RRadiata pine chips (Pinus radiata) were pretreated by steam explosion, for the simultaneous production of ethanol and pulp. Ethanol was produced fr om the depolymerized hemicellulose fraction recovered after the explosion, while kraft pulp was produced from the steam-exploded chips. The conditions that best balanced sugar recovery and fibre quality were the use of steam alone, at 220 degrees C and short reaction times (e.g. <2 min). After treatment with acid, to depolymerize short-chain oligosaccharides, the hemicellulose hydrolyzate was fermentable to ethanol by yeasts with sugar consumption above 80%. The use of steam explosion reduced the consumption of pulping chemicals. However fibre damage, although minimized significantly at lower reaction times, yielded pulps with lower physical properties than those obtained in conventional kraft pulping.