Ulcer healing and mechanism(s) of action involved in the gastroprotective activity of fractions obtained from Syngonanthus arthrotrichus and Syngonanthus bisulcatus

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

The mechanism of 234U 238U activity ratio enhancement in karstic limestone groundwater

Experimental etch/leach of Carboniferous Limestone gravels on a laboratory time-scale has demonstrated that 234U 238U activity ratios (AR's) greater than the radiochemical equilibrium value may be generated on short time-scales. The molar U/Ca and Mg/Ca ratios show that both U and Mg are leached preferentially relative to Ca whereas the molar U/Mg ratio is only slightly greater than that of the rock matrix. The generation of enhanced AR's is attributed to a two-stage process in which the limestone surface is dissolved by zero-order etch and silicate minerals so released are subjected to first-order chemical leach of U and Mg. The implications of these results for the production of enhanced AR's in Carboniferous Limestone groundwater are discussed. It is suggested that chemical leaching or exchange of U between groundwater and its particulate load or at the aquifer fluid-solid interface is an important mechanism controlling AR changes as groundwater migrates beyond a redox boundary. AR's for dissolved U in groundwater are more probably related to chemical equilibria than to groundwater age. © 1993.

Medium effects in the pion-pole mechanism [gamma gamma ->pi(0)->nu(R)(nu)over-bar(L)(nu(L)(nu)over-bar(R))] of neutron star cooling

Nuclear medium effects in the neutrino cooling of neutron stars through the reaction channel γγ→π0 →ν Rν̄L(νLν̄R) are incorporated. Throughout the paper we discuss different possibilities of right-handed neutrinos, massive left-handed neutrinos, and standard massless left-handed neutrinos (reaction is then allowed only with medium modified vertices). It is demonstrated that multiparticle effects suppress the rate of this reaction channel in the dense hadron matter by 6-7 orders of magnitude that does not allow to decrease existing experimental upper limit on the corresponding π0νν̄ coupling. Other possibilities of the manifestation of the given reaction channel in different physical situations, e.g., in the quark color superconducting cores of the most massive neutron stars, are also discussed. We demonstrate that in the color-flavor-locked superconducting phase for temperatures T≲ 0.1-10 MeV (depending on the effective pion mass and the decay width) the process is feasibly the most efficient neutrino cooling process, although the absolute value of the reaction rate is rather small.

Coupling between respiratory and sympathetic activities as a novel mechanism underpinning neurogenic hypertension

Enhanced sympathetic outflow to the heart and resistance vessels greatly contributes to the onset and maintenance of neurogenic hypertension. There is a consensus that the development of hypertension (clinical and experimental) is associated with an impairment of sympathetic reflex control by arterial baroreceptors. More recently, chronic peripheral chemoreflex activation, as observed in obstructive sleep apnea, has been proposed as another important risk factor for hypertension. In this review, we present and discuss recent experimental evidence showing that changes in the respiratory pattern, elicited by chronic intermittent hypoxia, play a key role in increasing sympathetic activity and arterial pressure in rats. This concept parallels results observed in other models of neurogenic hypertension, such as spontaneously hypertensive rats and rats with angiotensin II–salt-induced hypertension, pointing out alterations in the central coupling of respiratory and sympathetic activities as a novel mechanism underlying the development of neurogenic hypertension.