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Biomedical subjects

M W Messing

Publications and source records attributed to M W Messing.

6 recordsLinked to original sources
PubMed1992

Preferential small arteriolar vasodilatation by the potassium channel opener, BRL 38227, in conscious spontaneously hypertensive rats.

The microvascular effects of the potassium channel opener, BRL 38227 (the active enantiomer of cromakalim), were investigated in conscious spontaneously hypertensive rats (SHR) provided with a chronic dorsal microcirculatory chamber. BRL 38227 decreased blood pressure and increased heart rate in a dose-dependent manner. It dilated arterioles of different sizes, with the most pronounced effect on the smallest precapillary arterioles. Venule diameters were not significantly affected by BRL 38227. The data show a preferential sensitivity of small precapillary arterioles for potassium channel opening.

Animals↗
PubMed1992

The microcirculation and hypertension.

AIM: To review published evidence on the effects of arteriolar changes in primary and secondary hypertension. BACKGROUND: Pressure profile analyses have shown that the microcirculation is a major site of vascular resistance. With the recent refinement of intravital microscopy techniques detailed information has become available on mechanisms of the microvascular resistance increase in hypertension. Three mechanisms play an important role: (1) a decrease in arteriolar diameter; (2) arteriolar vessel wall hypertrophy; and (3) small arteriolar and capillary rarefaction. METHOD: The evidence was synthesized into a hypothesis on the role of the microcirculation in primary forms of hypertension. HYPOTHESIS: The hypothesis formulated contains two important elements in that (1) diminished outgrowth of the microvascular bed in different tissues is seen as an important early pathogenic mechanism; and (2) the decreases in arteriolar diameter and vessel wall hypertrophy are seen as adaptive mechanisms that maintain a constant wall stress. The three factors together maintain the increase in vascular resistance that is common to all established forms of primary hypertension.

Animals↗
PubMed1990

Hypertension, the microcirculation and serotonin.

Essential hypertension in humans and most experimental animal models of hypertension is hemodynamically characterized by an increased vascular resistance. The site of resistance increase has been localized by recent intravital microscopic studies in most vascular beds primarily in the microcirculation, i.e. in arterioles smaller than 150 microns. Three mechanisms are held responsible for the resistance increase: (1) a rarefaction of the smallest arterioles and capillaries, (2) an increased wall to lumen ratio and (3) a decreased internal diameter. The latter two effects have been localized primarily in the larger arterioles and arteries. The contribution of each of the three factors to the rise in total peripheral resistance depends on the vascular bed, the model of hypertension and its stage of development. Serotonin is one of the endogenous mediators of vascular tone. Its effects have thus far been mostly studied in relation to alterations of internal vascular diameter. Larger arterioles and arteries constrict, but resistance-sized smaller arterioles dilate in response to the exogenous application of serotonin.

Aging↗
PubMed1987

Effects of cadmium and zinc on steroid metabolism and steroid level in the sea star Asterias rubens L.

Steroid metabolism was studied in gonads and pyloric caeca of male and female sea stars which had been exposed to cadmium or zinc for 3 weeks. Steroid metabolism had increased in animals exposed to heavy metals. Significant increase of the enzyme activity was observed for 17 alpha-hydroxylase in the pyloric caeca of female animals exposed to zinc (pregnenolone----17 alpha-hydroxypregnenolone) or cadmium (progesterone----17 alpha-hydroxyprogesterone), for 17 beta-hydroxysteroiddehydrogenase in the gonads of female animals (dehydroepiandrosterone----androstenediol) and in pyloric caeca of male animals (androstenedione----testosterone) after exposure to cadmium, and for 5 alpha-reductase (progesterone----5 alpha-pregnane-3,20-dione) in ovaries of cadmium exposed sea star. There is some evidence that pregnenolone metabolism in male and female animals is affected by zinc in a different way. The effect of cadmium on the esterification of androstenedione differed highly significantly among male and female animals. It was concluded that the main way of entrance of cadmium into sea stars is via the surrounding medium and not via the food consumed. Testosterone and progesterone levels in, respectively, gonads of female and pyloric caeca of male sea stars which had been exposed to cadmium were significantly higher than the corresponding values in control animals. The effect of zinc exposure on testosterone level in pyloric caeca is significantly different for both sexes. Cadmium interacts directly with the esterification of testosterone, strongly stimulating this process. Cadmium stimulates the production of testosterone by action at the level of the biosynthesis of 17 beta-hydroxysteroiddehydrogenase.

17-Hydroxysteroid Dehydrogenases↗
PubMedDate not supplied

Alpha-adrenergic reactivity of the microcirculation in conscious spontaneously hypertensive rats.

The goal of this study was to determine the functional distribution of alpha 1- and alpha 2-adrenoceptors in the striated muscle microcirculation. Experiments were performed in intact conscious spontaneously hypertensive rats (SHR) that were provided with a dorsal microcirculatory chamber to allow microvascular diameter measurements. Administration of selective alpha 1- and alpha 2-agonists, phenylephrine and azepexole, respectively, induced different patterns of microvascular constriction. alpha 1-Adrenoceptor stimulation showed a preferential constriction of large arteries and venules. The entire arteriolar microvasculature was sensitive to alpha 2-adrenoceptor stimulation, whereas the venular vessels did not respond to azepexole. The selective alpha 1- and alpha 2-antagonists prazosin and yohimbine showed patterns of vasodilator activity comparable to those of the corresponding agonists. The specificity of the drug-induced effects was verified by comparing their effects with those of graded hemorrhage, a non-pharmacological method for blood pressure lowering. In the range of blood pressure decreases comparable to that obtained by alpha-adrenoceptor antagonists, graded hemorrhage did not influence microvascular diameters. These results show a differential functional distribution of alpha 1- and alpha 2-adrenoceptors along the microvascular tree in striated muscle of conscious SHR.

Adrenergic alpha-Agonists↗