摘要:

Physiological and morphometric studies were conducted on the microvascular endothelium of four individual cerebral structures having different neural activities – the inferior colliculus, sensorimotor cortex (both gray matter regions), genu of the corpus callosum (white matter), and the subfornical organ (a circumventricular organ) of rats. The physiological data, obtained by quantitative autoradiography, produced new findings: (1) the rate of blood-to-tissue flux across capillary endothelial cells of a neutral amino acid, 14C-alpha-aminoisobutyric acid, was 100–400 × more rapid in the subfornical organ than in gray and white matter regions, and (2) the transit time of labeled albumin in the subfornical organ microcirculation was 7–12 × longer than in the blood-brain barrier regions. These quantitative studies suggest that circulating messengers, such as hormones, would have more prolonged receptor contact with capillary endothelial cells and greater rates of transendothelial passage in the subfornical organ than in gray or white matter. Capillary densities, volume fractions, and surface areas were similar for the inferior colliculus (which has the highest rates of tissue glucose metabolism and blood flow among blood-brain barrier regions) and the subfornical organ, but were significantly smaller for sensorimotor cortex and corpus callosum (about 35 and 70% lower, respectively). Electron microscopic morphometry of capillary endothelial cells in the inferior colliculus and corpus callosum indicated the ultrastructural basis of blood-brain barrier mechanisms in these regions – intercellular junctions that appeared tight, few cytoplasmic vesicular profiles, and no fenestrations. Analysis of endothelial cells in the subfornical organ demonstrated 7 × more vesicular profiles and 4 fenestrations per cross section of capillary. These findings represent structural evidence for high rates of solute flux across the capillary endothelium of circumventricu

ISSN:1018-1172    

DOI:10.1159/000158652

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Direct blood pressure measurements were made on male rabbits from 3 to 55 months old to determine if blood pressure increases with age in this animal model as it does in humans. To assess the effects of age on vascular reactivity, strips of small ear artery and skeletal muscle artery were taken from these animals and tested with norepinephrine, potassium, histamine, and isoproterenol in vitro. Heart rate did not differ between age groups, but blood pressure was significantly higher in older age groups compared to 3-month-old rabbits. Vessels from older animals were thicker and less sensitive to norepinephrine. Responses to potassium, histamine, and isoproterenol were not different between age groups. The results suggest that male rabbits offer a good model of age-related increases in blood pressure, and that changes in vascular adrenergic rectivity may occur with age in male rabbits.

ISSN:1018-1172    

DOI:10.1159/000158654

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

We have examined the influence of endothelial cell removal upon the O-methylation of the isomers of isoproterenol in the isolated rabbit aorta. Endothelial cells were removed by mechanically abrading isolated segments of rabbit aorta. The latter procedure resulted in the abolition of acetylcholine-mediated relaxation of tissues, a process dependent upon the presence of endothelial cells. In addition, histological staining and electron-microscopic analysis indicated the presence of endothelial cells in tissues not subjected to mechanical abrasion and the absence of endothelial cells in tissues subjected to abrasion. Moreover, ultrastructural analysis revealed that the influence of abrasion was limited to the luminal side of the internal elastic lamina. The removal of endothelial cells from the isolated rabbit aorta was associated with a decrease (approximately 30%) in the O-methylation of the isomers of isoproterenol. Inhibition of the extraneuronal uptake process with deoxycorticosterone (DOCA) produced a predicted decrease in the O-methylation of isoproterenol in tissues with the endothelium intact. In the absence of endothelial cells, the inhibition of the O-methylation of isoproterenol mediated by DOCA persisted. The results suggest that the O-methylation of catecholamines can occur in both medial and endothelial structures in this blood vessel and support the results of immunohistochemical studies that suggested a presence of catechol-O-methyltransferase in vascular endothelial structures. In addition, the findings exclude a possibility that the extraneuronal uptake process for catecholamines resides exclusively in endothelial structures. The functional consequences of vascular endothelial cell O-methylation are discussed.

ISSN:1018-1172    

DOI:10.1159/000158655

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

In the present study, we utilized 2 perfused mesenteric vascular bed preparations in an examination of the responses of mesenteric vessels from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. One preparation involved perfusion of the mesenteric vascular bed dissected free from the intestine. The second preparation was essentially similar, with the exception that the intestine and the small arterioles feeding the jejunum were intact. The results suggested that the small vessels offer a significant contribution to the mechanical resistance to perfusion in the mesenteric vasculature and are important in the neurogenic responses of this preparation. In contrast, the arterioles in the arcade supplying the jejunum play only a minor role in the responses of the mesenteric vascular bed to intraluminally injected vasoactive substances. It was found that mesenteric preparations from SHR rats responded more forcefully to intraluminally administered norepinephrine and potassium, regardless of whether the intestine was absent or present. Similarly, the responses of mesenteric preparations to electrical nerve stimulation were greater in preparations from SHR rats, particularly when the intestine was present. It is concluded that the perfused mesenteric vasculature from SHR rats is more responsive to vasoactive substances and nerve stimulation and that this feature is not exclusively dependent upon a contribution to contraction by the arterioles supplying the jejunum.

ISSN:1018-1172    

DOI:10.1159/000158656

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Potassium transport has frequently been assessed by measurement of 86Rb. However, recent reports indicated that the K ion channels are selective to K over Rb. Therefore, the purpose of this study was to evaluate whether the basal and stimulated fluxes of Rb and K were equivalent in rat aorta in the absence of endothelium. The ouabain-sensitive (active) uptake of 86Rb and 42K was similar. However, the basal 86Rb efflux was only 80% of the 42K efflux. Norepinephrine and KCl depolarization stimulated 86Rb and 42K effluxes via a calcium-dependent process. The stimulated 86Rb efflux ranged from 56 to 74% of the 42K efflux. Diltiazem reduced the KCl-stimulated 86Rb and 42K effluxes. The 86Rb efflux was 82% of the 42K efflux in the presence of KCl plus diltiazem, similar to that under basal conditions. Substitution of Rb for K in the incubation solution was associated with a marked increase in spontaneous contractile activity. There was no change in the norepinephrine concentration required for a 50% stimulation of contraction or 86Rb efflux from Rb-loaded tissues. We conclude from these studies that the basal and calcium-activated potassium channels are selective for K over Rb and therefore 86Rb fluxes quantitatively underestimate that of 42K. However, 86Rb is an appropriate substitute for the measurement of active K transport.

ISSN:1018-1172    

DOI:10.1159/000158657

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158658

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158659

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:1018-1172    

DOI:10.1159/000158651

出版商:S. Karger AG    

年代:1986

数据来源: Karger