ISSN:1018-1172    

DOI:10.1159/000158923

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The role of the sympathetic nervous system in the regulation of large coronary artery tone has been well defined. Studies of adrenergic regulation of coronary-resistance vessels have largely been limited to indirect inferences based on flow measurement obtained in vivo. The purpose of the present study was to determine the effects of norepinephrine (NE) on the coronary microcirculation using direct in vitro approaches. Porcine coronary microvessels (80-200 µm in diameter) were pressurized in isolated organ chambers. Diameters were measured using a Halpern microvessel imaging apparatus. After preconstriction with leukotriene D4, NE caused complete relaxation. Relaxations to NE were inhibited by propranolol. Relaxations to NE were also inhibited by LY83583 (which depletes cGMP) and hemoglobin (which binds endothelium-derived relaxing factor, EDRF). NE caused minimal or no constriction in both preconstricted and nonpreconstricted microvessels even in the presence of hemoglobin and propranolol. In conclusion, NE predominantly dilates porcine coronary microvessels, both by β-adrenoceptor activation and by stimulating release of EDRF. There is minimal α-adrenoceptor-mediated constriction of coronary microvesse

ISSN:1018-1172    

DOI:10.1159/000158924

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

We have examined the disposition of catecholamines in cardiac tissue, mesenteric arteries and ganglia from normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHR-SP). The norepinephrine (NE) contents of mesenteric arteries from all three strains of rats adhered to a pattern which was characterized by the largest concentrations of the catecholamine in arteries from SHR and SHR-SP rats, and the smallest values present in mesenteric arteries from WKY rats. This pattern of NE disposition was not present in either ganglia or cardiac tissue from the three strains of rats. The results highlight two features of the hypernoradrenergic hypothesis in the SHR. Firstly, the enhanced NE contents observed in the blood vessels of the two hypertensive strains are not consistently increased in sympathetic cell bodies or cardiac tissue. Secondly, the significantly enhanced concentrations of NE in the vasculature parallel the elevated direct arterial blood pressure in the two strains of hypertensive rat when compared with the normotensive strain.

ISSN:1018-1172    

DOI:10.1159/000158925

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Rabbit fast hindlimb muscle (tibialis anterior, extensor digitorum longus and peroneal muscles) were stimulated for 14 days, 8 h/day using implanted electrodes, with two different frequencies of stimulation (continuous at 10 Hz or 3 bursts/min at 40 Hz) giving the same total number of stimuli. Both patterns of stimulation resulted in a different pattern of flow and perfusion pressure, with lowered perfusion pressure during contractions in muscles stimulated at 10 Hz and intermittent increase during the peak of tetanic contractions in muscle stimulated at 40 Hz. The arteries supplying the stimulated muscle (anterior tibial artery) were then tested for reactivity to noradrenaline in vitro. Maximal tension developed by control arteries (supplying the contralateral nonstimulated muscles) was 18 ± 1.4 g/mg dry weight in response to 10-5M noradrenaline. Arteries supplying muscle stimulated at 10 Hz showed a significant increase of the maximal response (22 ± 1.5 g/mg) with the same dose. Arteries supplying muscles that had been stimulated at 40 Hz showed decreased response with maximal tension 9.1 ± 1.2 g/mg. Noradrenaline uptake and clearance showed similar values in control vessels and those stimulated at either frequency. Thus, long-term stimulation of skeletal muscles can modify the reactivity of supplying arteries; the response varied with the pattern of contractions and may be explained by a different pattern of flow chang

ISSN:1018-1172    

DOI:10.1159/000158926

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

In endothelium-containing rings of rat aorta which had been precontracted with phenylephrine, addition of acetylcholine (ACh) (0.010-10 µM)resulted in concentration-dependent, graded relaxation through the release of endothelium-derived relaxing factor (EDRF). Hemoglobin (3 and 10 µM) and methylene blue (10 µM)both produced marked inhibition of this EDRF-mediated relaxation. In the perfused mesenteric arterial vasculature of the rat, ACh-induced vasodilation was also inhibited by hemoglobin and by methylene blue, although to a lesser extent than was ACh-induced relaxation of aortic rings by these two agents. These findings indicate that EDRF mediates in large part ACh-induced relaxation of resistance vessels in the mesenteric vascular bed as well as large arteries. The nitrovasodilator glyceryl trinitrate (GTN) caused endothelium-independent relaxation of aortic rings as well as vasodilation of mesenteric arterial vasculature. GTN-induced relaxation of aortic rings was antagonized by hemoglobin as well as methylene blue, but to a lesser extent than was ACh-induced relaxation. However, hemoglobin did not inhibit and methylene blue actually potentiated GTN-induced vasodilation in the perfused mesenteric vasculature. Possible explanations of these paradoxical results are discuss

ISSN:1018-1172    

DOI:10.1159/000158927

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

This paper describes the myoendothelial relations in ramus interventricularis anterior and its branches in the dog and rabbit. Endothelial cells (ECs) are separated from smooth muscle cells (SMs) by fenestrated internal elastic lamina (IEL). The number of fenestrations increases towards the periphery; the first- and second-order branches have only patches of elastin in some places. ECs and SMs emit protrusions of various shapes into the fenestrae. The distance between EC and SM protrusions varies. Close appositions were also found. The diffusion of autacoids, or transmitters, as well as the electrical and biochemical mechanism of transmission seem to be involved in the transfer of information from ECs to SMs and vice versa. Biomechanical transfer (for example shear stress), via EC-SM junctions is also considered.

ISSN:1018-1172    

DOI:10.1159/000158928

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The effects of chlorethylclonidine, WB 4101 and nifedipine on norepinephrine-induced contractions of rat, guinea-pig, rabbit and dog aortae were investigated in order to characterize the α1-adrenoceptor subtype(s) present in the aortae of these different species. The putative α1A-adrenoceptor antagonist, WB 4101, was significantly more potent in the rat aorta compared to the rabbit, guinea-pig and dog aortae which were not significantly different from each other. The calcium channel antagonist, nifedipine (1 µM), had little or no effect on norepinephrine-induced contractions in aortic segments from the rabbit, guinea pig and dog; whereas in the rat aorta, nifedipine significantly inhibited the response to norepinephrine. Based on the studies with WB 4101 and nifedipine, α1-adrenoceptors in rat aorta would be tentatively classified as α1A-adrenoceptors, whereas those in the guinea-pig, rabbit and dog aortae would be of the α1B-adrenoceptor subtype. The putative irreversible α1B-adrenoceptor antagonist, chlorethylclonidine, inhibited the response to norepinephrine in aortae from all species, but to dramatically different degrees. The response to norepinephrine was inhibited by 500-fold and 450-fold by chlorethylclonidine in the rat and dog aortae, respectively, whereas in the guinea-pig and rabbit aortae, the potency of norepinephrine was reduced by only 3- and 20-fold, respectively. Thus, based on studies with chlorethylclonidine, α1-adreno-ceptors in the rat and dog aortae would be classified as α1B-adrenoceptors (i.e., chlorethyl-clonidine-sensitive), whereas α1A-adrenoceptors (chlorethylclonidine-insensitive) would predominate in the guinea-pig aorta, and possibly both α1A- and α1B-adrenoceptors would coexist in the rabbit aorta. It is apparent that the subclassification of α1-adrenoceptors based on chlorethylclonidine does not agree with the subclassification based on WB 4101 and nifedipine in these tissues. Specifically, studies with WB 4101 and nifedipine indicate that the rat aorta contains primarily α1A-adrenoceptors, whereas the high sensitivity to chlorethylclonidine in the rat aorta would indicate the existence of α1B-adrenoceptors. Similar discrepancies exist in the aortae from the other species. The results indicate clearly that significant heterogeneity exists in α1-adrenoceptors in mammalian aortae. Furthermore, our findings suggest that chlorethylclonidine and WB 4101 are not sufficiently reliable tools to use in subclassifying α1-adrenoceptors in vascular smooth muscle, and the results obtained in the present study do not allow α1-adrenoceptors in mammalian aortae to be subclassified reliably as either α1A-or α1B<

ISSN:1018-1172    

DOI:10.1159/000158929

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

We have used nuclear fluorescent dyes to develop a technique for the study of vascular structure and function. Nuclear stained blood vessels, viewed with the appropriate filter sets, can be studied in great detail. Only the nuclei of the cells which form the walls are visible and so their positions relative to one another as well as their viability can be quickly assessed. The dyes are not toxic, therefore when the vessel contracts or relaxes, the changes in position of the nuclei can be monitored. In this paper we describe two original applications of fluorescent nuclear dyes in vascular research.

ISSN:1018-1172    

DOI:10.1159/000158930

出版商:S. Karger AG    

年代:1992

数据来源: Karger