Die agonistunabhängige Rolle des Angiotensin II-Rezeptors AT1A in der arteriellen Vasoregulation

In mammalians, myogenic vasoconstriction is a key factor for keeping up hydrostatic capillary pressure to prevent the formation of edema. In isolated arteries, myogenic vasoconstriction can be triggered by a rise in intravascular pressure, independent of neural and hormonal stimuli. This dissertation is about the role of the angiotensin II AT1A-receptor in myogenic vasoconstriction of arteries. In this dissertation pressure-induced myogenic vasoconstriction of isolated cerebral and mesenteric arteries was measured over a physiological intravascular pressure range of 5 to 160 mmHg. The intensity of myogenic vasoconstriction of arteries from AT1A receptor knock-out and wildtype mice was compared. A significant difference in the intensity of myogenic vasoconstriction was shown in mesenteric arteries in a pressure range from 120 to 160 mmHg. The biggest absolute difference in intensity of myogenic vasoconstriction between the two groups was 17,9% (at 160 mmHg) and the biggest relative difference in intensity of myogenic vasoconstriction between the two groups was 46,6% (at 150 mmHg). In zerebral arteries a significant difference in the intensity of myogenic vasoconstriction could only be detected at 50 and 60 mmHg intravascular pressure. Furthermore, the intensity of vasoconstriction after stimulation with pharmaceuticals was compared in mesenteric and cerebral arteries from AT1A-receptor knock-out and wildtype mice. A significantly reduced vasoconstriction was shown in zerebral arteries of AT1A-receptor knock-out mice. The applied pharmaceuticals showed a vasoconstrictor response in the following order of decreasing intensity: endothelin 1 > phenylephrin > angiotensin II > vasopressin. No significant difference in intensity of vasoconstriction could be detected in mesenteric arteries of AT1A-receptor knock-out and wildtype mice. For future application in the vasculature of animals, small interfering ribonucleid acid (siRNA) against the AT1A-receptor was tested on a cellular level. A plasmid containing the desoxyribonucleid acid (DNA) sequence of the AT1A-receptor physically linked to the sequence of a fluorescence protein was created. This plasmid was then transfected into cells, and a stable cell line was created after polyclonal and monoclonal selection. As the DNA sequence of the AT1A-receptor was physically linked to the sequence of a fluorescence protein, the reduction of intracellular fluorescence of cells treated with siRNA in comparison to cells not treated with siRNA could be taken as measurement of the intensity of reducing the genetic expression of the AT1A receptor. A maximal efficacy in the reduction of fluorescence of 87,6% was shown. Generally, by using a higher siRNA concentration and residence time, an increase in siRNA efficacy could be reached. The data on pressure-induced myogenic vasoconstriction from this dissertation confirm the thesis, that the AT1A-receptor has an influence in myogenic vasoconstriction. Further research on this thesis can be done by the future application of the siRNA against the AT1A-receptor in the vasculature of animals.