Summary
Dogs were anesthetized with sodium pentobarbital, relaxed with succinyl choline and were kept under artificial ventilation. Both carotid bifurcations were denervated and the Vagus nerves were cut in the neck. Regional blood flow in the skin and the intestine, cardiac output, heart rate and arterial pressure were determined before, during and after spinal cord heating and cooling. Further experiments were performed in which, in addition, sympathetic effects on the heart were excluded by exstirpation of the caudal cervical and stellate ganglia or by β-receptor blockade. The cardiovascular responses were compared with those obtained in a preceding investigation from dogs with intact baroreceptors and vagus nerves.
As in intact dogs, appropriate thermoregulatory adjustments of skin blood flow were induced by thermal stimulation of the spinal cord after baroreceptor denervation and vagotomy. However, blood pressure homeostasis was lost. The pattern of cardiovascular adjustments during heating consisted in cutaneous vasodilatation intestinal vasoconstriction and, due to sympathetic activation an increase of heart rate and cardiac output. This pattern was qualitatively identical with that in intact animals. During spinal cord cooling the cardiovascular response pattern consisted in cutaneous vasoconstriction, intestinal vasoconstriction and, depending on cooling intensity, a reduced or unchanged sympathetic influence on the heart. This pattern differed considerably from that in intact animals but basic features were still present as indicated by opposite changes of cardiac and vascular sympathetic tone during cooling.
It is concluded that the baroreceptor signals play no primary role in the generation of differential vasomotor responses under the present experimental conditions. This confirms assumptions made on the basis of observations in animals with intact baroreceptor input. However, baroreceptor signals contribute significantly to blood pressure homeostasis which is normally maintained during spinal thermal stimulation.
Zusammenfassung
Hunde wurden mit Pentobarbital narkotisiert, mit Succinylcholin relaxiert und künstlich beatmet. Beide Carotissinus wurden denerviert und die Nn. vagi durchschnitten. Die Durchblutung eines Haut- und eines Intestinalgefäßes, das Herzzeitvolumen, die Herzfrequenz und der arterielle Druck wurden vor, während und nach isolierter Wärmung oder Kühlung des Rückenmarks bestimmt. Kühlungen und Wärmungen wurden weiter nach zusätzlicher Ausschaltung des Herzsympathikus durch Ganglienexstirpation oder β-Rezeptor-Blockade durchgeführt. Die Kreislaufreaktionen auf die spinalen Temperaturreize wurden mit denen intakter Tiere verglichen, wie sie in früheren Untersuchungen ermittelt worden waren.
Auch nach Barorezeptor-Denervierung und Vagotomie führten Wärmung und Kühlung des Rückenmarks zu den typischen thermoregulatorischen Änderungen der Hautdurchblutung, doch konnte der arterielle Druck nicht, wie bei intakten Hunden, konstant gehalten werden. Das Muster der differenzierten Kreislaufreaktion bei Rückenmarkswärmung bestand in einer Vasodilatation der Haut, einer Vasokonstriktion im Darm und in einer Zunahme von Herzfrequenz und Herzzeitvolumen infolge Aktivierung des Herzsympathikus. Diese Kreislaufantwort war weitgehend identisch mit der eines intakten Tieres. Bei Rückenmarkskühlung bestand das Muster der Kreislaufreaktion in einer Vasokonstriktion in der Haut und im Darm sowie in einer unveränderten oder reduzierten Aktivität der sympathischen Antriebe des Herzens. Dieses Reaktionsmuster unterschied sich deutlich von dem intakter Tiere, doch zeigte das unterschiedliche Verhalten der sympathischen Innervation des Herzens und der Gefäße, daß im Prinzip noch eine qualitative vasomotorische Differenzierung bestand.
Die Befunde führen zu dem Schluß, daß die Signale der arteriellen Barorezeptoren am Zustandekommen regional antagonistischer vasomotorischer Reaktionen nicht entscheidend beteiligt sind. Damit werden entsprechende Annahmen bestätigt, die aus Versuchen an Tieren mit intakter reflektorischer Blutdruckregulation abgeleitet worden sind. Die Barorezeptoren tragen jedoch wesentlich zur Kreislaufstabilität bei thermischer Reizung des Rückenmarks bei.
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Conradt, M., Kullmann, R., Matsuzaki, T. et al. Arterial baroreceptor function in differential cardiovascular adjustments induced by central thermal stimulation. Basic Res Cardiol 70, 10–28 (1975). https://doi.org/10.1007/BF01905550
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DOI: https://doi.org/10.1007/BF01905550