Delineation of signalling pathway in alpha adrenoceptor mediated vasorelaxation using goat arterial strips

Alen Major Venis, (2019) Delineation of signalling pathway in alpha adrenoceptor mediated vasorelaxation using goat arterial strips. Masters thesis, Christian Medical College, Vellore.

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Abstract

Phenylephrine (PE) is a sympathomimetic agent belonging to a class of drugs known commonly as the alpha adrenergic agonists. This drug group is long known to cause constriction in vascular smooth muscles. Recently, our department has demonstrated that PE can also induce vasorelaxation in a nitric oxide (NO)-dependent manner under certain circumstances in goat leg arteries. Such vasorelaxation is shown to be mediated through alpha adrenergic receptors, particularly α1, and was demonstrated on spiral strip preparations of goat arteries. However, it was later demonstrated that the relaxant response was seen only in longitudinal strips and not in transverse preparations. In this study, we have tested if either the ring or longitudinal strip preparations of goat aorta demonstrate a vasorelaxant response to PE. AIM OF THE STUDY: To determine if the alpha adrenoceptor mediated vasorelaxant pathway described in small artery preparations is present in goat aorta too. OBJECTIVES: 1. To test the effect of vasoconstrictors on two different preparations of aorta – the longitudinal strip and transverse cylinder. a) To test if the alpha adrenergic agonist PE produces vasoconstriction or vasorelaxation in longitudinal strips made from aorta. b) To test if the alpha adrenergic agonist PE produces vasoconstriction or vasorelaxation in transverse cylinders (rings) made from aorta. 2. If vasoconstriction occurs in either of the above cases, then to test the response of PE in the presence of NO donors, SNP and L-Arginine. 3. If vasorelaxation occurs in objectives 1a and 1b, or 2, to test if the vasorelaxation produced by PE alone or PE/NO combination is preventable by prazosin (specific α1-blocker). METHODS: Aortae were isolated from fresh goat hearts and were cut into rings or longitudinal strips. The preparations were then suspended in an organ bath of 25 ml capacity which was filled with physiological salt solution, maintained at 37ºC by means of a circulating water bath, and also aerated with carbogen (95% oxygen and 5% carbondioxide). One end of the aortic preparation was fixed to the organ bath and the other end of the isolated tissue was connected to a force transducer and tension was recorded using a data acquisition system (PowerLab from AD Instruments). Drugs were then added to the organ bath and any change in tension recorded by the force transducer was recorded. Data of the viable tissue was analyzed using SPSS 23.0 and visualized using Igor pro. RESULTS: In both ring and longitudinal strips of aorta, Phenylephrine (PE) caused vasoconstriction under normal and high NO environment, unlike in small arteries. CONCLUSION: There is no alpha-adrenoceptor mediated vasorelaxant pathway in aortic smooth muscle.

Item Type: Thesis (Masters)
Uncontrolled Keywords: Phenylephrine, vascular smooth muscle, vasorelaxation, aorta
Subjects: MEDICAL > Physiology
Depositing User: Subramani R
Date Deposited: 23 Aug 2019 02:48
Last Modified: 23 Aug 2019 02:48
URI: http://repository-tnmgrmu.ac.in/id/eprint/11112

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