Actions of drugs on cardiovascular preparations
The experiment outlined in this report was carried out with the intention to observe and explore the effects of certain named drugs on a vascular preparation, in the cardiac region specifically. The cardiovascular preparation used in this experiment was an isolation of the descending aorta of a rat. This isolate is particularly useful as it mirrors the responses that would be observed in a human sample, thus this experiment will give rise to conclusions applicable to humans. The drugs which will be tested are as follows: acetylcholine, adrenaline, 5-hydroxytryptamine, isoprenaline, noradrenaline and sodium nitroprusside. As the preparation, inherently was not in a live organism this experiment was done in vitro. The drugs were tested in their capacity to produce a vasodilatory or vasoconstricting effect in the smooth muscle and hence their influence over the epithelium. In addition, the response of the tissue to varying concentrations of a single drug, namely adrenaline was measured. This broadened the scope of the experiment to understand how response varies with dosage.
The way in which different drugs affect cardiovascular system was observed by the dissection and removal of aortic tissue from a humanely killed rat. The tissue was prepared with care and kept in an environment to allow the sustained viability of the sample. The preparation was kept in this environment via use of an ‘organ bath’; this comprises of a glass compartment filled with a physiological salt solution. Krebs’ solution was used and was maintained at 37°C. The solution contains D-glucose as a source of energy for the suspended tissue, a vital component to maintain the preparation. Krebs’ solution also provided the necessary balance of various ions, including Na+, K+, Cl-, Ca2+ and Mg2+ respectively. Aeration of the solution is also vital. Carbogen was allowed to continuously pass through the solution. Carbogen, being a mixture of 95% oxygen and 5% carbon dioxide, was chosen as the carbon dioxide is needed as a buffer. The buffering of the solution permitted the maintenance of the pH at ~7.4. Aeration was also functional in its mixing effect due to the mechanical movement of particles as the bubbles passed through the solution. This meant that the required concentration of drug was reached more rapidly in each test and the preparation was met with an equipotent solution rather than a circulating bolus area of high concentration of the drug. This would have been problematic as the tissue would have been exposed to varying amounts of drug in each trial, consequentially producing inconsistent results. The tissue was prepared by dissecting the rat aorta transversely into a 3mm section. The section of tissue was then suspended in this solution and was mounted by two opposing stainless steel hooks; at one end secured to a fixed point and the other linked by thread to an isometric transducer. This was used to measure the contraction or dilation of the tissue by measuring the pull in millinewtons (mN), (as the tissue contracts the thread would be pulled down and therefore under more tension and vice versa for a dilation). The figure below depicts clearly the layout of the apparatus,
Figure 1. (Kenakin, 2001)
Fig. 1. An organ bath with aforementioned tissue held in place between the fixed point and thread leading to the isometric transducer held by the clamp. The carbogen is also shown here in a controlled flow portrayed by the bubbles.
The isometric transducer was then linked to a computer, and data was collected using the Biopac MP30 software. Thus when contractions or dilations are caused, the resultant changes in tension were recorded per time automatically by the software. Before any experimentation could be carried out, the tissue was left to equilibrate and reach its resting level of contraction. This was achieved by leaving the preparation for a one hour period and was...
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