Organ Bath Experiment

An organ bath experiment was conducted to investigate the effect of agonist, histamine on guinea pig ileum (GPI) and how the antagonists, mepyramine and SIPBSDrug A affect the GPI’s response (smooth muscle contractions). A GPI simulation was conducted to compare the potencies and nature of antagonists against histamine. The control Rmax and EC50 of histamine without antagonist were 16.49gms and 2.093 x 10-7M respectively. The concentration-response curves were shifted to right parallelly and EC50 increased while Rmax remained constant when mepyramine or SIPBSDrug A was added. Besides, both antagonists showed linear graphs in Schild plot, indicating that they acted as reversible competitive antagonists. The pA2 and KB of mepyramine were 10.148

Next, a basic stock solution was used to prepare various concentrations ranging from 1.0 x 10-8M to 1.0 x 10-1M by serial dilution. The tissue was washed by overflow with reservoir’s solution for 5 seconds to obtain baseline before adding 0.1ml, 0.3ml and 0.5ml for each concentration respectively into the tissue bath.The tissue’s peak response for each final bath concentration(FBC) was measured and recorded. Rmax and EC50 of histamine were recorded.
Later, 5ml of 1 x 10-6 M of mepyramine was added into the reservoir containing 1000ml of Krebs-Henssleit solution to produce a FBC of 5.0 x 10-9M. It was equilibrated with tissue for 10 minutes by flushing into the organ bath. After that, the steps above were repeated to test tissue response using 5ml of 1 x 10-5M and 1 x 10-4M of mepyramine. The experiment was repeated by replacing mepyramine with SIPBSDrug A as the antagonist. Lastly, concentration-response curve with Hill-Langmuir equation and Schild Plot were plotted using Bio-Graph. KB and pA2 values for mepyramine and SIPBSDrug A were calculated based on Schild plots and Gaddum

The Rmaz and EC50 of histamine control were 16.49gms and 2.093 x 10-7M respectively. In figure 1, when 5 x 10-9M, 5 x10-8M and 5 x 10-7M of mepyramine were added, the EC50 of histamine was increased to 6.254 x 10-6M, 4.752 x 10-5M and 0.0002428M respectively. The Rmaz of histamine in the presence of final bath concentration (FBC) of 5 x 10-9M, 5 x10-8M and 5 x 10-7M antagonist either mepyramine or drug A were remained almost constant in Figure 1 and 2. On the other hand, the EC50 of histamine was increased to 3.455 x10-5M, 0.0001693M and 0.0006647M during the presence of FBC of 5 x 10-9M, 5 x10-8M and 5 x 10-7M drug A respectively. Hence, higher histamine’s concentrations were needed to achieve EC50 as the antagonist’s concentration increased. The calculated pA2 and KB of mepyramine were 10.148 and 7.1143 x 10-11 respectively whereas the calculated pA2 and KB of Drug A were 11.771 and 1.6961 x 10-12