The threshold and the maximum range of pharmacological response of gastrointestinal smooth muscle of nigerian muscovy duck (cairina moschata) to acetylcholine, histamine and adrenaline.

The effective dose ranges of acetylcholine, histamine and adrenaline were determined in the gastrointestinal smooth muscle of Nigerian Muscovy duck (C. moschata) using the modified muscle-bath contractility method. The molar concentration at the threshold responses (T.R) and maximal responses (M.R) were determined for each of the agonists. ‘This study was carried out on the different regions of the gastrointestinal (G.I) tract namely; crop, proventriculus, duodenum, ileum, caecum and rectum. The study revealed that the dose at which the smooth muscle of the Nigerian Muscovy duck shows the first recordable contractile response to acetylcholine is between 1 x 10-13 and 1-x 10-9 M. The maximum molar concentration of acetylcholine was obtained at 3 x 10-6 - 1 x 10-4 which is the dose beyond which further increase in the concentration of the acetylcholine does not yield any corresponding increase in the muscular response. The proventriculus appears most sensitive to acetylcholine with threshold value being at 1x 10-15 while the highest efficacy was recorded in the proventriculus and ileum at 1 x 10-6. Histamine contracted the gastrointestinal smooth muscle with the threshold value (T.R) of 1 x 10-14- 3 x 10-8 M and the maximum response (M.R) was attained at 3 x 10-6 - 3 x 10-4 M. Rectum and ileum have the least T.R values of 1 x 10-14M and 1 x 10-13M respectively, which suggest that these two segments of the G.I tract were most sensitive to histamine. The ileum, caecum and rectum had the least M.R value (3 x 10-6 M), which shows that they responded maximally to increase in molar concentration of the agonist. Adrenaline recorded the shortest range of threshold value (1 x 10-10- 3 x 10-8 M). The highest relaxant responses were produced between molar concentrations of 1 x 10-5- 3 x 10-4M. The ileum had the least T.R (1 x 10-10M) value while the caecum and rectum had the least M.R values of 1x10-9-1x 10-8M and 1x 10-8 M, respectively , which indicate that these segments were highly sensitive to adrenaline compared to other regions of the gastrointestinal tract. It was observed that the gastrointestinal smooth muscle of G.I tract of C. moschata is relatively more sensitive to acetylcholine, histamine and adrenaline than what has been reported for domestic chicken and Guinea fowl. The need for further studies on the factors responsible for occurrence of anatomical or regional differences in the sensitivity of the gastrointestinal tract to the neurotransmitters was also stressed. Keywords :Pharmacological sensitivity, gastrointestinal smooth muscle, acetylcholine, histamine, adrenaline, Nigerian duck. Tropical Veterinarian Vol. 24 (1 & 2) 2006: pp. 16-22