The aim of this study was defining relationships between a five minute episode of mechanical colonic distensions (CD) of different degrees, which were provoked by the insertion of a balloon filled with 150 and/or200 ml of water (CD150 and/or CD200), and reticulo-ruminal motility changes, heart rate, respiration frequency as vegetative symptoms of the nociceptive effects. Futhermore, noting the influence of premedication by metabotropic glutamate receptor antagonist DL-AP3 i.c.v. 1 min. infusion in 3 different doses (4.0, 8.0 and 12.0 mg in toto) on the above symptoms in sheep. The experiment was carried out in 4 series using 12 female sheep, Polish Merinos with fistula of dorsal sac of the rumen, in the anoestrus period. In the first series (6 animals as a control group) the animals had a 200 ml 0.9% NaCl i.c.v. infusion. In the second series (6 animals) they had a 5 min episode of CD by insertion of a balloon filled with 150 and/or 200 ml of water (CD150 and/or CD200). In the third series of the experiment 6 animals had an i.c.v. DL-AP3 infusion in 3 different doses (4.0, 8.0 or 12.0 mg in toto), every week. In the fourth series, the animals had i.c.v. DL-AP3 infusions in 3 different doses (4.0, 8.0 or 12.0 mg in toto) ten minutes before CD. CD espisodes of five min duration provoke a very repetitive, statistically significant increase of heart rate/ min, reticulo-ruminal motility inhibition, and nociceptive symptoms intensivity, and this can be a new model for testing potential analgesic substances and drugs for small ruminants. DL-AP3 racemate, a metabotropic glutamate receptor mGluR₁ antagonist, can be an alternative drug in jejunal pain when it is provoked by colonic distension in sheep.
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