Abstract:
40A Role of opioid peptides in reticulo_rumen motility of sheep J. Chen and I.R. Godwin Physiology, School of Rural Science and Natural Resources, University of New England, Armidale NSW 2351 igodwin@metz.une.edu.au The opioid peptides have long been known to have a physiological role in gastrointestinal motility. Most studies in animals have shown they have an inhibitory role, the constipating effects of morphine being well known to physicians. However with the elucidation of three different opiate receptor types (�, and ), a greater understanding of the multiple roles of these receptors in the body is slowly being uncovered. We investigated the effects of a new agonist, U50,488 h, on rumen fluid dynamics and rumen contractions. Eight Coopworth ewes fitted with rumen cannulae were given intravenous injections of the agonist at rates of 0, 25, 50 and 100 �g/kg BW. The animals were fasted for 12 h before injection, and allowed free access to food 3 h after injection. The effects on rumen liquid outflow (CrEDTA dilution) and rumen contraction rates were recorded. (a) P e r i od % of P r i m ar y C o n t r a c 140 130 120 110 100 90 80 70 60 50 0 1 2 3 4 5 6 7 8 9 Time (h) The agonist decreased rumen fluid outflow in a dose dependent manner (data not presented). It had little effect on the frequency of contractions but did cause a dose_dependent increase in primary contraction period and decrease in secondary contraction period. The amplitude of these contractions was also affected by the high dose, producing a decrease in both primary and secondary contraction amplitude. The data indicate that the opioid receptors may play a role in the modification of the force and length of contractions of the reticulo _ rumen once the appropriate stimuli for contraction frequency have been set. The differing effects on primary and secondary contractions rule out a direct effect on smooth muscle contraction period, but because of the similar effect on amplitude in both types of contraction, a direct effect on smooth muscle tonus is likely. (b) 15 0 *** ** * ** ** * P e r i od % o f S e c o n d ar y C o n t r 14 0 S a lin e 5 ml Saline 5ml U50 ,488 h25ug/kg U50 ,488 h50ug/kg U50 ,488h 100ug/kg 13 0 12 0 11 0 10 0 90 80 70 60 50 U50, 488h2 5ug/kg U50, 488h5 0ug/kg U 50, 488h10 0ug/kg * * ** * ** ** * 0 1 2 3 4 5 6 7 8 9 Time (h) A m p l i t ude % o f Sec o n d a r y C o nt r a c t i o Amplitude% of Primary Contration (c) 150 140 130 120 110 100 90 80 70 60 0 1 2 3 4 5 Saline 5ml U50,488h25ug/kg U50,488h50ug/kg U50,488h100ug/kg (d) 16 0 15 0 14 0 13 0 12 0 11 0 10 0 90 80 70 60 0 1 2 3 4 5 S a l ine 5m l U 5 0, 4 88h2 5 u g/ k g U 5 0, 4 88h5 0 u g/ k g U5 0, 4 8 8 h 1 0 0 u g/ k g * * * * * * * 6 7 8 9 6 7 8 9 Time (h) Tim e ( h ) Figure 1 The effects of U50,488h on reticulo_rumen primar y (a) and secondar y (b) contraction periods and primary (c) and secondar y (d) contraction amplitude. Arrows indicate time of feeding. *P<0.05, **P<0.01, ***P<0.001 Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)