The effects of oxytocin on reticulo-rumen motility.

Abstract

246 The effects of oxytocin on reticulo-rumen motility L.A. Zaenuri and I.R. Godwin School of Rural Science and Natural Resources, University of New England, Armidale NSW 2351 Oxytocin is a nonapeptide secreted by the posterior pituitary gland. Its prime physiological target tissues are the uterus and the mammary gland. It increases the frequency and duration of action potentials during each burst of activity in uterine smooth muscle. Thus it may both initiate and/or increase the frequency and strength of uterine contractions. During lactation the hormone is released as a result of a neurohumoral reflex after a suckling stimulus occurs. The hormone acts to cause contraction of the myoepithelial cells lining the mammary ducts and consequently the ejection of milk contained within them. As gut motility in the sheep appears to be increased during lactation, we tested the effects of oxytocin on reticulorumen contractions. Six merino ewes (two months post par-turn) and fitted with rumen cannulae were housed in metabolism cages and fed a mixture of equal quantities of oaten and lucerne chaff ad libitum. A balloon pressure transducer was placed in the reticula-rumen and connected to a computerised recording apparatus allowing continuous recording of reticula-rumen contractions. The animals were fasted for 4 h and then given a bolus injection of either 25 IU of oxytocin or saline intravenously. The sheep were allowed to recommence eating after 1 h. Pressure peaks corresponding to rumen contractions were monitored for 1 h prior to the injection and for 2 h post injection. Primary mixing and secondary eructation contraction frequencies were determined from examination of the pressure traces. The pertinent data are displayed in Figure 1. Oxytocin significantly increased the frequency of both primary and secondary contractions immediately after injection and also during the period of eating which followed. This effect is directly opposite that caused by the related neuropeptide vasopressin (Kauter and Godwin 1995). It appears that oxytocin produces a similar action on the rumen musculature as it does on the uterine myometrium. However, further studies are warranted to determine the mechanism of action and to rule out any central effects of the drug. We suggest that one of the mechanisms allowing an increased food intake during lactation is the action of oxytocin in providing an adequate mixing and propulsion of digesta. Reference Kauter, KG and Godwin, I.R. (1995). The effects of lithium on reticula-rumen motility of sheep and goats. Recent Advances in Animal Nutrition in Australia. p. 186 (Eds. J.B. Rowe and J.V. Nolan). University of New England: Armidale, Australia. Recent Advances in Animal Nut&ion in Australia 7997 University of New England, Armidale NSW2351, Australia