Cholesterol is mainly located in the cell membrane, where, by modulating the degree of microviscosity of the lipid biiayer, it can have an important role in cell growth and differentiation. Shinitsky and Inbar (Biochim. Biophys. Acta, 433, 133, 1976) found reduced microviscosity in chronic lymphatic leukaemic (CLL) lymphocytes, which correlated with earlier reports of low cholesterol levels in isolated membranes from these cells. Using intact cells, Gottfried (J. Lipid Res. 8, 321, 1967) found abnormally low cholesterol in CLL lymphocytes but not in chronic myeloid leukaemic (CML) granulocytes. More extensive studies have been retarded by difficulty in obtaining adequate quantities of non-malignant human ]ymphocytes.

The vagal sensory inputs to and motor outputs from the hindbrain gastric centres required for reticuloruminal motility were sampled directly in anaesthetized sheep using electrophysiological 'single fibre' techniques and indirectly in conscious, surgically prepared sheep. Drugs were administered by close-arterial injection into a carotid artery to observe central effects and into the coeliac artery to observe peripheral effects on the reticulorumen. Escherichia coli lipopolysaccharide produced intermediates responsible for the smooth muscle relaxation in the first phase of reticuloruminal stasis and for gastric centre depression in the second phase. Adrenergic influences on reticuloruminal motility comprise (a) an alpha1 adrenoreceptor-induced contracture and raised tension receptor sensitivity, (b) an alpha2 adrenoreceptor-mediated depression of the gastric centres causing stasis, excitation of epithelial receptors evoking rumination, and interference with acetylcholine release in the parasympathetic pathway, (c) abeta1 adrenoreceptor-mediated inhibition of the gastric centres, and (d) abeta2 adrenoreceptor-mediated inhibition of intrinsic and extrinsic motility.

Contractile responses of uterine muscle strips to a saponin (DSS) isolated from the root of Dalbergia saxatilis was investigated in the rat. Uterine muscle response to the glycoside was characterized by a single but transient contraction that was concentration-dependent, with an ED50 of 0.13 mg/ml and 0.04 mg/ml as the lowest active concentration. Atropine sulphate (0.69 μmol) abolished uterine muscle responses induced by acetylcholine (1.82 μmol) but failed to block responses to submaximal concentration of DSS (0.24 mg/ml), suggesting that responses to DSS were not mediated by cell membrane cholinoceptor activation.

It has been suggested that the beneficial effects of yucca plant (Yucca shidigera) extract when used as a feed additive are based on its demonstrated ability to bind ammonium (Cromwell, et al., 1985; Johnston, et al., 1981). Benefits include the reduction of noxious gasses, the easing of waste management problems and the enhancement of livestock performance. However the amount of ammonium bound is very small (Ryan, et al., 1993; Quinn and Leek, 1994), and it is difficult to explain the observed enhancement of livestock performance, particularly in ruminants, in terms of this effect alone. Consequendy, in order to evaluate the overall effect of Y. shidigera extract on rumen fermentation in this study, samples of ruminal fluid from pre-conditioned hay-fed sheep were incubated with the extract and die effects on ammonium, pH and short chain fatty acids after 24 h were compared.

Sheep fed a “long fibre-free” diet undergo short spells of pseudorumination (cud regurgitation without cud chewing) and no true rumination. True rumination can be restored by the addition of inert fibre particles directly into the rumen. To assess whether sheep fed a “long fibre-free” diet would actively choose to ingest inert fibre particles, in a series of experiments, 10 sheep were offered a plastic box containing specific amounts of polyethylene fibre, chopped into 10 mm lengths. After 24 h, the remaining fibre was retrieved and weighed. At the same time, jaw movements were recorded for 24 h periods to monitor rumination. Feeding a “long fibre-free” diet for 7 days reduced true rumination to zero. In experiment 1, on offering a plastic box containing 50 g polyethylene fibre, three sheep ingested 34.8 ± 6.8 g of fibre and rumination was significantly (p < 0.05) increased. In experiment 2, when a plastic box containing 50 g chopped polyethylene fibre was offered daily to 4 fistulated sheep immediately upon switching from hay to the pelleted diet, the sheep commenced eating the fibre within 24 h. In experiment 3, when offered a choice between short-chop (3 mm) and long chop (15 mm) polyethylene fibre, the sheep showed a preference (p < 0.05) for the 3 mm length fibre, although this was of a length insufficient to evoke adequate rumination. Therefore, the actual choice of fibre consumed may be driven by ease of ingestion rather than which substrate is more ideally suited to induce rumination. In experiment 4, a polyethylene fibre pompom, fixed on a rod, introduced via the rumen cannula and placed so as to brush the reflexogenic areas of the reticulorumen, reduced voluntary polyethylene fibre intake. This suggests that the intake of inert fibre may be a result of the reduction of ruminal sensory input to the brain, normally provided by fibrous reticuloruminal contents.

Inert fibre particles were used in a series of experiments in order to quantify the effects of some physical characteristics of dietary long fibre on rumination. Removal of hay from the diet of hay/concentrate-fed sheep reduced true rumination to zero after a period of 8 days, although pseudorumination, much reduced in duration, persisted. Then by introducing loose, chopped, inert polyethylene particles through a rumen cannula, rumination was restored. When different masses of loose inert polyethylene particles chopped into 10-mm lengths were placed in the rumen, the time spent ruminating was found to be directly proportional to mass of fibre placed in the run ren (P < 0 . 001). By inserting a fixed mass of particles of different lengths, the optimum length of inert fibre for rumination to occur was found to lie between 7 and 30 mm. Finally, when, in place of loose fibre, a polyethylene fibre 'pompom', fixed on a rod, tons introduced via the cannula and placed so as to brush different areas of the reticulorumen, it was found that the greatest rumination response was evoked when the pompom was allowed to stimulate mechanically the cranial regions of the reticulorumen (P < 0 . 05). It is concluded that inert polyethylene fibre mimicked the peripheral excitatory effects of dietary fibre by stimulating mechanoreceptors (epithelial receptors) located in the cranial portions of the reticulorumen. Adding about 50 g of 7 to 30 mm inert fibre caused sheep on low-fibre diets to ruminate normally for over 3 h.

The ability of alpha-2 adrenoreceptor agonists and veratridine to evoke rumination and to modify reticular motility in adult Suffolk-cross sheep when injected by close-arterial injection into the forestomach was investigated. The specific alpha-2 adrenoreceptor agonists, xylazine and medetomidine, evoked rumination and increased reticular motility. The Na+ channel activator veratridine also evoked rumination and dramatically increased reticular motility. In contrast, injection of the alpha-1 adrenoreceptor agonist, phenylephrine, was ineffectual in evoking rumination and resulted in reduced reticular motility. It is concluded that the evocation of rumination by alpha-2 adrenergic agonists and veratridine is probably due to the activation of sensory nervous receptors (epithelial receptors) located in the reticulorumen.