Nitrogen transformations in soil as affected by bacterial-microfaunal interactions

We investigated the effects of soil microfauna feeding on a soil bacterium (Pseudomonas cepacia) and the resultant influence on net N mineralization. As the bacterial biomass increased, it assimilated N from the soil. Later, only if this bacterial biomass decreased was N remineralized. Grazing by amoebae (Acanthamoeba polyphaga) always reduced bacterial biomass, increased respiration, and increased nitrogen mineralization. Grazing by nematodes (Mesodiplogaster lheritieri) always reduced bacterial numbers and increased respiration, but only increased N mineralization when nematode populations themselves declined from peak values.A N budget calculated for the populations indicated that the nematode biomass was not sufficient to account for the unmineralized N, so we postulate change in excretory pathways as the bacterial food becomes limiting. This budget further indicated that amoebal and bacterial biomass could account for all of the non-mineral N when only these two species were present.Our experiments showed that microfauna can play an important role in N mineralization in soil and that the mechanism for this role is more likely to be through direct excretion by the grazers than through indirect physiological effects on the bacteria.     

Experimental Ostertagia spp. infection of sheep: development of worm populations and lesions resulting from different dose-levels of larvae

Worm-free sheep were dosed with 8 000, 64 000 or 512 000 infective Ostertagia spp. larvae and killed 4, 7, 10, 13, 18, 24 or 66 days later. Up to day 10 the worm counts ranged from 52 to 86% of the infecting dose and results suggested no substantial reduction either in rate of development or in percentage establishment with increasing dose level. However, a reduction of worm counts, which was substantial at the higher dose-rates but comparatively small at the low rate, occurred after day 10.Gross lesions in the abomasum ranged from little more than the development of a few nodules in the low-dose sheep, to a roughened congested surface with diptheritic membranes and severe oedema in the high-dose animals at days 10–24. These effects had subsided by day 66. Histopathological changes are described.The severity and extent of the reaction was related to the parasite dose-level, but not necessarily to the numbers of worms recovered post-mortem. The rate of return to normality was quicker at the lower dose rates.     

Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis

OBJECTIVE: To determine whether pasture, and specifically the addition of fructan carbohydrate to the diet, induces exaggerated changes in serum insulin concentration in laminitispredisposed (LP) ponies, compared with ponies with no history of the condition, and also to determine insulin responses to the dexamethasone suppression test. DESIGN: Prospective study. ANIMALS: 10 LP and 11 control adult nonobese mixed-breed ponies. PROCEDURES: Insulin-modified IV glucose tolerance tests were performed (5 ponies/group). In diet studies, ponies were kept on pasture and then changed to a hay diet (10 ponies/group). Second, ponies were maintained on a basal hay diet (4 weeks) before being fed a hay diet supplemented with inulin (3 g/kg/d [1.4 g/lb/d]). Serum insulin and plasma glucose concentrations were analyzed before and after dietary changes. Serum cortisol and insulin concentrations were also measured in a standard dexamethasone suppression test. RESULTS: The LP ponies were insulin resistant (median insulin sensitivity of 0.27 x 10(4) L min(-1) mU(-1) in LP ponies, compared with 0.64 x 10(4) L min(-1) mU(-1) in control ponies). Median insulin concentration in LP ponies was significantly greater than that in control ponies at pasture, decreased in response to feeding hay, and was markedly increased (5.5-fold) following the feeding of inulin with hay. The LP ponies had a greater increase in serum insulin concentration at 19 hours after dexamethasone administration (median, 222.9 mU/L), compared with control ponies (45.6 mU/L). CONCLUSIONS AND CLINICAL RELEVANCE: Nonobese ponies predisposed to develop laminitis had compensated insulin resistance, and this phenotype was revealed by feeding plant fructan carbohydrate or by dexamethasone administration.     

Effect of control of systolic blood pressure on survival in cats with systemic hypertension

BACKGROUND: Systemic hypertension is a common clinical problem, often occurring in association with renal disease in cats. Limited information is available to assess the effect of blood pressure and the treatment of hypertension on survival. HYPOTHESIS: That adequacy of blood pressure control is associated with the duration of survival in cats with systolic hypertension. ANIMALS: One hundred and forty-one client-owned cats with systolic hypertension. METHODS: Hypertensive cats were treated with amlodipine besylate and were followed until death or the study end point. Time-averaged systolic blood pressure (SBPOT) after implementation of antihypertensive medication and stabilization of systolic blood pressure (SBP) was calculated by using the equation (area under the curve/survival [days]). Cats were divided into quartiles based on their SBPOT, representing varying levels of blood pressure control (median [25th, 75th percentile]: Q1 = 137 [132, 141] mm Hg, Q2 = 148 [145, 151] mm Hg, Q3 = 157 [155, 158] mm Hg, Q4 = 170 [164, 175] mm Hg). Survival and clinical variables were compared between the quartiles. Cox proportional hazard regression analysis was used to determine the association of age, renal function, proteinuria, SBPOT, and the presence of hyperthyroidism on survival. Urine protein to creatinine ratio (UP:C) was compared at diagnosis of hypertension and after initiating treatment. RESULTS: Only UP:C and SBP at diagnosis differed significantly between SBPOT quartiles. Proteinuria was the only variable significantly related to survival in hypertensive cats. A significant decline in UP:C was found in cats treated with amlodipine besylate. CONCLUSIONS AND CLINICAL IMPORTANCE: Proteinuria before and after treatment of hypertension is strongly associated with survival in cats with systolic hypertension. Treatment with amlodipine besylate can result in a significant reduction in UP: C.     

Dietary fructan carbohydrate increases amine production in the equine large intestine: implications for pasture-associated laminitis

Pasture-induced laminitis in the horse is associated with the overconsumption of fermentable carbohydrate, in the form of simple sugars, fructans, or starch. The fermentation of carbohydrate in the cecum and large intestine results in the production of lactic acid and other toxins or "laminitis trigger factors." Vasoactive amines have been suggested as possible initiating factors. The aim of this study was to feed a commercially available form of fructan carbohydrate (inulin, 3 g/kg of BW per day) to normal ponies and to ponies predisposed to laminitis, to mimic a change from a basal hay diet to lush spring-summer pasture. Five normal and 6 laminitis-prone, native-breed ponies were acclimated to a basal hay diet before the inclusion of inulin and chopped dried grass. Blood samples, fecal samples, and foot temperature measurements were taken throughout the study. Amines were measured in the feces and plasma by HPLC and liquid chromatography-mass spectrometry, respectively. The pH of the fecal samples decreased from 6.89 +/- 0.11 on the hay diet to a minimum of 6.18 +/- 0.11 with the addition of inulin (P <0.05). An increase was observed in the fecal concentrations of a number of amines, including tryptamine (2.5-fold increase, P <0.05) and tyramine (2-fold increase, P <0.05). No changes were noted in plasma amine concentrations or plasma D- or L-lactate, indicating that there may be a threshold of hindgut pH change before mucosal damage can result in the release of these factors into the circulation. No differences in pH or any of the measured compounds were observed between the group of normal ponies and those predisposed to laminitis. This indicates that differences in the intestinal microflora do not account for this predisposition. However, the results from this study indicate that moderate increases in dietary fructan carbohydrate can produce increases in bacterial fermentation products and other compounds in the large intestine, which may be relevant to the pathogenesis of acute laminitis in ponies on pasture.     

Induction of interleukin 2 messenger RNA inhibited by cyclosporin A

Cyclosporin A blocked production of the lymphokine interleukin 2 by activated T lymphocytes. In a human and a murine cell line this inhibition reflected an absence of interleukin 2 messenger RNA. Under conditions in which these cells are normally stimulated to secrete high levels of interleukin 2, they failed to do so in the presence of cyclosporin A. In both cell lines this failure was accompanied by an absence of interleukin 2 messenger accumulation.