Effects of treatment with aspirin or aspirin/dipyridamole combination in heartworm-negative, heartworm-infected, and embolized heartworm-infected dogs.

To determine the drug dose required to inhibit platelet reactivity by at least 50%, 2 drug regimens were evaluated in heartworm-negative, heartworm-infected, and heartworm-infected dogs embolized with dead heartworms. Aspirin, or a combination of aspirin and dipyridamole, were administered to 2 groups of Beagles (n = 5 each) for 5 to 9 days; a third group of 5 Beagles served as nontreated controls. For heartworm-negative dogs, mean (+/- SD) aspirin dosage that inhibited collagen-induced platelet reactivity by at least 50% was 6 (+/- 2) mg/kg of body weight given once daily. The aspirin/diphridamole combination dosage was 1 mg of each drug/kg given every 12 hours. All dogs (n = 15) were implanted with 7 adult heartworms each and remedicated (or not treated) beginning at 21 days after heartworm implantation. In heartworm-infected dogs, mean aspirin dosage required to inhibit collagen-induced platelet reactivity greater than or equal to 50% was 10 (+/- 6) mg/kg. Mean dosage of aspirin/dipyridamole combination was 1.6 +/- (0.5) mg of each drug/kg given every 12 hours. When platelet reactivity in response to collagen was determined to be inhibited by at least 50% in all medicated dogs, each dog (n = 15) was embolized with 7 dead adult heartworms to mimic heartworm adulticidal treatment. Platelet reactivity was monitored for 21 days after treatment, and drug dose was adjusted to maintain platelet inhibition by at least 50%. In embolized dogs, mean aspirin dosage was 17 (+/- 14) mg/kg given once daily. Mean dosage of the aspirin/dipyridamole combination was 2.8 (+/- 1.3) mg of each drug/kg given every 12 hours. All dogs (n = 15) were euthanatized 21 days after heartworm embolization. Each lung lobe was evaluated for severity of lesions and presence of organized or fibrinous thrombi. Lesion severity in the aspirin- and aspirin/dipyridamole-treated dogs was not significantly different from that in control dogs.     

An Estimation of the Nitrogen and Phosphorus Loading by Wet Deposition over Lake Maracaibo,Venezuela

In order to make an estimation of thewet deposition levels of the major nitrogen compoundsin Lake Maracaibo system, the precipitation wascollected by events at five sites located on shorearound the Lake from 1991 to 1994. Also the phosphorusconcentrations were determined in rain samples. RainpHs averaged about 5 to 6. NH₄ ⁺ levels weresignificantly higher (up to 1.44 mg L^-1NH₄-N) than NO₃ ^-plus NO₂ ^-ions which resulted in the highest pHs values in thestrait Maracaibo. The strait is the nearest zone toAmmonia Plant located upwind at the TablazoPetrochemical Complex. At the strait, theinorganic-nitrogen ((NH₄ + NO₃ +NO₂)-N) concentrations were greater than organicnitrogen levels, but at the other sites were lower.Phosphorus levels were low, ranging from undetectableto 1.5 mg L^-1; organic-P was estimated to accountfor about 40% of total-P. Total mean nitrogen wetdepositions were 6.93 kg ha^-1 yr^-1 (≈59% asNH₄-N) at the strait and 9.85–16.84 kg ha^-1yr^-1 (≈55% as organic-N) around the lakeshore.Inorganic and organic nitrogen account for about equalportions of the total nitrogen loading. These amountsrepresents ≈24% of the annual total-N inputsby the tributary rivers to the lake and aresubstantially higher than those reported in the shoreof Lake Valencia (north-central part of Venezuela) andother tropical areas. The contribution ofprecipitation to P in lake is very small; ≈0.6 kg ha^-1 of total-P are added annually. The N and Pinputs were greater than the sewage contributions. Themean molar ratio N/P is ≈22 at the straitsite whilst at lake sites the N/P ratio isconsistently >22 (about 35～1 to 100～1). The results of this preliminary study show that the atmosphere represents a significant factor for the total nitrogen loading to Lake Maracaibo system.     

The growth and nitrogen economy of rice under sprinkler and flood irrigation in South East Australia

Summary ¹⁵N balances were compared in rice (Oryza sativa L., cv. Calrose) grown under continuous flood (CF) or sprinkler irrigation. Two sprinkler treatments with irrigation frequencies of once (S1W) and thrice (S3W) per week were studied. Five atom %¹⁵N-labelled urea (60 kg N ha^–1) was applied to microplots either 36 or 84 days after emergence (DAE). An equivalent amount of unlabelled urea was applied at the other application time, so that each microplot received a total of 120 kg N ha^–1 in an equal split. There was no significant effect of irrigation treatment on recovery of urea N by straw. Straw recovery from urea applied 36 DAE was almost half that from an application 84 DAE, and time of urea application produced a similar effect on recovery in grain. Grain recovery in S1W was less than half that in CF and S3W for both application times. Total plant recovery of urea N applied 36 DAE was similar for all irrigation treatments (average 29%), but for urea applied 84 DAE total plant recovery in CF (67%) was significantly higher than in S1W (49%). Total N uptake in the plant tops was considerably lower in both the sprinkler-irrigated treatments when compared with CF, and this was mostly due to reduced soil N uptake in S3W (one-half) and S1W (one-third). The proportion of N derived from fertilizer in the plant tops increased from 40% in CF to 60% in S1W. Immobilization of applied N in the soil of the sprinkler-irrigated treatments was greater than in CF by factors of 1.5 (S3W) and 2 (S1W). Immobilization of urea N applied 36 DAE was almost 50% greater than immobilization of urea N applied 84 DAE. There was a trend for lower losses of fertilizer N with sprinkler irrigation (mean loss 18% of the applied N) compared with CF (27%). Within all irrigation treatments, the loss from urea applied 36 DAE was more than double the loss from urea applied 84 DAE. An additional study in CF compared the ¹⁵N balance for split application versus a single dose applied 36 DAE (before permanent flood). Split application resulted in significantly increased plant recovery of applied ¹⁵N, and this was largely associated with increased recovery in the grain. Slightly more fertilizer N was immobilized in the soil with a single application. The effect of application method on N loss was not significant.