Molyneux R J, Johnson A E, Olsen J D, Baker D C
Western Regional Research Center, USDA, Albany, CA 94710.
Am J Vet Res. 1991 Jan;52(1):146-51.
The toxicity of Riddell groundsel (Senecio riddellii) gavaged to calves at a known lethal rate was compared with the toxicity of riddelliine and riddelliine N-oxide, the pyrrolizidine alkaloids isolated from the plant, which were fed by intraruminal infusion. Doses of the alkaloids were adjusted to the amount determined to be in the plant and fed individually and in combination. The relative toxicosis in the calves was measured by clinical signs, serum enzyme changes, survival time to morbidity, and histologic changes. Calves fed Senecio riddellii by gavage for 20 consecutive days to provide 45 mg of total pyrrolizidine alkaloids/kg of body weight/d developed clinical signs and serum enzyme changes typical of seneciosis, with 100% morbidity. However, calves receiving riddelliine at 4.5 mg/kg/d for 20 days had neither serum enzyme changes nor clinical signs of pyrrolizidine alkaloidosis. Calves treated with riddelliine N-oxide (40.5 mg/kg/d), and with riddelliine (4.5 mg/kg/d) and riddelliine N-oxide (40.5 mg/kg/d) in combination, had 100% morbidity, although the latter group had fewer liver lesions. These results establish that the N-oxide form of the alkaloid alone is capable of inducing typical Senecio toxicosis in cattle and that the free base level of the plant cannot be considered to be the sole factor in assessing the toxicity of S riddellii.
以已知致死率给犊牛灌喂Riddell千里光（Senecio riddellii），并将其毒性与从该植物中分离出的吡咯里西啶生物碱——阔叶千里光碱和阔叶千里光碱N -氧化物的毒性进行比较，后者通过瘤胃内输注给药。生物碱的剂量根据测定的植物中的含量进行调整，并单独和联合投喂。通过临床症状、血清酶变化、发病存活时间和组织学变化来衡量犊牛的相对中毒情况。连续20天给犊牛灌喂Riddell千里光，以提供45毫克总吡咯里西啶生物碱/千克体重/天，犊牛出现了千里光中毒的典型临床症状和血清酶变化，发病率为100%。然而，连续20天接受4.5毫克/千克/天阔叶千里光碱的犊牛既没有血清酶变化，也没有吡咯里西啶生物碱中毒的临床症状。用阔叶千里光碱N -氧化物（40.5毫克/千克/天）以及阔叶千里光碱（4.5毫克/千克/天）和阔叶千里光碱N -氧化物（40.5毫克/千克/天）联合处理的犊牛发病率为100%，尽管后一组的肝脏病变较少。这些结果表明，仅生物碱的N -氧化物形式就能够在牛中诱发典型的千里光中毒，并且该植物的游离碱水平不能被视为评估Riddell千里光毒性的唯一因素。
