USDA-ARS, Forage-Animal Production Research Unit, Lexington, KY 40546, USA.
J Anim Sci. 2012 Feb;90(2):682-93. doi: 10.2527/jas.2011-4323.
As part of a 2-yr study documenting the physiologic impact of grazing endophyte-infected tall fescue on growing cattle, 2 experiments were conducted to characterize and evaluate effects of grazing 2 levels of toxic endophyte-infected tall fescue pastures on vascular contractility and serotonin receptors. Experiment 1 examined vasoconstrictive activities of 5-hydroxytryptamine (5HT), α-methylserotonin (ME5HT; a 5HT(2) receptor agonist), d-lysergic acid (LSA), and ergovaline (ERV) on lateral saphenous veins collected from steers immediately removed from a high-endophyte-infected tall fescue pasture (HE) or a low-endophyte-infected mixed-grass (LE) pasture. Using the same pastures, Exp. 2 evaluated effects of grazing 2 levels of toxic endophyte-infected tall fescue on vasoconstrictive activities of (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), BW 723C86 (BW7), CGS-12066A (CGS), and 5-carboxamidotryptamine hemiethanolate maleate (5CT), agonists for 5HT(2A),( 2B), 5HT(1B), and 5HT(7) receptors, respectively. One-half of the steers in Exp. 2 were slaughtered immediately after removal from pasture, and the other one-half were fed finishing diets for >91 d before slaughter. For Exp. 1, maximal contractile intensities were greater (P < 0.05) for steers grazing LE pastures than HE pastures for 5HT (73.3 vs. 48.9 ± 2.1%), ME5HT (52.7 vs. 24.9 ± 1.5%), and ERV (65.7 vs. 49.1 ± 2.6%). Onset of contractile response did not differ for 5HT (P = 0.26) and ERV (P = 0.93), but onset of ME5HT contraction was not initiated (P < 0.05) in HE steers until 10(-4) compared with 10(-5) M in LE-grazing steers. For Exp. 2, maximal contractile intensities achieved with DOI were 35% less (P < 0.05), whereas those achieved with 5CT were 37% greater (P < 0.05), in steers grazing HE pastures. Contractile response to CGS did not differ between pasture groups, and there was an absence of contractile response to BW7 in both groups. There were no differences between endophyte content in contractile responses after animals were finished for >91 d. Experiment 1 demonstrated that grazing of HE pastures for 89 to 105 d induces functional alterations in blood vessels, as evidenced by reduced contractile capacity and altered serotonergic receptor activity. Experiment 2 demonstrated that grazing HE pastures alters vascular responses, which may be mediated through altered serotonin receptor activities, and these alterations may be ameliorated by the removal of ergot alkaloid exposure as demonstrated by the absence of differences in finished steers.
在一项为期 2 年的研究中，记录了放牧内生菌感染高羊茅对生长牛的生理影响，进行了 2 项实验，以描述和评估 2 种不同水平的有毒内生菌感染高羊茅草地对血管收缩性和血清素受体的影响。实验 1 检查了 5-羟色胺（5-HT）、α-甲基血清素（ME5HT；5-HT2 受体激动剂）、d-麦角酸（LSA）和麦角新碱（ERV）对来自立即从高内生菌感染高羊茅草地（HE）或低内生菌感染混合草草地（LE）中取出的侧隐静脉的血管收缩活性。使用相同的牧场，实验 2 评估了放牧 2 种不同水平的有毒内生菌感染高羊茅对（±）-1-（2,5-二甲氧基-4-碘苯基）-2-氨基丙烷盐酸盐（DOI）、BW723C86（BW7）、CGS-12066A（CGS）和 5-羧酰胺色胺半乙醇酸盐马来酸盐（5CT）的血管收缩活性的影响，分别为 5-HT2A、5-HT2B、5-HT1B 和 5-HT7 受体的激动剂。实验 2 中的一半牛在从牧场取出后立即屠宰，另一半牛在屠宰前饲养了>91 天的育肥日粮。对于实验 1，来自放牧 LE 草地的牛的最大收缩强度大于来自 HE 草地的牛（5-HT 为 73.3%对 48.9%±2.1%；ME5HT 为 52.7%对 24.9%±1.5%；ERV 为 65.7%对 49.1%±2.6%）。5-HT（P=0.26）和 ERV（P=0.93）的收缩反应起始时间没有差异，但在 HE 放牧牛中，ME5HT 收缩的起始时间直到 10-4 才开始，而在 LE 放牧牛中则在 10-5 M 时开始。对于实验 2，在放牧 HE 草地的牛中，DOI 达到的最大收缩强度降低了 35%（P<0.05），而 5CT 达到的最大收缩强度增加了 37%（P<0.05）。在两组中，CGS 的收缩反应没有差异，BW7 在两组中都没有收缩反应。在动物育肥>91 天后，内生菌含量对收缩反应没有影响。实验 1 表明，在 89 至 105 天内放牧 HE 草地会导致血管功能发生变化，这表现为收缩能力降低和血清素受体活性改变。实验 2 表明，放牧 HE 草地会改变血管反应，这可能是通过改变血清素受体活性来介导的，而通过去除麦角生物碱暴露可以改善这些变化，这在育肥牛中没有差异得到证明。
