by Jesse Bussard
As I explained last week, ergot alkaloids produced by the endophyte in tall fescue have adverse effects on cattle and negatively alter cardiovascular function. If you missed Part 1 and Part 2 of this series, you can read them here and here.
To evaluate the vasoconstriction caused by ergot alkaloids and it’s effects on arterial and venous contractility I examined two methods: a multimyograph system and Color Doppler ultrasonography. Cattle were pulled off endophyte-infected (E+) tall fescue pastures and were evaluated for vascular changes relative to time-off pasture for a 63 day period using the two methods mentioned previously. Our objectives were to determine if changes in vascular contraction and constriction occur in cattle as time-off E+ tall fescue pasture increases and to compare and contrast the multimyograph and Doppler ultrasonography as diagnostic tools for evaluation of hemodynamic and vascular changes in cattle recovering from fescue toxicosis.
The mutlimyograph system uses in vitro bioassays composed of biopsied blood vessels from select areas of the animal’s body to rapidly screen ergot alkaloids and other compounds for vascular activity, specifically contractility (measured in grams of force). Vascular tissue is mounted onto transducer pins in chambers filled with buffer solution to keep it viable. Various compound are added to the buffer solution and then contractile response to the addition is measured and recorded via a special software program.
In vitro experiments of this nature allow researchers to evaluate the direct effects of individual ergot alkaloids in pure form and combinations. This method eliminates the risk of indirect variable effects on physiological functions ergot alkaloids commonly induced in vivo (in the animal). Not only does this allow researchers to test blood vessels from various parts of the body, but also to conduct detailed dose response studies, determine molecular target sites, and provide comparative toxicity information for various ergot alkaloids.
In my particular study, three biopsies per collection day were taken at four different timepoints throughout the 63 day study after cattle were pulled off of endophyte-infected E+ tall fescue pastures. 5-cm sections of the cranial branch of the lateral saphenous vein were dissected from the right hind leg of steers. The vein sections were then taken back to our lab on campus and experiments were run on the multimyograph system the same day to measure contractility of saphenous veins from exposure to ergotamine, an ergot alkaloid. A control group of steers grazed only on bermudagrass were also biospied and contractile responses compared to that of steers that had previously grazed E+ tall fescue.
The second method examined, Color Doppler ultrasonography, was introduced to the medical field in the 1980s and in the 1990s was combined with B-mode (two dimensional, gray scale) scans to produce duplex images. This combination of scan provides an excellent diagnostic and research tool to examine the hemodynamics (the study of blood flow or the circulation), characteristics, and physiology of blood flow and the cardiovascular system. It has been used for this purpose successfully in human medicine, and more recently, in veterinary medicine to assess vasculature in horses. Use in cattle has been less common, but what research has been done has proven ultrasound imaging to be an efficient and non-invasive means of examining vascular changes in peripheral blood vessels (located in extremities). The field technique using Doppler ultrasonography to detect changes in blood flow characteristics of cattle suffering from fescue toxicosis was developed to examine the medial caudaul artery of the tail. Cross-sectional scans taken are useful to determine luminal area (inner area) of the artery, blood flow rate, and evaluate contractile responses of smooth muscle within vascular walls to environmental conditions, pharmaceuticals, and toxicants. Select groups of steers (control group and one group that had grazed E+ tall fescue) in my study were monitored for vascular changes in the caudal artery of the tail at various timepoints throughout the 63 day period. Comparisons were made between control steers and E+ steers and then results were contrasted with those of the multimyograph.
I’m not going to get into the details of the materials and methods of this study as their meticulous and time-consuming, however, if you have specific questions or would like to know more feel free to email me (email@example.com). In the last installment of my thesis post series I’ll go over some of the high points from our results and what this means for the future of diagnostics and research of fescue toxicosis in cattle.
As always, if you have any questions or comments, feel free to leave a comment below or email me (firstname.lastname@example.org). I’ll do my best to get you the right answer. Thanks for reading!