PLASMA-CONCENTRATIONS OF PROLACTIN, GROWTH-HORMONE, AND LUTEINIZING-HORMONE IN STEERS ADMINISTERED ERGOTAMINE OR ERGONOVINE

This research investigated whether ergot alkaloids associated with end ophyte-infected tall fescue could alter plasma concentrations of pitui tary hormones that regulate biological processes related to cattle per formance. Seven Angus yearling steers received single i.v. injections of ergotamine tartrate, ergonovine maleate, or saline vehicle in a sim ple cross-over design. Each steer was given a different compound each week. Blood samples were collected at 15-min intervals for 45 min befo re and 240 min after treatments to assess plasma concentrations of pro lactin, growth hormone, and LH. Respiratory rates were measured hourly to ascertain a systemic effect. Ambient temperature averaged 34 degre es C during data collection. Treatment x time was a significant source of variation for respiration rate and plasma concentrations of each h ormone evaluated. Respiration rates were higher for ergonovine than fo r saline (P < .02) and ergotamine (P < .07) 30 min after treatment, bu t they were higher (P < .05) for ergotamine than for ergonovine and sa line by 210 min after treatment. Both alkaloids transiently elevated ( P < .01) plasma growth hormone concentrations compared with before alk aloid treatment and after saline treatment. Ergotamine reduced (P < .0 1) plasma concentrations of prolactin and LH throughout the 120-min pe riod after treatment compared with concentrations before ergotamine tr eatment and after saline treatment. Ergonovine lowered (P < .01) prola ctin concentrations for a shorter time than ergotamine and did not aff ect mean LH concentrations. Results indicated that ergot alkaloids imp licated as contributing agents to fescue toxicosis can alter plasma co ncentrations of pituitary hormones important to cattle production.