Effects of exposure to chronic ergot alkaloids on phenylephrine contractile response of maternal pedal artery, umbilical artery, and umbilical vein in pregnant ewes.

Ergot alkaloids are known to cause devastating effects in livestock. The objectives of this study were to evaluate the effects of prolonged ergot exposure on selected vasculature in pregnant sheep and to examine the role of alpha-1 adrenergic receptors in mediating these effects. Twelve 60-day pregnant sheep were randomly placed into control and exposure groups (n = 6/group). Ergot-contaminated feed pellets were given orally once a day for 45 d to the exposure group [46.6 μg/kg body weight (BW) total ergot alkaloids]. The control group (Ctl) received ergot-free pellets. The maternal pedal artery from the left hindlimb and the umbilical artery and vein were dissected and mounted in a tissue bath. The vascular contractile response to a cumulatively increasing dose of phenylephrine (PE) in the exposure group (Exp) was compared with the control groups. Chronic exposure to ergot alkaloids resulted in a 70.6% and 91.3% increase in PE contractile response in the umbilical artery (Ctl EC₅₀ = 3.962 × 10^-6; Exp EC₅₀ = 1.161 × 10^-6, P < 0.0001) and the umbilical vein (Ctl EC₅₀ = 7.889 × 10^-6; Exp EC₅₀ = 6.801 × 10^-7, P < 0.0001), respectively, but there was no increase in the pedal artery (P = 0.3927), when compared to the control group. Fetal weight in the ergot-exposed group was significantly lower than in the control group (Ctl 3.3 ± 0.17 kg; Exp 2.07 ± 0.13 kg, P = 0.0002). The increase in contractile response in the umbilical vein may result in decreased blood supply to the fetus causing decreased fetal weight. Negative impact was seen at significantly lower levels of ergot alkaloids than what is currently allowed by Canadian standards, which suggests that these limits should be reevaluated to ensure livestock safety.