Effect of an acute ergotamine challenge on reproductive hormones in follicular phase heifers and progestin-treated cows

Abstract

The objective of this research was to determine if ergotamine, an ergopeptine alkaloid isolated from Neotyphodium-infected grasses and associated with toxicoses in livestock, altered plasma concentrations of reproductive hormones in follicular phase heifers and in cows given a progestin implant. In Experiment 1, blood was sampled for 8 h from four cycling heifers 2 days after synchronized luteolysis. Heifers were treated with ergotamine tartrate (19 μg/kg) i.v. or saline vehicle in a simple cross-over design after 1 h of pre-treatment blood sampling. Heifers received oxytocin (100 USP units) i.v. 4 h after ergotamine or saline treatment. Ergotamine reduced ( P<0.01) prolactin concentrations from 1 to 4 h post-treatment and increased ( P<0.01) 13,14-dihydro-15-keto prostaglandin F 2α (PGFM) concentrations from 2 to 5 h post-treatment. A PGFM response to oxytocin was not detected. In Experiment 2, blood was sampled for 8 h from six cycling cows 10 days after receiving a s.c. norgestomet implant. Cows were treated i.v. with ergotamine (20 μg/kg) or saline in a simple cross-over design after 1 h of pre-treatment blood sampling. Cows received gonadorelin (GnRH, 100 μg) i.v. 1 h after ergotamine or saline. Cows received oxytocin (100 USP units) i.v. 4 h after ergotamine or saline treatment. Ergotamine reduced ( P<0.01) serum prolactin concentrations by 120 min after treatment, with prolactin returning to pre-treatment concentrations by 200 min after treatment. Saline-treated cows had lower ( P<0.01) prolactin by 280 min after treatment. Ergotamine-treated cows had higher ( P<0.01) PGFM concentrations compared to saline-treated cows 120–240 min after treatments, but the groups exhibited similar increases in PGFM after oxytocin. Plasma LH and FSH concentrations increased to peaks 100–120 min after GnRH for both groups. However, the LH response to GnRH was greater ( P<0.01) for ergotamine-treated cows. In summary, ergotamine lowered prolactin and elevated PGFM concentrations in follicular phase heifers and cows on norgestomet therapy. Ergotamine increased the LH response to exogenous GnRH in cows with norgestomet implants. These data highlight the potential of ergopeptine alkaloids to affect reproduction through altered endocrine function.