Residual effects of abomasal 5-hydroxytryptophan administration on serotonin metabolism in cattle

5-hydroxytryphophan mitigates ergot alkaloid-induced suppression of serotonin and feed intake in cattle

The impact of ergot toxicosis on livestock industries is detrimental and treatments are needed in many countries. The objective of this study was to evaluate the effects of acute exposure to ergot alkaloids and 5-hydroxytryptophan (5-HTP) supplementation on feed intake, serotonin metabolism, and blood metabolites in cattle. Eight Holstein steers (538 ± 18 kg) fitted with ruminal cannulas were used in a replicated 4 × 4 Latin Square design experiment with a 2 × 2 factorial treatment structure. The treatments were the combination of 0 (E-) or 15 µg ergovaline/kg BW (E+) and 0 (5HTP-) or 0.5 mg of 5-hydroxy-l-tryptophan/kg BW (5HTP+) administered daily for 6 d. Toxic endophyte-infected tall fescue seed was used to supply the daily dose of ergovaline. Endophyte-free seed was used to equalize seed intake between treatments. Ground seed was placed into the rumen immediately before feeding. The 5-HTP was dissolved in water and infused into the abomasum via the reticulo-omasal orifice. Blood was collected from a jugular vein catheter at 0, 1, 2, 4, 8, and 24 h after treatment administration. Ergovaline without 5-HTP (E+/5HTP-) decreased dry matter intake (DMI) in comparison to steers without ergovaline and 5-HTP (E-/5HTP-). However, 5-HTP infusion in association with ergovaline (E+/5HTP+) normalized the DMI. Although E + did not affect (P > 0.05) the area under the curve (AUC) of serum 5-HTP, 5-hydroxyindoleacetic acid, tryptophan, and kynurenine, serum and plasma serotonin concentrations were decreased (P < 0.05). The infusion of 5-HTP increased (P < 0.05) the AUC of serum 5-HTP, serum and plasma serotonin, and serum 5-hydroxyindoleacetic acid. In conclusion, acute exposure to ergot alkaloids reduced DMI and circulating serotonin in cattle but 5-HTP administration showed potential to normalize both circulating serotonin and feed intake.

Influence of intra-abomasal administration of L-DOPA on circulating catecholamines and feed intake in cattle

Dopamine has multiple physiological functions including feed intake control in which it can act as an anorectic or orexigenic agent. This study had the objective to evaluate intra-abomasal administration of L-DOPA (levodopa; L-3,4-dihydroxyphenylalanine) from -Mucuna pruriens on circulating catecholamines, indicators of energy metabolism and feed intake in cattle. Eight Holstein steers (340 ± 20 kg) fitted with ruminal cannula were used in a replicated 4 x 4 Latin Square design experiment. Intra-abomasal infusion of L-DOPA at 0, 0.5, 1 and 2 mg/kg BW was carried out for seven days and blood samples were collected at 0, 30, 60, 120, 240 and 480 min from L-DOPA infusion on day 7. The area under the curve (AUC) of plasma L-DOPA and free dopamine increased quadratically with the administration of L-DOPA. However, the AUC of plasma total dopamine had a positive linear response with the increase of L-DOPA. Conversely, the serum 5-hydroxytriptophan (5-HTP), plasma serotonin, serum serotonin, serum tyrosine, plasma glucose and plasma free fatty acids were not affected by the intra-abomasal infusion of L-DOPA. The circulating concentration of the epinephrine, norepinephrine, serotonin, glucose and free fatty acids did not change with L-DOPA infusion. It can be concluded that intra-abomasal L-DOPA administration produced a strong increase in circulating dopamine with no change in energy metabolites and feed intake in cattle.

Influence of Prolonged Serotonin and Ergovaline Pre-Exposure on Vasoconstriction Ex Vivo

Ergot alkaloid mycotoxins interfere in many functions associated with serotonergic neurotransmitters. Therefore, the objective was to evaluate whether the association of serotonin (5-hydroxytryptamine, 5-HT) and ergot alkaloids during a 24 h pre-incubation could affect the vascular contractile response to ergot alkaloids. To evaluate the effects of 24 h exposure to 5-HT and ergot alkaloids (ergovaline, ERV), two assays were conducted. The first assay determined the half-maximal inhibitory concentration (IC₅₀) following the 24 h pre-exposure period, while the second assay evaluated the effect of IC₅₀ concentrations of 5-HT and ERV either individually or in combination. There was an interaction between previous exposure to 5-HT and ERV. Previous exposure to 5-HT at the IC₅₀ concentration of 7.57 × 10⁻⁷ M reduced the contractile response by more than 50% of control, while the exposure to ERV at IC₅₀ dose of 1.57 × 10⁻¹⁰ M tended to decrease (p = 0.081) vessel contractility with a response higher than 50% of control. The 24 h previous exposure to both 5-HT and ERV did not potentiate the inhibitory response of blood vessels in comparison with incubation with each compound alone. These results suggest receptor competition between 5-HT and ERV. More studies are necessary to determine the potential of 5-HT to treat toxicosis caused by ergot alkaloids.