Ruminal 5-hydroxytryptophan increases serum serotonin and peripheral vasodilation in growing beef cattle

Area of Science:

• Animal Science
• Biochemistry
• Physiology

Background:

• Serotonin synthesis involves tryptophan and 5-hydroxytryptophan (5-HTP) as the immediate precursor.
• 5-HTP bypasses the rate-limiting step, making it a potential tool to increase serotonin levels.
• The efficacy of ruminal 5-HTP in cattle, considering microbial degradation and peripheral effects, is not well understood.

Purpose of the Study:

• To evaluate the impact of abomasal and ruminal 5-HTP administration on peripheral serotonin metabolism.
• To assess the effects of 5-HTP on caudal artery hemodynamics in growing beef steers.
• To determine if ruminally-supplied 5-HTP can escape degradation and influence vascular function.

Main Methods:

• Five ruminally cannulated steers were used in a 5x5 Latin square design.
• Treatments included water, abomasal 5-HTP infusion (0.5 mg/kg BW), and ruminal 5-HTP infusions (1, 2, or 3 mg/kg BW).
• Blood samples analyzed for tryptophan metabolites; caudal artery hemodynamics assessed via Doppler ultrasonography.

Main Results:

• Abomasal 5-HTP increased serum 5-HTP and serotonin concentrations.
• Ruminal 5-HTP increased serum serotonin in a dose-dependent manner, indicating partial escape from degradation.
• High-dose ruminal 5-HTP (3 mg/kg BW) increased caudal artery cross-sectional area, suggesting vasodilation.

Conclusions:

• Ruminal supplementation of 5-HTP effectively increases circulating serotonin in beef steers.
• Sufficient doses of ruminal 5-HTP can induce peripheral vasodilation, as evidenced by increased caudal artery size.
• This study provides in vivo evidence for 5-HTP-associated vasodilation in cattle and supports ruminal delivery for modulating serotonergic and vascular function.