The effect of L-tryptophan on the food intake, rectal temperature, and blood metabolic parameters of 7-day-old chicks during feeding, fasting, and acute heat stress.

Abstract

Exposure to a high ambient temperature (HT) can cause heat stress, which has a negative impact on physiological functions. L-tryptophan (L-Trp) as a precursor of serotonergic and kynurenine (Kyn) pathways, has a calmative effect during different stress statuses. This study was carried out to determine the influence of intraperitoneal injection of Trp on feeding behavior, rectal temperature, and some blood parameters in the heat stress condition. L-tryptophan (25 and 50 mg/kg body weight, BW) was administered intraperitoneally during either HT (39°C) or control temperature (CT; 31°C) for 5 h whilst fed or fasted in 7-day-old chicks. L-tryptophan caused elevation in decreased food intake and significantly decreased rectal temperature during acute heat stress at the dose of 50 mg/kg BW. Rectal temperature reduced in the fasted state at the dose of 50 mg/kg BW, and at the dose of 25 mg/kg BW Trp in the fed state in comparison with the other experimental groups. Reduction of serum glucose, triglyceride, and corticosterone levels was seen during the fed state. L-tryptophan had a significant reducing effect on the serum corticosterone level in the fasted state in comparison with the fed state, and also revealed a significant decline at the dose of 25 mg/kg BW on the elevated serum corticosterone under heat stress. Administration of L-tryptophan leads to increase cumulative food intake and decrease rectal temperature during heat stress. Also, L-Trp causes to decline increased serum corticosterone level under heat stress and fasted state. These findings indicated the potential regulator role of Trp to modulate stress response in heat-exposed chicks.