Administration of triiodothyronine and dopamine to broiler chicks increases growth, feed conversion and visceral organ mass

Central administration of neuropeptide Y differentially regulates monoamines and corticosterone in heat-exposed fed and fasted chicks

Recently, we demonstrated that brain neuropeptide Y (NPY) mRNA expression was increased in heat exposed chicks. However, the functions of brain NPY during heat stress are unknown. This study was conducted to investigate whether centrally administered NPY affects food intake, rectal temperature, monoamines, stress hormones and plasma metabolites in chicks under high ambient temperatures (HT). Five or six-day-old chicks were centrally injected with 0, 188 or 375pmol of NPY and exposed to either HT (35±1°C) or a control thermoneutral temperature (CT; 30±1°C) for 3h whilst fed or fasted. NPY increased food intake under both CT and HT. NPY reduced rectal temperature 1 and 2h after central administration under CT, but not under HT. Interestingly, NPY decreased brain serotonin and norepinephrine concentrations in fed chicks, but increased concentrations of brain dopamine and its metabolites in fasted and fed chicks, respectively. Plasma epinephrine was decreased by NPY in fed chicks, but plasma concentrations of norepinephrine and epinephrine were increased significantly by NPY in fasted-heat exposed chicks. Furthermore, NPY significantly reduced plasma corticosterone concentrations in fasted chicks. Plasma glucose and triacylglycerol were increased by NPY in fed chicks, but triacylglycerol declined in fasted NPY-injected chicks. In conclusion, brain NPY may attenuate the reduction of food intake during heat stress and the increased brain NPY might be a potential regulator of the monoamines and corticosterone to modulate stress response in heat-exposed chicks.

Physiological responses of broiler chicks fed various level of dopamine and zinc

The influences of dopamine (DA) and zinc (Zn) on some physiological parameters of plasma such as growth hormone, cholesterol, 3-glyceride and growth rate, feed conversion ratio and abdominal fat of broilers between the ages of 21 to 42 day were investigated. The experiment was designed on a total of 180 commercial meat-type chicks as a randomized complete block with a 3x2x2 factorial arrangement of treatments with three levels of DA (0, 50 and 100 mg kg(-1)) and two levels of Zn (0 and 40 mg kg(-1)) in each sex. At the first day of trial, chicks were randomly distributed in 36 boxes at the same condition until day 15. Then, the treatments were administered in a low dosage for acclimating of chicks to them. From day of 21, the main dose of treatments was used. The effects of DA and Zn and interaction between them on cholesterol concentration of plasma were significant (p < 0.05). But the effects on concentration of growth hormone (GH) and 3-glyceride of plasma were not significant. The maximum concentration ofcholesterol in plasma was observed in male chicks administered 40 mg kg(-1) of Zn and the minimum concentration was related to female chicks administered 50 mg kg(-1) of DA. In this period, the main and interaction effects of all treatments on weight gain mean of chicks were significant. Also, Zn and DA and interaction of DA x sex improved feed conversion ratio (p < 0.05). The results of this experiment confirmed the lipolytic effect of DA on plasma cholesterol and abdominal fat and also showed that consumption of 100 mg kg(-1) of DA plus 40 mg kg(-1) of Zn cause to improve growth performance of male chicks.

Ontogenetic development of rat intestinal bile acid transport requires thyroxine but not corticosterone

Absorption of bile acids by the distal ileum is an essential component of the enterohepatic circulation. In neonatal rats, the appearance of the apical sodium-dependent bile acid transporter (ASBT) at 17 d of age coincides with increases in serum corticosterone and thyroxine. We tested the hypothesis that these hormones modulate ASBT expression during ileal development. Taurocholate uptake into the isolated ileum of normal 20-d-old pups exhibited saturable (K(m) = 0.52 mM, J(max) = 0.34 pmol mg/min) and nonsaturable (K(diff) = 0.015 min(-1)) components and was two to five times greater than uptake in the proximal intestine. Hypothyroid or euthyroid pups received daily thyroxine injections starting at 6 d of age. At 12 d of age, serum concentrations of thyroxine, ileal abundance of ASBT mRNA, and ileal rates of taurocholate uptake were low in hypothyroid pups that received an injection of vehicle (HT-) or thyroxine (HT+) and in euthyroid pups that received an injection of vehicle (ET-) or thyroxine (ET+). At 20 and 26 d, ileal ASBT mRNA abundance and taurocholate uptake rate remained low in HT- pups but increased dramatically in ET- and ET+ pups, paralleling the increase in serum thyroxine. Restoration of normal plasma thyroxine in HT- pups by thyroxine injections (HT+) restored normal ASBT development. Sodium-glucose co-transporter activity and mRNA expression were independent of serum thyroxine levels. Corticosterone levels were significantly lower in pups that were adrenalectomized at 10 d of age. ASBT mRNA abundance and taurocholate uptake rate increased markedly with age but were the same in adrenalectomized, sham-operated, and nonoperated pups. Hence, endogenous thyroxine but not corticosterone regulates the developmentally timed appearance of ASBT.