Role of brain nitric oxide in the thermoregulation of broiler chicks

Abstract

Nitric oxide (NO) plays a key role in body temperature (Tb) regulation of mammals, acting on the brain to stimulate heat loss. Regarding birds, the putative participation of NO in the maintenance of Tb in thermoneutrality or during heat stress and the site of its action (periphery or brain) is unknown. Thus, we tested if NO participates in the maintenance of chicks' Tb in those conditions. We investigated the effect of intramuscular (im; 25, 50, 100mg/kg) or intracerebroventricular (icv; 22.5, 45, 90, 180 microg/animal) injections of the non selective NO synthase inhibitor L-NAME on Tb of 5-day-old chicks at thermoneutral zone (TNZ; 31-32 degrees C) and under heat stress (37 degrees C for 5-6h). We also verified plasma and diencephalic nitrite/nitrate levels in non-injected chicks under both conditions. At TNZ, 100mg/kg (im) or 45, 90, 180 microg (icv) of L-NAME decreased Tb. A significant correlation between Tb and diencephalic, but not plasma, nitrite/nitrate levels was observed. Heat stress-induced hyperthermia was inhibited by all tested doses of L-NAME (im and icv). Tb was correlated neither with plasma nor with diencephalic nitrite/nitrate levels during heat stress. These results indicate the involvement of brain NO in the maintenance of Tb of chicks, an opposite action of that observed in mammals, and may modulate hyperthermia.

Dietary L-Citrulline supplementation modulates nitric oxide synthesis and anti-oxidant status of laying hens during summer season

“…Similar report by Kim et al (80) showed that citrulline ingestion improved NO synthesis rate. Also, N G -nitro-L-arginine methyl ester (L-NAME), a nonselective NOS inhibitor, when administered to chicks was able to inhibit heat stress induced hyperthermia, however, the plasma levels of Nitrite/ Nitrate levels were unaffected (22). This findings differ from Chowdhury et al (45) who reported that oral injections of L-Cit did not significantly increase plasma NOx concentrations both under ambient temperatures or heat stressed conditions.…”

“…During thermal stress, NO as an endothelial vasodilator (21) acts to stimulate peripheral blood flow, thereby increasing autonomic heat dissipation. Likewise in chicks, NO has been shown to act via the central nervous system (CNS) to regulate body temperature (22). Most biological functions of NO are mediated via the activities of the NO synthase (NOS), which includes, endothelial NOS (eNOS), neuronal NOS (nNOS) and the inducible NOS (iNOS) isoform (23).…”

Impact of Environmental Thermal Stimulation on Activation of Hypothalamic Neuronal Nitric Oxide Synthase during the Prenatal Ontogenesis in Muscovy Ducks

“…But in birds also under these conditions the role of NO seems to be different from that observed in mammals. In 5-days-old chicks under thermoneutral and heat stress conditions intramuscular as well as intracerebroventricular injections of NOS inhibitor L-NAME decreased body temperature and thus inhibited heat stress-induced hyperthermia [16]. …”

“…In mammals and birds, during different developmental periods, NO plays a crucial role in regulation of various physiological functions, which are mediated by the hypothalamus, like thermoregulation [12–16], water balance [17, 18] and fever [19, 20], feeding behaviour [21–25], energy balance [26], and cardiovascular regulation [27–29]. However, in birds under thermoneutral conditions or heat load, for instance, the thermoregulatory effect of NO seems to be different from that in mammals [16], in which central NO mostly induces heat loss responses and finally decreases body temperature [30].…”

“…However, in birds under thermoneutral conditions or heat load, for instance, the thermoregulatory effect of NO seems to be different from that in mammals [16], in which central NO mostly induces heat loss responses and finally decreases body temperature [30]. …”