| Taihe silky fowl (Gallus gallus domesticus brisson) is a special rare chicken withspecial nutritive and medicinal values, and is both consumed as a healthy food and usedparticularly as a kind of traditional Chinese medicine. The pharmacological property ofsilky fowl is mainly ascribable to the plentiful melanins distributed in its various internaltissues. The oxidant/antioxidant homeostasis is an important factor which affects melaninbiosynthesis in tissues. Research has demonstrated that oxidative stress resulted by heatstress is an important mediator for heat stress-induced damage. Whether heat stress couldinfluence melanin synthesis in tissues by affecting antioxidant capability of Taihe silkyfowls? The objective of this study was to investigate the effect of heat stress on melaninsynthesis in Taihe silky fowls and the regulation by selenium (Se) from the perspective ofheat stress-oxidative stress-melanin synthesis-related genes expression(α-MSH－MC1R－cAMP－TRP signaling pathway)-melanin synthesis. Experiments were conducted todetermine lipid peroxidation, antioxidative enzyme activity, tyrosinase activity, melanincontent and melanin synthesis-related genes expression in tissues fowls and effect ofdietary Se on these parameters in heat-stressed Taihe silky in this study.A total of30045-day-old Taihe silky fowls were randomly allotted to5groups with4replicates per group and15birds per replicate. The birds were housed in atemperature-controlled room at either24℃(normal temperature, NT) or daily cyclichigh temperature24℃-37℃-24℃(heat stress treatment, HS) for21days. The birds werefed a corn-based basal diet (TN group) or the basal diet supplemented with0(HS),0.3(HS+0.3),0.5(HS+0.5) and0.7(HS+0.7) mg/kg Se. Blood, hypothalamus, skin, pectoralmuscle, liver and kidney were sampled from Taihe silky fowls for measurements forphysiological and biochemical parameters, melanin contents and gene expression on d0,1,7,14and21during the trial period. The results showed as follows:1. Average daily feed intake (ADFI)(P<0.05or P<0.01) and average daily weightgain (ADG) on d8-14(P<0.01) were significantly decreased, and feed to gain ration(F/G) was increased by24℃—37℃—24℃cyclic heat stress during the experimentalperiod(P>0.05). Dietary Se supplementation significantly increased ADFI ofheat-stressed birds (P<0.05) as compared to heat-stressed birds fed basal diet. Nosignificant difference was observed between treatments with Se supplementation(P>0.05). ADG and F/G in heat-stressed birds were not influenced by dietary Sesupplementation (P>0.05). Serum T3concentration was not influenced by heat stress anddietary Se supplementation, but serum CORT concentration on d1and7during the trialperiod was significantly increased by cyclic heat stress (P<0.05). HSP70mRNA andprotein expression in skin, pectoral muscle and liver of Taihe silky fowls were increasedby heat stress, but decreased by dietary Se supplementation except for HSP70protein expression in skin.2. Cyclic heat stress significantly reduced selenium contents in skin, kidney andpectoral muscle on d1(P<0.01), and liver on1and in pectoral muscle on d7(P<0.05)during the heat stress treatment period. Dietary Se supplementation significantlyincreased Se contents in these tissues of Taihe silky fowls under heat stress (P<0.01).Heat stress significantly depressed the ability of scavenging O2·-in serum on d1and theability of inhibiting·OH in serum on d14post-heat stress (P<0.01). Dietary Sesupplementation improved the abilities of scavenging O2·-and inhibiting·OH in serum toa certain extent ((P<0.05or P>0.05) with the optimum Se supplemental level being0.3and0.5mg/kg. Total antioxidative capacity (T-AOC) and glutathione (GSH) content inserum an total superoxide dismutase (T–SOD), catalase (CAT) activity, glutathioneperoxidase (GSH-Px) activity in liver, kidney, skin and pectoral muschle tended todecrease when compared with normal temperature group. Supplementation with Seimproved T-SOD, CAT and GSH-Px activities in serum and tissues of heat-stressed Taihesilky fowls (P<0.05or P>0.05). Malondialdehyde (MDA) content in skin and pectoralmuscle on d7during the trial period were increased by heat stress (P<0.05), whereasMDA, H2O2and GSH content and T-AOC in tissues on other heat stress treatment dayswere not influenced by heat stress (P>0.05). Dietary Se supplementation improved GSHcontent and T-AOC and reduced MDA and H2O2contents in serum and tissues ofheat-stressed birds (P<0.05or P>0.05). The maximal GSH content and T-AOC, and theminimal MDA and H2O2in serum, liver, kidney, skin and pectoral muscle ofheat-stressed birds were obtained when dietary Se supplemental level was0.5mg/kg.3. Cyclic heat stress tended to reduce α-MSH content in hypothalamus and serum,and dietary Se supplementation tended to increase α-MSH content in these tissues withthe maximum amounts being observed in heat-stressed birds when dietary Sesupplemental level was0.5mg/kg. Heat stress tended to reduce cAMP content in pectoralmuscle, and dietary Se supplementation tended to increase the content in this tissue TheMC1R mRNA expression in liver, skin and pectoral muscle was decreased by heat stress,and dietary Se supplementation improved its expression in these tissues of Taihe silkyfowls exposed to long-term heat stress with the maximum expression being in0.5mg/kgSe supplementation birds. In conclusion, heat stress influenced α-MSH secretion andMC1R gene expression and then cAMP content which are associated with melaninbiosynthesis in Taihe silky fowls tissues. Dietary Se supplementation alleviates negativeeffects on these parameters caused by heat stress.4. Cyclic heat stress reduced TYR, TYRP1and TYRP2mRNA expression in skin,pectoral muscle and liver of taihe silky fowls to a certain extent without significanteffects. Dietary Se supplementation tended to improved the mRNA expression of thesemelanin synthesin-related genes in tissues of heat-stressed birds with the better effects being observed when Se supplemental level was0.3~0.5mg/kg, in which the expressionwas higher than that of NT group. Cyclic heat stress significantly reduced TYRP1proteinexpression in skin, pectoral muscle and liver of Taihe silky fowls (P<0.05or P<0.01) ascompared to NT group, while dietary Se supplementation promoted its expression inthese tissues of heat-stressed birds in comparison with those of HS group (P<0.05orP<0.01). TYRP1protein expression in tissues of heat-stressed birds fed the dietssupplemented with Se was slightly lower on d1post-heat stress, and was higher than thatof NT group on d7,14and21post-heat stress with the highest expression beingobserved when Se supplemental level was0.5mg/kg (P<0.05or P<0.01). TYR activityand melanin contents in skin, pectoral muscle, liver and kidney were decreased to adifferent extent by cyclic heat stress, and were, however, increased with differentpotential by dietary Se supplementation at0.3and0.5mg/kg (P<0.05or P<0.01). Insummary, cyclic heat stress depresses melanin synthesis-related genes expression, andreduces TYR activity and melanin synthesis in tissues of Taihe silky fowls, whereasdietary supplementation with Se may alleviate the negative effects caused by heat stressand better beneficial effect can be obtained when Se supplemental level is0.5mg/kg.In conclusion, heat stress reduced growth performance in Taihe silky fowls tissues,reduced antioxidant function and selenium contents in Taihe silky fowls tissues,heatstress influenced α-MSH secretion and MC1R gene expression and then cAMP contentwhich are associated with melanin biosynthesis in Taihe silky fowls tissues,heat stressdepresses melanin synthesis-related genes expression, and reduces TYR activity andmelanin synthesis in tissues of Taihe silky fowls. Dietary Se supplementation alleviatesnegative effects on these parameters caused by heat stress. So,dietary supplementationwith Se may alleviate the growth performance and melanin synthesis caused by heatstress when Se supplemental level is0.5mg/kg-0.7mg/kg. |
PDF Full Text Request