The Effects Of Salidroside On Growth Performance And Expression Of CaSR In Pulmonary Artery Of Plateau Broilers

Rhodiola is widely used in preventing and treating altitude sickness.The anti-hypoxia effect and clinical application of salidroside,the main active ingredient of Rhodiola,have been studied extensively,but the mechanism of preventing broilers ascites has not been reported yet.The incidence rate and mortality rate of broiler ascites are extremely high in the plateau area,there are two reasons for this phenomenon.On the one hand,increased hematokrit in the blood increases pulmonary vascular resistance,which will cause pulmonary artery pressure rise,and resulting in right cardiac hypertrophy.On the other hand,the up-regulated expression of calcium-sensitive receptor（CaSR）in the pulmonary artery smooth muscle promotes the increase of[Ca²⁺]_cytin the cells,leading to increased proliferation of the pulmonary artery smooth muscle cells（PASMCs）,which result in pulmonary vascular remodeling,and eventually form pulmonary hypertension（PAH）syndrome,named ascites（AS）.In order to reveal the molecular mechanisms of the salidroside targeted CaSR regulate pulmonary hypertension and preventing effect of plateau broilers AS,180 AA broilers raised in Tibet Agricultural and Animal Husbandry University（The altitude is 2 990 m）were randomly divided into three groups:hypoxia group（the air oxygen content of this broiler house in the natural plateau hypoxia environment with altitude of2 990 m is 14.0%～16.0%）,normal oxygen group（the air oxygen content of this broiler house is 20.8%～21.5%）and salidroside group（the diet supplemented with 0.2%salidroside powder in natural plateau hypoxia environment）,with four replicates in each group.The average daily gain（ADG）,average daily feed intake（ADFI）and feed conversion rate（FCR）of broilers in each group were measured during the trial period of 42 days,the mortality rate and the etiology was recorded and analyzed at the same time.The right ventricular（RV）hypertrophy index,serum Ig A,Ig G and Ig M levels and serum antioxidant indexes of broilers in each group were determined.Western blot and RT-q PCR assay were used to detect the expression levels of CaSR protein and m RNA,and immunohistochemical assay was used to study the distribution of CaSR protein in pulmonary artery tissue.Results:After 42 days of feeding,ADG,ADFI,SOD,GSH-Px,Ig A and Ig G of broilers in salidroside group and normal oxygen group were significantly higher than those in hypoxic group（P<0.05）,MDA index was significantly lower than that of hypoxia group（P<0.05）;CAT index in normal oxygen group was significantly higher than that in hypoxic group（P<0.05）;There were no significant differences in FCR and Ig M among the three groups（P>0.05）;Right ventricular index,total mortality and ascites mortality in salidroside group and normal oxygen group were significantly lower than those in hypoxic group（P<0.05）;The m RNA and protein expression levels of CaSR gene in salidroside group and normal oxygen group were significantly lower than those in hypoxia group（P<0.05）,there was no significant difference between the first two groups（P>0.05）;There was positive expression of CaSR protein in the cytoplasm of pulmonary artery smooth muscle cells of broilers in these three groups,the positive expression rate of CaSR protein in the salidroside group and normal oxygen group was lower than that in the hypoxia group.Conclusions:The expression of CaSR in pulmonary artery tissue reduced after feeding the salidroside,we presumed that the reduced CaSR can reduce[Ca²⁺]_cytin PASMCs,then inhibit cell proliferation and improve pulmonary vascular remodeling,at the same time,the salidroside can maintain normal right heart index and pulmonary artery pressure,which can prevent PAH of broilers.In addition,salidroside can enhance the body resistance and adaptability by improving the serum antioxidant,Ig G and Ig A levels of broilers.That would provide a new idea for the prevention and treatment of AS in broilers.