Regulation Effect Of Ghrelin On Dairy Goat Lactation

Ghrelin, isolated and purified from the rat stomach, is active peptide containing28amino acid residues, and involved in regulating many physiological function such as feeding,GH secretion, energy balance, immune, reproductive and lactation, the data about the effect ofGhrelin on regulating lactation are very few and mostly from rats. In this study, the dairy goatwas the research object. through detecting distribution of Ghrelin and GHSR-1a in dairy goatand the change of hormones related to lactation during lactating period, determine the effectof Ghrelin on regulating lactation of dairy goat, and then through the detection of effect ofGhrelin on the function of mammary tissue and mammary epithelial cells, further todetermine the role of Ghrelin in regulating lactating activity of mammary tissue, The resultswere as follows:1. Ghrelin and its functional receptor GHSR-1a mRNA expressed in the digestive tract,hypothalamus, pituitary, ovary and mammary tissue of dairy goat. In the digestive tract, theGhrelin mRNA and protein expression level was highest in the abomasum. Ghrelin and itsreceptor GHSR-1a positive cells could be detected in the digestive tract, and the Ghrelinpositive cells could be divided into two types: open and closed type. In the intestine, Ghrelinpositive cells located mostly in the intestinal gland epithelium cells, in the esophage, rumenand reticulum, Ghrelin positive cells were basal cells of stratified squamous epithelia, inmammary tissue, Ghrelin positive cells mostly were ductal and acinar epithelial cells.GHSR-1a distributed in the ganglion cells, smooth muscle cells, gland cells of digestive tractand ductal and acinar epithelial cells of mammary tissue. The results show that Ghrelin canregulat lactation by GHSR-1a in the mammary tissue directly，and also regulate lactation byregulating food intake, energy balance and reproduction of the ruminants indirectly.2. Ghrelin mRNA and protein could be detected in the dairy goat abomasum, and Ghrelinand its receptor GHSR-1a mRNA and protein could be also detect in the dairy goat mammarytissue during lactation, Ghrelin and GHSR-1a mainly expressed in mammary duct andmammary epithelial cells. The change trend of Ghrelin in the abomasum was in agreementwith that of β–CS in the mammary tissue. From early lactation to lactation decline period, threvariation trend of GHSR-1a was agreement with that of β-casein in the mammary tissue, it indicates that Ghrelin may regulate lactating via endocrine, paracrine and autocrine manners.3. The expression change of Ghrelin in abomasums, Ghrelin, GHSR-1a and GH inpituitary were consistent with that of milk production during lactation. Early lactation, theexpression of Ghrelin, GHSR-1a and GH expression was relatively low in pituitary, at thepeak of lactation, the expression of Ghrelin, GHSR-1a and GH reached the peak, thengradually decreased. The expression change of growth hormone releasing hormone (GHRH)and somatostatin (SST) were not adjusted to that of GH completely. Early lactation, Theexpression of GHRH and SST were at the lowest level, at the peak of lactation, GHRH levelreached the peak, at the same time the SST level was significantly increased compared withthat in early lactation, decline and dry period, The GHRH level showed the trend ofincrease-decrease-increase, and the SST level showed the trend of decrease-increase-decrease,while the level of GH showed steady downward trend. Results show that changes of Ghrelinand GHSR-1a levels are closely related to changes of amount of lactation, suggesting thatGhrelin can regulate GH secretion interacting with GHRH and SST, and affect lactating ofruminant animals at the hypothalamus and pituitary levels.4. Ghrelin could promote mammary tissue secreting β-casein in vitro, and in a certainrange, this effect of Ghrelin showed time and dose dependence. The effect of10~3pg/mLGhrelin to promote mammary tissue secreting β-casein in vitro was strongest, when theconcentration was increased to104,105pg/mL, The effect of Ghrelin became weakly. Treatedmammry tissue with10~3pg/mL Ghrelin for18h, the effect to promote mammary tissuesecreting β-casein strongest, When the treatment time was24h,30h, the effect of Ghrelindecreased. D-Lys3-GHRP6can inhibit Ghrelin effect on mammary tissue, and this inhibitoryeffect showed dose dependent.5. Ghrelin could promote induce the primary mammary epithelial cells secreting β-casein,and in a certain range, this effect of Ghrelin had time and dose dependence.10~3pg/mLGhrelin had the highest effect to promote primary mammary epithelial cells secreting β-casein,when the concentration was increased to104,105pg/mL, The effect of Ghrelin becameweakly.Treated primary mammary epithelial cells with10~3pg/mL Ghrelin for18h, the effectto promote mammary tissue secreting β-casein strongest, When the treatment time was24h,30h, the effect of Ghrelin decreased. Inhibitor D-Lys3-GHRP6could inhibit the effect ofGhrelin to up-regulating mammary epithelial cells secreting β-casein, and this inhibitingeffect showed dose dependence. Ghrelin can promote the proliferation of primary mammaryepithelial cell, and the effect of10~3pg/mL Ghrelin to promote the proliferation of mammaryepithelial cells was strongest, while the105pg/mL Ghrelin on proliferation of primarymammary epithelial cells have a certain inhibitory effect, but compared with the control group, the difference was not significant.This paper expounded the variation of Ghrelin and its receptor GHSR-1a in dairy goatduring lactation, and revealed the relationship between Ghrelin and its receptor GHSR-1a andother related hormones of dairy goat during lactation in vivo, detected the effect of Ghrelin onmammary tissue and epithelial cell in vitro, and provided the theory basis for furtherresearching molecular mechanism of Ghrelin role during lactation.