Regulation Effect & Mechanism Of Melatonin On Fur Development

Melatonin(MT)is an indole hormone secreted by pineal cells in animal.It has extensive biological activities.Many studies reported that MT could regulate the growth cycle of fur in minks,foxes and etc;and promoted the growth of fur and decrease the mature time of fur,but it needs to be corfirmed that MT regulates the development of fur in rabbits.In addition,the regulatory mechanism of MT on fur development has not been reported till now.In order to clarify these scientific problems,firstly,melatonin(MT-P group)and melatonin sustained-release agent(MT-H group)were intraperitoneally injected or implanted into young Kunming mice,respectively;body weight,fur thickness,hair growth and density of mice were weekly detected;the concentrations of MT,insulin-like growth factor-I(IGF-I)and epidermal growth factor(EGF)in blood were detected by ELISA and CCK-8.Melatonin receptor(MTNR1A)mRNA and the distribution of melatonin in skin,liver and brain were detected by fluorescence quantitative RT-PCR and immunohistochemistry.Secondly,melatonin(MT-P group)and melatonin sustained-release agent(MT-H group)were injected or implanted into Angola long-haired rabbits,respectively.Body weight,fur development,blood hormones and melatonin receptor were detected by the above methods.Thirdly,the effects of MT,MT+EGF,MT+IGF-I and MT+IGF-I+EGF on the proliferation of skin cells of mice and Angola rabbits were analyzed by CCK kits in vitro,and their effects on the cell cycle of the skin were detected by flow cytometry.The results were as follows:(1)Both in MT-P group and in MT-H group,body weight of male mice increased by 19.2% and 3% and the skin area increased by 18% and 7.3% in 4weeks,but the skin thickness of mice in MT-H group increased by-30% and the hair length on the back increased by-10.7%,and the intraperitoneal injection group had no significant changes.However,body weight of female mice increased by-9.7% and-22.2% in MT-P group and in MT-H group,respectively;the skin thickness increased by-41.7%,and the hairlength increased by-18.6% and-21.4%.The skin area of female mice in MT-P group increased by 6.3%.The concentration of MT of male mice in MT-H group and in increased by126.4% and 89.2%,respectively;and IGF-I concentration in MT-P group’ mice increased63.3%,and there was no significant difference in MT-H group.MTNR1 A mRNA in skin and liver tissues of mice both in MT-P group and in MT-H group was significantly increased.(2)Compared with control group,body weight in Angola rabbits of MT-P group was increased by6.3%,7.3%,28%,18%,9.2% and hair-length was increased by 19%,11%,11%,15%,7.9%in 0-1 week,in 0-2 weeks,in 0-3 weeks,in 0-4 weeks and in 0-5 weeks,respectively.Body weight in Angola rabbits of MT-H group was increased by 19.3%,21.2%,32.4%,20% and6.7% and hair length was increased by 5.1%,16.8%,7.9%,15.4%,and 6.7% in 0-1 week,in0-2 weeks,in 0-3 weeks,in 0-4 weeks,and in 0-5 weeks,respectively.However,body weight and hair growth both in two groups was decreased from the sixth week to the tenth week.At the tenth week,hair density of two groups’ rabbits was increased by 12.9% and 26.3%,respectively.The concentration of MT in the blood of MT rabbits was significantly increased in MT-P group and in MT-H group,and MTNR1 A mRNA in the skin and brain tissue of the rabbit was also significantly increased.(3)the results of proliferation test in vitro showed that MT could softly promot the proliferation of skin cells in mice and Angola rabbits,but the combination of MT with EGF,IGF-I and EGF+IGF-I could further improve the effects of MT on skin cells of mice and Angola rabbits.Flow cytometric analysis showed that MT could increase the M-phase ratio of mitosis cells in mice and Angola rabbits’ skin cells,and the combination of MT+EGF,MT+IGF-I and MT+EGF+IGF-I could further improve the ratio of M-phase and S-phase of mitosis cells.Conclusion:(1)Exogenous melatonin could promote body growth and fur development in male mice,but not in female mice.(2)Exogenous melatonin could promote body growth and fur development of the male hairy rabbit and improve the production performance in 5weeks,and especially in 3 weeks;and the effect of subcutaneous implantation is better than that of the abdominal cavity.(3)Exogenous melatonin could increase the concentration of MT and IGF-I in blood of mice and Angola rabbits and the expression of MT receptor in the skin and brain tissues.(4)MT-single or-combined with EGF/IGF-I could promote the skin cells of mice and long hair rabbits to enter the division cycle and promote the proliferation of skincells.Those may provide a basis for the scientific application of melatonin.