Effect And Mechanism Of Pirenzepine On Iens-induced Myopia In The Guinea Pigs

Refractive error in myopia in the world with the highest incidence rate, high myopia can seriously damaged the visual function. The study of the mechanism of myopia has more the 200 years history, but can not clearly explain its mechanism, it is looking forward to a better understanding of the mechanism of myopia and clinical effectively drug which can inhibit the development of myopia appeared.Three decades of the 20th century, it established two animal models of myopia: form deprivation myopia (FDM) and lens-induced myopia (LIM). LIM models are research animals which the basis is simulated on the models of human myopia, the mechanism of myopia they produced are different. LIM models are similar with the physiological mechanisms of human myopia prototype, so research the mechanism of LIM will contribute to the understanding of human myopia.Pirenzepine as a selective M1-receptor antagonist, currently the effect of pirenzepine on the LIM has been reported at home and abroad, pirenzepine ophthalmic solution has been proven to be effective at preventing the elongation of axial in the lens-induced experimented myopia in guinea pig, and it can inhibit the development of experimental myopia with no obvious damage to the ocular tissues. However, the nature of its role, mechanism, and position are not cleared, they need for further studies. Also there had few relevant reports about the relationship between dopamine system and effect of pirenzepine on LIM.This study was to establish LIM model in guinea pigs, to analyze the expression of tyrosine hydroxylaze (TH)-the rate limiting enzyme in the formation of DA and dopamine transporter (DAT), explore the mechanism of pirenzepine inhibiting LIM, and the relationship between pirenzepine and DA system.Materials and MethodsForty two-weak-old guinea pigs were randomly divided into 4 groups (n=10),Ⅰlens-induced myopia group:simply covered the right eye, no eye drop application.Ⅱ:0.9% Nacl solution group:the right eye was covered, and treated with 0.9% Nacl solution twice a day.Ⅲ:pirenzepine group:the right eye was covered, and treated with pirenzepine ophthalmic solution twice a day.Ⅳ:normal control group:no cover no eye drop application. In the all groups, the right eyes were the experimental eyes, wear -10.0D simple spherical goggles, on the bottom of goggles reserved spaces for convenient drop eye solution and wipe the lens. The left eyes served as control eyes with no treatment. Guinea pigs kept indoors, at 12h/12h circadian rhythm raise for 4 weeks.Ocular refraction and axial length measurement were made before experiment and 4 weeks later. Six were randomly selected in each group and immunohistochemistry was used to analyze the expression of TH and DAT in the retina.Results1. Comparing refraction change in groups before and after experiment There was no significant difference between every group before experiment. Compared with experimental eyes after 4 weeks:compared the refraction changes, lens-induced myopia group (-4.70±0.39D) and Nacl group (-4.50±0.75D) all formed myopia and had a significant difference compared with normal control group (0.40±1.50D) (P<0.05). Pirenzepine group's diopter (-2.15±1.02D) had a significant lower compared with lens-induced myopia grou and Nacl group. There was no significant difference between lens-induced myopia group and Nacl group(P>0.05).2. Comparing axial length change in groups before and after experimentThere was no significant difference between every group before experiment. Compared with experimental eyes after 4 weeks:compared the axial length changes, There was no significant difference between pirenzepine group (7.66±0.18mm) and normal control group (7.64±0.18mm) (P>0.05), lens-induced myopia group (8.02±0.17mm) and Nacl group (7.86±0.19mm) all formed longer axial length and had a significant difference compared with pirenzepine group (P<0.05). There was no significant difference between lens-induced myopia group and Nacl group (P>0.05).3. The result of immunohistochemistryThe express of TH in the retina:Immunohistochemistry staining shows that the positive expression of TH positive cells display as brown, TH positive cells were mainly distributed in the inner nuclear layer and outer nuclear layer, especially in the outer nuclear layer. Compared the number of positive cell count of TH in the retina: there had a significant difference between lens-induced group (29.80±3.59) and Nacl group (31.20±1.64) compared with normal control group (47.60±3.03) and pirenzepine group (44.80±4.66) (P＜0.05). There was no significant difference between pirenzepine group and normal control group (P>0.05)The express of DAT in the retina:Immunohistochemistry staining shows that the positive expression of DAT positive cells display as brown, DAT positive cells were mainly distributed in the inner nuclear layer and photoreceptor of the retina, a small portion of the outer nuclear layer and the pigment epithelium. Compared the number of positive cell count of DAT in the retina:there had a significant difference between lens-induced group (24.20±3.73) and Nacl group (23.40±2.77) compared with pirenzepine group (35.60±3.74) and normal control group (37.00±3.48) (P<0.05). There was no significant difference between pirenzepine group and normal control group (P>0.05)Conclusions1.-10.OD lens goggles covered with 4 weeks later, guinea pigs developed obvious myopia, axial length lengthen, lens-induced myopia modeling success.2. The expression of TH and DAT in the LIM retina was decreased, speculated that retinal dopamine system may be involved in the occurrence of LIM.3. Refraction and axial length showed that a certain degree of pirenzepine can inhibit the development of LIM and extend the axial length.4. Pirenzepine can prevent the reduction of TH and DAT expression in the LIM retina to a certain extent, speculates that pirenzepine may be by affecting retinal dopamine system and increasing the release of retinal dopamine to block the development of LIM.