| Objective: Levonorgestrel (LNG) is a sort of the second generation progesterone oral contraception. Inhibition of folliculogenesis and ovulation is the principal objective of oral contraception. The contraception mechanism of LNG is mainly attributed to a negative feedback regulation of synthetic steroids on hypothalamic-pituitary-ovary axis, which is thought to depress luteinizing hormone(LH) level and follicle-stimulating hormone(FSH) secretion during oral contraceptive use. However, most research about LNG on ovary focus on clinical hormone level and so on, the morphological reports had not been found till now. We observed the changes of histology and ultrastructure of rat ovary, LH positive cell, FSH positive cell and FSHR positive cell with immunohistochemistry and computer image processing technology, as well as transmission electron microscopy, so as to obtain target level's morphological data of hypothalamic-pituitary-ovary axis during progesterone contraceptive administration.Method: 24 normal Sprague Dawlay femal rats having regular sexed cycle (4-5 days) were used, and 14 of those were in treated group, which was divided into drug-given group and drug-stop group. LNG 50mg/kg/day(100mg LNGdissolves in 30ml oil) was administrated to rats in drug-given group at 9'oclock everyday. After having been fed for 90 days, seven rats were sacrificed as drug-given group, but the others continued to be fed normally, and were killed twenty days later as drug-stop group. 10 rats were administrated with the same dose of oil as contrast. Tissues were fixed through heart ascending aerta, then ovary tissues were taken quickly. After gradient alcohol dehydration, embedding and cutting into sections, we observed the changes of histology and ultrastructure of rat ovary, LH positive cell, FSH positive cell and FSHR positive cell with HE staining, transmission electron microscopy and immunohistochemistry.Results: 1. The results of HE staining showed that: compared with control group, there were more primordial follicles and less typical growing follicles and mature follicles in cortex of rat ovary in the drug-given group. However, both in drug-stop group and in its control group, we can observe follicles in different phases, especially many growing follicles. 2. Under electron microscope, we observed that, compared with control group, there were less organellas such as agranular endoplasmic reticulum, Golgi complex body and mitochondria in lutein cell of rat ovary. These changes indicated that function of cell was inhibited. But we also observed typical growing follicle in drug-stop group having normal ultrastructure. 3. Compared with contrast, optical density of LH positive cell decreased andimmune staining was lighter in drug-given group. There were no difference between drug-stop group and its control group. It means that the changes returned to the normal level. 4. Compared with contrast, optical density of FSH positive cell and FSHR positive cell decreased in drug-given group. Immune staining in drug-given group was lighter than those of drug-stop group. There were no differences between drug-stop group and its control group. 5. There were no difference between optical density of FSH positive cell and FSHR positive cell in the same group, and so was immune staining . Conclusion: After LNG being administrated to rats for a long time, LH, FSH, FSHR level in ovary follicle decreased. The reasons about changes were probably as follows: administration of LNG affected the synthesis of hypothalanic GnRH neuron, and the secretion of GnRH, meanwhile, gonadotrophin secreted by pituitary decreased and LH, FSH level in ovary follicle decreased also stimultaneously. Under low E and FSH density, the expression of FSHR decreased. Low FSH level effected ovary follicle development. LH surge before ovulation was blocked farther, then ovulation was inhibited. But all the changes mentioned can returned to the normal level after stopping drug, so we can concluded that LNG is a kind of progesterone oral contraceptive having...
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