Study On Mechanism Of Acute Regulation Of Piglet Testosterone Synthesis

Improving animal reproductivity is not only an aim of biology of reproduction ,but also a question which must be resolved in husbandry.The capacity of steroidogenesis is an important factor affecting animal reproductivity.In the past fifty years, regulatory mechanism of steroidogenesis has been a focus of Endocrinology.Many studies indicated that Gonadotropn regualated steroidogenesis in chronic reaction period in vitro or in vivo and these results formed a base for regulatory mechanism of steroidogenesis.Recentlysome studies have indicated that acute regulatory meachanism of steroidogenesis is also an important factor affecting animal reproduction.while these studies focused on experiment animals or female animals.studies on acute regulatory mechanism of domestic animal's steroidogenesis is necessary.Since swines were a breed with high reproductivity, we have studied mechanism of acute regulation of piglet testosterone synthesis.The rate-limiting step in steroid hormone production in the adrenal cortex and gonads, the translocation of cholesterol from the outer to the inner mitochondrial membranes, is mediated by the sieroidogenic acute regulatory protein (StAR). Heretofore, the localization of StAR in piglet from 1st to 5* week has not been defined. To this end, expression of StAR was detected in formalin-fixed, paraffin-embedded specimens using a polyclonal antiserum raised StAR and studied the relation between the expressions of StAR protein and the level of testosterone by immunohistchemistry and Radioimmunoassay(RIA).The results indicated that in the testes of piglets, StAR protein were expressed in Leydig cells of pig testes from l-5th week. The expression level of StAR protein was lower in 1th and 3rd week piglets but higher in 2rd and 4th week; the expression level of StAR protein in 5 th week was higher than that in 1th and 3rd week,but lower than that in 2rd, 4th week.The level of testosterone reached the highest point at 2 nd and 3 rd week- old. After that, The level of testosterone started to fall. The expression of StAR protein did not agree with the testosterone level.Because the above result didn't provide enough proofs for the level of StAR protein and the testosterone concentration in serum, we expected to resolve the question by culturing Leydig cells in vitro. We found that with the increase of culturing time ,the Leydig cell's reactivity to human Chorionic Gonadotropn(hCG)began to decrease. Different concentrations and the stimulating time of hCG could also affect the the stimulating effect, when the concentrationconcentration of hCG was 50IU/ml ,the stimulating effect were the best,but the concentration of testosterone gradually increase within 24h.Products could regulate secretion of themselves in endocrine action,therefore we study the effect of testosteron on hCG inducing testosteron synthesis. Testosterone( 50mg/ml) was added to these cultured bottles, cultivated for 48 hours.Then hCG were added to each bottle. The samples were collected at Omin,120th mm. The results were as follows :(1) the preuse of testosterone could decrease hCG binding rate and the concentration of cAMP (p<0.05), (3) The pre-conduct of testosterone made the expression level of StAR protein decrease apparently.Many hormones and factors regulate steroidogenesis through affecting the functions of Leydig cell.so we studied the effect of FSH on hCG inducing testosteron synthesis.We added to these bottles FSH(Follicle Stimulating Hormone,20ng/ml)and some doses of Cholesterol (5mg/ml), Pregnenolone (500ng/ml), Dehydroepiiandrosterone(500ng/rnl),Androstenedione(500ng/ml),22R-Hydroxycholesterol(3ug/ml)and cultivated for 48 h.Then hCG was added to each bottle for 2h. The results were as follows :(1) The preuse of FSH could increase hCG binding rate(p>0.05), but no significantly difference was observed among each group (p>0.05). FSH increased the concentrations of cAMP and significant difference was observed among each group (p<0.05); (2)The preuse of FSH had obvious effect on the conversion of the Cholesterol,...