抄録
Annexin A5 (AX5) is expressed in the mammary epithelial cells of lactating rats and the expression is dramatically increased after pups removal. As GnRH antagonist reversed the increase of AX5 expression and apoptosis of the epithelial cells, local GnRH is hypothesized to be involved in involution. In the present study, we examined the effect of local GnRH on lactating mammary gland and also observed the distribution of GnRH in mammary tissues. GnRH agonist (GnRHa) 200ng/25microl was mixed with same volume of sesame oil and emulsified before injection. GnRHa was administered to the hemilateral inguinal mammary gland once a day from day 10 to 12 of lactation. Emulsified saline was given to another side of mammary gland. Inguinal mammary glands of both sides were collected. GnRHa induced both the expression of AX5 and apoptosis to the mammary epithelial cells. Further, GnRHa administration reduced the weight of inguinal mammary gland slightly but significant (P<0.05). Immunohistochemistry with anti-GnRH demonstrated that large oval cells found in interlobular tissues and between alveoli were positive. They were confirmed also to be AX5 positive. The number of these cells in mammary tissues was counted for both lactating and force-weaned rats under a microscope (x20) for 20 different fields of 9 slides from two rats each. GnRH positive cells were significantly increased by pups removal. The GnRH positive cells were demonstrated to be mast cells by metachromatic granules after staining with 0.1% toluidine blue. Our results suggest that the local mammary GnRH supplied by mast cells appears to play an important role in the regression of mammary gland at involution.
