Mast cell degranulation in rat uterine cervix during pregnancy correlates with expression of vascular endothelial growth factor mRNA and angiogenesis.

Vascular growth of the uterine cervix during pregnancy is associated with mast cell (MC) degranulation. To better understand the mechanism underlying this process, uterine cervices of intact pregnant rats were dissected and endothelial cell proliferation was measured by a bromodeoxyuridine incorporation technique. Total vascular endothelial growth factor (VEGF) mRNA expression and the relative abundance of VEGF splice variants (120, 164, and 188) were determined by RT-PCR. VEGF protein expression was evaluated by immunohistochemistry. To investigate the role of MCs on cervical angiogenesis, a second set of pregnant animals were treated with an MC stabilizer (disodium cromoglycate) to inhibit MC degranulation. Furthermore, 17beta-estradiol (E(2)) serum levels were established by RIA. In intact pregnant rats, VEGF mRNA expression was positively correlated with endothelial cell proliferation and circulating E(2) levels. All selected splice variants of VEGF gene were detected and their relative abundance did not show any change throughout pregnancy. Animals treated with disodium cromoglycate showed a decrease in endothelial cell proliferation and in VEGF mRNA expression compared with controls. Relative abundance of VEGF mRNA splice variants and E(2) serum levels showed no differences between these experimental groups. These results show a time-dependent correlation between VEGF mRNA expression and E(2) serum levels in the uterine cervix of intact pregnant rats, while MC stabilizer-treated animals reduced the VEGF expression without modifying E(2) serum levels. We suggest that cervical angiogenesis during pregnancy could be regulated by a mechanism which involves endogenous E(2) and chemical mediators stored in MC granules via a VEGF-dependent pathway.

Mast cells degranulation affects angiogenesis in the rat uterine cervix during pregnancy.

During pregnancy, it is essential that sufficient nutrients are supplied by the vascular system to support the dramatic modifications of the rat uterine cervix. Angiogenesis refers to the growth of new blood vessels from pre-existing microcirculation and mast cells have been associated with this process. This study examined the modifications of the vascular compartment and the distribution of mast cells on cervical tissue during pregnancy. Using disodium cromoglycate as a mast cell stabilizer, we determined the effects of the mast cell degranulation on cervical angiogenesis. Mast cell distribution and their degranulation status were evaluated by immunohistochemistry. Endothelial cell proliferation was measured by bromodeoxyuridine incorporation. Vascular areas (absolute and relative) and maturation indices were assessed by quantitative immunohistochemistry of von Willebrand factor and alpha-smooth muscle actin respectively. Mast cells were predominantly observed during the first half of pregnancy in the perivascular zones. The values of bromodeoxyuridine incorporation, absolute vascular area and vascular maturation index exhibited a significant increase throughout pregnancy. All animals that received mast cell stabilizer showed more than 40% of non-degranulated mast cells. Treated rats exhibited a decrease in endothelial proliferation and in relative vascular area; in addition, a large proportion of mature blood vessels was observed, suggesting a diminished level of new vessel formation. The effects of the mast cell stabilizer were sustained beyond the end of treatment. This is the first report that brings evidence that mast cell degranulation could be a necessary process to contribute to the normal angiogenesis of the rat cervix during pregnancy. Further investigations are needed to elucidate the possible implications of abnormal vascular development of the uterine cervix on the physiological process of ripening and parturition.