Stimulation of matrix-metalloproteinase-1 and tissue inhibitor of metalloproteinase-1 gene expression in rats by the preovulatory prolactin peak

Since structural luteolysis involves deterioration of tissue, the gene expr ession of matrix-metalloproteinase-1 (MMP-1) and the respective tissue inhi bitor of this metalloprotease (TIMP-1) were measured at various times on th e day of pro-oestrus and in animals in which the preovulatory prolactin sur ge was blocked for the duration of 3 cycles by bromocriptine. An additional group of prolactin-blocked rats received a prolactin replacement injection on the afternoon of pro-oestrus, In spontaneously pro-oestrous rats, MMP-1 and TIMP-1 gene expression increased significantly (P < 0.01) prior to the occurrence of the preovulatory LH surge but simultaneously with the onset of the preovulatory prolactin surge, When prolactin release was blocked by bromocriptine for 3 cycles, no such changes were observed during the aftern oon of pro-oestrus. However, an intraperitoneal injection of bovine prolact in at the time when the preovulatory prolactin surge occurs normally increa sed MMP-1 and TIMP-1 gene expression (P < 0.01). These results indicate tha t MMP-1 and TIMP-1 gene expression are stimulated by the preovulatory prola ctin surge. Previous work has shown that the preovulatory LH surge activate s the enzqmatic cascade which leads to increased collagenase activity.