EXPRESSION AND ACTIVITY OF OVARIAN TISSUE INHIBITORS OF METALLOPROTEINASES DURING PSEUDOPREGNANCY IN THE RAT

The present study examined the role of tissue inhibitors of metallopro teinases (TIMPs) in tissue remodeling that occurs during luteal develo pment and regression throughout pseudopregnancy in the rat. Pseudopreg nancy was induced in immature female rats by eCG/ hCG priming, Animals (n = 4 per time point) were killed on Days 1, 2, 4, 8, 12, 14, and 16 of pseudopregnancy (post hCG administration), and ovaries were remove d and analyzed for metalloproteinase inhibitor activity or TIMP-1, TIM P-2, and TIMP-3 mRNA expression. Inhibitory activity was highest in Da y-1 samples (41.35 +/- 6.50 inhibitory units), and inhibitor activity significantly decreased (p < 0.05) thereafter to minimal values at Day 12 (8.14 +/- 2.71 inhibitory units). Methylamine hydrochloride treatm ent, which inactivates macroglobulin-type inhibitors, revealed that th e majority of the inhibitor activity in the Day-1 samples (82.6%) and the Day-16 samples (77.3%) could be attributed to TIMPs. To further di stinguish the contribution of each TIMP to this activity, Northern ana lysis for TIMP-1, -2, and -3 was performed. Analysis of TIMP mRNA expr ession revealed that TIMP-1 transcript expression was highest (p = 0.0 0009) at Day 1, decreased approximately 3- to 20-fold from Days 2 to 1 2, respectively, and again increased at Days 14-16. However, TIMP-2 ex pression did not change (p > 0.05) over any of the time points studied . in contrast to TIMP-1 and TIMP-2 expression, TIMP-3 mRNA expression was lowest during Days 1 and 2 of pseudopregnancy, increased approxima tely 4-fold at Day 4, peaked at Day 8, and remained elevated throughou t the remainder of pseudopregnancy. We conclude from these studies tha t TIMPs play a role in the regulation of connective tissue remodeling associated with luteal development and regression. Furthermore, the di stinct pattern of expression of the th ree TIMPs suggests that each ma y regulate either the site and extent of proteolytic action or specifi c matrix metalloproteinases at different periods of tile luteal life s pan.