REGULATION OF GRANULOSA CELL-DERIVED OVARIAN METALLOPROTEINASE INHIBITOR(S) BY PROLACTIN

Increased prolactin concentrations are known to inhibit the ovarian pr oteolytic enzyme cascade associated with follicular rupture. It is not known whether there is also an effect of prolactin on endogenous prot einase inhibitors such as the tissue inhibitors of metalloproteinases (TIMPs). We sought to study the effect of prolactin on ovarian metallo proteinase inhibitors in cultured rat granulosa cells. Granulosa cells were cultured for 24 h with prolactin (0-1000 ng ml(-1)) in the absen ce or presence of LH. Metalloproteinase inhibitor activity in the cond itioned culture media was measured by a colorimetric assay. Prolactin at 1000 ng ml(-1) increased inhibitor activity by 2.86 +/- 0.63 times. Expression of mRNA encoding TIMP-1 measured by Northern analysis incr eased by 2.34 +/- 0.34 times with 100 ng prolactin ml(-1) and by 2.43 +/- 0.42 times with 1000 ng prolactin ml(-1) compared with control cul tures (no LH, no prolactin). In the presence of LH, expression of mRNA encoding TIMP-1 and inhibitor activity increased by 2.60 +/- 0.6 and 4.60 +/- 0.54 times, respectively. However, no further change in mRNA expression or inhibitor activity was apparent with the addition of pro lactin to LH-treated cultures. Prolactin had no effect on expression o f mRNA encoding TIMP-3 in the absence or presence of LH, although LH s timulated a 1.7-fold increase in mRNA encoding TIMP-3 compared with co ntrols. Addition of prolactin had no effect on media concentrations of oestradiol or progesterone. These data demonstrate that metalloprotei nase inhibitor activity increases with increasing doses of prolactin; however, when LH was added this effect was no longer seen. With an inc rease in metalloproteinase inhibitor activity, tissue metalloproteinas e action could be decreased, providing a possible explanation for the local inhibition on pre- and peri-ovulatory pathways by hyperprolactin aemia.