Regulation of granulosa cell-derived ovarian metalloproteinase inhibitor(s) by prolactin

Increased prolactin concentrations are known to inhibit the ovarian proteolytic enzyme cascade associated with follicular rupture. It is not known whether there is also an effect of prolactin on endogenous proteinase inhibitors such as the tissue inhibitors of metalloproteinases (TIMPs). We sought to study the effect of prolactin on ovarian metalloproteinase inhibitors in cultured rat granulosa cells. Granulosa cells were cultured for 24 h with prolactin (0-1000 ng ml^-1) in the absence or presence of LH. Metalloproteinase inhibitor activity in the conditioned 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 increased 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 cultures (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 prolactin to LH-treated cultures. Prolactin had no effect on expression of mRNA encoding TIMP-3 in the absence or presence of LH, although LH stimulated a 1.7-fold increase in mRNA encoding TIMP-3 compared with controls. Addition of prolactin had no effect on media concentrations of oestradiol or progesterone. These data demonstrate that metalloproteinase inhibitor activity increases with increasing doses of prolactin; however, when LH was added, this effect was no longer seen. With an increase in metalloproteinase inhibitor activity, tissue metalloproteinase action could be decreased, providing a possible explanation for the local inhibition on pre- and peri-ovulatory pathways by hyperprolactinaemia.