Vascular matrix metalloproteinase-9 mediates the inhibition of myogenic reactivity in small arteries isolated from rats after short-term administration of relaxin.

UNLABELLED: During pregnancy and chronic relaxin administration to nonpregnant rats (for days), vascular MMP (matrix metalloproteinase)-2 is increased and mediates renal vasodilation, hyperfiltration, and inhibition of myogenic reactivity of small renal arteries. However, the renal vasodilatory actions of relaxin also occur after only several hours of hormone administration to nonpregnant rats, and we hypothesized a pivotal role for vascular MMP-2. Accordingly, we used gelatin zymography, which reveals not only vascular MMP-2, but also MMP-9 activity in small renal arteries isolated from rats administered recombinant human relaxin (rhRLX) or vehicle for 4-6 h. Furthermore, we tested whether myogenic reactivity is inhibited, and if so, whether the inhibition is mediated by increased vascular MMP-2. Surprisingly, we detected no significant difference in either pro or active MMP-2 in small renal arteries isolated from rhRLX and vehicle control treatment groups. In contrast, vascular MMP-9 was up-regulated by 70% (P < 0.0005 vs. vehicle). These results were completely unexpected and novel. MMP-9 protein expression was confined to the vascular smooth muscle. MMP-9, but not MMP-2 activity, was also increased in mesenteric arteries after short-term rhRLX administration (P < 0.005 and >0.05 vs. vehicle, respectively). Myogenic reactivity was inhibited in small renal arteries isolated from nonpregnant rats treated with rhRLX for 4-6 h (P < 0.01 vs. vehicle) and was completely restored by incubation with MMP-9, but not MMP-2 neutralizing antibodies in vitro. CONCLUSION: In contrast to chronic rhRLX administration, MMP-9 rather than MMP-2 plays a central role in the vasodilatory effect of short-term relaxin administration.

Matrix metalloproteinase-2 activity, protein, mRNA, and tissue inhibitors in small arteries from pregnant and relaxin-treated nonpregnant rats.

Vascular gelatinase activity is essential for pregnancy- and relaxin (Rlx)-induced renal vasodilation and hyperfiltration in rats. The objective of this study was to further elucidate the mechanisms for the increase in vascular matrix metalloproteinase (MMP)-2 activity caused by pregnancy and Rlx. We first corroborated our earlier work by showing that pro- and active forms of MMP-2 were increased in small renal arteries from pregnant compared with virgin rats and Rlx-treated compared with vehicle-treated nonpregnant rats. We next investigated other artery types and showed that MMP-2 activity was upregulated in mesenteric arteries from pregnant rats (pro-MMP-2 by 50% and active MMP-2 by 40%, both P<0.05) and from Rlx-treated nonpregnant rats (pro-MMP-2 by 50% and active MMP-2 by 90%, both P<0.005) compared with their respective controls. To corroborate these results obtained by gelatin zymography, pro-MMP-2 protein was determined by Western analysis in the same small arteries. Pro-MMP-2 protein was increased in small renal arteries from pregnant compared with virgin rats and from Rlx- compared with vehicle-treated nonpregnant rats: pro-MMP-2-to-beta-actin ratio=0.29 vs. 0.21 (P<0.01) and 0.43 vs. 0.32 (P<0.005). Findings were similar for mesenteric arteries. MMP-2 mRNA as measured by real-time PCR was increased in small renal arteries from pregnant and Rlx-treated nonpregnant rats compared with their respective controls. There were no significant differences in tissue inhibitor of metalloproteinase (TIMP-1 or TIMP-2) activity by reverse zymography in small renal arteries. Thus increases in MMP-2 mRNA and protein expression are major factors contributing to increased MMP-2 activity in small arteries from pregnant and Rlx-treated nonpregnant rats.