Differential regulation of somatostatin receptor types 1-5 in rat aorta after angioplasty

Treatment of restenosis after angioplasty with octapeptide somatostatin (SS T) analogs has met with variable success. These analogs bind with high affi nity to only two SST receptor (SSTR) subtypes (2 and 5), display moderate a ffinity for SSTR3, and low affinity for SSTR1 and 4. To optimize the vascul oprotective effect of SST, we have investigated the pattern of expression o f all five SSTRs in rat thoracic aorta in the resting state and at 15 min, 3, 7, and 14 days after balloon endothelial denudation. SSTR1-5 were analyz ed as mRNA by semiquantitative reverse transcriptase-polymerase chain react ion and as protein by immunocytochemistry. All five SSTRs were expressed in rat aorta both as mRNA and protein and displayed a time-dependent, subtype -selective response to endothelial denudation. mRNA for SSTR1 and 2 increas ed acutely (SSTR1 > SSTR2) on days 3 and 7, coincident with smooth muscle c ell (SMC) proliferation, and declined to basal levels by day 14. SSTR3 and 4 displayed a different pattern with a delayed, more gradual increase in mR NA beginning at days 3-7 and continued to increase thereafter. SSTR5 mRNA w as constitutively expressed at a low level and showed no change during the 2 wk postinjury period. By immunohistochemistry, SSTR1-5 antigens were loca lized predominantly in SMC that were present in the media or had migrated i nto the intima; antigen expression correlated with receptor mRNA expression . Notably, only SSTR1,3,4 were expressed in the intima: SSTR1 and 4 during the proliferative burst and SSTR3 and 4 after proliferation, when SMC migra tion into the intima continues. These results demonstrate dynamic changes i n SSTR1-5 expression after vascular trauma localized to areas of vascular S MC migration and replication. In view of their early and prominent inductio n, SSTR1 may be the optimal subtype to target for inhibition of myointimal proliferation, and SSTR3 and 4 for migration and remodeling.