Pharniacomechanical coupling ot vascular smooth muscle is believed to be mediated by inositol trisphosphate (lP3). Numerous studies have denionstrated an increase in inositol phosphates following tissue stimuldtion using either inlact aortic strips or cultured cells from mrta. However, little infornidion i 5 available concerning inositol phosphates in vascular tissue olher than in the large conduit vessel, the aorla. This presenl slutly was designed lo examine the role of inositol phosphate mctabolism following adrcncrgic stimulation of the niuscular rat tail artery as compared to the aorta. Segments of thoracic aorta and tail artery from male Sprague Ddwley rals were labeled with /'*IilinosituI arid stirnulated w i h t i ore pi nep h r i 11 e. The no re pi nc p I1 r i n c co 11 cent ratio t i that re5 11 I ted in a h a Ifm a xitnal stimulation of inositol phosphates was ==lop'' M in both the aorta and tail artery. Although the sensitivity of the two v r s s r l s to norepinephrine stimulation were similar, the stimulated levels ( i t IP, I P, , and IP, were from 1 to 2 order5 of magnitude greater in the tail artery than in aorta. IP production in aorta and tail artery was a linear function of time (from 0 to ' 30 miti). Significant levels of IP, (the 1 ,4,.5-lP3 isomer as determined by HPLC) could only be detwted it1 the tail artery and appeared to be produced optimally after 5 niin of stimulation. The several order of magnitude increase in adrenergic stimulated inositol phosphate production in the tail artery w a not due to either 'in increased magnitude of ['Hlinositol incorporated into PI, PIP, and PIP, or to a greater percentage of smooth muscle cells per unit lissue of h e rat tail arlery. We believe the results of this study tletnonstratc that the increased inositol phosphate mekholism in the vascular smooth muscle cells of the tail artery is an intrinsic property of the cell. Moreover, clue to the significant levels of all inositol phosphates produced in the [ail xlery, h i s niuscular artery may be a better model, as cornpared to [tie w r t a , iur iulure studies investigating phart-nacotncchanical coupling o i vascular smooth muscle.