A temporal study of ultrasound contrast agent-induced changes in capillary density.
OBJECTIVE
The ability of ultrasound (US) and ultrasound contrast agents (UCAs) to induce angiogenesis has been explored as a means of restoring blood flow to ischemic muscle. Because UCAs demonstrate an increasing percentage of collapse cavitation with increasing US pressure (Pr), this study sought to explore the effects of a US Pr that produces 100% collapse cavitation, determine the capillary density changes, and determine the time point of angiogenic rebound in a normal animal model.


METHODS
Using a 1-MHz focused transducer and a peak rarefactional US Pr of 3.8 MPa, rat gracilis muscles were exposed to US, and bioeffects were assessed. Capillary density, as a measure of angiogenesis, was examined. As an additional measure, inflammatory cells were quantified via a color threshold analysis to detect the presence of CD31 and CD34 as a percentage of the total section on stained slides. Six groups (0, 3, 6, 13, 20, and 27 days postexposure [DPE]; n = 3 each) and 5 cage controls were used to characterize the angiogenic response.


RESULTS
Ultrasound-UCA treatment caused the capillary density to decrease acutely (0 DPE) by 70% and inflammatory cells to increase by up to 250%. The angiogenic rebound was observed at 3 DPE but did not return to control levels by 27 DPE, suggesting an incomplete healing response.


CONCLUSIONS
Capillary destruction and inflammation played an important role in the angiogenic response induced by US-UCA. Exposure that causes 100% collapse cavitation causes capillary destruction from which normal rats are unable to recover and suggests a nontherapeutic effect.
Johnson
Chenara A
CA
Department of Bioengineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Sarwate
Sandhya
S
Miller
Rita J
RJ
O'Brien
William D
WD
D000704:Analysis of Variance; D000818:Animals; D002196:Capillaries / Q000187:drug effects*; D003287:Contrast Media / Q000494:pharmacology*; D005260:Female; D005466:Fluorocarbons / Q000494:pharmacology*; D007511:Ischemia / Q000188:drug therapy*; D018482:Muscle, Skeletal / Q000098:blood supply*; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013194:Staining and Labeling; D014465:Ultrasonics
D003287:Contrast Media; D005466:Fluorocarbons; C042852:perflutren