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Ann Thorac Surg 2004;77:126-132
© 2004 The Society of Thoracic Surgeons

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Original article: cardiovascular

Nitric oxide and prostacyclin in ultrasonic vasodilatation of the canine internal mammary artery

^a division of Cardiovascular Surgery, Mayo Clinic, Rochester, Minnesota, USA
^b Division of Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota, USA

Accepted for publication July 8, 2003.

^* Address reprint requests to Dr Schaff, Division of Cardiovascular Surgery, Mayo Clinic, 200 First St SW, Rochester, MN 55905, USA.
e-mail: schaff{at}mayo.edu

BACKGROUND: Investigators recently demonstrated increased free blood flow from radial artery free grafts harvested using ultrasonic technology. We investigated the mechanism underlying this phenomenon.

METHODS: Canine internal mammary artery segments (with and without intact endothelium) were precontracted with norepinephrine and sonicated 3 seconds in organ chambers with ultrasonic coagulating shears (Harmonic Scalpel; Ethicon Endo-Surgery, Cincinnati, OH) functioning at level 2. Vessel tension was continuously measured to examine vasoactivity in response to sonication alone (control) or with N^ù-Nitro-l-arginine (l-NNA) and indomethacin added to the chamber medium individually or in combination. Tissue heating, acoustic pressure, and endothelial damage as detected by scanning electron micrography were also assessed.

RESULTS: In vitro sonication with the Harmonic Scalpel induced predominately endothelium-dependent internal mammary artery vasorelaxation but a small endothelium-independent contribution was also observed. Early vasorelaxation (1 minute after stimulus) was maximally inhibited by l-NNA alone and in combination with indomethacin. Relaxation during this period was insignificantly affected by indomethacin alone. Only the combination of l-NNA and indomethacin maximally inhibited late vasorelaxation (5 minutes after stimulus), whereas inhibitory effects of l-NNA diminished during this time period. Indomethacin inhibited relaxation substantially during this phase, although significantly less than did l-NNA alone. The Harmonic Scalpel minimally heated the tissue surface (0.3 ± 0.03°C) and did not disrupt endothelial cell integrity while operating at 50 mW/cm² intensity (acoustic pressure 40 kPa).

CONCLUSIONS: Sonication induces vasorelaxation almost completely by time-dependent endothelial nitric oxide and prostacyclin release, which appears unrelated to tissue heating or endothelial architectural disruption.

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