While blood flow induced shear stress has been implicated as the principle stimulus for endothelial dependent vasodilator production, we now have evidence that the rate at which shear is applied is more important than is the shear magnitude. In this paper we describe an experimental apparatus in which both luminal shear magnitude and the rate at which shear is changed are dynamically controlled in isolated rat cremaster 1A microvessels. A novel flow sensor developed by us, a computer running Labview software, and adjustable pressure reservoirs constitute a feedback control system in which shear and the first time derivative of shear are dynamically controlled even during vasodilation. Results indicate that first, a graded dilation occurs with increases in stepped shear magnitude. Second, a shear linearly ramped to 20 dy/cm2 over 10, 30, 60, 120, or 300 seconds elicits a modest dilation (7%) that varies little between ramps. Third, a step in shear of the same final magnitude elicits a dramatically greater dilation (21%). These results indicate that endothelial dependent shear induced vasodilator production is rate sensitive and that the threshold ramp time likely falls between zero and ten seconds. Finally, it is observed that the impulse duration should be at least 60 seconds to achieve the response equal to that of the stepped shear. A model investigating regulation in a network must include rate sensitivity as well as shear sensitivity.
|Original language||English (US)|
|State||Published - Mar 20 1998|
All Science Journal Classification (ASJC) codes
- Molecular Biology