Responses of pulmonary allograft and cheek pouch arterioles in the hamster to alterations in extravascular pressure in different oxygen environments.

The responses to changes in transmural pressure were investigated in pulmonary allograft and cheek pouch arterioles in two oxygen environments. Neonatal hamster lung tissue was transplanted into adult hamster cheek pouches. After vascularization (8-10 days), pulmonary and cheek pouch vessels were observed by intravital microscopy in hamsters anesthetized with pentobarbital. By gassing the suffusion solution (bicarbonate-buffered Ringer's) (pH 7.4 at 35-37 degrees C) with either low oxygen (95% N2/5% CO2) or high oxygen (75% N2/5% CO2/20% O2) and after sealing the top of the chamber, extravascular pressure was altered by varying the fluid volume of the closed chamber. Changes in arteriolar diameters in response to positive and negative square-wave pressure pulses were quantified using a video micrometer and close-circuit TV system. Pulmonary arterioles showed a passive dilation or constriction in response to increases or decreases in transmural pressure (+/-20 mm Hg). These responses were not altered either by changes in PO2 or nitroprusside. In contrast, cheek pouch arterioles showed myogenic responses by constricting when transmural pressure was increased and vice versa. These responses were potentiated at high PO2 and abolished with nitroprusside. It is concluded that a myogenic response is dominant in cheek pouch arterioles but not in pulmonary arterioles under these conditions. These latter observations are consistent with results obtained from isolated, intact lung.