A direct effect of atrial peptide on arterioles of the terminal microvasculature

Responses to atrial peptide (AP) were observed in cheek pouch arterioles of anesthetized golden hamsters (pentobarbital sodium, 70 mg/kg ip). Vessels for observation were selected on the basis of their functional status in relation to controlling the perfused capillary surface area. Local application of AP onto microvessels at a final concentration of from 7 X 10(-9) to 3 X 10(-8) M was achieved via micropipettes; responses were compared with those produced by application of vehicle only. Individual vessels were observed during control conditions and during vasoconstriction of the microvascular bed induced via either equilibration of the superfusate with 10% oxygen or addition to the superfusate of 5 X 10(-7) M norepinephrine (NE). Compared with responses induced by the vehicle in each condition, AP produced a statistically significant dilation during control conditions, and during raised PO2, but no statistically significant effect during NE exposure. Mean diameter changes were from a base line of 27.8 +/- 4.7 to 29.7 +/- 4.5 microns with vehicle and 33.2 +/- 4.4 microns with AP in controls; from 22.7 +/- 4.6 to 25.8 +/- 4.5 microns with vehicle and 30.1 +/- 4.7 microns with AP during raised PO2; and from 25.2 +/- 4.7 to 29.8 +/- 5.4 microns with vehicle and 33.5 +/- 4.9 microns with AP during NE exposure. The data show that arterioles of the terminal microvasculature can respond selectively to AP.