Exogenous prostacyclin does not sensitize arterial baroreceptors

Abstract

It has been shown that prostacyclin (PGI2) sensitizes cardiac receptors. However, the effects of PGI2 on arterial baroreceptors are not well understood. In rabbits anesthetized with alpha-chloralose (n = 12), we examined reflex changes in multiunit efferent renal sympathetic nerve activity (RSNA) during hypotension caused by intravenous PGI2 (0.1, 0.2, 0.5, 1.0, 2.0 micrograms/kg), nitroglycerin (NG; 5, 10, 20, 50, 100 micrograms/kg), and sodium nitroprusside (SNP; 5, 10, 20, 50, 100 micrograms/kg) before and after bilateral vagotomy. Before vagotomy, RSNA increased during hypotension caused by NG or SNP (P less than 0.01) but did not significantly change during comparable hypotension caused by PGI2. After vagotomy, PGI2 increased RSNA as much as NG or SNP. In another group (n = 6), we examined the changes in aortic pressure (AoP), multiunit afferent aortic nerve activity (ANA), and the aortic diameter (AoD) during hypotension caused by intravenous PGI2, NG, and SNP. The relationship between changes in AoP and those in ANA did not differ during hypotension caused by the three drugs. The relationship between changes in AoP and those in AoD and that between changes in AoD and those in ANA also did not differ. Finally, we examined changes in AoP, ANA, and AoD during ramp increases or decreases of AoP caused by intravenous angiotensin II or NG under background infusion of saline, PGI2, or SNP (n = 6). The relationship among these variables did not differ during infusion of PGI2 and SNP. These results suggest that PGI2 stimulates cardiac receptors with vagal afferents but does not sensitize arterial baroreceptors.