Prostaglandins, catecholamines, and cardiovascular responses to hemorrhage

The effects of prostaglandins (PGE2 and 16,16-dimethyl-PGE1) on epinephrine (E) and norepinephrine (NE) release, in response to a hypotensive stimulus (bleeding 5 ml/300 g), were studied in relation to blood pressure and heart rate responses in the rat. PGE2 (10 micrograms/kg-1 . min-1) and 16,16-dimethyl-PGE1 (1 microgram . kg-1 . min-1) accelerated blood pressure and heart rate recovery rate following acute hemorrhage and increased plasma E and NE levels. Plasma levels of 3-methoxy-4-hydroxyphenylglycol (MHPG) and 3,4-dihydroxyphenylglycol (DHPG) were not affected by PG infusion. In bilaterally nephrectomized rats, PGE2 increased plasma levels of E, NE, and DHPG but failed to enhance the blood pressure and had only a mild effect on heart rate recovery following bleeding. In hexamethonium-treated rats, infusion of PGE2 had a small and transient effect on blood pressure recovery, but its effect on the heart rate was not affected; NE and E levels in the plasma of the hexamethonium-treated rats were still higher in the PGE2-infused rats. These studies indicate that in the intact rat, administered PGE potentiate the release of E and NE and facilitate blood pressure and heart rate recovery following acute hemorrhage. The hemodynamic effects of the PGE appear to be mediated by a renal factor whereas the effects of PGE on E and NE response to hemorrhage are independent of the presence of intact kidneys.