PGI2-specific antibodies administered in vivo suggest against a role for endogenous PGI2 as a circulating vasodepressor hormone in the normotensive and spontaneously hypertensive rat.

Immunoglobulins raised against 5,6-dihydro PGI2 crossreact with PGI2. When infused in vivo into the rat, these immunoglobulins are capable of 1) neutralising the vasodepressor effects (bolus or continuous infusion) of exogenous PGI2, 2) blocking the catabolism of exogenous 3H-PGI2 and prolonging its life-time in the circulation (t 1/2 approx 60 min) while that of 3H-PGE2 is unaffected, 3) trapping an endogenously produced substance which after extraction from blood and dissociation from the ligand-antibody complex, is immunoreactive with 6-keto PGF1 alpha-specific antiserum. Yet the anti-5,6-dihydro PGI2 immunoglobulins have no effect on resting arterial blood pressure both in the normotensive and spontaneously hypertensive rat. These experiments indicate that endogenously produced PGI2 does not play a significant systemic role in blood pressure control although in combination with other vasodilators it could still participate in the regulation of vascular tone at a local level.