Increased levels of platelet-activating factor (1-O-alkyl-2-acetylglycerophosphocholine) in blood after reversal of renal clip hypertension in the rat.

1. This study analyses whole blood in acutely unclipped one-kidney, one-clip (1K, 1C) hypertensive rats for the presence of platelet-activating factor (PAF), a potent vasodilator and a putative mediator of the rapid blood pressure (BP) fall seen after unclipping. 2. Hypertensive 1K, 1C rats were anaesthetized and a carotid and jugular cannula were inserted for BP measurement and anaesthetic infusion respectively. After a stable level of anaesthesia was attained, the constrictive clip was removed and BP was recorded for 30 min. 3. Blood was drawn from the aorta directly into ice-cold acetone. The extract was analysed for PAF by a bioassay using 5-hydroxy-[14C]tryptamine-labelled platelets. 4. Rats which showed a BP fall had elevated levels of PAF [55 +/- 6 (SEM) pg/ml] (P less than 0.01). 5. This supports the hypothesis that activation of PAF biosynthesis may be a mechanism contributing to the fall in BP seen after unclipping the 1K, 1C hypertensive rat.