THE INFLUENCE OF PARATHYROID-HORMONE ON PLATELET-ACTIVATING-FACTOR (PAF) BLOOD-LEVELS IN HEMODIALYSIS-PATIENTS

PAF represents a new family of glycerophospholipids and possesses mult iple biological activities including platelet aggregation. Production of I)AF has been demonstrated in a number of different cell types and in response to various stimuli. In this work an attempt is made to stu dy the effect of parathyroid hormone (PTH) on PAF production. In 13 he modialysis patients with severe secondary hyperparathyroidism, PAF lev els in blood as well as intact PTH (iPTH) and tot-al calcium in serum (tCa), before and 10 days after parathyroidectomy (PTHx), were measure d. Our results indicate that PAF levels in blood as well as iPTH and t Ca were higher before PTHx than after [a) PAF before 1.10 X 10(-4) +/- 9 X 10(-5) gamma/ml and after 2 X 10(-5) +/- 1 X 10(-5) gamma/ml, p < 0.001; b) iPTH before 880 +/- 392.9 pm/ml and after 121.6 +/- 61.9 pm/ ml, p <0.001; c) tCa before 9.96 +/- 0.35 mg/dl and after 8.38 +/- 0.3 0 mg/dl, p <0.001]. Using stepwise regression analysis it seems that P AF is dependent on calcium which is dependent mainly on iPTH. Since a) platelet dysfunction is among the factors which are incriminated for bleeding in uremia and b) PAF which induces platelet aggregation acts via specific receptors, we checked the response of platelets in terms of their ability to aggregate in vitro following increasing doses of e xogenous PAF in 5 of the above patients in order to investigate whethe r the high levels of PAF before PTHx may desensitize platelets. Decrea sed platelet aggregation before PTHx compared to after PTHx (EC(50):2. 06 X 10(-7) +/- 1.28 X 10(-7) M and 4.8 X 10(-8) +/- 1.3 X 10(-8) M fi nal concentrations, respectively, p <0.005) has been detected. It is p ossible that the high levels of PAF before PTHx desensitize platelets and in this manner platelet aggregation is reduced which may aggravate the bleeding tendency in hemodialysis patients.