Effects of an intravenous catheter on the local production of cytokines and soluble cytokine receptors in healthy men

Like many aspects of physiology, functions of the immune system show consid erable diurnal variation. Studies investigating diurnal variations in the c irculating amounts of cytokines, in general, used blood samples obtained fr om an intravenous catheter, The results of such studies may be confounded b y an effect of the catheter on local cytokine production. We measured the l evels of IL-6, tumour necrosis factor alpha (TNF-alpha) and soluble TNF rec eptors (sTNF-R) p55 and p75 in 20 healthy men between 09:00 and 19:00 h in plasma samples obtained from an intravenous catheter and in one additional sample obtained by a simple needle stick in the contralateral arm 10 h afte r baseline. In plasma from the catheter the levels of IL-6 increased signif icantly over time, TNF-alpha levels slightly decreased and the time courses of TNF receptor levels showed significant trends of a higher order. Contro l levels of IL-6, TNF-alpha and sTNF-R p75 measured in plasma obtained by n eedle stick after 10 h did not differ from baseline, and those of sTNF-R p5 5 were even higher. We conclude that local alterations in the production of cytokines and soluble cytokine receptors induced by an intravenous cathete r represent an important confounding factor for studies investigating diurn al variations in immune functions. (C) 2000 Academic Press.