The aims of the present study were to determine the profile of tumour necrosis factor (TNF) release, and the effect of monoclonal antibodies to TNF, on the changes in regional haemodynamics and the responses to vasodilator and vasoconstrictor challenges, during a continuous 24 h low dose infusion of lipopolysaccharide (LPS) in conscious rats. 2. Male Long Evans rats were chronically instrumented for measurement of regional haemodynamics (renal, superior mesenteric and hindquarters) and were challenged with 3 min infusions of acetylcholine (22 nmol min-1), methoxamine (120 nmol min-1), salbutamol (0.83 nmol min-1) and bradykinin (14.4 nmol min-1). The rats were given either saline, or the TNF antibodies, TN3g1 or TN3g2a, 1 h before the start of a continuous infusion of LPS (150 micrograms kg-1 h-1) and were subsequently re-tested with the vasodilator and vasoconstrictor challenges 2, 6 and 24 h after the start of the LPS infusion. 3. Prior to infusion of LPS, TNF was not detectable in the plasma. During continuous infusion of LPS there was a transient elevation in plasma TNF levels, reaching a maximum (approximately 2300 pg ml-1) after approximately 1 h, and returning to undetectable levels after approximately 3 h of LPS infusion. 4. In the saline pretreated group, after 1-2 h of LPS infusion, there was a small hypotension and a marked renal vasodilation; 6 h after the start of LPS infusion there was a minor elevation in MAP above control levels, renal vasodilatation was maintained and a hindquarters vasoconstriction occurred; after 24 h of LPS infusion, there was a hypotension and renal and hindquarters vasodilatation. There were significant reductions in the tachycardic and renal vasodilator responses and an enhanced depressor response to acetylcholine after 24 h of LPS infusion. LPS infusion also caused a generalized hyporesponsiveness to the cardiovascular effects of methoxamine and salbutamol. The major changes in response to bradykinin were reduced tachycardic and enhanced depressor responses throughout the LPS infusion, a biphasic decrease and increase in renal conductance and enhanced hindquarters vasodilatation at 24 h. 5. Pretreatment with either TN3g1 or TN3g2a antibodies had no major effects on the changes in resting haemodynamics, or on the changes in response to methoxamine, salbutamol or bradykinin challenges during LPS infusion. However, the tachycardic responses to acetylcholine were generally preserved, and its hypotensive effect after 24 h of LPS infusion was not enhanced after TN3g1 or TN3g2a pretreatment. Thus, despite substantial, but transient, elevation of plasma TNF levels during continuous LPS infusion, it appears that the majority of cardiovascular changes were dependent on factors other than plasma TNF.
