Abstract
Innate immunity not only mediates early host defenses to infection, but also contributes to septic hemodynamic compromise through nitric oxide synthase (NOS2) induction and inhibition of cardiovascular adrenergic responses. Because of increased age-related susceptibility to sepsis, we hypothesized that hearts from old (28–29 months) adult rats would exhibit greater β -adrenergic hyporesponsiveness than young (6–8 months) following lipopolysaccharide (LPS, 6 mg/kg) with and without interferon γ (INF- γ, 5000 units). LPS/INF- γ depressed baseline +d P/d t and isoproterenol-stimulated inotropy in both old and young hearts.β -adrenergic inotropic (+d P/d t) and lusitropic responses were more depressed in oldv young LPS/INF- γ hearts. Additionally isoproterenol-stimulated cAMP elaboration was less in old (1950±160 fmol/min/g) v young (2440±170 fmol/min/g, P=0.05) LPS/INF-γ hearts. LPS alone also depressed basal +d P/d t and prolonged myocardial relaxation in old and young hearts, but suppressed isoproterenol +d P/d t responses only in old hearts. Depressedβ -adrenergic inotropic responses were augmented with the selective NOS2 inhibitor N-iminoethyl-L-lysine. To establish biochemical mechanisms for this, we tested whether induction of NOS2 and innate immune system receptors (CD14 and Toll-like receptor 4, TLR4) were enhanced in old v young hearts. Induction of myocardial NOS2 and CD14 (not present in control) by LPS/INF- γ was 2–3-fold greater in old compared to young animals. TLR4 was constitutively expressed in old and young hearts and was unaffected by LPS/INF- γ. These findings indicate that advanced age is associated with augmented cardiac β -adrenergic depression and enhanced CD14-NOS2 signaling in response to cytokines. Upregulation of cardiovascular innate immunity may have clinical implications for increased mortality in older individuals with systemic inflammatory response syndromes.
