Nitric oxide synthase activity in healthy and interleukin 1 beta-exposed equine synovial membrane

Objective-To quantitate nitric oxide synthase (NOS) activity in healthy and interleukin 1 beta (IL-1 beta)-exposed equine synovial membrane. Animals-6 healthy horses, 2 to 8 years old. Procedure-Recombinant human IL-1 beta (0.35 ng/kg of body weight) was injec ted intra-articularly into 1 metacarpophalangeal joint of each horse. The c ontralateral joint served as an unexposed control. Ail horses were euthanat ized 6 hours after injection of IL-1 beta and synovial membrane specimens w ere assayed for NOS activity by measuring conversion of arginine to citrull ine. Severity of inflammation was semiquantitated by analysis of synovial f luids and histologic examination of synovial membrane. Results-Equine synovial membrane had minimal NOS activity. A significant di fference was not detected in NOS activity between control and IL-1 beta-exp osed specimens. Histologic examination revealed a neutrophilic infiltrate i n synovial membrane exposed to IL-1 beta. Synovial fluid from IL-1 beta-exp osed joints had a moderate inflammatory response and significantly greater concentrations of IL-1 beta and interleukin-6 than fluid from healthy joint s. Conclusion-Healthy equine synovial membrane had low NOS activity that was n ot affected by exposure to IL-1 beta.