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

OBJECTIVE: To quantitate nitric oxide synthase (NOS) activity in healthy and interleukin 1beta (IL-1beta)-exposed equine synovial membrane. ANIMALS: 6 healthy horses, 2 to 8 years old. PROCEDURE: Recombinant human IL-1beta (0.35 ng/kg of body weight) was injected intra-articularly into 1 metacarpophalangeal joint of each horse. The contralateral joint served as an unexposed control. All horses were euthanatized 6 hours after injection of IL-1beta, and synovial membrane specimens were assayed for NOS activity by measuring conversion of arginine to citrulline. Severity of inflammation was semiquantitated by analysis of synovial fluids and histologic examination of synovial membrane. RESULTS: Equine synovial membrane had minimal NOS activity. A significant difference was not detected in NOS activity between control and IL-1beta-exposed specimens. Histologic examination revealed a neutrophilic infiltrate in synovial membrane exposed to IL-1beta. Synovial fluid from IL-1beta-exposed joints had a moderate inflammatory response and significantly greater concentrations of IL-1beta and interleukin-6 than fluid from healthy joints. CONCLUSION: Healthy equine synovial membrane had low NOS activity that was not affected by exposure to IL-1beta.