Glucagon inhibits hepatocyte nitric oxide synthesis
B. G. Harbrecht, E. M. Wirant, Y. M. Kim and T. R. Billiar
Department of Surgery, University of Pittsburgh, Pa, USA.
OBJECTIVE: To investigate the effects of glucagon on nitric oxide (NO)
synthesis in cultured rat hepatocytes. SETTING: Laboratory. MATERIALS: Male
Sprague-Dawley rats (weight, 200-250 g). INTERVENTIONS: Isolated rat
hepatocytes were cultured with interleukin-1 to stimulate NO synthesis.
Glucagon was added at increasing concentrations (from 10(-9) to 2 x 10(-5)
mol/L) at the time of interleukin-1 stimulation. Selected cultures were
treated with the adenylate cyclase inhibitor, SQ 22536 (from 10(-5) to
10(-3) mol/L). MAIN OUTCOME MEASURES: Nitric oxide synthesis was assessed
by measuring the concentrations of culture supernatant nitrite and nitrite
plus nitrate, hepatocyte nitric oxide synthase-2 (NOS-2) messenger RNA
(mRNA), and NOS-2 protein. RESULTS: Interleukin-1 stimulated hepatocyte NO
synthesis, and this synthesis was inhibited by glucagon in a dose-dependent
manner. Glucagon inhibited the accumulation of supernatant nitrite and the
expression of NOS-2 mRNA and NOS-2 protein. SQ 22536 restored
glucagon-induced decreases in NO synthesis. CONCLUSIONS: Glucagon inhibits
NO synthesis in interleukin-1-stimulated hepatocytes in vitro. This
inhibition seems to be mediated by glucagon-induced changes in cyclic
adenosine monophosphate.
