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Glucagon inhibits hepatocyte nitric oxide synthesis
B G Harbrecht1, E M Wirant, Y M Kim
1Department 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.