Constitutive nitric oxide synthase (cNOS) activity in Langerhans islets from streptozotocin diabetic rats.
Nitric oxide synthase activity was measured in Langerhans islets isolated from control and streptozotocin diabetic rats. The activity of the enzyme was linear up to 150 micrograms of protein from control rats and was optimal at 0.1 microM calcium, when it was measured after 45 min of incubation at 37 degrees C in the presence of 200 microM arginine. Specific activity of the enzyme was 25 x 10(-4) nmol [3H]citrulline 45 min-1 mg protein-1. Streptozotocin diabetic rats exhibited less enzyme activity both in total pancreas homogenate and in isolated Langerhans islets when compared to control animals. Nitric oxide synthase activity measured in control and diabetic rats 15 days after the last streptozotocin injection in the second group of animals corresponded only to a constitutive enzyme since it was not inhibited by aminoguanidine in any of the mentioned groups. Hyperglycemia in diabetic rats may be the consequence of impaired insulin release caused at least in part by reduced positive modulation mediated by constitutive nitric oxide synthase activity, which was dramatically reduced in islets severely damaged after streptozotocin treatment.
Fonovich de Schroeder
T M
TM
Facultad de Farmacia y Bioquímica, Cátedra de Fisiología, PROSIVAD-CONICET, Universidad de Buenos Aires, Argentina.
Carattino
M D
MD
Frontera
M
M
Catanzaro
O L
OL
D000704:Analysis of Variance; D000818:Animals; D000900:Anti-Bacterial Agents; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D007515:Islets of Langerhans / Q000201:enzymology*; D008297:Male; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III; D051381:Rats; D017208:Rats, Wistar; D013311:Streptozocin
D000900:Anti-Bacterial Agents; D013311:Streptozocin; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat