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 mug of protein from control rats and was optimal at 0.1 muM calcium, when it was measured after 45 min of incubation at 37ºC in the presence of 200 muM 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.

Streptozotocin induced hyperglycemia is decreased by nitric oxide inhibition

1. Diabetes mellitus type 1 was induced in 3-month old maleC57 BL/KS-mdb mice (N = 24)) by ip injection of streptozotocin (STZ, 45 mg/Kg body weight) for 5 days. 2. To determine the possible protective effects of nitric oxide inhibition against hyperglycemia, the STZ-diabetic rats received two doses of Ng-nitro-l-arginine-methyl ester (L-NAME) (10 mg/Kg body weight and 10 mg/mouse) dissolved in PBS for 45 consecutive days. Another group of STZ-treated rats was similarly treated with L-arginine (5 mg/mouse). 3. Blood glucose levels were 118 ñ 37 mg/dl after 8 days of L-NAME administration (10 mg/Kg body weight, N = 12) and 186 ñ 22 mg/dl (N = 12) after 5 days of L-NAME administration at the 5 mg/mouse dose. Treatment with L-arginine (5-mg/mouse, N = 12) caused a significant increase in blood glucose level to 151 ñ 17,5 mg/dl, showing the relevance of nitric oxide formation in this type of diabetes. 4. In STZ-diabetic mice treated with L-NAME (N = 12), diuresis was reduced by approximately 58 per cents compared to STZ animals, whereas in L-arginine-treated animals (N = 12) diuresis returned to STZ levels. Urinary protein excretion, which, was significantly affected by STZ (123 per cents compared to control) was significanty reduced by 66 per cents after treatment with L-NAME for 45 days, whereas treatment with-L-arginine caused a return to STZ values. 5. Urinary kallikrein excretion, which was reduced by 80 per cents in STZ mice compared to control, returned to control levels after L-NAME treatment. 6. The present results suggest a relationship between nitric oxide levels and the reduction of diabetic state improved renal function by L-name