Figure 2. Effects of elevated D-glucose on basal and histamine-stimulated cGMP accumulation and L-citrulline production in umbilical vein endothelial cells isolated from gestational diabetic pregnancies.

Diabetic cells were cultured for 24 h in M199 containing 5 mm D-glucose (□) or 25 mm D-glucose (▪) and then preincubated for 15 min with 0.5 mm 3-isobutyl-methylxanthine (IBMX, 15 min, 37 °C) and 100 μM L-arginine. A, cGMP accumulation was measured in the presence of 100 μM L-arginine and absence or presence of histamine (10 μM, 5 min, plus 0.5 mm IBMX) and/or 100 μM L-NAME. *P < 0.03 relative to values in diabetic cells cultured in 5 mm D-glucose in the presence or absence of histamine. Basal cGMP accumulation in non-diabetic cells cultursed in 5 mm D-glucose was 0.8 ± 0.3 pmol (10⁶ cells)⁻¹ (5 min⁻¹). B, cells were incubated with 4 μCi ml⁻¹ L-[³H]arginine (100 μM) for 30 min (37 °C) in the absence or presence of 10 μM histamine (last 5 min of a 30 min incubation period) and/or 100 μM L-NAME. Aliquots (300 μl) of formic acid-digested endothelial cells were passed through a cation ion-exchange resin Dowex50W (50X8-200) and radioactivity for L-[³H]citrulline was determined in 200 μl aliquots of H₂O eluates. Basal L-citrulline production in non-diabetic cells cultured in 5 mm D-glucose was 3872 ± 339 d.p.m. (10⁶ cells)⁻¹ (30 min)⁻¹, n = 3. Values denote the means ±s.e.m. of 3 different cell cultures.