Vitamin E is known to be an inhibitor of platelet prostaglandin production and aggregation. The rate of platelet aggregation induced by adenosine diphosphate was significantly increased in diabetics with proliferative retinopathy and the enhanced production of thromboxane B2, a stable metabolite of thromboxane A2, was demonstrated in those patients. On the other hand, vitamin E in platelets was significantly reduced in diabetics compared with age matched controls. In addition, it was shown that vitamin E content in platelets examined in diabetic and control subjects inversely correlated with both the rate of platelet aggregation and thromboxane B2 production during aggregation. It is suggested that the reduced vitamin E levels in diabetic platelets can contribute to the mechanisms of the enhanced platelet thromboxane production and aggregation which relate to the development of vascular complications.
A reduction in production of prostacyclin (PGI2) by the cells in the vascular wall may play a role in the pathogenesis of atherosclerosis in diabetic patients. The present study was undertaken to evaluate the effect of glucose on PGI2 production by endothelial cells in vitro. It was shown that PGI2 production by cultured bovine aortic endothelial cells was significantly reduced in the presence of a high concentration of glucose (300 mg/dl) compared with physiological concentrations of glucose (100 mg/dl). In contrast, no reduction in PGI2 production was observed in cells cultured with equimolar mannitol, suggesting that glucose itself, rather than the effect of osmolality, inhibited PGI2 production by cultured endothelial cells. In addition, a high concentration of glucose also inhibited the proliferation of cultured endothelial cells.
In order to evaluate age-related changes in glucocorticoid receptor and androgen receptor of cultured human pubic skin fibroblasts in young and aged men, we determined both [3H]dexamethasone binding and [3H]methyltrienolone (R1881, potent androgenic steroid) binding, using dispersed whole cell assay. Scatchard analyses of specific [3H]dexamethasone binding to the fibroblasts of young and aged men showed a single class of high-affinity binding sites with a mean ( ± SD) binding site concentration (Bmax) of 12.69 ± 2.36 × 104 and 12.87 ± 12.21 X 104 sites/cell, respectively, and mean ( ± SD) dissociation constant (Kd) of 5.60 ± 0.41 and 7.36 ± 2.17 nM, respectively. Scatchard analyses of specific [3H]R1881 binding to the same cultured skin fibroblasts of young and aged men showed a single class of high-affinity binding sites with a mean Bmax of 5.77 ± 1.02 × 103 and 2.82 ± 0.97 × 103 sites/cell, respectively, and a mean Kd of 0.56 ± 0.23 and 0.50 ± 0.28 nM, respectively. These findings indicate that there were no significant age-related changes in binding site and affinity of glucocorticoid receptor in cultured human pubic skin fibroblasts, whereas binding sites of androgen receptor significantly decreased in those of aged men as compared to young men, without significant change in affinity.
GHRH receptors in pituitary adenoma cell membranes from five patients with acromegaly were characterized using [125I] [His1,Nle27]GHRH-(1–32)NH2 ([125I]GHRHa) as a ligand. Specific binding of [125I]GHRHa to adenoma cell membranes was maximal within 20 min at 24 C, remained stable for 60 min, and was reversible in the presence of 500 nmol/L human GHRH-(1–44)NH2 (hGHRH). The specific binding increased linearly with 10–160 μg cell membrane protein. This binding was inhibited by 10−11–10−6 mol/L hGHRH in a dosedependent manner, with an ID50 of 0.20 nmol/L, but not by 10−7 mol/L vasoactive intestinal peptide, glucagon, somatostatin-14, somatostatin-28, TRH, LHRH, and CRH. The specific binding of [125I] GHRHa to the membranes was saturable, and Scatchard analysis of the data revealed an apparent single class of high affinity GHRH receptors in five adenomas from acromegalic patients; the mean dissociation constant was 0.30 ± 0.07 (±se) nmol/L, and the mean maximal binding capacity was 26.7 ± 7.0 (±se) fmol/mg protein. In three nonfunctioning pituitary adenomas, GHRH receptors were not detected. The plasma GH response to hGHRH (100 μg) injection was studied in four acromegalic patients before surgery. Plasma GH levels increased variably in response to hGHRH injection in all four patients. However, there was no correlation between the characteristics of the tumor GHRH receptors and plasma GH responsiveness in these patients. We conclude that pituitary GH-secreting adenomas have specific GHRH receptors. Exogenously administered GHRH presumably acts via these receptors, but the variations in plasma GH responsiveness to hGHRH in these patients cannot be directly related to the variations in binding characteristics of the GHRH receptors on the GH-secreting adenoma cells.
