Prostacyclin and thromboxane in diabetic children

Prostanoid production in umbilical vessels and its relation to glucose tolerance and umbilical artery flow resistance

OBJECTIVE

To study prostanoid synthesis in umbilical vessels relative to maternal glucose tolerance and umbilical artery blood flow resistance.

STUDY DESIGN

Umbilical artery pulsatility index was determined by Doppler velocimetry in 21 women with diabetes or impaired glucose tolerance and 10 healthy women. Segments from the umbilical artery and vein were incubated and prostacyclin (PGI2) and thromboxane (TxA2) metabolites determined. Statistical analyses with the Mann-Whitney U test, Kruskal-Wallis test, Wilcoxon signed-ranks matched-pairs test, contingency table analysis, Fisher's exact test, and simple linear regression analysis were used and a two-tailed P value of < 0.05 considered statistically significant.

RESULTS

No significant difference in PGI2 or TxA2 production was found in umbilical vessels between the women with diabetes/impaired glucose tolerance and controls, but the PGI2/TxA2 ratio in the vein was significantly lower in the diabetes/impaired glucose tolerance group. The umbilical artery pulsatility index was positively correlated to the PGI2/TxA2 ratio in cord vessel segments and to cord plasma TxA2 concentration. The cord plasma TxA2 concentration was significantly higher in cases with a high umbilical artery pulsatility index. The prostanoid production was not correlated to maternal HbA1c or cord plasma C-peptide concentrations.

CONCLUSIONS

In association with diabetes, an increased 'peroxide vascular tone' and an enhanced 'endoperoxide shift' between platelets and vascular endothelium may explain the unexpected positive correlation found between the umbilical artery pulsatility index and the vascular PGI2/TxA2 synthesis ratio.

Prostacyclin release from the human saphenous vein in diabetics in lower than in nondiabetics

The balance between prostacyclin and thromboxane has been suggested to be of great importance for the maintenance of patency in veins. In order to investigate prostacyclin and thromboxane release, segments from the human saphenous veins were investigated in 53 patients. Twenty-seven patients (10 males, 17 females) underwent surgery for varicose veins. Twenty-six patients (14 nondiabetics, 12 diabetics) underwent surgery for lower limb ischemia (rest pain or gangrene) with use of the saphenous vein as arterial conduit. Vein segments were gently excised and perfused ex vivo for five 15 minute periods, with a balanced salt solution and determination of the stable degradation products 6-keto-PGF1 alpha and TxB2. Saphenous veins from patients with varicose veins had an initial prostacyclin release of 61 +/- 13 pg/mm2/15 min declining to 4 +/- 1 pg/mm2/15 min after 60 min (p < 0.001) and increasing after addition to arachidonic acid to 37 +/- 7 pg/mm2/15 min (p < 0.001). Segments from nondiabetic patients with lower limb ischemia did not differ from those of varicectomy patients, but diabetic segments had a significantly lower prostacyclin release than both these groups, 34 +/- 11 pg/mm2/15 min, 1 +/- 1 pg/mm2/15 min, and 7 +/- 5 pg/mm2/15 min, respectively (p < 0.05). The addition of arachidonic acid failed to increase the prostacyclin release in diabetics. Three patients from each group were studied regarding thromboxane release and there was almost no detectable thromboxane in any group. These findings suggest that diabetics have a lowered prostacyclin release from the saphenous vein and that the deficiency is at the cyclo-oxygenase level.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular sensitivity changes to eicosanoids in rats with experimentally induced diabetes mellitus

This paper attempts to provide a short review of the evidence for: 1. Increased platelet production of thromboxane A2 and reduced vascular production of prostacyclin in the human and also animal models of diabetes. 2. Reduced depressor responsiveness to arachidonic acid of anaesthetized alloxan- and streptozotocin-induced diabetic rats. 3. Enhanced constrictor responsiveness to arachidonic acid in blood-perfused hindquarters of alloxan-induced diabetic rats. 4. Potentiation by the thromboxane A2-mimetic, U46619, of constrictor responses to 5-hydroxytryptamine in Krebs'-perfused hindquarters and kidneys of both control and alloxan-induced diabetic rats. 5. Alterations during diabetes in production of, and responsiveness to, eicosanoids may contribute to the cardiovascular changes which occur in this disease.

In vivo measurement of thromboxane B2 and 6-keto-prostaglandin F1 alpha in humans in response to a standardized vascular injury and the influence of aspirin

The effects of smoking, aspirin ingestion, and sex differences on bleeding times and bleeding time thromboxane B2 and 6-keto-prostaglandin (PG)F1 alpha production were examined. Nonsmoking men produced more thromboxane B2 (3.99 +/- 0.76 ng/ml) than nonsmoking women (2.13 +/- 0.24 ng/ml). Female smokers produced more thromboxane B2 (5.01 +/- 0.97 ng/ml) than nonsmoking women. Twenty-four hours after a single dose of 600 mg aspirin, in vitro production of thromboxane B2 in response to collagen fell by 95%, whereas in vivo production of thromboxane B2 and 6-keto-PGF1 alpha in bleeding time blood fell by 87% and 66%, respectively. Subjects with the lowest absolute levels of thromboxane B2 24 hours after aspirin were also those with the longest postaspirin bleeding times. Recovery of 6-keto-PGF1 alpha production was faster than recovery of thromboxane B2 production, but 6-keto-PGF1 alpha production for most subjects was still below basal 72 hours after aspirin. The influence of two different doses of long-term aspirin (80 mg every other day and 325 mg daily) on the in vivo production of thromboxane B2 and 6-keto-PGF1 alpha was studied in normals and diabetics. After 14 days of 80 mg aspirin every other day, thromboxane B2 and 6-keto-PGF1 alpha production were both substantially inhibited (93% and 78%, respectively). After 14 days of 325 mg aspirin daily, thromboxane B2 production was similarly substantially inhibited (93%), whereas 6-keto-PGF1 alpha was significantly less affected (only 45% inhibition). Study of a second group of five normal subjects confirmed that 6-keto-PGF1 alpha production was significantly inhibited 24 hours after the first dose of 325 mg aspirin but was not significantly less than basal after 14 days of 325 mg aspirin. The results suggest that 325 mg aspirin daily is more antithrombotic compared with 80 mg every other day due to the superior preservation of prostacyclin production.

Effects of purified fish oil on platelet lipids and function in diabetic women

Purified fish oil (MaxEpa, 10 g/day) treatment for six weeks increased consistently the content of eicosapentaenoic (20:5, n-3), docosapentaenoic (22:5, n-3) and docosahexaenoic acid (22:6, n-3) and decreased that of arachidonic acid (20:4, n-6) and other n-6 polyunsaturated C-20 fatty acids (PUFA) of platelets both in insulin dependent diabetic (IDDM) (n = 13) and healthy women (n = 7), but it had no effect on the number and aggregation of platelets or on plasma beta-thromboglobulin. Serum TxB2, produced by diabetic platelets was reduced, but the urine 6-keto PGF1 alpha excretion, believed to reflect prostacyclin (PGI2) production was normal in the diabetics. During the MaxEpa treatment the response of thromboxane B2 (TxB2) release to ADP was decreased in platelet-rich plasma in the healthy subjects. However, in diabetics the fish oil treatment resulted in increased TxB2 formation from exogenous arachidonic acid. The results demonstrate the dependence of platelets fatty acid composition on dietary sources and suggest that at least in the diabetic platelets the diminished arachidonic acid content could be compensated by an activation of enzymes of thromboxane B2 pathway.