Effects of glucose, glycerol, 3-hydroxybutyrate, insulin, and leptin on placental growth hormone secretion in placental explants.

Placental growth hormone (PGH) is secreted from the syncytiotrophoblast in increasing amounts during pregnancy. The physiology and regulation of PGH is not well known; however, low glucose levels appear to stimulate PGH liberation IN VITRO and IN VIVO. PGH appears to have lipolytic effects, and inverse correlations between maternal body mass index and serum PGH levels have been reported. Therefore, substances related to maternal adipose tissue metabolism could influence PGH secretion. The effect of insulin, glycerol, 3-hydroxybutyrate (3-OHB), and leptin on PGH and human placental lactogen (hPL) secretion from cultured placental explants was studied. In glucose-free media, PGH content increased upto 237.5+/-28.4% of control media (p<0.001, ANOVA). Insulin levels were without effect on PGH secretion, as were 3-OHB, leptin, and glycerol at 0.02 mmol/l. Glycerol at 0.2 mmol/l increased PGH in all of the placental explants studied (n=8; mean increase 27.3+/-7.1%), and this difference was significantly different from the control explants (p=0.004). The liberation of hPL to culture media was different from PGH and was influenced by glucose and insulin. In conclusion, the absence of glucose profoundly increased PGH secretion in cultured placental explants. Addition of glycerol in physiologically relatively high concentrations showed a less pronounced stimulatory effect.

Platelet activity and in vivo arterial thrombus formation in rats with mild hyperhomocysteinaemia.

Elevated plasma levels of total homocysteine (hcy) have been associated with an increased occurrence of arterial thrombosis. In the present study, we investigated the influence of hyperhomocysteinaemia on platelet aggregation and arterial thrombus formation in vivo. Fifty-one rats were included in the study, of which 29 received hcy in the drinking water for 4 weeks. Blood samples were withdrawn for measurement of platelet count and mean platelet volume. Platelet aggregation response in platelet-rich plasma following adenosine diphosphate or collagen stimulation were examined. In vivo thrombus formation was investigated by transillumination and videotape recording of the rat femoral artery after a thrombogenic injury was established. Off-line videotape analysis using computer-assisted planimetry permitted quantification of the thrombus area, and area versus time curves were obtained. In the intervention group receiving hcy, total hcy in plasma increased two-fold to 14.3 micromol/l, as compared with 7.3 micromol/l in the control group (P < 0.001). The platelet count and mean platelet volume did not differ between the two groups. In vivo thrombus formation expressed as the area under the curve or maximum thrombus area was not found to be altered in the presence of an increased homocysteine level, neither was adenosine diphosphate-induced platelet aggregation. However, collagen-induced platelet aggregation significantly decreased in the hcy group (P = 0.02). Pro-thrombotic effects of isolated mild hyperhomocysteinaemia are not supported by the present study in rats.

Local application of FFR-rFVIIa reduces thrombus formation at arterial anastomosis in rats.

Thrombosis is still a significant problem in microvascular surgery. The aim of this study was to evaluate the antithrombotic effect of topically applied active site-inhibited recombinant human factor VIIa (FFR-rFVIIa) in a rat model with microvascular thrombosis. Forty-five male rats were allocated to one of three groups: local treatment with vehicle only, local treatment with 0.035 mg of FFR-rFVIIa, or local treatment with 0.35 mg of FFR-rFVIIa. An arteriotomy was made in the right femoral artery. Ten minutes following topical application, a thrombogenic anastomosis was performed. Using a transilluminator, thrombus formation and anastomotic bleeding episodes were observed and registered for 40 min. Local application of FFR-rFVIIa resulted in a 85-90% reduction of thrombus formation in both treated groups compared to the control group, but the reduction was only statistically significant in the group treated with 0.035 mg of FFR-rFVIIa. An increased occurrence and duration of anastomotic bleeding episodes were observed in both FFR-rFVIIa-treated groups.

Intravenous acetylsalicylic acid, magnesium and their combination in experimental arterial thrombosis in rats.

Intravenous acetylsalicylic acid (ASA) and magnesium (Mg) both possess antiplatelet properties and are thus potential inhibitors of the formation of arterial thrombi. Their effect on the dynamic aspects of arterial thrombus formation was investigated following intravenous administration of both substances alone and in combination. A blinded, placebo-controlled, in-vivo study was performed in 71 rats. Thrombus formation was induced by a standardized arteriotomy in the right femoral artery with inversion of the vessel wall during subsequent closure. Thrombus formation was recorded on video tapes and analysed off-line for 30 min. Animals were randomly assigned to one of four groups: 20 mg bolus of ASA followed by 0.3 mmol/h Mg (ASA/Mg group); NaCl followed by 0.3 mmol/h Mg (Mg group); 20 mg bolus of ASA followed by NaCl (ASA group); or NaCl throughout the experiment (control group). In the ASA-treated groups, serum levels of thromboxane B2 were reduced significantly, and the Mg-treated groups reached a serum level of Mg just above 2.0 mmol/l. No significant differences were observed in initial or maximum thrombus area or in mean thrombus area during the study period. In the ASA/Mg group, a trend towards reduced thrombus formation was observed (P = 0.06). In the same group, seven of 22 animals developed an occlusive thrombus (P < 0.01), an unexpected adverse event possibly related to the combined administration of ASA and Mg.

Aprotinin attenuates platelet accumulation in ischaemia-reperfusion-injured porcine skeletal muscle.

This purpose of this study was to evaluate the effect of aprotinin, a serine protease inhibitor, in ischaemia- and reperfusion-injured myocutaneous flaps and skin flaps. Flap survival, microcirculatory platelet accumulation, and regional blood flow were investigated in seventeen pigs which had been subjected to 8 h of ischaemia and 18 h of reperfusion. The pigs were randomly assigned to aprotinin treatment (n = 9) or saline (n = 8). In-vitro studies were performed to investigate the influence of aprotinin on the activated partial thromboplastin time. The survival of skeletal muscle correlated positively with the concentration of aprotinin (P = 0.02) and could not be explained by regional changes in blood flow. Platelet accumulation was decreased in aprotinin-treated muscle (P = 0.04). In-vitro (n = 10), 100 kallikrein inactivator units/ml aprotinin prolonged the activated partial thromboplastin time both in plasma (P = 0.001) and in blood (P = 0.002), suggesting an anticoagulant rather than a procoagulant effect. In conclusion, aprotinin at high concentrations may be beneficial for the survival of skeletal muscle and provides protection from platelet accumulation in the microcirculation of skeletal muscle exposed to ischaemia and reperfusion injury.

Microvascular damage secondary to thromboembologenic arterial injury--a new experimental model.

BACKGROUND AND AIMS: The isolated rat cremaster model is used extensively for evaluating the microcirculation secondary to arterial injury. Current techniques, however, do not allow for assessment of injury and effect within the same animal. The purpose of this study was to develop a model incorporating the following points: visualization of the upstream arterial injury and the downstream microvascular damage in the same animal, analysis of capillary density by randomization of measuring windows throughout the cremaster muscle, and simplification of the arterial injury. MATERIALS AND METHODS: Thirteen male Wistar rats were randomized into two groups. In group I, the entire isolation of the cremaster muscle was performed, without arterial damage. In group II, arterial damage consisting of a standardized pinch was applied to the feeding vessel. RESULTS AND CONCLUSIONS: It was possible to produce a simplified arterial injury and visualize the resulting downstream microvascular damage in the same animal, in a quantitative and randomized fashion. In group I, no thrombus formation was seen. In group II, all animals produced an embolizing arterial thrombus, which was dynamic within the first hour of observation. Capillary density was reduced from 6.5 to 3.5 capillaries/measuring window within the first hour after arterial thromboembolism.