Proaggregatory effect of fasting on platelet aggregation in the microcirculation of mice with streptozotocin diabetes

Specific non-saturable binding of insulin by human platelets

Studies on the nature and characterization of the specific binding of 125I-insulin to intact human platelets have been undertaken. Although under conditions of physiological buffer osmolality, a binding equilibrium was attained in 4-6 h at 4 degrees C, at higher temperatures (17 degrees C or 24 degrees C) equilibrium was reached only in the presence of very high buffer osmolality or 25 mM NaF. Under conditions of normal osmolality and in the absence of NaF, binding at 17 degrees C was not saturable. This phenomenon was specific for insulin or insulin-like hormones (the insulin-like growth factors) and did not occur with 125I-labelled growth hormone, ACTH or beta-endorphin. The non-saturable uptake of insulin appeared due to an energy-dependent specific sequestration or internalization of insulin by mechanisms probably involving the microtubule system. This study emphasizes the need to restrict this non-saturable uptake of insulin if one wishes to adequately study the platelet plasma membrane receptors for insulin. These data also indicate that there is a major interaction of insulin and insulin-like hormones with normal human platelets and support previous demonstrations of major insulin effects on platelet physiology in both normal and diabetic states.

Insulin delays platelet accumulation in injured cerebral microvessels of diabetic and normal mice

Pial arterioles of mice were injured by exposure to a noxious light/dye stimulus and resultant accumulation of platelets at the damaged site was monitored in vivo. When normal mice were injected with insulin 2 hr before damaging the arterioles, the accumulation of platelets was significantly delayed, but single injections of even higher doses failed to alter accumulation in mice with streptozotocin diabetes. When diabetic mice were placed on a schedule of daily injections of ultra lente insulin until normoglycemic, the treatment significantly delayed the accumulation of aggregating platelets in damaged vessels.

Some properties of mouse platelets

Mouse platelets were aggregated by arachidonate, thrombin, collagen and ADP. In general they were, like rat platelets, more aggregative in heparinized PRP than in citrated (3.8%) PRP. Mouse platelets underwent the release reaction when aggregated by arachidonate, collagen and thrombin, but not when stimulated by ADP. The aggregation of the platelets to arachidonate was inhibited by cyclooxygenase inhibitors and by prostacyclin. Studies with tritiated arachidonate showed that mouse platelets possess the lipoxygenase and cyclooxygenase pathways found in other mammalian platelets and produce thromboxane and 12-HETE. The mouse provides a convenient model for the study of many conditions known to affect platelet aggregation. The similarity of mouse platelets to the platelets of other mammals together with the ability to study large numbers of animals at low cost, should encourage further use of mouse platelets.

Effect of fasting on production from exogenous arachidonic acid of thromboxane and 12-hydroxy 5, 8, 10, 14-Eicosatetraenoic acid (12-HETE) by washed platelets of normal and streptozotocin diabetic mice

Washed mouse platelets produced thromboxane B2 (TXB2) and 12-hydroxy 5, 8, 10, 14-Eicosatetraenoic acid (12-HETE) in vitro from tritiated arachidonic acid. When diabetes was induced by injecting streptozotocin i.p 200 mg/kg the TXB2 production fell significantly and 12-HETE production significantly increased compared with that of control animals. Eighteen hours of food deprivation caused significant reductions in TXB2 and 12-HETE production in both the control and diabetic groups.