Kinetic study of thrombogenesis on stroke-prone spontaneously hypertensive rats (SHRSP). (1) Thrombopoiesis and platelet consumption in early stage (10 weeks) associated with remarkable increase of blood pressure [proceedings]

Megakaryocytopoiesis in spontaneously hypertensive rats (SHR)

Bone marrow megakaryocytes and their progenitors were studied in SHR in order to obtain more information about megakaryocytopoiesis in hypertension since it is known that various anomalies of platelet function occur in hypertension. Megakaryocytopoiesis under steady state conditions and following stimulated erythropoiesis and thrombocytopenia was not found to be significantly different in SHR from that in normotensive Wistar controls.

Platelet serotonin content and uptake in spontaneously hypertensive rats

Platelet serotonin (5-HT) content and uptake were studied in male SHR and WKY at various ages. Blood was withdrawn from the carotid artery under anesthesia and 5-HT levels determined from platelet rich plasma (PRP) using a HPLC technique coupled with an electrochemical detection method. Platelet 5-HT uptake was studied by incubating PRP at 37 degrees C for 10 sec with increasing concentrations of 3H-5HT. Lineweaver- Burk plots of 3H-5HT uptake were linear suggesting simple Michaelis- Menten uptake kinetics. The SHR had more platelets than age-matched controls and consequently a higher blood circulating pool of 5-HT. Nevertheless, the 5-HT platelet levels were similar to those of their age-matched rats. The 5 week-old SHR and WKY had greater numbers of platelets and higher 5-HT platelet levels than the older rats of both strains. The affinity constants (Km) and the maximal velocities (Vmax) of platelet 5-HT uptake did not differ significantly between the 12 week- and the 6 month-old SHR and WKY. These data suggest that the SHR do not show the same impairment in platelet 5-HT metabolism as observed in essential hypertension in man.

Hypoaggregability of washed platelets from stroke-prone spontaneously hypertensive rats (SHRSP)

The aggregation properties of washed SHRSP platelets were investigated in comparison with normotensive WKY platelets at prehypertensive (4 weeks), early hypertensive (11 weeks) and late hypertensive (17 weeks) ages in the absence of plasma factors. The number of platelets in SHRSP was markedly lower with the development of hypertension than that in WKY. The thrombin- and collagen-induced aggregation was markedly reduced in the platelets from 11 and 17 week old SHRSP compared with that of age-matched WKY, whereas the degree of platelet aggregation in 4 week old SHRSP showed a tendency to be even greater than that in WKY. The changes in blood pressure and platelet aggregability were correlated inversely. ADP did not induce aggregation in the same system used for thrombin and collagen stimulation but in another system it aggregated washed rat platelets. Aggregation responses to ADP and ionophore A23187 were also significantly lower in 14 week old SHRSP platelets than age-matched WKY platelets. Together with other evidence, these results suggest that defective Ca2+ function, rather than the presence of exhausted platelets, is responsible for hypoaggregability in SHRSP platelets.