Platelet alpha 2-adrenoceptor density in pregnancy-induced hypertensive patients: effect of epidural analgesia
Sánchez, A.; Sáiz, J.; Sáez, B.; Carrasco, S.; Díaz, R.
Journal of Hypertension 10(8): 831-837
1992
ISSN/ISBN: 0263-6352 PMID: 1325516 Document Number: 392802
Objectives: Although pregnancy induced hypertension (PIH) is an important and relatively common medical problem, its pathophysiology remains unresolved and the search for a biochemical marker that precedes the hemodynamic abnormalities of PIH continues. Since human platelets contain .alpha.2-adrenoceptors, these receptors were measured in women with PIH to determine whether patients with PIH have .alpha.2-adrenoceptor abnormalities that might cause or exacerbate the hypertensive process. The effect of epidural analgesia upon blood pressure and its relation to changes in platelet .alpha.2-adrenoceptor density was also investigated. Design: Biochemical measurements and radioligand binding assays in platelets were performed on 33 patients with the criteria for PIH and on 26 healthy pregnant women. Results: Blood pressure was significantly elevated in hypertensive women when compared with normotensive pregnant women although, in this group, blood pressure returned to normal levels in response to epidural analgesia. In drug-free hypertensive patients, the specific binding of 3H-yohimbine to platelet membranes increased significantly compared with that in control pregnant subjects. In contrast, the dissociation constant was not significantly different in the two groups. Furthermore, .alpha.2-adrenoceptor density in the group with PIH returned to normal levels in response to epidural analgesia. Conclusion: Our findings indicate that PIH is characterized by an exaggerated response of platelet .alpha.2-adrenoceptor density to a rise in blood pressure and that this alteration could be significant in the pathogenesis of hypertension. Furthermore, human .alpha.2-adrenoceptors undergo regulatory mechanisms similar to those recently described for adrenergic receptors in a variety of animal models.