An ultrasonographic method to measure the sensitivity of the baroreflex in clinical practice: application to pharmacological studies.

To determine whether it is possible to assess baroreceptor sensitivity by measuring changes in blood velocity in the carotid artery and changes in the heart rate, we performed a series of 108 experiments in 19 hypertensives aged 20-57 years (mean 46.6 +/- 8.6). In each experiment, we took simultaneous measurements of carotid artery blood flow velocity (Doppler technique), the brachial intra-arterial blood pressure and the heart rate, during a rapid and transient increase in blood pressure induced by injections of phenylephrine. We then calculated the maximum slope of the regression lines correlating blood velocity with the heart period (Trieste method) and blood pressure with the heart period (Oxford method). We obtained good accuracy from the Trieste method compared with the Oxford method, as assessed by the mean of the sum of the squares (difference + 5%, NS). After the administration of 4 mg oral lacidipine to 13 essential hypertensives, aged 37-54 years (47.6 +/- 5.3), baroreflex sensitivity was not changed, as assessed by either method (Oxford method 10.1 +/- 5.5 versus 9.8 +/- 6.2 ms/mmHg; Trieste method - 0.57 +/- 0.32 versus - 0.49 +/- 0.31 ms/Hz). The coefficients of variation for the two methods, calculated for the measurements taken before and after the administration of lacidipine, were not statistically different (Oxford method 25.0 +/- 18.4 versus 36.2 +/- 16.0; Trieste method 36.7 +/- 19.2 versus 39.7 +/- 19.2). The new non-invasive Trieste method thus showed the same accuracy and precision as the invasive Oxford method in measuring baroreflex sensitivity and can be used in pharmacological studies.

[Regulation of platelet alpha2 adrenergic receptors in a population of patients with essential arterial hypertension and in normotensive subjects]. / Regolazione dei recettori alfa2 adrenergici piastrinici in una popolazione di pazienti con ipertensione arteriosa essenziale ed in una di soggetti sani.

The development of specific binding techniques for the study of adrenergic receptors on circulating human blood cells has allowed a better understanding of the physiological alterations of adrenergic receptors and changes of adrenergic receptors in pathological conditions such as hypertension. Alpha adrenoceptors play an important part in blood pressure regulation at several sites. There are contradictory and conflicting reports on whether alpha receptor mechanisms are altered in essential hypertension. To address further the role of alpha 2 adrenoceptors in human essential hypertension the number and the affinity of alpha 2 adrenergic receptors and plasma catecholamine levels were measured in 20 normotensive and 24 hypertensive subjects. The median number of receptors (Bmax) was 159.10 +/- 14.38 fmol/mg protein for controls versus 179.09 +/- 13.26 fmol/mg protein for hypertensives. The median dissociation constant (KD) of the receptors for 3H-Yohimbine was 1.43 +/- 0.17 nmol/l for controls and 1.85 +/- 0.19 nmol/l for hypertensives patients. There were no differences in catecholamine plasma levels between the two groups. In controls platelet alpha 2 receptor number correlated with age (p less than 0.003) but not with blood pressure values. Our results show that measurement of platelet alpha 2 receptor levels and affinity is unable to differentiate a group of hypertensives from normotensives. Nevertheless, we cannot exclude a possible role of peripheral alpha 2 adrenergic receptors in the pathogenesis of high blood pressure.