Beta-adrenergic receptor characteristics were investigated in peripheral blood mononuclear leukocytes taken from patients before and after partial thyroidectomy. In order to discriminate the effect of surgical stress per se from that of thyroidectomy, the analysis was also performed on patients before and after cholecystectomy. Receptor characteristics were determined by using dihydroalprenolol as ligand in direct equilibrium binding experiments. The binding affinity showed no changes either when two different surgical treatments were compared or when the same patient was analysed before and after the operation. On the contrary, a significant decrease in receptor density was found in thyroidectomized patients when compared pre-and post-operatively. This fall in receptor number seems to be linked with thyroid function since no statistically significant changes were observed in cholecystectomized patients in relation to surgical operation. This view is further supported by data on T3 serum levels, which show a significant fall after thyroidectomy but no statistically significant modifications after cholecystectomy. It is concluded that betaadrenoceptor modulation plays an important role in the relationship between thyroid and beta-adrenergic system.Many clinical signs of hyperthyroidism are known to mimic the effects of beta-adrenergic stimulation. Manifestations such as increased myocardial con¬ tractility, tachycardia, hyperkinesis and diaphoresis
β2-Adrenoceptor characteristics of human mononuclear leukocytes were assayed in hypertensive patients before and after treatment with 100 mg/day atenolol. While no changes have been observed in receptor affinity, a statistically significant increase (36%) has been demonstrated in receptor density following treatment. Blood pressure and heart rate were also measured in order to test the efficacy of the administered drug. All these parameters showed a fall in the post-treatment values. It is concluded that at therapeutic concentration, β2-adrenoceptors undergo up-regulation by atenolol in spite of its cardioselectivity. Such a regulation, which may represent a fundamental step in the mechanism leading to withdrawal syndrome, may, therefore, be suggested being quite widespread.
The regulatory action exerted on receptors by acebutolol, a cardioselective β-blocker containing intrinsic sympathomimetic activity, has been investigated. β-Adrenoceptor affinity and density of human mononuclear leukocytes were assayed in hypertensive patients before and after treatment with 400 mg/day acebutolol. While receptor affinity showed no changes between pre- and post-treatment values, a statistically significant decrease has been demonstrated in receptor density following treatment. Blood pressure and heart rate were also measured in order to test the efficacy of the administered drug. All these parameters showed a fall in the post-treatment values. It is concluded that the partial agonist acebutolol, in spite of the fact that it acts clinically as a β-blocker, has the regulatory mechanism characteristic of agonists.
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