The influence of propranolol on the thyrotropin receptor.

Propranolol, a beta adrenergic blocking drug, is known to inhibit the thyrotropin (TSH) stimulation of adenosine-3',5'-monophosphate (cyclic AMP production in thyroid membranes but the mechansim of this inhibitory action is known. We have therefore investigated the influence of propranolol on the binding of 125I-labelled TSH to human thyroid membranes. Both d- and l-propranolol were found to enhance the binding of 125I-labelled TSH to thyroid membranes. The amount of label bound increased from about 30% in the absence of propranolol to about 60% in the presence of 3.3 x 10(-3)M propranolol. Scatchard analysis of the binding data indicated that propranolol increased the association constant of the thyrotropin-thyrotropin receptor interaction. Practolol, lithium carbonate, methimazole, and somatostatin had no effect on thyrotropin binding. This effect of propranolol appeared to be due to a direct reversible action of propranolol on the thyroid membranes and could be attributed to the membrane-disrupting properties of the drug rather than its beta-blocking activity. The increased TSH receptor occupancy which resulted from the increased association constant of the TSH-thyroid membrane interaction corresponded with a decrease in TSH-stimulated cyclic AMP formation. These data could indicate that propranolol reduced the efficiency of the receptor-adenylyl cyclase coupling system.

Labelling of the thyroid cell surface with 125I.

The surface membrane proteins of cultured porcine thyroid cells have been labelled with 125I by the lactoperoxidase method. Evidence that the labelling was restricted to the cell surface was supported by the high viability of the cells in suspension, the high proportion of labelled material in the particulate fraction after homogenization and electron-microscopic autoradiographic studies. The labelled proteins were analysed by electrophoresis on polyacrylamide gels containing sodium dodecyl sulphate and this indicated the presence of ten major labelled protein bands with approximate molecular weights of 175 000, 155 000, 135 000, 88 000, 80 000, 52 300, 39 000, 30 000, 21 000 and 14 300. Comparison of the electrophoretic patterns obtained with cultured human and porcine thyroid cells suggested that there were species differences in the proportions of lower-molecular-weight proteins.

Shedding of surface proteins by porcine thyroid cells.

Isolated porcine thyroid cells were surface-labelled with 125I using the lactoperoxidase technique. Samples of the cells were then cultured and harvested at various intervals for up to 7 days. The labelled proteins remaining on the cells or shed into the culture medium were analysed by electrophoresis on polyacrylamide gels run in sodium dodecyl sulphate. These studies indicated that the several different surface proteins of the thyroid cells were lost from the cell surface at similar rates (half-time of approximately 28 h) as the result, at least in part, of a process which depended on active cell metabolism. In addition, the gel profiles obtained from analysis of both medium and membrane-bound labelled proteins were similar and this suggested that peptide cleavage was not involved in the shedding of the majority of these proteins.

The clinical development of ondansetron for use in the prevention and treatment of postoperative nausea and vomiting.

An international clinical trial programme has been established to assess the efficacy and safety of ondansetron in the prevention and treatment of postoperative nausea and vomiting. The programme included nine pilot studies and six key placebo-controlled studies. These studies have evaluated both oral and intravenous formulations of ondansetron in the prevention of postoperative nausea and vomiting, and intravenously administered ondansetron in the treatment of established symptoms. Most patients included in the trials were adult women, less than 50 years of age, receiving anaesthesia for gynaecological surgery. The primary efficacy analysis for emesis was based on the assessment of complete response (i.e. absence of emetic episodes or nausea in the first 24 h postoperatively). These trials clearly demonstrated the anti-emetic efficacy of ondansetron in the prevention and treatment of postoperative nausea and vomiting.