Comparison of guinea pig uterine and rat vas deferens preparations for assessment of beta 2-adrenoceptor-mediated activity.

In the present study, investigations were performed to determine the subtype(s) of beta-receptor-mediating relaxation in K+-depolarized guinea pig uterine preparations, and inhibition of twitches in field-stimulated rat vas deferens preparations. The relative activities of (-)-isoprenaline, salbutamol, terbutaline, noradrenaline, and RO363, and the affinity constants determined for the beta 1-receptor antagonist atenolol, and the beta 2-receptor antagonist lCl 118551, indicated that all the inhibitory responses in both preparations were mediated solely through beta 2-adrenoceptor stimulation. In the uterine preparations there was a small population of alpha-receptors which were of little consequence when assessing beta 2-receptor-mediated activity. During K+-induced contractures, both neuronal and extraneuronal uptake systems were inactivated. In rat vas deferens preparations, it was necessary to pretreat the tissues with phenoxybenzamine in order to prevent alpha-receptor actions and neuronal and extraneuronal uptake systems interfering with beta-receptor-mediated activity. In both tissues, 6-8 highly reproducible concentration-effect curves to (-)-isoprenaline could be established. However, the uterine preparation responded more robustly to repeated washings, required less sensitive recording apparatus, and showed responses to individual concentrations of drugs that were more readily quantified. However, in general, both preparations appear to be suitable as tissues for assessing the beta 2-adrenoceptor actions of drugs.