Quantitative pharmacological characterization of beta-receptors and two types of alpha-receptors mediating sympathomimetic smooth muscle response in the human Fallopian tube at various cyclic stages.

The dissociation constants for adrenoceptor-antagonist complexes (KB) were determined in vitro in circular and longitudinal smooth musculature from the ampullary and isthmic regions of the human Fallopian tube. High extracellular potassium concentrations were used to eliminate the spontaneous contractile activity. Neuronal and extraneuronal amine uptake mechanisms were blocked. The parallel shift of the log dose-response curves was secured in Arunlakshana-Schild plots. KB for the beta-receptor, mediating sympathomimetic relaxation, were determined during alpha-receptor blockade: the values for propranolol were the same (approximately 10(-6) M) in all preparations and at all cyclic stages, as determined from plasma estradiol and progesterone levels. KB for the complex between the alpha-receptor (mediating contraction) and phentolamine were determined during beta-receptor blockade. The values were the same in all types of smooth musculature, but varied with cyclic stage: they were around 7 x 10(-8) M when plasma estradiol and progesterone were both minimum, and around 2 x 10(-7) M when these steroid levels were moderate to high, suggesting that the properties of the contractile receptors of the human Fallopian tube are modified during the menstrual cycle.