The beta-adrenoreceptors mediating uterine relaxation throughout the oestrous cycle of the rat are predominantly of the beta 2-subtype.

1 The beta-adrenoreceptor subtype(s) mediating uterine relaxation throughout the 4-day oestrous cycle of the rat were determined by using pharmacological techniques. 2 The order of potency of the test beta-adrenoreceptor agonists in dioestrus, proestrus, oestrus and metoestrus was the same, being isoprenaline = fenoterol greater than salbutamol greater than noradrenaline greater than prenalterol greater than BRL 28410. 3 The pA2 values for the antagonists atenolol and ICI 11851 against both noradrenaline and fenoterol were not altered by the stage of oestrus and were consistent with the receptor being solely of the beta 2-subtype. 4 It is concluded that the beta-adrenoreceptors mediating uterine relaxation are of the beta 2-subtype throughout the natural oestrous cycle.