Effects of adrenaline and noradrenaline in separated longitudinal and circular myometrial preparations from the guinea-pig: selective modulation by ovarian steroids.

Field-stimulated strips of circular and longitudinal myometrium from virgin adult guinea-pigs were used to study the influence of ovarian steroids upon uterine responses to adrenaline and noradrenaline. Preparations were taken from animals (i) untreated, on day 9 or 10 of the oestrous cycle; (ii) treated for 14 days with oestradiol cypionate, beginning on day 9 or 10; and (iii) treated as in (ii) then given both oestradiol cypionate and progesterone for a further four days. Oestradiol treatment led to a 2-fold increase in the circulating level of progesterone; subsequent treatment of oestradiol-primed animals with progesterone resulted in even higher circulating progesterone levels, comparable with those occurring during mid-pregnancy in this species. Both adrenaline and noradrenaline produced phentolamine-sensitive motor responses of circular myometrial preparations from each treatment group. Steroid treatment was without significant effect on the potencies or maximal effects of the two amines on the circular muscle layer. Both catecholamines effected phentolamine-sensitive excitatory responses of longitudinal myometrial preparations from untreated guinea-pigs. Adrenaline usually produced propranolol-sensitive inhibitory responses of longitudinal preparations from oestradiol-treated animals, while noradrenaline did so only in a minority of cases. The potencies of adrenaline as an inhibitory agonist and noradrenaline as an excitatory agonist were markedly increased in preparations from oestradiol-primed animals.(ABSTRACT TRUNCATED AT 250 WORDS)