title: Effects of ovarian steroids upon responses mediated by adrenoceptors in separated layers of the myometrium and in the costo-uterine muscle of the guinea-pig.
abstract: 1 This study describes the effects of ovarian steroid hormones upon the responses to adrenoceptor agonists of isolated myometrium, separated into its longitudinal and circular layers, and of costo-uterine muscle from guinea-pigs. The preparations were field-stimulated at 100 s intervals, and the adrenoceptor agonists phenylephrine and isoprenaline produced enhancement or inhibition of the evoked contractions.2 Isoprenaline produced propranolol-sensitive inhibitory effects in longitudinal and circular myometrium and costo-uterine muscle preparations from animals from all experimental groups: i.e. from nonsteroid-treated animals (ovariectomized and intact); intact animals treated with either oestrogen or progesterone alone; ovariectomized animals treated with oestrogen; ovariectomized and intact animals treated with progesterone following oestrogen priming; and from animals 1-4 days post-partum. Longitudinal myometrial preparations from progesterone-treated oestrogen-primed and from post-partum animals were most sensitive to this agonist.3 Phenylephrine produced phentolamine-sensitive excitatory effects in circular myometrial and costo-uterine muscle preparations from animals from all the experimental groups. In contrast, propranolol-sensitive inhibitory responses to phenylephrine occurred in longitudinal myometrial preparations taken from animals treated with progesterone following oestrogen priming, and from post-partum animals. Longitudinal myometrium from animals from the remaining experimental groups exhibited phentolamine-sensitive excitatory responses to phenylephrine.4 The basis for the selective effect upon the longitudinal myometrium of exposure to progesterone following a period of oestrogen priming, is discussed. The results described are consistent with the possibility that in the longitudinal layer of guinea-pig uterus exposed to progesterone following oestrogen priming there is an increase in the proportion of beta-adrenoceptors in this layer. This increase may reduce the likelihood of contractions arising via direct stimulation of alpha-adrenoceptors in this layer in response to sympathetic activation during pregnancy.
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009215:Myometrium / Q000187:drug effects*; D010053:Ovary / Q000502:physiology*; D010656:Phenylephrine / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology*; D011941:Receptors, Adrenergic / Q000187:drug effects*; D014590:Uterine Contraction / Q000187:drug effects; D014599:Uterus / Q000187:drug effects*
chemical_list: D011941:Receptors, Adrenergic; D010656:Phenylephrine; D011374:Progesterone; D004958:Estradiol; C007630:estradiol 17 beta-cypionate; D007545:Isoproterenol