Effects of adrenaline on the isolated uterus of the cat

Hormonal influence on the response of the uterus of the Brazilian marsupial Didelphis albiventris to adrenergic drugs

The influence of catecholamines on the estrogenized uterus of the Didelphis albiventris was studied in an in vitro preparation. It was observed that the D. albiventris uterus reacts to both alpha and beta-adrenergic agonists but not dopaminergic ones. Adrenaline is more potent in inducing a contractile response than is noradrenaline. Isoprenaline, when added to the bath, is able neither to induce a response nor to interfere with a contraction previously induced by acetylcholine. It is, however, able to block the contractile response brought about by electric field stimulation. In an in vitro preparation from animals previously treated with estrogen and progesterone, the sensitivity to both alpha- and beta-adrenergic drugs was greatly increased. This is demonstrated by a higher pD2 in progesteronized animals compared to that in estrogenized ones. The increased sensitivity to beta-agonists after progesterone treatment is illustrated by the fact that isoprenaline is effective in inducing a relaxation of the uterus, in these conditions. These results indicate that the Brazilian opossum should be included among those animals in which progesterone enhances uterine sensitivity to drugs.

Responses to catecholamines of the rat isolated uterus throughout the natural oestrous cycle

The effects of noradrenaline (NA), adrenaline (Adr) and isoprenaline (Iso) on rat isolated uterus were studied, throughout the natural oestrous cycle. The beta-inhibitory effects of the catecholamines were measured as a percentage inhibition of a standard acetylcholine (ACh)-induced contraction. Iso produced approximately 80% maximum inhibition of the standard ACh-contraction in all 4 stages of the oestrous cycle. Adr and NA produced 80% maximum inhibition in oestrus only, and 50-60% maximum inhibition in proestrus, metoestrus and dioestrus. The differences in the degree of inhibition produced by the catecholamines were overcome (i.e. the maximum inhibition produced by Adr and NA was increased to become equal to that produced by Iso) when experiments were repeated in the presence of the uptake inhibitors desmethylimipramine (DMI) and normetanephrine (NMN), but not in the presence of an alpha-adrenoceptor antagonist (azapetine 10(-7) M). Variations in the uptake of 3H-Iso and 3H-Na were observed in the different stages of the oestrous cycle. Small alpha-adrenoceptor mediated motor responses to NA and Adr were observed only in the presence beta-antagonist (propranolol 10(-5) M), in uteri from rats in oestrus, metoestrus and dioestrus, but not proestrus. It is concluded that in the rat isolated uterus, beta-inhibitory receptors predominate throughout the natural oestrous cycle, although the existence of alpha-excitatory receptors has been shown in 3 of the 4 stages.

Effects of catecholamines on pregnant rat uterus

1 The effects of noradrenaline (NA), adrenaline (Adr) and isoprenaline (Iso) have been studied on pregnant rat uterus, at various stages of gestation--on the 10th and 20th days of pregnancy and on the first day post-partum. 2 The three catecholamines were inhibitory in all stages of gestation, with the same order of potency as observed in non-pregnant uteri (ie Iso greater than Adr greater than NA). However, mean pD2 values for the catecholamines tended to decrease as gestation progressed. 3 In 20 day pregnant and 1 day post-partum uteri, in the presence of propranolol, NA and Adr produced consistent alpha-adrenoreceptor mediated motor responses. 4 It is concluded that in the rat uterus, a form of pregnancy reversal occurs, in that there is a decrease in beta-adrenoreceptor responsiveness, and an increase in alpha-adrenoreceptor responsiveness towards the end of gestation, and immediately post-partum.