Actions of some autacoids and peptides, including relaxin, on costo-uterine muscle from rats.

1. The actions of angiotensin II, bradykinin, oxytocin, arginine vasopressin, relaxin, serotonin and the prostaglandins E2 and F2 alpha were examined on preparations of costo-uterine muscle from stilboestrol-treated rats. 2. All the agonists, except relaxin, when used in concentrations which contract the rat uterus, also produced contractions of costo-uterine muscles. Concentration-response curves were steep and maximal responses to the agonists were comparable. The negative log molar EC50 values were: serotonin, 6.5; angiotensin II, 8.8; bradykinin, 8.4; PGE2, 8.3; PGF2 alpha, 7.1. The EC50 values (units/L) for oxytocin and vasopressin were 4.4 and 2.7 respectively. 3. Indomethacin (2.8 or 5 mumol/L) did not decrease the contractile effects of the peptides or serotonin. The effects of serotonin were reduced, but not reversed, by methysergide (0.94 mumol/L). 4. Porcine relaxin inhibited field stimulation-induced contractions of costo-uterine muscle and uterine horns from immature rats pretreated with oestradiol cypionate and from stilboestrol-treated mature rats. It was much less potent, and its effects were less clearly concentration-related, on costo-uterine muscle. 5. The inhibitory effects of relaxin on the uterus were unaffected by propranolol (1 mumol/L), confirming that on this tissue relaxin acts independently of the release of catecholamines. Progesterone (30 mumol/L) was also without effect on the action of relaxin on the uterus. 6. These results taken together indicate that the costo-uterine muscle of the rat: (i) contracts in response to serotonin and the peptides angiotensin II, arginine vasopressin, bradykinin and oxytocin independently of the release of the contractile prostaglandins F2 alpha and E2; and (ii) in contrast to the uterus, may lack a significant population of receptors for relaxin.(ABSTRACT TRUNCATED AT 250 WORDS)

(+/-)-Pindolol has beta 2-adrenoceptor antagonist but not agonist action on the costo-uterine muscle of the rat.

1. The effects of isoprenaline and (+/-)-pindolol on rat isolated costo-uterine muscle have been compared. 2. Isoprenaline produced reproducible concentration-dependent inhibition of contractions, and maximal doses (less than 0.1 mumol/l) produced mean inhibition of 87, 94 and 97% of field, carbachol and potassium-stimulated preparations, respectively. 3. (+/-)-Pindolol, when effective, produced inhibition only in concentrations greater than its pA2 value (9.87) as an antagonist of isoprenaline; mean maximal effects were less than 60% of those produced by isoprenaline. 4. It is concluded that (+/-)-pindolol is a potent antagonist, but has only variable agonist action, at the beta 2-adrenoceptors of the rat costo-uterine muscle.

Cholinoreceptors in the isolated costo-uterine muscle of the rat.

1 The aim of this study was to examine the cholinoreceptor population in the rat costo-uterine muscle. 2 The nicotinic cholinoreceptor agonists nicotine and DMPP, and the ganglionic muscarinic cholinoreceptor stimulant McNeil A-343, had no effects upon isolated preparations of this tissue. 3 Acetylcholine was more potent than carbachol and approximately equipotent with methacholine (the mean EC50 values were 7.0, 6.3 and 6.7 respectively) in producing contractions of the preparation; each was a full agonist. The potencies of carbachol and methacholine were similar in preparations taken from animals in oestrus and in dioestrus. 4 Atropine competitively antagonised the effects of carbachol and methacholine, the pA2 values were 9.37 and 9.41 respectively. The pA2 value for pirenzepine with carbachol as the agonist was 6.69. 5 Pilocarpine produced phasic contractions of the tissue (EC50 value = 4.17), and competitively antagonised the effects of carbachol with a pA2 value of 5.26. The anticholinesterase, physostigmine, produced only a small potentiation of the effects of acetylcholine. 6 It is concluded that the cholinoreceptors which mediate contraction of the rat costo-uterine muscle are muscarinic, homogeneous in nature and unaffected by fluctuating levels of ovarian hormones occurring during the oestrous cycle. The consequences of inhibition of cholinesterase activity in isolated preparations of the tissue are minimal.

Uterine contractility and actions of catecholamines in longitudinal and circular uterine layers from ovariectomised guinea-pigs: the effects of ovarian steroids.

The influence of ovarian steroids upon responses to electrical stimulation and to activation of adrenoreceptors in field-stimulated preparations of longitudinal and circular myometrium from ovariectomised guinea-pigs has been investigated. Adult virgin guinea-pigs were bilaterally ovariectomised and were treated two weeks later with thrice-weekly injections of oestradiol cypionate for two weeks, or treated as in then given oestradiol cypionate and progesterone for a further four days. Control groups of bilaterally ovariectomised and sham ovariectomised animals remained untreated. Both myometrial layers from untreated ovariectomised guinea-pigs were atrophied. Responses to field stimulation in the circular myometrium were much smaller than those in the longitudinal layer. Steroid pretreatment, most notably treatment with oestradiol and progesterone, were associated with decreased and increased responsiveness to electrical stimulation in the circular and longitudinal myometrial layers respectively. Adrenaline and noradrenaline were consistently excitatory on preparations of circular myometrium from ovariectomised animals. Responses comprised either enhancement of electrically-evoked contractions, or, with the higher concentrations, the appearance of rapid contractions superimposed upon an increase in basal tone. The latter effects were also evident in preparations of circular myometrium from sham operated animals. In preparations of longitudinal myometrium from untreated ovariectomised animals noradrenaline consistently and adrenaline usually caused a simple enhancement of the magnitude of the evoked contractions. Phentolamine reduced the excitatory effects of both amines in both layers. In circular myometrium from the oestrogen-treated group both catecholamines produced phentolamine-sensitive enhancement of electrically-evoked contractions, but did not cause high frequency contractions or increased tonus. Noradrenaline and adrenaline produced qualitatively similar phentolamine-sensitive effects in preparations of longitudinal myometrium from this group.(ABSTRACT TRUNCATED AT 250 WORDS)

The costo-uterine muscle of the rat contains a homogeneous population of beta-adrenoceptors.

The effects of two selective beta-adrenoceptor antagonists on the inhibitory responses to some sympathomimetic amines of electrically-stimulated preparations of costo-uterine muscle, taken from virgin rats, have been examined quantitatively. pA2 values for the antagonist, atenolol (beta 1-selective) and ICI 118,551 (beta 2-selective) were obtained using as agonists, fenoterol (beta 2-selective agonist) and noradrenaline (alpha- and beta-adrenoceptor agonist, beta 1-selective); and in addition, with ICI 118,551 only, isoprenaline (beta-agonist, non-selective) and adrenaline (alpha- and beta-adrenoceptor agonist, beta 2-selective). Catecholamine uptake mechanisms and alpha-adrenoceptors were not blocked in any of these experiments. Atenolol competitively antagonized the effects of fenoterol and noradrenaline to a similar extent, the pA2 values being 5.4 and 5.7, respectively. ICI 118,551 competitively antagonized the effects of fenoterol, isoprenaline, adrenaline and noradrenaline to a similar extent; pA2 values ranged from 8.7 with noradrenaline to 9.1 with isoprenaline. These results extend our previous observations which indicated that the adrenoceptors mediating inhibition of electrically-evoked contractions of costo-uterine muscle of the virgin rat are homogeneous and of the beta 2-subtype. The potency of the beta 1-selective agonist RO 363 in producing inhibition of electrically-evoked contractions of this tissue was also examined. RO 363 was 200 times less potent than isoprenaline but was a full agonist. This indicates that there is efficient coupling between beta 2-adrenoceptor activation and tissue response in this non-innervated preparation.

The rat costo-uterine muscle: a preparation of smooth muscle containing a homogeneous population of beta-adrenoreceptors.

This paper describes some histological features of the costo-uterine muscle of the rat together with the effects of some sympathomimetic amines upon contractions evoked by field electrical stimulation of isolated preparations. Light and electron microscopy confirmed that the costo-uterine muscle of the rat consists of smooth muscle bundles, arranged longitudinally and interspersed with collagen. There were close contacts between individual cells within bundles. No axon profiles were observed. Histochemical techniques revealed only sparse catecholamine fluorescence at the border of the tissue in association with blood vessels. Isoprenaline, fenoterol, adrenaline, noradrenaline, salbutamol and phenylephrine consistently inhibited contractions evoked by field stimulation (40V, 30Hz, 2 ms for 5 sec every 200 sec). In contrast, tyramine was without effect upon electrically evoked contractions in concentrations of up to 200 mumol/l. The slopes of the log concentration-response curves of effective amines were similar, and all of these were capable of producing 100% inhibition of contraction. The potencies of the amines relative to isoprenaline = 100 were: fenoterol 135; salbutamol 16; adrenaline 16; noradrenaline 0.7; phenylephrine 0.1; tyramine less than 0.001. Propranolol, added to preparations in the absence of inhibitors of amine uptake and alpha-adrenoreceptors, competitively antagonised the effects of the amines. Schild plots had slopes which did not differ significantly from minus one, and the mean pA2 values fell within a narrow range, e.g. 8.65 with salbutamol; 9.20 with fenoterol. Mean pA2 values for propranolol with noradrenaline and isoprenaline were unaffected by the combined presence of phentolamine (10 mumol/l), cocaine (10 mumol/l), and corticosterone (10 mumol/l). The potencies of the agonists were also unaffected by the presence of these drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

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.

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.

Responses mediated by adrenoceptors in the separated layers of the myometrium and in the costo-uterine muscle of the guinea pig during the estrous cycle.

The mechanical responses of field-stimulated preparations of the longitudinal and circular myometrium, and of the costo-uterine muscle of the guinea pig to adrenoceptor agonists have been examined on Days 1, 4, 10 and 15-16 of the estrous cycle. The alpha-adrenoceptor agonist, phenylephrine, was exclusively excitatory in all three preparations taken from animals at each of the cycle days studied. Concentration-response curves for phenylephrine in all three tissues were unaffected by the fluctuations in ovarian hormones occurring during the estrous cycle. Isoproterenol (1 nmol/1-5 mumol/1) usually inhibited field-stimulation-induced contractions of the longitudinal uterine layer and the costo-uterine muscle; higher doses usually caused enhancement of contractions. In neither tissue did the potency or maximum effect of this inhibitory agonist differ at differing cycle stages. In the circular myometrium, the inhibitory effects of isoproterenol were less consistently observed, particularly in preparations taken at proestrus (Days 15-16). It is concluded that, except perhaps in the circular myometrium at proestrus, the fluctuations in ovarian hormones occurring during the estrous cycle in this species are insufficient to modify uterine responses mediated via alpha- and beta-adrenoceptors. It remains to be established whether the steroid hormones are capable of modulating responses mediated by adrenoceptors in the costo-uterine muscle.

The influence of neuronal uptake upon the relative potencies of agonists acting at prejunctional alpha 2-adrenoceptors in the rat isolated vas deferens.

The effects of inhibition of neuronal uptake upon the potency of the alpha-adrenoceptor antagonist phentolamine and upon the potencies of several agonists which produce inhibition of twitches evoked by field stimulation of the prostatic third of the rat vas deferens are described. In doses producing similar inhibition of the uptake of 3H-noradrenaline, cocaine produced a greater inhibition of the effects of (-)-noradrenaline than did desipramine or diphenhydramine. Cocaine differentially potentiated the effects of the sympathomimetic amines used such that the relative order of agonist potency was changed from xylazine greater than (-)-adrenaline greater than (+)-noradrenaline greater than (-)-metaraminol greater than or equal to (-)-noradrenaline greater than or equal to dopamine, to xylazine greater than (-)-adrenaline greater than (-)-noradrenaline greater than (-)-metaraminol greater than dopamine greater than or equal to (+)-noradrenaline. Prazosin enhanced and yohimbine reduced the twitch inhibition produced by (-)-noradrenaline in the absence of uptake blockers. In contrast, phentolamine had little effect upon the position of the log concentration curve for (-)-noradrenaline except when uptake was inhibited. These experiments demonstrate the marked influence of neuronal uptake upon estimates of the relative potencies of agonists activating alpha 2-adrenoceptors, and upon the estimate of the potency of phentolamine as an antagonist of noradrenaline at these receptors in this densely innervated tissue.