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  • Title: Actions of some autacoids and peptides, including relaxin, on costo-uterine muscle from rats.
    Author: Fox D, Handberg GM, Hartley ML, Monagle J, Pennefather JN.
    Journal: Clin Exp Pharmacol Physiol; 1989 Jul; 16(7):561-9. PubMed ID: 2572364.
    Abstract:
    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)
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