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Response of the rat myometrium to phenylephrine in early pregnancy and the effects of 6‐hydroxydopamine
Author(s) -
Kaulenas Andrew,
Parkington Helena C.,
Coleman Harold A.
Publication year - 1991
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1991.tb09806.x
Subject(s) - phenylephrine , myometrium , medicine , endocrinology , denervation , muscle contraction , gestation , uterus , pregnancy , biology , blood pressure , genetics
1 The contractile responses of the longitudinal and circular muscle layers of the rat uterus to the α 1 ‐adrenoceptor agonist phenylephrine were measured on days 3–6 of gestation. There was a progressive increase in sensitivity to phenylephrine in both muscle layers between days 3 and 6 of gestation. Overall, this amounted to a 13 and 9 fold increase in sensitivity in longitudinal and circular muscles, respectively. In longitudinal muscle the slope of the Hill plot was 2 on day 3 of pregnancy and was decreased to 1 thereafter. 2 The sympathetic nerve terminals innervating the smooth muscle of the uterus were destroyed by administration of 6‐hydroxydopamine (2 × 50 mg kg −1 ) 4–7 days before testing with phenylephrine. Following this treatment there was a significant increase in sensitivity to phenylephrine on day 3 in both muscle layers. After day 4, the longitudinal muscle was less sensitive to phenylephrine. 3 In the longitudinal muscle there was a progressive increase in the contractile response to maximal concentrations of phenylephrine and to high potassium (100 m m ) between days 3 and 6 of pregnancy. In the circular muscle the responsiveness to both phenylephrine and potassium remained unchanged between days 3 and 6 of gestation. 6‐Hydroxydopamine had no effect on the maximal responses to phenylephrine or high potassium in either muscle layer. 4 In conclusion, denervation supersensitivity of uterine smooth muscle following injection of 6‐hydroxydopamine is observed only on day 3 of pregnancy and appears to be replaced by subsensitivity by day 6. The decrease in the slope of the Hill plot in longitudinal muscle after day 3 may be explained by changes in events between activation of α 1 ‐adrenoceptors and contraction.