Response of the rat myometrium to phenylephrine in early pregnancy and the effects of 6‐hydroxydopamine

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Abstract

The contractile responses of the longitudinal and circular muscle layers of the rat uterus to the α1‐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. 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. In the longitudinal muscle there was a progressive increase in the contractile response to maximal concentrations of phenylephrine and to high potassium (100 mm) 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. 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 α1‐adrenoceptors and contraction. 1991 British Pharmacological Society

Original languageEnglish
Pages (from-to)1429-1434
Number of pages6
JournalBritish Journal of Pharmacology
Volume103
Issue number2
DOIs
Publication statusPublished - 1 Jan 1991

Keywords

  • blastocyst
  • blastocyst spacing
  • chemical
  • Denervation supersensitivity
  • drug effects
  • hydroxydopamines
  • myometrium
  • peri‐implantation phase
  • rat
  • sympathectomy
  • sympathomimetics
  • uterus

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