Absence of the oxytocin-induced prostaglandin F2 alpha secretory response in uterus from ovariectomized ewes and activation of the response in vitro.

Oxytocin-induced prostaglandin F2 alpha (PGF2 alpha) responses were measured in explants of uterus from ovariectomized ewes on the day of tissue collection or after culture for 72 h in the presence or absence of oestradiol-17 beta (100 nmol/l). Oxytocin receptor binding activity was 210 +/- 47 fmol [3H]oxytocin bound per mg protein in fresh tissue and 89 +/- 24 and 90 +/- 17 fmol/mg in tissue cultured with control medium or with oestradiol respectively (means +/- S.E.M.). PGF2 alpha production during the hour following oxytocin administration to freshly collected tissue was 272 +/- 77 ng/g/h compared with 193 +/- 35 ng/g/h in the absence of oxytocin. These rates were 2789 +/- 1085 and 353 +/- 135 ng/g/h after culture for 72 h in control medium and 2022 +/- 496 and 342 +/- 134 ng/g/h after culture with oestradiol. Thus oestradiol had no effect on the culture-induced maturation of the PGF2 alpha response. Short-term exposure to arachidonic acid (66 mumol/l) did not increase PGF2 alpha production in fresh tissue but significantly increased basal but not oxytocin-induced PGF2 alpha production after 72 h in culture (P < 0.05). There was an absence of oxytocin-induced inositol phosphate turnover in fresh tissue but after culture concentrations of inositol mono-, bis- and trisphosphates were all significantly increased by oxytocin (P < 0.005). Antisera directed against G-protein alpha sub-units alpha i3, alpha o, alpha q, alpha 11 and the common beta subunit, and prostaglandin H-synthase-1 detected proteins that were present before and after culture.(ABSTRACT TRUNCATED AT 250 WORDS)