Determination of 9α,11β-prostaglandin F2 by stereospecific antibody in various rat tissues

In view of the recent finding that prostaglandin D₂ is stereospecifically converted to 9α,11β-prostaglandin F₂, an isomer of prostaglandin F₂α, a highly specific and sensitive radioimmunoassay for 9α,11β-prostaglandin F₂ was developed and applied to determine the content of this prostaglandin in various rat tissues. Antisera against 9α-11β-prostaglandin F₂ were raised in rabbits immunized with the bovine serum albumin conjugate, and [³H]9α,11β-prostaglandin F₂ was enzymatically prepared from [³H]prostaglandin D₂. The assay detected 9α,11β-prostaglandin F₂ over the range of 20 pg to 1 ng, and the antiserum showed less than 0.04% cross-section with prostaglandin F₂α, prostaglandin F₂β and 9β,11β-prostaglandin F₂. To avoid postmortem changes, tissues were frozen in liquid nitrogen immediately after removal. The basal level of 9α,11β-prostaglandin F₂ was hardly detectable in various tissues of the rat examined, including spleen, lung, liver and brain; although it was found to be 0.31 ± 0.06 ng/g wet weight in the small intestine. During convulsion induced by pentylenetetrazole, enormous amounts of prostaglandin D₂ (ca. 180 ng/g wet weight) and prostaglandin F₂α (ca. 70 ng/g) were produced in the brain; however, 9α,11β-prostaglandin F₂ was detected neither there nor in the blood. This result demonstrates that the conversion to 9α,11β-prostaglandin F₂ is a minor pathway, if one at all, of prostaglandin D₂ metabolism in the rat brain.