CHARACTERIZATION OF MESSENGER-RIBONUCLEIC-ACID EXPRESSION FOR PROSTAGLANDIN-F2-ALPHA AND LUTEINIZING-HORMONE RECEPTORS IN VARIOUS BOVINE LUTEAL CELL-TYPES

LH and prostaglandin F-2 alpha (PGF(2 alpha)) control the life span an d function of the corpus luteum (CL). Nevertheless, identification of the various cell types (steroidogenic and nonsteroidogenic) expressing the receptors for these hormones remains controversial. In this study we characterized LH and PGF(2 alpha) receptor (r) expression in the v arious luteal cell types using quantitative reverse transcription-poly merase chain reaction. We found, in agreement with previously describe d functions of PCF2 alpha, that the two steroidogenic cell types, as w ell as luteal endothelial cells, expressed PGFr. In contrast, LHr was mainly expressed by small luteal cells. A similar pattern of PGFr and LHr expression was observed in steroidogenic cells luteinized in vitro and in cells derived from the mature CL. The expression of these two receptors was inversely affected by increased levels oi cAMP (achieved by incubating cells with varying doses of forskolin); LHr expression was down-regulated by 50% in the presence of 10 mu M forskolin (p < 0. 05), while an increase was observed in PGFr expression. In granulosa-d erived luteal cells, maximal expression of PGFr was higher (approximat ely by 3-fold, p < 0.05) than in the theca-derived luteal cells. PCF2 alpha, mimicking its in vivo effect, markedly down-regulated LHr expre ssion in theca-derived luteal cells, abolishing expression at a concen tration of 100 ng/ml. In summary, these studies depict cAMP and PCF2 a lpha as major regulators of PGFr and LHr expression in the two steroid ogenic cell types. All three major cell types of the CL (steroidogenic and endothelial) express PGFr. LHr mRNA, on the other hand, was detec ted mainly in small luteal cells. Such broad cellular distribution of PGFr may highlight the significant role played by this prostaglandin i n the bovine CL.