GnRH has been suggested to participate in corpus luteum function. Here we studied the expression of
GnRH mRNA and
peptide in two models of rat luteinized tissues: ovarian cells from
PMSG-hCG treated prepubertal rats (SPO) and from intrasplenic ovarian
tumors (
Luteoma). A
GnRH autoregulatory effect was evaluated as well as its action on cell proliferation and apoptosis.
GnRH mRNA was present in SPO, isolated corpora lutea from SPO and
Luteoma from 1 week to 7 months of development. In vitro cultures of
Luteoma cells expressed 2-fold higher
GnRH mRNA and 10-fold higher
GnRH peptide than SPO cells.
Buserelin (
GnRH analog) increased
GnRH mRNA and
peptide expression in SPO but not in
Luteoma cells. While basal proliferation was very low in
Luteoma cells, SPO cells showed a significant increase in cell number by both the
thymidine and the MTS methods after 72 h in culture.
Buserelin induced a decrease in cell number in both cell types to a similar degree. Although basal apoptosis levels were higher in SPO than in
Luteoma cells,
Buserelin-induced apoptosis was only detected in
Luteoma cells after 48 h treatment. These results show that the two types of rat, luteinized tissues,
Luteoma and SPO, markedly differed in some intrinsic properties and in their local
GnRH systems.
Luteoma cells proliferate very weakly, express and secrete high amounts of
GnRH, do not show an autoregulatory effect and respond to the decapeptide with apoptosis stimulation. In contrast SPO cells proliferate significantly, secrete low levels of
GnRH but possess a positive, autoregulatory mechanism and respond to
GnRH stimulation with impairment of proliferation.