ESTROGEN POSITIVE FEEDBACK STIMULATES THE SYNTHESIS OF LHRH MESSENGER-RNA IN NEURONS OF THE ROSTRAL DIENCEPHALON OF THE RAT

Our aim was to determine whether oestrogen administered to ovariectomized rats in a manner which stimulates the release of LHRH also stimulates the synthesis of LHRH mRNA. Adult female Wistar rats were ovariectomized under halothane anaesthesia between 09.00 and 11.00 h of dioestrus, immediately injected with either oil or 10 μg oestradiol benzoate (OB) and then killed by cervical dislocation between 16.00 and 17.00 h of the next day (presumptive pro-oestrus) In-situ hybridization carried out with a 30 mer. 32P-labelled, oligonucleotide probe complementary to LHRH mRNA showed that the concentrations of LHRH mRNA in perikarya in the medial preoptic area, diagonal band and medial septum were significantly greater in OB-compared with oil-treated rats. Plasma LH concentrations were significantly increased in three out of four of the OB-treated rats. These results show for the first time that as well as stimulating LHRH and LH release, oestrogen positive feedback also stimulates the synthesis of LHRH mRNA.