Tissue Levels of Luteinizing Hormone-Releasing Hormone in the Preoptic Area and Hypothalamus, and Serum Concentrations of Gonadotropins Following Anterior Hypothalamic Deafferentation and Estrogen Treatment of the Female Rat
Female rats were ovariectomized prior to anterior hypothalamic deafferentation (AHD) or sham AHD of the medial basal hypothalamus (MBH). LHRH [luteinizing hormone-releasing hormone] in the MBH and the preoptic area (POA), and blood concentrations of LHRH, FSH [follicle stimulating hormone] and LH were measured following decapitation at the end of 30 days in experiment 1 and 28 days in experiment 2. Interruption of anterior neural links of the MBH drastically reduced the amounts of LHRH in the MBH and significantly increased the POA. Circulating levels of FSH (experiments 1 and 2) and LH (experiment 2) were significantly depressed, whereas serum LHRH was unaltered following deafferentation. In experiment 3 rats were ovariectomized 25 days following either AHD or sham AHD, and were given estradiol benzoate (EB, 10 .mu.g/rat in oil, s.c.) or oil alone on day 7 postovariectomy and sacrificed 2 days later. Relative to sham AHD, a reduction in the MBH LHRH and a pronounced elevation in the POA LHRH was observed in AHD rats. Serum LH and FSH concentrations were significantly decreased. EB treatment significantly lowered serum gonadotropins, whereas LHRH levels in the MBH of both AHD and sham AHD rats increased 2-fold. Serum LHRH concentrations were significantly reduced in AHD rats following EB injection. Since a substantial portion of the LHRH activity normally detected in the MBH of female rats appears to be derived from that synthesized in the rostral regions, POA LHRH may be involved in the tonic and the cyclic discharge of LH, and an increase in the LHRH content of the MBH after estrogen treatment may be due to a partial inhibition in release and/or an increased rate of synthesis of LHRH in the MBH.