Gonadotropin-releasing hormone (GnRH) content in the median eminence after superior cervical ganglionectomy in ovariectomized and estrogen-treated rats

Summary

The aim of the present study was to examine if superior cervical ganglionectomy (SCGx) modifies the gonadotropin-releasing hormone (GnRH) content in the median eminence in female rats. Intact, ovariectomized (OVX) and ovariectomized, 17β-estradiol implanted (OVX + E₂) female rats were subjected to SCGx or sham operation (sham-SCGx). After 12 or 48 hours they were decapitated and the GnRH content in the median eminence was determined by radioimmunoassay.

SCGx performed 12 hours earlier decreased GnRH con- tent in the median eminence in cycling female rats (p < 0.05) as compared with sham-operated control. No changes in GnRH content were observed 48 hours after SCGx. Ovariectomy decreased GnRH content in the median eminence (p < 0.05) and SCGx caused a further decrease in GnRH content (p < 0.05). Implantation of 17β-estradiol suppressed the dramatic decrease in GnRH content in the median eminence observed after SCGx in ovx rats without estrogen treatment. After SCGx the GnRH content in OVX + E₂ rats was significantly higher than in OVX rats (p < 0.05).

Our present results demonstrate that SCGx has some transient influence on the GnRH content in the median eminence. It may be assumed that noradrenaline released from degenerating sympathetic neurons located at the superior cervical ganglia (SCG) affects the GnRH-ergic terminals in the median eminence. The data support the hypothesis that SCG have a modulatory role in the mechanisms controlling the function of the hypothalamic-hypophyseal axis.

Key words

Superior cervical ganglionectomy - gonadotropin releasing hormone - GnRH - median eminence