**5. Conclusion**

In the present study we clearly demonstrate a significant attenuation of the LH surge at the age of 8.5 compared to 4 months old regular 4-day cycling females. This attenuation of the LH surge was not accompanied by changes in the releasable pool of LH, timing of the surge, GnRH priming or preovulatory P levels, supporting the notion that an attenuation of the LH surge may result from a change in the hypothalamic drive. Strikingly, we found clear changes in hypothalamic SOM peptide regulation following a physiological dose of estrogen in middle-aged animals. We hypothesize that the age dependent effects of an E2 stimulus on SOM-ir cell distribution and SOM-ir numbers indicate alterations in the regulation of hypothalamic SOM peptide release in response to estrogen feedback could underlie an attenuation of the LH surge with age. These observations suggest that changes in the regulation of the GH axis with age indeed coincide with the process of reproductive aging in the female rat and suggest that the proposed interaction between these neuroendocrine axes may occur via alterations in hypothalamic somatostatin release.
