In vivo release of neurotensin from the median eminence of ovariectomized estrogen-primed rats as estimated by push-pull perfusion: correlation with luteinizing hormone and prolactin surges.

In order to assess the physiological role of neurotensin (NT) in regulating the secretions of luteinizing hormone (LH) and prolactin (PRL), we examined whether the in vivo release of NT from the push-pull cannulated median eminence (ME) was altered in association with the LH and PRL surges in free-moving ovariectomized rats primed with estradiol. For comparison, LH-releasing hormone (LHRH) was also measured in the same perfusates from the ME in which NT was determined. NT and LHRH in the ME started to significantly increase roughly concurrently with the initial significant rises in LH and PRL in the plasma, and the highest levels of the neuropeptides clearly preceded the peak levels of LH and PRL. These in vivo data strongly suggest that NT, independently of or in concert with LHRH, may have a facilitatory role in the generation of estradiol-induced LH surge. In addition, these data may not disagree with a similar facilitatory role of NT in the PRL surge. This is the first characterization of the temporal profile of NT secretion in rat ME in terms of its relationship to the estradiol-induced surges of LH and PRL.