Evidence that neurotensin participates in the central regulation of the preovulatory surge of luteinizing hormone in the rat.

Neurotensin (NT) has been implicated in the central regulation of LH and PRL secretion in the rat. We investigated the importance of NT release to the neural events that trigger the preovulatory LH surge and coincident PRL surge, using as our animal model ovariectomized (OVX) rats treated with estrogen and progesterone to induce reliable and robust surges. To interfere with the action of endogenous NT in the basal forebrain, we administered a NT antiserum (NTAS) in a series of bilateral microinjections aimed at the anterior border of the medial preoptic area. One week after OVX, rats bearing cerebral guide cannulae received Silastic capsules (3 x 15 mm; sc) containing 17 beta-estradiol. Two days later, beginning at 0830 h, conscious rats were administered either NTAS or control serum bilaterally in a series of four 100-nl injections spaced at 30-min intervals. After an initial blood sample, rats received progesterone (4 mg, sc) at 1200 h; blood samples were then taken at 1-h intervals from 1400-2100 h. Blood samples were obtained from conscious, freely moving rats via a chronic atrial catheter implanted previously. Plasma levels of LH and PRL were measured by RIA, and the location of microinjection sites was verified histologically. Administration of NTAS caused a 66% reduction in the magnitude of the LH surge without altering its timing, whereas the PRL surge was unaffected. These results provide strong evidence that NT in the basal forebrain participates in the steroid-induced LH surge and suggest that NT plays a role in the preovulatory LH surge.