Inhibition by catecholaminergic blockers of the neurotensin-induced enhancement of luteinizing hormone secretion in the ovariectomized estrogen-primed rat.

We have shown that the injection of neurotensin (NT) in the medial preoptic area significantly enhanced the estrogen-induced circadian secretion of luteinizing hormone (LH) in the ovariectomized rat. Unaltered timing of the LH secretion, despite the increased magnitude of its secretion, after the peptide injection has suggested a certain relationship between NT and other neurotransmitter systems which are involved in regulating LH secretion. The present study was undertaken to examine whether the activity of brain catecholaminergic systems are necessary for the manifestation of the peptide effect. The medial preoptic injection of NT elevated the peak value of the estrogen-induced LH secretion in vehicle-treated ovariectomized rats. Pretreatment of the animal with either alpha-methyl-p-tyrosine, pimozide or phenoxybenzamine delayed the timing or reduced the peak value of the LH surge. In these drug-treated animals, the preoptic NT injection failed to induce a change in serum LH levels. It is concluded that dopaminergic and alpha-adrenergic systems are required to be intact for the manifestation of the peptide effect on LH secretion.