Differences in the luteinizing hormone and prolactin responses to multiple injections of kainate, as compared to N-methyl-D,L-aspartate, in cycling rats.

We have previously reported that repetitive iv injections of NMA [N-methyl-D,L-aspartate, the mixed analog acting on the N-methyl-D-aspartate (NMDA) receptor] can induce a consistent increase in LH and PRL secretion in cycling rats, but not in lactating rats. To further explore the use of excitatory amino acids (EAAs) as tools for understanding the regulation of the neuroendocrine reproductive axis, we have examinedthe effects of multiple injections of kainate, an agonist to another subclass of EAA receptor,on LH and PRL secretion in cycling rats. Recent studies suggest that kainate receptors may be more abundant than NMDA receptors in the hypothalamus. Five iv injections of kainate were administered at 50-min intervals to diestrous or estrous rats. Blood samples were collected every 10 min and assayed for LH and PRL. LH, but not PRL secretion, was stimulated by this regimen of kainate treatment. Surprisingly, the LH response to kainate, unlike NMA, decreased with repetitive injections of the drug. The re...