Paradoxical effect of imipramine in hyperprolactinemic female rats exposedto the forced swimming test

This study was designed to investigate the effect of hyperprolactinemia, wi th high or low estrogen levels, on the response to imipramine in the forced swimming test. Three groups of female rats were studied: (1) ovariectomize d controls, with low serum prolactin (PRL) and estrogen levels, (2) ovariec tomized, estrogen-treated rats, with high PRL and high estrogen levels, and (3) pituitary-grafted rats, with high PRL and low estrogen levels. The hyp erprolactinemic groups did not show significant behavioral changes in the f orced swimming test preceded by saline injection. Imipramine decreased the immobility time by 37.5% in ovariectomized controls but not in the pituitar y-grafted group, and there was an increment of 48.4% in immobility time fol lowing imipramine administration in the estrogen-treated group (p < 0.05). This paradoxical response to imipramine was significantly correlated with s erum PRL (r = 0.59, p < 0.01) but not with estradiol levels. These findings suggest that, at least in female rats submitted to the forced swimming mod el, PRL may induce reversed behavioral effects in response to imipramine, i ndependently of circulating estrogen levels. (C) 2000 Elsevier Science Inc. All rights reserved.