Effects of L-dopa on expression of prolactin and synaptotagmin IV in 17-estradiol-induced prolactinomas of ovariectomized hemiparkinsonian rats

Abstract

Parkinson's disease (PD) is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. Dopamine precursor L-dopa is used as the first-line treatment for PD. Evidence suggests neuroprotective effects of estrogens in PD. Since both E2 and L-dopa act as regulators of prolactin secretion from the pituitary gland, we investigated their effect on the expression of prolactin (PRL) in prolactinomas that developed in ovariectomized hemiparkinsonian rats treated with 17b-estradiol (E2). We also investigated the effect of E2 and L-dopa on the expression of synaptotagmin IV (Syt IV), an immediate early gene whose product is abundant in the pituitary gland and was found to be highly co-expressed with PRL in lactotrophs (> 90%). The hemiparkinsonian rat model was obtained by unilateral lesioning of dopaminergic nigrostriatal neurons. Rats received silastic tubing implants with E2 and were treated with L-dopa. ELISA and immunohistochemistry were used to assess the serum concentrations of PRL and E2 and expression of PRL and SytIV in the tissue of adenohypophysis, respectively. We found that high levels of serum 17b-estradiol were associated with the upregulation of Syt IV and PRL in PRL-ir cells, while treatment with L-dopa decreased the size of prolactinomas and downregulated Syt IV but had no effect on PRL expression or serum concentrations.