Evaluation of the Association Between Serum Levels of Testosterone and Prolactin With 6- Hydroxydopamine-Induced Parkinsonism in Male Rats

INTRODUCTION: Parkinson’s Disease (PD) associates with changes in sex hormones; however, it remains unknown whether this is either a cause for or a result of the disease. To further evaluate it, we investigated if the development of 6-Hydroxydopamine (6-OHDA)-induced Parkinsonism changes the serum levels of testosterone and prolactin or not. METHODS: 6-OHDA was injected into the medial forebrain bundle using stereotaxic surgery. The development of Parkinsonism was evaluated by apomorphine-induced rotational test and the immunofluorescence labeling of Dopaminergic (DA) neurons in substantia nigra. The necessary blood samples were collected before the toxin and in the third and sixth weeks afterward. The hormones levels were determined using Enzyme-Linked Immunosorbent Assay (ELISA) kits. RESULTS: The severity of rotations was different among 6-OHDA-treated rats; accordingly, they were divided into two subgroups of severe and mild parkinsonian rats. The degeneration of DA neurons was observed in both subgroups; however, it was significantly less in the mild group. In the sixth week after the toxin, testosterone level increased but only in the severe subgroup. Prolactin increased in both subgroups in the third week after the toxin but returned to normal in the sixth week. There was no association between the pre-toxin levels of these hormones and the intensity of Parkinsonism. CONCLUSION: Our findings indicated that the development of 6-OHDA-induced Parkinsonism increases the serum levels of testosterone and prolactin. Increased prolactin occurred earlier and was observed in rats with less DA neuronal loss. Therefore, prolactin levels can predict the death of DA neurons before the clinical signs of PD were revealed.