Prolactin and cyclosporine modulate adenosine transporters and adenosine A1 receptors in the rat brain

The existence of adenosine A(1) receptors and adenosine transporters in the central nervous system has been well demonstrated, although their possible modulation by hormones and/or exogenous drugs is poorly understood. To fur ther analyze these modulatory mechanisms, the effects of prolactin and cycl osporine (CyA) on adenosine A(1) receptors and transporters were analyzed i n the central nervous system. For this purpose the number and affinity of a denosine A1 receptors were measured using the specific antagonist 1,3-dipro pyl-8-cyclopentylxanthine (DPCPX) and the transporters with the high affini ty ligand nitrobenzylthioinosine (NBTI). This procedure was carried our in hyperprolactinemic and control male rats treated with CyA or its vehicle fo r 8 days. As expected, pituitary grafting increased plasma prolactin levels (p<0.01). CyA treatment reduced but did not normalize (p<0.05) this parame ter in hyperprolactinemic rats and did not modify circulating prolactin in control animals. Both hyperprolactinemia and CyA treatment reduced the numb er of adenosine transporters by 70% and by 40% the number of A(1) receptors . The K-d for transporters was also reduced in all experimental groups. Hyp erprolactinemia increased the affinity of A(1) receptors (p<0.01) and CyA t reatment did not further modify this parameter. These data demonstrated tha t prolactin and CyA influence adenosine transporters and A(1) receptors at the central nervous system and suggest the existence of an interaction betw een prolactin and CyA may be operating to modulate these processes.