Prolactin-stimulated mitogenesis in the Nb2 rat lymphoma cell: Lack of protoporphyrin IX effects

Pharmacological characterization of the Nb2 cell peripheral-type benzodiazepine receptor (PBR) was determined using selected 1,4-benzodiazepines, PK 11195, and protoporphyrin IX (PPIX) to compete for specific [ 3H] Ro5-4864 binding. These data suggest that PPIX possesses an affinity for the Nb2 cell PBR (K i=142 nM). We have previously reported that the peripheral benzodiazepine ligands, Ro5-4864 and PK 11195, modulate prolactin- stimulated mitogenesis in the Nb2 cell(1). In contrast, PPIX, a putative endogenous ligand for the PBR had no effect on prolactin- stimulated mitogenesis in the Nb2 cell over the concentration range from 10 −15 M to 10 −6 M. Taken together these data show that PPIX has an affinity for the Nb2 cell PBR but does not modulate prolactin- stimulated mitogenesis at concentrations which should bind to the Nb2 cell PBR.