Prolactin binding sites in the brain and kidneys of the toad, Bufo arenarum Hensel

(125I)-ovine prolactin (oPRL) binding was found in several brain areas of the toad, Bufo arenarum Hensel. The olfactory bulb, cerebral hemispheres, and both dorsal and ventral mesencephalic regions showed saturable, high affinity, (125I)-oPRL binding, ranging between 5.6 to 29.9 fmol/mg protein, while the association constant (Ka) by Scatchard analysis was between 4.0 to 8.7 x 10(9) M-1. This binding was compared with the Scatchard plot of the kidney, which has been already described by other groups, and gave 41.7 fmol/mg protein and Ka 2.5 x 10(9) M-1. Liver showed no binding and in the cerebral hemispheres (125I)-oPRL was not displaced by non-lactogenic hormones, indicating that binding was hormone and tissue specific.