Characterization of progesterone-3-[125I-BSA] binding sites in the medial preoptic area and anterior hypothalamus.
In this study we utilized radiolabeled progesterone (P) conjugated to bovine serum albumin (BSA) at position 3 (P-3-[125I-BSA]) to examine steroid receptors in membrane fractions from the medial preoptic area-anterior hypothalamus (MPOA-AH) of ovariectomized (OVXed) rats. In the MPOA-AH binding of P-3-[125I-BSA] was linear across a tissue concentration range of 0.005 to 0.02 mg protein/0.1 ml of membrane suspension. Kinetic experiments revealed an association t(1/2) of 51.4 min and a dissociation t(1/2) of 122.5 min for P-3-[125I-BSA] at 0 degrees C. Analysis of data from competition binding experiments using P-3-BSA revealed high- and low-affinity binding sites in the MPOA-AH. Involvement of MPOA-AH binding sites with a G-protein was suggested by a reduction of P-3-[125I-BSA] binding in the presence of the non-hydrolyzable GTP analog GTPgammaS but not ATPgammaS. In addition, if homogenates from the MPOA-AH were preincubated with 10(-5) M of the G-protein antagonist cholera toxin for 30 min at 37 degrees C, competition binding data indicated only high-affinity binding sites. Once daily injections of OVXed rats with 4 mg P for 12 days significantly increased the density of P-3-[125I-BSA] binding sites in the MPOA-AH. This treatment did not affect P-3-[125I-BSA] binding in the dorsal tectum, medial basal hypothalamus, ventral tegmental area or the thymus.
Caldwell
J D
JD
Brain and Development Research Center, School of Medicine, University of North Carolina at Chapel Hill 27599-7250, USA.
Walker
C H
CH
Faggin
B M
BM
Carr
R B
RB
Pedersen
C A
CA
Mason
G A
GA
D000418:Albumins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive; D002772:Cholera Toxin / Q000494:pharmacology; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007032:Hypothalamus, Anterior / Q000378:metabolism* / Q000648:ultrastructure; D007457:Iodine Radioisotopes / Q000378:metabolism*; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D011301:Preoptic Area / Q000378:metabolism* / Q000648:ultrastructure; D011374:Progesterone / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011980:Receptors, Progesterone / Q000032:analysis; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000418:Albumins; D007457:Iodine Radioisotopes; D008565:Membrane Proteins; D011980:Receptors, Progesterone; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011374:Progesterone; D002772:Cholera Toxin; D019204:GTP-Binding Proteins