Characterization and measurement of [125I]iodopindolol binding in individual rat pineal glands: existence of a 24-h rhythm in beta-adrenergic receptor density.
A simple procedure has been developed that permits measurement of beta-receptors in membrane preparations from individual rat pineal glands using [125I]iodopindolol ([125I]PIN). [125I]PIN binding to pineal membranes was stereospecific and saturable. Scatchard analysis of saturation isotherms yielded a Kd of 147.3 +/- 54 pM and a Bmax of 11.1 +/- 1.5 fmol/pineal gland. Binding was linear suggesting that [125I]PIN binds to a single population of pineal beta-adrenergic receptors. This procedure was used to evaluate 24-h variations in density of pineal [125I]PIN binding sites in male rats maintained in a 14:10 h light:dark cycle. Binding remained uniformly low during the daytime, increased slightly prior to lights off and peaked after 6 h of darkness decreasing abruptly 2 h later, before lights on. In animals maintained in light at night, the number of binding sites also increased, but did not exhibit the darkness-related decrease. The results demonstrate that beta-adrenergic receptors defined via [125I]PIN binding can be measured in tissue samples equivalent to less than one pineal gland. Moreover, the technique can be used in studies concerning the noradrenergic regulation of pineal function.
Gonzalez-Brito
A
A
Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284-7762.
Jones
D J
DJ
Ademe
R M
RM
Reiter
R J
RJ
D000818:Animals; D001667:Binding, Competitive; D002940:Circadian Rhythm; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D010869:Pindolol / Q000378:metabolism*; D010870:Pineal Gland / Q000378:metabolism* / Q000502:physiology; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D013696:Temperature
D007457:Iodine Radioisotopes; D011943:Receptors, Adrenergic, beta; D010869:Pindolol