Specific binding of naloxone to ovine brain tissue: comparison of brain regions and endocrine states.
Binding of [3H]naloxone ([3H]NAL) to brain membranes was quantified by Scatchard analysis using two methods of separating bound from free [3H]NAL. In the centrifugation method, membranes that were soluble at 1,000 x g, but sedimented at 20,000 x g, were incubated with [3H]NAL. For filtration, all membranes that sedimented at 20,000 x g were incubated and filtered through glass filter fibers. Nonspecific binding was estimated using greater than 500-fold excess of unlabeled naloxone (10(-6) M). Specific binding of [3H]NAL was used to generate linear multiple-point Scatchard plots, which indicated a single class of high-affinity sites. In Exp. 1, 10 ovariectomized (OVX) ewes were injected with estradiol-17 beta alone or in combination with progesterone. Compared with OVX controls, these hormonal treatments did not affect binding of [3H]NAL (centrifugation method) to combined hypothalamus (HYP) + preoptic (POA) tissues. In cyclic ewes (Exp. 2, filtration method), affinity constants (2.4 +/- .2 x 10(8) M-1) did not differ among HYP, POA and basal forebrain (BF) tissues, but BF had more sites (39 +/- 3 fmol/mg) than either HYP (14 +/- 1) or POA (17 +/- 1). Binding affinity and concentration of sites within each brain area (HYP, POA, BF) did not differ between d 8 and d 16 (preovulatory but after luteolysis) in normally cycling ewes. Overall, neural tissue dissected from BF had a greater concentration of binding sites than HYP or POA. Exogenous and endogenous fluctuations in ovarian steroids did not affect binding of [3H]NAL to these tissues.
Weesner
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Purdue University, West Lafayette, IN 47907.
Trout
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Malven
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D000818:Animals; D001665:Binding Sites; D004958:Estradiol / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D009270:Naloxone / Q000378:metabolism*; D010052:Ovariectomy / Q000662:veterinary; D011301:Preoptic Area / Q000187:drug effects / Q000378:metabolism*; D011374:Progesterone / Q000378:metabolism / Q000494:pharmacology; D012756:Sheep / Q000378:metabolism*
D009270:Naloxone; D011374:Progesterone; D004958:Estradiol