Quantification of naloxone binding sites in brains from suckled beef cows during postpartum anestrus and resumption of estrous cycles.
Thirty beef cows, approximately 3 yr of age, were randomly assigned to be slaughtered on d 7, 14, 28, 42 or 56 postpartum. Each cow suckled one calf until slaughter. Data from cows slaughtered on d 42 and 56 were pooled and further classified as anestrous or cyclic based on the presence of a corpus luteum and elevated serum concentrations of progesterone at slaughter. Specific binding of [3H]naloxone (3H-NAL) to homogenates of tissue from hypothalamus (HYP), preoptic area (POA) and basal forebrain (BF) was assessed using multiple-point Scatchard analyses. Nonspecific binding was estimated in the presence of 10(-6) M naloxone. Separation of bound from free 3H-NAL was achieved by centrifugation at 20,000 X g. Concentration (fmol/mg original tissue wet wt) of 3H-NAL binding sites in POA tissue was higher (P less than .05) on d 28 postpartum in anestrous cows than in cyclic cows on d 42 + 56 postpartum (2.58 +/- .32 vs 1.58 +/- .10). When all anestrous cows were compared with cyclic cows, concentrations of 3H-NAL binding sites in POA tissues and in BF tissue were higher (P less than .05) in anestrous cows (anestrous POA, 2.12 +/- .17, cyclic POA, 1.58 +/- .10; anestrous BF, 2.94 +/- .41, cyclic BF, 2.19 +/- .16). Compared across brain regions for all cows, the concentration of specific binding sites for 3H-NAL was greater (P less than .01) in BF (2.5 +/- .2) than in POA (1.9 +/- .1) and greater (P less than .01) in POA than in HYP (1.5 +/- .1).(ABSTRACT TRUNCATED AT 250 WORDS)
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Dept. of Anim. Sci., Purdue University, West Lafayette, IN 47907.
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D000780:Anestrus / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002417:Cattle / Q000378:metabolism*; D004971:Estrus / Q000378:metabolism*; D005260:Female; D007031:Hypothalamus / Q000032:analysis; D009270:Naloxone / Q000032:analysis*; D049590:Postpartum Period / Q000378:metabolism*; D011247:Pregnancy; D011301:Preoptic Area / Q000032:analysis; D011957:Receptors, Opioid / Q000032:analysis*
D011957:Receptors, Opioid; C034565:naloxone receptor; D009270:Naloxone