The somatotrophic axis in young steers: influence of nutritional status and oestradiol-17 beta on hepatic high- and low-affinity somatotrophic binding sites.
The binding of bovine GH (bGH) to hepatic membranes obtained from steers on either high (3% dry matter of body weight per day) or low (1% dry matter of body weight per day) planes of nutrition with or without an oestradiol-17 beta implant was studied (n = 5 per group). Binding studies were performed on both crude membrane homogenates and on 100,000 g microsomal membrane fractions; identical results were obtained using both preparations. In all four groups of animals, linear Scatchard plots were obtained, but following pretreatment of the membranes with MgCl2 to remove endogenously bound hormone, curvilinear plots were obtained in the groups on the high plane of nutrition. Analysis of these curves suggested the presence of a high- and low-affinity binding site, the high-affinity site being fully occupied in the absence of MgCl2 pretreatment. The specific binding of bGH in MgCl2-pretreated crude membranes was greater (P less than 0.01) in well-fed steers (14.8 +/- 1.6%) than in poorly fed steers (9.8 +/- 0.9%). Scatchard analysis showed this to be due to the presence of a high-affinity site (dissociation constant (Kd) = 11.6 +/- 3.3 pmol/l) in the well-fed animals only. In addition, there was an increase (P less than 0.01) in the affinity, but not in the capacity, of the low-affinity site (Kd = 106.4 +/- 22.8 pmol/l in well-fed steers and 197.0 +/- 23.8 pmol/l in poorly fed steers).(ABSTRACT TRUNCATED AT 250 WORDS)
Breier
B H
BH
Department of Paediatrics, University of Auckland, New Zealand.
Gluckman
P D
PD
Bass
J J
JJ
D000818:Animals; D001667:Binding, Competitive; D001835:Body Weight; D002417:Cattle / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D013006:Growth Hormone / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D015636:Magnesium Chloride; D008297:Male; D009752:Nutritional Status; D011986:Receptors, Somatotropin / Q000187:drug effects / Q000378:metabolism*
D011986:Receptors, Somatotropin; D015636:Magnesium Chloride; D004958:Estradiol; D013006:Growth Hormone; D008274:Magnesium