Hormone receptors in the epiphysial cartilage

In order to assess which hormones may exert direct effects on skeletal growth at the epiphysial growth plate, the specific binding of hormones to the epiphysial cartilage of growing dogs and rabbits was studied. Membrane fractions obtained by centrifugation of homogenates prepared from dog and rabbit growth plate cartilage at 600, 15 000 and 105 000 g showed significant specific binding of serum insulin-like activity and insulin. Binding of growth hormone and prolactin by the three membrane fractions was negligible. Saturable binding sites for triiodothyronine could be demonstrated in nuclei from the dog growth plate. Nuclear binding showed an apparent Kd of 11 +/- 3.6 nmol/l and a maximum binding capacity of 4.1 +/- 1.6 pmol/mg DNA, a level comparable to dog liver. Using a viable chondrocyte suspension prepared from dog epiphysial cartilage, specific steroid binding in the cells could be demonstrated for [3H]dexamethasone but not 17 alpha-methyltrienolone, oestradiol-17 beta or 1 alpha, 25-dihydroxycholecalciferol. Scatchard analysis of dexamethasone binding showed high affinity binding sites having a Kd of 1.2 +/- 0.35 nmol/l and a capacity of 1700 sites/cell, and a low affinity binding with a Kd of 109 +/- 57 nmol/l and a capacity of 24 000 sites/cell. Steroid competition for the specific binding showed the following sequence of affinity: dexamethasone greater than corticosterone greater than 11-deoxycortisol greater than testosterone greater than oestradiol-17 beta.(ABSTRACT TRUNCATED AT 250 WORDS)