Uremia decreases nuclear 3,5,3'-triiodothyronine receptors in rats

The maximal binding capacity (MBC) of hepatic T3 nuclear receptors was decreased in uremic rats (132 +/- 37 fmol/mg DNA) compared to sham-operated controls (212 +/- 44 fmol/mg DNA; P < 0.025), while the equilibrium affinity constants (Ka) remained unaltered (1.8 +/- 0.4 and 1.5 +/- 0.3 X 10(9) M-1 in the uremic and control rats, respectively, P = NS). There was also a reduction in the MBC of the kidney T3 receptors, from 73 +/- 14 fmol/mg DNA in the control animals to 32 +/- 7 fmol/mg DNA in the uremic rats (P < 0.10), while the Ka values were identical in both groups (1.9 +/- 0.5 X 10(9) M-1). In addition, there were significant reductions in serum T4 (1.5 +/- 0.7 microgram/dl) and T3 (92 +/- 10 ng/dl) in the uremic rats compared to control rats, whose T4 levels averaged 4.4 +/- 0.1 microgram/dl (P < 0.005) and whose T3 levels averaged 140 +/- 13 ng/dl (P < 0.005). Further, insulin levels averaged 83 +/- 21 microU/ml in uremic rats and 38 +/- 7 microU/ml in control rats (P < 0.025), while glucagon levels averaged 457 +/- 114 pg/ml in the uremic rats and 101 +/- 30 pg/ml in the control animals (P < 0.0125). These data suggest that 1) in addition to starvation and hepatectomy, uremia is another pathological condition associated with the modification of the number of T3 receptors, 2) the reduction in MBC observed may be generalized rather than organ specific for hepatic nuclear receptors, and 3) elevated glucagon levels are associated with reduced MBC in uremia, but it is indeterminate whether hyperglucagonemia is the etiology of the decrease.