Developmental changes and molecular weight of immunoreactive glucocorticoid receptor protein in the ovine fetal hypothalamus and pituitary

Parturition in the sheep is initiated by increased activity of the hypothalamus-pituitary-adrenal (HPA) axis in the fetus. Late in gestation, ACTH secretion increases because of increased stimulation to the HPA axis and a decreased cortisol negative feedback inhibition of ACTH secretion. We hypothesized that this alteration in cortisol negative feedback efficacy might result from a decrease in glucocorticoid receptor (GR) protein in the hypothalamus or pituitary. Fetal hypothalami and pituitaries were collected from healthy animals (74 days gestation to 4 weeks postnatally) and analyzed by Western blot for immunoreactive GR (iGR) protein. We detected two forms of iGR: a form consistent in molecular weight with the GR, and a form which is approximately half the size of the full-length receptor. We were not able to detect a developmental change in the intensity of immuno-staining for the full-length GR receptor protein in these tissues. However, the proportion of half-length relative to full-length GR increased significantly with developmental age. Exogenous estrogen, androgen,, or tamoxifen treatment did not significantly affect the expression of GR protein. In conclusion, we detected a 97 kD iGR protein corresponding to the full-length receptor and a 45 kD iGR protein, or half-length receptor. The proportion of this half-length receptor protein relative to the full-length receptor increased significantly with development. (C) 1996 Academic Press.