[Specific glucocorticoid receptor activity in the lungs and concentration of corticosteroids in the plasma of newborn rabbits during the first hours of life (author's transl)].

Nine pure-bred albino New Zealand white rabbits were delivered on the 30th day of gestation (term 31 days) by Caesarean section. The concentration of dexamethasone binding receptors in the cytosol and nucleus of the lungs as well as the total plasma corticosteroid levels were measured in the newborns before the first breath, after 30 min, 1, 2, 4, 6 and 24 h after birth. The level of plasma corticosteroids increased after birth while the concentration of the receptors in the cytosol and nucleus decreased but was still present after 24 h as well as in the lungs of adult animals. A temporary increase in the concentration of the nuclear receptors after 1 and 2 h is explained by the translocation and binding of the abundantly produced steroid-receptor-complex to the nucleus. The stress of hypo- and hyperthermia on the newborns showed variable behaviour with respect to receptor activity. However, the relationship between the corticosteroid levels in the plasma and the concentrations of the receptors in the cytosol and the nucleus of the lungs was similar as in fetuses kept under "physiological" conditions. It may be concluded from these results that in the rabbit the specific glucocorticoid receptor activity in the lungs decreases after birth but is present throughout life.