Estrogen increases beta-adrenergic binding in the preterm fetal rabbit lung.

Tritium-labeled dihydroalprenolol was used to quantify beta-adrenergic-receptor sites in day 28 fetal rabbit lung tissue. Each of the amniotic sacs of pregnant New Zealand White rabbits on day 26 of gestation was injected in vivo with estrogen (estradiol phosphate, 1.6 micrograms) in one horn and normal saline solution in the contralateral one. The animals were put to death 48 hours later and the fetal lung tissues were assayed. Estrogen increased the number of beta-adrenergic-receptor sites in the treatment group compared to the control group (216 versus 163 fmol/mg of protein, p less than 0.02 by paired t test). In the presence of estrogen, beta-adrenergic-receptor activity is enhanced in the preterm fetal rabbit. This effect may be implicated in the beta-adrenergic mediation of phospholipid synthesis and release in fetal alveolar cells.