Fenoterol treatment and desensitization of beta-adrenoceptors in rabbit foetal lung.

The foetal lung responds to beta-receptor agonists with a release of surfactant from alveolar cells. The aim of the present study was to investigate whether the administration of the betamimetic fenoterol could influence the desensitization - associated decrease of beta-adrenoreceptors in the rabbit foetal lung. With experiments on pregnant rabbits, this hypothesis was put to the test and found to be true. At a gestational age of 27-28 days, does were infused 7.5-10.0 mg of fenoterol or given Ringer's solution. The does and foetuses were sacrificed at 12 hours from the start of the infusion, and the number and affinity of beta-adrenergic receptors in lung tissues were determined by a direct binding technique using 3H-dihydroprenolol. These studies show that fenoterol can induce desensitization of beta-receptors in the foetal lung but not in the doe. Thus, it is concluded that desensitization of foetal pulmonary adrenoreceptors may result in diminished lung function after long-term treatment with beta-2 sympathicomimetics.