Abstract
1. Fetal rat tracheas and lung buds form liquid-filled cysts in submersion culture. The volume that accumulates in cysts is driven by active Cl- secretion. 2. We examined the effects, on these explants, of hormones that induce liquid absorption by fetal sheep lung in vivo. Explants were impaled with microelectrodes to measure potential difference (PD). Liquid was estimated from explant weight. 3. Water/dry weight ratio of lung buds and tracheas after 8 days in culture averaged 12 and 22. Exposure of triiodothyronine (T3) and hydrocortisone (HC) followed by a physiological dose of adrenaline on day 7 for 24 h or by a maximal dose of terbutaline on day 8 for 4 h induced a 35% decrease in water/dry weight ratio of distal buds but not tracheas. No hormone, or combination of two hormones, affected the ratio for tracheas or lung buds. 4. Basal PDs of tracheas (18.9 mV) and lung buds (3.7 mV) were increased about 50% by terbutaline. The terbutaline response was inhibited by bumetanide, but not by amiloride injected into the cysts. 5. T3 and HC pretreatment reduced basal PD by one-third. Subsequent exposure to terbutaline raised the PD of hormone-pretreated lung buds by more than 150%, a response that was blocked by amiloride, but was antagonized minimally by bumetanide. Responses of hormone-pretreated tracheas were not different from those of untreated tracheas. 6. We conclude that: (a) absorption of liquid from lung buds is driven by an amiloride-sensitive process (active Na+ transport?) and (b) only distal lung contributes to the adrenaline-sensitive reabsorptive process required for perinatal adaptation to air breathing.