Distal air space epithelial fluid clearance in near-term rat fetuses is fast and requires endogenous catecholamines.
Knowledge about the conversion of the epithelium in the distal air spaces of the lung from secretion to absorption is imperative to the understanding of postnatal lung development; little such information is available in rats. Distal air space fluid clearance was therefore measured in 21- to 22-day gestation rat fetuses and newborn (40 h) rats. Distal air space fluid clearance was measured from the increase in (131)I-albumin concentration in an isosmolar, physiological solution instilled into the developing lungs. There was no net fluid movement across the distal air space epithelium in the lungs of 21-day gestation fetuses. Twenty-four hours later, distal air space fluid was cleared at a rapid rate in the 22-day gestation fetuses. Within the first 40 h after birth, the rate rapidly declined to adult levels. The high distal air space fluid clearance at 22 days gestation and at 40 h after birth was mediated by beta-adrenergic receptors as demonstrated by elevated plasma epinephrine levels and inhibition by propranolol. Interestingly, the elevated distal air space fluid clearance in the 22-day gestation fetuses was only minimally amiloride sensitive; however, amiloride sensitivity increased over the first 40 h after birth. In conclusion, these studies demonstrate that 1) rapid rates of net alveolar fluid clearance occur late in gestation in the rat and 2) this clearance is driven by elevations of endogenous epinephrine.
Folkesson
Hans G
HG
Department of Physiology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272-0095, USA. hgfolkes@neoucom.edu
Matthay
Michael A
MA
Chapin
Cheryl J
CJ
Porta
Nicolas F M
NF
Kitterman
Joseph A
JA
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D001826:Body Fluids / Q000378:metabolism*; D001834:Body Water / Q000378:metabolism; D002395:Catecholamines / Q000502:physiology*; D005314:Embryonic and Fetal Development; D004837:Epinephrine / Q000097:blood; D004848:Epithelium / Q000378:metabolism; D005260:Female; D005333:Fetus / Q000187:drug effects / Q000378:metabolism; D005865:Gestational Age; D008168:Lung / Q000187:drug effects / Q000196:embryology* / Q000378:metabolism; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D000319:Adrenergic beta-Antagonists; D002395:Catecholamines; D011433:Propranolol; D004837:Epinephrine