Impaired alveolar liquid clearance after 48-h isoproterenol infusion spontaneously recovers by 96 h of continuous infusion

We previously demonstrated that 48-h isoproterenol (Iso) infusion in rats impaired the ability of beta-adrenoceptor (beta-AR) agonists to increase alveolar liquid clearance (ALC). In this study, we determined whether this impairment persisted over longer time periods by infusing 400 mug.kg(-1).h(-1) Iso by osmotic minipump for 24-144 h (n = 6-7/group). ALC in control rats was 19.0 +/- 2.4 (SD)% of instilled volume absorbed per hour. In Iso-infused rats, ALC was elevated at 24 h (34.9 +/- 2.4%) and decreased at 48 h (15.2 +/- 4.4%) and had recovered to 24 h values at 96 h (37.3 +/- 3.8%) and 144 h (35.2 +/- 3.3%). Plasma Iso concentrations remained elevated at all Iso infusion times. Peripheral lung beta(2)-AR expression exhibited a parallel time course, with a reduction in expression observed at 48 h, followed by an increase to 24 h values at 96 and 144 h. Propranolol prevented the increase in ALC observed at 96 and 144 h, indicating that the recovery in ALC was mediated by a recovery of beta-AR function and beta-AR signaling. ALC at 96 and 144 h could not be further increased by terbutaline, indicating that ALC was maximally stimulated. These data indicate that recovery of beta-AR-stimulated ALC can occur in the continued presence of Iso and is mediated by a recovery of the ability of the distal lung epithelium to respond to beta-AR stimulation.     

Identified taste bud cell proliferation in the perihatching chick [published erratum appears in Chem Senses 1998 Aug;23(4):459]

Developing taste buds in the anterior mandibular floor of perihatching chicks were studied by high voltage electron microscopic autoradiography in order to identify proliferating gemmal cell types. Montaged profiles of 29 taste buds in five cases euthanized between embryonic day 21 and posthatching day 2 were analyzed after a single [3H]thymidine injection administered on embryonic day 16, 17 or 18. Results showed that dark cells comprised 55% of identified (n = 900 cells) and 62% of labeled (n = 568 cells) gemmal cells as compared with light, intermediate, basal or perigemmal bud cells. Dark cells had both a greater (P < 0.05) number of labeled cells and a greater amount of label (grains/nucleus) than the other four bud cell types, irrespective of injection day. The nuclear area (micron 2) of dark cells was not significantly larger (P > 0.05) than that of the other gemmal cell types and therefore cannot account for the greater amount for label in the dark cells. Interestingly, only dark cells showed a positive correlation (P < 0.003) between amount of label and nuclear area. Results suggest that, during the perihatching period of robust cell proliferation, dividing dark cells may give rise primarily, but not exclusively, to dark cell progeny.