S. Matsui et al., LOCALIZATION OF [D-ALA(2)]DELTORPHIN I-LIKE IMMUNOREACTIVITY IN PERINATAL RAT RESPIRATORY SYSTEM, Histochemical Journal, 26(8), 1994, pp. 648-654
The localization of [D-Ala(2)]deltorphin I, a delta-opioid receptor li
gand, was studied in the lower respiratory tract of developing rats us
ing an immunohistochemical method. [D-Ala(2)]-like immunoreactive cell
s were detected first in the principal bronchus as early as embryonic
day 16. As embryos grew, positive cells became gradually visible every
where from principal bronchi to respiratory bronchioles. The density o
f positive cells reached the highest level on embryonic day 21, but de
creased gradually after birth. Positive cells were no longer seen on p
ostnatal day 30 in any region of the airways. No positive cells were e
ver found in the trachea or alveoli of rats at any age studied. Ultras
tructural examination indicated that the immunoreactive cells possesse
d a similar morphology to serous or Clara cells of the respiratory epi
thelium. Immunoreaction products tended to locate at the apical cytopl
asm of positive cells. The result suggests that [D-Ala(2)]-like molecu
le(s) may be expressed transiently in serous cells or Clara cells, or
both, of the rat bronchopulmonary tract. Such a molecule may act as a
pulmonary growth-promoting or a differentiation-initiating factor in a
n early period of lung development.