L. Marin et al., MATURATIONAL CHANGES INDUCED BY 1-ALPHA,25-DIHYDROXYVITAMIN-D(3) IN TYPE-II CELLS FROM FETAL-RAT LUNG EXPLANTS, The American journal of physiology, 265(1), 1993, pp. 120000045-120000052
Specific binding sites for la,25 dihydroxyvitamin D3 [1alpha,25-(OH)2D
3] localized to type II pneumocytes have been evidenced in fetal rat l
ung at the end of gestation, suggesting a role for vitamin D3 in the c
ontrol of lung maturation. In this study, we describe the morphologica
l changes that occur in lung explants from 18-day-old rat fetuses grow
n for 1 and 2 days in control conditions and in the presence of 1alpha
,25(OH)2D3 (10(-9) M) or dexamethasone (10(-7) M). Point Counting and
planimetric measurements on light and electron micrographs show that 1
alpha,25-(OH)2D3 1) dramatically decreases the mean glycogen content o
f type II cell profiles between days 1 and 2 of the culture, suggestin
g an acceleration of the glycogenolytic processes normally occuring at
that stage and 2) does not change the intracellular osmiophilic lamel
lar body (OLB) content of cell profiles, but increases the amount of i
ntraluminal sufactant by 126% when expressed as surfactant clusters su
rface area/section sur face area and by 129% when expressed on a per c
ell basis, suggesting a stimulation of surfactant synthesis and secret
ion. By contrast, dexamethasone, increases the mean intracellular OLB
content of type II cell profiles by 306% and decreases the relative su
rface area of secreted material by 53 and 73%. In conclusion, 1alpha,2
5(OH)2D3 accelerates the physiological maturation of fetal rat type II
pneumocytes and could represent a key factor for the onset of normal
lung function at birth.