Mechanisms of glucocorticoid receptor function

Mouse major histocompatibility complex (H-2) and fetal lung development: implications for human pulmonary maturation

Using C57/10Sn (B10, H-2b) and B10.A/SgSn (B10.A,H-2a) congenic mice, we measured 1) the level of endogenous pulmonary corticosterone during mouse development; 2) the degree of lung morphological maturation on gestation day 17, with or without corticosteroid treatment; and 3) the maternal influence on normal lung development and fetal response to corticosteroids. The results of our study indicate that there was a progressive increase in the level of endogenous hormone with time in fetal B10 (H-2b) and B10.A (H-2a) mice; throughout mid- to late gestation, the detectable amount of hormone was almost identical in lungs of both strains. Evaluating the degree of lung maturation by morphometry, B10.A mouse lungs were found to be less mature than B10 mouse lungs. Following corticosteroid treatment on day 12 of gestation, H-2a lungs were equal to or more mature than H-2b lungs. We also compared heterozygous mouse lungs from reciprocal crosses (B10.B10.A, b/a and B10.A.B10, a/b). Mice with a maternally derived H-2a haplotype had less mature lungs than those with a maternally derived H-2b haplotype, suggesting a maternal effect. When exogenous hormone was administered, all heterozygous mouse lungs increased in maturity regardless of the origin of the H-2a haplotype. The treated a/b or b/a lungs were more mature than homozygous b/b and less mature than homozygous a/a lungs. We conclude that progressive lung maturation is associated with a gene(s) at or near the H-2 complex, as is the ability to respond to corticosteroids.

A quantitative electron microscopic study of the effect of glucocorticoids in vivo on the early postnatal differentiation of paraneuronal cells in the carotid body and the adrenal medulla of the rat

The postnatal differentiation of carotid body chief cells and endocrine adrenal medullary cells was comparatively examined during ontogenesis and in rats which were treated with dexamethasone for 7 days after birth. Ultrastructure and innervation of carotid body chief cells are mature in neonates according to the functional requirements of chemoreception. By the end of the first postnatal week, only an increase in number of dense core vesicles can be noticed, the concentration of which then will reach the adult level. Under the effect of dexamethasone most of the heterochromatin is transformed into finely dispersed euchromatin within the nuclei of carotid body chief cells. In the cytoplasm, the Golgi apparatus becomes larger and the granular endoplasmic reticulum hypertrophic. The number of catecholamines storing dense core vesicles increases considerably. The innervation density remains constant. In contrast to the carotid body chief cells, the adrenal medullary cells have not reached their definitive maturity at the time of birth. Besides phenotypes of adrenaline-cells, noradrenaline-cells and small granules containing cells, pheochromoblasts and intermediary cells can be seen as well. Their cytoplasm is sparse, the concentration of dense core vesicles and the innervation density very low. After 8 days of postnatal ontogenesis, pheochromoblasts and intermediary cells are no longer present in the adrenal medulla. In adrenaline-cells and noradrenaline-cells, important processes of growth can be noticed, the cytoplasm has grown in extent, the number of dense core vesicles doubled and the innervation density of single cells triplicated. Only the few small granules containing cells remain small. Under the effect of dexamethasone also in the nuclei of chromaffin cells a transformation of heterochromatin into euchromatin occurs. The increase in number of dense core vesicles is relatively lower than in carotid body chief cells. The significant growth of innervation density during the first postnatal week was inhibited. Our observations suggest that dexamethasone stimulates the synthesis of catecholamines in adrenal medullary cells of newborn rats less pronouncedly than in carotid body chief cells. This could be attributed to the inhibited formation of synapses of growing chromaffin cells and to the in vivo active endocrine counter-regulation.

Inhibition of the biosynthesis of deoxyribonucleic acid, ribonucleic acid and protein in HeLa S3 cells by cucurbitacins, glucocorticoid-like cytotoxic triterpenes

Cucurbitacins were found to inhibit the incorporation of radioactive precursors into DNA, RNA and protein in intact and permeabilized HeLa S3 cells. The observed inhibition was rapid and irreversible although the maximal effect (almost complete inhibition) required several hours of cell exposition to the agent. The magnitude of the inhibition was, with some exceptions, nearly the same for all three precursors within the entire range of cucurbitacin concentrations examined. The ID50 values (concentrations required to produce half-maximal inhibition of the macromolecule biosynthesis) determined for several cucurbitacins were very close to their respective ED50 values (those for half-maximal inhibition of cell proliferation). Parallel with the inhibition of [3H]-labelled precursor incorporations into nucleic acids, cucurbitacin diminished the [3H]thymidine and [3H]uridine nucleotides' pool sizes of HeLa S3 cells. No effect of cucurbitacin on the [3H]leucine pool was observed. The studies presented prove that cucurbitacins inhibit the biosynthesis of DNA, RNA and protein in HeLa S3 cells, and that these inhibitory effects are closely related to the inhibition of HeLa S3 cell proliferation by cucurbitacins. The mechanism of the inhibition is unknown but the obtained results suggest that cucurbitacins act upon an unidentified target, which results in the inhibition of macromolecule biosynthesis. It was also found that these inhibitory effects of cucurbitacins are neither mediated by glucocorticoid receptors nor require replication, transcription or translation.