Proliferation of epithelial cells in the jejunal crypts of adrenalectomized and adrenocortical hormone treated rats

MODULATION OF INTESTINAL BARRIER FUNCTION BY GLUCOCORTICOIDS: LESSONS FROM PRECLINICAL MODELS

Glucocorticoids (GCs) are widely used drugs for their anti-inflammatory and immunosuppressant effects, but they are associated with multiple adverse effects. Despite their frequent oral administration, relatively little attention has been paid to the effects of GCs on intestinal barrier function. In this review, we present a summary of the published studies on this matter carried out in animal models and cultured cells. In cultured intestinal epithelial cells, GCs have variable effects in basal conditions and generally enhance barrier function in the presence of inflammatory cytokines such as tumor necrosis factor (TNF). In turn, in rodents and other animals, GCs have been shown to weaken barrier function, with increased permeability and lower production of IgA, which may account for some features observed in stress models. When given to animals with experimental colitis, barrier function may be debilitated or strengthened, despite a positive anti-inflammatory activity. In sepsis models, GCs have a barrier-enhancing effect. These effects are probably related to the inhibition of epithelial cell proliferation and wound healing, modulation of the microbiota and mucus production, and interference with the mucosal immune system. The available information on underlying mechanisms is described and discussed.

Effects of glucocorticoid hormones on cell proliferation in dimethylhydrazine-induced tumours in rat colon

Adrenocortical hormones have previously been shown to influence cell proliferation in many tissues. In this report, their influence on cell proliferation in the colonic crypt epithelium and in colonic adenocarcinomata is compared. Colonic tumour cell proliferation was found to be retarded following adrenalectomy and this retardation was reversible by administration of hydrocortisone, or by administration of synthetic steroids with predominantly glucocorticoid activity. Tumour cell proliferation in adrenalectomized rats was not promoted by the mineralocorticoid hormone aldosterone. Neither adrenalectomy, nor adrenocortical hormone treatment, significantly influenced colonic crypt cell proliferation.

Physiologic and pharmacologic effects of glucocorticoids on ion transport across rabbit ileal mucosa in vitro

Physiologic and pharmacologic effects of glucocorticoids on ileal ion transport were examined in vitro. Tissues were obtained from the three following groups of rabbits: (a) normal; (b) glucocorticoid deficient, which were treated with aminoglutethimide (AG), 100 mg twice daily for 3 d, with a resulting marked reduction in urinary cortisol excretion but no decrease in urinary aldosterone; and (c) methylprednisolone-treated (MP), 40 mg daily for 2 d. Transileal NaCl fluxes were measured with radioisotopes under short-circuit conditions, and the net HCO(3) flux was assumed equal to that portion of the short-circuit current (I(sc)) not accounted for by Na and Cl. In NaCl Ringer's solution containing 25 mM HCO(3) (pH 7.4), normals absorbed both Na and Cl and secreted HCO(3); the I(sc) was greater in both AG and MP groups than in normals; in the AG group, no Na was absorbed, and Cl as well as HCO(3) was secreted; in the MP group, more Na was absorbed and more HCO(3) secreted than in normals. Addition of glucose to the luminal side caused similar increments in I(sc) in all three groups, suggesting similar rates of Na-coupled glucose absorption. Secretory response was assessed with a maximal secretory simulus (8-Br-cAMP) and also a submaximal, cGMP-related secretory stimulus (Escherichia coli heat-stable enterotoxin). After addition of 8-Br-cAMP, the rates of net Cl secretion were similar in all three groups, suggesting no effect of glucocorticoids on maximal secretory capacity. Because the AG group was already secreting Cl, however, the cAMP-induced change in net Cl flux was least in this group. After addition of heat-stable enterotoxin, there were similar changes in net Cl flux in all three groups. To examine specifically Cl-independent, electrogenic Na transport, we used a 10 mM HCO(3), Cl-free SO(4)-Ringer (ph 7.2) in which net Na absorption was previously shown to be equal to the I(sc). Under these conditions, I(sc) was greatest in the MP group and least in the AG group. In vitro addition of hydrocortisone, 50 mug/ml, to AG tissues had no effect on Cl fluxes or I(sc) over a 3.5-h period. No differences among groups were observed with respect to morphology, electrical resistance, or cGMP concentration. We conclude that (a) the effect of glucocorticoid deficiency is similar to that of a submaximal secretory stimulus in that Na absorption is inhibited and some Cl secretion develops; (b) electrogenic Na absorption is depressed in glucocorticoid deficiency and enhanced in glucocorticoid excess; (c) glucocorticoid excess increases HCO(3) secretion; and (d) glucocorticoid status does not affect maximal secretory capacity.

Genetic differences of DNA and RNA synthesis in the epithelium of the lens of the chick

The genetically unrelated chick strains Hy-1 and Hy-2, which have been strongly selected for growth rate, both exhibit hyperplasia of the lens epithelium. These two strains and a control strain N, not selected for growth rate, were compared with respect to incorporation of3H-thymidine and14C-uridine by freshly excised lenses in culture at different times throughout a 24-h period. The levels of incorporation of label into the lens cells were found to vary according to the time of day. The pattern of diurnal variation in both thymidine and uridine incorporation was found to be strain specific. Hy-1 and Hy-2 showed a greater degree of synchrony than did normal (N) lenses, and the frequency of the peaks of incorporation was also higher. Autoradiography confirmed that only lens epithelium incorporates thymidine during culture and that the number of labelled nuclei depends on the time of day when the lenses were explanted. These data point to genetic control of the cell cycle.

Circadian rhythms of presumptive stem cells in three different epithelia of the mouse

Variation in the percentage of labelled cells (LI), mitoses (MI) and apoptosis (AI: i.e. shrinkage necrosis) have been studied throughout a 24 hr period (40 min after labelling with 3H-TdR) for tongue epithelium, epidermis and intestinal epithelium in the mouse. A room with reversed light cycle was used to obtain data for half of the 24 hr period. All three tissues showed marked variations in LI with peak values between 24.00 and 03.00 hours. In the intestine a maximum value for MI was observed 3-6 hr after that for LI and with a maximum value for AI slightly later. In all three epithelia the circadian rhythm was most striking in cells at positions which can be correlated with presumptive stem cell activity; e.g. in the crypts the labelling and mitotic peaks reflecting a circadian rhythm were most clearly distinguishable at the basal part of the crypts. These observations are discussed in relation to the validity of various proliferative models.