Abstract

The effect of glucocorticoids on the expression of intestinal cholecystokinin (CCK) was investigated both in vivo and in cell culture systems. In vivo, 2-day administration of methylprednisolone to adult male rats induced a decrease in CCK-like immunoreactivity (CCK-LI) and CCK mRNA levels in mucosal extracts. In two CCK-producing cell lines, RIN 1056E and STC-1 of pancreatic and intestinal origin respectively, dexamethasone induced dose-dependent decreases in both CCK-LI and steady-state CCK mRNA levels. The decrease in CCK mRNA was totally prevented by incubation of cells with an excess of RU 38486, a competitive inhibitor for the binding of glucocorticoids to their receptor. Actinomycin D, used to prevent RNA synthesis, did not modify CCK mRNA stability in dexamethasone-pretreated cells as compared with cells not exposed to dexamethasone. When cells were first incubated with actinomycin D, subsequent addition of dexamethasone left the steady-state CCK mRNA levels unaltered in both cell lines. Nuclear run-on assays performed in RIN 1056E cells showed that glucocorticoids decreased the rate of transcription of the CCK gene. In addition, cycloheximide, used to prevent protein synthesis, abolished the inhibitory effects of dexamethasone on steady-state CCK mRNA levels. These results demonstrate that glucocorticoids down-regulate CCK gene expression in the rat intestinal mucosa and in two CCK-producing cell lines. The effect is blocked by a glucocorticoid receptor antagonist. Inhibition of CCK gene expression may result from a decrease in the transcription rate, and probably involves one or several steps that depend on protein synthesis.

Journal of Endocrinology (1996) 151, 137–145

ABSTRACT

The ultrastructure of the luminal surface epithelium was compared in endometrial samples taken from 23 normally cycling women and from 22 patients submitted to ovarian stimulation with clomiphene citrate (100 mg/day for 5 days), human menopausal gonadotrophin (hMG) and human chorionic gonadotrophin (hCG). On day 2 after ovulation, only four out of nine specimens taken from the women in the hormone-treated group were identical to those of normally cycling women. On day 6 after ovulation, only two out of the 13 biopsy specimens from the treated group were the same as those from normally cycling women at that stage. Apical protrusions (pinopodes), typical for this period of the cycle, were missing in 11 of the 13 endometrial samples from the treated group.

These observations suggest that the hormonal treatment applied to induce ovulation (clomiphene citrate, hMG and hCG) can modify the normal development of the prenidatory endometrium, and may thus have a negative effect on the rate of egg implantation.

J. Endocr. (1987) 114, 319–324

Gonadotropin-releasing hormone receptor I (GnRHR I) has been localized to the limbic system of the rat brain, although the functional consequences of GnRH signaling through these receptors is unknown. In this paper, we characterize the expression of GnRHR I in the human hippocampus and cortex, and the functionality of GnRHR I in human neuroblastoma cells. Robust GnRHR I immunoreactivity was detected in the cell body as well as along the apical dendrites of pyramidal neurons in the CA2, CA1, and end plate, but was clearly lower in the subiculum of the hippocampus. Immunolabeling was also evident in cortical neurons, including those located in the entorhinal cortex and occipitotemporal gyrus but was not observed within the granular layer of the dentate gyrus. No differences in immunohistochemical staining were observed between control and Alzheimer’s disease brain. GnRHR I mRNA and protein (mature, immature, and other variant) expression was detected in human neuroblastoma cells (M17, SH-SY5Y) and rat embryonic primary neurons and varied with differentiation and GnRH treatment. Since GnRHR I was expressed by extrapituitary cells, and hypothalamic GnRH I secretion markedly increases post-menopause/andropause, we treated human M17 neuroblastoma cells cultured in serum-free conditions with GnRH I for 6 h and measured LH expression. M17 neuroblastoma cells express LHβ mRNA, while immunoblot analysis indicated the presence of three LH variants (approximately 30, 47, and 60 kDa) that were upregulated by low concentrations of GnRH I, but down-regulated at higher GnRH I concentrations. LH expression was also found to increase in differentiating embryonic rat primary cortical neurons. Our results demonstrate that neurons expressing GnRHR I are functional, responding to GnRH I by upregulating LH production. Post-reproductive surges in GnRH I secretion may explain the accumulation of LH in pyramidal neurons of the aged human and rat.