Objective:Previous studies have shown that anterior pituitary expression of corticotropin-releasing hormone type 1 receptor (GRH-R1) decreases during late gestation. This study sought to determine whether this reduction is from a decrease in the number of cells expressing CRH receptors of a decrease in the number of CRH receptors per cell.
Methods:Fetuses were studied at 100 days' gestational age (100 dGA), 120 dGA, or 140 dGA. Dispersed anterior pituitary cells were incumbated with or without fluorescein-conjugated CRH (FL-CRH). FL-CRH binding was assessed by flow cytometry.
Results:The number of CRH receptors per cell decreased at 120 dGA and 140 dGA. However, because of an increase in the percentage of cells expressing CRH receptors at 120 dGA, the total receptor index was similar at 100 dGA and 120 dGA. The receptor index tended to decrease at 140 dGA.
Conclusion:FL-CRH binding was decreased at 140 dGA due to a decrease in the percentage of cells binding CRH and the number of CRH receptors per cell. This could contribute to the decrease in CRH-stimulated adrenocorticotropin release during late gestation in fetal sheep.
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