Prenatal glucocorticoid exposure alters hypothalamic-pituitary-adrenal function and blood pressure in mature male guinea pigs

Abstract

Pregnant guinea pigs were treated with dexamethasone (1 mg kg(-1)) or vehicle on days 40-41, 50-51 and 60-61 of gestation, after which animals delivered normally. Adult male offspring were catheterized at 145 days of age and subjected to tests of hypothalamic-pituitary-adrenal (HPA) axis function in basal and activated states. Animals exposed to dexamethasone in utero (mat-dex) exhibited increased hippocampus-to-brain weight ratio, increased adrenal-to-body weight ratio and increased mean arterial pressure. There were no effects on gestation length, birth weight and postnatal growth. There were no overall differences in diurnal plasma adrenocorticotropic hormone (ACTH) and cortisol profiles, though there were subtle differences during the subjective afternoon between control and mat-dex offspring. A significant decrease in initial ACTH suppression was observed following dexamethasone injection in mat-dex offspring compared to control offspring. Molecular analysis revealed significantly increased MR mRNA expression in the limbic system and particularly in the dentate gyrus in mat-dex offspring. In the anterior pituitary, both pro-opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels were significantly elevated in mat-dex offspring. In conclusion, (1) repeated prenatal treatment with synthetic glucocorticoid (sGC) permanently programmes organ growth, blood pressure and HPA regulation in mature male offspring and these changes involve modification of corticosteroid receptor expression in the brain and pituitary; (2) the effects of prenatal sGC exposure on HPA function appear to change as a function of age, indicating the importance of investigating HPA and cardiovascular outcome at multiple time points throughout life.

Figure 1. Mean arterial, systolic and diastolic blood pressure (mean ± s.e.m.) in adult male offspring whose mothers had been injected with vehicle (control) or dexamethasone (mat-dex)

Open column, control (n = 10); Filled column, mat-dex (1 mg kg⁻¹; n = 8). Circles and bars inside the columns represent mean arterial pressure: systolic pressure is represented by the top bars and diastolic pressure is represented by the bottom bars. *P < 0.05, significant difference between prenatal treatments.

Figure 2. Resting (basal) plasma ACTH (A) and cortisol (B) concentrations during the subjective day (07.00–18.00 h) in adult male offspring whose mothers had been injected with vehicle or dexamethasone on days 40–41, 50–51, and 60–61 of gestation

Data are means ± s.e.m. ○ control (n = 9); •, dexamethasone (1 mg kg⁻¹; n = 10).

Figure 3. Plasma ACTH (A) and cortisol (B) concentrations before and during dexamethasone and corticotropin-releasing hormone challenge in adult male offspring whose mothers had been injected with vehicle or dexamethasone on days 40–41, 50–51, and 60–61 of gestation

Data are means ± s.e.m. Dexamethasone (dex), 1 mg kg⁻¹; corticotropin-releasing hormone (CRH), 0.5 μg kg⁻¹. ○, control, (ACTH n = 8, cortisol n = 7); •, dexamethasone (ACTH n = 6, cortisol n = 6) *P < 0.05, significant difference between prenatal treatments.

Figure 4. Plasma cortisol concentrations before and during ACTH challenge (0.5 μg kg⁻¹; A) and restraint (30 min; B) in adult male offspring whose mothers had been injected with vehicle or dexamethasone on days 40–41, 50–51 and 60–61 of gestation

Data are means ± s.e.m. ○, control (ACTH n = 8, restraint n = 8); •, dexamethasone (1 mg kg⁻¹; ACTH n = 7, restraint n = 8).

Figure 5. Hippocampal MR mRNA

A, representative expression of MR mRNA in the hippocampus (CA1/2, CA3, CA4) and dentate gyrus (DG) in adult male offspring whose mothers had been injected with vehicle (control) or dexamethasone (1 mg kg⁻¹; mat-dex) on days 40–41, 50–51 and 60–61 of gestation. Bar = 1 mm. B, relative optical density (ROD) of MR mRNA expression (mean ± s.e.m.) in the hippocampus (CA1/2, CA3, CA4) and dentate gyrus (DG) in adult male offspring whose mothers had been injected with vehicle (control, open columns, n = 8) or dexamethasone (1 mg kg⁻¹; filled columns, n = 8) on days 40–41, 50–51 and 60–61 of gestation. *P < 0.05, significant difference between prenatal treatments.

Figure 6. GR mRNA and POMC mRNA in the pituitary gland

A, relative optical density (ROD) of GR mRNA expression (mean ± s.e.m.) in the anterior pituitary (inferior and superior) in adult male offspring whose mothers had been injected with vehicle (control, open columns, n = 7) or dexamethasone (1 mg kg⁻¹; filled columns, n = 8) on days 40–41, 50–51 and 60–61 of gestation. *P < 0.05, **P < 0.01, significant difference between prenatal treatments. B, representative expression of GR mRNA (left panel, GR) and POMC mRNA (right panel, POMC) in the inferior (inf) and superior (sup) regions of the anterior pituitary and in the intermediate pituitary (ip). Bar = 1 mm. C, relative optical density (ROD) of POMC mRNA expression (mean ± s.e.m.) in the anterior pituitary (inferior and superior) in adult male offspring whose mothers had been treated as described above.

Figure 7. Representative expression of MC2-R (A), CYP 17 (B), StAR (C) and SF-1 (D) mRNA in the glomerulosa (glom) and fasciculata/reticularis (f/r) regions of the adrenal cortex (CTX)

Adrenal medulla is represented by M. Bar = 1 mm.