Christopher G. Schyvens

The nitric oxide system in glucocorticoid-induced hypertension

The blood pressure-raising effects of adrenocortical steroids with predominantly glucocorticoid activity, both naturally occurring and synthetic, are well known. Recent evidence suggests that the nitric oxide system plays a key role in the hypertension produced by glucocorticoids. Glucocorticoid actions at various sites in the nitric oxide synthase (NOS) pathway may result in elevated blood pressure. These include: alterations in l-arginine availability or transport; NOS2 and NOS3 downregulation; reduced cofactor bioavailability; NOS uncoupling; a concomitant elevation in reactive oxygen species and removal of nitric oxide (NO) from the vascular environment; alterations in whole body antioxidant status; and erythropoietin induced resistance to NO.

Glucocorticoid-induced hypertension: from mouse to man

1. Adrenocorticotrophic hormone (ACTH) raises blood pressure in humans, sheep, rat and mouse. In rat and humans, but not sheep, the hypertension can be explained by glucocorticoid excess.

The anti-oxidant Tempol reverses and partially prevents adrenocorticotrophic hormone-induced hypertension in the rat

Objective To investigate the effects of the antioxidant Tempol on prevention and reversal of adrenocorticotrophic hormone (ACTH)-induced hypertension in the rat, a model of hypertension characterized by nitric oxide deficiency. Methods Male Sprague–Dawley rats (n = 10 in each group) were treated with either saline or ACTH (0.2 mg/kg per day, s.c.) for 12 days. Tempol (1 mmol/l in drinking water) treatment was started on either day 8 (T8) of ACTH or saline treatment (reversal study), or 4 days prior to ACTH or saline treatment (prevention study). Systolic blood pressure (SBP) was measured using tail-cuff sphygmomanometry. Plasma F2-isoprostanes, a marker of oxidative stress, were measured by gas chromatography–mass spectrometry. Results ACTH increased SBP (mean ± SEM: 119 ± 5 to 147 ± 7 mmHg, P < 0.0005) and plasma F2-isoprostane concentration (8.4 ± 1.2 saline versus 12.9 ± 1.6 nmol/l ACTH, P < 0.05). Tempol alone did not alter SBP, but administration of Tempol on T8 reversed ACTH-induced hypertension (from 134 ± 4 T8 to 118 ± 3 mmHg, P < 0.005). Tempol pre-treatment partially prevented ACTH-induced hypertension (123 ± 2 mmHg, P′ < 0.05). However, Tempol had no effect on F2-isoprostane concentrations at the dose used in this study. Conclusions ACTH-induced hypertension in the rat is associated with increased oxidative stress. Tempol treatment reversed, and pretreatment partially prevented ACTH-induced hypertension, independent of improvement in systemic oxidative stress.

N-Acetylcysteine Antagonizes the Development But Does Not Reverse ACTH-Induced Hypertension in the Rat

We investigated the effect of antioxidant N-acetylcysteine (NAC) on adrenocorticotropic hormone (ACTH)-hypertension. Male Sprague-Dawley rats received NAC (10 mg/L) or water 4 days before ACTH/saline treatment for 13 days (prevention study). In a reversal study, NAC commenced on day 8 of ACTH/saline treatment and continued for 5 days. ACTH increased systolic blood pressure (SBP) in water drinking rats (111 ± 1 to 131 ± 3 mmHg, p < 0.001). In the prevention study, NAC + ACTH increased SBP (108 ± 2 to 120 ± 2 mmHg, p < 0.001) but less than ACTH alone (p′ < 0.05). In the reversal study, NAC had no significant effect (132 ± 4 to 124 ± 3 mmHg, ns). Thus, NAC partially prevented but did not reverse ACTH-induced hypertension.

Role of Tetrahydrobiopterin in Adrenocorticotropic Hormone‐Induced Hypertension in the Rat

Adrenocorticotropic hormone (ACTH)‐induced hypertension in the rat is characterized by nitric oxide deficiency. Tetrahydrobiopterin (BH4) is an essential cofactor for the enzyme nitric oxide synthase and glucocorticoids have been reported to reduce cytokine‐induced BH4 production. Accordingly we hypothesized that ACTH‐induced hypertension would be reversed by BH4 supplementation. Male Sprague–Dawley rats (n = 33) were treated with BH4 in vehicle (10 mg/kg/day i.p.) or vehicle alone (5 mg/kg/day i.p. of ascorbic acid in 4 mM HCl) for 10 days. ACTH (0.2 mg/kg s.c.) or saline daily injection was started 2 days after BH4 or vehicle treatment and continued for 8 days. Systolic blood pressure (SBP) was measured on alternate days using the tail cuff method. Treatment with HCl, ascorbic acid or BH4 alone had no effect on SBP. In saline treated rats, neither BH4 nor its vehicle modified SBP. In ACTH treated rats, SBP was increased in both BH4 (from 128 ± 6 to 142 ± 4 mmHg, T0 to T10, P < 0.0005, one way ANOVA) and vehicle groups (from 127 ± 3 to 158 ± 7 mmHg, T0 to T10, P < 0.001, one way ANOVA). There was no significant difference in SBP between BH4 + ACTH treated and vehicle + ACTH treated rats. Thus, daily injection of BH4 (10 mg/kg i.p.) failed to prevent the development of ACTH‐induced hypertension in rat.

Nitric oxide donation lowers blood pressure in adrenocorticotrophic hormone-induced hypertensive rats.

Adrenocorticotrophic hormone (ACTH) elevates systolic blood pressure (SBP) and lowers plasma reactive nitrogen intermediates in rats. We assessed the ability of NO donation from isosorbide dinitrate (ISDN) to prevent or reverse the hypertension caused by ACTH. In the prevention study, male Sprague Dawley rats were treated with ACTH (0.2 mg/kg/day) or saline control for 8 days, with either concurrent ISDN (100 mg/kg/day) via the drinking water or water alone. Animals receiving ISDN via the drinking water were provided with nitrate‐free water for 8 hours every day. In the reversal study ISDN (100 mg/kg) or vehicle was given as a single oral dose on day 8. SBP was measured daily by the indirect tail‐cuff method in conscious, restrained rats. ACTH caused a significant increase in SBP compared with saline (P < 0.0015). In the prevention study, chronic administration of ISDN (100 mg/kg/day) did not affect the SBP in either group. In the reversal study, ISDN significantly lowered SBP in ACTH‐treated rats at 1 and 2.5 hours (132 ± 3 mmHg (1 h) and 131 ± 2 mmHg (2.5 h) versus 143 ± 3 mmHg (0 h), P < 0.002), but not to control levels. It had no effect in control (saline treated) rats. In conclusion, the lowering of SBP by NO donation is consistent with the notion that ACTH‐induced hypertension involves an impaired bioavailability or action of NO in vivo.

Antioxidant Vitamins and Adrenocorticotrophic Hormone-Induced Hypertension in Rats

This study examined whether the anti-oxidants ascorbic acid, α- or γ-tocopherol, could modify adrenocorticotrophic hormone (ACTH)-hypertension in Sprague-Dawley rats, a model associated with increased oxidative stress. Systolic blood pressure (SBP) was measured by the tail-cuff method. After four days of ascorbic acid (AA) (200mg/kg/day drinking) or α-tocopherol (500 mg/kg/d i.p. or feed), rats were co-administered ACTH (0.2 mg/kg/day s.c.) or saline for 11 days (prevention studies). In reversal studies, ACTH/saline was administered for 15 days, and from day 9, α- or γ-tocopherol (20 mg/kg/day) was added. ACTH increased SBP compared to saline (p < 0.05). AA or α-tocopherol failed to prevent and α- or γ-tocopherol failed to reverse ACTH-induced hypertension. Thus, neither vitamin C (water soluble) nor E (lipid soluble) modified ACTH-induced hypertension in the rat.

The glucocorticoid receptor is required for experimental adrenocorticotrophic hormone-induced hypertension in mice

1. In the present study, we have (i) measured basal blood pressure by telemetry in wild‐type (WT) and glucocorticoid receptor knockout (GRKO) mice; (ii) investigated whether or not adrenocorticotrophic hormone (ACTH) can induce hypertension in GRKO mice; and (iii) investigated the effect of mineralocortocoid receptor blockade on the cardiovascular physiology of GRKO mice.