Nitric Oxide Donation Lowers Blood Pressure in Adrenocorticotrophic Hormone‐Induced Hypertensive Rats

Glucocorticoid-induced hypertension and the nitric oxide system

Glucocorticoid hormones, both naturally occurring and synthetic, have long been recognized as a major cause of hypertension. There are well-described experimental models of glucocorticoid-induced hypertension, such as adrenocorticotropic hormone- and dexamethasone-induced hypertension in rats, although the exact mechanism of glucocorticoid-induced hypertension remains unclear. It was initially considered to be due to mineralocorticoid receptor activation but more recent studies have not supported this notion. Current evidence demonstrates the importance of the nitric oxide (NO) system and interactions between NO and reactive oxygen species in the development of glucocorticoid-induced hypertension. This review highlights the pathways contributing to NO deficiency, which encompass the availability of l-arginine, endothelial NO synthase function and the extent of NO inactivation during oxidative stress.

How do glucocorticoids cause hypertension: role of nitric oxide deficiency, oxidative stress, and eicosanoids

The exact mechanism by which glucocorticoid induces hypertension is unclear. Several mechanisms have been proposed, although there is evidence against the role of sodium and water retention as well as sympathetic nerve activation. This review highlights the role of nitric oxide-redox imbalance and their interactions with arachidonic acid metabolism in glucocorticoid-induced hypertension in humans and experimental animal models.

Effects of sepiapterin supplementation and NOS inhibition on glucocorticoid-induced hypertension

BACKGROUND

Glucocorticoid-induced hypertension is associated with imbalance between nitric oxide (NO) and superoxide. One of the pathways that causes this imbalance is endothelial NO synthase (eNOS) uncoupling. In the present study, adrenocorticotrophic hormone (ACTH)- and dexamethasone-treated rats were further treated with sepiapterin, a precursor of tetrahydrobiopterin, or N-nitro-L-arginine (NOLA), an inhibitor of NOS, to investigate the role of eNOS uncoupling in glucocorticoid-induced hypertension.

METHODS

Male Sprague-Dawley (SD) rats (n = 7-13/group) were treated with either sepiapterin (5 mg/kg/day, IP) or saline (sham) 4 days before and during ACTH (0.2 mg/kg/day, SC), dexamethasone (0.03 mg/kg/day, SC), or saline treatment. NOLA (0.4 mg/ml in drinking water) was given to rats 4 days before and during dexamethasone treatment. Systolic blood pressure (SBP) was measured by the tail-cuff method.

RESULTS

Both ACTH (116 +/- 2 to 135 +/- 3 mm Hg (mean +/- s.e.m.), P < 0.001) and dexamethasone (114 +/- 4 to 133 +/- 3 mm Hg, P < 0.0005) increased SBP. Sepiapterin alone did not alter SBP. Sepiapterin did not prevent ACTH- (129 +/- 4 mm Hg, NS) or dexamethasone-induced hypertension (135 +/- 3 mm Hg, NS), although plasma total biopterin concentrations were increased. NOLA increased SBP in rats prior to dexamethasone or saline treatment. NOLA further increased SBP in both saline- (133 +/- 4 to 157 +/- 3 mm Hg, P < 0.05) and dexamethasone-treated rats (135 +/- 5 to 170 +/- 6 mm Hg, P < 0.05). ACTH and dexamethasone increased plasma F(2)-isoprostane concentrations. Neither sepiapterin nor NOLA significantly affected this marker of oxidative stress.

CONCLUSION

Sepiapterin did not prevent ACTH- or dexamethasone-induced hypertension. NOLA exacerbated dexamethasone-induced hypertension. These data suggest that eNOS uncoupling does not play a major role in the genesis of glucocorticoid-induced hypertension in the rat.