Etiopathogenesis of excess methylprednisolone arterial hypertension in the rat

Potential adverse interaction between aspirin and lisinopril in hypertensive rats

The potential clinical effect of aspirin (ASA) in patients treated with angiotensin converting enzyme (ACE) inhibitors is debatable. Several studies have suggested that ASA attenuates the beneficial effects of ACE inhibitors in hypertension, congestive heart failure (CHF) or coronary artery disease (CAD) and have questioned the safety of using ASA concomitantly with these agents. The present study aims to investigate the possible interaction between ASA and ACE inhibitor in hypertensive rats. Hypertension was induced in adult male Wistar rats using Methylprednisolone (MP) 20 mg/kg per week s.c. for 2 weeks. The systolic blood pressure (SBP) was measured by noninvasive BP technique. The effect of Lisinopril (LS) 15 mg/kg per day and that of combination of LS and ASA; 100 and 25 mg/kg per day p.o. was studied on hypertension induced by glucocorticoid. Concurrent ASA treatment with LS did not hinder the hypotensive effect of LS at either dose. However ASA 100 mg/kg per day caused mortality in animals and produced massive cardiac necrosis and renal damage as evident from histopathology. Treatment with ASA 25 mg/kg per day caused lower mortality with variable effects on cardiac and renal tissues. These results indicate that ASA attenuates the beneficial effects of ACE inhibitor on survival in hypertensive rats and this effect was more pronounced at higher dose of ASA.

Kallikrein-kinin system in severe experimental hypertension

Plasma levels of low and high molecular weight kininogens, prokallikrein and active kallikrein were determined in four models of experimental hypertension and in genetically hypertensive rats. The high molecular weight kininogen remained essentially unaltered in all groups, whereas the low molecular weight kininogen was decreased in the renovascular groups. In the glucocorticoid hypertensive rats low molecular weight kininogen increased, but rats with hypertension induced both by renovascular and glucocorticoid mechanisms had normal kininogen. Genetically hypertensive rats had levels of low molecular weight kininogen similar to the ones observed in control group. The data presented reinforce the hypothesis of a participation of the kallikrein-kinin system in the etiopathogenesis of hypertension, indicating an implication of the low molecular weight kininogen in some types of severe experimental hypertension.

Angiotensin converting enzyme inhibition does not prevent development of ACTH-induced hypertension in sheep

The role of the renin-angiotensin system in the onset of ACTH-induced hypertension was examined in five conscious sheep. Captopril infusion alone (15 mg/kg per day) for 2 days produced a small fall in blood pressure. After 2 days of captopril ACTH was infused (20 micrograms/kg per day) for 3 days together with captopril. The blood pressure and electrolyte effects of ACTH administration were not modified by captopril pretreatment. These experiments establish that angiotensin II is not important in the onset of ACTH-induced hypertension in sheep.

Corticosteroid modulation of the renin system and blood pressure in the spontaneously hypertensive rat

This study examines the role of gluco- and mineralcorticoids in the regulation of the renin-angiotensin system and blood pressure in the spontaneously hypertensive rat (SHR). Effects of adrenalectomy and selective treatment with either aldosterone (30 micrograms/kg/day) or dexamethasone (60 micrograms/kg/day) on plasma renin substrate, active renin (PRA), total renin and blood pressure were studied in 10 week old SHR and control WKY rats. Systolic blood pressure was moderately lower in adrenalectomized rats (129 +/- 2 mm Hg vs 137 +/- 4 mm Hg in control WKY and 145 +/- 4 mm Hg vs 160 +/- 3 mm Hg in control SHR) but could be restored to the control range by aldosterone. Dexamethasone repletion induced substantial increments of systolic blood pressure to comparable levels in both species (202 +/- 8 mm Hg in WKY and 192 +/- 6 mm Hg in SHR). Renin substrate was markedly lower in adrenalectomized, saline repleted rats. This could be reversed by dexamethasone in both species and by aldosterone in WKY rats only. Both PRA and total renin were higher (p less than 0.01) in the adrenalectomized, saline repleted state. This increase was not observed in aldosterone repleted rats. However, dexamethasone inhibited the adrenalectomy associated increase of PRA and total renin in SHR but not in WKY rats. Differences in blood pressure between SHR and WKY persist even in adrenalectomized state despite comparable stimulation of the renin system. Conversely, while blood pressure of both species responds similarly to selective corticosteroids therapy, the response of the renin-angiotensin system in SHR and WKY rats is distinct. Therefore factors other than the adrenal gland and the renin system must be involved in the determination of the high blood pressure in SHR.