Study on the mechanisms of glucocorticoid-induced hypertension: Glucocorticoids increase transmembrane Ca²⁺ influx in vascular smooth muscle in vivo

Abstract

Blood pressure (BP) and ex vivo influx rate of Ca²⁺ in excised aortae were measured in rabbits implanted with silastic rubber strips impregnated with glucocorticoids (GC) [dexamethasone (DEX) or cortisol (F_K)], or carbenoxolone (CX) [inhibitor of 11β-hydroxysteroid dehydrogenase (11-HSD), in a large (lg) or a small (sm) (10 times smaller) concentration], or F_K plus CX (sm), or DEX plus RU 38486 (a specific GC-receptor blocker). After 4-6 weeks rabbits implanted with DEX, CX (lg), and F_K + CX (sm) developed hypertension. Those implanted with F_K alone (yielding physiological serum concentration of F_K), CX (sm), and DEX + RU 38486 did not develop hypertension. Rates of unidirectional influx of Ca²⁺ measured in rings of excised aortae were in all hypertensive rabbits more than twice those in the control rabbits (implanted with silastic strips not containing any steroids). In all normotensive rabbits, Ca²⁺ influx rates remained normal. We conclude that, in analogy with the in vitro findings in cultured vascular smooth muscle (VSM) cells treated with GC, also in vivo, the elevation of tissue levels of GC causes an increase in the influx rate of Ca²⁺ in VSM. We propose that this may be the main pathogenic mechanism of GC-induced hypertension.