Beta-adrenergic stimulation of renin expression in vivo.

OBJECTIVE: To characterize the effect of beta-adrenergic activation on renal production of renin in the intact organism. DESIGN AND METHODS: Renal expression of renin [renin messenger RNA (mRNA)], plasma renin activity (PRA), inactive renin level, intrarenal renin distribution (immunohistochemistry), and the time course of activation of renin as well as hemodynamic parameters were determined during the subcutaneous infusion of isoproterenol (ISO) into rats. To examine whether beta-adrenergic activation of the renin system is modulated by the rate of salt intake rats were fed diets with normal, low and high salt contents.
RESULTS: Systolic blood pressure was not altered. PRA was elevated as much as fourfold after 40 h of ISO infusion. Although renal renin mRNA levels were elevated dose-dependently up to 4.2-fold, no significant recruitment of renin-containing cells could be detected. The time course of PRA revealed a marked transient rise of PRA during 6 h of ISO infusion with a subsequent decline. Inactive renin level was elevated during 3 to 18 h of ISO infusion. In contrast, renin mRNA level increased steadily with a lag phase of 3 h. Infusion of ISO increased PRA and renin mRNA level under a high-salt diet, but had no additional effect either on PRA or on renin mRNA level under low-salt diet.
CONCLUSION: Activation of beta-adrenergic receptors is a powerful stimulus of renin secretion and renin gene expression in juxtaglomerular cells in vivo, albeit the kinetics of upregulation of renin secretion and renin expression are markedly different. Therefore, the sympathetic tone might be a major factor determining the activity of the renin system in vivo. The ability of adrenergic agonists to stimulate the renin system appears to be modulated by the steady-state level of salt intake.