Differential responses of circulating and tissue adrenomedullin and gene expression to volume overload

Adrenomedullin (AM), which is produced by various tissues and organs, also circulates in the blood. Circulating AM levels increase during disease states such as essential hypertension, heart failure, and renal failure. However, little is known about how circulating AM or AM production responds to volume overload (VOL).

Progressive VOL was induced in rats by an aortocaval shunt (AC) or by an aortocaval shunt with banding of the abdominal aorta distal to the shunt (AC + B), which created a larger shunt volume. Plasma and tissue AM concentrations, as well as AM gene expression levels, were measured at 1, 5, and 14 days after operation. Plasma concentrations of atrial natriuretic peptide (ANP), aldosterone, and renin activity (PRA) were also examined. Pulmonary congestion, pleural effusion, and ascites rapidly progressed in the AC + B group, suggesting that VOL caused more rapid heart failure under these conditions. Plasma AM concentrations in the AC + B and AC groups at day 1 compared with those in sham-operated rats were increased by 300% and 140%, respectively, and then gradually declined. The time course of plasma AM over 14 days was similar to that of plasma aldosterone and PRA, but not of plasma ANP or intracardiac filling pressure. The increase in plasma AM was accompanied by upregulated AM gene expression in the lung and aorta and by decreased AM concentrations in the atrium, ventricle, and adrenal gland. Cardiac AM gene expression levels were increased in the hypertrophied ventricles of AC and AC + B rats.

The major findings of the present study were 1) a rapid increase in plasma AM after the imposition of VOL in association with increased plasma aldosterone and PRA, 2) the contribution of several organs to this increase, and 3) a late increase in the AM messenger RNA (mRNA) level in the ventricles as VOL-induced ventricular hypertrophy developed.