Release of atrial natriuretic peptide from rat myocardium in vitro: effect of minoxidil‐induced hypertrophy

Abstract

1 Ventricular hypertrophy is characterized by stimulation of ventricular synthesis of atrial natriuretic peptide (ANP). To examine the role of ventricular ANP levels in the secretion of ANP into the circulation, atrial and ventricular levels of immunoreactive-ANP (IR-ANP) as well as ANP messenger RNA (mRNA), and the release of IR-ANP from isolated perfused hearts, both before and after atrialectomy, were measured simultaneously in control and minoxidil-treated Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. 2 IR-ANP levels in the ventricles of untreated, 12 month-old SHR with severe ventricular hypertrophy were increased when compared to age-matched WKY rats. Minoxidil treatment for 8 weeks in both strains resulted in a decrease in mean arterial pressure and increases in ventricular weight to body weight ratios, plasma IR-ANP concentrations (in WKY from 133 + 20 to 281 + 34pgml-1, P < 0.01; in SHR from 184 + 38 to 339 + 61 pgml-', P < 0.05), and in ventricular IR-ANP contents (in WKY: 53%; in SHR: 41%). A highly significant correlation was found between ventricular IR-ANP content and ventricular weight to body weight ratio (r = 0.59, P < 0.001, n = 26). 3 When studied in vitro, in isolated perfused heart preparations, the hypertrophied ventricular tissue after atrialectomy secreted more ANP into the perfusate than ventricles of the control hearts; ventricles contributed 28%, 22%, 18% and 15% of the total ANP release to perfusate in the minoxidil-treated SHR, control SHR, minoxidil-treated WKY and control WKY, respectively. A significant correlation was found between the IR-ANP release from ventricles and ventricular weight to body weight ratio (r = 0.56, P < 0.01, n = 24). 4 These studies demonstrate that the ventricles contribute substantially to the circulating level of ANP, and that the amount released depends on the degree of ventricular hypertrophy.

Effect of phorbol ester on the release of atrial natriuretic peptide from the hypertrophied rat myocardium

“…The results suggest that this protein kinase C activity may be involved in the regulation of ANP secretion from ventricular cells, as has already been shown for atrial myocytes (Ruskoaho et al, 1985;Matsubara et al, 1988;Iida & Page, 1989;Shields & Glembotski, 1989). Further, the amount of ventricular ANP release correlated with the degree of hypertrophy, which is in good agreement with previous in vitro data obtained from an isolated heart preparation (Ruskoaho et al, 1989a;Thibault et al, 1989;Kinnunen et al, 1990).…”

“…The right and left ventricles were not separated because only 2.8% and 0.9% of the IR-ANP released from the ventricles in WKY and SHR, respectively, would be generated in the right ventricle (Ruskoaho et al, 1989a;Kinnunen et al, 1990 (Cathala et al, 1983). As shown previously (Ruskoaho et al, 1989a), Northern blot hybridization analysis using fulllength rat cDNA probe identified a single 0.9 kb mRNA species in the atria and ventricles of these strains.…”

“…As shown previously (Ruskoaho et al, 1989a), Northern blot hybridization analysis using fulllength rat cDNA probe identified a single 0.9 kb mRNA species in the atria and ventricles of these strains. For the RNA dot blot analysis, 1 pg and 20ug samples of the RNA from atria and ventricles, respectively, were transferred to a nitrocellulose membrane (Kinnunen et al, 1990). The fulllength rat ANP cDNA probe Car-55 (Flynn et al, 1985) antiserum in the final dilution of 1:25.000 (Vuolteenaho et al, 1985).…”

“…After perfusion, the aorta and pulmonary artery were carefully cut close to the ventricular surface. The right and left ventricles were not separated because only 2.8% and 0.9% of the IR-ANP released from the ventricles in WKY and SHR, respectively, would be generated in the right ventricle (Ruskoaho et al, 1989a;Kinnunen et al, 1990). To avoid the possible contamination of the ventricular sample by atrial tissue, ventricles were cut into the superior (about 15-20% of total weight) and inferior part.…”

“…ANP is released into the perfusion fluid, the amount of the peptide released depending on the degree of ventricular hypertrophy (Ruskoaho et al, 1989a;Thibault et al, 1989;Kinnunen et al, 1990). Moreover, in vivo physical excercise causes release of ANP from the hypertrophic ventricle with depletion of endocardial left ventricular stores (Ruskoaho et al, 1989a).…”