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

Abstract

1 To determine the cellular mechanisms of atrial natriuretic peptide (ANP) release from ventricular cardiomyocytes, the secretory and the cardiac effects of a phorbol ester, 12-0-tetradecanoyl-phorbol-13-acetate (TPA), known to stimulate protein kinase C activity in heart cells, were studied in isolated, perfused heart preparations from 2-and 21-month-old Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. TPA was added to the perfusion fluid for 30 min at a concentration of 46 nm after removal of atrial tissue. Additionally, atrial and ventricular levels of immunoreactive ANP (IR-ANP) and ANP mRNA, the distribution of ANP within ventricles as well as the relative contribution of atria and ventricles in the release of ANP were studied. 2 Ventricular hypertrophy that gradually developed in hypertensive rats resulted in remarkable augmentation of ANP gene expression, as reflected by elevated levels of immunoreactive ANP and ANP mRNA. The total amount of IR-ANP in the ventricles of the SHR rats increased 41 fold and ANP mRNA levels 12.9 fold from the age of 2 to 21 months. At the age of 21 months, levels of IR-ANP and ANP mRNA in the ventricles of SHR rats were 5.4 fold and 3.7 fold higher, respectively, than in the normotensive WKY rats. Immunohistochemical studies demonstrated ANP granules within the hypertrophic ventricles of the old SHR rats, but not within normal ventricular tissue. 3 In isolated perfused heart preparations, the severely hypertrophied ventricular tissue of SHR rats after atrialectomy secreted more ANP into the perfusate than did the control hearts. The phorbol ester TPA caused a marked vasoconstriction in both the 2-month and 21-month old normal and hypertrophied hearts. Interestingly, the ANP release from the hypertrophied ventricles of the old SHR rats increased considerably (from 413 + 30 to the maximum of 623 + 75 pgml-1, F = 10.8, P < 0.001, two-way analysis of variance), whereas only a small increase was seen in old WKY rats and no effect was observed in young animals of either strain. When intact rat hearts (without atrialectomy) were used, infusion of phorbol ester also increased the ANP secretion into the perfusate in young animals. 4 Our present results indicate that the phorbol ester TPA increases the release of ANP from the hypertrophied, but not from normal rat myocardium. Thus, hypertrophied rat ventricular myocytes appear to possess the cellular mechanisms necessary to secrete ANP by a regulated pathway. The results further suggest that protein kinase C activity may be involved in the the regulation of ANP secretion from ventricular cells, as has been shown earlier for atrial myocytes.

Quinapril treatment and arterial smooth muscle responses in spontaneously hypertensive rats

“…The finding that plasma ANP was similar in WKY rats and quinapril-SHR and markedly lower than in untreated SHR supports this conclusion. Elevated ANP content in the left atrium of SHR on quinapril, in turn, probably results from reduced ANP release, since the rate of ANP synthesis in atrial tissue of SHR is known to be constant (Kinnunen et al, 1991). Thus, the results on plasma and tissue ANP concentrations confirm the normalization of blood pressure in quinapriltreated SHR.…”

Antihypertensive and cardioprotective effects of different monotherapies and combination therapies in young spontaneously hypertensive rats – A pilot study

“…However, ANP mRNA expression in LV was equal in young SHR and WKY. At 21 months of age, ventricle weight of SHR had increased further to about 170%, and ANP mRNA reached 3.7-fold values compared to age-matched WKY ( Kinnunen et al, 1991 ). We found a similar relation of HW/BW between our young SHR and WKY.…”

Obesity is Associated with Impaired Ventricular Protein Kinase C-MAP Kinase Signaling and Altered ANP mRNA Expression in the Heart of Adult Zucker Rats

“…Concerning ANP mRNA expression, we also found that activation of PKC resulted in the induction of myocardial ANP mRNA with a transient maximum at 60 minutes in lean Zucker rats. Because it has been shown that in the adult heart ventricles PMA had no effect on ANP secretion, 37,38 it can be speculated that the transient increase in ANP mRNA observed in heart ventricles from adult lean Zucker rats results from a possible negative feedback mechanism resulting from ANP accumulation. With a finding similar to our own, Cornelius et al 39 reported a transient increase in ANP mRNA 120 minutes after imposition of elevated wall stress and 90 minutes after forskolin stimulation.…”