Factors Derived from Adrenals Are Required for Activation of Cardiac Gene Expression in Angiotensin II-Induced Hypertension

Abstract

The mechanisms mediating the activation of cardiac gene expression during pressure overload are not fully understood. We examined whether angiotensin II-induced activation of ventricular gene expression is related to blood pressure and ventricular mass or requires other factors by infusing angiotensin II in sham-operated and adrenalectomized rats. In sham-operated rats, angiotensin II (33 microg/kg x h, sc) produced a significant increase in mean arterial pressure (measured by telemetry) within 3 h. Mean arterial pressure (up to 45 h) and the increase in left ventricular hypertrophy in adrenalectomized rats during angiotensin II infusion were similar to those in sham-operated rats. Angiotensin II produced 3.6-fold (P < 0.01) and 20.4-fold (P < 0.001) increases in ventricular atrial natriuretic peptide mRNA levels at 12 and 72 h, respectively. Angiotensin II infusion for 12 h also significantly increased the ventricular mRNA levels of B-type natriuretic peptide (5.2-fold) and adrenomedullin (1.4-fold). Adrenalectomy either abolished (atrial natriuretic peptide and adrenomedullin) or blunted (B-type natriuretic peptide) the early activation of ventricular gene expression by angiotensin II. The baseline synthesis of atrial natriuretic peptide, B-type natriuretic peptide, and adrenomedullin in the ventricle remained unchanged in adrenalectomized rats. In conclusion, our results indicate that factors derived from the adrenals are required for angiotensin II-induced early activation of cardiac gene expression.

Evidence for a Functional Role of Angiotensin II Type 2 Receptor in the Cardiac Hypertrophic Process In Vivo in the Rat Heart

“…In agreement with previous studies, 12-15 PD123319 infusion alone had no effect on MAP; moreover, it did not modify Ang II-induced increase in blood pressure ( Figure 1A), showing that AT 2 -R is not involved in the regulation of blood pressure. As described previously, the increase in MAP by Ang II was associated with a significant decrease in heart rate, 16 remaining unaffected by PD123319 ( Figure 1B). Echocardiographic measurements showed that LV ejection fraction ( Figure 1C) and LV fractional shortening ( Figure 1D) were similar in all groups, suggesting that LV function was preserved in Ang II-induced hypertension.…”

“…16 Full-length rat atrial natriuretic peptide (ANP) cDNA probe (a gift from Dr Peter Davies, Queen's University, Kingston, Canada), a 390-bp rat B-type natriuretic peptide (BNP) cDNA probe, and an 18S cDNA probe were prepared as previously reported. 16 cDNA probes for rat ␣-actin and myosin isoforms were made by reverse transcription-polymerase chain reaction (RT-PCR) and ligated to dT-tailed pCR2.1 vector by use of a TA Cloning Kit (Invitrogen).…”

“…16 Full-length rat atrial natriuretic peptide (ANP) cDNA probe (a gift from Dr Peter Davies, Queen's University, Kingston, Canada), a 390-bp rat B-type natriuretic peptide (BNP) cDNA probe, and an 18S cDNA probe were prepared as previously reported. 16 cDNA probes for rat ␣-actin and myosin isoforms were made by reverse transcription-polymerase chain reaction (RT-PCR) and ligated to dT-tailed pCR2.1 vector by use of a TA Cloning Kit (Invitrogen). Sequencing with ABI PRISM 310 Genetic Analyzer (Applied Biosystems) confirmed that the probes correspond to bases 2950 to 3184 of rat skeletal ␣-actin (GenBank Accession Number v01218), 289 to 447 of rat cardiac ␣-actin (x00306), 5794 to 5923 of rat ␤-myosin heavy chain (␤-MHC) (x15939), and 5830 to 5921 of rat ␣-myosin heavy chain (␣-MHC) (x15938).…”

“…cDNA probes were labeled, and the membranes were hybridized, washed, and quantified as previously described. 16 …”

“…PD123319 has high affinity (K i Ͼ12 nmol/L) for the AT 2 -R but a low affinity (K i Ͼ100 mol/L) for the AT 1 -R. Therefore, administration of PD123319 at a dose of 1.25 mg · kg Ϫ1 · h Ϫ1 , yielding a plasma concentration of Ϸ500 nmol/L, would result in an effective AT 2 -R blockade without affecting the AT 1 -R. 15 After 12 or 72 hours of treatment, LVs were weighed, frozen in liquid nitrogen, and stored at Ϫ80°C, as described previously. 16 …”