We tested the hypothesis that preventing
cyclic GMP degradation with
zaprinast, (a selective
cyclic GMP-
phosphodiesterase inhibitor) would produce a blunted reduction in myocardial O2 consumption in
renal hypertension (One Kidney-One
Clip, 1K1C)-induced
cardiac hypertrophy. Four groups of anesthetized open-chest New Zealand white rabbits (n = 26) were utilized. Either vehicle or
zaprinast (3 x 10(-3) M) was applied topically to the left ventricular surface of control or 1K1C rabbits. Coronary blood flow (radioactive
microspheres) and O2 extraction (microspectrophotometry) were used to determine O2 consumption. Myocardial
cyclic GMP levels were determined by radioimmunoassay. The 1K1C rabbits had a greater heart weight-to-
body weight ratio (2.94 +/- 0.08 g/kg) than controls (2.58 +/- 0.17). Systolic blood pressure was higher in 1K1C (102 +/- 9 mm Hg) than in controls (86 +/- 3).
Zaprinast significantly and similarly increased
cyclic GMP in both control (3.90 +/- 0.47 to 4.66 +/- 0.89 pmol/g) subepicardium (EPI) and (5.08 +/- 0.69 to 7.06 +/- 1.36) subendocardium (ENDO) and 1K1C hearts (5.53 +/- 0.61 to 7.48 +/- 1.51 EPI and 6.48 +/- 0.42 to 8.88 +/- 1.08 ENDO). Myocardial O2 consumption (ml O2/min/ 100 g) was significantly lower in controls treated with
zaprinast (EPI: 8.8 +/- 0.1; ENDO: 9.5 +/- 1.9) than in controls treated with vehicle (EPI: 13.6 +/- 1.3; ENDO: 16.2 +/- 2.9). This effect was diminished in 1K1C rabbits treated with
zaprinast (EPI: 10.3 +/- 2.4; ENDO: 11.2 +/- 2.6) compared with the vehicle-treated 1K1C group (EPI: 13.3 +/- 1.2; ENDO: 14.5 +/- 2.4). There was a similar increase in myocardial
cyclic GMP after treatment with
zaprinast, but a greater depression of myocardial O2 consumption in control animals than in 1K1C
after treatment with
zaprinast. This suggested that the reduction in myocardial O2 consumption, related to increases in
cyclic GMP caused by
cyclic GMP-
phosphodiesterase blockade, was less in 1K1C
cardiac hypertrophy.