EFFECTS OF ALPHA-1-ADRENERGIC BLOCKADE ON INTRARENAL HEMODYNAMICS IN HEART-FAILURE RATS

To investigate intrarenal hemodynamics and effects of alpha(1)-adrenergic blockade on glomerular functions in congestive heart failure (CHF), micropuncture studies were performed before and after intravenous injection of terazosin (1-mu-g/100 g body wt iv) in eight myocardial infarction (MI) and in nine sham-operated rats after intraperitoneal injection of Inactin (70 mg/kg). CHF was characterized by elevated left ventricular end-diastolic pressure and increased total heart weight. In CHF rats, single nephron glomerular filtration rate (SNGFR), single nephron plasma flow (SNPF), and ultrafiltration coefficient (K(f)) were decreased compared with sham-operated rats (SNGFR, 21.9 +/- 1.6 vs. 39.2 +/- 2.9 nl.min-1.g-1, P < 0.01; SNPF, 66.6 +/- 6.1 vs. 133.8 +/- 10.5 nl.min-1.g-1, P < 0.01; K(f), 0.019 +/- 0.001 vs. 0.041 +/- 0.004 nl.s-1.mmHg-1.g-1, P < 0.01). Single nephron filtration fraction (SNFF), glomerular pressure (P(g)), and efferent arteriolar resistance (R(e)) were higher in the CHF-MI rats than in the sham-operated rats (SNFF, 33.4 +/- 1.3 vs. 27.7 +/- 1.0, P < 0.05; P(g), 60.2 +/- 1.6 vs. 53.3 +/- 0.8 mmHg, P < 0.01; R(e), 3.92 +/- 0.66 vs. 1.62 +/- 0.15 x 10(10) dyn.s.cm-5.g, P < 0.05). With terazosin infusion, SNGFR, SNPF, and K(f) increased (SNGFR, to 24.9 +/- 2.1 nl.min-1.g-1, P < 0.05; SNPF, to 91.3 +/- 9.2 nl.min-1.g-1, P < 0.01; K(f), to 0.027 +/- 0.002 nl.s-1.mmHg-1.g, P < 0.01), whereas SNFF, P(g), afferent arteriolar resistance (R(a)), and R(e) decreased (SNFF, to 27.7 +/- 1.0, P < 0.05; P(g), to 51.0 +/- 0.8 mmHg, P < 0.01; R(a), to 2.60 +/- 0.29 x 10(10) dyn.s.cm-5.g, P < 0.01; R(e), to 2.35 +/- 0.32 x 10(10) dyn.s.cm-5.g, P < 0.05) in CHF-MI rats. These results suggest that alpha(1)-adrenoceptor activity participates in regulating cortical glomerular hemodynamics in MI-CHF rat model.