Glomerular response to verapamil by isolated spontaneously hypertensive rat kidney

We investigated the possibility that altered cell calcium regulation may affect function of isolated Kyoto spontaneously hypertensive rat (SHR) kidneys as compared with kidneys from Wistar-Kyoto control (WKY) rats. The kidneys were perfused at 120 and 160 mmHg. At 120 mmHg, SHR glomerular filtration rate (GFR) was 0.24 +/- 0.04 compared with WKY GFR of 0.70 +/- 0.10 ml/min (P = 0.001). At 160 mmHg, SHR GFR was 0.48 +/- 0.05 compared with WKY GFR of 1.09 +/- 0.05 ml/min (P less than 0.001). At 120 mmHg, addition of norepinephrine increased renal vascular resistance (RVR) by 50% and decreased SHR GFR by 27% and WKY GFR by 57% (P = 0.04). At 160 mmHg, norepinephrine elicited similar changes. Addition of verapamil, 5-10 microM, in the presence of norepinephrine returned RVR to 100-110% of control. With verapamil at 120 mmHg, SHR GFR increased to 0.84 +/- 0.23 ml/min, a value 3.5 times that of control (P = 0.03). In contrast, WKY GFR in the presence of norepinephrine and verapamil was 0.97 +/- 0.07 ml/min, unchanged from control (P = 0.07). At 160 mmHg, norepinephrine and verapamil also failed to increase WKY GFR above control (P = 0.4) but increased SHR GFR to 52% above control (P = 0.03). Isolated SHR kidneys exhibited exaggerated GFR responses to verapamil but not to norepinephrine. Abnormal cell calcium regulation may underlie the marked decrease in GFR when SHR kidneys are perfused acutely at normotensive perfusion pressures.