Tubuloglomerular feedback and autoregulation of glomerular filtration rate in Wistar-Kyoto spontaneously hypertensive rats

Abstract

Experiments were done in Wistar-Kyoto spontaneously hypertensive rats (SHR) to examine the efficiency of autoregulatory adjustments of kidney and nephron filtration rate (GFR) to acute changes in blood pressure (BP) over a broad blood pressure range. When BP of the SHR was reduced from 158±7 to 118 ±3 mm Hg$(\bar x \pm {\text{SEM}})$ by aortic clamping, kidney-GFR remained unchanged from 1.19±0.11 to 1.17±013 ml·min⁻¹·g⁻¹ kidney weight (KW), respectively. Single nephron GFR (SNGFR) measured at early distal tubule sites was similarly unchanged with the same BP change, 27.9±1.5 vs. 24.9±2.1 nl·min⁻¹·g⁻¹ KW (P>0.10). Proximal and distal estimates of SNGFR were significantly different from each other at high BP (7 nl·min⁻¹·g⁻¹,P<0.025), but were not different at low BP (2.0 nl·ml⁻¹·g⁻¹,P>0.10). Studies assessing tubuloglomerular feedback activity were done with orthograde perfusion of the loop of Henle using recollections of early proximal flow rate (EPFR) as an index of change of glomerular filtration rate. A change in perfusion rate from 0 to 45 nl·min⁻¹ induced a reduction in early proximal flow rate of 40.5 ±4.5%. Juxtaglomerular renin activity of superficial nephrons was 36.2±4.3 in the SHR, a value insignificantly different from 23.7±4.4 ng Angiotensin II amide·0.1 ml⁻¹·h⁻¹. 5 glomeruli⁻¹ in normal controls (P>0.05). The SHR appears to behave as a normal animal with respect to tubologlomerular feedback and autoregulatory renal vascular adjustments. Like normal rat models, the SHR demonstrated dependence on maintenance of distal filtrate delivery to achieve single nephron GFR autoregulation.