Impaired myogenic response of the afferent arteriole contributes to the increased susceptibility to renal disease in Milan normotensive rats.

Milan normotensive (MNS) rats are more susceptible to the development of renal disease than Milan hypertensive (MHS) rats, but the genes and pathways involved are unknown. This study compared the myogenic response of isolated perfused afferent arterioles (Af-Art) and autoregulation of renal blood flow (RBF) and glomerular capillary pressure (Pgc) in 6-9-week-old MNS and MHS rats. The diameter of the Af-Art of MHS rats decreased significantly from 14.3 ± 0.5 to 11.5 ± 0.6  μ m when perfusion pressure was elevated from 60 to 120 mmHg. In contrast, the diameter of Af-Art of MNS rats did not decrease. RBF was well autoregulated in MHS rats, but it increased by 26% in MNS rats. Pgc rose by 11 mmHg when renal perfusion pressure (RPP) was increased from 100 to 140 mmHg in MNS but not in MHS rats. Protein excretion increased from 10 ± 1 to 245 ± 36 mg/day in MNS rats as they aged from 3 to 11 months but it did not increase in MHS rats. We also compared the development of proteinuria in MNS and MHS rats following the induction of diabetes with streptozotocin. Protein excretion rose from 16 ± 3 to 234 ± 43 mg/day in MNS rats, but it remained unaltered in MHS rats. These data indicate that the myogenic response of the Af-art is impaired in MNS rats and increased transmission of pressure to the glomerulus may contribute to renal injury in MNS rats similar to what is seen in fawn-hooded hypertensive and Dahl salt-sensitive rats.