Sex differences in autoregulation of juxtamedullary glomerular blood flow in hydronephrotic rats

The technique of the split hydronephrotic kidney of anesthetized Wistar rats was used for the first time to study afferent and efferent arterioles of juxtamedullary (JM) glomeruli in vivo and to compare their behavior with that of the cortical glomeruli in female (F, 270 g body wt) and male (M, 400 g body wt) rats. The mean length of cortical efferent arterioles (F, 260; M, 380 microns) was less than 10% the length of JM efferent arterioles. Luminal diameters of the JM afferent arteriole (F, 17.1; M, 18.3 microns) and efferent arteriole (F, 25; M, 33.4 microns) were much larger than those of cortical arterioles (afferent: F, 9.1, M, 10.5 microns; efferent: F and M, 11.1 microns). In the hydronephrotic kidney, cortical glomerular blood flow (F, 17.5; M, 18.3 nl/min) is much reduced compared with the normal filtering kidney. This, however, is not true of JM glomerular blood flow (F, 120; M, 262 nl/min). During the reduction of renal perfusion pressure in females blood flow was autoregulated in cortical glomeruli within the pressure range of 110 to 80 mmHg; JM glomeruli failed to show any autoregulation. In males the glomerular blood flow was similarly autoregulated down to 90 mmHg in both cortical and JM nephrons. Local application of indomethacin to the kidneys from female rats reduced the glomerular flow rates by 30% but changed the autoregulatory behavior of cortical and JM glomerular blood flow so that it resembled that observed in untreated males. The data suggest that in females the autoregulatory response, particularly in JM glomeruli, is modified by prostaglandins.