Intrarenal blood flow distribution in the desert quail following salt loading.

The total-kidney glomerular filtration rate (GFR) falls when birds are salt loaded. This fall in GFR is caused by glomerular intermittency. The nephrons that stop filtering are small, surface nephrons without loops of Henle. Larger nephrons with loops of Henle in the deeper regions of the kidney continue to filter during salt loading. Microfil casts were made of the renal microvasculature of the desert quail, Lophortyx gambelii, in an attempt to determine at what points intrarenal blood flow is regulated to cause glomerular intermittency. Casts of the renal vasculature were made in quail that were hydrated and in quail that were salt loaded. The results indicate that the small, surface nephrons stop filtering during salt loading because of a vasoconstriction at the level of the afferent arterioles of these nephrons. At the same time, blood flow is maintained to the large nephrons with loops of Henle. Reducing GFR at the expenses of excreting wastes can be viewed as a mechanism to conserve body water during periods of water deprivation.