Two distinctly different renal functional states were obtained in parallel series of non‐diuretic rats anesthetized with Amytal and Inactin, respectively. In the Amytal series proximal reabsorption rates ranged from 0.34 to 1.19 ml.min‐1· g KW‐1 (mean value 0.72 ml.min‐1· g KW‐1). The reciprocal of the occlusion time (1/OT) and of transit time (1/TT) increased in direct proportion to the inulin clearance (ClIN) indicating that proximal luminal diameter remained unchanged over the “spontaneous” range of values. Proximal as well as distal reabsorption rates were independent of serum‐ and tissue Amytal concentrations while proximal reabsorption rate was inversely correlated with log renin activity of serum. In the Inactin‐series proximal reabsorption rate was depressed and ranged from 0.20 to 0.74 ml.min‐1· g KW‐1 (mean value 0.46 ml.min‐1· g KW‐1). 1/OT and 1/TT was constant indicating a direct relationship between luminal diameter and ClIN. Proximal reabsorption rate was inversely correlated with serum Inactin concentration, while no relationship between proximal reabsorption rate and log renin activity was apparent. It is concluded that the variation in proximal reabsorption rate (and filtration rate) observed in Inactin anesthetized rats is induced by the anesthetic which in some way limits the reabsorption rate. The variation observed in Amytal anesthetized rats, on the other hand, is “spontaneous”, i.e. the rate is limited by factors other than the anesthetic.
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Elmer et al. (1972) studied this question.