Ellepsis and akairial disproportion in the hypothyroid rat

Renal structural and functional changes observed in rats during hypothyroidism have been employed to illustrate the concepts of "ellepsis" and "akairia" that have emerged from the work of Cournand and Richards. Ellepsis--the inadequate homeostatic response--is evident in the failure of corrective adjustments in glomerular filtration rate to prevent the excessive natriuresis and detrimental salt loss typical of this disorder in the rat but not in man. A slowing in overall bodygrowth is associated with an inappropriate (akairial) disproportion in the growth of glomeruli and tubules. Comparison of the changes in body weight, glomerular diameters, and tubular lengths in euthyroid and hypothyroid (radioiodine) littermates showed that glomeruli continued to grow in proportion to total body weight following administration of radioiodine while tubular growth almost ceased. Since disproportional failure of pulmonary growth has also been observed in these studies (0.829 +/- SEM 0.040 g in hypothyroid rats as compared with 1.14 +/- 0.034 g in euthyroid weight-matched controls), it may be profitable to look for abnormalities in respiratory homeostasis in the hypothyroid rat.