Ultrastructure of mesangial and juxtaglomerular cells in the kidney of a hibernator

Summary The mesangial and juxtaglomerular cells were studied in kidneys of hibernating and non-hibernating ground squirrels, Citellus tridecemlineatus. In the hibernating animal, as compared with the non-hibernating, the mesangial cells show signs of increased activity. The cells are relatively larger, and numerous vacuoles appear in the cytoplasm. The juxtaglomerular cells also show signs of hyperactivity. Secretion droplets, mitochondria and free ribosomes increase in number and the endoplasmic reticulum becomes dilated. It is postulated that during hibernation, increased activity of mesangial cells slows glomerular filtration by absorption of filtrate into the mesangial matrix, and increased activity of juxtaglomerular cells results in increased renin secretion which in turn may stimulate hypersecretion of aldosterone to conserve sodium for water balance mechanisms necessary at the time.Supported by Research Grant A-2027 from the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health.We wish to gratefully acknowledge the technical assistance of Mary Gandia.