Abstract
Sex-dependent protein reabsorption droplets (PRD) were observed in the kidneys of beagle dogs. Seventy-six untreated males and seventy-eight untreated females were examined histologically. Microscopically, two types of PRD were detected in the proximal tubules (P3 segment). One was large and palely eosinophilic, and the other was small and deeply eosinophilic. Ultrastructural features of the large droplets were cytoplasmic vacuoles filled with electron lucent, proteinaceous, fine granular material. The small droplets were irregular clumps of electron lucent material without a boundary membrane. These PRD are likely to arise from intense reabsorption of protein from the urine by tubular cells as evident by histological or ultrastructural forms and response to various staining methods. The incidence of PRD in male beagle dogs was 36.8% (28/76), but there was no PRD in females. The highest incidence of PRD occurred in males 9-11 months of age. Since this finding was seen only in males and since no glomerular changes were evident, it was suggested that male beagle dogs have a low-molecular-weight, sex-dependent urinary protein like α 2μ-globulin in adult male rats.
