EXPERIMENTAL ASCENDING PYELONEPHRITIS

Light, Scanning Electron and Transmission Electron Microscopic Observations

Abstract

In order to clarify the important initial renal lesions of ascending pyelonephritis, the fate of pyelonephritis, the fate of pyelonephritis experimentally produced in rats, which received transurethral inoculation of 0.5ml heart infusion broth containing 10⁴ cells of Proteus mirabilis into the bladder after deprivation of drinking water for 24 hours, was traced for a period from one hour to 30 days after inoculation using light and electron microscopes.
The results obtained are as follows:
1. Pyelonephritis occurred in 110 of the 219 kidneys examined, the incidence being 6.9, 13.8, 24.1, 71.9, 63.2, 79.3, 75.0 and 100%, one two, 4, 8, 24 hours, 3, 7 and 30days after inoculation, respectively.
2. A slight inflammatory change defined as grade I occurred in 46 of 157 kidneys in 5 groups studied for a period from one to 24 hours after inoculation. In 40 of the 46 kidneys, inflammatory lesions were confined to the renal fornix mucosa, and bacteria adhered to the superficial mucous epithelial cells with their pili, particularly to the cells bearing increased microplicae or microvilli.
3. Even in the case of slight pyelonephritis, the exfoliative epithelial cells incorporating the bacteria, fibrin precipitates from the inflammatory region and polymorphonuclear leukocytes phagocytizing bacteria were observed in the pelvic cavity.
4. The slight pyelonephritis progressed into the renal parenchyma 8 hours after inoculation, and the pelvic mucosa demonstrated a considerable multilayering indicating a reparative process 3 days after inoculation.
The results obtained indicate that the renal fornix mucosa can be considered as a preferential site for bacterial adhesion and penetration. For the development of this entity, an adhesion capacity of the bacterial pili to the superficial cells showing surface structual changes mentioned above was also thought to be an important pathogenic factor. In addition, the desquamation of the cells incorporating the bacteria was assumed to play an important role as a defense mechanism in the host in the early developing phase of the pyelonephritis in cooperation with the phagocytic action of granulocytes.