Sendai virus infected a hysterectomy derived, barrier maintained breeding colony and a conventional aging rat colony. The virus produced seroconversion in the colonies followed by a 7-month period of decreasing titers. Clinical signs were absent during the months when titers were highest, and there was no increase in mortality, but multifocal interstitial pneumonia with perivascular and peribronchial cuffing by lymphocytes and plasma cells was present in rat lungs examined histologically. Such lesions were absent before the period of seroconversion. During the months of declining titers, the interstitial and perivascular lesions decreased in frequency and severity. The peribronchial lesions did not decrease, however, and were still present in many rats 7 months after the acute infection. Attempts to isolate the virus from weanling rats were unsuccessful.

Cells from seven different rat tumours and a mouse sarcoma have been transplanted in syngeneic animals and were cultured in vitro. Tumours produced by inoculation of cultured cells in animals have been compared with the primary tumours. For the transplanted tumours, volume doubling times, Td, have been compared with doubling times, Td(cult), of cell numbers in cultures. Volume doubling times of the transplanted tumours generally decrease with increasing volume. At volumes of about 0.5 cm3, Td values range from 2.2 days to 10 days, while Td(cult) values ranged from 11 to 24 hr. A systematic correlation between Td and Td(cult) could not be established. During sequential transplantation of the tumours for many generations, as well as during continuous propagation of derived cell cultures, significant changes occurred which resulted in a decrease in the expression of differentiation characteristics in tumours.

On the basis of our study of 12 cases of granular cell tumors in the brains of rats of different inbred strains, it seems that granular cell tumors are not rate in the central nervous system of untreated, aging BN/Bi rats. In none were metastases found. Awareness of the occurrence of these tumors in the central nervous system of these rats may stimulate further studies into the cellular origin of granular cell tumors that form in the central nervous system of the rat and might help to elucidate the origin of these tumors in general.

Kidney transplantations were carried out according to the microvascular technique. These syngeneic orthotopic kidney transplantations from donors of different ages shortened the life-span of young recipients. The result was that only a few so-called “superannuated” kidneys were observed. An explanation for this phenomenon is that almost all animals died with severe hydronephrosis. The kidney function, which was assessed by periodic determinations of blood urea, urine osmolality, and 24-hour urine production, was better in control animals than in unilateral nephrectomized rats. The latter showed a better function than did the recipients of donor kidneys. Moreover, the older the donor kidney, the less was the observed function. There was a large change immediately after transplantation in all functions studied. These stabilized within 6 weeks after transplantation. A significant decrease in urine osmolality and hematocrit with age was found in all groups, whereas blood urea and 24-hour urine production remained constant during the life-span of the rat.

An awareness of spontaneous lesions occurring in an experimental animal is essential in evaluating long-term experiments in that animal. This is especially crucial in gerontological studies. With this in mind rats from several strains at our institute have been set aside specifically to determine incidences of various lesions occurring during aging. The feamle WAG/Rij (Wistar derived) rat was the first animal to be investigated. The rats were allowed to complete their life-span, and 290 female WAG/Rij rats had an average life-span of 31 mo. (range 11-43). In these animals, a total of 519 tumors was seen histologically, almost 80% of which involved the endocrine glands. The most common tumor, adenoma of the pituitary, was found in 69% of all females. Two unusual tumors were a mesothelioma of the pleura occurring in a 39-mo.-old rat and an ameloblastic fibro-odontoma in the jaw of a 28-mo.-old rat. Tumors, and not degenerative or infectious lesions, were the main reason for the rat coming to necropsy.