A study was conducted on Dutch rabbits to examine their applicability for the pyrogen test in comparison with the Japanese white rabbit which, conventionally, has been mainly used for the test in Japan. The following results were obtained. Adult Dutch rabbits, so small as to weigh only about 60 % of average adult weight of the Japanese white, showed a food consumption as low as 40 of that in the latter. None in the Dutch rabbit group suffered dislocation of the hip-joint during restraint on a neck stock while it was frequently encountered among Japanese white rabbits. The body temperature during restraint was unstable in infantile Dutch rabbits (7-8 weeks old), but stable in the young (14 weeks old) and in the adult (20-47 weeks old) . Adult Dutch rabbits exhibited greater febrile responses to intravenously injected bacterial pyrogen (LPS) than infantile and young Dutch rabbits and adult Japanese white rabbits. A good linear regression was observed between the dose of LPS (0.01-0.1μg/kg, iv) and the febrile response in adult Dutch rabbits as well as in adult Japanese white rabbits.
From these data, it is concluded that the Dutch rabbit has an advantage over the Japanese white for the pyrogen test in respect of febrile responsiveness and cost of rearing.

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Pathological examination was carried out on 16 male Sprague-Dawley rats received single i. v. injection of 60 mg/kg of streptozotocin (SZ) at 5 weeks of age and maintained for 22 months. Insulinoma (63%), renal adenoma (50%), hepatocellular tumor (69 %), cholangioma (31%) and Leydig cell tumor (56%) were found in a high incidence, and therefore occurrence of these tumors was considered to be attributable to the treatment with SZ. In addition to these tumors, though in a low incidence, various such tumors as leukemia, reticulum cell sarcoma, mammary tumor and glioma were also found.

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A testicular hypoplastic (T-H) rat strain, originating from the WistarImamichi rat colony at the Institute for Animal Reproduction, has been maintained by full-sib matings since 1974 for eight filial generations. There were no abnormal signs in external features and growth patterns of the T-H strain. Testicular hypoplasia was detectable at about 8 weeks of age by palpation around the scrotum. Unilateral or bilateral testicular abnormalities were detected in 80 out of 391 males of this strain. The incidences were 32.5% for right side, 48.8% for left and 18.8% for both respectively. Reproductive performance of unilateral T-H males were not different from that of normal. While bilateral ones showed normal sexual behavior, they failed to produce their progenies. In adult T-H rats testicular weight was approximately two-fifth of the normal, and the accessory organs such as the seminal vesicules, epididymis and etc., especially located in the same side of the testicular hypoplasia, reduced their size and weight. Occasionally was seen lack or denaturation of the deferent duct or epididymis. At adult age, no spermatogenesis was observed in all hypoplastic testes with a few exception, and normal spermatogenesis in the testis of the normal side of unilateral T-H male.

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Atresia or stricture of the orifice of vagina was detected in 100% of female Sprague-Dawley rats injected subcutaneously within 24 hours after birth with testosterone propionate (1mg), 5α-dihydrotestosterone (lmg) or 5α-androstane-3α, 17β-diol (lmg) but was not found in any neonatally intact female rats. On the contrary, a single injection of estra-1, 3, 5 (10) -triene-3, 17jS-diol (10μg) in female rats had no effects. When 5α-dihydrotestosterone (1mg) was given into female rats at 0, 1, 2, 3 or 5 days of age, the incidences of the atresia were 85.7%, 63.6 %, 25.0%, 0% and 0%, respectively.

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The AJR (alb/alb, j/j) strain is semi-lethal and the rats die at about two weeks of age. Cross breeding with a pair of ACJ (alb/alb, j/+) is required for maintenance and production. We studied the treatment of AJRs for improvement of the breeding system. AJRs with jaundice on the skin at about 7 days of age were intraperitoneally administered 1 ml/rat of normal rat serum every few days and irradiated with visible light for 14 hours a day in an irradiation box. This treatment allowed us to obtain mature AJRs. The treatment was effective when applied for short periods of 1-4 weeks of age. The frequency of maturation of the treated AJRs was about 27% and the best mating combination was a female ACJ and male AJR. The treatment of AJRs, made the progeny test for the selection of ACJs for breeding pairs of ACJXACR unnecessary and increased the frequency of appearance of AJRs to 50%.

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