The Himalayan rabbit (Oryctolagus cuniculus L.): spontaneous incidences of endpoints from prenatal developmental toxicity studies.

The historical database represents the spontaneous, i.e. normal changes of characters, in laboratory animals, and is a must for the assessment of toxic effects of compounds. For the Himalayan rabbit (CHBB:HM, SPF) background data were collected from the control groups of regulatory studies between 1968-1999 in the Biberach laboratory of Boehringer Ingelheim (Germany). In the present study these data were compared with the background data from the years 1974-1984, with those from the Ingelheim laboratory, Germany (1977-1984) and those from the breeding colony at Kawanishi, Japan (1971-1991, 1972-1984). Fertility in the Biberach laboratory was relatively constant through the years, due to the strict breeding system. Litter parameters (corpora lutea, implantations and viable fetuses), including fetal sex distribution and fetal weight, were constant in the Biberach laboratory through the years and compared well with the data from Ingelheim and Kawanishi. From these three laboratories the results of spontaneous changes in fetal morphology above 0.1% incidence suggest a pattern of deviations from the Bauplan (fundamental body plan). These comprise synosteosis of sternebrae, lumbar (additional) ribs, hypoplasia of 12th rib, status of ossification, aplasia of gall bladder, hypoplasia of gall bladder, incompletely subdivided lung, dilated ventricle of heart, deviations at the A. carotis and at the aortic arch and flexure of paw. The absence of a time-dependent statistical trend indicates that the spontaneous change of endpoints remained constant through the time axis. Comparison with the spontaneously changed fetal morphology of the other strains (NZW, JW, SF rabbits) does not provide support for their being a totally strain-specific pattern, and this pattern may be closer to the species than specific to a single strain. The firm patterns of deviations in fetal morphology provide suitable and valuable markers for assessing toxic effects on ontogenesis. According to our experience these morphological endpoints react very sensitively to teratogenic compounds, which is demonstrated by increased incidences. Our knowledge of evolution of organisms and of mechanisms leading to morphological deviations points to a strict selection of phenotypes. For laboratory animals the decisive selection factors are defined by man. These are nutritive factors, environmental conditions, the mating system, handling and treatment, and experimental design. All these factors have to be held constant through the years, which is an absolute pre-condition for the application of valid historical data. The Himalayan rabbit is highly suitable for use in developmental toxicity studies due to the stability of reproductive data within the same laboratory over a period of more than 30 years, due to the similarity of reproductive data among three different laboratories, and due to an absence of relevant differences to the reproductive data of other rabbit strains.