title: The effects of two retinoids on limb regeneration in Pleurodeles waltl and Triturus vulgaris.
abstract: The effects of two vitamin A analogues, retinol palmitate and retinoic acid, on pattern formation during limb regeneration in larvae of two European newts, P. waltl and T. vulgaris are described. The response of the regenerating limb to retinoid treatment differed according to the larval stage of development for P. waltl. Young larval limbs, which were anterior limb buds at the time of amputation, duplicated transversely while limbs of older larvae duplicated proximodistally. Proximodistal duplications were usually limited to the production of supernumerary carpals or a second zeugopod. Complete limbs regenerating from a distal amputation plane were rarely seen. T. vulgaris larvae regenerated limbs with either one or the other type of duplication, but never both on the same limb, at all larval stages tested. When larval P. waltl were kept in normal laboratory light during the treatment with retinol palmitate suspended in the rearing water the percentage of limbs which duplicated was very small for young larvae and increased with the age of the larvae used. Keeping the animals in the dark during the treatment period greatly increased the percentage of duplicate limbs obtained on the young larvae but not on the older larvae. This result is discussed in terms of the photodegradation of the retinoid and the length of the sensitive period for the regenerating limb. A dose-response relationship between the dose of retinol palmitate and either the percentage of limbs duplicated or the degree of duplication was not found. Such a relationship, however, was observed when retinoic acid was injected intraperitoneally into stage-54+ P. waltl larvae. Additionally, this technique revealed a peak of sensitivity to retinoic acid on the 6th day after amputation. Limb regeneration in older larvae was temporarily blocked by retinoid treatment. The limbs showed little or no regression and began blastemal development shortly after the treatment ended. Limbs of young larvae, however, often regressed. Such regressions were followed by blastemal formation and middle- to late-bud blastemas were found at the end of 11 or 14 days treatments with retinol palmitate.
mesh_terms: D000818:Animals; D004224:Diterpenes; D004305:Dose-Response Relationship, Drug; D005121:Extremities / Q000502:physiology*; D007814:Larva; D008027:Light; D010999:Pleurodeles; D012038:Regeneration / Q000187:drug effects*; D012176:Retinoids / Q000494:pharmacology*; D000084562:Retinyl Esters; D014212:Tretinoin / Q000494:pharmacology; D014319:Triturus; D014801:Vitamin A / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D004224:Diterpenes; D012176:Retinoids; D000084562:Retinyl Esters; D014801:Vitamin A; C014794:retinol palmitate; D014212:Tretinoin