Local metamorphic action of thyroxine analogues in Rana pipiens larvae,

Abstract

To determine whether or not various thyroxine analogues accelerate metamorphosis by acting directly upon target organs, analogue-cholesterol pellets were prepared and implanted into the dorsal tail fins of Rana pipiens larvae. Many analogue implants caused localized fin resorption, a response attributed to the direct action of the analogue upon the fin. Analogues with acetic or propionic acid side chains or with an isopropyl group but no iodine atoms in the j 3 ring were effective in lower concentrations than was thyroxine; on this basis, the most active compounds were triiodothyropropionic acid and isopropyldiiodothyronine. Fin resorption was not induced by implants of diiodophenoxyacetic acids or of dihalogenated methoxythyranilines. Yet, intraorbital implants of these compounds did stimulate glandular development in the skin dorsal to the eye ( a region with a lower threshold of response to thyroxine than the tail fin). The causation of local metamorphic responses, either in the tail fin or in the orbital region, by various thyroxine analogues indicates the direct action of such compounds upon peripheral tissues of the tadpole.

Reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles

“…My results do not rule out a role for higher or lower thyroxine concentrations in inducing carnivore development, but thyroxine's effects on developing tadpoles have been investigated for approximately 90 years, and the results consistently indicate that it stimulates early metamorphosis and slows or stops growth in tadpoles of a variety of species (Frieden 1961;Kollros 1961;Kaltenbach 1970;Das et al 2002), regardless of the level of environmental stress or initial growth history (Beachy 2001). It has never been observed to produce the faster growth and larger size observed in field-collected carnivores.…”

“…Clearly, the huge dose of exogenous thyroxine used here elicited the typical anuran response to such conditionsimmediate termination of somatic growth and premature, uncoordinated metamorphosis (Kollros 1961;Frieden and Just 1970;Kaltenbach 1970;Beachy 2001;Das et al 2002) and not carnivore development. In addition, feeding on conspecifics did not induce the carnivorous phenotype.…”

“…Tadpoles reared in the laboratory, and those collected from the field, differed in their exposure to many environmental factors known to affect developmental rate, such as temperature, food type, food quantity, and larval density (Semlitsch and Caldwell 1982;Steinwascher and Travis 1983;Travis and Trexler 1986;Newman 1987Newman , 1994Newman , 1998Harkey and Semlitsch 1988;Blouin and Brown 2000) and, in addition, exposure to thyroxine is known to increase developmental rate (Kollros 1961;Frieden and Just 1970;Kaltenbach 1970;Beachy 2001;Das et al 2002). Therefore, for developmental trajectory analyses of OH and SVL, I standardized development of laboratory-reared and field-collected tadpoles by Gosner developmental stage rather than by time, and tadpole age was not recorded for field-collected tadpoles.…”

“…First, experimental studies using exogenous thyroxine have universally shown that it causes somatic growth to slow or stop and induces premature metamorphosis (Kollros 1961;Frieden and Just 1970;Kaltenbach 1970;Beachy 2001;Das et al 2002). Field-collected carnivores show faster somatic growth and larger size than omnivores (Pomeroy 1981;Pfennig 1992a;Fig.…”

Phenylalanyl-tRNA synthetases of rat liver: differential effects of thyroid hormone

“…3,5-Diiodothyronine, which also inhibits C¡, is formed in liver homogenates by deiodination of triiodothyronine (Plaskett, 1961), and has been suggested as a possible intermediate in the action of thyroid hormone (Barker, 1964). Related compounds (e.g., diiodothyroacetic acid) are hormonally active in certain systems (Kaltenbach, 1970). Similarity in structure to the amino acid substrate of the inhibited enzymes (Table I) suggests a binding site at the amino acid binding site.…”