Studies on the Nature of the Thyroidpituitary Interrelationship12

The effect of 2,4‐dinitrophenol on the tissue concentration of iodine‐containing compounds in isotopically equilibrated intact rats

“…1 show typical examples of both types of response. This difference in response to the administration of DNP from one experimental group to another was most unsatisfactory; similar variability in the response to DNP of other parameters had also been observed by others (Goldberg & Chaikoff, 1951;Goldberg et al 1957). It did not appear to depend on the sex of the animals used.…”

“…(b) As is shown here, the concentration of iodine-containing compounds in peripheral tissues, pituitary included, remains within normal limits; the over-all peripheral deiodination of L-thyroxine is also unaltered or somewhat increased (Escobar del Rey & Morreale de Escobar, 1958a, b). (c) It has been repeatedly shown (Wolff et al 1950;Goldberg & Chaikoff, 1951;Goldberg et al 1955Goldberg et al , 1957Escobar del Rey & Morreale de Escobar, 1958a, b), and is confirmed here, that there is a very sharp and rapid decrease of the plasma PBI. (d) DNP alters both in vivo and in vitro the distribution of thyroid hormone between plasma and tissues in favour of the latter; data reported elsewhere (Morreale de Escobar & Escobar del Rey, 1961) support the conclusion that this effect of DNP is mainly exerted by a direct action on the cells.…”

“…The situation during DNP administration in the rat may be summarized as follows: (a) There is no increase in the TSH-secreting activity of the pituitary (Goldberg & Chaikoff, 1951;Goldberg et al 1955Goldberg et al , 1957. (b) As is shown here, the concentration of iodine-containing compounds in peripheral tissues, pituitary included, remains within normal limits; the over-all peripheral deiodination of L-thyroxine is also unaltered or somewhat increased (Escobar del Rey & Morreale de Escobar, 1958a, b).…”

“…3 and 4). Moreover, we think that changes in dose level, mode and frequency of administration of DNP might lead to quantitatively different pattems of distribution of iodinated compounds in plasma and tissues; this is a possible explanation for many of the differences in the response to DNP described by others (Goldberg & Chaikoff, 1951;Goldberg et al 1957). Total perfusion of the animals to eliminate plasma from the tissues is also a necessity if data on the iodine content of the latter are sought.…”

“…These findings are usually considered to be due to 'disruption' of the classical thyroid-pituitary feed-back mechanism. Goldberg et al (1957) showed that the pituitaries of DNP-treated animals had not lost the ability of reacting to other stimuli, and concluded from their results that the data 'were not consistent with the simple classical feed-back theory of thyroid-pituitary interrelationships. It is likely that the pituitary cells secreting TSH are influenced not only by the actual circulating level of thyroid hormone(s) but by one or more of its peripheral actions'.…”