Time Required for Low Temperature to Influence Thyroxine Secretion Rate in Fowls

IT HAS been shown that thyroxine secretion rate (TSR) of fowls increases during the winter months (Stahl and Turner, 1961). Under normal decreasing environmental temperature, the transition from summer to winter would be gradual in relation to the secretion rate. The question arises as to the time required for the TSR to become adjusted to sudden low environmental temperature. The answer to this question is of importance in two experimental situations, namely, where the influence of graded temperature adjustments are being studied and where maximum inherited TSR of individual fowls under low environmental temperature is desired. On the basis of the studies of Brown-Grant et al. (1954), Del Conte and Stux (1954), and Bottari (1957), using rabbits and guinea pigs, activation of the pituitary and thyroid gland to sudden low temperature might be expected within a matter of hours. That similar rapid adjustment to sudden low temperatures does not occur…