238 /. J. Christian 



Gordon, 1955), although others report adrenal atrophy following blockade 

 of the thyroid with antithyroid compounds (Seifter et al., 1949). Finally, 

 thyroxine augments the adrenal hypertrophy produced by growth hor- 

 mone, although it does not augment the adrenal hypertrophy produced 

 by ACTH (Bois and Selye, 1957). 



There are many other factors which affect thyroid function. A high 

 dietary salt intake can increase thyroid activity, even with a reduced iodine 

 intake, in a rather circuitous way (Isler et al., 1958). The mechanism ap- 

 pears to be that with increased NaCl intake, and consequently an increase 

 in the excretion of NaCl, there is apparently an increase in the excretion of 

 iodine with the sodium chloride. The loss of iodine produces a low serum 

 concentration of iodine and secondarily a low output of thyroxine. The low 

 thyroxine in turn stimulates increased secretion of TSH from the pituitary 

 and a resulting stimulation of the thyroid gland. 



5. Thyroidal-Gonadal Ixterrelatioxships 



In addition to its more or less reciprocal relationship with the adrenal 

 cortex, the thyroid, and therefore thyroidal adaptive responses, has im- 

 portant effects on reproduction and the reproductive organs. These effects 

 are of particular interest here, because they may occur in response to 

 alarming stimuli and must be evaluated as possible factors producing the 

 changes in reproductive function seen in mammals, especially in relation 

 to the density of the population. A thyroidal-gonadal relationship is indi- 

 cated by the tendency for goiters to occur at puberty, during pregnane}^, 

 or during estrus; also the serum protein-bound iodine is elevated during 

 pregnancy, and stilbesterol increases the release of iodine by the thyroids 

 of rats and mice (Sollman, 1957) . There is considerable evidence indicating 

 that hypothyroidism is associated with abnormal ovarian function in 

 humans (Rawson et al., 1955). Cold exposure causes a marked increase in 

 the length of the estrous cycle in rats which is prevented by administering 

 thyroxine (Dempsey and Uotila, 1940; Denison and Zarrow, 1955) . Thyrox- 

 ine also augments the recover}^ of function of the testes of immature rats 

 from the atrophic effects of starvation (Horn, 1955) . The recovery of the 

 testes in this case is not related to the recovery in body weight, and the 

 recovery of the sex accessories following treatment with thyroxine was only 

 partial and required a greater period of time. jMaqsood and Reineke (1950) 

 found that high temperatures (30° C.) decreased the weights of the testes 

 and seminal vesicles of mice, but the administration of thyroprotein in- 

 creased the weights of these organs at that temperature. Alild hj^perthy- 

 roidism stimulated, and hypothyroidism inhibited, sexual development in 

 growing male mice (Maqsood and Reineke, 1950). Higher doses of thyroid 



