1212 



HORMONAL REGULATION 



rabbits thyroidectomized by Krichesky 

 (1939) mated, but the oxygen consumption 

 of those that did varied from 14 to 38 per 

 cent l)elow average. 



Results from the only experiments in 

 which the measurement of sexual behavior 

 was attempted are consistent with the hy- 

 pothesis that marked deviations from the 

 normal level of thyroid activity are not in- 

 compatible with the capacity for mating. In 

 a study in which the male guinea pig was 

 used (Young, Rayner, Peterson and Brown, 

 1952; Young and Peterson, 1952) it was 

 found that, within the limits of an extreme 

 hyperthyroidism and an extreme hypothy- 

 roidism, as estimated from measurements of 

 oxygen consumption, heart rate, and the 

 concentration of serum protein-bound io- 

 dine, the change in sexual behavior was not 

 greater than in the controls. It was also 

 shown that thyroid activity in groups of un- 

 treated high score and low score males was 

 not different, thus eliminating the possibility 

 that a deficiency of thyroid function could 

 have accounted for the differences. In thy- 

 roid-parathyroidectomized male rats mating 

 performance within 30 days after the opera- 

 tion was not significantly different from that 

 in the preoperative tests (Heidenreich, Alex- 

 ander and Beach, 1953). Transitory de- 

 creases in sexual behavior followed the ad- 

 ministration of thyroxine and benzylthi- 

 ouracil to male rats (Soulairac, Desclaux 

 and Coppin, 1950), but by the 6th day the 

 activity of the animals receiving thyroxine 

 was again normal and by the 14th day nor- 

 mal or nearly normal activity was being dis- 

 played by those receiving the goitrogen. The 

 circumstance that the changes following the 

 establishment of opposite states were so 

 nearly parallel made interpretation difficult. 



A study of the female guinea pig in which 

 measurements of sexual behavior were made 

 revealed that the percentage of surgically 

 thyroidectomized animals showing heat re- 

 sponses w^as 57.8 compared with 84.6 in 

 the controls, 89.7 in females fed propylthi- 

 ouracil in the drinking water, and 94.7 in 

 animals injected with thyroxine (Peterson, 

 Webster, Rayner and Young, 1952). The 

 sensitivity of propylthiouracil-fed ovari- 

 ectomized individuals to estrogen and pro- 

 gesterone was not different from that of the 

 controls, but later tests of females thyroid- 



ectomized and given P'^^, ovariectomized, 

 and injected with estradiol and progesterone 

 revealed that fewer animals came into heat 

 and that heat was shorter than in the con- 

 trols (Hoar, Goy and Young, 1957). The re- 

 duced number of corpora lutea was sug- 

 gestive of a hypo-ovarian condition; prob- 

 ably therefore the effect was general rather 

 than confined to the neural tissues mediat- 

 ing mating behavior, but a lowered respon- 

 siveness of the experimental females to es- 

 tradiol was also shown. 



These data from the male and female 

 guinea pig and from the male rat do not 

 necessarily contradict the claims based on 

 studies of other species such as the bull 

 (Peterson, Spielman, Pomeroy and Boyd, 

 1941) that sexual behavior is inhibited 

 in hypothyroid individuals. It is thought 

 rather that the relationship between the 

 tliyroid and reproduction varies from species 

 to species and from individual to indi- 

 vidual (Young and Peterson, 1952) : 



"There may be species or individuals in 

 whicli the range of thyroid activity com- 

 l)atiljle with reproduction extends from a 

 relatively high degree of hyperthyroidism to 

 a relatively low degree of hypothyroidism. 

 The male guinea pig would seem to fall in 

 this category. There may be other species 

 in which the limits compatible with repro- 

 duction are narrower and they may lie in 

 the middle of what we refer to as the spec- 

 trum of the thyroid activity, or they may lie 

 toward either end. Reproduction in a species 

 or individual dependent on a high level of 

 thyroid activity might be adversely af- 

 fected by a change toward hypothyroidism, 

 whereas the converse might be true for a 

 species or individual normally functioning 

 at a relatively low level." 



The nature of any stimulating or support- 

 ing action of the thyroid on mating behavior 

 is unknown. When the male guinea pig was 

 being studied the rate of oxygen consump- 

 tion was increased from 52.4 to 80.1 cc. per 

 100 gm. body weight per hour by the in- 

 jection of thyroxine without increasing the 

 average strength of sexual behavior (Young, 

 Rajmer, Peterson and Brown, 1952), and 

 depressed to 37.3 cc. by thyroidectomy and 

 injections of I^^^ without decreasing the 

 average score significantly (Young and 

 Peterson, 1952). In another experiment 



