Relationship Between Female Sex Hormone and Dewlap in the Rabbit

Abstract

Summary and Conclusion

Judging from the evidence at hand we believe that the dewlap is normally a secondary sex character of the adult female rabbit, and that its presence is dependent upon the action of a substance (or substances) related primarily to the ovary. It may develop to a limited degree in the male rabbit in which case it is assumed that the female sex hormone is present in amounts sufficient to initiate and maintain the existence of the dewlap. The following observations support these conclusions: (1) A prominent dewlap was present in about 50% of the normal adult females and in only 7% of the adult males examined. When present in the male animal the fold of skin was usually so small that it could not be seen in profile. (2) The administration of a butyl alcohol extract of the urine of pregnant women induced a pronounced dewlap in all treated male animals. The developmental process was reversible, the fold of skin disappearing when the administration of estrogenic substance was reduced. (3) The dewlap failed to develop in animals ovariectomized before the age of sexual maturity, but did develop in normal female litter-mates with a frequency equal to that observed in the breeding colony. (4) When ovariectomy was performed after the appearance of the dewlap, it gradually underwent almost complete involution.

It is apparent that the female sex hormone did not exert its influence directly upon the skin during the development of the dewlap. In the breeding colony, the animals normally showed no evidence of dewlap before they were 6 months old, the age at which the rabbit reaches adult status. In spite of the daily administration of estrogenic substance even in large amounts, normal immature male and female rabbits did not respond with a dewlap until they had reached the age of 6 months. It would seem, therefore, that the action of the female sex hormone depends upon an intermediary to stimulate the growth of the dewlap, and that this intermediary factor is present only in the adult animal.