Endocrine control of postcranial body proportions. An experimental study of allometry.

Abstract

(1) Large amounts of testosterone have a growth-promoting effect on the relative to trunk (tr) length of the cervical section.(2) Castration produces relative lengthening of the thoracic section, i.e. stabilization of that section under conditions of tr depression. A similar stability of the thoracic section occurs in hyperpituitary females, in which that section does not participate in the growth increase of the trunk.(3) The absence of estrogen and the presence of testosterone have a growth-inhibiting effect on the length of the lumbar section, and the presence of estrogen promotes its growth.(4) The role of endocrines on sacral length is not clear.(5) The foot is the most stable part of the entire skeleton followed by the neurocranium, the long bones and the trunk, irrespective of whether growth changes have a nutritional or endocrine etiology. Among the long bones, the sternum, clavicle and tibia resist depressive changes most frequently and sacral width resists them the least.(6) Pelvic length and sacral width manifest allometric resistance to growth depression in the female but not the male rat. This helps maintain the integrity of pelvic space necessary for procreation.(7) Castration has a specific growth-depressing effect on the humerus, femur, pelvic length, sacral width, and interiliac distance. The depressing effect on pelvic space is aggravated by the androgenic function of progesterone and testosterone, but is eliminated by these androgenic hormones in interiliac space.(8) In males, an overdose of estrogen and testosterone has a growth-depressing effect on the tibia. But estrogen restores the growth-depressing effect of castration in the length of the pelvis and the width of the sacrum.(9) Testosterone treatment after ovariectomy has a growth-promoting effect on sacral width, the humerus, femur, tibia, sternum and clavicle.