Functional and hormonal control of pelvic width in the rat

Abstract

Absolute sacral dimensions of the rat are influenced by muscular, ovarian and testicular action, and all affect absolute sacral length more than absolute width. However, relative to trunk-length dimensions are rather stable and drop with a higher level of significance only in castration combined with estrogen or progesterone treatment. Relative pelvic width, as expressed by the transverse interiliac distance, is greatly widened in extreme muscular hypofunction but the sacrum does not participate in this widening. The widening results from a broadening of the proximal part of the ilium, following a genral response of long bones to extreme muscular hypofunction. Pelvic width is reduced in castration and ovariectomy with and without testosterone or estrogen treatment, but not in the combination of castration with progesterone treatment. Changes of sacral width are, however, more often independent from than concomitant with the width changes of the pelvis. The transverse interventral spine distance is dependent on rectus femoris muscle activity and drops drastically in hind-leg removal. It also drops in castration and particularly when castration is combined with estrogen treatment; but progesterone adds little to the effect of castration alone. The effect of ovariectomy alone or combined with testosterone treatment is negligible.