Responsiveness of mouse parametrial fat to relaxin

The effects of relaxin on the hypertrophy of the parametrial fat cells in ovariectomized virgin mice have been studied histologically and morphometrically. This hormone has been previously demonstrated by us to induce hypertrophy also in the adipose cells of the mouse mammary gland. This effect produced by relaxin on mammary adipocytes was greater than that due to estrogen alone and independent of pretreatment with estrogen. When insulin was given after estrogen in place of relaxin the effect was nearly the same as that following relaxin alone. On the contrary, in parametrial adipocytes under the same hormonal conditions, we found an increase in the mean diameter of 28% following estrogen alone, 57% following relaxin alone, 80% when relaxin was given after pretreatment with estrogen, and 60% when insulin was given after pretreatment with estrogen at the same dose as relaxin. These results clearly reveal that relaxin is a very active hormone in promoting lipid deposition in the parametrial adipose cells, and that such an effect attains a maximum following a pretreatment with estrogen. Moreover, these findings indicate that the parametrial fat cells can be included in the list of the targets of relaxin.