Sexual skin in rodents: an across body region, gender, and species analysis.

The effect of estrogen on the thickness of skin layers were examined in male and female mice and in female rats. Skin samples were taken from prepubertally castrated subjects given either 17 beta-estradiol or control implants. In agreement with an earlier report, the subcutaneous areolar tissue (SAT) of the lower back was nearly six times thicker, on average, in female mice with estradiol implants than in controls. Estrogen did not effect the thickness of the epidermis or dermis but preferentially increased the thickness of the deepest layer of the SAT. Analysis of skin samples from different body regions revealed that this response to estrogen was limited to the skin of the dorsum and was greatest in the area of the lower back. Castrated male mice with estradiol implants had markedly thicker SAT layers in the lower back region than controls. However, the magnitude of the response was less than that seen in estrogen-treated females. In contrast, the SAT in the lower back regions of castrated female rats with estrogen implants was not significantly different from controls, despite a pronounced uterine response to the hormone treatment. Thus, mice exhibit a species-specific, localized hypertrophy of one of the skin layers in response to estradiol. Mouse mating behavior involves the vigorous grasping and biting of the lower back region of the female. We suggest that at least one function of this estrogen-dependent hypertrophy is to protect the female from injury during mating.