Effects of progesterone on the metabolism of cancellous bone in young oophorectomized rats

The effect of menopause on the skin and other connective tissues

Cutaneous ageing manifests itself as a progressive reduction in function and reserve capacity of skin tissue. Collagen atrophy is a major factor in skin ageing. There is a strong correlation between skin collagen loss and oestrogen deficiency due to the menopause. Skin ageing is associated with a progressive increase in extensibility and a reduction in elasticity. With increasing age, the skin also becomes more fragile and susceptible to trauma, leading to more lacerations and bruising. Furthermore, wound healing is impaired in older women. Oestrogen use after the menopause increases collagen content, dermal thickness and elasticity, and it decreases the likelihood of senile dry skin. Large-scale clinical trials are necessary to help make informed recommendations regarding postmenopausal oestrogen use and its role in the prevention of skin ageing. Oestrogen has profound effects on connective tissue turnover, no matter the site. It has been shown that menopause has similar effects on the connective tissue of the carotid artery media, intervertebral discs and bones.

Bone growth and turnover in progesterone receptor knockout mice

The role of progesterone receptor (PR) signaling in skeletal metabolism is controversial. To address whether signaling through the PR is necessary for normal bone growth and turnover, we performed histomorphometric and microcomputed tomography analyses of bone from homozygous female PR knockout (PRKO) mice at 6, 12, and 26 wk of age. These mice possess a null mutation of the PR locus, which blocks the gene expression of A and B isoforms of PR. Body weight gain, uterine weight gain, and tibia longitudinal bone growth were normal in PRKO mice. In contrast, total, cancellous, and cortical bone mass were increased in the humerus of 12-wk-old PRKO mice, whereas cortical and cancellous bone mass in the tibia was normal. At 26 wk of age, cancellous bone area in the proximal tibia metaphysis of PRKO mice was 153% greater than age matched wild-type mice. The improved cancellous bone balance in 6-month-old PRKO mice was associated with elevated bone formation and a tendency toward reduced osteoclast perimeter. Taken together, these findings suggest that PR signaling in mice is not essential for bone growth and turnover. However, at some skeletal sites, PR signaling attenuates the accumulation of cortical and cancellous bone mass during adolescence.

Effects of progesterone on serum levels of IGF-1 and on femur IGF-1 mRNA in ovariectomized rats

Local and systemic insulin-like growth factors (IGFs) may be involved in the regulation of bone formation by sex hormones. The present studies describe the in vivo effects of estradiol, progesterone, or both on IGF-1 mRNA abundance in bone, serum IGF-1 levels, and bone formation. Rats were sham-operated (SHAM) or ovariectomized (OVX) at 12 weeks of age and used a week later in three experiments. First, OVX rats were treated with vehicle, estradiol, and/or medroxyprogesterone (MPA) for 3 weeks, and bone formation was assessed in the tibial metaphysis. Second, OVX rats were treated in the same manner and serum IGF-1 levels measured. Third, OVX rats were treated with an injection of vehicle, estradiol, and/or progesterone, and 24 h later, levels of IGF-1 mRNA in the femur were analyzed. The mineralized surface, mineral opposition rate, and bone formation rate (BFR) were higher in OVX than in SHAM rats. The BFR was decreased in estrogen-treated but increased in MPA-treated rats compared with vehicle-treated OVX rats. Circulating levels of IGF-1 were higher in OVX than in SHAM rats but were not affected by sex hormones in a 3-week experiment, whereas these levels were not different among groups in a 24-h experiment. Northern analysis detected 7.5 and 0.8 kb IGF-1 mRNA transcripts. The abundance of IGF-1 mRNA was higher in OVX than in SHAM rats. IGF-1 transcripts 7.5 and 0.8 kb were decreased by 72 and 29%, respectively, in estrogen-treated and increased by 44 and 43%, respectively, in progesterone-treated rats compared with vehicle-treated OVX rats. We conclude that in the short term, estrogen lowers and progesterone raises bone IGF-1 mRNA and these changes are followed by coordinated changes in bone formation rate.