Protective effects of a combination of estrogen and progestin on ovariectomized rats with osteoporosis

Yuyu LIU; Liao CUI; Tie WU; Bilian XU

ABSTRACT

BACKGROUND:

It has been reported that a combination of estrogen and progestin has a protective synergistic effect on osteoporosis with only little side effects.

OBJECTIVE:

This study was designed to investigate the effect of a combination of norethisterone and ethinyl estradiol (EE) on bone mass in ovariectomized rats.

DESIGN:

This study was a randomized controlled experiment.

SETTING:

It was conducted at the Department of Pharmacology of Guangdong Medical University.MATERIALS Twenty-four specific pathogen free (SPF) unmated SD rats were selected, aging 4 and half months and weighing 230±15 g.

METHODS:

The experiment was conducted in the Department of Pharmacology of Guangdong Medical College from May to November 2002.These rats were randomly divided into 3 groups pseudo-operation group, ovariectomy group and compound norethisterone group, each containing 8 rats. For the former two groups, ethanol solution (volume fraction=0.056), at a dose of 5 mL/(kg.d), was administered by gavage. While for compound norethisterone group, 60μg/(kg·d) norethisterone and 3.5μg/(kg·d) EE were given by gavage (according to the dosage for human, which was 20-35 μg EE combined with norethisterone). Duration of treatment was 90 days for all the animals. Then their tibias were removed. Employing a fullyautomatic imaging analysis system, osteoclasts and the relevant dynamic and static parameters reflecting secondary trabeculaes formation region in proximal tibias were measured. Respectively, the humeral samples were removed and employing the palsma emission spectrograph of full-spectrum direct reading, calcium content and hydroxyproline content in bone samples were measured. Meanwhile, urine calcium and hydroxyproline concentrations were examined as well.MAIN OUTCOME

MEASURES:

①The trabecular area (Th. Ar), trabecular thickness (TbkTh), trabecular number (Tb.N) and trabecular separation (Tb. Sp) and the changes in static parareters of perimeters of osteoclasts were investigated. Variance in percent labeled perimeter (L. Pm ％), mineral apposition rate (MAR) and bone formation rate (BFR/BV) were also calculated. ②Changes in serum alkaline phosphatase (AKP), calcium and hydroxyproline contents in bone and urine were all measured.

RESULTS:

All the 24 rats entered the analysis procedure. Compared to pseudo-operation group, for the ovariectomy group, Tb. Ar and Tb.N decreased, Tb. Sp increased and osteoclast perimeter significantly increased (P＜0.01). Addtionally, the bone formation markers increased apparently with an increase in L. Pm ％ and MAR (P＜0.05) and a significant increase in BFR/BV (P＜0.01). Compared with the ovariectomy group, for the compound norethisterone group,the bone mass and the Tb.N increased, marked by an increase of 82％ in Tb. Ar and an increase of 83％ in Tb.N (P＜0.05), and the Tb.Sp decreased, marked by a decrease of 51％ (P＜0.05). Meanwhile, there was a decrease of 52.5％ in osteoblast perimeter (P＜0.01), an increase in organic bone matrix and a decrease in urine hydroxyproline (P＜0.05).

CONCLUSION:

A combination of estrogen and progestin has a protective synergistic effect on ovariectomized rats with osteoporosis, and it is capable of increasing the organic bone matrix without significant inhibitory effects on bone formation. The experimental dosage of the compound was calculated according to the clinical dosage, 20-35 μg estrogen combined with a progestin, which will yield optimal protective effects on bone sometimes.