Endocrine Abstracts

The aim of the study was to evaluate the influence of high levels of thyroid hormones on bone mineral density in male rats as a function of experimental hyperthyroidism duration and age.

Research object: Research is conducted on 56 white male rats of ‘Wistar’ breed. There were three age-dependent groups (1.5 month rats are pre-pubertal, 5–6 month are reproductive animals and 24 month – old). Animals were subdivided into 6 groups: group 1 – 10 pre-pubertal male rats (mass – 0.105±0.01 kg) made up a control group; group 2 – 10 pre-pubertal rats of experimental group (mass – 0.094±0.006 kg) getting L-thyroxin injection in a dose of 25 μg/100 g of body weight/day i.m., during 15 or 30 days;. group 3 – 10 reproductive males of control group (mass – 0.18±0.005 kg); group 4 – 8 reproductive males (mass – 0.20±0.007 kg) getting L-thyroxine; group 5 – 10 old males of control group (mass – 0.317±0.010 kg); group 6 – 8 old males experimental group (mass – 0.300±0.011 kg) getting L-thyroxine.

Research methods: Bone mineral density (BMD) was measured using dual energy X-ray densitometry (DEXA) and ‘Experimental animals’ software. Examination was made before and over 15 and 30 days after start of experiment. Increase of percentage of bone mineral density at various skeletal sites was determined. The index was calculated according to the formula:

ΔBMD (%)=(ΔBMD/BMD ref.)×100.

BMD ref. – initial indexes of bone mineral density of the entire body.

Research results: Comparative dynamics indexes of bone mineral density in male rats of control group and of experimental group: group 1 (BMD₀=0.081±0.002 g/cm², ΔBMD₁₅=11.05±0.83%, ΔBMD₃₀=24.89±2.41%), group 2 (BMD₀ =0.084±0.002 g/cm², Student’s t-criterion=−0.036, P_1–2=0.972; ΔBMD₁₅=−2.87±4.97%, Student’s t-criterion=2.76, P_1–2=0.013; ΔBMD₃₀=8.46±3.60%, Student’s t-criterion=4.48, P_1–2<0.0001), group 3 (BMD₀=0.105±0.001 g/cm²; ΔBMD₁₅=1.87±2.208%; ΔBMD₃₀=9.63±0.97%); group 4 (BMD₀=0.121±0.004 g/cm², Student’s t-criterion=4.29, P_3–4<0.0001; ΔBMD₁₅=−12.17±1.75%, Student’s t-criterion=4.79, P_3–4<0.0001; ΔBMD₃₀=−4.89±3.06%, Student’s t-criterion=4.96, P_3–4<0.0001); group 5 (BMD₀=0.123±0.003 g/cm²; ΔBMD₁₅=−2.94±1.99%; ΔBMD₃₀=1.43±1.20%); group 6 (BMD₀=0.143±0.009 g/cm², Student’s t-criterion =−2.30, P_5–6=0.035; ΔBMD₁₅=−15.34±2.97%, Student’s t-criterion =3.58, P_5–6=0.002; ΔBMD₃₀=−9.707±3.66%, Student’s t-criterion =3.16, P_5–6=0.006).

Conclusions: It was revealed that high doses of thyroid hormones would cause the decline of BMD in all age-dependent groups. The maximum loss of BMD occurred among the male rats of reproductive and old age. The development of experimental osteoporosis under the influence of high levels of thyroid hormones may be divided in two phases: the first phase is an acute loss of BMD (15 days), while the second phase is a slower loss of BMD (30 days).