Effect of hypothyroidism and thyroxin replacement on growth of long bones in prenatally treated albino rats.

OBJECTIVE To study the effect of induced hypothyroidism and thyroxin replacement on bone growth. DESIGN An animal study carried out on experimental Albino rats. PLACE AND DURATION OF STUDY The study was carried out in the Department of Anatomy, Basic Medical Sciences Institute (BMSI), Jinnah Postgraduate Medical Centre (JPMC), Karachi, from June 1999 to May 2002. METHOD Pregnant female Albino rats obtained from the animal house of Basic Medical Sciences Institute, JPMC, Karachi were treated with carbimazole and carbimazole plus thyroxin from 10th day of gestation till parturition. Another group of pregnant rats did not receive any treatment and acted as controls. Pups born to the treated as well as control animals were sacrificed on 10th postnatal day and fixed in formal saline. They were then processed through 95% ethanol and acetone, bulk stained with alizarin red and cleared in 4% KOH to reveal their bony and cartilaginous elements. The ulna and tibia of both sides were disarticulated from the treated and control animals and measured for intact bone length and diameter. The measurements of the three groups were then compared statistically. RESULTS The retardation in length observed at the end of experimental period in ulna was by 13.67% and in tibia by 27.84% in carbimazole treated group while in carbimazole plus thyroxin treated group the reduction in length of ulna was 5.08% and of tibia 3.91% when compared with their age matched controls. CONCLUSION Prenatal hypothyroidism has an adverse effect on bone growth and results in reduction of long bone length.