Methods
The study protocol was approved by the local Animals Ethics Committee.
Twenty-eight female Sprague-Dawley rats (one-month-old, mean weight 55g,
weight range: 3-85g) were divided into four equal groups to carry out
statistical analyses in a 95% confidence interval and at a sample power
of 0.9. The subjects were kept at standart fabricated cages of 40x25x25
cm in size with a stainless steel roof, plastic walls, and a plastic
floor covered with wood shavings. The cages were exposed to 12 hours
light and 12 hours dark cycles in a day. All procedures were carried out
in compliance with the guidelines for the care and use of laboratory
animals in the Declaration of Helsinki. The groups in the experiment and
the diets given to the subjects in each groups are listed below:
Group 1 (n=7): Standard pellet rat food (8g/day)
Group 2 (n=7): Soy-free formula (8g/day, Hipp®)
Group-3 (n=7): Low-dose (1.12g/100ml) soy-containing formula (8 g/day,
Similac®)
Group 4 (n=7): High-dose (2.64g/100ml) soy-containing formula (8g/day,
Modilac®).
Before starting the feeding regimens, blood samples were collected from
the tail veins of the rats on day 0 and days 30, 60, and 90 to evaluate
the levels of free T3, free T4, thyroid stimulating hormone (TSH) ,
antithyroglobulin antibody (Anti TG), and anti-troponin antibody (Anti
TPO). All subjects were weighed weekly and the measured body weights
were recorded. All subjects were sacrificed by cervical dislocation on
the 90th day of the experiment. After making an anterior longitudinal
incision in the necks of the rats; their thyroid glands were totally
excised, placed in containers containing formaldehyde, and submitted to
the pathology laboratory for the histopathological examination. The
tissue sections obtained from the thyroid glands of the rats were
stained with hematoxylin and eosin. A pathologist blinded to the
experimental groups examined the specimens and scored the
histopathological findings according to the histopathological fibrosis
scoring system (Table 1).