[Age dependent morphokinetics of the thyroid gland. Histochemical, morphometric, light-microscopical and functional...

The aim of the animal experiments was to investigate the question of the age dependence of the morphokinetic reactions of the thyroid gland under standardised conditions. Through the administration of pharmaceutical substances, it was possible to produce defined functional states of the thyroid in the various age groups. Materials and Methods 700 Albino rats of the Chbb: Thom (SPF) strain, age 0 days (newborn) to 110 weeks, were used in the investigations. The animals were divided into 4 groups each with 12 subgroups according to age. One group received 300 mug/kg/day triiodothyronine (T3) for 10 days for the suppression of thyroid gland function, one group received methylthiouracil (MTU) for 10 days to block hormone synthesis, and one group received 10 IU/kg/day thyrotrophic hormone (TSH) for 5 days to stimulate the gland. The control group received distilled water. Investigations carried out: Protein-bound iodine (PBI) and total thyroxine (T4) in the serum; enzyme histochemical demonstration in the thyroid of alkaline phosphatase (a. Ph.), acid phsophatase (s. Ph.), cytochrome oxidase (Cyt. ox.), succinic dehydrogenase (SDH), iso-citric acid dehydrogenase (ICDH), ATP-ase and nonspecific esterase. The height of the follicular epithelium and the nuclear diameters of the follicular epithelial cells were estimated in embedded material. Light-microscopical investigations were performed using Paraplast and Epon embedded material. Staining methods: H. and E., Azan, PAS-alcian blue, Elastica-van Gieson, Perl's method for iron, Gomori's reticulin stain and von Kossa's calcium method (in aged animals). Staining of semithin sections with toluidine blue, Movat's stain and Morgenroth's stain. Biometric analysis of results: Simple and two factor analysis of variance, Scheffé test, graphic demonstration after polynomial fitting of third to fifth degree. Results a. Histochemical findings In the thyroid gland, all the above mentioned enzyme histochemical reactions studied show a mostly distinct age dependent relationship in the intensity of enzyme activity. Age dependent changes in the histo-topochemical behaviour of individual reactions are also demonstrable on light-microscopical examination. In control animals at the time of birth, alkaline phosphatase and cytochrome oxidase react moderately, the others weakly. With hydrolases the activity of alkaline phosphatassr remains at a moderate level throughout the life span, while acid phosphatase and ATP-ase show a marked increase up to puberty, and the reaction is still mnd I.C.D.H. an increase during the growth period, a marked response in middle life, and a lessening of activity in ageing animals can be demonstrated. Cytochrome oxidase increases up to the seventeenth week of life, and then decreases in older animals. The activity of nonspecific esterase increases up to the eleventh week, remains at a high level up to the forty fourth week and then lessen after one year of life...