Acta Stereologica



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Draga Štiblar-Martinčič

Seasonal variation in the influence of pinealectomy on rat follicular and parafollicular cells

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The aim of this investigation, using systematical stereological analysis, was to test the hypothesis that pinealectomy increases thyroid gland activity and that this effect may vary with the season.

Two identical experiments were carried out, the first in summer and the second in winter. Each experiment was performed on 9 adult male rats of the Wistar strain, 3 of them being pinealectomized (P), 3 sham pinealectomized (SP) and 3 left intact as controls (C). After surgery all 3 groups were exposed to the natural light-dark rhythm for one month.

The summer experiment revealed significant differences between group P and C in the numerical volume density of follicular cells (P≤0.01) and in the average nuclear diameter of parafollicular cells (P≤0.02), in addition to the already published results.

In the winter experiment a significant increase in the numerical volume density of parafollicular cells (P≤0.05) was seen in group P as compared to group C, indicating a stimulating effect of pinealectomy on these cells, whereas significant increases in the epithelium volume density (P≤0.05), the thyroid gland activation index (P≤0.02) and the average volume of parafollicular cells (P≤0.05) observed in group SP as compared to group C could indicate a stimulating effect of trauma on the thyroid gland.

Regarding the seasonal variation in the effect of pinealectomy on the thyroid gland it is assumed that in winter the influence of trauma predominates whereas in summer pinealectomy has a stimulating effect.

Keywords : pinealectomy, rat, season, thyroid gland

To cite this article

Draga Štiblar-Martinčič, «Seasonal variation in the influence of pinealectomy on rat follicular and parafollicular cells», Acta Stereologica [En ligne], Volume 13 (1994), Number 1 - Proceedings of the sixth European congress for stereology - Part two - May 1994, 21-26 URL :

About: Draga Štiblar-Martinčič

Institute of Histology and Embryology, Faculty of Medicine, Korytkova 2, 61105 Ljubljana, Slovenia