Morphometric investigations of the pineal gland after ganglionectomy and thyroidectomy under the aspect of circadian and seasonal variations.

It is well established that the pineal gland is involved in the regulation of thyrotropin (TSH) secretion. Previous investigations in our laboratory showed that under hypothyroid conditions the nuclear size of pinealocytes was diminished while an increase in the size of nuclei was seen under hyperthyroid conditions. In the present study we confirmed these results while considering circadian and circannual oscillations. After ganglionectomy (GX, removal of the sympathetic superior cervical ganglia) the mean annual values of the nuclear size of pinealocytes, pineal weights and thyroxine (T4) levels were diminished, whereas the pituitary weights increased. Comparable, but more drastical reactions were found after thyroidectomy (TX). The diminution of the nuclear size of pinealocytes was more pronounced in the wintertime (December, L: D = 8: 16), the finding for the summertime (June, L: D = 16: 8) being similar. Under short-day conditions the nuclear size was larger than under long-day regimes. In the winter the enhancement of the nuclear size was accompanied by decreased pituitary weights and increased T4 levels while under long-day conditions lower size of pinealocytes and T4 levels were associated with higher weights of pituitary glands. The statistically significant circadian patterns of the nuclear size of pinealocytes showed that the largest nuclei occurred at the end of the light phase or at the onset of the dark phase. In June, the largest nuclei were found in the middle of dark (control) or in the early light phase (ganglionectomy). Considering the circadian patterns of pineal weights and T4 levels, these results underline the existence of a functional connection between the pineal gland and the thyroid axis.(ABSTRACT TRUNCATED AT 250 WORDS)