Simultaneous changes of the perivascular contact area and HIMOT activity in the pineal organ after bilateral adrenalectomy in the rat.

In the pineal organ of the female rat, proportional changes in the area of contact of pinealocyte processes and glial processes with the perivascular space were found after bilateral adrenalectomy. The contact area was evaluated by measuring the length of pinealocyte and glial cell membranes directly abutting on the basal lamina. In the normal female rat, 40% of the contact area is occupied by pinealocyte and 60% by glial cell processes. Fourteen days after bilateral adrenalectomy, this proportion is reversed. In addition, cell counts demonstrate that more pinealocytes gain access to the pericapillary space due to the experimental conditions. In order to prove whether or not these results indicate an increase of pineal endocrine activity, the melatonin-forming enzyme hydroxyindole-O-methyltransferase (HIOMT, E.C. 2.1.1.4) was assayed. After bilateral adrenalectomy the HIOMT activity was found to significantly increase.