Experimental and spontaneous pineal tumors: Findings relating to endocrine and oncogenic factors and mechanisms

Abstract

Pineocytomas have been induced in a high percentage of hamsters inoculated intracerebrally within 24 hours after birth with particular strains of a human papovavirus. Studies on biochemical and ultrastructural charactertistics and transformation of such experimentally induced pineal tumors have led to important conclusions and implications: (1) Many of the differentiated pineocytoma cells contained organelles and related structures that are characteristic of hamster pineocytes, and others that are reminiscent of possible phylogenetic precursors, including pineal photoreceptor cells. (2) An inverse relationship was noted between degree of cytological differentiation and level of hydroxyindole-O-methyltransferase (HIOMT) activity in the pineocytomas. (3) It is therefore apparent that even when pineal tumor formation leads to great increase in pinealocyte-like cells, their enzymatic capacity for synthesis fo melatonin, and possibly of other humoral products, may be only 4 to 7% of that of normal pinealocytes if they are of a relatively less differentiated type. A number of important and basic questions are accessible and remain to be investigated via experimental pineocytomas, such as: (1) nature and significance of cytological interactions within the pineal; (2) probable occurrences, correlations and transformations of other pineal biosynthetic and hormonal processes; (3) degree and nature of environmental (photic, circadian and circannual factors) and physiologic controls; and (4) kinds of modifications of pineal-related functions.

Histological features and expression of enzymes implicated in melatonin synthesis in pineal parenchymal tumours and in cultured tumoural pineal cells

“…This suggests that neoplastic pinealocytes retain certain specific markers of their normal counterparts. This agrees with previous reports on HIOMT activity in an experimental pineal tumour induced by a human papovavirus [16], in a biopsy specimen of a pineocytoma [7], in post mortem analysis of this enzyme in a pineocytoma [6] and with the presence of serotonin in a pineocytoma [9]. Taken together, these data suggest that the cells of pineocytoma and maybe the cells of other PPT are able to synthesize melatonin.…”

Histopathology of Tumors of the Pineal Region

“…Various amounts of HIOMT have been found in homogenates of experimental pineal parenchymal neoplasms induced in the hamster by the John Cunningham (JC) papovavirus, with levels being lower than those from normal pinealocytes [59,60]. mRNAs encoding three enzymes involved in melatonin synthesis, TPH, N-acetyltransferase and HIOMT, have been reported in PCs and cells cultured from some of these tumors [52,61].…”

The role of the pineal gland in neuroendocrine control mechanisms of neoplastic growth

“…Tumour Growth Quay (1980) published findings related to endocrine and oncogenic factors and mechanisms on the base of his investigations on experimental and spontaneous pineal tumours. An inverse relationship was noted between the degree of cytological differentiation and the level of hydroxyindole-O-methyltransferase (HIOMT) activity in pinealocytomas.…”