Proliferation of endothelial component of parathyroid gland in multiple endocrine neoplasia type 1. Potential relationship with a mitogenic factor.

The basic fibroblast growth factor-like mitogen detected in the plasma of patients with the multiple endocrine neoplasia type 1 (MEN-1) syndrome was found to have a specific mitogenic effect on parathyroid endothelial cells in vitro. To investigate its pathogenic role in humans, the endothelial component of parathyroid glands was evaluated by ultrastructural morphometry in six MEN-1 patients. The results were compared with those found in six patients with uremic hyperparathyroidism (UHPT) and in three subjects with histologically normal glands. Plasma mitogenic activity was found in all MEN-1 patients but not in those with UHPT or in normal subjects. All morphometric parameters investigated (fractional volume and nuclear density of capillary endothelial cells, volume fraction and number per unit area of capillaries) showed 1.5- to 2-fold higher values in patients with MEN-1 than in those with UHPT (P < 0.05). In contrast, no difference was found between MEN-1 cases and normal subjects. Quantitative evaluation of parathyroid pericytes yielded results similar to those of endothelial cells. These data indicate that the proliferation of parathyroid cells in MEN-1 patients is accompanied by parallel increase in the associated endothelial component that does not occur in patients with UHPT and may support the hypothesis of an in vivo role of the MEN-1 mitogen factor on the endothelial component of parathyroid glands in MEN-1 patients.