Autotransplantation of rat parathyroid glands: a study on morphological changes

Autotransplantation of parathyroid glands in man is performed to preserve parathyroid function after surgery. In a rat model, we performed autotransplantation into the renal subcapsular space to examine reinnervation and changes in cell activity in the transplanted glands.

Parathyroids grafted for 1-20 weeks were examined immunocytochemically for general and specific neuroendocrine markers to visualize nerve fibers and glandular cells and for bromodeoxyuridine to determine cell proliferation. In situ hybridization was used to localize and quantitate chromogranin A and parathyroid hormone (PTH) mRNA expression.

Reinnervation was observed as early as 1 week after transplantation in that nerve fibers containing the general neuronal marker protein gene product 9.5 appeared along blood vessels. During the following 20 weeks, the nerve fiber density increased gradually. One week after transplantation, the immunoreaction intensity for PTH, chromogranin A, and pancreastatin was lower than in control glands. Bromodeoxyuridine-labeled cells were fewer than in control glands at 1 week and at 5-10 weeks after transplantation. The density of PTH mRNA labeling was lower than in control glands during the whole time period studied and reached a minimum after 10 weeks. The density of chromogranin A mRNA labeling was unaffected at 1 and 3 weeks after transplantation and then decreased to a minimum at 10 weeks after transplantation; at 20 weeks, the chromogranin A mRNA labeling had again reached the level in control glands.

The changes in PTH and chromogranin A immunoreaction intensity and mRNA density indicate reduced hormone production for several weeks after transplantation. Our results using transmitter-specific markers indicate a rapid ingrowth of mostly sympathetic nerve fibers, preferentially around blood vessels. Later on, parasympathetic and sensory nerve fibers reached the grafts. The parathyroid innervation may be of importance for parathyroid hormone regulation, and the finding of an early reinnervation could be of clinical importance.