Elevation of calcitonin immunoreactivity in the pituitary and thyroid glands of genetically obese rats (fa/fa)

This paper contains the first demonstration of quantitative changes in the levels of calcitonin-like immunoreactivity in the pituitary. The concentration of calcitonin-like material in lean Zucker rats (?/+) was 0.42 ± 0.09 ng/mg wet weight of pituitary. The pituitaries of obese rats (fa/fa) contained significantly greater levels (1.56 ± 0.56 ng/mg wet weight). This 271% increase represents the first indication that pituitary calcitonin-like material may have a physiological role in genetically obese rats. Thyroidal calcitonin also was elevated in the obese (111%). These large elevations in the calcitonin content of the glands of obese rats were not accompanied by significant elevations of calcitonin in the blood. This suggests that obese rats have problems with mechanisms for the release of calcitonin into the blood and might not be able to combat hypercalcemia as effectively as leans. However, this hypothesis remains to be tested.