Morphology of thyroid C-cells and parathyroid glands in summer-active little brown bats, Myotis lucifugus lucifugus, with particular reference to pregnancy and lactation.

Morphological studies of thyroid C-cells and morphometric analyses of parathyroid glands in summer-active little brown bats indicated concomitant regulatory endocrine functions correlating with bone remodeling. C-cells apparently maintain maximal activity throughout the summer-active period in all bats. However, the hyperactivity of the parathyroid glands in summer-active female bats can be correlated with the maintenance of plasma calcium concentrations during lactation, when the female skeleton undergoes a period of bone demineralization. In summer-active male bats, which did not lose bone, the parathyroid glands did not show morphological evidence of hyperactivity; instead they were found to exhibit moderate parathyroid activity.