aintaining extracellular calcium concentrations within a narrow range is
critical for the survival of most vertebrates. PTH, together with
vitamin D, responds to hypocalcemia to increase extracellu- M lar
calcium levels, by acting on bone, kidney and intestine. The recent
intro- duction of PTH as a major therapeutic agent in osteoporosis has
directed renewed interest in this important hormone and in the
physiology of the parathyroid gland. The parathyroid is unique in that
low serum calcium stimulates PTH secretion. As hypocalcemia persists,
there is also an increase in PTH synthesis. Chronic hypocalcemia leads
to hypertrophy and hyper- plasia of the parathyroid gland together with
increased production of the hormone. Phosphate is also a key modulator
of PTH secretion, gene expres- sion and parathyroid cell proliferation.
Understanding the biology of the parathyroid as well as the mecha- nisms
of associated diseases has taken great strides in recent years. This
book summarizes the molecular mechanisms involved in the function of the
para- thyroid gland. The first chapter reviews the development of the
parathyroid gland and the genes involved in this process as identified
using genetically manipulated mice. Then the biosynthetic pathway of PTH
from gene ex- pression to its intracellular processing and the sequences
in the gene control- ling its transcription as well as those regulating
mRNA processing, stability and translation are described.