Prolactin and Calcitonin Responses to Parathyroid Hormone Infusion in Hypoparathyroid, Pseudohypoparathyroid, and Normal Subjects*

Since parathyroid hormone (PTH) has been reported to release PRL in normal humans, we studied the effects of exogenous PTH infusion (150 U) on the secretion of PRL, TSH, and calcitonin in 10 normal subjects, 5 with hypoparathyroidism, and 10 with pseudohypoparathyroidism, type I (PHP). PTH produced a rise in serum PRL in the normal subjects from 5.1 +/- 0.8 ng/ml (SE) to 14.9 +/- 3.0 ng/ml (P less than 0.01), while levels similarly rose from 4.0 +/- 0.2 to 8.5 +/- 0.8 ng/ml (P less than 0.01) in the patients with hypoparathyroidism. In 6 PHP patients with deficient PRL responses to TRH, the PRL response to PTH was also blunted (basal, 3.2 +/- 0.81 ng/ml; peak, 4.1 +/- 1.3 ng/ml; P greater than 0.1). Three of 4 PHP patients with normal PRL responses to TRH demonstrated a normal PRL increment in response to PTH infusion. Serum TSH and calcitonin were not changed by PTH infusion in any of the groups. These findings demonstrate that the resistance to PTH seen in PHP does not extend to the pituitary gland.