AJP - Renal Physiology, Vol 252, Issue 5 916-F921, Copyright © 1987 by American Physiological Society
Examination of hypercalciuria in anterior pituitary-implanted rats
L. S. Costanzo, B. Smith and R. A. Adler
The anterior pituitary (AP) grafted, adrenalectomized, steroid
hormone-replaced male rat is characterized by hyperprolactinemia and
hypercalciuria. To determine the origin of the hypercalciuria, clearance
experiments were performed under Inactin anesthesia in adrenalectomized
Fischer rats 8-10 wk after implantation of extra AP glands under the kidney
capsule. Glomerular filtration rate, ultrafilterable calcium, and
fractional sodium excretion were comparable in the AP and control groups.
However, fractional calcium excretion was significantly higher in the
AP-implanted rats, P less than 0.05, resulting in a marked dissociation of
the calcium/sodium clearance ratio. Because filtered calcium load did not
change, these results clearly demonstrate that AP-implanted animals have a
defect in tubular calcium reabsorption. The dissociation of calcium
transport from sodium transport suggests the distal tubule as a likely site
of action. Parathyroidectomy did not alter the calciuric response to AP
implantation. To test whether hyperprolactinemia was responsible for
decreased calcium reabsorption in AP-implanted rats, purified rat prolactin
was infused into normal rats to achieve high blood prolactin levels, or was
injected into normal rats daily for 8 days. Changes in fractional calcium
excretion and the ratio of calcium to sodium clearance were identical in
animals receiving prolactin or control infusions. Thus, hypercalciuria in
the AP-implanted rat may be attributed to an unidentified factor, perhaps
secreted from the implanted anterior pituitaries, rather than to prolactin
excess.
