Prostaglandins and Medicine 6: 641-645, 1981 EFFECT OF PROSTAGLANDIN El, E2 OR INDOMETHACIN ON SERUM PARATHYROID HORMONE AND CALCITONIN IN THE RAT Walter P. Shemerdiak, Subhash C. Kukreja and Patricia A. Johnson Section of Endocrinology and Departments of Medicine and Nuclear Medicine, VA West Side and University of Illinois Medical Centers, Chicago, Illinois (Reprint Requests to SCK, VA West Side Medical Center, P.O. Box 8195, Chicago, IL 60680). ABSTRACT Infusion of 100 or 200 ng/min of Prostaglandin El (PGEl) or of 100 ng/min of PGE2 increased serum parathyroid hormone (PTH) in the rat. These infusions, however, had no significant effect on serum calcitonin (CT). Administration of 10 mg/kg of indomethacin for 3 days had no significant effect on basal serum PTH, CT or Calcium (Ca). EDTA infusion increased serum PTH to a similar degree in the vehicle- or indomethacin-treated rats. Therefore, endogenous prostaglandins do not appear to play a role in the secretion of PTH or CT. INTRODUCTION Prostaglandins, especially of the E series (PGE) have been shown to stimulate secretion of several hormones, presumably by stimulating adenyl cyclase in the responsive tissue (1). Cyclic AMP (CAMP) is involved in the secretion of PTH (2,3) and CT (4). Recently, Gardner et al demonstrated that PGE2 stimulated CAMP accumulation and PTH -- secretion in vitro from dispersed bovine parathyroid cells (S), and -- also from dispersed human parathyroid cells derived from adenomas or from hyperplastic tissue (6). In vitro studies have also shown that PGEl, or E2 can stimulate calcitonin secretion (7). Present studies evaluated the effects 1) of exogenous PGEl, or E2 and 2) of blockade of endogenous prostaglandin synthesis by indomethacin on serum PTH and CT in the rat. MATERIALS AND METHODS Fasting male Sprague Dawley rats weighing 250-300 g were anes- thetized with pentobarbital. Left jugular vein was exposed and a 641