Dose-related influence of indomethacin on parathyroid hormone-stimulated adenosine 3',5'-monophosphate release from the perfused rat hindlimb.

We examined the effect of indomethacin (INDO) on PTH-stimulated cAMP release from the perfused rat hindlimb. Since this preparation has not been used previously to study the effects of PTH, we first determined the dose-response curve for cAMP release in response to the 1-34 fragment of synthetic bovine PTH. cAMP release peaked 3-6 min after the PTH bolus and declined gradually toward baseline, even with sustained PTH infusion. The rate of cAMP release was directly related to the PTH dose. The lowest PTH priming dose that provoked a significant increase in cAMP release was 0.6 IU. Maximal cAMP release, occurring in response to a PTH priming dose of 30 IU, was 3- to 4-fold greater than baseline. PTH caused no increase in cAMP release from or the cAMP content of isolated skeletal muscle in vitro, suggesting that cAMP released from the hindlimb in response to PTH is derived solely from bone. PTH-stimulated cAMP release was unaltered by pretreatment of the intact rat with 2 mg/kg INDO, a dose that blocks prostaglandin synthesis. In contrast, PTH-stimulated cAMP release was significantly attenuated by pretreatment with 75 mg/kg INDO. The effect was not dependent on the addition of drug to the perfusate and was not altered by thyroparathyroidectomy at the time of INDO administration. We conclude that 1) the perfused rat hindlimb can be used to examine PTH effects on bone; 2) 2 mg/kg INDO has no effect on PTH-stimulated cAMP release from the perfused rat hindlimb; and 3) INDO in high doses blunts PTH activation of adenylate cyclase.