Effect of parathyroid hormone fragments on calcium transport in toad bladder

Parathyroid hormone (PTH) has a variety of biologic effects which are both dependent and independent on activation of adenylate cyclase. We studied the effects of intact PTH and PTH fragments on water flow and Ca transport in isolated toad bladder sacs. As reported previously by us, PTH (1-84) significantly stimulated basal water flow in isolated toad bladder sacs. Synthetic PTH 1-34, 44-68, 53-84 and 65-84 (1 microgram/ml) had no effect on basal water flow after a 60-min incubation period. Intact PTH (1-84) and synthetic 1-34 PTH significantly inhibited both arginine-vasopressin and cyclic AMP-stimulated water flow. Synthetic PTH 44-68, 53-84 and 65-84 (1 microgram m/ml) had no effect on arginine-vasopressin or cyclic AMP-stimulated water flow after a 60-min incubation. Intact PTH (1-84) and synthetic 1-34 PTH significantly stimulated 45Ca uptake without affecting 45Ca efflux. Synthetic PTH 44-68, 53-84 and 65-84 had no effect on either 45Ca uptake or 45Ca efflux. Although these results suggest that the intact hormone is required for the maximal effect of PTH on water flow, substantial activity resides in the amino terminal fragment of the hormone. No activity per se resides in the carboxy terminal portion of the hormone as regards water flow. Alterations in Ca transport appear to mediate the effect of PTH on water flow. These effects are independent of activation of adenylate cyclase because these hormones also inhibit cyclic AMP-stimulated water flow.