Characteristics of parathyroid hormone‐specific cyclic changes of glucose‐6‐phosphate dehydrogenase activity in the distal convoluted tubule of the guinea pig

The effect of parathyroid hormone (PTH) on the time course of glucose‐6‐phosphate dehydrogenase (G6PD) activity in the distal convoluted tubule of a vitamin D‐depleted guinea pig was determined using quantitative cytochemistry. G6PD activity decreased to the stable basal level 5 hrs after the initiation of the kidney segment maintenance cultures. The exposure of the tissues to 1 pg/ml of bovine PTH‐(1–84) induced a cyclic change of G6PD activity, whereas neither carboxyl‐terminal PTH nor other hormones tested showed such activity. After a 16‐min exposure to bovine PTH‐(1–84), the peak height of each cycle began to decrease until it disappeared at 34 min. The second exposure to this hormone at 46 min reinduced a similar cyclic change with a similar peak, indicating full viability of the cells. When bovine PTH‐(1–84) was incubated with an excess amount of anti‐bovine PTH antibody, the PTH‐induced G6PD activity was completely abolished. Throughout a 14‐min exposure to either human PTH‐(1–84), human PTH‐(1–34) or bovine PTH‐(1–84), similar cyclic changes were observed with the constant peak height regardless of the dose (10 −16 ‐10 −12 M ), although the cycle length shortened progressively as the dose was increased. They were equipotent on a molar basis between the concentrations of 10 −16 and 10 −13 M at 6 min of hormone exposure. The present data demonstrate that the cytochemical bioassay of PTH in a vitamin D‐depleted animal is based on a dose‐dependent difference in the time course of G6PD activity.