Ontogenesis of hormone-dependent adenylate cyclase in isolated rat nephron segments

Ontogenesis of hormone-dependent adenylate cyclase (AC) was investigated in rat kidney by single tubule microassay between two days postnatal and adulthood. This approach allowed us to analyze the kinetics of vasopressin-sensitive AC maturation in its tubular target sites, namely the thick ascending limb and collecting tubule. It was also possible to compare in a single segment--the thick ascending limb--the kinetics of AC ontogenesis for three hormones-- vasopressin, calcitonin, and parathyroid hormone. The results show that 1) 2 days after birth AC is still poorly responsive to vasopressin, especially in the thick ascending limb. By contrast, this segment exhibits marked AC responses to calcitonin and parathyroid hormone. 2) For a given hormone, the kinetics of AC ontogenesis depends on the segment in which the receptor-enzyme complex is located. 3) For a given segment, the pattern of AC maturation is specific for each hormone. These data indicate that the process of tubular AC maturation cannot be accounted for simply by an increase in basolateral membrane area or by the synthesis of new catalytic units. More specific mechanisms must be involved that regulate independently the synthesis of each kind of hormone receptor and/or its coupling to cyclase.