[Renal receptors of parathyroid hormone and calcitonin (author's transl)].

The two first steps of the renal cellular action of parathyroid hormone and of calcitonin are the hormonal binding onto specific receptors and the stimulation of adenylate cyclase by the hormone-receptor complex producing an increase in the intra-cellular concentration of 3'-5' cyclic adenosine monophosphate (cyclic AMP). Specific glomerular and tubular receptors for parathyroid hormone have been demonstrated using either tritiated parathyroid hormone or an indirect technique with 125 I labelled specific antibodies. Tubular receptors are localized both in the proximal and distal segments of the nephron. Parathyroid hormone stimulates glomerular and tubular adenylate cyclase. The main unsolved problem is the difficulty for demonstrating high affinity binding sites and stimulation of adenylate cyclase at low physiological concentrations of parathyroid hormone. In man, administration of parathyroid hormone produces a marked increase in the urinary excretion of cyclic AMP chiefly concerning its nephrogenous fraction. The peak of excretion is early and precedes the decrease in phosphate tubular reabsorption. Tubular receptors for calcitonin have been demonstrated using 125 I labelled salmon calcitonin. Calcitonin stimulates renal adenylate cyclase in only some segments of the nephron allowing receptors for calcitonin to be localized in the wide ascending branch of Henle's loop and the initial part of the convoluted distal tubule. In the presence of guanylnucleotides, binding of calcitonin onto its receptors and activation of adenylate cyclase are observed in the range of physiological concentrations of calcitonin in the rat. In man, administration of calcitonin produces a moderate increase in the urinary excretion of cyclic AMP coming from a non renal tissue.