IS THERE LOW-DIMENSIONAL CHAOS IN PULSATILE SECRETION OF PARATHYROID-HORMONE IN NORMAL HUMAN-SUBJECTS

In many biological systems information is transferred by hormonal liga nds, and it is assumed that these hormonal signals encode developmenta l and regulatory programs in mammalian organisms. The specificity of t he biological response on activation by a hormone has so far been loca ted within the interaction of a specific conformation of the ligand wi th the corresponding receptor structure. According to these classical explanations, the constant circulating hormonal pool described by the rate of its production and metabolic clearance is a major determinant of this interaction. Recently it has become apparent that hormone puls es contribute to this hormonal pool. Phase-space analysis of dynamic p arathyroid hormone (PTH) secretion allowed the definition (in comparis on to normal subjects) of a relatively quiet ''low dynamic'' secretory pattern in osteoporosis, and a ''high dynamic'' state in hyperparathy roidism. We now investigate whether this pulsatile secretion of PTH in healthy humans exhibits characteristics of low-dimensional determinis tic chaos. Our findings suggest that this indeed appears to be the cas e. PTH secretion thus seems to be a first example of a chaotic hormona l rhythm in human physiology.