Multi-hormonal regulations of nephron epithelia: are they achieved
through combinational mode?.
Rouffignac, Christian De.
D[acute]epartement de Biologie Cellulaire et Mol[acute]eculaire,
CEA - Centre d'Etudes de Saclay, France
APStracts 2:0167R, 1995.
The kidney is the main organ regulating the composition of body
fluids. A considerable number of hormones controls the activity of
renal cells to maintain hydromineral equilibrium . It becomes more
and more difficult to interpret this multi-hormonal control in terms
of regulatory processes. To illustrate this complexity, the hormonal
regulation of electrolyte transport in the nephron thick ascending
limb is taken as an example. This nephron segment is largely
responsible for two kidney functions: the urinary concentrating
ability (by its capacity to deliver hypertonic sodium chloride into
the medullary interstitium) and the regulation of magnesium excretion
into final urine. Six hormones are presently identified as acting on
the transport of both NaCl and Mg2- in this nephron segment.
Therefore, the pertinent question is how the thick ascending limb
and, hence, the kidney,is capable of regulating water balance
independently from magnesium balance. It is proposed that the
hormones act in combination : circulating levels of the individual
hormones acting on these cells may determine the configuration of the
paracellular and transcellular transport pathways of the epithelium
either in the "sodium" or "magnesium" mode. The
configuration would depend on the distribution and activity of the
receptor at the surface of the basolateral membrane in contact with
the circulating hormones. This distribution along with stimulation of
respective signal transduction pathways would lead to the final
biological effects. It is already known that the distribution of cell
receptors may vary according to factors such as age, nutritional
variability, hormonal status, degree of desensitization of the
receptors, etc. The modulation of hormonal responses would depend
therefore on the degree of coupling of hormone-receptor complexes to
different intracellular transduction pathways and on the resulting
negative and/or positive interactions between these pathways.
Received 24 February 1995; accepted in final form 29 June 1995.
APS Manuscript Number R32-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.