AJP - Renal Physiology, Vol 249, Issue 2 282-F290, Copyright © 1985 by American Physiological Society
Role of the pituitary in reflex natriuresis following acute unilateral nephrectomy
S. Y. Lin, E. Wiedemann and M. H. Humphreys
We studied the role of altered pituitary function in the reflex natriuresis
that occurs after acute unilateral nephrectomy (AUN). In normal rats, AUN
increased both sodium (UNaV) and potassium excretion within 90 min. In
hypophysectomized rats, no increase in cation excretion after AUN occurred,
results which were duplicated in rats in which pituitary function was
altered by prior treatment with dexamethasone (2 mg/kg ip for 3 days). In
adrenalectomized rats, AUN led to increases in cation excretion similar to
those seen in normal rats, indicating that intact adrenal function was not
necessary for this excretory response following AUN. These changes in
cation excretion were correlated with measurements in peripheral plasma of
two peptides derived from the pituitary precursor molecule
pro-opiomelanocortin (POMC). Radioimmunoassayable plasma beta-endorphin
failed to change after AUN in any of the conditions studied. However, a
sensitive radioimmunoassay for the N-terminal fragment (NTF) of POMC
indicated that plasma NTF rose significantly after AUN in normal and
adrenalectomized rats but did not change in hypophysectomized,
steroid-pretreated, or shamoperated rats. The increase in NTF concentration
correlated with the increase in UNaV after AUN. These results demonstrate
that the reflex increase in cation excretion after AUN is dependent on an
intact pituitary gland and is associated with an increase in peripheral
plasma concentration of NTF. NTF, or some other peptide residing in the
N-terminal portion of POMC, could promote the natriuresis after AUN; the
importance of the pituitary gland in this response could be the secretion
of this peptide.
