Vasopressin release in response to intracerebroventricular L-alanine and L-arginine, and its dependence upon CSF NaCl concentration.
Influences on renal water, electrolyte, and arginine vasopressin (AVP) excretions of 1 h infusions (20 microliters/min) of a neutral (L-alanine) and two basic (L-lysine and L-arginine) amino acids into the lateral cerebral ventricle were studied in hydrated goats, and were compared to effects of control infusions of hypertonic (0.25 M) NaCl. L-alanine (0.11 M) dissolved in hypotonic NaCl caused more pronounced inhibition of the water diuresis and greater increase in AVP excretion than did the control infusions, but, in comparison to the latter, the responses developed very slowly. The effects were further delayed and were much attenuated when L-alanine was administered in isotonic glucose, but became considerably accentuated when isotonic NaCl was used as the solvent. L-lysine (0.09 M) in hypotonic NaCl did not inhibit the water diuresis or cause any apparent AVP release, whereas the corresponding L-arginine infusions caused inhibition of the water diuresis and increase in AVP excretion of approximately the same magnitudes and time courses as the control infusions. Like for L-alanine, these effects became accentuated when L-arginine was dissolved in isotonic NaCl, and became delayed and much attenuated when isotonic glucose was used as the solvent. L-arginine induced a more pronounced increase in renal Na excretion than did L-alanine and 0.25 M NaCl. Since transport together with Na (increasing the Na influx) generally is much more important for cellular uptake of neutral than of basic amino acids, the possibility is discussed that L-alanine here might have caused AVP release by increasing transmembrane Na transport of juxtacerebroventricular Na sensors regulating the AVP secretion--a suggestion supported by the lack of response to the basic L-lysine. The antidiuretic effect of the other basic amino acid, L-arginine, can not be explained along this line. However, with regard to the characteristic differences observed between the responses to L-alanine and L-arginine, the possibility is discussed that the latter might not have acted at a sensory level, but on the final neuronal link in the release of neurohypophyseal hormones, the hypothalamic neurosecretory cells. In contrast to L-alanine and L-arginine, L-lysine appeared to stimulate the appetite of the goats.