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Renal, cardiovascular and endocrine responses of fetal sheep at 0.8 of gestation to an infusion of amino acids
Author(s) -
Marsh Amanda C.,
Lumbers Eugenie R.,
Gibson Karen J.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.013448
Subject(s) - endocrinology , medicine , chemistry , natriuresis , kaliuresis , reabsorption , plasma renin activity , renal blood flow , sodium , renal physiology , renal function , filtration fraction , renal sodium reabsorption , excretion , kidney , renin–angiotensin system , blood pressure , organic chemistry
Amino acid infusions increase renal blood flow (RBF) and glomerular filtration rate (GFR) and stimulate tubular reabsorption in adults. To characterize the effects of amino acids on fetal renal haemodynamics, tubular sodium reabsorption, acid‐base homeostasis and plasma renin levels, 11 chronically catheterized fetal sheep aged 121 ± 1 days (term ∼150 days) were infused i.v for 4 h with alanine, glycine, proline and serine (0.1, 0.1, 0.06 and 0.06 mmol min −1 , respectively) in 0.15 m saline at 0.165 ml min −1 . Eight control fetuses were given saline. During amino acid infusion, plasma amino acid levels increased up to 20‐fold ( P < 0.005 ). GFR increased by 50 ± 8 % ( P < 0.001 ); there was only a small transient increase in RBF. Proximal fractional sodium reabsorption fell from 74.6 ± 2.9 to 55.5 ± 5.4 % ( P < 0.005 ). Distal sodium delivery increased, but a smaller percentage of this distal sodium load was reabsorbed ( P < 0.005 ). Thus fractional sodium reabsorption fell from 95.5 ± 0.9 to 81.4 ± 2.0 % ( P < 0.005 ). There was a large diuresis, natriuresis, kaliuresis and increase in osmolar excretion ( P < 0.005 ). Plasma sodium and chloride concentrations fell ( P < 0.005 ). Plasma osmolality did not change. Plasma renin levels fell ( P < 0.05 ), cortisol levels increased ( P < 0.05 ), and there was a compensated metabolic acidosis. Thus the fetal sheep kidney demonstrated a remarkable functional capacity to respond to amino acid infusion. The increase in filtration fraction and the lack of an increase in RBF suggest that efferent arteriolar vasoconstriction occurred, a very different response from the renal vasodilatation seen in adult animals.