The aims of this study were 1) to determine whether transfer of blood urea to the gastrointestinal tract (GIT) or the efficiency of capture of urea N within the GIT is more limiting for urea N salvage, and 2) to establish the relationship between plasma urea concentration and recycling of urea N to the GIT. We used an i.v. urea infusion model in sheep to elevate the urea entry rate and plasma c...

We measured plasma concentrations of immunoreactive endothelin-1 (irET-1) in the prehypertensive and hypertensive phases in spontaneously hypertensive rats (SHR) and in malignant hypertension caused by deoxycorticosterone acetate (DOCA)-salt administration in SHR. We also measured concentrations of this peptide in another model of malignant hypertension, the two-kidney, one clip (2K1C) renovasc...

We examined the relationship between plasma cortisol levels, hepatic glutamine synthetase (GNS) activity and the form of nitrogen excreted (e.g. urea, ammonia) in undisturbed versus confined/crowded (acutely stressed) gulf toadfish. Specifically, we tested the hypothesis that acute increases in plasma cortisol levels are required to trigger the increase in GNS activity induced by the confinemen...

Urea is the principal nitrogenous waste product of metabolism and is generated from protein breakdown. It is eliminated from the body almost exclusively by the kidneys in urine, and measurement of its concentration, first in urine and later in blood, has had clinical application in the assessment of kidney (renal) function for well over 150 years. This is the first of two articles that together...

Gulf toadfish, Opsanus beta, are one among a group of unusual teleosts that excrete urea as their predominant nitrogen end product in response to stressful conditions. Under conditions of crowding or confinement, fasted toadfish excrete the majority of their nitrogen waste in large pulses of urea (>90% of total nitrogen) lasting up to 3 h. An earlier study demonstrated that cortisol has an inhi...

Nitrogen is the most important essential nutrient that plays a major role in achieving maximum crop yield in agriculture. Therefore, nitrogen fertilizers such as ammonium sulfate and urea have been extensively used in modern agriculture. These fertilizers are generally oxidized to nitrate via nitrite by nitrifying microorganisms in the agricultural field (4, 10, 11). The serious environmental p...

In previous papers (1, 2) it was shown that when the urine volume output falls below about 0.35 ml. per minute, the urine becomes " maximally" concentrated with respect to urea. The urea concentration of the urine is constant below this critical volume, and thus the urea clearance (U V/B) varies directly and quantitatively with the urine volume (V). In an effort to analyze the mechanism of rena...

33 days. In five, who served as controls, urine urea nitrogen excretion remained constant for 2 wk thereafter. The other six were given seven daily infusions containing 6-8 mmol each of the a-keto-analogues of valine, leucine, isoleucine, phenylalanine, and methionine (as sodium salts) plus 3-4 mmol each of the remaining essential amino acids (lysine, threonine, tryptophan, and histidine). Rapi...

Two feeding trials with baby pigs were conducted to evaluate the effects of additions of L-tryptophan and L-giutamic acid to a low protein (16%) starter diet on performance and plasma urea nitrogen, a-amino nitrogen and free tryptophan. In experiment 1, but not in experiment 2, glutamic acid addition (3.36%) improved rate of gain and feed efficiency. Tryptophan addition did not improve performa...