Urinary excretion of adrenaline metabolites in man during intervals of 2 minutes, 5 minutes, and 10 minutes after intravenous injection of adrenaline

Sources of human urinary epinephrine

The kidney is a likely source for some urinary epinephrine (E) since adrenalectomized animals and humans continue to excrete urinary E and the human kidney contains E synthesizing enzymes. We studied subjects during an intravenous infusion of 3H-E to determine the fraction of urinary E derived from the kidney. Eight normal subjects (CON) and 5 older, heavier hypertensives (OHH) ate a light breakfast along with ascorbic acid supplementation and had intravenous and arterial lines placed. They received an infusion of 3H-E and had an oral water load. During the final hour of 3H-E infusion, urine and arterial blood samples were collected for 3H-E and E levels. After the 3H-E infusion was abruptly discontinued, arterial blood samples were collected to measure 3H-E kinetics. The total body clearance of 3H-E was about 2,500 ml/min from plasma and clearance of 3H-E to urine was about 170 ml/min. CON had plasma E levels of 43 +/- 4 pg/ml. Their predicted rate of clearance of E from plasma to urine of 7,471 +/- 865 pg/min was less than (P = 0.018) the actual urinary E excretion of 15,037 +/- 2,625 pg/min. Thus, 43 +/- 9% of urinary E in CON was apparently derived from renal sources and not filtered from blood. Among OHH 85 +/- 4% of urinary E was derived from the kidney, significantly (P < 0.01) different from CON. The OHH also produced much more urinary E than predicted from plasma 3H-E clearance into urine (P = 0.03). A major fraction of urinary E is not filtered from the blood stream but is apparently derived from kidney. A small fraction of urinary E may be derived from E stored in nerve endings along with norepinephrine, but this probably represents less than 2% of urinary E. Renal cleavage of E sulfate into E may be another potential source of urinary E. Some, and perhaps most, urinary E not filtered from the bloodstream is derived from renal N-methylation of norepinephrine as the human kidney has two enzymes capable of converting norepinephrine to E. In conclusion, a major portion of urinary E is derived from the kidney and not filtered from the bloodstream. This is an important factor in the interpretation of urine E levels. Renal E could alter renal blood flow, electrolyte reabsorption, and renin release prior to excretion into urine.

Measurement and kinetic study of the formation of adrenaline sulphate in vitro

The sulpho-conjugation of [14C]adrenaline form inorganic sulphate and ATP or preformed adenosine 3'-phosphate 5'-sulphatophosphate was demonstrated in the high-speed supernatant prepared from the liver and small intestine of various animals. Hydrolysis with sulphatase indicated the sulphate nature of the conjugate. The overall sulphation reaction has a pH optimum of 9.0. Maximal activity was obtained with a ratio of ATP/Mg2+ of 1 at 4--6mM. Above their optimal concentrations, ATP and Mg2+, separately or in combination, were inhibitory. Dithiothreitol at 3 mM stimulated the reaction by about 30%. The Km for adrenaline, determined by the sulphotransferase reaction and by the three-step (sulphate-activating and sulphotransferase) reactions was 125 micrometer. The rate of synthesis of [14C]-adrenaline sulphate, expressed in pmol/min per mg of protein for the livers of dog, monkey, rat, guinea pig and rabbit were, respectively, 144, 77, 47, 11 and 6. The corresponding values for the small intestines of dog and monkey were 60 and 62. Brain and heart tissues showed no measurable activity.

Demonstration of 3,4-dihydroxy(14C)benzoic acid and (14C)vanillic acid after administration of (14C)noradrenaline in the rat

Rats were injected with 40 μCi (±)-[1-3H]noradrenaline and 10 μCi ±-[1-14C]noradrenaline. Three fractions with a decreased 3H:14C ratio were isolated from the urine by a combined alumina adsorption-ethyl acetate extraction procedure. Two of the fractions were identified as [14C]vanillic acid and 3,4-dihydroxy[14C]benzoic acid, respectively. Vanillic acid represented between 1.5 and 3.0% of the total [14C]activity excreted within 24 h and the contribution of dihydroxybenzoic acid was 0·2-0·5%. The third fraction with a decreased 3H: 14C ratio has not been identified and represented about 2% of the total [14C]activity excreted within 24 h. After monoamine oxidase blockade with 100 mg/kg of iproniazid, the excretion of vanillic acid, 3,4-dihydroxybenzoic acid and the unknown fraction was greatly diminished. The probability that these three substances represent those metabolites arising simultaneously with the formation of tritium water from (±)-[1-3H]noradrenaline is discussed.