Robert E. Wehmann

Sources of Cyclic Nucleotides in Plasma

In order to determine the sites of net production and removal of the cyclic nucleotides in plasma, various blood vessels were catheterized in 17 anesthetized dogs and arterial and venous concentrations of adenosine 3,5-monophosphate (cAMP) and guanosine 3,5-monophosphate (cGMP) were measured by radioimmunoassay. Aortic cAMP was 30+/-2 nM (mean+/-SE) and cGMP was 13+/-1 nM. There were no significant differences for either cyclic nucleotide between the concentration in the aorta and that in the inferior vena cava, coronary sinus, hepatic vein, and femoral vein. The concentration of cAMP in renal venous plasma was 25% lower than in aortic plasma, and renal venous cGMP was 51% lower than in the aorta. The pulmonary arterial concentrations of cAMP and cGMP were slightly lower than in the aorta. The concentration of cGMP in the superior mesenteric vein plasma was 83% greater than in aortic plasma; the concentration of cAMP in this vessel was only 16% greater than that in the aorta. Superior vena cava concentrations of both cyclic nucleotides were slightly greater than arterial concentrations. THE RESULTS SUGGEST THAT: (a) the kidneys are a major site of removal of both cyclic nucleotides from plasma. (b) The lungs may be a site of net addition of both cyclic nucleotides to plasma. (c) The small intestine is a site of net production of both cyclic nucleotides, particularly cGMP. (d) The liver probably removes cyclic nucleotides from plasma. (e) Since no other organs or regions studied added detectable net amounts of cyclic nucleotides to plasma, and since the turnover of these compounds in plasma is known to be rapid, the production of plasma cyclic nucleotides under basal conditions may well be the result of small net contributions may well be the result of small net contributions from many tissues or bidirectional fluxes between tissues and plasma, or both.

Characterization of a carboxyterminal peptide fragment of the human choriogonadotropin beta-subunit excreted in the urine of a woman with choriocarcinoma.

We have observed low-molecular weight carboxyterminal fragments of the human choriogonadotropin (hCG) beta-subunit in the urines of several women with choriocarcinoma, and we have characterized one fragment in detail. Its apparent molecular weight by gel chromatography on Sephadex G-100 was 14,200. The fragment was not adsorbed to concanavalin A-Sepharose, indicating that it lacked the asparagine-linked carbohydrate groups of intact hCG beta. It was active in radioimmunoassays (RIA) using antisera either to the hCG beta carboxyterminal peptide (CTP) or to the desialylated hCG beta CTP (hCG beta as-CTP), indicating the presence of not only the hCG beta carboxyterminus but also desialylated O-serine-linked carbohydrate side chains on the fragment. It lacked luteinizing hormone/choriogonadotropin radioreceptor activity and hCG beta conformational immunoreactivity (SB6 RIA). On Sephadex G-100 gel chromatography, the elution profiles of this fragment and the hCG beta as-CTP(115-145) prepared by trypsin digestion of as-hCG were essentially indistinguishable (apparent molecular weights 14,200 and 14,000, respectively). The immunological characteristics of the fragment in both hCG beta CTP and hCG beta as-CTP RIA were indistinguishable from those of the hCG beta as-CTP(115-145) glycopeptide. Carboxyterminal fragments of hCG beta were evident in urine specimens obtained from 10 of 11 patients with choriocarcinoma but not in those obtained from normal subjects who were given an intravenous infusion of highly purified hCG. Of six pregnant women, only the one at term excreted carboxyterminal fragments of hCG beta and then only in trace amounts. We conclude that hCG beta carboxyterminal fragments, including one that is indistinguishable from the tryptic glycopeptide hCG beta as-CTP(115-145), can occur naturally in the urine of patients with choriocarcinoma.

Plasma clearance rates and renal clearance of 3H-labeled cyclic AMP and 3H-labeled cyclic GMP in the dog.

Previously, in an attempt to understand the mechanisms involved in the regulation of plasma cyclic nucleotides, we measured concentrations of adenosine 3,5-monophosphate (cAMP) and guanosine 3,5-monophosphate (cGMP) in plasma from selected blood vessels of anesthetized dogs. The observation that the renal venous plasma concentrations of both cyclic nucleotides were less than arterial concentrations suggested that the kidney might be an important site for the elimination of these compounds from plasma and prompted further investigation of the renal handling of these compounds. Tracer doses of either [(3)H]cAMP or [(3)H]cGMP were administered to anesthetized dogs by constant intravenous infusion, and metabolic clearance rates were determined. Concentrations of endogenous cyclic nucleotide and of cyclic nucleotide radioactivity were measured in aortic and renal venous plasma as well as in urine. Renal venous plasma [(3)H]cGMP was 39% and [(3)H]cAMP was 65% of the concentration in arterial plasma. Endogenous cyclic nucleotide levels showed a similar relationship. The plasma clearance rates (PCR) were 271+/-27 ml/min (mean+/-SE) for cGMP and 261+/-17 for cAMP. The total kidney clearance (calculated as the renal plasma flow x renal cyclic nucleotide extraction ratio) accounted for 52+/-4% and 30+/-2% of the PCR for cGMP and cAMP, respectively. Only about two-thirds of the total kidney clearance of each cyclic nucleotide could be accounted for by urinary excretion, the remainder presumably being the result of renal metabolism. The urinary clearances of (3)H-labeled cGMP (40.9+/-4.2 ml/min) and endogenous cGMP (45.0+/-2.3 ml/min) were not significantly different from each other. Both were approximately 50% greater than the glomerular filtration rate, which was 27.1+/-2.0 ml/min, indicating that a significant amount of urinary cGMP is derived from plasma by tubular secretion. In contrast, the urinary clearances of (3)H-labeled cAMP (23.7+/-1.9 ml/min) and endogenous cAMP (27.2+/-2.6 ml/min) were nearly equal both to each other and to the glomerular filtration rate, which was 24.6+/-1.7 ml/min. Thus, in the dog, glomerular filtration of plasma cAMP appears to be responsible for most of the cAMP found in urine. Renla production of cAMP, which in humans contributes from a third to a half of the urinary cAMP, was quantitatively of minor importance in the dog.Thus, under the conditions of these experiments in dogs, renal elimination appears to be responsible for half of the PCR of cGMP and about a third of the PCR of cAMP. About a third of the renal elimination of both cyclic nucleotides appears to be due to metabolic degradation within the kidney, and the balance is due to excretion in the urine.

β-Core chemical and clinical properties

Abstract β-Core is the most abundant hCG-related molecule in pregnancy urine. The structure of β-core as well as aspects of its metabolic clearance suggest that β-core is a metabolic fragment of the hCG-β subunit. The occurrence of β-core in the urine of patients with a broad spectrum of malignancies imparts an important role to β-core as a tumor marker. The recent development of antisera with enhanced specificity and sensitivity for β-core will facilitate further studies on the clinical significance of this molecule.