Parathyroid hormone stimulation of glucose and urea production in isolated liver cells

Non-Conventional Treatment of Hepatic Failures

It is our intention to present a short review of various approaches to the non-conventional treatment of hepatic failures of the fulminant type. Our review is directed to the scientist, technologist, and clinician with a budding interest in the hepatic assist area. We shall discuss parabiosis, liver transplants, and various extracorporeal devices including hemoperfusion, hemodialysis, and enzymic detoxification systems.

We feel that the present technological approaches to the treatment of hepatic failure are very primitive at this stage. Some of the recent advances are very encouraging, and it is our opinion that these approaches show great promise in the long term.

Body Composition in Diabetic Subjects with Chronic Kidney Disease: Interest of Bio-Impedance Analysis, and Anthropometry

BACKGROUND/AIMS

Lean body mass (LBM) is reduced in uremia, but this has not been reported in diabetic nephropathy.

SUBJECTS AND METHODS

We compared predicted % LBM to DEXA measurements in 10 non-diabetic uremic, 10 non-uremic diabetic and 10 uremic diabetic subjects matched for age, gender and BMI. We also measured % LBM by anthropometry, bio-impedance analysis (BIA) and compared them with DEXA in 49 diabetic subjects with a wide range of renal failure. The results were compared and a Bland & Altman procedure was performed. Associations between glomerular filtration rate (GFR) and % LBM were tested.

RESULTS

In matched groups, predicted % LBM values were overestimated in non-diabetic uremic subjects, and underestimated in non-uremic diabetic subjects. In uremic diabetic subjects, the error was intermediary. As compared to DEXA (% LBM: 69.0 +/- 7.1%), measurement of % LBM by anthropometry (71.4 +/- 8.0%, p < 0.05) and BIA (67.2 +/- 7.6%, p < 0.05) were biased in the 49 diabetic subjects. The mean of anthropometric and BIA (Ant+BIA) were similar to DEXA results (69.3 +/- 6.8%, p = 0.64), with best correlation coefficients and Bland & Altman plots. GFR was correlated to % LBM assessed by DEXA, BIA and Ant+BIA.

CONCLUSION

In diabetic subjects with chronic kidney disease, LBM should be measured, rather than predicted. A good evaluation is possible, even without DEXA.

Protein and energy nutrition among adult patients treated with chronic peritoneal dialysis

Protein-energy malnutrition (PEM) in adult patients treated with chronic peritoneal dialysis (CPD), which is highly prevalent and frequently severe in its manifestation, poses a significant therapeutic dilemma. The causes of PEM include inflammation, low nutrient intake, nutrient losses during dialysis, metabolic acidemia, coexisting illnesses, and possibly the endocrine disorders of uremia. Treatment strategies for PEM in CPD patients include the following: attempt to treat the potentially reversible causes of anorexia, increase nutrient intake (by nutritional counseling, oral food supplements, consideration of appetite stimulants and intraperitonial amino acid solutions), and the correction of metabolic acidosis. Coexisting illnesses engendering PEM should be treated. Experimental evidence suggests that such agents as anabolic steroids, human growth hormone, insulin-like growth factor-I, and L-carnitine may engender positive protein balance in these individuals. Finally, the use of anti-inflammatory agents to improve the nutritional status of malnourished CPD patients remains to be defined. There is a need to carry out clinical trials that examine whether an improvement in the nutritional status of CPD patients is associated with an improvement in their mortality, morbidity and/or quality of life.

Important factors other than dialysis adequacy associated with inadequate dietary protein and energy intakes in patients receiving maintenance peritoneal dialysis

BACKGROUND

Anorexia that results in inadequate nutrient intake is considered one of the most important causes of malnutrition in dialysis patients.

OBJECTIVE

The objective was to determine factors other than dialysis adequacy that are associated with inadequate protein and energy intakes in patients receiving continuous ambulatory peritoneal dialysis.

DESIGN

Dietary protein and energy intakes were assessed with a food-frequency questionnaire in 266 patients, and factors other than dialysis adequacy that are potentially associated with reductions in energy and protein intakes were examined.

RESULTS

Only 39% of the patients had protein intakes > or = 1.2 g x kg(- 1) x d(- 1), and 26% had energy intakes > or = 126 kJ x kg(- 1) x d(- 1). Other than having a greater total urea clearance and glomerular filtration rate, patients with protein intakes > or = 1.2, as opposed to < 1.2, g x kg(- 1) x d(- 1) had lower high-sensitive C-reactive protein concentrations and fewer complications with volume overload (29% compared with 46%; P = 0.006). Patients with energy intakes > or = 126, as opposed to < 126, kJ x kg(- 1) x d(- 1) were younger, had lower high-sensitive C-reactive protein concentrations, and had a lower prevalence of diabetes (P = 0.006), atherosclerotic vascular disease (P = 0.020), and history of volume overload (P = 0.013). Multiple regression analysis showed that other than increasing age, diabetes, and total urea clearance, having a history of volume overload was independently associated with a 0.22-g x kg(- 1) x d(- 1)decrease in protein (P = 0.001) and a 13.07-kJ x kg(- 1) x d(- 1) decrease in energy intake (P = 0.006).

CONCLUSION

An important yet unrecognized association was observed between a history of volume overload and dietary intake in peritoneal dialysis patients.

The National Kidney Foundation K/DOQI clinical practice guidelines for dietary protein intake for chronic dialysis patients

This paper discusses two of the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (K/DOQI) clinical practice guidelines for nutrition in chronic renal failure. These are the guidelines that recommend a dietary protein intake of 1.2 g protein/kg body weight/day for clinically stable maintenance hemodialysis (MHD) patients (Guideline 15) and 1.2 to 1.3 g protein/kg/day for clinically stable chronic peritoneal dialysis (CPD) patients (Guideline 16). These recommended protein intakes are greater than the usually ingested protein intakes of MHD and CPD patients and are also greater than the recommended protein intakes for healthy, nonpregnant, nonlactating adults. The possible mechanisms that engender these increased protein needs include (1) the substantial quantity of amino acids, peptides, and proteins removed by the dialysis procedure and (2) the protein catabolic or antianabolic state caused by the uremic milieu, the inflammatory state, the oxidative and carbonyl stress, and the bioincompatible dialysis materials to which MHD and CPD patients are exposed. There are a number of nitrogen balance studies that have been performed to identify the dietary protein needs of MHD and CPD patents. The results of this research as well as some of the methodological limitations of these studies are reviewed. The concepts of the average dietary protein intake required to maintain protein balance in MHD or CPD patients and the safe protein intake that will maintain protein balance in virtually all MHD and CPD patients are discussed.

Parathyroid hormone induces hepatic production of bioactive interleukin-6 and its soluble receptor

Interleukin-6 (IL-6) is an important mediator of parathyroid hormone (PTH)-induced bone resorption. Serum levels of IL-6 and its soluble receptor (IL-6sR) are regulated in part by PTH. The PTH/PTH-related protein type 1 receptor is highly expressed in the liver, and in the current study we investigated whether the liver produces IL-6 or IL-6sR in response to PTH. Perfusion of the isolated rat liver with PTH-(1-84) stimulated rapid, dose-dependent production of bioactive IL-6 and the IL-6sR. These effects were observed at near physiological concentrations of the hormone such that 1 pM PTH induced hepatic IL-6 production at a rate of approximately 0.6 ng/min. In vitro, hepatocytes, hepatic endothelial cells, and Kupffer cells, but not hepatic stellate cells, were each found to produce both IL-6 and IL-6sR in response to higher (10 nM) concentrations of PTH. Our data suggest that hepatic-derived IL-6 and IL-6sR contribute to the increase in circulating levels of these cytokines induced by PTH in vivo and raise the possibility that PTH-induced, liver-derived IL-6 may exert endocrine effects on tissues such as bone.

Pathophysiology of protein-energy wasting in chronic renal failure

There is a high prevalence of protein-energy malnutrition in both nondialyzed patients with advanced chronic renal failure and in those individuals with end-stage renal disease who are receiving maintenance hemodialysis or chronic peritoneal dialysis therapy. Approximately one-third of maintenance dialysis patients have mild to moderate protein-energy malnutrition, and about 6 to 8 percent of these individuals have severe malnutrition. These statistics are of major concern because markers of protein-energy malnutrition are strong predictors of morbidity and mortality. The causes of protein-energy malnutrition in patients with chronic renal failure include: (1) decreased energy or protein intake; (2) concurrent chronic illnesses, and superimposed acute illnesses and possibly increased inflammatory cytokines; (3) the catabolic stimulus of hemodialysis; (4) losses of nutrients into dialysate, particularly amino acids, peptides, protein (with peritoneal dialysis), glucose (when hemodialysis is performed with glucose-free dialysate) and water-soluble vitamins; and (5) diagnostic or therapeutic (e.g., prednisone therapy) procedures that reduce nutrient intake or engender net protein breakdown. Other theoretically possible causes for protein-energy malnutrition include (6) chronic blood loss; (7) endocrine disorders (especially resistance to insulin and insulin-like growth factor-I, hyperglucagonemia, hyperparathyroidism and deficiency of 1,25-dihydroxycholecalciferol); (8) products of metabolism that accumulate in renal failure and may induce wasting, such as organic and inorganic acids; (9) loss of the metabolic actions of the kidney; and (10) the accumulation of toxic compounds that are taken up from the environment (e.g., aluminum).

Studies on the effect of parathyroid hormone (1-84) on glucose output in the liver: comparison of effects in isolated hepatocytes and in perfused liver

This study was conducted to determine the action of parathyroid hormone (1-84) (PTH(1-84)) on glucose output both in perfused liver and in isolated hepatocytes. In isolated rat hepatocytes, PTH(1-84) stimulated glucose output in a concentration-dependent manner. The action was detected at 10(-11) M and, at 10(-9) M, PTH produced its maximal effect. The magnitude of the maximal effect of PTH(1-84) was about 65% of that of phenylephrine. In contrast, PTH(1-84) had no effect on glucose output in perfused rat liver. Concentration of PTH(1-84) in effluent of perfused liver was less than that in the inflow. However, when the effluent obtained from liver perfused with 10 nM PTH(1-84) was added to isolated hepatocytes, a considerable amount of glucose was released, which was reversed by PTH(7-34), a competitive inhibitor of PTH receptor. These results indicate that PTH(1-84) increases glucose output in isolated hepatocytes but not in intact liver. It is suggested that the action of PTH(1-84) is blocked in intact liver by a yet unknown mechanism.

Calcium rather than cyclic AMP is an intracellular messenger of parathyroid hormone action on glycogen metabolism in isolated rat hepatocytes

The synthetic 1-34 fragment of human parathyroid hormone (1-34hPTH) stimulated glucose production in isolated rat hepatocytes. The effect of 1-34hPTH was dose-dependent and 10(10) M-1-34 hPTH elicited the maximum glucose output, which was approx. 80% of that by glucagon. Although 1-34hPTH induced a small increase in cyclic AMP production at concentrations higher than 10(-9) M, 10(-10) M-1-34hPTH induced the maximum glucose output without significant elevation of cyclic AMP. This is in contrast to the action of forskolin, which increased glucose output to the same extent as 10(-10) M-1-34hPTH by causing a 2-fold elevation of cyclic AMP. In addition to increasing cyclic AMP, 1-34hPTH caused an increase in cytoplasmic free calcium concentration ([Ca2+]c). When the effect of 1-34hPTH on [Ca2+]c was studied in aequorin-loaded cells, low concentrations of 1-34hPTH increased [Ca2+]c: the 1-34hPTH effect on [Ca2+]c was detected at as low as 10(-12) M and increased in a dose-dependent manner. 1-34hPTH increased [Ca2+]c even in the presence of 1 microM extracellular calcium, suggesting that PTH mobilizes calcium from an intracellular pool. In line with these observations, 1-34hPTH increased the production of inositol trisphosphate. These results suggest that: (1) PTH activates both cyclic AMP and calcium messenger systems and (2) PTH stimulates glycogenolysis mainly via the calcium messenger system.

Ca2+ concentration influences the hepatic extraction of bioactive human PTH-(1-34) in rats

The regulation of bioactive human parathyroid hormone [hPTH-(1-34)] hepatic extraction was studied in vitro by means of an isolated rat liver perfusion system. A standard buffer containing 20% red blood cells, 2% albumin, and variable concentrations of hPTH-(1-34) and Ca2+ was used in nonrecirculation experiments. Hepatic blood flow was kept constant at approximately 1.8 ml.g liver-1.min-1. hPTH in portal and hepatic veins was measured by a radioimmunoassay specific for hPTH-(1-34), and the results obtained were validated by gel chromatography analysis of the hormone measured. Results are expressed as mean +/- SD of five to six different experiments. In normocalcemic conditions (Ca2+ approximately 1.2 mmol/l), the hepatic extraction ratio of hPTH remained stable at 0.357 +/- 0.011 and 0.370 +/- 0.010 for hPTH-(1-34) concentrations of 0.156 +/- 0.002 and 1.314 +/- 0.014 pmol/ml; it decreased to 0.145 +/- 0.013 (P less than 0.001) for a hPTH-(1-34) concentration of 5.817 +/- 0.167 pmol/ml. Kinetics analysis of the normocalcemic data disclosed a Vmax of 1.971 +/- 0.18 pmol.min-1.g liver-1 and a Km of 1.410 +/- 0.39 pmol/ml. When hPTH-(1-34) concentration was kept stable with varying Ca2+ concentrations, elevated (1.62 +/- 0.01 mmol/l) Ca2+ gave an hepatic extraction ratio similar to normocalcemic conditions (0.335 +/- 0.014 vs. 0.357 +/- 0.011 mmol/l), whereas it significantly decreased in hypocalcemia (0.78 +/- 0.01 mmol/l) to 0.219 +/- 0.014 mmol/l (P less than 0.001). Kinetics were similar to normocalcemic conditions when Ca2+ concentration was elevated but appeared modified by hypocalcemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of short chain fatty acid administration on hepatic glucose, phosphate, magnesium and calcium metabolism

Intra peritoneal administration of the short chain fatty acids, acetate, propionate and butyrate, in amounts calculated to reach 20 mM in total body water were given to fed and 48 hour starved male Wistar rats. One half hour after administration, the livers were freeze-clamped and the hepatic contents of various intermediary metabolites were measured. The liver content of total glycolytic intermediates was elevated by short chain fatty acids. In fed animals, the portion of glycolysis from fructose 1,6-bisphosphate (FBP) to PEP was elevated 2 to 4 fold. In 48 hour starved animals, where gluconeogenesis is active, the portion of the gluconeogenetic pathway from FBP to glucose was elevated 1.5 to 3.5 fold with the exception of the butyrate treated animals where blood glucose was not elevated. The metabolites of the hexose-monophosphate pathway that were measured, namely 6-phosphogluconate, ribulose 5-phosphate and xylose 5-phosphate were increased in both fed and starved animals. The free cytoplasmic [NAD+]/[NADH], [NADP+]/[NADPH], and [epsilon ATP]/[epsilon ADP] X [epsilon Pi] ratios were all decreased in both fed and starved animals after short chain fatty acid administration. The liver content of calcium increased 1.2 to 2 fold in fed animals and 2 to 3 fold in starved animals while total liver magnesium was either unchanged or increased only 1.2 times. The liver pyrophosphate (PPi) content increased a minimum of 10 fold in fed animals and over 100 fold in starved animals. In all cases no PPi could be detected in vivo by 31P NMR even though in the starved rats the PPi levels approached those of ATP. The liver content of inorganic Pi increased 1.3 to 1.5 fold in fed animals and 1.5 to 2 fold in starved animals. The total "rapidly metabolizing" Pi pool, that includes adenine and guanine nucleotides, glycolytic and shunt intermediates, Pi and PPi increased 1.3 times in fed animals (from 13.8 mumole/g fresh weight) and 1.5 to 1.7 fold in starved animals (from 15.7 mumol/g fresh weight). The total phosphate taken up from blood and entering the rapidly turning over pool of liver phosphate ranged between 4 and 12 mumols/g of liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of parathyroid hormone in the glucose intolerance of chronic renal failure

Evidence has accumulated suggesting that the state of secondary hyperparathyroidism and the elevated blood levels of parathyroid hormone (PTH) in uremia participate in the genesis of many uremic manifestations. The present study examined the role of PTH in glucose intolerance of chronic renal failure (CRF). Intravenous glucose tolerance tests (IVGTT) and euglycemic and hyperglycemic clamp studies were performed in dogs with CRF with (NPX) and without parathyroid glands (NPX-PTX). There were no significant differences among the plasma concentrations of electrolytes, degree of CRF, and its duration. The serum levels of PTH were elevated in NPX and undetectable in NPX-PTX. The NPX dogs displayed glucose intolerance after CRF and blood glucose concentrations during IVGTT were significantly (P less than 0.01) higher than corresponding values before CRF. In contrast, blood glucose levels after IVGTT in NPX-PTX before and after CRF were not different. K-g rate fell after CRF from 2.86 +/- 0.48 to 1.23 +/- 0.18%/min (P less than 0.01) in NPX but remained unchanged in NPX-PTX (from 2.41 +/- 0.43 to 2.86 +/- 0.86%/min) dogs. Blood insulin levels after IVGTT in NPX-PTX were more than twice higher than in NPX animals (P less than 0.01) and for any given level of blood glucose concentration, the insulin levels were higher in NPX-PTX than NPX dogs. Clamp studies showed that the total amount of glucose utilized was significantly lower (P less than 0.025) in NPX (6.64 +/- 1.13 mg/kg X min) than in NPX-PTX (10.74 +/- 1.1 mg/kg X min) dogs. The early, late, and total insulin responses were significantly (P less than 0.025) greater in the NPX-PTX than NPX animals. The values for the total response were 143 +/- 28 vs. 71 +/- 10 microU/ml, P less than 0.01. There was no significant difference in the ratio of glucose metabolized to the total insulin response, a measure of tissue sensitivity to insulin, between the two groups. The glucose metabolized to total insulin response ratio in NPX (5.12 +/- 0.76 mg/kg X min per microU/ml) and NPX-PTX (5.18 +/- 0.57 mg/kg X min per microU/ml) dogs was not different but significantly (P less than 0.01) lower than in normal animals (9.98 +/- 1.26 mg/kg X min per microU/ml). The metabolic clearance rate of insulin was significantly (P less than 0.02) reduced in both NPX (12.1 +/- 0.7 ml/kg X min) and NPX-PTX (12.1 +/- 0.9 ml/kg X min) dogs, as compared with normal animals (17.4 +/- 1.8 ml/kg X min). The basal hepatic glucose production was similar in both groups of animals and nor different from normal dogs; both the time course and the magnitude of suppression of hepatic glucose production by insulin were similar in both in groups. There were no differences in the binding affinity, binding sites concentration, and binding capacity of monocytes to insulin among NPX, NPX-PTX, and normal dogs. The data show that (a) glucose intolerance does not develop with CRF in the absence of PTH, (b) PTH does not affect metabolic clearance of insulin or tissue resistance to insulin in CRF, and (c) the normalization of metabolism in CRF in the absence of PTH is due to increased insulin secretion. The results indicate that excess PTH in CRF interferes with the ability of the beta-cells to augment insulin secretion appropriately in response to the insulin-resistant state.

Primary hyperparathyroidism is associated with decreased insulin receptor binding and glucose intolerance

We studied insulin receptor-binding and carbohydrate and metabolism in 15 patients with symptomatic primary hyperparathyroidism in comparison with 20 healthy controls. Insulin binding to monocytes and erythrocytes was measured by radioreceptor-ligand-assay. Furthermore, patients and controls were characterized by testing oral (100 g glucose load) glucose tolerance as well as insulin tolerance (0.1U insulin/kg body weight). Compared with controls, patients with primary hyperparathyroidism exhibited marked hyperinsulinemia (P less than 0.01) and significantly higher glucose levels (P less than 0.01) after an oral glucose load. The glucose lowering effect of intravenous insulin was significantly diminished in primary hyperparathyroidism compared with controls (P less than 0.01). Receptor studies revealed a significantly lower (P less than 0.01) insulin binding to monocytes and to erythrocytes in patients with primary hyperparathyroidism compared with controls. The present data indicate an insulin-resistant state in primary hyperparathyroidism, which is caused at least in part, by a downregulation of insulin receptors.

Evidence of two forms of hepatic extraction of parathyroid hormone in dogs in vivo

The fractional hepatic extraction (FHE) of oxidized 125iodine-labeled bovine parathyroid hormone, 125I-bPTH-(1-84), is dependent on the integrity of the 28-48 sequence of the bPTH structure. A second type of FHE, related to the biologically active core of the hormone, is suggested by liver adenylate cyclase activation or cAMP production by bPTH-(1-84) or bPTH-(1-34). We have thus compared the FHE of biologically active bPTH-(1-84), bPTH-(1-34), and of 125I-[Nle8, Nle18, Tyr34]bPTH-(1-34) amide with that of oxidized 125I-bPTH-(1-84). The preparations, together with reference substances, were injected into the portal vein of anesthetized dogs and dilution curves obtained by counting the radioactivity or assaying the immunoreactivity present in hepatic vein samples. FHE was calculated from these curves. Results were validated by gel chromatography analysis of the 125I-radioactive or immunoreactive preparation injected and recovered. In six dogs, the FHE of bPTH-(1-84) was 59.9 +/- 8.9%, 23% higher than the value of 39.6 +/- 9.3% obtained for 125I-bPTH-(1-84) injected simultaneously (P less than 0.0005). This difference was similar to the FHE of 125I-[Nle8, Nle18, Tyr34]bPTH-(1-34) amide (16.4 +/- 7.2%) and bPTH-(1-34) (23.5 +/- 10.4%) measured in seven dogs. Analysis of the various gel chromatography profiles revealed that the entire FHE process could be explained by extraction of the appropriate peak of each preparation; a small amount of fragment was also generated across the liver in the case of bPTH-(1-84) (1.6%) and 125I-[Nle8, Nle18, Tyr34]-bPTH-(1-34) amide (2.8%), with a larger quantity in the case of bPTH-(1-34) (17%).(ABSTRACT TRUNCATED AT 250 WORDS)

Peripheral insulin resistance in primary hyperparathyroidism

Carbohydrate metabolism was investigated in 9 patients with symptomatic primary hyperparathyroidism. Before and after parathyroidectomy intravenous and oral glucose tolerance test, tolbutamide test, arginine infusion test and insulin tolerance test were performed. During intravenous and oral glucose tolerance tests, patients with primary hyperparathyroidism exhibited hyperinsulinemia and impaired glucose tolerance without normalization after surgery. Tolbutamide-induced induced insulin release did not differ pre- or postoperatively. After restoration of normocalcemia and normocalcemia and normophosphatemia we found significantly lower glucose and insulin levels following arginine infusion and a significantly increased hypoglycemic response to parenterally administered insulin, probably indicating partial improvement of glucose tolerance after surgery. Our findings suggest that biochemical abnormalities associated with primary hyperparathyroidism, like hypercalcemia, hypophosphatemia, and elevated parathyroid hormone levels may cause and sustain a form of endogenous insulin resistance, which consequently leads to hyperinsulinemia and to impaired glucose tolerance. Since hyperinsulinemia as well as impaired glucose tolerance seem to be only slowly and partially reversible in symptomatic primary hyperparathyroidism, these data could be considered as an additional argument for early surgical intervention in this disorder.

The short term hormonal control of cytoplasmic protein phosphorylation in hepatocytes from fed rats

Exposure of 32P-prelabelled isolated hepatocytes to vasopressin affected the phosphorylation of nine of the 26 phosphoproteins resolved by sodium dodecyl sulphate gel electrophoresis. Glucagon (2 nM) or cyclic AMP elicited significant changes in the phosphorylation of only four phosphoproteins. A very high concentration of glucagon (1000 nM) affected additional phosphoproteins. Insulin alone significantly increased the phosphorylation of a single protein. Vasopressin, A23187, glucagon and cyclic AMP all induced the dephosphorylation of a single phosphoprotein of mol. wt 20,000. The significance of these results with respect to the short-term control of hepatic metabolism is discussed.

Parathormone promotes glycogen formation from [14C]glucose in cultured osteoblast-like cells

Parathyroid hormone stimulates [U-14C]glucose incorporation into glycogen of cultured osteoblast-like calvaria cells. This effect is detectable only several hours after the addition of PTH and it is mimicked by dibutyryl cyclic AMP. In contrast to insulin (in pharmacological concentrations), PTH enhances glycogen formation only in calvaria cells, but not in fibroblasts. Insulin-like growth factor I in physiological concentrations promotes glycogen-synthesis shortly after addition.

Characteristics of bovine parathyroid hormone extraction by dog liver in vivo

The metabolic fate of various 125I-labeled preparations of bovine parathyroid hormone (bPTH) during a single passage through the liver was studied in anesthetized dogs. Each 125I-bPTH preparation was injected in the portal vein with 131I-albumin and 99mTc-erythrocytes, two reference indicators. A dilution curve was obtained for each indicator by counting the radioactivity present in tubes collected by hepatic vein sampling. Hepatic blood flow (HBF) and fractional hepatic extraction (FHE) were calculated from these curves. Extraction results were further validated by comparing the gel chromotography profile of the 125I injected and of the 125I recovered. The FHE of 125I after an injection of 125I-bPTH-(1--84) was 32.75 +/- 9.39% (mean +/- SD; n = 23) for a mean HBF of 48.18 +/- 11.83 ml . kg-1 . min-1. The FHE was independent of the dose of hormone injected (0.34-812 ng) but was inversely related to the HBF (r = -0.6768, P less than 0.001). 125I was not extracted after an injection of 125I-bPTH-(1--34) ( n = 8) or of 125I-bPTH-(34/43--84) (n = 5). On the other hand, after an injection of 125I-bPTH-(28--48), 18.7 +/- 5.5% (n = 8) of the 125I was extracted for an HBF of 47.3 +/- 17.0 ml . kg-1 . min-1. Analysis of the gel chromotography profiles further disclosed that 7.6 +/- 4.2% of the 125I-bPTH-(1--84) injected was transformed into carboxyl terminal fragments; 13.1 +/- 2.6% of the 125I-bPTH-(28--48) and 20.9 +/- 4.9% of the 125I-bPTH-(1--34) injected were also cleaved into smaller molecular weight products. We conclude that the integrity of the sequence 28--48 is important for the FHE of 125I-bPTH-(1--84). Although nonsaturable, this process is inversely related to the HBF. Liver inactivation of intact PTH or of its fragments also proceeds through rapid cleavage into smaller molecular weight products.

Peripheral metabolism of intact parathyroid hormone. Role of liver and kidney and the effect of chronic renal failure

The plasma disappearance rate (metabolic clearance rate) of administered intact parathyroid hormone (intact PTH) was analyzed in awake dogs with indwelling hepatic and renal vein catheters. The metabolic clearance rate (MCR) of intact PTH was found to be very rapid, 21.6 +/- 3.1 ml/min per kg in 11 normal dogs. The liver accounted for the greatest fraction of the MCR of intact PTH (61 +/- 4%) by virtue of an arterial minus venous (a - v) difference across the liver of 45 +/- 3%. The renal uptake of intact PTH accounted for 31 +/- 3% of the MCR of intact PTH. The renal a - v difference for intact PTH of 29 +/- 2% was significantly greater than the filtration fraction indicating renal uptake of intact PTH at sites independent of glomerular filtration. Together, the hepatic and renal clearances of intact PTH accounted for all but a small fraction of the MCR of intact PTH. The MCR of intact PTH, rendered biologically inactive by oxidation, was markedly decreased to 8.8 +/- 1 ml/min per kg. The a - v difference of oxidized intact PTH was reduced both in the liver and kidney. These data suggested that the high uptake rates of intact PTH are dependent, at least in part, upon sites recognizing only biologically active PTH. Chronic renal failure (CRF) decreased the MCR of intact PTH to 11.3 +/- 1.3 ml/min per kg (n = 10). Both the hepatic and renal a - v differences of intact PTH were reduced in dogs with CRF. This resulted in reductions in the hepatic and renal clearances of intact PTH. These studies identify the liver as a major extrarenal site of PTH metabolism affected by CRF. They suggest that CRF impairs the function of the major uptake sites involved in intact PTH metabolism.

Carbohydrate metabolism and uraemia-mechanisms for glycogenolysis and gluconeogenesis

Disturbances of carbohydrate metabolism during acute uraemia are characterized by the degradation of liver and muscle glycogen with a simultaneous activation of hepatic gluconeogenesis. After binephrectomy, the substitution of essential amino acids and keto analogues stimulate liver, but not skeletal muscle glycogen synthesis. Serine proves to be an optimal substrate for liver gluconeogenesis and muscle glycogen generation under acute uraemic conditions. Propranolol does not influence glycogenolysis of skeletal muscle in acutely uraemic rats. During starvation, acute uraemia leads to an increase of total carbohydrate content as well as of glycogen and glucose concentrations in heart muscle Alterations in carbohydrate contents are not observed in the kidney after ureter ligation. Enhanced glycogenolysis of skeletal muscle and liver during acute uraemia may be due to activation of phosphorylase kinase caused by the increased serum concentrations of various hormones (glucagon, catecholamines, parathormone) as well as free proteolytic activity, an increase of intracellular Ca2+-concentration and finally by alterations in the structure of contractile proteins.

Phosphate, calcium and lipid metabolism

Ca and Pi interact with lipid metabolism in several different ways. The enzymes of lipolysis and lipogenesis are sensitive to Ca. Ca and Pi concentrations affect insulin secretion and insulin action. Raising intestinal Ca lowers serum cholesterol and triglycerides presumably by sequestration of cholesterol and bile acids. Administration of vitamin D or increased sensitivity to vitamin D raise serum cholesterol levels. PTH acts primarily by activating adipose tissue lipase. Increased FFA delivery to the liver should increase hepatic lipoprotein synthesis. Experimental data in secondary hyperparathyroidism of renal insufficiency are consistent with this notion. Clinical observations in primary or renal secondary hyperparathyroidism, however, are not explicable by this simple schema.

Impact of hemodialysis on the abnormal glucose and alanine kinetics of chronic azotemia

Rates of alanine and glucose turnover and precursor-product interrelationships were determined in patients on chronic hemodialysis and in matched controls using simultaneous primed injection-continuous infusions of [U-14C] alanine and [2-3h] glucose. In eight chronically dialyzed patients studied before their first dialysis of the week, glucose turnover was 866 +/- 120 micromole/min (mean +/- SE); after their last dialysis of the week, glucose turnover was 880 +/- 63 micromole/min. These rates were 35% (p less than 0.05) and 37% (p less than 0.01) greater than rates observed in ten normal volunteers (642 +/- 28.3 micromole/min). Fasting glucose and insulin levels in dialyzing patients were unchanged from normal. Alanine turnover was increased predialysis (318 +/- 55.2 micromoles/min; p less than 0.01) and postdialysis (248 +/- 32.4 micromole/min; p less than 0.01) as compared to normal (168 +/- 14.3 micromole/min). In patients pre- and postdialysis, gluconeogenesis from alanine was increased to 34.6 +/- 10.9 micromole/min (p less than 0.05) and 39.0 +/- 6.33 micromole/min (p less than 0.05) compared to 20.9 +/- 1.63 micromole/min in normal subjects. We conclude that neither acute nor chronic hemodialysis corrects the increased glucose and alanine production and utilization and gluconeogenesis observed in chronic renal failure.

Abnormal carbohydrate metabolism in chronic renal failure. The potential role of accelerated glucose production, increased gluconeogenesis, and impaired glucose disposal

To delineate the potential role of disordered glucose and glucose-precursor kinetics in the abnormal carbohydrate metabolism of chronic renal failure, alanine and glucose production and utilization and gluconeogenesis from alanine were studied in patients with chronic compensated renal insufficiency and in normal volunteers. With simultaneous primed injection-continuous infusions of radiolabeled alanine and glucose, rates of metabolite turnover and precursor-product interrelationships were calculated from the plateau portion of the appropriate specific activity curves. All subjects were studied in the postabsorption state. In 13 patients with chronic renal failure (creatinine = 10.7+/-1.2 mg/100 ml; mean+/-SEM), glucose turnover was found to be 1,035+/-99.3 mumol/min. This rate was increased 56% (P = 0.003) over that observed in control subjects (664+/-33.5 mumol/min). Alanine turnover was 474+/-96.0 mumol/min in azotemic patients. This rate was 191% greater (P = 0.007) than the rate determined in control subjects (163+/-19.4 mumol/min). Gluconeogenesis from alanine and the percent of glucose production contributed by gluconeogenesis from alanine were increased in patients with chronic renal failure (192% and 169%, respectively) as compared to controls (P < 0.05 for each). Alanine utilization for gluconeogenesis was increased from 40.2+/-3.86 mumol/min in control subjects to 143+/-39.0 mumol/min in azotemic patients (P < 0.05). The percent of alanine utilization accounted for by gluconeogenesis was not altered in chronic renal insufficiency. In nondiabetic azotemic subjects, mean fasting glucose and immunoreactive insulin levels were increased 24.3% (P = 0.005) and 130% (P = 0.046), respectively.These results in patients with chronic renal failure demonstrate (a) increased glucose production and utilization, (b) increased gluconeogenesis from alanine, (c) increased alanine production and utilization, and (d) a relative impairment to glucose disposal. We conclude that chronic azotemia is characterized by increased rates of glucose and glucose precursor flux and by a relative impairment to glucose disposal. These findings may suggest an underlying hepatic and peripheral insensitivity to the metabolic action of insulin in patients with chronic renal insufficiency.

Selective uptake of intact parathyroid hormone by the liver: differences between hepatic and renal uptake

Hepatic and renal extraction of immunoreactive parathyroid hormone (i-PTH) was studied in awake dogs with explanted kidneys and chronic indwelling hepatic vein catheters. After a single injection of bovine PTH 1-84 (b-PTH 1-84), hepatic arteriovenous (A-V) differences for immunoreactive PTH (i-PTH) was 39% at 2 min after injection but decreased to 0% by 25 min, despite high levels of i-PTH in the arterial circulation. Gel filtration of arterila and hepatic venous samples obtained when hepatic A-V differences for i-PTH were demonstrable revealed hepatic uptake of the intact hormone and addition of a smaller COOH-terminal fragment, eluting just after the intact hormone, to the hepatic venous blood. Gel filtration of samples obtained 20-30 min after injection of b-PTH was demonstrable) revealed no detectable intact hormone in the circulation. Levels of COOH-terminal fragments of the hormone at the time were identical in arterial and hepatic venous samples. In additional experiemtns no hepatic A-V difference was observed after the injection of the synthetic bovine PTH 1-34 (syn b-PTH 1-34). By comparison there was a demonstrable A-V difference of 20% across the kidney for both intact PTH and COOH-terminal fragments that persisted until i-PTH disappeared from the circulation. The kidney also demonstrated an A-V difference of 22% after injection of syn b-PTH 1-34. These studies demonstrate selective extraction of intact PTH but not of its fragments by the liver. The kidney, on the other hand, extracted the intact hormone and both COOH and NH2 terminal fragments. The studies demonstrate that the kidney was the only organ of those examined that detectably removed the fragments of PTH from the circulation.

Studies of hormonal regulation of metabolism using isolated hepatocytes

A number of enzymatic methods have been developed to prepare hepatocytes using collagenase and hyaluronidase. However, best cell preparations are obtained by using only low concentrations of collagenase and exposing the liver to the enzyme for a very short period of time. These isolated cells with intact cell membranes and large numbers of microvilli on the cell surface respond to hormones at physiological concentrations suggesting that these microvilli contain hormone receptors. In addition, high glycogen content is essential to maintain the in vivo metabolic characteristics of the hepatocytes suggesting that intracellular glycogen plays an important role in the hormonal regulation of metabolism in hepatocytes. Studies with glucagon and insulin on carbohydrate metabolism show that the molar ratios of these hormones control gluconeogenesis and glycogenolysis. Furthermore, in vitro addition of insulin stimulates glycogen synthesis and activates glycogen synthase. Insulin also stimulates protein synthesis in cells containing high glycogen and maintains more normal parallel strands of polyribosomes. Studies with isolated hepatocytes from diabetic, hypophysectomized and adrenalectomized animals show a reduced glucagon response to glycogenolysis. This lack of glucagon response was not due to reduction in glycogen levels. Other hormones such as somatostatin and parathyroid also give rise to alterations in carbohydrate metabolism in isolated hepatocytes.

On the lipolytic action of parathyroid hormone in man

An investigation was carried out to determine whether bovine PTH stimulates lipolysis in human fat tissue, whether this action is mediated by cyclic adenosine 3', 5'-monophosphate and whether the N-terminal 1-34 peptide of bovine PTH is responsible for the lipolytic effect. Studies were also performed to determine if parathyroid extract (PTE) produces lipolysis in normal subjects and in patients with pseudohypoparathyroidism in whom there is a defect in the adenylate system in response to PTH in the renal cortex and presumably in the skeletal system as well. It was found that highly purified bovine PTH in the concentration range between 10(-9) M and 10(-5) M stimulated lipolysis in vitro by human fat in a dose-dependent manner. Significant increases in glycerol production were observed at concentrations of PTH as low as 10(-9) M and maximal increases were seen at 10(-6) M. The hormone significantly increased the concentration of cyclic adenosine 3' ,5'-monophosphate in fat tissue. The synthetic N-terminal 1-34 peptide of bovine PTH was as effective as the native hormone in stimulating glycerol production at a concentration of 10(-9) M-10(-6) M. PTE, 100 mU per kg per min for 30 min given intravenously, produced transient increases in the concentration of plasma free fatty acid in each of eight normal subjects, three patients with hypoparathyroidism and eight patients with pseudohypoparathyroidism. Purified bovine PTH also increased plasma free fatty acid in each of two normal subjects. It is concluded that PTH stimulates lipolysis in human subcutaneous fat, that this action of the hormone is mediated through cyclic adenosine 3', 5'-monophosphate and that the N-terminal 1-34 peptide portion of the hormone is responsible for this lipolytic action. Further, PTE stimulates lipolysis in vivo in man. There appears to be no defect in the adenylate cyclase system in the fat cell in response to PTH in patients with pseudohypoparathyroidism.

Studies on gluconeogenesis, protein synthesis and cyclic AMP levels in isolated hepatocytes from alloxan diabetic rats

Alloxan diabetic rats maintained on protamine zinc insulin for two weeks were used for these studies. Hepatocytes were isolated from these rats at various time intervals after withdrawal of insulin (0, 48, 72 and 96 hr). Gluconeogenesis with various concentrations of lactate and fructose was studied. Both lactate and fructose stimulated gluconeogenesis and showed progressive increases in glucose production up to 72 hr after the insulin withdrawal. Glucose production decreased at 96 hr. Protein synthesis in isolated hepatocytes from diabetic liver cells, as measured by the incorporation of radioactive isoleucine, valine and phenylalanine into protein, showed a decrease (5- to 6-fold) with time after insulin withdrawal. Glucagon (10(-6)M) alone increased cyclic AMP levels 10-fold in liver cells, in isolated cells from rats maintained on insulin (0 hr) or from rats withdrawn from insulin for 48 hr. The ability of glucagon to elevate cyclic AMP levels in isolated diabetic liver cells decreases 72 hr following insulin withdrawal.

Hormone responsiveness of plasma membrane-bound enzymes in normal and regenerating rat liver

The hormonal responsiveness of plasma membrane-bound enzymes (Na-+-K-+)-ATPase and adenylate cyclase has been investigated in normal and regenerating rat liver. (Na-+-K-+)-ATPase basal activity is not affected by surgery and only slightly affected by partial hepatectomy; its response to epinephrine and cyclic AMP is decreased only 15 h after hepatectomy. Adenylate cyclase activity of plasma membranes from untreated animals is stimulated by parathyroid hormone and thyroxine; partial hepatectomy increased basal activity as well as the stimulation exerted by the aforementioned hormones, when glucagon and epinephrine sensitivity is essentially unaltered.