Hepatic clearance of human growth hormone

Altered endogenous growth hormone secretory kinetics and diurnal GH-binding protein profiles in adults with chronic liver disease

OBJECTIVE

Increased serum GH concentrations and GH responses to a variety of stimuli have been reported in patients with chronic liver disease (CLD). We investigated the pulsatile pattern of endogenous GH release and GH-binding protein (GHBP) and insulin-like growth factor-I (IGF-I) diurnal profiles in adults with cirrhosis, in comparison with healthy, matched control subjects.

DESIGN

Case-control, cross-sectional.

PATIENTS

Seven patients with biopsy proven cirrhosis, and sex, age, height, weight and oestrogen status matched controls.

MEASUREMENTS

Serum immunoreactive GH concentrations in samples collected at 20-minute intervals for 24 hours were analysed using a multi-parameter deconvolution method to simultaneously resolve endogenous GH secretory and disappearance rates. Diurnal patterns of GHBP (specific immunoprecipitation method) and serum IGF-I (RIA after acid-ethanol extraction) were assessed.

RESULTS

The mean daily GH secretion rate in patients with CLD was increased (210 +/- 93 vs 100 +/- 55 mU/I/day; P = 0.025), and GH disappearance half-time was prolonged (43 +/- 10 vs 24 +/- 9 min; P = 0.006) compared to controls. Detectable GH secretory bursts were more frequent in patients with CLD (10 +/- 1 vs 6 +/- 3/day; P = 0.038), but of similar mean mass (21 +/- 10 vs 17 +/- 8 mU/I) compared to controls. In patients with CLD, mean serum GHBP was slightly lower (63 +/- 36 vs 71 +/- 14% pooled control; P > 0.1). Fasting serum IGF-I concentrations (after size-exclusion HPLC) were lower in the patients with CLD (13 +/- 5 vs 21 +/- 2 nmol/l; P < 0.0001). Multiple regression analysis showed that GH secretion rate was increased in patients with CLD with higher Child's classifications (R2 = 0.86; P = 0.002) and with lower serum IGF-I concentrations measured after HPLC (R2 = 0.11; P = 0.044).

CONCLUSIONS

Adults with chronic liver disease have (1) increased total daily GH secretion rates, which appear to be influenced by disease severity and diminished serum IGF-I-mediated negative feedback; (2) markedly impaired endogenous GH clearance, possibly reflecting changes in hepatic GH-receptor status; and (3) GHBP levels which do not correlate with GH kinetics or serum IGF-I concentrations.

Serum growth hormone-binding protein, insulin-like growth factor-I, and growth hormone in patients with liver cirrhosis

We determined serum growth hormone-binding protein (GHBP), insulin-like growth factor-I (IGF-I), and growth hormone (GH) levels in patients with cirrhosis and in age-matched control subjects, and investigated their relationships. Serum GHBP levels in cirrhotic patients (14.6% +/- 3.9%) (means +/- SD) were significantly lower than those in normal subjects (20.4% +/- 4.7%). GHBP levels had positive correlations with cholinesterase (r = .58, P less than .001) and Normotest (r = .66, P less than .001), both of which represent liver function in cirrhotic patients. Basal GH levels in cirrhotic patients (range, 0.35 to 13.0 micrograms/L; median, 3.9 micrograms/L) were significantly higher than those in normal subjects (0.015 to 6.0 micrograms/L; 0.19 microgram/L). GHBP levels in cirrhotic patients correlated positively with IGF-I levels (r = .39, P less than .01), and negatively with GH levels (r = -.33, P less than .01). These results may indicate that the serum GHBP level reflects the number of hepatic GH receptors, and that the high basal GH level observed in cirrhotic patients is, at least in part, attributable to decreased clearance of GH by these receptors.

Metabolic zonation of the liver: regulation and implications for liver function

Liver parenchyma shows a remarkable heterogeneity of the hepatocytes along the porto-central axis with respect to ultrastructure and enzyme activities resulting in different cellular functions within different zones of the liver lobuli. According to the concept of metabolic zonation, the spatial organization of the various metabolic pathways and functions forms the basis for the efficient adaptation of liver metabolism to the different nutritional requirements of the whole organism in different metabolic states. The present review summarizes current knowledge about this heterogeneity, its development and determination, as well as about its significance for the understanding of all aspects of liver function and pathology, especially of intermediary metabolism, biotransformation of drugs and zonal toxicity of hepatotoxins.

Plasma growth hormone and digital clubbing in carcinoma of the bronchus

Growth hormone is a secretory product of some primary bronchial neoplasms and has been associated with the development of hypertrophic pulmonary osteoarthropathy and acromegaly in occasional patients with such tumours; it has not, however, generally been considered important in the pathogenesis of digital clubbing. Plasma levels of growth hormone at the time of diagnostic bronchoscopy were measured in 60 patients with histologically proved bronchial carcinoma, divided according to whether clubbing was present (n = 21) or absent (n = 39), and in 13 control subjects undergoing the same procedure but with no neoplasm. The median plasma level of growth hormone ( and interquartile range) was 0.74 (0.5-1.0) mU/l in five control subjects with no pulmonary disease, 0.83 (0.4-1.3) mU/l in eight subjects with non-neoplastic pulmonary disease, 1.1 (0.6-3.3) mU/l in patients with carcinoma but without clubbing, and 3.1 (0.8-9.0) mU/l in 21 patients with carcinoma and clubbing. The highest growth hormone level was seen in a patient with a small cell carcinoma and pronounced clubbing; levels had fallen to normal by the time chemotherapy was completed and clubbing completely resolved. Thus growth hormone or a similar substance might have a role in the pathogenesis of clubbing in patients with bronchial neoplasms.

Abnormal growth hormone dynamics in chronic liver disease do not depend on severe parenchymal disease

Abnormal basal serum levels of growth hormone (GH) and abnormal GH dynamics have been observed in patients with alcoholic cirrhosis (AC). To further characterize these abnormalities, patients with AC or schistosomal hepatic fibrosis (SHF) were evaluated. The former patients have parenchymal liver disease, portal hypertension, and portosystemic shunting. SHF, in contrast, is characterized by periportal fibrosis with minimal or no parenchymal cell disease, portal hypertension, and portosystemic shunting. We studied 20 patients with SHF and normal stature and 15 patients with AC. In these two groups of patients, basal serum GH was higher than normal (P less than .01). A paradoxical increase in GH was observed during the oral glucose tolerance test (OGTT) in 55% of SHF and in 40% of AC patients. Significant GH elevation followed thyrotropin-releasing hormone (TRH) administration in 80% of SHF and 66% of AC patients, but not in normals. Serum nonsuppressible insulin-like activity (NSILA) and serum somatomedin C (Sm-C) levels were reduced significantly in both groups. In SHF patients, the paradoxical increase in GH during OGTT correlated inversely with Sm-C (r = -.6, P less than .05). We conclude that (1) abnormal GH secretion occurs in both SHF and AC, (2) serum Sm-C and NSILA are diminished in both forms of liver disease, and (3) portosystemic shunting of blood appears to be the important pathology shared by both forms of liver disease.

Impaired glucose tolerance and growth hormone in chronic liver disease

Of 30 patients with chronic liver disease 16 showed some degree of impairment of glucose tolerance, and 16 patients had lack of suppression of raised fasting growth hormone levels or showed an anomalous rise after oral glucose. No relationship, however, existed between the state of glucose tolerance and the presence of abnormal growth hormone levels. Plasma glucose in those with normal growth hormone response at 0, 1/2, 1, 1-1/2, and 2 hours, after 50 g glucose were 5.55 +/- 0.41 mmol/l, 8.71 +/- 0.59, 10.66 +/- 0.99, 10.28 +/- 1.37, 8.90 +/- 1.40 (mean +/- SEM; n = 14). Under the same conditions those with abnormal growth hormone responses showed values of 5.32 +/- 0.59, 7.83 +/- 0.81, 9.41 +/- 0.95, 9.46 +/- 0.99, 8.69 +/- 0.98. At no time were the differences significantly different as judged by Student's t test. Measurement of serum insulin indicated a relative deficiency in patients with impaired tolerance. It is concluded that the abnormal growth hormone is not directly responsible for the impaired glucose tolerance.

The role of growth hormone in the glucose intolerance of uremia

The fasting plasma growth hormone (GH) concentration and the plasma growth hormone response to sustained hyperglycemia was examined in 8 chronically uremic subjects before and after hemodialysis employing the hyperglycemia clamp technique. The plasma glucose concentration was acutely raised and maintained at +125 mg/100 ml above basal levels. Since the glucose concentration was held constant, the glucose infusion rate is an index of glucose metabolism (M) and M divided by the plasma insulin response (I) is a measure of tissue sensitivity to insulin. Predialysis, the fasting GH concentration, 4.0 +/- 1.0 ng/ml, was significantly greater than controls, 0.3 +/- 0.1 ng/ml (p less than 0.01), and failed to suppress normally following sustained hyperglycemia. Both M, 4.23 +/- 0.36 mg/kg x min, and M/I, 5.05 +/- 0.79 mg/kg x min per microU/ml, were significantly reduced compared to controls (p less than 0.001). There was no correlation between either the fasting GH concentration or the GH response to sustained hyperglycemia and either M or M/I. Following dialysis both M, 6.30 +/- 0.64 mg/kg x min, and M/I, 8.39 +/- 1.06 mg/kg x min per microU/ml, increased (p less than 0.01) without significant change in either the fasting GH level, 4.0 +/- 1.2 ng/ml, or the plasma GH response to hyperglycemia. It is concluded that while deranged GH physiology is a common accompaniment of the uremic state, it is not responsible for the glucose intolerance and tissue insensitivity to insulin observed in uremia.

Carbohydrate metabolism in liver disease

Most forms of liver disease are probably associated with impaired gluconeogenesis, although hypoglycaemia is rarely an important clinical feature. Blood concentrations of the gluconeogenic precursors, lactate, glycerol and alanine are elevated although, in certain situations, alanine levels may be decreased. Abnormal glucose tolerance is present in both acute and chronic liver disease, but is usually not of clinical importance. The mechanism of glucose intolerance remains uncertain, with diminished hepatocyte mass, portal diversion and insulin resistance the major postulates. Indeed, the importance of the liver in disposing of an oral glucose load, is still questioned. Both hyperinsulinism and hypoinsulinism are found in liver disease, with hyperinsulinism common in cirrhosis and acute viral hepatitis. This is accompanied by insulin resistance. The hyperinsulinism is probably due to defective hepatic clearance of insulin rather that to over-production. The cause of the insulin resistance remains to be established. Glucagon levels are raised and may contribute to this resistance. Growth hormone levels are also increased but are associated with low somatomedin levels and the role of growth hormone in insulin resistance is therefore questionable. Future developments include use of new animal models, studies of biopsy specimens and studies of hepatic hormone receptors.

Prolactin in hypertensive pregnancy

Plasma prolactin levels were measured in 68 pregnant women with hypertension at 32 weeks gestation. They were raised in pregnancies with pre-eclamptic features, most significantly in women with a rising plasma urate level. No correlation was found between the level of the untreated blood pressure and prolactin. Proteinuria did not influence prolactin levels independently of changes in the plasma urate. The differences in prolactin levels could not be ascribed to the drugs administered.