Disappearance rates of plasma growth hormone after intravenous somatostatin in renal and liver disease

Insulin-like growth factors in normal and diseased kidney

This article reviews the physiology of the insulin-like growth factor (IGF) system in the kidney and the changes and potential role of this system in selected renal diseases. The potential therapeutic uses of recombinant human IGF-I for the treatment of acute and chronic kidney failure are briefly discussed.

Growth hormone/insulin-like growth factor system in children with chronic renal failure

Disturbances of the somatotropic hormone axis play an important pathogenic role in growth retardation and catabolism in children with chronic renal failure (CRF). The apparent discrepancy between normal or elevated growth hormone (GH) levels and diminished longitudinal growth in CRF has led to the concept of GH insensitivity, which is caused by multiple alterations in the distal components of the somatotropic hormone axis. Serum levels of IGF-I and IGF-II are normal in preterminal CRF, while in end-stage renal disease (ESRD) IGF-I levels are slightly decreased and IGF-II levels slightly increased. In view of the prevailing elevated GH levels in ESRD, these serum IGF-I levels appear inadequately low. Indeed, there is both clinical and experimental evidence for decreased hepatic production of IGF-I in CRF. This hepatic insensitivity to the action of GH may be partly the consequence of reduced GH receptor expression in liver tissue and partly a consequence of disturbed GH receptor signaling. The actions and metabolism of IGFs are modulated by specific high-affinity IGFBPs. CRF serum has an IGF-binding capacity that is increased by seven- to tenfold, leading to decreased IGF bioactivity of CRF serum despite normal total IGF levels. Serum levels of intact IGFBP-1, -2, -4, -6 and low molecular weight fragments of IGFBP-3 are elevated in CRF serum in relation to the degree of renal dysfunction, whereas serum levels of intact IGFBP-3 are normal. Levels of immunoreactive IGFBP-5 are not altered in CRF serum, but the majority of IGFBP-5 is fragmented. Decreased renal filtration and increased hepatic production of IGFBP-1 and -2 both contribute to high levels of serum IGFBP. Experimental and clinical evidence suggests that these excessive high-affinity IGFBPs in CRF serum inhibit IGF action in growth plate chondrocytes by competition with the type 1 IGF receptor for IGF binding. These data indicate that growth failure in CRF is mainly due to functional IGF deficiency. Combined therapy with rhGH and rhIGF-I is therefore a logical approach.

Metabolic clearance of recombinant human growth hormone in health and chronic renal failure

Despite the increasing therapeutic use of recombinant human growth hormone (rhGH), its metabolic clearance has not been investigated in detail. To evaluate the kinetics of rhGH as a possible function of GH plasma concentration and glomerular filtration rate (GFR), we investigated the steady state metabolic clearance rate (MCR), disappearance half-life, and apparent volume of distribution of rhGH at low and high physiological as well as supraphysiological plasma GH levels during pharmacological suppression of endogenous GH secretion in human subjects with normal and reduced renal function. GH in plasma and urine was determined by an immunoradiometric assay, and GFR by inulin clearance. In all subjects MCR decreased and plasma half-life increased with increasing plasma GH concentrations (P < 0.001). MCR of rhGH was approximately half in patients with chronic renal failure at each GH level and plasma half-life was increased by 25-50%. Allowing for the linear dependence of MCR on GFR and assuming single-compartment distribution, the estimated renal fraction of total MCR was 25-53 and 4-15% in controls and patients, respectively. Saturation of extrarenal disposal of GH was suggested by an inverse hyperbolic relationship between extrarenal MCR and plasma GH concentrations in all subjects. Fractional GH excretion was up to 1,000-fold higher in patients than in controls. We conclude that MCR of hGH is a function of plasma GH concentrations and GFR. Extrarenal elimination is saturable in the upper physiological range of GH concentrations, whereas renal MCR is independent of plasma GH levels. The kidney handles GH like a microprotein involving glomerular filtration, tubular reabsorption, and urinary excretion.

Metabolic clearance rate of biosynthetic growth hormone after endogenous growth hormone suppression with a somatostatin analogue in chronic renal failure patients and control subjects

OBJECTIVE

Several disturbances in the regulation of growth hormone secretion have been reported in chronic renal failure. The general assumption is that an altered hormonal clearance is at the basis of such GH alterations. Nevertheless, details of GH elimination kinetics in uraemia are not available. To clarify the role played by the kidney in its catabolism, GH elimination kinetics were studied in uraemic and control subjects after suppression of endogenous secretion of GH.

DESIGN

In all subjects an analogue of somatostatin (octreotide 100 micrograms i.v.) was administered as a bolus before GH (-60 minutes). Sixty minutes later (0 min) biosynthetic GH (0.5 IU = 200 micrograms) was administered intravenously as a bolus.

PATIENTS

Six chronic renal failure patients before dialysis and six matched normal volunteers.

MEASUREMENTS

Plasma GH levels were measured by an immunoradiometric assay.

RESULTS

In both groups, the GH elimination curve fitted a bi-exponential model. The calculated plasma volume and GH concentration at 0 minutes were similar in both groups, while uraemic patients presented a reduced distribution volume. In all parameters measuring GH elimination, chronic renal failure patients showed an impaired clearance. In fact, the area under the curve (mU/l/150 min) was 912.8 +/- 170.6 for controls and 3524.8 +/- 642.8 for chronic renal failure patients (P < 0.005). The GH half-life was 13.8 +/- 1.6 and 26.4 +/- 2.9 minutes for control and uraemic subjects respectively (P < 0.05), and the metabolic clearance rate MCR (ml/min/m2) was 265.3 +/- 50.6 for controls and 79.9 +/- 16.4 for uraemic patients (P < 0.05). The GH mean residence time (minutes) (MRT) calculated was 12.0 +/- 0.5 for controls and 31.8 +/- 4.6 for chronic renal failure patients (P < 0.05).

CONCLUSIONS

Contrary to previous estimates, GH elimination kinetics follows a bi-exponential model and in normal subjects the GH half-life of the second phase is 13.8 +/- 1.6 minutes. Uraemic patients have impaired clearance of GH, suggesting that the kidney plays a role in GH disposal. However, the degree of impairment does not fully explain the alterations in GH secretion previously described in chronic renal failure.

Growth failure in renal disease

Children with congenital CRF lose height potential mainly during two distinct growth periods; infancy and puberty. The onset of puberty is late, the pubertal growth spurt starts from a very low rate of growth velocity, and peak height velocity is lower than normal although the absolute increment of height velocity is comparable to the increment in normal children. Furthermore, the duration of pubertal growth spurt is reduced in CRF. During infancy and early childhood, malnutrition, electrolyte disturbances and metabolic acidosis are the main contributing factors for reduced growth, whereas hormonal disturbances are responsible for growth impairment during puberty. There is evidence for resistance to growth hormone in CRF, which starts in early childhood and persists until the end of puberty. Growth hormone secretion is normal in CRF, but GH half-life is prolonged. The binding activity of the stable growth hormone binding protein is reduced, which points to a low receptor expression in the liver. Hepatic IGF-I production is diminished. However, the serum concentration of IGF binding proteins (IGFBP) is increased due to reduced renal filtration of low molecular weight subunits of IGFBP. Mainly, the accumulation of IGFBP-3 leads to increased IGF-binding capacity of the uraemic serum. Both, reduced IGF-I production and increased binding of IGF to IGFBP-3 result in decreased IGF bioactivity. During infancy, loss of growth potential can be prevented by adequate nutrition. Later in life, catch-up growth cannot be induced by nutritional intervention or dialysis. Renal transplantation allows catch-up growth in only a small percentage of patients. Treatment with one IU rhGH/kg/week improves growth velocity and growth in all stages of renal disease. The mean increment of height in prepubertal children is +1.5 SDS within two treatment years. The effect of rhGH during puberty as well as the effect on final height remain to be determined.

Pulsatile growth hormone secretion in peripubertal patients with chronic renal failure. Cooperative Study Group on Pubertal Development in Chronic Renal Failure

The pubertal growth spurt has been associated with changes of physiologic pulsatile growth hormone (GH) secretion, and abnormalities of the central regulation of GH release have been found by pharmacologic testing in patients with chronic renal failure. To assess the characteristics of GH pulsatility in chronic renal failure and their relationship to pubertal growth, we studied spontaneous nighttime GH plasma profiles in 80 patients (61 boys) aged 10 to 20 years receiving conservative treatment (n = 29) or dialysis (n = 18) or after renal transplantation (n = 33). Tanner genital stages 1 to 4 in boys and breast stages 1 to 3 in girls were represented. Growth hormone pulse analysis was performed by the PULSAR algorithm. Growth hormone concentration profiles were pulsatile in each patient. Growth hormone mean and baseline levels and pulse amplitudes were higher in patients receiving conservative or dialysis treatment than in patients who had undergone renal transplantation. Peak frequency was similar in all treatment groups in boys but higher in girls who had undergone transplantation than in girls receiving conservative or dialysis treatment. Growth hormone peak amplitude and mean levels were lowest in patients in late puberty. The physiologic elevation of GH amplitudes around midpuberty was observed in boys receiving conservative and dialysis treatment but not after transplantation. Growth hormone mean and baseline levels were positively correlated with plasma androgen levels in boys. Growth hormone peak amplitude was correlated with 6-month height velocity after transplantation but not in patients receiving conservative treatment or dialysis. A strong inverse relationship was observed between GH peak amplitude and corticosteroid dosage in patients undergoing transplantation. The lack of relationship between circulating GH levels and growth in patients receiving conservative or dialysis treatment is compatible with end-organ hyporesponsiveness to GH. Pubertal growth failure despite successful transplantation appears to be related to steroid-induced GH hyposecretion.

Increased growth hormone response to growth hormone releasing hormone induced by erythropoietin in uraemic patients

This study was designed to assess the response of growth hormone (GH) to growth hormone releasing hormone (GHRH) and the possible interaction of acutely administered recombinant human erythropoietin (rhEPO) on GH response to GHRH in a group of uraemic patients. Eight patients on maintenance haemodialysis, not previously treated with rhEPO, and six healthy controls were tested with GHRH (100 micrograms i.v. in bolus), and with GHRH (100 micrograms i.v. in bolus) plus rhEPO (40 U/kg in constant infusion for 30 min) on different days. GHRH injection provoked a GH release in five out of eight uraemic patients; the overall mean response did not differ significantly from the GH response obtained in controls (P = 0.30). Erythropoietin infusion significantly increased GH release after GHRH (P less than 0.01 at 15, 30, 45, 60 min after GHRH injection) in uraemic patients; in controls, on the contrary, stimulation with GHRH plus rhEPO did not induce a greater increase of GH release compared with that observed after GHRH alone (mean GH peak 37.66 +/- 7.68 mU/l after GHRH; and 38.0 +/- 9.18 mU/l after GHRH plus rhEPO; P greater than 0.5). In this study acutely administered rhEPO significantly potentiated the GH response to GHRH in uraemic patients whereas the same effect was not demonstrable in subjects with normal renal function.

Disturbance of growth hormone--insulin-like growth factor axis in uraemia. Implications for recombinant human growth hormone treatment

The growth hormone/insulin-like growth factor (IGF) axis is disturbed in uraemia. Elevated plasma growth hormone (GH) levels despite diminished growth suggest GH resistance, which may be due in part to a decreased expression of the growth hormone receptor at the cell membrane. The hepatic production of IGFs under the control of GH is impaired. Furthermore, there is an excess of IGF-binding protein over total IGF as a consequence of reduced renal clearance of low-molecular-weight subunits of the IGF-binding protein (IGF-BP). This results in an absolute (diminished production) and a relative (low bioavailability) deficiency of IGF. Recombinant human growth hormone (rhGH) in doses of 4 IU/m2 per day is able to induce catch-up growth in children with preterminal and terminal renal failure. The growth stimulation of exogenous GH is attributed to its potency to increase the ratio of IGF-I to IGF-BP, followed by a normalization of IGF bioactivity. In renal transplanted children growth is not only disturbed by decreased renal function but also by steroid treatment. Corticosteroids are responsible for catabolism, for suppression of pituitary GH secretion and for inhibition of local production of IGFs. Exogenous rhGH is able to counteract these growth-inhibiting effects. However, it remains to be seen whether long-term GH treatment definitely improves final adult height.

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.

Growth hormone hyperresponsiveness to growth hormone-releasing hormone in patients with severe liver cirrhosis

Patients with severe liver disease often have high baseline plasma GH levels and/or paradoxical GH release in response to several secretagogues, e.g. TRH. In this paper, we have investigated in a group of cirrhotic patients the GH response to GH-releasing hormone (GHRH) and evaluated the effectiveness of GHRH to cause GH release in TRH responder and non-responder patients. Ten patients and seven age- and sex-matched control subjects were given bolus injections of GHRH (0.1 and 1.0 microgram/kg i.v. on separate occasions). GHRH 0.1 microgram/kg failed to cause a GH response in both control and cirrhotic subjects, but 1.0 microgram/kg caused a significantly higher GH response in patients than in controls. Evaluation of the GH response curve after GHRH revealed a similar pattern of secretion in the TRH-responders (four subjects) and non-responders (six subjects). These results suggest that the enhanced GH responsiveness to GHRH in cirrhotic patients may contribute to their high baseline GH levels and/or secretory rate, and the mechanism(s) of the paradoxical GH rise after TRH seems to be separate from that for GH hyperresponsiveness to GHRH.

Hypothalamic-pituitary dopaminergic function in hepatic failure in man

The growth hormone (GH) response to apomorphine HCl (Apo) (0.75 mg sc), a dopamine (DA) receptor agonist, was assessed in healthy chronic alcoholics without cirrhosis (N = 20) and in patients with alcoholic cirrhosis both with (N = 5) and without (N = 14) hepatic encephalopathy (HE). A significant number of cirrhotic patients with (P less than 0.004) and without (P less than 0.002) HE had an impaired GH response (peak increment less than 5 ng/ml) compared with non-cirrhotic individuals. An impaired GH response was independent of the presence of HE. The magnitude of the GH response was unrelated to plasma oestrone, oestradiol, or progesterone concentrations but was significantly correlated with plasma testosterone levels (P less than 0.01). None of the patients with an abnormally low testosterone concentration showed a normal GH response. None of the subjects with HE showed an arousal response to Apo. These results suggest that DA receptor sensitivity is decreased in liver cirrhosis and that this decrease is related to inadequate circulating levels of testosterone. The occurrence of HE is independent of impaired DA function. The present study only evaluates DA function in the hypothalamic-pituitary axis and therefore may not reflect changes in other regions of brain.

Effect of protein intake and dialysis on the abnormal growth hormone, glucose, and insulin homeostasis in uremia

To evaluate the role of protein intake in the altered growth hormone (GH) secretion of chronic renal failure, GH responses to mild exercise and to an oral glucose tolerance test were measured in ten uremic patients ingesting both low and normal protein diets. To delineate the effect of uremia on any interaction between GH and protein intake, tests were performed before dialysis, after daily dialyses for 3-4 days and after withholding dialysis for 3-4 days. Results were as follows: (1) exercise-stimulated GH release was increased compared to controls; (2) protein intake did not alter GH secretion, (3) basal GH concentrations were significantly correlated with creatinine levels and were significantly lower after dialysis, (4) dialysis did not improve the oral glucose tolerance test, (5) there was no correlation between glucose tolerance and exercise-stimulated GH levels, basal GH concentrations, or the sum of GH values after glucose, and (6) dialysis significantly increased the insulin response to glucose.

CONCLUSIONS

In chronic renal failure enhanced GH secretion is not affected by protein intake, does not cause glucose intolerance, and may be related to the degree of uremia. Dialysis does not improve glucose tolerance, but does increase glucose-stimulated insulin release suggesting that insulin antagonism is not ameliorated.