Pattern of growth hormone response to insulin, arginine and haemodialysis in uraemic children

Human Growth and Growth Hormone: From Antiquity to the Recominant Age to the Future

Since antiquity Man has been fascinated by the variations in human (and animal) growth. Stories and art abound about giants and little people. Modern genetics have solved some of etiologies at both extremes of growth. Serious study began with the pathophysiology of acromegaly followed by early attempts at treatment culminating in modern endoscopic surgery and multiple pharmacologic agents. Virtually at the same time experiments with the removal of the pituitary from laboratory animals noted the slowing or stopping of linear growth and then over a few decades the extraction and purification of a protein within the anterior pituitary that restored, partially or in full, the animal's growth. Human growth hormone was purified decades after those from large animals and it was noted that it was species specific, that is, only primate growth hormone was metabolically active in primates. That was quite unlike the beef and pork insulins which revolutionized the care of children with diabetes mellitus. A number of studies included mild enzymatic digestion of beef growth hormone to determine if those "cores" had biologic activity in primates and man. Tantalizing data showed minimal but variable metabolic efficacy leading to the "active core" hypothesis, for these smaller peptides would be amenable to peptide synthesis in the time before recombinant DNA. Recombinant DNA changed the landscape remarkably promising nearly unlimited quantities of metabolically active hormone. Eight indications for therapeutic use have been approved by the Food and Drug Administration and a large number of clinical trials have been undertaken in multiple other conditions for which short stature in childhood is a sign. The future predicts other clinical indications for growth hormone therapy (and perhaps other components of the GH?IGF-1 axis), longer-acting analogues and perhaps a more physiologic method of administration as virtually all methods at present are far from physiologic.

Excessive dietary protein and suboptimal caloric intake have a negative effect on the growth of children with chronic renal disease before and during growth hormone therapy

Although diet and nutrition are an integral part of the management of individuals with chronic renal failure (CRF), little has been written on the effect of nutrition on the growth response to growth hormone (GH) in CRF. We studied the GH axis and nutritional status of 31 prepubertal children aged 8.7 +/- 0.5 years with a height standard deviation score (SDS) of -3.2 +/- 0.2 (mean +/- SEM) with CRF. Sixteen CRF patients on hemodialysis and 15 on peritoneal dialysis were studied. Forty-four age-matched normal short children without GH deficiency served as controls. Spontaneous 12-hour GH and stimulated GH values were significantly higher and GH binding protein (GHBP) was significantly lower in the CRF patients than in the normal short children. Both before the initiation of GH therapy and after the first year of treatment, the growth velocity (SDS) was inversely correlated with dietary protein intake and positively correlated with caloric intake. GH was administered at a dosage of 28 and 21 IU/m2/wk to the CRF group and the normal short children, respectively, divided into seven daily doses. The growth response of the normal short children was significantly greater than that of the CRF patients. GH therapy induced a smaller increment in GHBP and IGF-I in the CRF patients versus the normal short children (8.8 +/- 2.2 and 10.2 +/- 2.7 v 24.8 +/- 1.3 and 27.6 +/- 2.5 nmol/L, respectively, P < .01). The 1-year growth velocity of the CRF children was most closely correlated with dietary protein and caloric intake. The nutritional status of CRF patients is concluded to be a major factor in growth both before and during GH therapy.

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.

Altered growth hormone response after growth hormone releasing hormone administration in chronic renal failure

Eleven chronic renal failure patients and 11 matched controls, received growth hormone GHRH (1 microgram/kg iv) or TRH (400 microgram iv) on separate occasions, immediately before undergoing hemodialysis. GHRH-induced GH peak in uremics (22.7 +/- 5.2 micrograms/l) was not different from that obtained in control subjects (16.0 +/- 4.3 micrograms/l). However, the uremic patients did not show the habitual post-peak fall, remaining GH levels over 10 micrograms/l till the end of the test. Differences between the two groups were significant (p less than 0.05). Uremic patients showed PRL values higher than in controls, however their TRH-induced PRL peak (20.6 +/- 6.6 micrograms/l) was not different from that of controls (26.5 +/- 3.0 micrograms/l). Again chronic renal failure patients showed PRL plasma values abnormally elevated till the end of the test. Differences between the two groups were significant (p less than 0.05). Administration of placebo to a different group of seven uremic patients did not alter GH and PRL plasma levels. This sustained secretion of both GH and PRL in uremia could be attributed to reduced kidney clearance. However, when subjects were examined individually both the GHRH- and the TRH-induced hormonal peaks and the subsequent fall were not different in both groups. Unlike with controls, in uremic patients GHRH-stimulated GH and TRH-stimulated PRL/GH peaks were dispersed throughout the 120 min period. In controls GH and PRL peaks clustered around 15-30 min. The peak dispersion created a false impression of flattened curves or sustained hypersecretion in uremia.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoglycemia in pediatric renal allograft recipients

Symptomatic hypoglycemia developed 5 to 45 months after transplantation in nine children who had renal transplants before 6 years of age. During hypoglycemia, serum glucose levels ranged from 14 to 39 mg/dl (0.8 to 2.1 mmol/L). Hypoglycemic episodes occurred between 1.7 and 7.5 years of age. Six patients had generalized seizures; the remaining three had diaphoresis with stupor or lethargy. None of the children had serious infections, diabetes, congenital defects of glucose metabolism, or a history of treatment with insulin or oral hypoglycemic agents. Six patients had hypoglycemic symptoms after a prolonged fast, and at least four had ketosis. Eight of the nine patients were receiving propranolol when hypoglycemia occurred. No differences in the daily prednisone dose, the number of transplant rejection episodes, or the frequency of treatment with medications other than propranolol were noted between hypoglycemic patients and 56 normoglycemic age-matched renal transplant recipients. All hypoglycemic patients were subsequently treated with frequent feedings and discontinuation of propranolol. No further hypoglycemic episodes have occurred in eight of nine patients. Symptomatic hypoglycemia should be recognized as a potentially devastating complication of pediatric renal transplantation.

Prolactin response to exercise, metoclopramide and other provacative agents in children

Metoclopramide (MCP), a derivative of procainamide was compared with exercise, arginine, insulin and thyrotropin releasing hormone (TRH) as a prolactin (PRL) releaser in children. The peak response of plasma PRL after oral administration of MCP was greater than that after strenuous exercise and after i.v. administration of pharmacodynamic agents. Normal PRL and TSH responses were observed after TRH administration in all subjects. Variable PRL responses were seen after exercise and after i.v. administration of arginine and insulin, despite significant growth hormone (GH) release following the administration of these agents. MCP produced no increase in plasma TSH. Metoclopramide may be useful for dynamic testing of PRL release in children. It can be taken orally and is free of side-effects.

Serum prolactin levels in renal insufficiency in children

Basal prolactin concentrations in forty-eight children with acute or chronic renal disease have been compared with those in thirty-four healthy control subjects. Elevated basal prolactin levels and an abnormal prolactin response to intravenous thyrotropin-releasing hormone were found in children with chronic renal failure on maintenance intermittent haemodialysis. No significant change in plasma prolactin concentrations and osmolality was observed before and after haemodialysis, despite a fall in plasma creatinine concentrations. The elevated prolactin levels fell to normal in three patients after successful renal transplantation. It is suggested that the kidney has an important role to play in prolactin metabolism.