M. Joycelyn Elders

Differential effects of cranial radiation on growth hormone response to arginine and insulin infusion

The growth hormone responses to arginine infusion and to insulin-induced hypoglycemia were studied in 13 patients with neoplastic disease after treatment with radiation and chemotherapy. Patients who received intensive cranial radiation (greater than 2,400 rads) had no response to either arginine or insulin; those who received moderate cranial radiation (greater than or equal to 2,400 rads) had GH response to arginine but not to insulin; patients receiving no cranial radiation responded to both arginine and insulin. These data support the hypothesis that GH secretion in response to arginine infusion has a different mechanism in contrast to the response to insulin-induced hypoglycemia and that the latter is more vulnerable to cranial radiation.

GROWTH WITHOUT GROWTH HORMONE: EVIDENCE FOR A POTENT CIRCULATING HUMAN GROWTH FACTOR

A potent growth factor was detected in the serum of a child with growth hormone (GH) deficiency and early growth delay whose growth velocity spontaneously increased to supranormal levels despite persistent GH deficiency by both radioimmunoassay (RIA) and radioreceptor assay. Thyroid function, prolactin, insulin response to oral glucose, glucose response to intravenous insulin, and computerised tomography of the head were all normal. Whilst somatomedin-C levels measured by RIA were low or low-normal, in vitro somatomedin bioactivity measured by bioassay was normal, suggesting the presence of a growth factor other than somatomedin-C. By way of confirmation, the patients serum was incubated with erythroid progenitor cells from peripheral blood of a normal individual and a Laron dwarf. In this system, proliferation of normal erythroid progenitors was almost double that obtained with physiological concentrations of GH or control sera, and Laron erythroid progenitors, which were completely resistant to added GH, also responded strongly to the patients serum. The patients growth is therefore independent of GH and other known growth factors.

Isolation of a biotin receptor from hepatic plasma membranes.

Biotin, one of the growth promoting members of the B complex vitamin family, was found in the present investigation to have a specific receptor on isolated plasma membranes. Biotin bound to its receptor in a linear manner at 20 degrees C with some binding as early as 30 minutes and full equilibrium binding being present at 20 hours. The best binding was found at 0.6 mg/ml of protein, but significant binding was still present at 0.6 microgram/ml. The saturation of ligand binding sites was at 10(-7)M. Half maximal saturation of binding was between 10(-9) and 10(-10)M. These results demonstrate that a receptor for biotin does exist on purified plasma membranes.

Alterations in cartilage metabolism by neurostimulant drugs

Suppression of growth without significant alterations in hormonal patterns has been demonstrated for the neurostimulant drug pemoline. Comparison of the in vitro effect of pemoline, methylphenidate, and methamphetamine on somatomedin-stimulated sulfate uptake by cartilage showed all three drugs to be inhibitory. Sulfate uptake by cartilage can be directly related to growth and glycosaminoglycan biosynthesis. Assay of two of the enzymes involved in the glycosaminoglycan biosynthetic pathway showed that methamphetamine and methylphenidate caused a marked depression of xylosyl- and galactosyltransferase enzyme activity. These data suggest an interference with cartilage metabolism as one possible mechanism for the growth retardation observed in children on neurostimulant drug therapy.

Impaired Growth in Hyperkinetic Children Receiving Pemoline.

Decreased longitudinal growth was observed in 24 hyperkinetic children receiving pemoline therapy. Mean height velocity was 3.67 +/- 0.25 cm/year during therapy but 5.35 +/- 0.42 cm/year after treatment had been discontinued (P less than 0.01). There appeared to be an inverse relationship between growth velocity and drug dosage. All patients receiving less than the median dose of 3.72 mg/kg grew 4 cm/year or more, while seven of 12 patients receiving more than this dose grew at a slower rate. Body weight, basal and stimulated growth hormone values, and plasma somatomedin concentrations were not significantly altered by pemoline treatment, suggesting that this drug may have a direct effect on cartilage metabolism.

Decreased cyclic guanosine 3',5' monophosphate and guanylate cyclase activity in leprechaunism: evidence for a postreceptor defect.

ABSTRACT. Patients with leprechaunism have hyperinsulinemia and extreme insulin resistance. The mechanism of the insulin resistance has not been delineated. To examine postreceptor events in this unusual syndrome we have assayed the enzyme guanylate cyclase [E.C.4.6.12], which is modulated by insulin, and the concentration of the intracellular messenger cyclic GMP in liver from two children with leprechaunism and extreme insulin resistance. Both patients exhibited down regulation of the red blood cell insulin receptors, but normal insulin receptor binding to Ebstein-Barr transformed IM-9 lymphocytes and monocytes. There was no evidence of antireceptor or antiinsulin antibodies. Activity of liver guanylate cyclase expressed as pmol/mg protein/10 min incubation in the soluble and paniculate fractions were, respectively, Ark-1 133 ± 18, 25 ± 6; Ark-2 129 ± 17, 23 ± 8; control children (six average) 287 ± 16, 55 ± 9. The concentration of cyclic GMP was also 50% lower (0.08 ± 0.03 in Ark-1 and 0.07 ± 0.04 in Ark-2), compared to 0.19 ± 0.07 pmol/mg protein/min in the control livers. There was no change in adenylate cyclase activity in children with leprechaunism versus the control children. These data suggest an abnormality of a postreceptor event in this rare genetic disease. These data, however, do not rule out that in some cases of leprechaunism a receptor binding abnormality may be the primary defect. We speculate that a defect in insulin action distal to plasma membrane receptor binding may be etiological in this unusual syndrome.

Metabolic effects of forskolin in chick chondrocytes

The effects of forskolin on parameters of energy metabolism and proteoglycan synthesis have been investigated in chick embryo sternal chondrocyte cultures. After 8 h exposure to 100 microM forskolin, ATP levels and oxygen consumption were unaltered. Protein synthesis was unaffected up to 50 microM forskolin and protein degradation was unaffected by forskolin up to 100 microM. In contrast, incorporation of the proteoglycan precursors, 35SO4 and [3H]glucosamine, was more sensitive to forskolin. Inhibition was linear with dose between 10 and 100 microM, reaching 70% at 100 microM. Incorporation of 35SO4 into glycosaminoglycan chains initiated on an artificial beta-xyloside acceptor was inhibited in the same manner. cAMP accumulation was maximal at 10 microM forskolin, a concentration which did not alter proteoglycan synthesis. We conclude that a major, acute effect of forskolin in these short-term experiments is inhibition of proteoglycan synthesis in a cAMP-independent manner.

Hepatic ultrastructure in leprechaunism

Leprechaunism is a congenital syndrome with characteristic habitus and facies, with fasting hypoglycemia and hyperinsulinism. In response to a glucose challenge there is prolonged severe hyperglycemia with an increased hyperinsulinemia. Our studies on such a patient showed a normal response of the serum glucose to glucagon stimulation in the fed state but no response in the postabsorptive state. Ultrastructural studies on the hepatocytes demonstrated that a lack of hepatic glycogen was not responsible for the biochemical features, since there was abundant normal β-glycogen in both the fed and fasting state, the granules being smaller in the fasted state. We speculate that carbohydrate intolerance in leprechaunism may be due to a relative insulin resistance of cell receptors in the fed state. Reactive hyperinsulinemia persisting into the postabsorptive phase appears to antagonize the usual glycogenolytic response to glucagon during fasting, resulting in hypoglycemia despite the presence of large hepatic glycogen stores.

Effects of dideoxyforskolin on proteoglycan synthesis and structure in embryonic chick chondrocyte cultures

1,9‐Dideoxyforskolin inhibits proteoglycan synthesis and xyloside‐initiated glycosaminoglycan (GAG) synthesis in chick embryo chondrocytes. Dideoxyforskolin does not affect the length of xyloside‐initiated GAG chains secreted into the medium but chains from the dense proteoglycan secreted into the medium appear slightly longer. Incorporation of labeled serine into the dense proteoglycan and subsequent digestion with Pronase revealed a dramatic decrease in percent of total radioactivity associated with GAG chains in the proteoglyean from cultures treated with forskolin or dideoxyforskolin. These observations suggest that these diterpenes have a specific inhibitory effect on chain initiation reactions and thus may be useful tools in the study of proteoglycan synthesis and processing.

ROLE OF GROWTH HORMONE ON PLASMA EPIDERMAL GROWTH FACTOR CONCENTRATIONS

Epidermal growth factor (EGF) is known to accelerate proliferation and differentiation of multiple cell types. We previously reported that growth hormone deficient (GHD) children have decreased urinary EGF excretion compared to normal children and the excretion of EGF increases with growth hormone (GH) administration. We developed a heterologous, double antibody radioimmunoassay (RIA) based on mEGF to estimate plasma concentrations of EGF in humans. The detection limit of the assay was 0.10 ng/ml. Using this method, mean concentration of EGF in plasma from adults was 4.8±1.7 ng/ml and the mean concentration in normal children was 8.4±0.3 ng/ml. Plasma and urinary EGF in GHD children before and during treatment (0.08 U GH/kg t.i.w.) are shown in the table below:These data suggest that the plasma concentrations of EGF do not change with GH treatment of GHD children despite increases in urinary excretion. We conclude that the increased urinary excretion of EGF could reflect increased urinary clearance of this factor rather than increased production.