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Objective: To carry out a multicenter, prospective, randomized trial of human growth hormone (GH), alone or in combination with oxandrolone (OX), in patients with Turner's syndrome (TS)., Methods: In an initial phase lasting 12 to 24 months, 70 girls with TS, verified by karyotype, were randomly assigned to one of four groups: (1) observation, (2) OX, (3) GH, or (4) GH plus OX. After completion of the first phase, group 3 subjects continued to receive GH only. All other subjects were treated with GH plus OX. Subjects were followed up until attainment of adult height and/or cessation of treatment. Data from this trial were compared with growth characteristics of 25 American historical subjects with TS (matched for age, height, parental target height, and karyotype) who never received either GH or androgens., Results: Of the 70 subjects enrolled, 60 completed the clinical trial. The 17 subjects receiving GH alone all completed the trial and reached a height of 150.4+/-5.5 cm (mean +/- SD), 8.4+/-4.5 cm taller than their mean projected adult height at enrollment (95% confidence interval [CI]: 6.3 to 10.6 cm). The 43 subjects receiving GH plus OX attained a mean height of 152.1+/-5.9 cm, 10.3+/-4.7 cm taller than their mean projected adult height (95% CI: 8.9 to 11.7 cm). The historical control subjects had a mean adult height of 144.2+/-6.0 cm, precisely matching their original projected adult height of 144.2+/-6.1 cm., Conclusions: GH, either alone or in combination with OX, is capable of stimulating short-term growth and augmenting adult height in girls with TS. With early diagnosis and initiation of treatment, an adult height of more than 150 cm is a reasonable goal for most girls with TS.

This study was undertaken to determine the prevalence of clinical diagnoses in a group of children with extremely short stature (standard deviation score for height, < -2.5) and to determine whether the classification might help in predicting response to human growth hormone (hGH) treatment. We classified 49 children referred consecutively to our outpatient clinic for evaluation of short stature with heights < -2.5 standard deviation score and bone ages < 9 years for girls or < 10 years for boys (to avoid an effect of puberty on the response to hGH). The diagnostic categories were growth hormone (GH) deficiency, constitutional delay, familial short stature, and primordial short stature. After referral, Turner syndrome was diagnosed in two children. The remaining 47 children were classified according to primary criteria, considered essential for the diagnosis, and secondary criteria, considered necessary but of lesser importance. There were five children, four children, no children, and one child classified, respectively, with GH deficiency, constitutional delay, familial short stature, and primordial short stature by using the most rigorous definitions of the diagnoses. There was significant overlap in the diagnoses other than GH deficiency. Growth hormone deficiency defined by the primary criterion of peak stimulated GH values < 5 micrograms/L was the most definitive. Of the 47 children, 7 were classified as GH deficient by this criterion and 5 were classified as GH deficient by the primary and secondary criteria. The mean pretreatment growth rate (3.1 +/- 1.9 cm/yr) of the group with stimulated GH values < 5 micrograms/L was significantly less than that in the other groups (4.2 +/- 1.5 cm/yr). The mean growth rate of the children with GH deficiency during treatment with hGH was greater than that in the other groups and was 3.4 times greater than the pretreatment growth rate. The mean growth rate of children in the other groups during hGH treatment was twofold greater than the pretreatment growth rate. We conclude that except for GH deficiency, children with an extreme degree of short stature are not easily classified by standard diagnostic criteria, and that most short children have a positive response to hGH therapy regardless of the diagnosis; therefore a specific clinical diagnosis should not be used to exclude children from hGH therapy.

Children with short stature but normal growth rate and/or normal growth hormone response to sleep and secretagogues were treated with recombinant methionyl human growth hormone, 0.3 mg/kg per week. In each year of treatment, about 80% of the subjects maintained an increase in growth rate greater than the defined limit (greater than 1 cm/yr above pretreatment growth rate) for continuation of human growth hormone treatment. Comparison of the group that continued to respond to human growth hormone with the group that did not maintain an accelerated growth rate did not reveal differences in bone age delay, sleep or secretagogue-stimulated human growth hormone secretion, degree of short stature either absolute or relative to target height, and somatomedin C concentration before or after initiation of therapy. The group that failed to respond to the human growth hormone treatment in the first year of treatment was younger and had a higher pretreatment growth rate. Review of the longitudinal growth curves revealed five patterns of response to human growth hormone treatment: (1) failure to increase growth rate in two subjects with height SD scores within 1 SD of target height, (2) failure to increase growth rate in five subjects with height SD scores greater than 1 SD less than the target height, (3) acceleration in growth rate in three subjects that was not maintained until achievement of a height within 1 SD of the target height, (4) acceleration of growth rate in five subjects that was maintained until achievement of a height within 1 SD of the target height, and (5) acceleration in growth rate that was maintained during the 3 years of treatment in 15 subjects who had not attained a height within 1 SD of the target height. We conclude that human growth hormone treatment of some but not all short children with "normal" growth hormone secretion will result in sustained acceleration of growth rate and attainment of prepubertal heights that are closer to but do not exceed their genetic height potential. A clinical trial of human growth hormone may be necessary to determine which subjects will benefit from the treatment.

A pilot study was carried out to examine the safety and efficacy of recombinant human growth hormone for growth-promoting therapy of achondroplasia. The data suggest that the agent in doses used to treat non-GH-deficient forms of short stature (0.3 mg/kg/wk) modestly increases overall height velocity in some children with achondroplasia. The effect was seen mainly in children with the lowest growth velocities prior to treatment. No untoward effects were noted. Several questions were raised that require further study.

We examined the correlation between urinary GH, urinary albumin, and beta-2-microglobulin excretion to determine how the excretion of GH relates to markers of renal glomerular and tubular function. Urinary albumin and GH excretion was determined in timed daytime and nighttime urine collections obtained from both subjects with diabetes mellitus and subjects with short stature. For subjects with diabetes, urinary GH excretion rate correlated highly with urinary albumin concentration and excretion rate in both the range of 0 to 1.6 g/L (r = 0.75), P less than 0.001) and in the microalbuminuria range, 0 to 0.4 g/L (r = 0.53, P less than 0.001). Changes in GH and albumin excretion occurred in parallel in 71% of the subjects with diabetes and elevated albumin excretion. The mean GH excretion rate was higher in the group with elevated albumin excretion rate (AER) during both day and night compared to the group with microalbuminuria during the day and normal AER at night. For subjects with short stature, the mean albumin excretion rate was 0.7 +/- 1.3 micrograms/min (range 0.05-8.3 micrograms/min) using a sensitive enzyme-linked immunosorbent assay to measure albumin concentration. The correlation of GH and albumin excretion rates for the subjects with short stature was not statistically significant (r = 0.14, P less than 0.5). About half of the subjects with diabetes and elevated AER (greater than 10 micrograms/min) had a GH excretion rate within the range observed in subjects with short stature. The GH and albumin excretion rate were not correlated in this group. There was a positive correlation of both albumin and GH excretion rate with age in the subjects with diabetes. Urinary GH and beta-2-microglobulin excretion rates were determined in a larger group of subjects with diabetes and a separate group with short stature. Urinary GH and beta-2-microglobulin excretion were correlated both in subjects with diabetes (r = 0.46, P less than 0.001) and with short stature (r = 0.64, P less than 0.001). The association was present in urine collected either during the day or night. The mean GH excretion rate of the group with diabetes was greater than the group with short stature. In conclusion, there was an association of urinary GH and albumin excretion rate in subjects with abnormal glomerular function as indicated by elevated albumin excretion rate. An association of urinary GH and beta-2-microglobulin excretion was observed in subjects with normal tubular function.(ABSTRACT TRUNCATED AT 400 WORDS)

GH influences the immune response. The mechanism is not known; however, the presence of receptors for GH on human lymphocytes as well as its ability to influence and modulate immune responses in animals suggest an association between GH and immune function in man. We evaluated the effect of recombinantly derived natural sequence human GH (hGH) on lymphocyte surface antigen expression, response to mitogenic stimulation, expression of interleukin-1 receptors, and production of anti-hGH antibodies in GH-deficient children. The only observed changes were a decrease in the percentage of B-cells and a transient increased reactivity to phytohemagglutinin stimulation. It appears from the results of our studies that the administration of hGH has a selective effect on lymphocyte immune function; however, we cannot eliminate a role for hGH in the initiation or regulation of antigen-mediated immune responses.

The binding characteristics of hGH to Golgi and liver plasma membranes isolated from normal adult female rats have been compared to assess the biological differences between the Golgi and plasma membrane receptor. The effect of cations and the time course of binding were qualitatively similar for both Golgi and plasma membranes. The Golgi membranes from normal rats exhibited maximum binding at pH 6-7 compared to 5-6 for other membrane fractions. The highest apparent affinities (approx. 1 x 10(9) M-1) for hGH were observed in the light Golgi membranes from normal rats and the light and intermediate Golgi membranes from ethanol treated rats. The lowest apparent affinities (0.026 -0.1 x 10(9)M-1 if determined by competitive binding curves or 0.07 - 0.32 x 10(9)M-1 by Scatchard plots) for hGH were observed in plasma membranes isolated by either Neville's or Ray's method or a combination of both methods. The hGH receptors were determined to be lactogenic by competitive binding curves. The affinities of Golgi membranes were not affected by alterations in isolation procedures. Ethanol treatment of the rats prior to sacrifice and membrane isolation resulted in linear Scatchard plots for hGH binding to Golgi membranes compared to curved Scatchard plots for the Golgi membranes of normal rats. The marker enzyme activities of glucose-6-phosphatase and adenylate cyclase were lower in Golgi from ethanol treated rats while the galactosyl transferase activity increased in lighter golgi fractions from ethanol treated rats.

The binding of 125I-labeled oGH, rGH and hGH to homologous liver membranes is compared to define the characteristics of somatotropic hormone-receptor interactions. The effect of pH and cations and the time-course of binding of these different GHs was similar when binding was determined in liver membranes from the homologous species. The time-course of binding was characterized by stable binding by 90-120 min of incubation at 22 degrees C with relatively high nonspecific binding that continued to increase with time. This resulted in a peak of specific binding for each hormone. Addition of excess unlabeled hormone at 30 min of the binding incubation resulted in partial displacement of the bound GH. The binding of rGH was somewhat dependent upon the presence of divalent cations (Mg2+, Ca2+) in the incubation medium. In the absence of added divalent cation, a small but appreciable amount of binding was detected at pH 7-8. With 10 mM calcium, binding increased several-fold with a definite peak of rGH binding at pH 4-5. Both oGH and hGH exhibited a broad peak of binding at pH 5-7. Monovalent cations (Na+, K+) were either ineffective in enhancing GH binding or produced a slight enhancement at higher concentrations (100 mM). Competitive displacement curves confirm the somatotropic nature of the GH-receptor interaction. Human P1 was ineffective in competing for GH binding. We conclude that 'somatotropic' growth hormone binding to its homologous liver receptor exhibits phylogenetically consistent and distinguishing characteristics of binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Forty-eight children with short stature, growth rate less than 4 cm/yr, and normal growth hormone response to secretagogues were given exogenous human growth hormone (hGH) for 6 months to determine its effect on the short-term growth rate in these children. All except three had an increase in growth rate with hGH therapy. The mean +/- SD pretreatment growth rate (3.4 +/- 0.8 cm/yr) was significantly less than either the growth rate during 6 months of hGH therapy (6.9 +/- 2.6 cm/yr) or after therapy (4.1 +/- 1.8 cm/yr). Several patterns of response were observed after treatment was stopped: the mean growth rate in 22 children decreased after treatment but remained above basal rates, the mean growth rate in seven children was similar to the rates during treatment, and the mean growth rate in 16 children was less than basal rates. Twenty children received therapy for an additional 6 months and had a mean increase in growth rate from 3.6 +/- 1.3 to 6.7 +/- 2.4 cm/yr. The decreased growth rate after discontinuation of treatment and increased rate with resumption of therapy indicates that maintenance of the increased growth rate might be dependent on continuation of hGH therapy.

The binding of [125I]bGH and [125I]hGH to bovine liver membranes is compared to characterize the somatotrophic hormone-receptor interaction. [125I]bGH binding exhibits higher nonspecific binding than [125I]hGH while the time-course of binding and displacement with unlabeled GH are similar. Divalent and monovalent cations enhance [125I]hGH binding with well-defined peaks of binding at specific cation concentrations. Monovalent cations do not enhance [125I]bGH binding at concentrations of 100 mM while divalent cations enhance binding over a range of cation concentration (4-80 mM). The binding of [125I]bGH is dependent upon the presence of divalent cations, with minimal effect of pH upon binding in the absence of calcium. Scatchard plots of bGH and hGH binding data indicate at least two binding sites. We conclude that somatotrophic GH exhibits unique and distinguishing characteristics of binding. The characteristics of hGH binding to the bovine liver membranes suggest that its binding may differ from bGH binding to its homologous receptor.

We determined the effect of pituitary human growth hormone treatment on the growth rate of 52 children with Turner syndrome. The pretreatment growth rate was 3.2 +/- 0.8 cm/yr. Growth hormone treatment (0.2 IU/kg three times per week) resulted in enhancement of the growth rate to 5.9 +/- 1.4 cm/yr for the first year of therapy. The bone age advanced approximately 1 year during the year of therapy. The growth hormone therapy was discontinued at 12 months, and the mean growth rate decreased to pretreatment levels, 3.1 +/- 1.9 cm/yr; 26 of 41 patients actually had post-treatment growth rates that were less than the pretreatment rate. Glucose tolerance tests at 6-month intervals did not indicate an effect of hGH treatment on glucose intolerance. Several patients had glucose intolerance that preceded hGH treatment, but this remained stable during treatment; glucose intolerance likely was related to obesity in this group of patients. Basal and hGH-stimulated somatomedin C levels (32 patients) correlated with age of the patient but not with growth rate during therapy. We conclude that hGH therapy can accelerate the growth rate of patients with Turner syndrome. The growth rate increased to "normal" levels and was dependent on continued treatment with hGH. If the response continues, long-term treatment of Turner syndrome may result in increased adult height.

The sc and im administration of human GH (hGH) was compared in the therapy of GH deficiency. The peak and integrated concentrations of hGH in the plasma of the patients were similar after sc and im injection of an initial dose (0.1 U/kg) of hGH. The peak hGH concentration occurred at 2 h in both groups. The posttreatment height velocity and the change in height velocity at 3-month intervals were also similar in the im and sc groups. The somatomedin generation test resulted in a higher mean peak of somatomedin C after sc injection; however, if the individual peaks of somatomedin C were averaged, there was no difference between sc and im injection. A cross-over at 9 months of therapy to determine patient acceptance of im vs. sc injections indicated overwhelming acceptance of the sc route. The antibody responses to hGH were similar in both groups. We conclude that sc injection of hGH is an effective and safe mode of therapy for GH deficiency. The lipoatrophy that occurred infrequently at the injection site can be eliminated by rotation of sites. Subcutaneous administration of hGH will be more acceptable by the patients with less pain and less noncompliance.

To evaluate the reproducibility of overnight growth hormone (GH) testing and the effect of daytime administration of levodopa and clonidine on overnight GH secretion, we examined consecutive 12-hour overnight GH profiles of 48 short subjects, ages 5 to 16 years, who had GH stimulation testing with levodopa and clonidine. In six subjects (12%) the overnight pool GH concentration on the second night increased by greater than 100% from the first-night result (night-to-night changes of +1.2 to +5.2 ng/ml). In the remaining subjects, night-to-night changes in pool GH concentrations ranged from -1.2 to +1.8 ng/ml (-60% to +88% changes from the first night value). Night-to-night changes were less than 25% of the first-night value in 17 subjects (35%), 25% to 50% in 18 subjects (38%), and 50% to 100% in 7 subjects (15%). Night-to-night changes in pool GH concentrations correlated with differences in peak nighttime GH concentrations but not with differences in duration of observed sleep. There was no discernible effect of daytime levodopa-clonidine administration on overnight pool GH concentrations. These results demonstrate the potential for night-to-night variation in overnight GH profiles and suggest the need for some means of confirming that overnight GH testing reflects normal physiologic GH secretion. Without such confirmation, the results from a single overnight GH profile should be interpreted with caution.

The effect of disulfide reduction on the binding of [125I]rat GH (rGH) to rat liver plasma membranes and hepatocytes was studied to determine the role of disulfide bonds in the binding of GH to its receptor. The total amount of [125I] rGH bound to the liver receptors increased severalfold in the presence of dithiothreitol and mercaptoethanol. The nonspecific binding also increased at higher concentrations of the reductant, but the amount specifically bound was still greater in the presence of disulfide reductant. In contrast, the disulfide reductant inhibited [125I] human GH (hGH) binding and enhanced its displacement from hypophysectomized female rat hepatocytes. This was similar to the effect of reductants on [125I]hGH binding to normal female rat hepatocytes. The effect of the disulfide reductants on [125I]rGH binding could be prevented or reversed by the simultaneous or subsequent addition of an oxidizing agent such as NAD or oxidized glutathione. Sulfhydryl-reactive agents such as iodoacetamide prevented additional binding of [125I]rGH when added at 30 min of the incubation. The additional [125I] rGH bound in the presence of disulfide reductant was displaceable by excess unlabeled rGH. Both rGH and hGH exhibited similar degrees of disulfide reduction in the presence of mercaptoethanol. The disulfide reductant produced effects on binding at concentrations that resulted in less than 10% reduction of the GH disulfides. We conclude that: 1) the disulfides and sulfhydryls of the hepatocyte membrane are intimately involved in the binding of GH to hepatic receptors; 2) the locus of the disulfides and sulfhydryls may be in the subunit structure of the membrane receptor, but this will require verification using soluble receptors; and 3) the effect of disulfide reducing agents reveals basic differences in the mechanism of binding of rGH and hGH to somatotropic hormone receptors on the hepatocytes.

Significant increases in basal, and glucagon and fluoride stimulated adenylate cyclase activity were observed in liver plasma membranes of hypophysectomized rats compared to normal adult and weanling rats. The fluoride stimulated adenylate cyclase activity was 2-3 fold greater in the membranes from hypophysectomized animals while the glucagon stimulated activity was 5-7 fold greater, and the basal activity was approximately double that of membranes from normal adult animals. Administration of growth hormone to hypophysectomized rats by an intramuscular or intravenous route decreased adenylate cyclase activity to levels equivalent to those in normal adult rats. Estradiol and thyroxine replacement did not alter the adenylate cyclase activity of the membranes from hypophysectomized animals. The fluoride or epinephrine stimulated adenylate cyclase activity of rat diaphragm homogenates was not affected by hypophysectomy.

The binding characteristics of hGH to rat liver macrophages ( Kupfer cells) and hepatocytes have been compared to determine the role of each in the binding of hGH to liver tissue. The time course of binding, displacement of bound 125I-hGH and effect of pH on binding was qualitatively similar for macrophages and hepatocytes. Since the macrophage isolation depends upon their phagocytosis of iron particles, we determined that exposure of the isolated hepatocytes to the iron did not affect their binding of 125I-hGH. The relative capacity of the macrophage preparations was two-fold less than the hepatocyte preparations. This indicated that the hepatocyte is responsible for the majority of the hGH binding by the liver. In contrast, the cell surface concentration of the hGH receptor on the macrophage is greater than the hepatocyte. Ovine prolactin and hPrl were equipotent in competing for the binding of 125I-hGH to the macrophage receptor while only oPrl was significantly competitive in the hepatocytes. Bovine GH and hPI exhibited minimal interaction for 125I-hGH binding in both cell preparations. We conclude that even though significant differences in 125I-hGH binding do exist between hepatocytes and liver macrophages, the macrophages contribute significantly to hGH binding by hepatic tissue. The demonstration of somatomedin production by fibroblasts in culture suggest a possible role of the hepatic macrophage in GH responsiveness of the liver.

The binding of 125I-labeled human growth hormone (hGH) to liver membranes from several different species was studied to determine the lactogenic or somatotropic hormone nature of the receptors. Liver membranes from several species of the class of Mammalia bound significant quantities of 125I-hGH. Goat, sheep, rat, mouse, and rabbit liver membranes exhibited the highest binding with cow, pig, human, and hamster liver membranes exhibiting severalfold less binding. The binding of the dog and cat liver membranes exhibited relatively high nonspecific binding. Fish and chicken liver membranes did not bind appreciable quantities of 125I-hGH. In all species except for dog and cat in which 125I-hGH bound to the membranes, hGH was the most effective competitor for binding. The mean ID50 for hGH and all membranes was 2.4 X 10(-9) M. Human liver membranes exhibited the smallest ID50, 4.9 X 10(-10) M. In sheep liver membranes, bovine growth hormone (bGH) was equipotent to hGH in competing for 125I-hGH binding. bGH also demonstrated significant competition for 125I-hGH binding in pig and cow membranes. Ovine prolactin (oPrl) exhibited significant competition for 125I-hGH only in rodent membranes. The ID50 for oPrl was 3- to 10-fold greater than for hGH in the rat, hamster, and mouse liver membranes. The ID50 for oPrl in the sheep liver membranes was 13-fold greater than that of hGH. We conclude the following: (1) There appears to be a species specificity of hGH binding that may be phylogenetically significant and may result from variations in the structure of the hormone or the receptor. (2) The competitive binding properties of hGH are fairly consistent within phylogenetic orders. (3) The simple designation of lactogenic or somatotropic for hormones and receptors is insufficient to characterize the binding properties of this group of hormones.

Macrophages isolated from female rat liver as well as hepatocytes bind 125I-hGH. This study compares the effect of sex of the rat, hypophysectomy (hypox) and preincubation of the cells with oPrl on the binding of 125I-hGH to the cells. The percent of 125I-hGH to the hepatocytes was decreased in cells from hypox female and male rats, and hepatocytes preincubated with oPrl to 0.43, 0.21 and 0.39, respectively, of that observed in hepatocytes from normal female rats. In the hepatocytes from normal female, hypox female, and male rats, hGH was the most effective competitor for 125I-hGH binding with an ID50 of 0.73-0.99 nM. The concentration of oPrl, bGH and rGH that produced half-maximal inhibition (ID50) of 125I-hGH binding to hepatocytes from female rat liver was 6.3, 100, and 420 nM respectively. In hepatocytes from male and hypox female rats, and hepatocytes preincubated with oPrl, the ID50 for bGH and rGH varied from 2.1 to 15.9 nM. The percent of 125I-hGH bound by the macrophages from hypox female and male rats, and macrophages preincubated with oPrl was 0.06, 0.15 and 0.18, respectively, of that bound by macrophages from normal female rat liver. In contrast to hGH binding to the hepatocytes, the ID50 for hGH was 6 to 180-fold greater in macrophages from hypox female and male rats, and macrophages preincubated with oPrl compared to that observed in macrophages from normal female rats, Rat GH was the most effective competitor for 125I-hGH binding in the macrophages from the hypox female and male rat liver with ID50 of 5.5 and 85 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Two weekly (biw) injections of pituitary human growth hormone (hGH) were compared with three weekly (tiw) injections of hGH (0.24 IU hGH/kg body weight/wk for both groups) for effect on growth rate in children with idiopathic and organic hypopituitarism. Both dosage schedules resulted in increased growth rate during the first 12 months of therapy; the tiw dosage was more effective in the first 6 months in patients with organic hypopituitarism, and in the second 6 months in patients with idiopathic hypopituitarism. There was no advantage to tiw therapy during the second year of therapy in either group. The additional increment in height after 1 year of therapy using tiw compared with biw therapy was 2 cm and 1 cm for the patients with organic and idiopathic hypopituitarism, respectively. This increment should be weighed against the cost, pain, and inconvenience of tiw versus biw doses of hGH in the treatment of hGH deficiency. With the dosages used in this study, tiw therapy was more effective during the first year, when patients are more responsive, and should be recommended. Twice weekly therapy could be considered for the second and possibly subsequent years of therapy. Other schedules of treatment may be more effective than either of these schedules.

The role of disulfide bonds and sulfhydryl groups in rat hepatocytes and rat liver plasma membranes in the binding of human GH (hGH) has been studied. Since hGH binding involves uptake and irreversible binding, the effect of disulfide reducing agents [dithiothreitol (DTT) and 2-mercaptoethanol (ME)] and an alkylating agent [N-ethylmaleimide (NEM)] on the time course of binding and displacement of [125I]hGH was determined in the hepatocytes and membranes. The time course of binding and displacement of [125I]hGH was similar in membranes and cells, indicating that the irreversible nature of hGH binding is not dependent upon an intact cellular structure. Both 1% ME and 10 mM DTT prevented further binding of [125I]hGH when added at 60 min of the 300-min binding incubation for both hepatocytes and plasma membranes. The ME caused some initial dissociation of bound [125I]hGH, with subsequent binding to levels that were present when the ME was added. Only ME caused an increase in nonspecific binding with the plasma membranes. Both ME and DTT caused an increase in displacement of [125I]hGH in the presence of excess unlabeled hGH. The amount of [125I]hGH remaining bound in the presence of DTT and unlabeled hGH approached nonspecific levels by 240 min of incubation. NEM caused an increase in the total [125I]hGH bound, but this was apparently due to increased nonspecific binding in the presence of NEM. The effect of the reducers on binding was not secondary to an effect on hGH, since the disulfides of [125I]hGH were not reduced under the conditions of binding with either ME or DTT. The effect of the ME or DTT on binding could be reversed or prevented by subsequent or simultaneous addition of an oxidizer such as NAD or oxidized glutathione. The data indicate that disulfide bonds in the membranes are intimately involved in the maintenance of a receptor structure necessary for hGH binding. The disruption of the disulfides also results in increased dissociation and displacement of the bound [125I]hGH, indicating a possible role in the irreversible nature of hGH binding. This represents a partial delineation of the hGH binding process.

The binding of human growth hormone (hGH) and a naturally occurring variant of hGH (20K) to rat and rabbit liver membrane has been compared. The concentration of hormone causing half maximal displacement (ED50) of 125I-hGH from rat liver plasma membranes was 1.6 nM for hGH and 46 nM for 20K. The ED50 for hGH and 20 K against 125I-hGH binding to rabbit liver plasma membranes was 1.6 mM for hGH and 28 nM for 20K. Significant binding of 125I-20K did occur to rat and rabbit liver membranes but the relative capacities for 20K were 12 and 6 fold less in rat and rabbit liver membranes, respectively when compared to hGH. The competitive binding characteristics of 20K to pregnant rabbit liver membranes indicated lack of competition between bovine GH and 125I-20K for binding. However, significant binding of 125I-20K to male rabbit liver membranes was present and displaceable by hGH and oPrl. We conclude that deletion of a portion of the hGH molecule (defined as residues 32-46) results in significant alterations in the binding characteristics of the molecule. This indicates primary or secondary involvement of this portion of the hGH molecules in the binding process and may define a portion of the binding domain for hGH.

[14C]-3-O-Methyl-D-glucose transport in response to GH stimulation was measured in freshly prepared and cultured hepatocytes from hypophysectomized (hypox) adult female rats. Sugar transport in freshly isolated hepatocytes from hypox animals was stimulated by 10(-9) M human GH (hGH) and 10(-9) M rat GH (rGH) during 0-30 and 60-90 min of incubation, respectively. Monosaccharide transport in freshly isolated hepatocytes from normal female rats was unaffected by either hGH or rGH addition. Specific [125I]iodo-hGH binding to freshly isolated hepatocytes from hypox rats was detectable as early as 9 min of incubation and reached maximum binding levels by approximately 30-60 min. Specific [125I]iodo-rGH binding was not detectable until 30 min of incubation and reached a binding plateau after 60 min of incubation. Porcine insulin at 10(-9) and 10(-7) M was ineffective in stimulating sugar transport in either freshly isolated or cultured hepatocytes from hypox animals. Sugar transport in cultured hepatocytes was stimulated by 10(-7) M hGH ad 10(-7) rGH, with 30-60 and 60-90 min of incubation being the most frequent stimulatory intervals observed. Maximum specific [125I]iodo-hGH binding was observed at 60 min of incubation and decreased by 72% and 77% at 90 and 120 min, respectively. Specific [125I]iodo-rGH binding, however, was not detectable in cultured hepatocytes. Both hGH at 10(-9) M stimulated glucose oxidation to CO2 in freshly isolated hepatocytes from hypox animals. Stimulation was observed after 30 min of incubation with GH and indicated a regulatory function for GH in maintaining basal levels of glucose oxidation. The results presented here suggest a possible role for GH in glucose uptake and metabolism in the liver and indicate that differences may exist between the effects of hGH and rGH on glucose uptake.