Dose regimens of human growth hormone: effects of continuous infusion and of a gelatin vehicle on growth in rats and rate of absorption in rabbits

The effect of injecting or infusing low doses of bovine growth hormone on milk yield, milk composition and the quantity of hormone in the milk serum of cows

The effects of administering bovine growth hormone (bGH) on milk production in cattle were examined in two experiments.

In experiment 1, a Latin-square design, three groups of four Friesian cows were injected daily with one of two doses of bGH (6 ng/kg and 30 ug/kg; 0·82 unit/mg) or with saline (control) throughout three successive 21-day periods in mid-lactation. At 30 ug/kg daily bGH stimulated a significant increase in milk yield (P < 0·001) and this response increased with the duration of treatment. Changes in the yields of milk fat, protein and lactose closely followed the changes in milk production. The concentrations of milk fat (P < 0·05) and protein (P < 0·05) rose and fell respectively during the 1st week of injections.' A daily dose of 6 ug/kg bGH failed to stimulate an increase in milk yield but milk lactose content was reduced (P < 0·05) during the 2nd and 3rd weeks of treatment. The proportion of milk serum samples containing detectable quantities of the hormone was increased by the higher dose of bGH.

In experiment 2 the milk yields of four Friesian cows were measured when bGH (21·0 to 37·9 mg/day) or saline was infused intravenously for 6 days. The infusions produced up to eight-fold increases in plasma bGH. These were within physiological limits, and remained at elevated levels throughout the 24-h period. Three of the cows demonstrated a clear increase in milk production.

“Statistics” is not a Sausage Machine: A Statistician's Viewpoint and Some Comments on Experimental Design

Any experiment involving the use of animals which is not well-planned, meticulously carried out, and scrupulously analysed, is unethical. Planning, or good experimental design, followed by analysis appropriate for the design, will help to ensure the optimal use of animals. Thus, collaboration between biologist and statistician, especially at the planning and analysis stages, is one of the best ways of achieving an ethical and successful experiment. However, genuine communication is necessary for any collaboration, and this requires time and patience, on the part of both biologist and statistician. Although the three fundamental principles of experimental design, replication, randomisation and local control, are straightforward in theory, there is substantial scope for misunderstanding and misinterpretation in practice. Each experiment presents unique and interacting biological and statistical problems, and both the right design and the correct analysis should be decided on a case-by-case basis.

Comparison of methods of analysis of body composition in hypophysectomized rats treated with rat growth hormone

The present study compared estimates of body composition derived from dual-emission X-ray absorptiometry (DEXA) and from chemical analyses. The primary aim was to compare the two methods because growth hormone (GH) may cause fluid retention, and DEXA does not distinguish water from lean mass. Hypophysectomized rats were fed ad libitum and were treated with continuous infusions of rat GH in doses of 0, 10, 30, and 100 microg/day for 14 days. By chemical analysis, a decrease in percentage fat from 12.9% in the control group to 11.3%, 11.0%, and 10.2% in the low, medium, and high dose groups was observed (P < 0.0001). The fat percentages were about 3-4% higher by DEXA, but showed the same decline (P < 0.03). Lean mass increased from 74.4% in the control group to 75.8%, 78.0%, and 78.6% in the treatment groups (P < 0.001). A significant increase in the wet weight of the quadriceps muscle, but no difference in dry weight was observed in all four treatment groups, indicating that the increase in muscle weight was exclusively caused by water. This accumulation of water was reflected in the total water content of the carcasses, which increased from 62.0% in the control group to 64.9%, 66.1%, and 66.8% in the GH groups (P < 0.0001). The protein content decreased from 19.8% in the control group to 19.4%, 19.1%, and 18.9% in the GH groups (P < 0.001). Regardless of the decrease in protein, the GH treated groups contained more water in relation to protein as the g water/g protein ratio was increased by 13% from 3.14 in the control group to 3.55 in the group treated with the highest GH dose (P < 0.0001). Also, a close relationship between feed intake and body weight were found, together with increases in epiphyseal growth plate width, insulin-like growth factor I (IGF-I), and insulin-like growth factor binding protein 3 (IGFBP-3). In conclusion, the study shows that estimation of lean mass by DEXA should be carefully evaluated when used in connection with treatment of drugs that cause water retention.

Periodic growth in rats

Microknemometry, a novel non-invasive technique, allows the accurate measurements of the lower leg length in the conscious rat, not only daily but even in periods smaller than 24 hours. Its use revealed the presence of nonlinear growth increments (mini-growth spurts) with periods between 4 and 5 days, that presented a gradual decline in amplitude when the animals were getting older, and a maximal growth rate between 0600h and 0900h. A sexual dimorphic growth pattern could be established with females growing less and presenting spurts of lower amplitude and smaller duration than males. High doses of recombinant human Growth Hormone (rhGH) stimulated growth velocity in female rates, but did not show any effect on males. Neonatal Monosodium Glutamate (MSG) treatment reduced growth both in males and females. Growth hormone (GH) replacement therapy in MSG treated animals was capable of increasing growth velocity, from day 30 onwards. The recovery was partial in males and complete in females. In intact male rats growth blockade induced by fasting was not followed by a catch up effect after refeeding, although growth velocity tended to increase and a clear catch up effect on weight was detected. Male rats seemed to grow at a maximal speed over at least the first 60 days of life, that cannot be accelerated with GH treatment, whereas female rats did respond to exogenous GH.

Growth responses to patterned GH delivery

We have investigated the effects of different patterns of administration of recombinant human growth hormone (rhGH) on weight gain, organ growth, serum GH binding protein (GHBP) and insulin-like growth factor-l (IGF-1) levels in a series of studies using hypophysectomized (Hx) or GH-deficient dwarf (dw/dw) rats. Animals were given rhGH either by subcutaneous (s.c.) injections (1 or 2 per day) or s.c. infusions and rhlGF-1 (2 mg/kg/day) by s.c. infusion. In Hx rats, all rhGH regimes increased body weight, tibial epiphyseal plate width, and organ weights in a dose-related manner. Dwarf rats showed a smaller growth response to rhGH than Hx rats, whereas rhGH induced greater elevations in serum GHBP in drarf rats. Growth responses depended on the pattern of rhGH administration (twice daily injections > continuous infusions > daily injections). The shape of the body growth curves also differed; rhGH injections increased weight gain linearly, whereas infusions gave an initial rapid weight gain which slowed with time (a curvilinear response). For both regimens, tibial epiphyseal plate width increased linearly with rhGH dose but infusions were 5-fold more potent than daily injections. Spleen and thymus weights were markedly increased by rhGH and were also affected by the pattern of GH exposure. At 5 mg rhGH/kg/day, thymus weights were 390±35 mg for injectionsvs. 613 ± 34 mg for infusions (P<0.001) compared with 248 ± 16 mg in vehicle-treated Hx controls. Infusions of rhlGF-1 also stimulated specific organ growth but caused less weight gain. RhlGF-1 additively increased the weight gain caused by rhGH injections but not by rhGH infusions. Circulating IGF-1 and GHBP levels were increased in a dose-dependent manner by rhGH infusion, whereas daily injections were ineffective. Thus, differential organ growth could be related to the higher serum IGF-1 concentrations induced by continuous rhGH administration. These studies show that whole body growth is best maintained by intermittent rhGH exposure, whereas, paradoxically, differential organ growth is most pronounced with continuous rhGH administration.

Metabolic effects of growth hormone administered subcutaneously once or twice daily to growth hormone deficient adults

OBJECTIVE

The aim of this study was to compare the metabolic effects of GH administered subcutaneously either once or twice daily. The actions of GH might depend upon a pulsatile pattern of serum GH. Pulsatile and continuous intravenous delivery of GH, however, induce similar short-term metabolic effects in GH deficient patients. An improved growth response is obtained in GH deficient children when a fixed weekly GH dose is administered by daily subcutaneous injections instead of twice or thrice-weekly intramuscular injections. A more pulsatile pattern and serum GH levels above zero might be achieved by further increasing the injection frequency. Increased daytime GH levels might, however, adversely affect the circadian patterns of metabolic indices, which have been demonstrated to be more successfully reproduced by evening compared with morning GH administration.

DESIGN AND MEASUREMENTS

In a cross-over study, 8 GH deficient patients (age 16-43 years) were treated with 3 IU/m2/24 h of human GH. The dose was injected in the evening for 4 weeks and for another 4 weeks two-thirds was injected in the evening and one-third in the morning. At the end of each period the patients were admitted to the hospital for 37 hours. Steady-state profiles of GH, IGF-I, IGF binding proteins 1 and 3, insulin, glucose, lipid intermediates and metabolites were obtained following administration of 3 IU/m2 of GH (at 1900 h (one injection) and at 1900 and 0800 h (two injections)).

RESULTS

Similar mean integrated levels of serum GH (mU/l) were obtained (7.46 +/- 0.84 (one injection) vs 6.46 +/- 0.62 (two injections) (P = 0.15)). Mean levels +/- SEM of serum IGF-I (micrograms/l) were significantly increased (P < 0.01) following two daily GH injections (330.3 +/- 48.1 (one injection) vs 399.1 +/- 53.0 (two injections)). Serum IGFBP-3 levels were not significantly different on the two occasions, while levels of the GH independent IGFBP-1 (micrograms/l) were slightly but significantly lower following twice-daily GH injections (1.61 +/- 0.42 vs 1.13 +/- 0.56, respectively (P < 0.04)). The pattern of IGFBP-1 was opposite to that of insulin. Similar levels of insulin and glucose were obtained with both GH regimens, while levels of non-esterified fatty acids were significantly higher following once-daily GH injection (P < 0.001).

CONCLUSIONS

Twice-daily GH injections, apart from producing a more physiological serum GH profile, were superior to one injection in increasing serum IGF-I and decreasing IGFBP-1 levels. Both of these changes tend to amplify the effects of the administered GH. Twice-daily injections, however, resulted in lower night-time levels of lipid intermediates.

Galactopoietic effects of recombinant somatotropin and growth hormone-releasing factor in dairy cows

Eight Holsteins per group received 12 mg/d of recombinant growth hormone-releasing factor or 29 mg/d of recombinant bST or served as untreated controls for 60 d. Milk yield and composition were measured for 10 d before infusion, during infusion (d 0 to 59), and for 20 d after infusion ended. Compared with controls, bST and growth hormone-releasing factor increased SCM during infusion. The SCM yield of cows treated with growth hormone-releasing factor was greater than that of bST-treated cows during the final 20 d of infusion. Relative to controls, bST and growth hormone-releasing factor increased serum concentrations of somatotropin and IGF-I during infusion. Concentrations of somatotropin and IGF-I in serum of bST- and growth hormone-releasing factor-treated cows did not differ during infusion. In summary, growth hormone-releasing factor increased SCM yield more than bST, despite similar serum concentrations of somatotropin and IGF-I. Thus, the galactopoietic action of growth hormone-releasing factor was not explained solely by elevation of total radioimmunoassayable somatotropin and IGF-I in serum.

Comparison of somatotropin and growth hormone-releasing factor on milk yield, serum hormones, and energy status

Holstein cows received 12 mg/d of growth hormone-releasing factor (continuous i.v. infusion, n = 5), 14 mg/d of bST (single daily i.m. injection, n = 8), or no treatment (controls, n = 8) for 60 d. Compared with controls (31.6 kg/d), bST and growth hormone-releasing factor increased milk yield to 34.2 and 37.0 kg/d, respectively. The increase in milk yield induced by the growth hormone-releasing factor was greater than that for bST. Milk yield was not different among groups following cessation of treatment. Milk energy output was 24.2 Mcal/d in controls, and growth hormone-releasing factor increased milk energy output to 28.5 Mcal/d. Milk energy output of cows receiving bST was 26.1 Mcal/d. Growth hormone-releasing factor increased DMI (23.2 kg/d) over that of controls (21.1 kg/d), whereas bST (21.5 kg/d) did not. Relative to controls, bST increased averaged daily serum somatotropin from 1.3 to 7.6 ng/ml and insulin-like growth factor-I from 67.5 to 116.0 ng/ml. Relative to bST, growth hormone-releasing factor increased serum somatotropin to 16.3 ng/ml and insulin-like growth factor-I to 202.6 ng/ml. Relative to control (115.8 meq/dl) and bST (158.1 meq/dl), growth hormone-releasing factor increased plasma NEFA (230.3 meq/dl). During treatment, calculated energy balance was negative for cows receiving growth hormone-releasing factor but positive for bST and control cows. Milk composition, body condition score, BW, and apparent digestibility of DM were not different among treatments. We conclude that i.v. infusion of 12 mg/d mg of growth hormone-releasing factor has greater galactopoietic activity than i.m. injections of 14 mg/d of bST.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone formation in demineralized bone transplants treated with biosynthetic human growth hormone

The influence of local administration of biosynthetic human growth hormone on the bone formation in a rabbit bone defect grafted with demineralized autologous bone was studied and compared to contralateral saline administration. The growth hormone was produced by hybrid DNA-technique and administered locally to the bone defect with the demineralized bone implant by an osmotic pump delivering 5 microliters/h during 14 days. At 14 and 28 days after operation the bone forming process was evaluated by roentgenography, planimetry included, and scintigraphy after injection of 99Tcm-labelled DPD. At 28 days after operation also autoradiography was performed. The roentgenographic and scintigraphic examinations revealed no influence from growth hormone neither 14 nor 28 days postoperatively. Centrally in the remineralized grafts the roentgenograms 28 days after operation showed radiolucent areas which in corresponding autoradiograms showed no uptake of 99Tcm. These areas turned out to be remnants of matrix. It is suggested that growth hormone has no influence on the bone induction process during the first 14 days when administered to bone matrix, probably due to relative lack of osteogenic cells. This study contributes a base for further evaluation of factors pertinent to hormonal stimulation of bone matrix transplants.

Glucose transport in adipocytes and its control by growth hormone in vivo

Previous results showed maximally enhanced basal glucose transport in adipocytes of hypophysectomized rats and restoration to normal after human growth hormone (hGH) administration. The data suggested a hGH-dependent "limiting factor" for glucose transport in the adipocyte membrane, which is acutely inhibited by insulin resulting in enhanced glucose transport. In this study the effect of hGH was investigated with respect to dose and time dependence. hGH was administered by continuous infusion from subcutaneously implanted Alzet minipumps. A significant decrease of basal glucose transport was obtained at the lowest hGH dose of 50 mU/day for 6 days. This effect of hGH was strictly correlated to the effects on growth (tibial epiphyseal width, DNA synthesis, body weight, serum level of insulin-like growth factor). The effect of hGH on basal glucose transport was already observed after 12 h of infusion, and it increased to a maximum after 3 days. The data support the concept that GH regulates the glucose transport system in adipose tissue in vivo.