Tibial Epiphyseal Width Research Articles

The somatostatin analog octreotide inhibits GH-stimulated, but not IGF-I-stimulated, bone growth in hypophysectomized rats.

IGF-I mediates growth-promoting actions of GH. In the present study we investigated whether the somatostatin analog octreotide blunts the stimulatory effects of GH and/or IGF-I on bone growth in hypophysectomized rats infused for 6 d with vehicle, GH, or IGF-I. We found that octreotide significantly suppressed the GH-induced rise in liver IGF-I mRNA (-27%) and peptide (-32%) and the serum IGF-I level (-26%) and concomitantly inhibited GH-stimulated, but not IGF-I-stimulated, body weight gain (-31%), tibial epiphyseal width (-14%), and bone growth rate (-24%). Furthermore, octreotide significantly reduced the GH-induced increase in the number of IGF-I immunoreactive chondrocytes in all layers (except in the upper hypertrophic zone) of the tibial growth plate cartilage (P < 0.0001 for stem cell and proliferative zone; P < 0.0005 for lower hypertrophic zone). These findings demonstrate that octreotide does not interfere with IGF-I action, but does interfere with local GH-stimulated IGF-I production in the growth plate. Thus, besides inhibiting pituitary GH secretion, octreotide exerts inhibitory peripheral effects on GH-stimulated longitudinal bone growth.

IGF-I and GH stimulate Phex mRNA expression in lungs and bones and 1,25-dihydroxyvitamin D(3) production in hypophysectomized rats.

X-linked hypophosphatemia, a renal phosphate (Pi)-wasting disorder with defective bone mineralization, is caused by mutations in the PHEX gene (a Pi-regulating gene with homology to endopeptidases on the X chromosome). We wondered whether changes in Phex and neprilysin (NEP) (another member of the family of zinc endopeptidases) mRNA expression could be observed in relation to vitamin D and Pi metabolism during GH- and IGF-I-stimulated growth of hypophysectomized rats. Animals were infused s.c. for 2 days with vehicle, 200 mU (67 microg) GH or 300 microg IGF-I/rat per 24 h. We determined serum osteocalcin and osteocalcin mRNA in bone, Phex mRNA in bone and lungs, serum 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) and serum Pi levels, and renal expression of 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase), of 25-hydroxyvitamin D(3)-24-hydroxylase (24-hydroxylase) and of the Na-dependent Pi-cotransporter type I and II (Na(d)Pi-I and -II). As compared with vehicle-treated controls, body weight and tibial epiphyseal width significantly increased in GH- and IGF-I-treated animals. Serum osteocalcin and osteocalcin mRNA levels in bone, Phex mRNA in bone and lungs, serum 1,25-(OH)(2)D(3) and renal 1alpha-hydroxylase mRNA rose concomitantly, whereas expression of NEP in lungs was barely affected and renal 24-hydroxylase mRNA decreased. Na(d)Pi-I and -II gene expression in the kidney and serum Pi levels remained unchanged. Our findings suggest a coordinate regulation of Phex mRNA expression in lungs and bone and vitamin D metabolism during GH- and IGF-I-stimulated growth.

Failure of IGF-I Infusion to Promote Growth in Zn Deficient Hypophysectomized Rats

The retarded growth of zinc-deficient rats is associated with low plasma insulin-like growth factor-I (IGF-I). To determine whether the low circulating IGF-I concentrations are responsible for the stunted growth, the growth response of zinc-deficient hypophysectomized rats to supplementation with recombinant human IGF-I (hIGF-I) was investigated. There were three dietary groups: zinc-deficient (0.9 mg zinc/kg diet), controls (66 mg zinc/kg diet) and zinc-adequate pair-fed (66 mg zinc/kg diet). All rats in each group received hIGF-I (150 micrograms/day) by subcutaneous infusion for 12 days, except for half of the animals in the control group which were sham-treated and which received vehicle infusion for the same period of time. The magnitude of the change was small, nevertheless infusion of hIGF-I significantly increased (p < 0.05) the body weight, tail length, liver weight and tibial epiphyseal width of control animals. This growth effect of hIGF-I was inhibited by lack of zinc in the diet, as evidenced by continuous weight loss, no increase in tail length and lowered tibial epiphyseal width in zinc-deficient animals. We conclude that systemic supplementation of hIGF-I can promote growth in hypophysectomized rats. The absence of weight gain and bone growth in zinc-deficient animals during the infusion period suggests that the growth promoting effect of circulating IGF-I is impaired by zinc deficiency.

Growth promotion by insulin-like growth factor I in hypophysectomized and diabetic rats

Two animal models, the hypophysectomized (hypox) and the streptozotocin-diabetic rat, both of which are GH-deficient, were used to study the effects of infused IGF I and its molecular size distribution in serum, and to investigate whether GH and IGF I act identically on growth plate chondrocyte maturation. In hypox rats, IGF I (300 μg/rat per day) stimulated body weight gain, total growth plate height and longitudinal growth rate, although less than GH (200 mU/rat per day), and mimicked the effect of GH at all stages of chondrocyte differentiation, including stem cells. Infused IGF I was nearly exclusively found in a <100 kDa IGF binding protein (IGFBP) complex, whereas free IGF I was barely detectable. These findings argue against the ‘dual effector theory’ in vivo which postulates priming of the stem cells by GH before IGF I stimulates proliferation. They also suggest that IGF I bound to the <100 kDa IGFBP complex is bioavailable for growth. In diabetic rats infused with 2.5 mg/rat per day of IGF I, body weight, tibial epiphyseal width and accumulated bone growth increased dramatically despite persisting hyperglycemia. Insulin infusion (2.5 U/rat per day), which nearly normalized elevated blood sugar values, raised endogenous IGF I serum levels and stimulated growth parameters to a similar extent as IGF I, in line with a similar distribution of the infused exogenous and the insulin-induced endogenous IGF I between the free and the <100 kDa-bound form. Since GH secretion is inhibited in diabetic rats and the animals are resistant to GH action, these results, like those in hypox rats, demonstrate that IGF I can act on growth independently of GH. Because insulin restores GH secretion and the responsiveness of the liver to GH in diabetic rats, one may conclude that insulin acts on growth of diabetic rats mainly via restoration of the GH/IGF I axis.

Zinc deficiency inhibits the direct growth effect of growth hormone on the tibia of hypophysectomized rats.

The effect of zinc deficiency on the direct-growth effect of growth hormone (GH) on tibia growth in hypophysectomized rats was studied. There were three dietary groups. Zinc deficient (ZD) group (0.9 mg/kg diet), control (C) group (66 mg/kg diet) and zinc adequate pair fed (PF) group (66 mg zinc/kg diet). All rats in each group received local infusion of recombinant human-growth hormone (hGH) (1 microgram/d), except for half of the animals in the control group, which were sham-treated, receiving vehicle infusion only. The substances were infused continuously for 13 d by osmotic minipumps through a catheter implanted into the right femoral artery. Food intake was lower and body weight loss was greater in ZD, and PF animals compared with C animals (p < 0.001). Tissue-zinc concentration and plasma alkaline-phosphatase activity were decreased (p < 0.05) by dietary-zinc deficiency. GH infusion increased the tibial-epiphyseal width of the treated right limb, but not of the noninfused left limb in C and PF animals. However, in ZD rats, no difference was found between the infused and the noninfused limbs. These results demonstrate that zinc deficiency inhibits the direct-growth effect of GH on long-bone growth.

Evidence suggesting that insulin-like growth factor-I is necessary for the trophic effects of insulin on cartilage growth in vivo.

The possibility that insulin-stimulated cartilage growth in hypophysectomized rats involves local production of insulin-like growth factor I (IGF-I) was investigated. Osmotic minipumps with attached catheters were used to infuse insulin into the right hindlimb of rats via the common iliac artery for 7 days starting 14 days after pituitary removal. The left, noninfused limb served as an internal control. Doses of insulin ranging from 0.25 to 50 mU/day caused significant increases in the tibial epiphyseal plate width (TEPW) of the infused limbs. The optimal dose of 1.25 mU/day increased the TEPW by 51 microns. Immunohistochemical analysis with an antiserum to human IGF-I showed that the growth response to the optimal dose was accompanied by the accumulation of IGF-I in the chondrocytes in the tibial plate. Infusion of insulin at a dose of 10 mU/day increased the TEPW by 18.6 +/- 3.0 microns. When the same dose of insulin was infused with the antiserum to human IGF-I, the growth response was completely nullified. These results indicate that cartilage cells in hypophysectomized rats are highly sensitive to the direct growth-promoting action of insulin. Furthermore, the growth effect appears to be mediated by or dependent on local production of IGF-I.

Administration of Growth Hormone to Pregnant Rats on a Reduced Diet Inhibits Growth of Their Fetuses*

During gestation, female rats become resistant to the anabolic actions of GH. The importance of this resistance for conceptus growth was investigated by treating pregnant dams on a reduced diet with ovine (o) or bovine (b) GH during days 10-20 of gestation. Reducing food intake to 60% that of ad libitum-fed controls significantly depleted maternal inguinal fat stores by day 20 of gestation, but it did not affect the growth of the fetuses or the placentas. In the food-restricted dams, twice daily injections of oGH (1 mg/day) or bGH (5 mg/day) during days 10-20 of gestation increased their inguinal fat pad wet weight by 28% and 62%, respectively, but had no effect on the wet weight of maternal heart, liver, or spleen. The dams treated with bGH had significantly heavier kidneys than the PBS- or oGH-treated females. On day 20 of gestation, control animals fed a 60%-diet had total serum insulin-like growth factor-I levels that were depressed to the same extent as those in ad libitum fed dams (i.e. to about 25% of the levels in nonpregnant females). Both the oGH and bGH treatments significantly elevated maternal serum insulin-like growth factor-I to 42% and 300%, respectively, of the levels in the untreated underfed dams. Compared to virgin controls, maternal tibial epiphyseal plate width was also significantly diminished in dams fed ad libitum or a 60% diet. Nevertheless, oGH and bGH were effective at augmenting maternal tibial epiphyseal plate width to equal those in virgin controls. Both doses of GH significantly reduced placental and fetal weights compared to those of PBS-injected dams on a 60% diet, and dams treated with the higher dose of GH were in an advanced stage of fetal and placental resorption by day 20 of gestation. Thus, maternal resistance to the anabolic actions of GH appears to be an important adaptation for diverting nutrients from the mother to the fetus.

Production of Generalized Learning Deficit and Permanent Growth Stunting by Bilateral Brain Stem Lesions

Bilateral lesions of the globus pallidus, ventrolateral thalamus, substantia nigra, or the median raphe produce a generalized learning deficit in rats. Bilateral lesions of the dorsomedial hypothalamic nuclei stunt growth in rats without significantly disturbing endocrine functions and without producing a generalized learning deficit. Globus pallidus, ventrolateral thalamus, substantia nigra, median raphe, and dorsomedial hypothalamic nuclei lesions were produced in weanling Sprague-Dawley rats to compare their effect on physical growth. At approximately 72 d of age, all lesions had resulted in reduced body wt, tail length, and tibial length. The differences lacked significance only in body wt after median raphe lesions and tail length after ventrolateral thalamus lesions. In rats with the generalized learning deficit, body size was most stunted after substantia nigra lesions. Tibial epiphyseal width was modestly increased in rats with the generalized learning deficit. Food intake/average body wt ratio in substantia nigra and dorsomedial hypothalamic nuclei rats did not differ significantly from control values. Decreases in brain, heart, liver, kidney, and testes tended to occur after all the lesions, but brain and testis organ wt/body wt ratios were either increased or unchanged. We conclude that brain lesions producing a generalized learning deficit in rats result in impaired physical growth. The results indicated that the stunted animals maintain adequate food intake and have normal growth hormone function. The anatomical substrate for generalized learning impairment may overlap with that of a set point for body size.

The role of insulin-like growth factor I in growth of diabetic rats.

Insulin-deficient, streptozotocin-diabetic rats show severe metabolic disturbances and stop growing. Besides insulin, these animals also lack growth hormone and insulin-like growth factor-I. We examined whether or not growth parameters correlate with IGF-I serum levels in young rats with streptozotocin-diabetes of different severity. In the diabetic rats, blood glucose varied between 18.4 and 38.6 mmol/l (healthy controls between 6.1 and 9.3), IGF-I serum levels between 2.6 and 15.6 nmol/l (controls between 19.6 and 26.5), and serum insulin levels between 0.05 and 0.14 nmol/l (controls between 0.36 and 0.55). We found a highly significant linear correlation between IGF-I serum levels and the two investigated growth parameters, tibial epiphyseal width and longitudinal tibial bone growth. The finding that these indices of growth are strongly correlated with IGF-I serum levels in young rats with diabetes of different severity, suggests that IGF-I is a major determinant of growth. This is in keeping with our earlier demonstration that exogenously infused IGF-I promotes growth in diabetic rats.

Rats stunted by high-dose glucocorticoid treatment are capable of undergoing catch-up growth after fasting.

Experiments were carried out to test the hypothesis that permanent growth retardation after glucocorticoid-induced growth suppression is due to an alteration of a central set point for target size rather than an inability of peripheral tissues to carry out catch-up growth. Rats were injected subcutaneously with saline, as controls, or with cortisone acetate, 1 mg/25 g body wt/d, for 4 d, beginning at 37 d of age. The treated animals were submitted to acute fasting for 48 h, beginning at 47 d of age, after which they were allowed to feed ad libitum. Cortisone treatment significantly stunted body wt, tail length, and tibia length. During recovery after fasting, both the cortisone-treated and the saline-injected rats exhibited catch-up growth in body wt and tibial length. In other rats killed at different time intervals during recovery after cortisone treatment, only, there was no pattern of catch-up growth in tibia length. There was no difference in tibial epiphyseal width between fasted and nonfasted rats within the saline- or cortisone-treated group. The findings demonstrate that rats that are permanently stunted by high-dose glucocorticoid treatment retain the capability for catch-up growth in both soft and skeletal tissues. The data support the hypothesis that catch-up growth is regulated by a central control with a mechanism (set point) for setting target size of the body. Stunting resulting from glucocorticoid treatment may be the result of a reset of the putative set point.

Recombinant DNA-derived human insulin-like growth factor II (hIGF-II) stimulates growth in hypophysectomized rats.

Sustained subcutaneous administration of recombinant DNA-derived insulin-like growth factor II to immature female hypophysectomized rats stimulated significant increases in body weight gain, tibial epiphyseal cartilage width, femur hydroxyproline concentrations and a significant decrease in serum urea nitrogen concentrations. Recombinant DNA-derived human growth hormone (Humatrope), administered in the same manner produced similar biological effects. The data support the contention that hIGF-II has anabolic effects when administered to hypophysectomized rats and may be a locally acting mediator of pituitary hormone actions.

Discordance of serum and tissue somatomedin levels in growth hormone-stimulated growth in the rat.

Although the somatomedins are believed to mediate GH-induced somatic growth, circulating levels of insulin-like growth factor I (IGF-I) do not always correlate with growth rate. To evaluate a paracrine or autocrine effect that might explain this discordance, the concentrations of plasma and tissue IGF-I were compared with indices of growth in hypophysectomized rats treated with rat GH (rGH). The rats received a total of 250 micrograms rGH by either continuous pump infusion (P) or twice daily injections (I). After 4 days of treatment, the amounts of IGF-I present in acetic acid extracts of liver and kidney and in native serum were determined by RIA and related to proximal tibial epiphyseal plate width. Tibial epiphyseal plate width increased from 198 +/- 6 microns (mean +/- SE) in untreated controls to 339 +/- 13 microns in group P and 347 +/- 9 micron in group I; weight gain was 11.6 +/- 1.0 g in group P and 9.6 +/- 0.8 g in group I, while control animals lost 1.0 g. Serum concentrations of IGF-I were no different between control animals and those in the injection group (0.91 +/- 0.06 vs. 0.90 +/- 0.06 U/ml), whereas levels in the infusion group increased slightly (1.1 +/- 0.05 U/ml). In contrast, rGH administration caused tissue IGF-I to double in liver (control, 0.24 +/- 0.04 U/g; P, 0.51 +/- 0.03 U/g; I, 0.46 +/- 0.05 U/g) and nearly triple in kidney (control, 0.52 +/- 0.05 U/g; P, 1.51 +/- 0.09 U/g; I, 1.36 +/- 0.08 U/g). There was no detectable change in somatomedin-binding protein by gel exclusion chromatography. Since the rGH administered was sufficient to stimulate growth and increase tissue somatomedin levels without corresponding increases in circulating IGF-I, an autocrine or paracrine action of IGF-I appears to mediate GH's initial somatogenic actions in the young rat.

Recombinant human insulin-like growth factor I stimulates growth and has distinct effects on organ size in hypophysectomized rats.

Recombinant human insulin-like growth factor I (rhIGF-I) was infused subcutaneously into hypophysectomized rats for as long as 18 days. Three hundred micrograms (39 nmol) of rhIGF-I per day and 200 milliunits (4.5 nmol) of human growth hormone (hGH) per day increased body weight, tibial epiphyseal width, longitudinal bone growth, and trabecular bone formation similarly. Weight gains of the kidneys and spleen, however, were greater with rhIGF-I than with hGH, whereas the weight of the epididymal fat pads was reduced with rhIGF-I. The weight of the thymus was increased by rhIGF-I treatment. Thus, IGF-I administered over a prolonged period of time mimics GH effects in hypophysectomized rats. Quantitative differences between rhIGF-I and hGH treatment with respect to organ weights may be related to different forms of circulating IGF-I or may be due to independent effects of GH and IGF-I. The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action.

Insulin-like growth factor I stimulates growth in normal growing rats

The scarcity of purified somatomedin/insulin-like growth factor (SM/IGF) has prevented investigation of the mechanisms of SM/IGF action. Recently insulin-like growth factor I (IGF-I) has been synthesized by recombinant DNA technology. The availability of large quantities of the biosynthetic IGF-I made it possible to study its effects by administering 120 μg/day via s.c. implanted minipump to rats for 7 days. After this 7 day administration of IGF-I, the body weight increased to 197.6 ± 3.5% of initial values; the value was significantly greater than that of the control (179.4 ± 3.7% of initial values, P < 0.01). The body length and tibial epiphyseal width in IGF-I-treated rats were also significantly increased over those of control rats. The weights of kidneys, liver, testes and pituitary in IGF-I-treated rats were greater than those in control rats as well. These results provide a first demonstration that IGF-I stimulates growth in normal rats in vivo, and suggest that IGF-I-might be useful in the treatment of growth retardation.

Effect of zinc deficiency on serum somatomedin levels and skeletal growth in young rats.

We have studied potential mechanisms by which zinc deficiency (ZD) may result in growth impairment in young animals. Dietary-induced ZD in young rats resulted in diminished skeletal growth as measured by tibial epiphyseal width. Treatment with bovine GH (bGH) did not increase skeletal growth suggesting GH resistance rather than GH deficiency in zinc-deficient rats. Serum levels of basic somatomedin (SM) were lower in zinc-deficient rats than in control rats receiving a zinc adequate diet, either ad libitum or in pair matched amounts, and were restored to normal by zinc repletion but not by bGH treatment, suggesting that SM production is impaired by ZD. There was a high correlation between tibial epiphyseal widths and serum or femur zinc concentrations. These findings, along with observations that despite similar levels of serum basic SM the bGH-treated zinc-deficient rats had smaller tibial epiphyseal widths than pair fed control rats, additionally suggest that the action of SM on skeletal growth is impaired by ZD.

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.

Effect on growth of prolactin deficiency induced in infant mice.

The effect of lowering PRL levels in blood during early infancy on subsequent growth and development was studied in mice. PRL was reduced by injecting either an antiserum raised against homologous PRL or a PRL-inhibiting drug, 2-chloro-6-methylergoline-8 beta-acetonitrile methanesulfonate (ergoline), into 4-day-old mice for a period of 4 or 5 days. Both the anti-PRL serum and ergoline rapidly killed some of the injected animals, but the effect of anti-PRL serum was much more severe than that of ergoline (39% vs. 8.7% mortality during the period of injection). Similar administration of an antiserum against mouse GH or the GH-inhibiting peptide somatostatin did not cause a significant number of deaths. The deaths from the anti-PRL serum largely ceased when the antiserum was neutralized with rat PRL (NIH-RP-1) before injection. The gain in body weight of baby mice was markedly retarded within 24 h of injecting anti-PRL serum and ergoline, in contrast to the anti-GH serum and somatostatin injections, which took 3--4 days to inhibit growth perceptibly. The anti-PRL serum, despite having only one eighth the titer of anti-GH serum, was by far the most effective of the two antisera in diminishing tibial epiphyseal cartilage width as well as weights of pituitary glands, testes, and adrenals and retarding sexual maturity. The more severe and generalized developmental abnormalities and the incidence of mortality as a result of anti-PRL serum administration suggest that PRL in mice may be involved in the maintenance of some vital function during infancy.

Causes of Failure of Catch-up Growth After Certain Forms of Growth Retardation

These experiments were carried out in order to elucidate regulation of catch-up growth and occasional failures in catch-up which are observed clinically. Growth retardation was produced in Long-Evans rats, 37 to 41 days of age, by fasting, by cortisone injections, or by propylthiouracil (PTU) feeding. The cortisone or PTU treatments were adjusted to produce maximum differences in body weight between control and experimental groups that were equivalent to the differences produced in fast periods. Light and electron microscopy of epiphyseal cartilage and tibial epiphyseal width determinations were performed in representative groups. Serial measurements of body weight and tail length were carried out for 60 to 80 days from the start of the experimental treatments. Food intake was recorded. In the fast experiments refeeding was followed by nearly complete catch-up in body weight and tail length. After cortisone treatment there was no catch-up in body weight or tail length growth. After PTU there was a slight tendency to catch-up in body weight and tail length. The latter appeared to show a pattern of late catch-up. The results correlated with anatomic changes in cartilage. The findings suggest that in the rat cortisone treatment in post-weaning period permanently damages growth mechanisms and prevents growth recovery in certain circumstances. Hypothyroidism also results in a delayed catch-up in skeletal growth. These experiments illustrate certain complexities in the problem of clucidating the underlying basis of catch-up growth. The usefulness of this experimental model in studies of catch-up growth is demonstrated.

Pituitary content of somatotropin, gonadotropin, and thyrotropin in rats with stunted linear growth following head x-irradiation.

SummaryThe injection of homogenates of the pituitaries of rats stunted by 600 R of X-irradiation administered to the head and of nonirradiated controls into hypophysectomized immature female rats resulted in comparable responses in terms of tibial epiphyseal width, gonadal weight, and thyroidal 131I uptake. An exception occurred in 121-day-old females in which the pituitary homogenate of the stunted animals produced about twice the gonadal weight in the assay animals as did those of controls. These findings combined with those of earlier experiments, suggest that the permanent stunting resulting from head X-irradiation is not the result of hormonal deficit.

STUDIES ON GROWTH HORMONE SECRETION IN RATS WITH THE HYPOPHYSIS AUTOTRANSPLANTED TO THE KIDNEY CAPSULE.

ABSTRACT The secretory capacity of the pituitary gland, autotransplanted to the kidney capsule, was studied with special regard to the secretion of growth hormone (GH). Body weight, body length, tibial epiphyseal width and the mammary gland development after testosterone stimulation were studied. Body growth and tibial epiphyseal width were markedly reduced in the rats with transplanted hypophysis, but not as much as in the hypophysectomized controls. After injections of 0.25 mg testosterone propionate daily for 10 days, only a few groups of alveoli were seen in the mammary glands of the transplanted rats. These observations show that there is a considerable deficiency of GH in rats with the pituitary gland autotransplanted to the kidney capsule. However, the development of a few alveoli in the mammary glands is in favour of the theory that a small amount of GH is secreted from the transplanted pituitary tissue. Injections of a purified vasopressin preparation (Pitressin) in the rats with autotransplanted hypophysis did not influence body growth, tibial epiphyseal width or mammary gland development. Further, no effect of Pitressin was seen on the tibial epiphyseal cartilage of rats with intact pituitary gland as has been reported by Del Vecchio et al. (1958) and Hiroshige &amp; Itoh (1960). These experiments therefore do not support the view that vasopressin acts as a GH releasing factor.