Decreased reverse T3 levels in neonates with central hypothyroidism.

Concern arises when a sick infant is found to have a low serum T4, normal thyroid hormone binding, and a nonelevated thyroid-stimulating hormone. Hypothyroxinemia in this situation can result from either euthyroid sick syndrome or central hypothyroidism. To help distinguish between these diagnostic possibilities, we have measured reverse T3 and other thyroid function chemistries in six neonates who have central hypothyroidism in association with hypopituitarism. We found that these infants all had reverse T3 levels that were much lower than reported normal levels for premature and term neonates. This finding suggests that low reverse T3 levels can help to distinguish infants with central hypothyroidism from sick and well infants who tend to have relatively elevated reverse T3 levels.

Growth promoting peptides in diabetic and non-diabetic pregnancy: interactions with trophoblastic receptors and serum carrier proteins.

Infantile macrosomia in diabetic pregnancy (DP) is commonly attributed to fetal hyperinsulinism. However, insulin-like growth factors in the mother and the fetus, their binding proteins and their placental receptors may also play roles in the process of fetal overgrowth. We measured levels of maternal and cord serum IGF-I, IGF-II, C-peptide, IGFBP-1, IGFBP-2 and IGFBP-3 in 8 White Class B insulin dependent DP and 8 non-diabetic pregnancies (NP). These results were correlated with the concentration and affinity of placental trophoblastic membrane receptors (TR) for insulin (IN), IGF-I and IGF-II as well as with infant and placenta weights and maternal body mass indices. Significant respective differences between the diabetic and non-diabetic groups were found in mean infant weight, 4248 +/- 114 vs 3555 +/- 119 g (p < 0.001), placental weight 765 +/- 51 vs 575 +/- 24 g (p < 0.01), maternal body mass index 32.8 +/- 3.8 vs 21.3 +/- 1.2 (p < 0.02), cord serum IGF-I 136.8 +/- 6.6 vs 85.9 +/- 5.7 ng/ml (p < 0.01), cord serum C-peptide 18.7 +/- 3.5 vs 9.0 +/- 1.7 ng/ml (p < 0.025), cord serum IGFBP-1 21.9 +/- 4.7 vs 133.2 +/- 43.2 ng/ml (p < 0.025), cord serum IGFBP-2 672.0 +/- 76 vs 1206 +/- 220 ng/ml (p < 0.05) and cord serum IGFBP-3 11.5 +/- 1.0 vs 5.6 +/- 0.6 ng/ml (p < 0.001). No significant differences were found between DP and NP with respect to cord serum IGF-II, maternal serum IGF-I, IGF-II, C-peptide, IGFBP-1, IGFBP-2 and IGFBP-3, and the concentration and affinity of TR for IN, IGF-I and IGF-II. Analysis of variance revealed an interaction between infant weight and the weight of the placenta (p < 0.01), cord IGF-I (p < 0.02), cord C-peptide (p < 0.01) and cord IGFBP-3 (p < 0.01). Regression analysis revealed significant correlations of cord IGF-I with cord values of IGFBP-2 (r = -0.52, p = 0.04) and IGFBP-3 (r = 0.66, p < 0.005). Maternal serum IGF-I significantly correlated only with maternal IGFBP-3 (r = 0.65, p < 0.01). These results suggest that increased fetal production of insulin and IGF-I may contribute to the development of infantile macrosomia in DP. Concomitant changes in fetal production of IGFBPs, particularly IGFBP-2 and IGFBP-3, may modulate the action of insulin and IGFs. The lack of change in number or binding affinity of placental trophoblastic receptors for insulin, IGF-I and IGF-II tends to exclude a significant regulatory role of these receptors in the production of fetal macrosomia.

Spontaneous growth hormone release in term infants: changes during the first four days of life.

Healthy term infants have higher umbilical cord GH levels compared to older infants and children. In the sheep, GH concentrations rapidly fall within an hour of birth; the physiology of GH release after parturition in the human term infant is less well known. The purpose of this study was to investigate spontaneous 12-h GH release in male and female term infants of varying postnatal ages. We studied 14 infants (7 males and 7 females). Subjects were divided into those studied earlier following delivery (28.2 +/- 3.4 h of age, mean +/- SE) and into those studied at a later time (74.8 +/- 3.5 h, P < 0.0005). The age at study was defined as the age (hours) when blood sampling began. There were eight infants studied at an early age (four males and four females) and six studied at a later age (three males and three females). Subjects were comparable with respect to gestational age, birth weight, and length; all were biochemically euthyroid. One infant was large for gestational age although his head circumference was in the normal range. Blood (0.1 mL) was taken every 30 min over a 12-h period from an indwelling umbilical catheter; no stress occurred during the blood withdrawal. GH was determined by a double-antibody RIA using 0.01 mL plasma. GH pulse detection was undertaken using Cluster, a computerized pulse detection algorithm. Total insulin-like growth factor I (IGF-I) was measured following separation of the IGFs from the serum binding proteins. Spontaneous pulsatile GH release was observed in all infants studied. No differences in GH characteristics were found between male and female subgroups in the early or late study groups. In subsequent analysis, the data for the males and females are combined. The GH pulse frequency per 12 h was greater in the earlier studied group, 5.1 +/- 0.9 (mean +/- SE) vs. 2.5 +/- 0.7 in the later group (P < 0.05). The maximal pulse amplitude was 47.1 +/- 7.9 micrograms/L in the early and 27.1 +/- 4.1 in the later studied group (P < 0.06). The incremental pulse amplitude was 26.4 +/- 3.4 micrograms/L in the early and 12.8 +/- 2.7 in the later group (P = 0.01). The pulse width was greater in the later studied group (202.8 +/- 71.1 min vs. 84.1 +/- 21.6, P < 0.06).(ABSTRACT TRUNCATED AT 400 WORDS)

Food efficiency in rats following brain lesions which affect target body size: implications on the set point for target size.

Target size, i.e. body size appropriate for age, may be reset by bilateral lesions of several brain areas. The mechanism for control of target body size is unknown, but some of the loci have marked effects on gustatory behavior and/or energy metabolism. We have tested the possibility that a disturbance in energy metabolism may be a common factor in resetting target size. Food efficiency for body weight gain and for metabolic size (the 0.75 power of body weight) was determined in rats that were experimentally stunted by neonatal head-irradiation or by bilateral electrolytic lesions produced soon after weaning in the dorsomedial hypothalamic nuclei (DMH) or the substantia nigra (SN). The irradiations were carried out in males and females; the surgical lesions were produced only in males. Observations were carried out from weaning through early adulthood. Subgroups of irradiated rats and controls were fasted for 48 hours at 40 days of age. Irradiated rats had reduced food efficiency for weight gain and for metabolic size, more marked in males than in females. DMH or SN lesions did not change food efficiency for weight gain. Food efficiency for metabolic size increased after DMH lesions and declined after SN lesions. During refeeding after a fast, irradiated rats showed a normal transient increase in food efficiency for weight gain, but not for metabolic size. The differences in food efficiency following different lesions tend to exclude altered energy metabolism as a common factor in the reset of target body size.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous pulsatile growth hormone release in male and female premature infants.

Although premature infants have high umbilical cord GH levels, little is known about spontaneous GH release in these individuals. The purpose of our study was to investigate spontaneous 12-h GH release in appropriate for gestational age male and female premature infants. We studied 22 premature infants (15 males and 7 females) of appropriate length and weight for age. Gestational ages, birth weights, birth lengths, and ages at the time of study were similar in male or female infants. All infants were biochemically euthyroid. Blood was taken every 30 min over a 12-h period from an indwelling umbilical catheter; no stress occurred during the blood withdrawal. GH was determined by a double antibody RIA, using 0.01 mL plasma. GH pulse detection was undertaken using Cluster, a computerized pulse detection algorithm. Total insulin-like growth factor-I and -II (IGF-I and -II) levels were measured after separation of the IGFs from the serum binding proteins. Spontaneous pulsatile GH release was observed in all infants studied. No differences were found between males and females in the pulse characteristics of frequency, maximal amplitude, incremental amplitude, width, or area. The GH pulse frequency per 12 h was 3.2 +/- 0.3 (mean +/- SE) in males and 3.0 +/- 0.7 in females. The maximal pulse amplitude was 50.7 +/- 6.2 micrograms/L in males and 44.7 +/- 9.0 micrograms/L in females. The incremental pulse amplitude was 24.3 +/- 3.2 micrograms/L in males and 20.2 +/- 3.9 micrograms/L in females. The mean 12-h GH level was 37.1 +/- 4.8 micrograms/L in males and 35.8 +/- 8.5 micrograms/L in females; the average GH nadir was 26.1 +/- 4.0 micrograms/L in males and 24.4 +/- 8.3 micrograms/L in females. Both IGF-I and IGF-II concentrations were similar in males and females. The mean IGF-I levels were 10.7 +/- 1.5 ng/mL in males and 7.5 +/- 1.1 ng/mL in females; IGF-II levels were 96.0 +/- 12.0 ng/mL in males and 115.4 +/- 17.1 ng/mL in females. These results demonstrate similar pulsatile GH release in male and female premature infants at a mean age of 32-33 weeks. Compared with previously reported values for mean GH concentration and average GH nadir in older children, the values in these premature infants were much higher. We speculate that the higher GH levels in premature infants may result from decreased negative feedback associated with low IGF-I levels. The premature infant's somatotrophs may also not fully respond to the GH inhibitory action of somatostatin.

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.

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.

Successive resetting of the set point for target body size.

Previous studies support the existence of a central set point for target body size. The set point is a hypothetical fixed reference for body size. The present experiments were carried out to determine whether target body size and, by implication, the putative set point can be consecutively reset or whether, once set by an extraneous factor, it is refractory to another extraneous factor. Male and female rats were given 6.0 Gy whole head X-irradiation at two days of age or were sham-irradiated as controls. Significant permanent reduction of body weight, tibia length, and pituitary weight resulted from head-irradiation in both males and females; gonad weight was reduced in males but not significantly in females. At 41 days of age the irradiated animals were injected sc with cortisone acetate, 1 mg/25 g body weight/day, or saline. During cortisone treatment the head-irradiated rats had a decrease in body weight velocity; the effect was greater in males than in females. Following treatment growth velocity approached normal in treated males, and slightly exceeded normal in treated females. Treated males had significantly reduced body weight, tail length, and tibia length at the end of the study. Treated females showed a similar pattern of body weight growth to the treated males, but there was not a significant long term reduction of body weight or change in tail length or tibia length. Final pituitary and gonad size was not affected by cortisone treatment in either sex. The results indicate that the reset of target size after head-irradiation does not result from damage to putative control.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glucocorticoids on plasma insulin-like growth factor I concentration in the rat fetus.

Radioimmuno- and radioreceptor-assayable insulin-like growth factor I (IGF-I) concentration was determined in plasma pools of rat fetuses on gestation day 21 following treatment of the pregnant rats with pharmacologic doses of betamethasone, dexamethasone, or cortisone on gestation days 12 and 13. Dose-related reduction of plasma concentration of IGF-I occurred after betamethasone or dexamethasone treatment. There was no change in IGF-I concentration after cortisone treatment. The changes in fetal IGF-I concentration after steroid treatment were parallel between the two assays. Comparison of the results with previous data showing the effects of identical treatment of pregnant rats on fetal body and organ growth suggests that the IGF-I changes correlate better with reduction of liver/body ratio than with reduction of body weight. The findings indicate that growth retardation after steroid treatment in the fetus is in part the result of factors other than IGF-I. This may include a direct effect of the glucocorticoids on skeletal tissue. Reduced IGF-I concentration may contribute to the growth deficit.

Lack of synchrony between feeding activity and pulsatile growth hormone secretion in rats.

Plasma growth hormone (GH) was determined in blood sampled at 15 minute intervals in undisturbed chronically cannulated adult male rats while continuously monitoring feeding activity. Ten animals were studied; five were optic nerve sectioned from 24 days of age and five were intact. The sampling time was from 15:00 hours to 21:00 hours, which included 5 hours of light and the first hour of dark. Both GH secretion and feeding activity exhibited a pulsatile pattern. There was no consistent coordination of bursts of feeding activity and GH secretion. We conclude that feeding activity and GH secretion may be controlled by central timing mechanisms; however, it appears that these mechanisms are separate and are not synchronized.

A frequency of growth hormone secretion associated with catch-up growth in the rat detected by time domain (Box-Jenkins) analysis.

A time domain technique has been applied to the analysis of temporal patterns of GH concentrations determined at 15 min intervals for 24 h in rats undergoing catch-up growth after a fast and in controls. Three tests were performed on the data. The first compared the autocorrelation functions (ACF's) and partial autocorrelation functions (PACF's) of the series of the GH measurements for the two groups. The second determined whether the model which best fit the control group removed all the regular behavior from the fasted group. The third test, which was similar to the second, was carried out with the assumption that the behavior of both groups is best conceptualized as a binary pattern of periods in which GH is either secreted or not. In the first test the ACF's and PACF's indicated that both groups have a memory of 15 min and a cycle(s) with a periodic interval in the range of 75 to 105 min. There was an indication of a cycle with a periodic interval of 180 to 210 min in the fasted group. The second test confirmed that the cycle was present in only the fasted rats. The third test confirmed the result of the second test. The findings demonstrate the usefulness of time domain analysis in determining periodic behavior of GH secretion in the rat. We conclude that a frequency of GH secretion with a periodic interval of approximately 195 min is superimposed on normal basal rhythms of GH secretion during catch-up growth following a fast in rats.

Dissociation of catch-up growth control and neural control of growth hormone secretion in the stunted head-irradiated rat.

Male Long-Evans rats were irradiated to the head only at 2 days of age; littermates of the same sex were sham-irradiated. At 40 days of age the irradiated rats were divided into two groups, one of which was fasted 48 h and the other fed a normal diet. The irradiated rats, fasted and nonfasted, were cannulated in the superior vena cava at 48 to 50 days of age. Between 54 and 58 days of age the cannulated undisturbed rats had blood samples withdrawn at 15-min intervals over an 18-h period (9 h light and 9 h dark). Body weight and tail length data showed characteristic stunting following irradiation. The superimposed fast caused transient growth retardation; on refeeding, the fasted rats showed a pattern of catch-up growth limited to the irradiated non-fasted body size. Plasma growth hormone (GH) concentration in the fasted-refed rats as compared with the nonfasted irradiated rats showed no change in the average period of the bursts of GH secretion, the numbers of values in ranges of GH concentration, or the area under the curve of the plasma GH concentration versus time. No difference in these parameters was present in light or dark, considered separately. We conclude 1) that the link between the catch-up growth control and neural mechanisms controlling GH secretion is impaired as a consequence of the neonatal head-irradiation and 2) that catch-up growth acceleration is not dependent on increased GH secretion.

The control of catch-up growth.

Catch-up (compensatory) growth following transient growth retardation due to illness or starvation has long been recognized in biology and in clinical medicine. This report summarizes work utilizing experimental models in rats in efforts to elucidate the control of catch-up growth. The results support the hypothesis that the catch-up growth mechanism includes a set-point or reference for body size appropriate for age and that the control resides in the central nervous system. Growth hormone (GH) secretion is increased during catch-up growth, although the results also show that increased GH secretion is not required for catch-up growth acceleration. Environmental light modulates the effect of catch-up growth on GH secretion. The mechanisms for sensing a deficit in body size and for stimulating catch-up growth acceleration remain unknown.

Increased synthesis of glycosaminoglycans of the cornea during fasting and refeeding in rats.

The effect of a 48 hour fast on sulfate incorporation of corneal mucopolysaccharides was investigated in the rat. After fasting for 24 hours, experimental and control rats were injected intraperitoneally with 35S-sulfate. After fasting an additional 24 hours, the rats were sacrificed and incorporation of the label into the acid mucopolysaccharide fraction of the cornea was determined. Incorporation of the label into the acid mucopolysaccharide fraction was significantly increased in the fasted rat cornea. Increased synthesis of corneal sulfated mucopolysaccharides during fasting in the rat contrasts with the well known decreased synthesis in cartilage under the same conditions. These findings suggest that corneal acid mucopolysaccharide synthesis is selectively preserved and/or increased during fasting.

A simplified method for chronic portal vein cannulation in the rat.

A simple technique is described for chronic cannulation and repeated blood sampling from the portal vein of the conscious undisturbed rat. The method employs a straight cannula and allows precise location of the tip. Blood flow in the portal vein is not obstructed. The present technique was used in combination with chronic cannulation of the superior vena cava. Simultaneous blood sampling from the two cannulas was successfully carried out at fifteen minute intervals over six hour periods. The system and the sampling were well tolerated by the rats.

The effects of different steroids on costal and epiphyseal cartilage of fetal and adult rats.

The effects of different doses of various steroids on growth, and on costal and epiphyseal chondrocytes, have been studied in prenatal, immature, and adult Long-Evans rats using histochemical techniques, and both light and electron microscopy. Both prenatal and postnatal treatments have been employed. The steroids used were cortisone (CA), betamethasome (BM), and, in the prenatal group only, dexamethasone (DM). Body weight is reduced in all treated rats (except the low dose of CA) by day 17 of gestation, with greater weight reductions occurring in rats receiving the higher dose level of each steroid. In rats treated prenatally or neonatally, and sacrificed postnatally on days 39-43 or days 116-127, body weights, and tibial and tail lengths, are less than in correspondingly aged controls, thus showing a persistence of the effects of treatment. Costal and epiphyseal cartilages in prenatal rats show cellular, synthetic, and ultrastructural alterations induced by treatment with glucocorticoids but the responses are not necessarily comparable. Except for the low dose of DM, the higher doses of each steroid are more effective in inhibiting, or altering, growth and cellular differentiation in the developing fetuses. Surprisingly, a low dose of DM has a more devastating effect on the cells and extracellular matrix of both costal and epiphyseal cartilage, than do higher dose-levels of the various steroids. Low doses of CA and BM are also effective in inhibiting or altering growth and cellular differentiation, but their effectiveness is largely limited to 17 days of gestation. The order of effect of the various doses of the different steroids on fetal cartilage, listed in decreasing order of severity, is as follows: 0.12 DM, 0.24 DM, 0.42 BM, 50 CA, with 25 CA and 0.18 BM being approximately equal and only slightly different from control cartilages. The effect of prenatal or neonatal glucocorticoid treatment on chondrocytes is minimal in the 30-43 days, or 116-127 day, postnatal groups. In immature and adult rats, cortisone affects the chondrocytes more deleteriously than does betamethasone, and a 5.0 mg dose of CA seems to affect chondrocytes, body weight, and tibial and tail lengths more than 0.2 or 7.5 mg doses.

Growth hormone secretion in the stunted head-irradiated rat.

Pulsatile secretion profiles of pituitary growth hormone (GH) and size and number of cells of brain, heart ventricles, liver, kidney, and gastrocnemius muscle were determined in male Long-Evans rats which received 600 rad x-irradiation to the head only at 2 days of age. Controls consisted of sham-irradiated littermates. The irradiated rats showed significant stunting of body weight and tail length beginning prior to weaning and lasting throughout the period (64 days) of observation. In irradiated rats at 20-21 days of age, just prior to weaning, organ weight was significantly reduced in all organs studied. Brain showed a decrease in organ/body ratio (p less than 0.0005) and in total DNA content (p less than 0.0005), but these values were not significantly changed in the other organs. DNA/organ ratio was increased significantly in heart (p less than 0.025) and gastrocnemius muscle (p less than 0.025); brain, liver, and kidney had nonsignificant increases. Protein/DNA ratios were decreased significantly in brain (p less than 0.005), heart (p less than 0.01), and gastrocnemius muscle (p less than 0.05); liver and kidney had nonsignificant decreases. Blood samples were removed for GH determination from cannulated undisturbed irradiated and control rats at 15-min intervals for 18-h periods (9 h light and 9 h dark) at 47-64 days of age. Irradiated rats had normal periodicity of bursts of GH secretion. The area under the curve of GH concentration versus time of the irradiated rat was decreased in light (p less than 0.025) and in dark (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in pulsatile secretion of growth hormone during failure of catch-up growth following glucocorticoid-induced growth inhibition.

The pattern of growth hormone (GH) secretion was determined in rats injected with cortisone acetate, 5 mg/rat/day subcutaneously, or with an equivalent volume of saline for 4 days from age 40 days. Cortisone injections resulted in inhibition of growth of body weight and tail length. During recovery the rats resumed a normal rate of growth but failed to show catch-up growth acceleration. From 17 to 27 days of recovery, plasma was sampled at 15-min intervals through the lights-on period, 06:00 to 18:00, via a catheter chronically implanted in the superior vena cava. During sampling each rat was housed singly in an insulated chamber, unrestrained, and with food and water ad lib. Cortisone-treated animals had a normal periodicity of GH plasma concentration, but they showed a reduction in values in the range of 50 to 99 ng/ml (P less than 0.01) and an increase of values in the range of 200 to 499 ng/ml (P less than 0.025) and above 1000 ng/ml (P less than 0.05). The area under the GH concentration curve of the cortisone-treated rats was significantly greater than that of the controls, 100.9 +/- 18.7 (mean +/- SE) units vs 55.3 +/- 7.4 (P less than 0.025). Thus, increased growth hormone secretion during the light phase persisted in spite of failure of catch-up growth acceleration. The findings indicate that the mechanism involved in GH release is linked to the catch-up growth control.