Regina A. Jansons

The Effect of Glucocorticoids on Plasma Insulin-Like Growth Factor I Concentration in the Rat Fetus

ABSTRACT: 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.

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

SummaryThe 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 day, 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.

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

Abstract 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 (P0.01) and an increase of values in the range of 200 to 499 ng/ml (P0.025) and above 1000 ng/ml (P 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 (P0.025). 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.

Cartilage Metabolism during Growth Retardation following Irradiation of the Head of the Neonatal Rat

Abstract The heads of 2-day-old male and female rats were irradiated with a single dose of 600 rads X irradiation, a dose which is known to stunt body weight, tibial length, and tail length, in order to ascertain its effect on synthesis by cartilage of sulfated proteoglycans, DNA, chondroprotein, and collagen as determined by utilization of [35S]sulfate, [Me-3H]thymidine, [1-14C]leucine, and [3,4-3H]proline, respectively. Data have been collected at 20-21, 23, 41-45, and 70-71 days of age. In comparison to controls, growth in body weight, tibial length, and tail length was significantly retarded in irradiated rats of both sexes. Although slow catch-up growth was observed with respect to tail length in both sexes and tibial length in females, a significant deficit in body weight in irradiated rats in both sexes remained at 70-71 days. Cartilage metabolism as evidenced by incorporation of the labeled substances showed no significant disturbance just prior to weaning (20-21 days) or after completion of the principal growth surge (70-71 days). Reduced sulfate and thymidine incorporation attributable to a brief period of undernutrition associated with weaning occurred in head-irradiated rats immediately following weaning (23 days). Increased isotope incorporation occurred at 41-45 days of age in cartilage of irradiated rats incubated with labeled sulfate, leucine, and proline; it did not increase with labeled thymidine. We conclude that neonatal head irradiation slows the rate of growth through the age of most rapid postnatal growth in normal rats. The pattern of cartilage metabolism during this time can be the result either of stimulation by a factor other than somatomedin, or selective inhibition of cartilage thymidine incorporation acting in combination with somatomedin.

Growth Hormone Secretion in the Stunted Head-Irradiated Rat

ABSTRACT: 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 < 0.0005) and in total DNA content {p < 0.0005), but these values were not significantly changed in the other organs. DNA/organ ratio was increased significantly in heart (P < 0.025) and gastrocnemius muscle (p < 0.025); brain, liver, and kidney had nonsignificant increases. Protein/DNA ratios were decreased significantly in brain (p < 0.005), heart (p < 0.01), and gastrocnemius muscle (p < 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 < 0.025) and in dark (p < 0.05). Assessments of cell size and cell number suggest that neonatal hypopituitarism and/or undernutrition are unlikely causes of the delayed growth of the head-irradiated rat, and the GH results show that brain controls of rhythmic secretion of GH are intact in this model. The finding of reduced GH secretion, is compatible with the hypothesis that the head irradiation has altered a centrally located control of catch-up growth.

Dissociation of Catch-Up Growth Control and Neural Control of Growth Hormone Secretion in the Stunted Head-Irradiated Rat

ABSTRACT: 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 fastedrefed 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.

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 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.

EPINEPHRINE (E) SECRETION IN THE RAT FETUS IN RESPONSE TO NICOTINE ADMINISTERED TRANSPLACENTALLY - RESISTANCE TO CHANGE OF FETAL PLASMA LIPIDS

We have shown previously that nicotine readily crosses the rat placenta. The present experiments were undertaken to determine whether nicotine causes catecholamine release by the feat rat adrenal, and whether acute or chronic dosage of the fetus with nicotine causes lipid increases in fetal plasma. Pregnant Long-Evans rats were fed stock diets containing 0.05 or 0.1 mg/g added nicotine during 10-20 or 0-20 d of pregnancy. Control rats were fed stock diet during 0-20 d. Mean nicotine intake ranged up to 6.03 mg/kg/d. No significant changes occurred in fetal plasma on day 20 with respect to triglyceride (TG), P-lipid or cholesterol levels. Pregnant rats were given single doses of 1 mg/kg nicotine ip on day 20. Maternal plasma free fatty acids (FFA) and TG rose, but fetal values did not change. Fetal adrenal E content decreased after nicotine injection and then rose to slightly higher than control values. There was no decrease after saline injection. The results indicate that the fetal adrenal of the rat secretes E in response to nicotine entering the fetus trans-placentally. The resistance of fetal FFA to change after nicotine is probably due to resistance to E induced elevation of FFA. The placenta may be responsible for maintaining the steady state of fetal plasma lipids.

166 DO TROPHOBLASTIC RECEPTORS FOR INSULIN, IGF-I, AND IGF-II PLAY A ROLE IN FETAL OVERGROWTH IN DIABETIC PREGNANCY?

Fetal overgrowth in diabetic pregnancy (DP) is popularly attributed to hyperinsulinism. However, the roles of other growth-promoting peptides in the mother and the fetus and of their receptors in the placenta remain unclear. We measured at term, concentration and affinity of placental trophoblastic membrane receptors (TR) for insulin (I), IGF-I and IGF-II in 8 DPs (White Class B, 1-dependent) and 8 non-DPs and correlated these with maternal and cord serum IGF-I and IGF-II levels, infant and placenta weights, and maternal body mass index (BMI). DP and non-DP differed significantly in infant weight (g), 4248±114 (M±SEM) vs 3555±119 (P<.0001); placental weight (g), 765±51 vs 575±24 (P<.005); cord IGF-I (ng/ml), 137±15 vs 86±12 (P<.025); and maternal BMI, 33±4 vs 21±1 (P<.02). No significant differences existed in cord IGF-II, maternal IGF-I and -II, and concentration and affinity of TR for I, IGF-I and IGF-II. ANOVA revealed an interaction between placenta weight and infant weight (P<.01), cord IGF-I (P<.02) and maternal IGF-I (P<.025); there was no significant interaction between BMI and infant weight. We conclude that in DP: placental overgrowth is concomitant with fetal somatic overgrowth; fetal and maternal IGF-I may contribute to fetal overgrowth; concentration and affinity of TR for I, IGF-I, and IGF-II play no roles in fetal overgrowth.