Lyle C. Dearden

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.

Ultrastructural evidence of pulmonary capillary endothelial damage from paraquat.

Because of lack of agreement concerning the toxicity of paraquat to the pulmonary microvasculature, we have undertaken an electron microscopic study of lungs of paraquat-treated rats. Rats were injected with paraquat or sterile water (controls) intraperitoneally; the animals were then killed at 24-h intervals for 10 days post-injection. In the control animals, lung ultrastructure remained normal throughout the study. In treated animals, the initial evidence of alveolar epithelial injury occurred 24 h post-paraquat. By 48 h, severe fragmentation and desquamation of membranous pneumocytes occurred, and both alveolar and interstitial edema were present. Epithelial damage was maximal 72-96 h post-paraquat. Pulmonary capillary endothelial abnormalities were less extensive than the alveolar epithelial lesions. Endothelial damage was first observed 48 h post-paraquat. In endothelial cells on the septal (thick) side of the capillaries, the number of pinocytotic vesicles was significantly increased (P less than 0.05) from 48 to 96 h post-paraquat. In endothelium adjacent to damaged epithelium, abnormalities included hydration, fragmentation, discontinuity, and widened intercellular junctions; these were maximal 72-96 h post-paraquat. Although other mechanisms are probably important, damaged pulmonary capillary endothelium seems to be a factor favoring paraquat-induced pulmonary edema.

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.

Effect of dimethylthiourea on paraquat toxicity in rats

We evaluated the utility of dimethylthiourea ( DMTU ), a hydroxyl radical scavenger, as potential therapy for paraquat poisoning. Seventy-five male Sprague-Dawley rats were divided into four groups ( DMTU -paraquat, paraquat, DMTU , control) and studied for up to 10 days. Clinical observations (dyspnea, weakness), mortality, hepatic and renal function tests, body weights, and histologic studies were performed. There was no mortality in the DMTU and control groups although various histologic and biochemical studies suggested that DMTU may be both hepatotoxic and nephrotoxic. In contrast, 74% of DMTU -paraquat rats and 39% of paraquat rats died (p less than 0.01). In addition, toxicity was clearly earlier in the DMTU -paraquat group than in the paraquat group. Hence, rather than being protective, treatment with dimethylthiourea was associated with increased mortality in paraquat-poisoned rats.

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.

Stomach and Pyloric Sphincter Histology in Certain Microtine Rodents

The stomach and pyloric sphincter of four genera of microtine rodents (27 specimens) have been investigated grossly and histologically. Two distinct types of stomach can be demonstrated by means of the type of epithelium lining the stomach. the first consists of a forestomach (cornified stratified squamous epithelium) and pyloric or fundo-pyloric stomach (glandular mucosa) with continuity of glandular mucosa through the pyloric sphincter. the second stomach type consists of three stomach areas, forestomach (cornified stratified squamous epithelium), narrow glandular stomach, and pylorus with forestomach type lining in the pylorus and at the pyloric sphincter. Inferred muscle action at the pyloric sphincter also consists of two types: one, a nearly symmetrically circular action, and, two, a milking action. in both cases the closing mechanism of the pyloric sphincter is assisted in forming a tight seal at the gastroduodenal junction by means of the type of epithelium present at this junction. Cell types in the glandular mucosa are also noted and discussed.

473 GROWTH HORMONE AND STUNTED GROWTH FOLLOWING HEAD IRRADIATION

The role of growth hormone (GH) in stunting following head-irradiation in rodents and humans is unclear. We have reported no response to GH treatment in the stunted head-irradiated rat. Secretion profile of GH and cell size and number in brain, heart, liver, kidney and gastrocnemius muscle (gastroc) were determined in rats X-irradiated with 600 rads to the head only or sham-irradiated at 2 d of age. Blood was sampled for GH RIA from cannulated undisturbed rats at 15 min intervals for 18 h periods (9 h light and 9 h dark) at 47 to 64 d of age. Irradiated rats were significantly stunted in body weight and tail length. At 20-21 d of age they had significantly reduced weight of all organs; decreased brain organ/body ratio (p<0.0005) and total DNA (p<0.0005); increased DNA/organ in all organs, significant in heart (p<0.025) and gastroc (p<0.025); decreased protein/DNA in all organs, significant in brain (p<0.005), heart (p<0.01) and gastroc (p<0.05). Irradiated rats had normal rhythm of GH pulses; reduced numbers of GH values from 200 to 499 ng/ml (p<0.05) and 500 to 999 ng/ml (p<0.005), and reduced area under GH concentration vs time (p<0.025). We conclude that GH secretory rhythm is intact in the head-irradiated rat. Cell size and number results exclude neonatal hypopituitarism and/or undernutrition as causes of the growth stunting. Reduced GH secretion may thus only reflect setting of a putative centrally located growth regulator for a smaller body size.

34 EXPERIMENTAL EVIDENCE FOR CENTRAL NERVOUS SYSTEM CONTROL OF CATCH-UP GROWTH

In rats permanent stunting follows neonatal head-irradiation (Head-X); during the post-weaning period full catch-up growth (CU) occurs after fasting (F); failure of CU occurs after cortisone treatment (C); and superimposition of F or C on Head-X results in similar responses in the stunting after Head-X. In this study growth hormone (GH) secretory profiles were determined in rats treated with Head-X, F or C. Superior vena cava blood was sampled at 15 min intervals during the light phase in chronically cannulated undisturbed animals. Sampling duration was 9 h in Head-X, 6 h in F, and 12 h in C. The results, expressed as area units/15 min under the curve of plasma GH concentration vs. time, are as follows:Normal pulsatile GH rhythm existed in all three models. The data indicate that GH controls are linked to the CU control. That GH secretion is decreased in Head-X is compatible with the concept that brain injury has reset growth controls for a smaller body size. We conclude that GH release is linked to the putative CU control through a mechanism which senses the discrepancy between actual body size and normal body size for age.