Biomedical subjects

J R Challis

Publications and source records attributed to J R Challis.

At least 109 records · Page 6Linked to original sources

PubMed1994

Opposite effects of glucocorticoid on hepatic 11 beta-hydroxysteroid dehydrogenase mRNA and activity in fetal and adult sheep.

The level of 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) mRNA in the fetal sheep liver increases dramatically between day 130 and term (term = day 145), but the causal factors remain unknown. The present study was designed to determine the effects of exogenous glucocorticoid on the fetal hepatic 11 beta-HSD gene expression. Dexamethasone (dex; 2 micrograms/min over 15 min every 2 h) or saline was infused into chronically-catheterized fetal sheep at day 130 of gestation for 4 days. At the end of infusion, the lower right lobe of the liver was collected, total cellular RNA extracted and subjected to Northern blot analysis. It was found that the level of the hepatic 11 beta-HSD mRNA in dex-treated fetuses was about four times higher than that in the saline-treated controls. To examine whether changes occur in the response of hepatic 11 beta-HSD gene expression to glucocorticoids in adulthood, we also treated non-pregnant ewes with dex (10 mg/day) for 4 days. By contrast, this treatment regime in adult sheep produced a small but significant decrease in hepatic 11 beta-HSD mRNA levels. We also determined whether age-specific changes in the hepatic level of 11 beta-HSD mRNA following dex treatment were reflected in the level of 11 beta-HSD enzyme activity. Hepatic 11 beta-HSD activity was determined by a standard in vitro conversion assay using cortisol and cortisone as physiological substrates. In both fetal and adult livers, 11-oxoreductase activity (cortisone-->cortisol) was predominant.(ABSTRACT TRUNCATED AT 250 WORDS)

11-beta-Hydroxysteroid Dehydrogenases↗

PubMed1994

Regulation of ovine fetal pituitary function by corticotrophin-releasing hormone, arginine vasopressin and cortisol in vitro.

Parturition and fetal organ maturation in sheep are associated with increased activity of the fetal hypothalamic-pituitary-adrenal (HPA) axis during late pregnancy. However, the factors responsible for HPA activation remain unclear. In the fetal pituitary, levels of pro-opiomelanocortin (POMC) mRNA increase, but the numbers of binding sites for corticotrophin-releasing hormone (CRH), and ACTH responsiveness to exogenous CRH decline during the last 20 days of pregnancy. We have examined regulation of CRH binding, pituitary ACTH responsiveness, and levels of POMC mRNA in cultures of adenohypophysial cells from term fetal sheep. After a 4-day stabilization period, output of immunoreactive (ir) ACTH was increased over 48 h in a dose-dependent fashion by both CRH and arginine vasopressin (AVP) but decreased by cortisol. Subsequent output of ir-ACTH to a 3-h challenge with 100 nM CRH was attenuated after pretreatments with CRH, AVP or cortisol; the effect of CRH being greater than that of cortisol or AVP. At the end of 48 h of treatment with CRH, AVP or cortisol, there was a 40-50% reduction in the number of CRH-binding sites, but the levels of POMC mRNA decreased significantly only after cortisol treatment and were not altered significantly by CRH or AVP. We conclude that under the conditions of these experiments, CRH and AVP increase ir-ACTH output without increasing the level of steady-state POMC mRNA, but may contribute to loss of pituitary responsiveness to CRH by down-regulation of CRH receptor number. Cortisol exerts negative feedback on POMC mRNA and decreases the number of CRH receptors. Thus, any one or all of CRH, AVP and cortisol could be responsible for the decline in CRH binding in the fetal sheep pituitary during late pregnancy. Although CRH and AVP may affect secretion of ir-ACTH, the present results do not support a role for these neuropeptides in affecting the level of POMC mRNA in the fetal sheep pituitary.

Adrenocorticotropic Hormone↗

PubMed1993

Tentativeness and fervor in cell biology require negative and positive feedforward control.

End-product feedback regulates early steps in metabolic pathways, affecting activation and the rate of end-product synthesis. Early formation of end-product also modifies later steps in the synthesis of end-product. We designate this form of regulation feedforward. Negative feedback/feedforward by end-products may result in homeostasis, but also in physiologic tentativeness. Positive feedback/feedforward by end-product gives rise to fervid events. Tentativeness and fervor, due to negative and positive feedforward rather than feedback, explain otherwise puzzling aspects of immunology and endocrinology.

Animals↗

PubMed1993

Tissue distribution of alpha 1-proteinase inhibitor messenger ribonucleic acid and its regulation by glucocorticoids in fetal and neonatal sheep.

alpha 1-Proteinase inhibitor (alpha 1-PI) controls several proteinases that play important roles during inflammation and tissue remodeling, but its function during mammalian development remains obscure. We have therefore studied the ontogeny of alpha 1-PI mRNA in selected fetal and newborn sheep tissues by Northern blotting. Furthermore, because glucocorticoids play important roles in fetal maturation and parturition in sheep, we measured the relative amounts of glucocorticoid receptor (GR) mRNA in the same tissues and compared the effect of dexamethasone (DEX) administration on alpha 1-PI mRNA levels in liver and kidney of fetal and adult sheep. In the ontogeny study, a 1.8-kb alpha 1-PI mRNA was found in fetal adrenal gland and lung at Days 60-70 but was low or undetectable in these tissues at later gestational ages. By contrast, the abundance of hepatic alpha 1-PI mRNA did not vary between Days 60 and 130 of gestation, but decreased significantly (p < 0.05) at term (Days 145-147) and in newborn lambs. In the fetal kidney, it was also present between Days 60 and 130, and its relative abundance increased significantly (p < 0.05) in term and newborn lambs. These changes did not correlate with GR mRNA abundance, which was relatively stable in all tissues except the kidney, where a significant (p < 0.05) decrease was observed in neonates.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗

PubMed1993

Foetal endocrine maturation.

In domestic ruminants such as the sheep, birth is effected through sequential maturation of the foetal hypothalamic-pituitary-adrenal (HPA) axis, leading to the increased output of cortisol. Factors regulating foetal pituitary adrenocorticotrophin (ACTH) secretion have been delineated, and these include corticotrophin releasing hormone (CRH), arginine vasopressin, prostaglandin (PG) E2 and endogenous opioids. The pre-partum increase in foetal plasma ACTH is associated with a rise in pro-opiomelanocortin (POMC) mRNA in the foetal pars distalis, and with an altered pattern of POMC post-translational processing. Foetal adrenal activation results from an increase in ACTH receptors and enhanced coupling through the Gs protein to adenylate cyclase, and increased expression of key steroidogenic enzymes including P450c17. Cortisol modulates the mechanism by which ACTH activates foetal adrenal function, through specific glucocorticoid receptors (GR) in the foetal adrenal cortex. Although the numbers of GR change with gestation, the relative abundance of GR mRNA does not, pointing to post-translational regulatory mechanisms. Cortisol also stimulates an increase in the concentration of its own high affinity binding protein (corticosteroid binding globulin; CBG) in the foetal circulation, apparently by increasing CBG gene expression in the foetal liver, and by altering the extent of foetal CBG glycosylation in a manner that would be expected to decrease the metabolic clearance of this glycoprotein. Clear evidence for placental CRH and ACTH production is lacking in sheep, but PGE2, produced in increasing amounts by the placenta during late pregnancy, may augment the drive to HPA maturation. Aspects of the maturational pathway of cortisol biosynthesis have been described in other species, including the horse, and some comparison is made with the more detailed information currently available from species such as the sheep.

Animals↗

PubMed1993

Regional adrenal blood flow responses to adrenocorticotropic hormone in fetal sheep.

To determine whether adrenocorticotropic hormone (ACTH) at plasma concentrations measured during mild hypoxemia and at term affects adrenal blood flow, we measured regional blood flows in five unanesthetized normoxemic fetuses (125-130 days gestation) during a 24-h intravenous infusion of ACTH-(1-24) in isotonic saline solution. Another five fetuses received an infusion of vehicle. Blood flows were determined before the infusion, at 2 and 24 h from its onset, and 24 h afterward using radionuclide-labeled microspheres. Blood flow to the adrenal medulla was fivefold greater than that to the adrenal cortex. Adrenal blood flow rose 99% at 24 h of the ACTH infusion. There was a large increase in adrenal cortical blood flow of 272% at this time but medullary blood flow did not change significantly during ACTH infusion. The rise in cortical blood flow was attributable to decreased vascular resistance. No significant alterations occurred in fetal arterial blood pressure and heart rate, or in blood flow to other lower body organs of the fetus or to the placental cotyledons. These findings are consistent with the hypothesis that the increase in adrenal blood flow observed during fetal hypoxia is associated with changes in plasma ACTH concentration. They are also indicative of selective regulation of cortical and medullary blood flows in the sheep fetus at this stage of gestation.

Adrenal Cortex↗

PubMed1993

Increased uteroplacental production of prostaglandin E2 during ethanol infusion.

Experiments were conducted in 14 pregnant sheep to determine the effect of a 1-h maternal infusion of ethanol (1 g/kg maternal body wt) on placental efflux of prostaglandin E2 (PGE2), umbilical blood flow (Qum), and carbohydrate metabolism at 123-130 days gestation. This ethanol dosage regimen produced peak ethanol concentrations in fetal and maternal blood in the range of 1.48-1.64 mg/ml at the end of the infusion. Umbilical venous and fetal arterial PGE2 concentrations increased (P < 0.05) from 315 +/- 47 and 202 +/- 25 pg/ml to 740 +/- 172 and 489 +/- 67 pg/ml, respectively, at the end of the infusion. Placental secretion of PGE2 into the fetal circulation increased by 45% (P < 0.05). Uterine venous and maternal arterial PGE2 concentration increased (P < 0.05) from 370 +/- 27 and 262 +/- 28 pg/ml to 705 +/- 51 and 487 +/- 69 pg/ml, respectively. Fetal and maternal blood glucose concentration decreased (P < 0.05) from 0.98 +/- 0.11 and 2.88 +/- 0.25 mmol/l to 0.81 +/- 0.21 and 2.44 +/- 0.16 mmol/l, respectively. Fetal and maternal blood lactate concentration increased (P < 0.05) from 1.40 +/- 0.11 and 0.68 +/- 0.07 mmol/l to 1.67 +/- 0.14 and 1.82 +/- 0.16 mmol/l, respectively. Qum, fetal heart rate, fetal blood pressure, and fetal and maternal blood gases were unchanged by the ethanol infusion. These results support the hypothesis that the placenta is the major source of the elevated fetal and maternal plasma PGE2 concentrations produced in pregnant sheep by maternal ethanol administration.

Animals↗

PubMed1993

Changes in the abundance of mRNA for type-I 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase in the human placenta and fetal membranes during pregnancy and labor.

A local decrease in progesterone synthesis in the placenta and fetal membranes has long been proposed as a possible mechanism in the control of human labor. We have examined whether changes occur in the abundance of mRNA for 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase (3 beta-HSD), the enzyme which catalyzes the conversion of pregnenolone to progesterone in human placenta and fetal membranes, by Northern blot analysis using a cDNA probe to human placental type-I 3 beta-HSD, the predominant isoenzyme in the placenta. The abundance of 3 beta-HSD mRNA (1.7-kb transcript) was about 10-fold greater in term placenta than in chorio-decidua, but undetectable in total RNA from amnion. There was no change in the abundance of 3 beta-HSD mRNA in either placenta or chorio-decidua obtained after elective cesarean section at term, after preterm labor, or after term or postterm vaginal delivery. We conclude that the abundance of 3 beta-HSD mRNA does not change in the placenta or fetal membranes with labor, consistent with the view that changes in 3 beta-HSD gene expression and decreased progesterone production are unlikely to effect intrauterine paracrine/autocrine regulatory mechanisms leading to term or preterm labor in women.

Blotting, Northern↗

PubMed1993

Glucocorticoid-induced increase in plasma corticosteroid-binding globulin levels in fetal sheep is associated with increased biosynthesis and alterations in glycosylation.

In fetal sheep, there is a concomitant prepartum rise in cortisol and corticosteroid-binding globulin (CBG) that maintains a low free plasma cortisol level and allows for a low negative feedback effect of cortisol on the secretion of ACTH from the fetal pituitary. However, the stimulus for the prepartum increase in CBG and the mechanism(s) of this effect are not known. It has been proposed that glucocorticoids increase CBG concentrations, and therefore, we infused fetal sheep with the synthetic glucocorticoid dexamethasone (DEX; 2 micrograms/min over 15 min every 2 h for 96 h, n = 5) or saline (n = 5). The plasma corticosteroid-binding capacity increased from 30.0 +/- 2.4 to 55.6 +/- 7.7 and 92.6 +/- 11.1 ng/ml at 48 and 96 h, respectively, of DEX infusion. To examine possible mechanisms of increasing fetal plasma CBG, we first cloned and sequenced a sheep CBG cDNA and purified the protein. This allowed us to deduce the primary structure of ovine CBG and to demonstrate that hepatic CBG mRNA abundance (single transcript of 1.8 kilobases) rose from 0.9 +/- 0.2 to 3.6 +/- 1.6 arbitrary units after 96 h of DEX treatment. Fetal DEX treatment produced a significant increase (7.1 +/- 1.2% to 13.1 +/- 1.4%) in the Concanavalin-A-binding forms of CBG that predominate in adult sheep plasma. There was negligible transfer of purified [125I]CBG from the ewe to fetal plasma, urine, or amniotic fluid. We also injected adult sheep with DEX (10 mg/day for 4 days) and demonstrated a significant decrease in plasma corticosteroid-binding capacity by 24 h, which remained suppressed for the duration of the study. After 96 h of DEX treatment, there was also a significant decrease in adult hepatic CBG mRNA abundance. We conclude that glucocorticoids increase fetal plasma CBG in part by increased hepatic biosynthesis. It may also be accentuated by a change in the glycosylation of CBG, but cannot be attributed to transplacental transfer. Furthermore, glucocorticoid treatment exerts opposite effects on CBG biosynthesis in fetal and adult sheep.

Amino Acid Sequence↗

PubMed1993

Preferential increase in prostaglandin endoperoxide H synthase compared with lipoxygenase activity in sheep placenta and amnion at term pregnancy and after intrafetal glucocorticoid administration.

Prostaglandins (PGs) have been implicated as stimulants to myometrial contractility at parturition in many species. To determine whether the increased production of PGs at parturition reflects a general increase in the metabolism of arachidonic acid or a specific increase in PG endoperoxide H synthase (PGHS) compared with lipoxygenase activities, and to determine intrauterine sites of these activities, we examined the metabolism of [3H]arachidonic acid by homogenates of placenta, amnion and chorion from sheep at days 78-80, 100-105, 135-140 of pregnancy and at term (day 145). Tissues were also obtained from fetuses at day 125; four of these were infused for 84 h with cortisol and four were used as saline-treated controls. The endogenous arachidonic acid content at the start of incubation was measured by capillary gas chromatography. Radioactive metabolites were separated and quantified by reverse-phase high-pressure liquid chromatography. At each gestational age arachidonic acid was converted to PGs, leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs). Conversion to PGs was greater in amnion than in chorion or placenta between days 78 and 140. The formation of PGs rose in placenta at term to a mean value twice that of amnion and ten times that of chorion. In amnion, the ratio of PG:LT rose significantly at term relative to 100-140 days of gestation. In placenta, the ratio of PG:LT produced from arachidonic acid and the ratio of total PGHS:lipoxygenase products rose significantly at term. In the day-125 fetuses treated with cortisol there was a significant increase in PG production relative to that in control fetuses infused with saline in placenta, amnion and chorion; the placenta and amnion being the major sites of PG production. Production of LTs and HETEs also rose significantly in the chorion and the placenta relative to controls. In both the placenta and the amnion there was a significant increase in the ratio of total PGHS to lipoxygenase products formed. We conclude that at term labour and in labour induced by intrafetal cortisol infusion, the placenta is the major site of arachidonic acid metabolism, and that there is a preferential increase in the formation of PGs over lipoxygenase products. These results are consistent with the suggestion that there is an increase in the expression or activity of PGHS in the placenta of sheep in late pregnancy.

Amnion↗

PubMed1992

Ontogeny of the distribution and colocalization of calbindin D28K within neural and endocrine cells of the gastrointestinal tract of fetal and neonatal sheep.

Using immunocytochemical techniques we have demonstrated that Calbindin D28K (CaBP) is present in the gastrointestinal tract of ovine fetuses early in development (by day 45). At day 45, CaBP was limited to neuronal elements in the developing intestine. By day 100, CaBP immunoreactivity was abundant in both epithelial endocrine cells and nerves of the submucous and myenteric ganglia. The location of CaBP containing cells and fibers was similar in duodenal sections taken from day 100 and term (145 days), as well as those taken from 24-48 h postnatal lambs. CaBP is colocalized in endocrine cells containing gastrin, glucagon, somatostatin and neurotensin, but not glucose dependent insulinotrophic peptide (GIP). Furthermore, it is extensively colocalized in nerve fibers and cells containing neurotensin but not somatostatin or vasoactive intestinal peptide. The colocalization of CaBP within various endocrine and nerve cells does not change in fetal sheep over the last one-third of gestation and there is no difference between fetal and neonatal sheep.

Animals↗

PubMed1992

Effects of restricting uteroplacental blood flow on concentrations of corticotrophin-releasing hormone, adrenocorticotrophin, cortisol, and prostaglandin E2 in the sheep fetus during late pregnancy.

We have examined the effects of reduced uterine blood flow and prolonged fetal hypoxemia on the temporal relationship between changes in hormones associated with the activity of the pituitary-adrenal axis (corticotrophin-releasing hormone (CRH), adrenocorticotrophin (ACTH), cortisol, and prostaglandin E2 (PGE2) in the ovine fetus at 120-125 days of pregnancy, and we sought evidence for placental secretion of CRH and ACTH during prolonged hypoxemia. Uterine blood flow was reduced by placing an adjustable Teflon clamp around the maternal common internal iliac artery to decrease fetal arterial oxygen saturation from mean values of 59.1 +/- 3.3 to 25.7 +/- 4.6% (+/- SEM, n = 10). There was a transient peak in immunoreactive (IR-) CRH at 1-2 h after reducing uterine blood flow. IR-ACTH rose to peak values at +2 h, then gradually decreased to control level by +12 h. Fetal plasma cortisol and PGE2 concentrations were elevated significantly by +2 and +4 h, respectively, and at 20-24 h. The identity of IR-CRH in fetal plasma and in ovine placental extracts was confirmed by HPLC, but there was no consistent umbilical vein--femoral arterial concentration difference for either IR-CRH or IR-ACTH during normoxemia or hypoxemia. We conclude that a sequence of endocrine changes involving CRH, ACTH, PGE2, and cortisol occurs in the fetus during a prolonged reduction in uterine blood flow. However, we did not obtain evidence, for placental secretion of either CRH or ACTH in response to this manipulation.

Adrenocorticotropic Hormone↗

PubMed1992

Dexamethasone inhibits basal and stimulated prostaglandin E2 output from human placental cells by inhibition of prostaglandin H synthase.

In view of the temporal relation between elevated concentrations of glucocorticoids and prostaglandins (PG) at the time of parturition, we have examined the effects of dexamethasone on PGE2 output by mixed cell preparations from human placentae at term maintained in short-term (48 or 96 h) culture. Dexamethasone inhibited placental PGE2 output in a dose-dependent fashion. The effect on placental cells was more marked than on short-term cultures of amnion cells and was not influenced by the presence of progesterone. Dexamethasone also inhibited stimulated PGE2 output after addition of arachidonic acid. These results suggest that glucocorticoids inhibit placental PG output by a mechanism involving attenuation of PG synthase activity or expression and do not support a direct causal role for elevated maternal or fetal glucocorticoids at term on increased placental PG biosynthesis.

Arachidonic Acid↗

PubMed1992

Localization of 15-hydroxy prostaglandin dehydrogenase in human fetal membranes, decidua, and placenta during pregnancy.

Localization of NAD(+)-dependent 15-hydroxy prostaglandin dehydrogenase (type I-PGDH) may influence local concentrations of bioactive eicosanoids within intrauterine tissues. In early pregnancy (6-9 weeks), IR-PGDH was localized by immunohistochemistry to syncytiotrophoblast, cytotrophoblast, and intermediate trophoblast of placenta. At 23-30 weeks of gestation and at term IR-PGDH was present in syncytiotrophoblast and intermediate trophoblast, but not in cytotrophoblast in placenta. It was absent from amnion, and distributed within the trophoblast cell layer of extraplacental chorion variably at 23-30 weeks, but consistently at term. We speculate that PGDH is ideally localized to metabolize and to maintain low concentrations of primary prostaglandins in the fetal membranes for much of gestation.

Decidua↗

PubMed1992

Gastrin releasing peptide immunoreactivity is present in ovine amniotic fluid and fetal and maternal circulations. MRC Group in Fetal and Neonatal Health and Development.

Using antisera directed towards the C-terminal region of gastrin releasing peptide (GRP), significant quantities of GRP-like immunoreactivity (GRPLI) were detected in ovine amniotic fluid and in the fetal and maternal circulations. The highest GRPLI levels were found in amniotic fluid (2135 +/- 829 fmol/ml, n = 12; mean +/- SEM), followed by those in ovine fetal (604 +/- 267 fmol/ml, n = 13) and maternal plasma (229 +/- 89 fmol/ml, n = 13). On gel filtration chromatography, the predominant GRPLI form in each fluid eluted in an identical position consistent with the entity being of apparently larger molecular size than porcine GRP1-27. Certain fetal plasma samples contained a second GRPLI peak eluting at the void volume. Hence, during ovine pregnancy a GRPLI entity circulates in fetal and maternal plasma; the entity is of apparently larger molecular size than GRP1-27 but contains a structure immunologically indistinguishable from the bioactive c-terminal region of GRP1-27. Given the recognized bioactivities of GRP, this entity may be an important hormone during ovine fetal life.

Amniotic Fluid↗

PubMed1992

Cloning of an ovine 11 beta-hydroxysteroid dehydrogenase complementary deoxyribonucleic acid: tissue and temporal distribution of its messenger ribonucleic acid during fetal and neonatal development.

Glucocorticoids promote the development of many organ systems vital for extrauterine survival, and fetal cortisol provides the trigger for birth in sheep. The activity of glucocorticoids may be influenced at a cellular level by 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD), which is responsible for the interconversion of cortisol and cortisone. To examine 11 beta-HSD gene expression during fetal development, two overlapping clones which yield a 1.4 kilobase (kb) complementary DNA encoding sheep 11 beta-HSD from a liver library were isolated by using a rat 11 beta-HSD cDNA as the probe. This cDNA contains a 879 base pair open reading frame for a protein of 292 amino acids that has more than 70% sequence identity to rat and human 11 beta-HSDs. To define the tissue distribution of 11 beta-HSD messenger RNA in sheep, selected tissues were collected from one fetus at day 130 and term (approximately 145 days), and from a nonpregnant ewe. Cellular RNA was extracted and subjected to Northern blot analysis, and a single 1.8 kb transcript was detected in the fetal and adult liver, lung, hypothalamus, anterior pituitary, and placenta. This was undetectable in adrenals and kidneys, but a smaller (1.5 kb) transcript was present in fetal and adult kidney RNA. The relative abundance of 11 beta-HSD mRNA was greatest in fetal and adult livers, and it was much higher in adult liver, lung, and kidney than in the corresponding fetal tissues. To examine whether 11 beta-HSD gene expression is developmentally regulated in the fetal sheep, liver, lung, and kidney tissues were taken from fetuses at day 60-70, day 100-110, day 125-130, at term, and from newborn lambs (24-48 h old). In the lung and kidney, the relative abundance of 11 beta-HSD mRNA did not change from day 60 to term but increased in the lungs of newborn lambs. In contrast, 11 beta-HSD mRNA levels in the liver increased between day 125 and term and rose further in the newborn. Collectively, these results demonstrate that 11 beta-HSD gene expression in sheep is regulated in a tissue-specific and developmentally programmed manner.

11-beta-Hydroxysteroid Dehydrogenases↗

PubMed1992

Diminished insulinotropic effects of gastrin-releasing peptide in pregnant sheep are reproduced by progesterone treatment of nonpregnant animals.

Gastrin-releasing peptide (GRP) is insulinotropic in several species, but possible alterations in this action during pregnancy have not been explored. Therefore, changes in plasma insulin and glucagon concentrations were examined in response to exogenous GRP in nonpregnant and pregnant sheep that were feed restricted, fed ad libitum, or infused with glucose. Administered GRP provoked insulin and glucagon release in pregnant and nonpregnant fed animals. This effect was reduced with feed restriction and potentiated in the presence of glucose. The responses were less in pregnant than in nonpregnant animals. Interpretation of this result, however, was confounded by lower plasma immunoreactive concentrations of GRP achieved in pregnant than in nonpregnant sheep in response to the same infusion rate (picomoles per kg BW) of exogenous GRP. Therefore, nonpregnant ovariectomized sheep were treated with estradiol (E2) or E2 plus progesterone (P4), given to reproduce circulating steroid levels in pregnancy, in order to examine insulinotropic responses to GRP in the absence or presence of concurrent glucose administration. Similar plasma GRP and glucose concentrations were achieved by exogenous infusions in the different groups of nonpregnant animals treated with steroids and in control animals not receiving steroids. E2 alone did not alter the insulin response to GRP compared to control, but E2 plus P4 treatment attenuated these responses to values similar to those in pregnant animals. We conclude that GRP is insulinotropic in sheep, and this action is modulated by the circulating glucose concentration. The response to GRP is less in pregnant than in nonpregnant animals, and this attenuation is mimicked in nonpregnant animals treated with E2 plus P4. We suggest that in species such as sheep, GRP is a potentiator of glucose-stimulated insulin release. This action is diminished in response to the altered endocrine environment of pregnancy and may contribute to the metabolic changes that occur at this time.

Animals↗

PubMed1992

Insulin-like growth factor-II (IGF-II) messenger ribonucleic acid is expressed in steroidogenic cells of the developing ovine adrenal gland: evidence of an autocrine/paracrine role for IGF-II.

Insulin-like growth factors (IGFs) are potent mitogenic and differentiation-promoting factors that regulate the growth and development of many fetal tissues. Their role in the development of the adrenal gland and activation of its function is not known. The latter is crucial in providing the stimulus for the maturation of various fetal organs and determines the onset of parturition in sheep. To examine the hypothesis that IGFs are important autocrine/paracrine regulators of fetal adrenal development in vivo, we localized IGF-I and IGF-II mRNAs and peptides in the adrenal glands of developing sheep fetuses and correlated the cellular distribution with localization of 3 beta-hydroxysteroid dehydrogenase, tyrosine hydroxylase, and phenylethanolamine-N-methyltransferase enzymes by immunohistochemistry. Adrenal glands from 60- to 75-day-old (n = 4), 100- to 110-day-old (n = 4), 120- to 130-day-old (n = 4), and 145- to 147-day-old (term; n = 4) fetal sheep and 1- to 4-day-old newborn lambs (n = 4) were dissected and either snap-frozen or fixed. Total RNAs were subjected to Northern analysis using ovine IGF-I and IGF-II cDNA probes. Seven IGF-II transcripts of 1.2-6.0 kilobases (kb) were identified in the adrenal glands of fetuses at all gestational ages, and in the newborn. By densitometry, the abundance of IGF-II mRNA was highest in the fetal adrenal gland at 60 days, decreased slightly between 60 and 100 days, remained relatively constant until term, and decreased significantly after birth. At all gestational ages, IGF-II mRNA was detectable in significantly greater abundance than IGF-I mRNA. IGF-I and IGF-II mRNAs were localized by in situ hybridization using 35S-labeled anti-sense cRNA probes, and the peptides by immunohistochemistry using specific antisera. Low levels of IGF-I mRNA were detected in the zona fasciculata, but not in the zona glomerulosa. There was strong hybridization of the IGF-II cRNA to the zona glomerulosa and fasciculata and to the capsule. The hybridization signal was greater in the zona fasciculata than in the zona glomerulosa. IGF-II mRNA was also detected in groups of cells within the medulla. Localization of IGF-II mRNA by in situ hybridization correlated well with the distribution of IGF-II immunoreactivity and with 3 beta-hydroxysteroid dehydrogenase-positive cells in the cortex and in groups of cells within the medulla.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Cortex↗