In a previous study, we showed that exposure of rats to dexamethasone (Dex) selectively in late pregnancy produces permanent induction of hepatic phosphoenolpyruvate carboxykinase (PEPCK) expression and hyperglycaemia in the adult offspring. The mechanisms by which glucocorticoids cause this programming are unclear but may involve direct actions on the fetus/neonate, or glucocorticoids may act indirectly by affecting maternal postnatal nursing behaviour. Using a cross-fostering paradigm, the present data demonstrate that switching the offspring at birth from Dex-treated dams to control dams does not prevent induction of PEPCK or hyperglycaemia. Similarly, offspring born to control dams but reared by Dex-treated dams from birth maintain normal glycaemic control. During the neonatal period, injection of saline per se was sufficient to cause exaggeration in adult offspring responses to an oral glucose load, with no additional effect from Dex. However, postnatal treatment with either saline or Dex did not alter hepatic PEPCK activity. Prenatal Dex permanently raised basal plasma corticosterone levels, but under stress conditions there were no differences in circulating corticosterone levels. Likewise, Dex-exposed rats had similar plasma catecholamine concentrations to control animals. These findings show that glucocorticoids programme hyperglycaemia through mechanisms that operate on the fetus or directly on the neonate, rather than via effects that alter maternal postnatal behaviour during the suckling period. The hyperglycaemic response does not appear to result from abnormal sympathoadrenal activity or hypothalamic-pituitary-adrenal response during stress.
You are looking at 1 - 6 of 6 items for
- Author: Seckl JR x
- Refine by Access: All content x
MJ Nyirenda, LA Welberg, and Seckl JR
CM Leckie, LA Welberg, and Seckl JR
11beta-Hydroxysteroid dehydrogenases (11beta-HSDs) interconvert active corticosterone and inert 11-dehydrocorticosterone. In tissue homogenates, 11beta-HSD type 1 (11beta-HSD-1) exhibits both 11beta-dehydrogenase (corticosterone inactivating) and 11beta-reductase (corticosterone regenerating) activities, whereas 11beta-HSD type 2 (11beta-HSD-2) is an exclusive dehydrogenase. In the rat testis, 11beta-HSD has been proposed to reduce glucocorticoid inhibition of testosterone production, promoting puberty and fertility. This hypothesis presupposes dehydrogenation predominates. 11beta-HSD-1 immunoreactivity has been localised to Leydig cells. However, recent studies suggest that 11beta-HSD-1 is predominantly an 11beta-reductase in many intact cells. We therefore examined the expression and reaction direction of 11beta-HSD isozymes in cultures of intact rat Leydig cells. Reverse transcriptase PCR demonstrated expression of 11beta-HSD-1, but not 11beta-HSD-2 mRNA in rat testis. Primary cultures of intact rat Leydig cells showed predominant 11beta-reductase activity, activating 50-70% of 11-dehydrocorticosterone to corticosterone over 3 h, whereas 11beta-dehydrogenation was <5%. Although both dexamethasone (10 nM) and corticosterone (1 microM) modestly inhibited LH-stimulated testosterone production by Leydig cells, inert 11-dehydrocorticosterone (1 microM) had similar effects, suggesting 11beta-reductase is functionally important. Carbenoxolone (10(-5) M) inhibited 11beta-reduction in intact Leydig cells. However, although carbenoxolone reduced Leydig cell testosterone production, this also occurred in the absence of glucocorticoids, suggesting effects distinct from modulation of corticosteroid access to Leydig cells. In conclusion, rat Leydig cell 11beta-HSD-1 is unlikely to reduce glucocorticoid access to testicular receptors. More likely, 11beta-reductase amplifies glucocorticoid action, perhaps to maintain Leydig cell metabolic and endocrine functions.
HJ Speirs, Seckl JR, and RW Brown
Glucocorticoids play important roles in organ development and 'fetal programming'. Fetal exposure to excess glucocorticoids reduces birth weight and causes later hypertension. To investigate these processes further we have determined the detailed ontogeny in the mouse of the glucocorticoid receptor (GR) and 11beta-hydroxysteroid dehydrogenase type-1 (11beta-HSD1), which amplifies glucocorticoid levels locally; the ontogeny was determined using in situ hybridisation from embryonic day 9.5 (E9.5, term=E19) until after birth. At E9.5 fetal GR mRNA levels are very low, except in fetal placenta. GR gene expression rises during gestation with striking tissue-specific differences in timing and extent. Before E13.5, an increase is clear in gastrointestinal (GI) and upper respiratory tracts, discrete central nervous system (CNS) regions, precartilage and especially in the liver (E10.5-E12). Later, further increases occur in lung, GI and upper respiratory tracts, muscle, pituitary and thymus. In a few tissues such increases are temporary, e.g. ureteric ducts (E13.5-E16.5) and pancreas (E14.5-E16.5, expression later falling sharply). Fetal 11beta-HSD1 mRNA expression is first clearly observed at E14.5-E15, initially in the fetal placenta then in the umbilical cord. Later, 11beta-HSD1 expression is seen as follows: (i) from E15 in lung and liver, rising strongly; (ii) thymus, from E15 (lower level); (iii) at low levels in a few brain regions, including the hippocampus (E16.5+); and (iv) in muscle group fascial planes and tendon insertions. This is the first detailed study of the ontogeny of these two genes and, in combination with previous work on the ontogeny of 11beta-HSD2 and the mineralocorticoid receptor, suggests potential critical periods of glucocorticoid sensitivity during development for several organ systems.
PM Jamieson, BR Walker, KE Chapman, R Andrew, S Rossiter, and Seckl JR
11 beta-Hydroxysteroid dehydrogenase type 1 (11 beta-HSD-1), a regulator of intrahepatocellular glucocorticoid activity, is bidirectional in homogenates but catalyses 11 beta-reduction (regenerating glucocorticoid) in intact primary hepatocytes in culture. To examine this discrepancy at the whole-organ level, we examined 11 beta-HSD-1 activity in the intact bivascularly perfused rat liver. On a single pass through male rat liver, 44+/-5% of 11-dehydrocorticosterone (11-DHC) recovered was 11 beta-reduced to corticosterone, whereas 10+/-1% of corticosterone was 11 beta-dehydrogenated to 11-DHC. 11 beta-Reduction was less in female liver (21+/-2%, P<0.01) and was significantly greater with perfusion of all substrate via the portal vein (50+/-3%) than via the hepatic artery (30+/-2%, P<0.05). 11 beta-Reductase activity was not saturated by 11-DHC (10(-)(9)-10(-)(6) M). Perfusion with carbenoxolone (CBX, 10(-)(6)-10(-)(3 )M) did not alter 11 beta-reduction of 11-DHC. In contrast, pretreatment with CBX in vivo (10 mg/day) for 7 days inhibited 11 beta-reductase (19+/-4% conversion, P<0.01). Concentrations of 11-DHC in male rat plasma were 44+/-6 nM. Thus 11 beta-HSD-1 is predominantly an 11 beta-reductase in the intact rat liver and is only inhibited by chronic administration of CBX. The substantial concentrations of plasma 11-DHC as substrate suggest that 11 beta-HSD-1 activity and its potential selective inhibition could modify glucocorticoid action in vivo.
P MacDonald, S MacKenzie, LE Ramage, Seckl JR, and RW Brown
Corticosteroid control of distal nephron sodium handling, particularly through the amiloride-sensitive sodium channel (ENaC), has a key role in blood pressure regulation. The mechanisms regulating ENaC activity remain unclear. Despite the generation of useful mouse models of disorders of electrolyte balance and blood pressure, there has been little study of distal nephron sodium handling in this species. To investigate how corticosteroids regulate ENaC activity we isolated cDNA for the three mouse ENaC subunits (alpha, beta and gamma), enabling their quantitation by competitive PCR and in situ hybridisation. Kidneys were analysed from mice 6 days after adrenalectomy or placement of osmotic mini-pumps delivering aldosterone (50 microg/kg per day), dexamethasone (100 microg/kg per day), spironolactone (20 mg/kg per day) or vehicle alone (controls). In controls, renal ENaCalpha mRNA exceeded beta or gamma by approximately 1.75- to 2.8-fold. All subunit mRNAs were expressed in renal cortex and outer medulla, where the pattern of expression was fully consistent with localisation in collecting duct, whereas the distribution in cortex suggested expression extended beyond the collecting duct into adjacent distal tubule. Subunit mRNA expression decreased from cortex to outer medulla, with a gradual reduction in beta and gamma, and ENaCalpha decreased sharply ( approximately 50%) across the outer medulla. Expression of ENaCbeta and gamma (but not alpha) extended into inner medulla, suggesting the potential for inner medulla collecting duct cation channels in which at least ENaCbetagamma participate. Aldosterone significantly increased ENaC subunit expression; the other treatments had little effect. Aldosterone caused a 1.9- to 3.5-fold increase in ENaCalpha (particularly marked in outer medullary collecting duct), but changes for beta and gamma were minor and limited to the cortex. The results raise the possibility that medullary ENaCalpha upregulation by aldosterone will create more favourable subunit stoichiometry leading to a more substantial increase in ENaC activity. In cortex, such a mechanism is unlikely to have a major role.
PM Jamieson, MJ Nyirenda, BR Walker, KE Chapman, and Seckl JR
In vitro, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1) catalyses the interconversion of active corticosterone and inert 11-dehydrocorticosterone. 11beta-HSD-1 is highly expressed in liver, where the reaction direction is 11beta-reduction, thus potentially increasing intrahepatic active glucocorticoid levels. Inhibition of 11beta-HSD-1 increases insulin sensitivity in humans in vivo suggesting that hepatic 11beta-HSD-1 plays a role in the maintenance or control of key glucocorticoid-regulated metabolic functions. We have selectively repressed hepatic 11beta-HSD-1 in rats by oestradiol administration for 42 days. This nearly completely repressed hepatic 11beta-HSD-1 mRNA expression and enzyme activity and reduced expression of hepatic glucocorticoid-inducible genes including phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting step in gluconeogenesis. Similar effects were seen after 3 weeks of oestradiol treatment. To examine whether this was due to any direct effect of oestradiol upon PEPCK, the experiment was repeated in adrenalectomised rats+/-glucocorticoid replacement. In adrenalectomised rats, oestradiol did not attenuate hepatic PEPCK, whilst glucocorticoid replacement restored this action. Oestradiol did not alter hepatic metabolism of corticosterone by pathways other than 11beta-HSD-1. These data suggest 11beta-HSD-1 plays an important role in maintaining expression of key glucocorticoid-regulated hepatic transcripts. Enzyme inhibition may provide a useful therapeutic target for manipulating glucose homeostasis.