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D. J. Nichols, M. Weisbart and J. Quinn

ABSTRACT

Cortisol kinetics were examined in brook trout (Salvelinus fontinalis) to assess possible relationships with body fluid distribution during acclimation to sea water (SW). The disappearance curve of [3H]cortisol in plasma, after a bolus injection, was analysed by compartmental analysis using a three-pool mammillary model. The results indicated that only ∼ 10% of the total exchangeable cortisol was located in the plasma pool. Over 75% of the total cortisol was associated with a large slowly exchanging pool and the remaining cortisol was located in a second extravascular tissue pool which was in rapid exchange with the plasma pool.

Two days after transfer of trout from fresh water to SW, when plasma chloride concentration was at a new steady state, body weight, intracellular fluid volume, haematocrit and inulin clearance rate were lowered but plasma, blood and extracellular volumes were unaltered. Cortisol plasma clearance rate was unaltered but plasma cortisol concentration, cortisol secretion rate, total cortisol pool size and interpool transport rates were increased. These results are consistent with an acute role for cortisol in SW adaptation of brook trout.

The fraction of the total cortisol cleared was smaller and the average time that cortisol spent in the tissue pools was slightly longer in trout after transfer to SW, possibly reflecting altered fluid dynamics. The fractional disappearance rate was larger at higher plasma cortisol concentrations in the SW trout. This relationship is compatible with the hypothesis that cortisol protein binding protects cortisol from metabolism.

J. Endocr. (1985) 107, 57–69

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J F Trahair, S J Wing, K J Quinn and P C Owens

Abstract

Fetuses swallow large volumes of amniotic fluid. Absence of swallowing results in gastrointestinal tract (GIT) growth deficits. While it is not yet known to what extent the growth factors present in amniotic fluid are involved in GIT ontogeny, milk-derived growth factors are considered to be important for neonatal growth. Our experiment tested the hypothesis that a luminal growth factor (insulin-like growth factor-I, IGF-I) can sustain or promote GIT growth in utero in a model of gastrointestinal tract growth retardation. Ten-day infusion of either human recombinant IGF-I or vehicle into twin fetal sheep at 80 days gestation via an indwelling esophageal catheter resulted in altered GIT growth. Weight of the forestomach and small intestine increased. Significant histological changes were noted in the proximal small intestine, i.e. the region most exposed to the luminal infusion. Mucosal tissues were reduced in size. While the enterocytes in the proximal small intestine were generally more mature with regard to the ontogeny of the apical endocytic complex (which is responsible for uptake and transport of whole peptides), there were also many abnormal cytological features present. These included the development of large lysosomal-like inclusion bodies and many surfactant-like particles within the apical cytoplasm. Plasma IGF-I levels were on average 20% higher in treated siblings, suggesting that luminal IGF-I crossed the fetal gut and entered blood. IGF-II levels were not significantly affected. These observations are consistent with the suggestion that growth factors, which are present in swallowed amniotic fluid, influence fetal ontogeny.

Journal of Endocrinology (1997) 152, 29–38

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K L Kind, J A Owens, J S Robinson, K J Quinn, P A Grant, P E Walton, R S Gilmour and P C Owens

Abstract

To determine whether tissue production of the IGFs is altered when fetal growth is retarded, IGF-I and -II mRNAs were measured in tissues of fetal sheep subjected to placental restriction and the relationships between IGF gene expression, circulating IGF protein and fetal growth were examined. The majority of potential placental attachment sites were surgically removed from the uterus of 12 non-pregnant ewes to restrict placental size in a subsequent pregnancy. Blood and tissues were collected at 121 days of gestation (term=150) in 12 fetuses with restricted placental size and eight normal fetuses. IGF-I and IGF-II mRNA was detected by solution hybridization/ribonuclease protection assay in placenta and all fetal tissues studied. IGF-I mRNA was most abundant in skeletal muscle and liver and IGF-II mRNA was highest in kidney and lung. Restriction of placental size reduced fetal weight by 17% and reduced the pO2 (18%) and glucose concentration (23%) of fetal blood. Placental restriction also reduced IGF-I mRNA in fetal muscle (P<0·002), lung (P<0·05) and kidney (P<0·01) but had no significant effect on IGF-II mRNA in any tissue. IGF-I mRNA in fetal liver, kidney and skeletal muscle correlated positively with the concentration of IGF-I protein in fetal blood (P<0·01). There was no relationship between the concentration of IGF-II protein in fetal blood and IGF-II mRNA in any fetal tissue examined. The concentration of IGF-binding protein-3 (IGFBP-3) in fetal arterial blood plasma measured by RIA correlated positively with fetal weight and with plasma IGF-I. This study shows that restriction of placental growth in sheep reduces circulating levels of IGF-I and IGFBP-3 in the sheep fetus and reduces the capacity of the fetus to produce IGF-I at a number of tissue sites. Altered production of IGF-I, but not IGF-II, by fetal tissues may contribute to retarded fetal growth.

Journal of Endocrinology (1995) 146, 23–34

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Amy R Quinn, Cynthia L Blanco, Carla Perego, Giovanna Finzi, Stefano La Rosa, Carlo Capella, Rodolfo Guardado-Mendoza, Francesca Casiraghi, Amalia Gastaldelli, Marney Johnson, Edward J Dick Jr and Franco Folli

Erratic regulation of glucose metabolism including hyperglycemia is a common condition in premature infants and is associated with increased morbidity and mortality. The objective of this study was to examine histological and ultrastructural differences in the endocrine pancreas in fetal (throughout gestation) and neonatal baboons. Twelve fetal baboons were delivered at 125 days (d) gestational age (GA), 140d GA, or 175d GA. Eight animals were delivered at term (185d GA); half were fed for 5 days. Seventy-three nondiabetic adult baboons were used for comparison. Pancreatic tissue was studied using light microscopy, confocal imaging, and electron microscopy. The fetal and neonatal endocrine pancreas islet architecture became more organized as GA advanced. The percent areas of α-β-δ-cell type were similar within each fetal and newborn GA (NS) but were higher than the adults (P<0.05) regardless of GA. The ratio of β cells within the islet (whole and core) increased with gestation (P<0.01). Neonatal baboons, which survived for 5 days (feeding), had a 2.5-fold increase in pancreas weight compared with their counterparts killed at birth (P=0.01). Endocrine cells were also found in exocrine ductal and acinar cells in 125, 140 and 175d GA fetuses. Subpopulation of tissue that coexpressed trypsin and glucagon/insulin shows the presence of cells with mixed endo–exocrine lineage in fetuses. In summary, the fetal endocrine pancreas has no prevalence of a α-β-δ-cell type with larger endocrine cell percent areas than adults. Cells with mixed endocrine/exocrine phenotype occur during fetal development. Developmental differences may play a role in glucose homeostasis during the neonatal period and may have long-term implications.