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Biomedical subjects

J R Challis

Publications and source records attributed to J R Challis.

At least 217 records · Page 12Linked to original sources
PubMed1983

Activation of ovine fetal adrenal function by pulsatile or continuous administration of adrenocorticotropin-(1-24). II. Effects on adrenal cell responses in vitro.

We have examined 1) the effects of mode of ACTH administration to fetal sheep in vivo on the pattern of corticosteroid output by dispersed adrenal cells in vitro, and 2) the time course of fetal adrenal activation during pulsatile ACTH administration to the fetus. Fetal sheep received the same amount of ACTH either as a continuous infusion (C-ACTH; 0.5 microgram/h) or as 15-min pulses every 2 h for 72 h (P-ACTH). Other fetuses received P-ACTH until labor occurred (mean, 100 h) or saline for 72 or 100 h. Adrenal cells from fetuses that received C-ACTH for 72 h produced more corticosterone from endogenous precursors after the addition of ACTH in vitro and after the addition of 0.3 microM progesterone (P4) or pregnenolone (P5) than cells from fetuses treated with P-ACTH for 72 h. There was no difference in cortisol (F) response between the two groups, although in both groups F output was greater than in controls. Adrenal cells from control fetuses produced more P4 in vitro during incubation with ACTH plus guanosine-5'-(beta, gamma-imido)triphosphate [Gpp(NH)p] or N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate [(Bu)2cAMP] than after ACTH alone. There was no significant F response to the agonists, and F output was quantitatively less than that of P4. After 72-h P-ACTH, the mean P4 output after ACTH addition was not significantly different from that after ACTH plus Gpp(NH)p or (Bu)2cAMP. By 100 h of P-ACTH, the output of F exceeded that of P4 and was not different in response to ACTH, ACTH plus Gpp(NH)p, or (Bu)2cAMP. After 72 h of P-ACTH, incorporation of exogenous P4, but not P5, 17 alpha-hydroxyprogesterone, or 17 alpha-hydroxypregnenolone, into F was greater than that in cells from control fetuses. By 100 h of P-ACTH, incorporation of all substrates into F was greater than that after P-ACTH for 72 h. We conclude that 1) both C-ACTH and P-ACTH for 72 h increase fetal adrenal responses, but the pattern of corticosteroid output in vitro is determined by the mode of ACTH administration in vivo; 2) adrenal responsiveness is increased further between 72 and 100 h of P-ACTH, and activation probably involves changes in ACTH receptor-GTP coupling as well as enzyme activities on the pathway to F biosynthesis.

Adrenal Glands↗
PubMed1983

Prostaglandin output in relation to parturition by cells dispersed from human intrauterine tissues.

Collagenase-dispersed cells from human amnion, chorion, decidua, and placenta have been maintained in short term cultures to study prostaglandin (PG) biosynthesis in relation to parturition. Cells retained metabolic function during the 6-h incubation period, as determined by the apparently linear utilization of radioactive glucose and the formation of tritiated water. All cells synthesized PGs (E, F, and 6-keto F1 alpha) from endogenous precursors. The output of all three PGs significantly increased in amnion and chorion, but not in decidua or placenta, obtained from women who had entered labor spontaneously at term and delivered vaginally (SL) when compared to women at term, but not in labor, delivered by elective cesarean section (CS). For example, PGE output (picograms per 10(5) cells/6 h) increased from 207 +/- 77 (n = 5) to 908 +/- 334 with labor (mean +/- SEM). The addition of indomethacin (10(-7)-10(-5) M) to SL amnion cells significantly decreased (P less than 0.001, by analysis of variance) PGE and PGF, but not 6-keto PGF1 alpha output. Comparison of PGF output with its metabolite, 13,14-dihydro-15-keto PGF2 alpha (PGFM); indicated that PGF values were similar to or higher than PGFM for all tissues other than CS chorion, where PGFM output was significantly greater (142 +/- 63 vs. 486 +/- 95; n = 5; P less than 0.05). PGFM levels in amnion increased with labor [104 +/- 51 (n = 5) to 341 +/- 96 (n = 5); P less than 0.05], suggesting that PG output increased with labor in the fetal membranes as a result of increased synthesis and not decreased metabolism.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Changes in the responsiveness of adrenal cells from foetal goats at different times during pregnancy.

To understand the factors responsible for the increased pre-partum output of cortisol from the adrenal glands of the goat foetus, we measured changes in responsiveness to ACTH in vitro of dispersed adrenal cells from foetal goats of various gestational ages and we determined the output of cortisol (F) and corticosterone (B) in the presence of exogenous progesterone (P4) and 17 alpha-hydroxyprogesterone (17 alpha-OHP4). The increment in F output after ACTH increased 5-fold between day 100 and days 147 or 154 (term). This increase was not associated with changes in the ED50 for ACTH stimulation of F output. The basal and ACTH-stimulated output of F was similar to that of B at day 100 but 5-7 times greater than that of B at day 154. There was a significant effect of ACTH on P4 output on days 77, 100 and 147 but net utilization of P4 by the cells at term. The ratio of exogenous P4: 17 alpha-OHP4 converted to F varied with gestation and increased from 0.11 at day 100 to 0.99 at day 154. Exogenous P4 was converted to B at all stages of pregnancy. We conclude that in the goat there is an increase in the responsiveness of foetal adrenal cells to ACTH between day 100 of gestation and term. One factor associated with this change in adrenal responsiveness may be an increase in the activity of the enzyme 17 alpha-hydroxylase.

17-alpha-Hydroxyprogesterone↗
PubMed1983

Activity of 3 beta-hydroxysteroid dehydrogenase-5,4-en isomerase in chorioallantois and amnion from pregnant sheep.

Activity of 3 beta-hydroxysteroid dehydrogenase-5,4-en isomerase (3 beta-HSD; pregnenolone to progesterone) was investigated in homogenates of chorioallantois and amnion obtained from sheep at three gestational ages (day 50, day 100 and term) using an isotope assay. Chorioallantois and, to a lesser extent, amnion possessed 3 beta-HSD at each gestational age studied. Activity in the chorioallantoic membrane was greater at term than at days 50 and 100, and was similar to that in the placenta at day 100 and term. Activity in the placenta was considerably greater at day 50 than at day 100 and term. The subcellular distribution of 3 beta-HSD in chorioallantoic membrane was particulate in nature. The mean Km values (+/- S.E.M.) were 56.8 +/- 5.5 and 39.0 +/- 8.7 nmol/l at day 50 and term respectively. The mean Vmax values were 14.1 +/- 3.1 and 62.7 +/- 11.4 pmol/min per mg protein at day 50 and term respectively. Several steroids inhibited the conversion of pregnenolone to progesterone, particularly dehydroepiandrosterone (DHEA), oestrone and oestradiol. Oestrone and DHEA were competitive inhibitors. The Ki values were 19.6 +/- 5.9 and 40.2 +/- 14.7 nmol/l for oestrone and DHEA inhibition respectively. The results show that ovine fetal membranes have the capacity to convert pregnenolone to progesterone and demonstrate the possibility of inhibition by other steroids. Progesterone produced by the fetal membranes might influence the local intra-uterine steroid milieu during pregnancy and before parturition.

Animals↗
PubMed1983

Accelerated prepartum maturation of the fetal sheep lung with physiological doses of andrenocorticotrophin.

The role of Adrenocorticotrophin (ACTH), administered in physiological doses (12 micrograms/d), on lung maturation was investigated in the intact ovine fetus at 127-130 days of gestation. ACTH1-24 was administered in a pulsatile or continuous dose for 72 hours. Compared to untreated twins (n = 4) and saline infused fetuses (n = 4), the lungs of the pulsatile-ACTH (n = 10) and continuous-ACTH (n = 4) treated fetuses showed accelerated prepartum maturation by all indices used. Lung distensibility (V40-ml of air per g of wet lung at 40 cm H2O pressure), as determined by pressure-volume curves with air was 1.62 +/- 0.18 vs 0.72 +/- 0.23 and 0.66 +/- 0.12 while the stability (Vo-ml of air per g of wet lung at atmospheric pressure) was 0.33 +/- 0.07 vs 0.10 +/- 0.01 and 0.21 +/- 0.09 for the P-ACTH group vs the control groups (P less than 0.005). In the continuous-ACTH group vs their untreated twins the distensibility was 1.58 +/- 0.10 vs 0.56 +/- 0.11 while the stability was 0.83 +/- 0.20 vs 0.09 +/- 0.01 respectively (less than 0.005). Phosphotidylcholine concentration in lavage fluid increased from 0.05 +/- 0.02 mg/g of lung to 0.24 +/- 0.07 in the pulsed-ACTH group compared to untreated twin fetuses (P less than 0.05). Morphologically the lungs of the treated groups were well aerated with thin walled airsacs. In both treated groups, there was a doubling of the adrenal weight (P less than 0.005). Fetal plasma cortisol basal level increased from less than 5 ng/ml to 143.5 +/- 66.5 ng/ml in the continuous-ACTH group while it only rose to 36.6 +/- 7.5 ng/ml in the pulsed-ACTH group by 72 hours. Superimposed on the rise in basal fetal cortisol, there was an acute increase in cortisol temporally related to each ACTH pulse; the peaks reaching levels indistinguishable from the levels of the continuous-ACTH infusion. It is concluded that the administration of low doses of ACTH markedly accelerate prepartum maturation of the intact ovine lung over 72 hours. The mechanism by which ACTH exerts this powerful maturation effect on the fetal lung remains to be elucidated.

Adrenocorticotropic Hormone↗
PubMed1982

Activation of adrenal function in fetal sheep by the infusion of adrenocorticotropin to the fetus in utero.

We determined whether ACTH1-24, infused into fetal lambs at a rate that is known to cause premature labor, elicits changes in the responsiveness of the fetal adrenal glands, and alters the pattern of corticosteroid output. Plasma cortisol (F), corticosterone (B) and progesterone (P4) were measured during 72 h of infusion of saline or ACTH (10 micrograms/h) beginning on Day 127 of pregnancy. Adrenals were then dispersed into isolated cells, and the output of F, B and P4 after exogenous ACTH determined in vitro. Plasma concentrations of F and B were higher in ACTH-treated fetuses. The increment in F (5-to 7-fold) was greater than that in B (2-fold) such that the F:B ratio in plasma of ACTH-treated fetuses on Days 2 and 3 of infusion was 2.5 times higher than in controls. After 72 h of infusion, the adrenal weights in ACTH-treated fetuses (741 +/- 38 mg, +/- SEM; n = 4) were greater than in the control animals (349 +/- 11 mg). There was a significant effect of ACTH pretreatment in vivo on F output by isolated adrenal cells in vitro. Mean increments in F output after addition of ACTH1-24 (5000 pg/ml) in vitro rose from 368 +/- 235 pg/50,000 cells in controls, to 64,639 +/- 19,875 pg/50,000 cells after ACTH in vivo. There was no significant effect of ACTH in vivo on B output in vitro; the ratio of F:B output, either in the absence or presence of ACTH in vitro, was significantly higher in cells from ACTH-pretreated fetuses. There was a significant effect of in vivo ACTH on in vitro P4 output. After ACTH treatment in vivo there was an increase in the vitro output ratio of F:P4, but no change in the output ratio of B:P4. We conclude that ACTH treatment of the fetal lamb in vivo results in activation of fetal adrenal function, increased fetal adrenal responsiveness to ACTH, and directed corticosteroid biosynthesis towards cortisol. Our results are consistent with an increase in fetal adrenal 17 alpha-hydroxylase activity after ACTH treatment.

Adrenal Glands↗
PubMed1982

Changes in plasma cortisol and progesterone after administration of enkephalins to newborn lambs.

Methionine-enkephalin and leucine-enkephalin were injected into the brachiocephalic artery of lambs at 8-18 days of age. There was a significant increase in the concentration of cortisol in plasma 15-30 min after leucine-enkephalin (10-, 100-, and 500-micrograms bolus). After the 100-micrograms bolus, there was a biphasic response and a second significant rise in cortisol was seen at 90 min. Plasma progesterone was elevated significantly at 15-30 min and at 90 min after the 100- and 500-microgram injections of leucine-enkephalin. Methionine-enkephalin (100 micrograms) produced a transient rise in plasma cortisol at 15-30 min, although the mean concentrations were not statistically different from the control period. We conclude that in newborn lambs, enkephalins may influence adrenal function. It is likely that such an action is secondary to effects on brain or pituitary hormone release.

Animals↗
PubMed1982

The fetal membranes as a possible source of progesterone in the amniotic and allantoic fluids of pregnant sheep.

To assess the possible source of progesterone in the fetal fluids of pregnant sheep, we measured the changes in progesterone concentrations in amniotic fluid (AF) and allantoic fluid (ALF) during pregnancy and compared these values with those in the maternal and fetal circulations. In acute experiments, the concentration of progesterone in ALF was greater than that in AF, and in both compartments, progesterone rose progressively between day 50 of pregnancy and term (day 145). In contrast, in maternal peripheral and uterine venous blood as well as in umbilical cord blood the mean concentration of progesterone increased until day 130, but fell at term. Similar results were obtained in chronically catheterized sheep during late pregnancy. The pattern of progesterone change in the AF and ALF suggested that the steroid might originate from a different source than progesterone in the vascular compartments. By means of in vitro incubation studies, we showed that the chorioallantoic membrane and amnion from sheep at term pregnancy had the capacity to convert [3H]pregnenolone to [3H]progesterone. These results raise the possibility that there may be local changes in steroid hormone concentrations within the tissues and fluids of the pregnant uterus. These changes could be of importance in altering the intrauterine endocrine milieu at the time of birth.

Allantois↗
PubMed1982

The effects of adrenocorticotropin, guanylylimidodiphosphate, dibutyryl adenosine 3',5'-monophosphate, and exogenous substrates on corticosteroid output by ovine fetal adrenal cells at different times in pregnancy.

To examine the factors responsible for the changing responsiveness of ovine fetal adrenals during pregnancy, we incubated dispersed adrenal cells obtained from fetal sheep on days 50, 100, and 130 of pregnancy and at term with ACTH (1--24), a GTP analog [guanosine 5(1)-(beta, gamma-imido)triphosphate], dibutyryl cAMP, and potential substrates for corticosteroid production, pregnenolone, progesterone, 17 alpha-hydroxypregnenolone, and 17 alpha-hydroxyprogesterone (17OHP4). We determined the output of cortisol (F), corticosterone (B) and progesterone (P4) by these cells during in vitro incubation. ACTH stimulated F and B output on day 50 and at term, but not in midpregnancy. The mean F to B output ratio for all concentrations of ACTH rose from 3.3 on day 50 to 11.3 at term. The GTP analog stimulated F, B, and P4 output at term, but not on day 100 or 130. Dibutyryl cAMP stimulated F and B output on day 50 and at term and stimulated P4 output at all stages of pregnancy examined. Exogenous 17OHP4 was converted to F at all times in pregnancy. The relative conversion of P4 to F and 17OHP4 to F (conversion quotient) rose from 0.09 on day 100 to 0.80 at term. P4 was converted to B at all times in gestation. At term, formation of F from delta 4 substrates (P4, and 17OHP4) was greater than that from delta 5 substrates (pregnenolone and 17 alpha OH-pregnenolone). We conclude that (1) the output of F in response to ACTH was highest on day 50 and at term pregnancy; 2) the loss of response in midpregnancy may be associated with a defect in GTP and cAMP generation and with reduced 17 alpha-hydroxylase activity; and 3) a term, 17 alpha-hydroxylase appears to be less limiting to F production than in midgestation, but delta 5, 3 beta-hydroxysteroid dehydrogenase may be more so.

Adrenal Cortex Hormones↗
PubMed1982

Inhibition by PGI-2 of myometrial activity in vivo in non-pregnant ovariectomized sheep.

The effects of PGI-salt and PGI-2 methyl ester on intrauterine pressure (IUP) and uterine electromyographic activity (EMG) were examined in vivo in non-pregnant ovariectomized sheep. PGI-2 salt and PGI-2 methyl ester (50--200 micrograms) reduced significantly the frequency and amplitude of IUP cycles and also inhibited the associated uterine EMG activity. Injections of oxytocin (50 mU) or PGF-2 alpha (2 micrograms) partly overcame the inhibiton of IUP induced by the PGI-2 methyl ester. These results suggest that endogenous PGI-2 may be involved in the regulation of uterine activity in sheep.

Animals↗
PubMed1981

Adrenal responses to prostaglandin E2 in newborn lambs.

Prostaglandin E2 (PGE2) is present in fetal sheep and stimulates adrenal steroidogenesis in the fetal and newborn sheep. We have examined the site of this prostaglandin effect and the changes in adrenal responsiveness to exogenous PGE2 and adrenocorticotropic hormone (ACTH) in in vivo studies with newborn lambs. A bolus injection of PGE2 (50 micrograms) into the brachiocephalic trunk or descending aorta raised plasma cortisol (F) 25.3 +/- 4.5 (SE) ng/ml to 75.5 +/- 5.4 ng/ml at 15 to 30 minutes and 23.2 +/- 3.0 to 60.5 +/- 7.1 ng/ml at 15 to 30 minutes, respectively (both P less than 0.001). Intra-aortic infusion of PGE2 (1.25 micrograms/ml) produced a similar significant rise in F. Basal plasma F decreased from 34.3 +/- 7.4 ng/ml at 9 to 11 days to 14.1 +/- 4.0 ng/ml at 12 to 13 days and 18.2 +/- 5.7 ng/ml at 17 to 18 days. Peak F during a 60-minute PGE2 infusion was significantly greater at 9 to 11 days (127.3 +/- 14.6 ng/ml) than at the two later times (57.2 +/- 7.07 and 55.7 +/- 14.6 ng/ml, respectively, both P less than 0.01). The response to ACTH was greater 24 hours after birth than at 7 or 28 days of age. Injection of ACTH or alpha-melanocyte-stimulating hormone during an intra-aortic PGE2 infusion did not further elevate plasma F over the rise seen with PGE2 alone. The results suggest both direct and indirect stimulatory effects of PGE2 on adrenal function in newborn sheep, and are consistent with a role of endogenous PGE2 as an intermediate factor in ACTH action.

Adrenal Glands↗
PubMed1981

The development of fetal adrenal function.

The response profiles of fetal sheep adrenals to tropic stimulation have been examined ih vivo and in vitro. Isolated adrenal cells from sheep fetuses in early pregnancy (Day 50) reduced cortisol in response to ACTH, dibutyryl cyclic AMP and GTP. The response was minimal on Day 100, but reappeared near term. 17 alpha-Hydroxyprogesterone was converted to cortisol by adrenals of all ages, but pregnenolone and progesterone were converted to cortisol only in early and late, but not mid-pregnancy. These studies suggested that the mid-gestation loss of fetal adrenal responsiveness was associated with post-receptor/adenylate cyclase events and involved loss of 17 alpha-hydroxylase activity. Fetal adrenal function was activated by exogenous ACTH in vivo, and was reflected in an increase in the ratio of cortisol to corticosterone in fetal plasma and in augmented cortisol output in vitro from dispersed fetal adrenal cells. The results were consistent with an effect of ACTH administration on 17 alpha-hydroxylation. Fetal pituitary cells, prostaglandin E2, alpha-MSH and term placental extract are other potential (sources of) corticotropins, although further studies are required to delineate the nature and origin of the active substances, and/or their primary sites of action.

Adrenal Glands↗
PubMed1981

Maternal steroid changes after fetal death until delivery of the dead sheep fetus.

Progesterone, estrone, and estradiol have been determined during late pregnancy and at parturition in the maternal plasma of sheep bearing live and dead fetuses. Mean concentrations of the steroids at days 125--130 after mating were lower after fetal death, although the differences were not significant. The mean interval between fetal death and delivery was 11.8 +/- 5.8 (0.01 +/- 0.01 ng/mL) on the day of delivery. There was no preparturient rise in maternal estrogen levels in animals with dead fetuses. The ratios of progesterone:estradiol and progesterone:estrone fell from 130 and 140 to 2.9 and 1.2, respectively, during the 5 days prior to delivery due entirely to the fall in progesterone. In normal animals the ratios of progesterone:estradiol and progesterone:estrone decreased from 186.1 and 81.7 at 5 days before parturition to 9.4 and 2.0 on the day of birth. This was attributable partly to a fall in progesterone but largely to the preparturient rise in estrone and estradiol. We conclude that some placental steroid output continues after fetal death in the sheep but that deliveries of both dead and live fetuses are associated with an abrupt change in the ratio of progesterone:estrogens in maternal blood.

Animals↗
PubMed1981

Short-term fluctuations in the concentration of cortisol and progesterone in fetal plasma, maternal plasma, and amniotic and allantoic fluids from sheep during late pregnancy.

Fluctuations in the concentrations of cortisol and progesterone in fetal plasma, maternal plasma, and amniotic and allantoic fluids were measured in samples taken at 10-min intervals over a 90-min period from three groups of sheep sampled at different times during late pregnancy. During the last 30 days of gestation there was a significant rise in the mean concentration of cortisol in fetal plasma and amniotic fluid and a significant correlation between the cortisol concentration in these two fluids. The concentration of cortisol in allantoic fluid exceeded that in amniotic fluid. The concentration of cortisol in fetal plasma varied in a pulsatile manner, however the coefficient of variation (CV) within animals was greater (36%) on days -11 to -20, relative to the day of parturition (day 0), than on days -21 to -30 or days -5 to 0(15-19%). The CV values for cortisol in amniotic fluid and maternal plasma during the last 30 days of pregnancy were 20-50% and two at five times greater than the intraassay CV. The concentration of progesterone in amniotic fluid increased after day -20 but was not correlated with that in maternal plasma or fetal plasma. The concentrations of progesterone in paired samples of amniotic fluid and allantoic fluid were similar. The CV values for progesterone (18-34%) were similar in fetal and maternal plasma and amniotic fluid and did not change significantly during late pregnancy. Changes in the concentration of progesterone were unrelated to changes in cortisol. Interpretation of steroid profiles in fetal plasma and fluids through late pregnancy should take into account these short-term fluctuations in hormone concentrations.

Allantois↗