Fractographic analysis of separated endodontic file designs.

Endodontic rotary files are cutting instruments used to perform root canal procedures within a tooth interior. Focusing on quantitative fractographic analysis increases necessary, clinical performance understanding of file separation failure. This research employed controlled, dynamic testing to failure of commercial rotary files, analyzing the fractographic, forensic characteristics in relation to Weibull reliability determination, considering: (1) design analysis; (2) stress concentrations; (3) times to failure; (4) number of cycles to failure (NCF). Ex vivo testing included three file designs, each having constant tip size (0.035 mm), taper (0.06 mm/mm), and length (25 mm). Files were individually tested using an electric, torque-controlled handpiece, rotating within a standardized, simulated canal until fracture separation occurred. Fractographic analysis, including critical measurements, was conducted using the scanning electron microscope (SEM) (PhenomProX, PhenomWorld, NL). Weibull statistical analysis established reliability factors per design group. Fractographic analysis identified separation fractures, processing inclusions, flexural-fatigue striations, and stress concentrations at flute pitches. Calculated NCF median values (1277-EE; 899-VB; 713-PI) demonstrated significant statistical differences among groups (p < 0.001). Separated apical fragments yielded statistically significant differences (p ≤ 0.05) for varying file design groups. Weibull moduli among groups were statistically equivalent. Fractographic analysis exposed a presence of multiple failure factors in addition to defect distribution, governing cyclic fatigue failure originating at stress concentration points irrespective of file design. Fractographic analysis indicated that a change in file design, specifically at the working edges, in addition to improved surface finish, has the potential of reducing failures by lowering points of stress concentration and reducing fracture initiating surface cracks.

Assessment of leakage pressure following enterotomy closure reinforced by tissue adhesive in a caprine cadaver model.

AIMS: To compare the combination of suture and tissue adhesive with suture alone for closure of enterotomy incisions in an ex vivo caprine jejunal model, by measuring the intraluminal pressure at which leakage occurred and the proportion of closures that leaked at intraluminal pressures <40 mmHg. METHODS: Jejunal tissue was harvested from a goat following euthanasia, and enterotomy incisions (4 mm in length) were made in each of 24 isolated jejunal segments. The enterotomies were randomly assigned to be closed using a single interrupted suture alone (n=12) or in combination with biopolymer tissue adhesive (n=12). The jejunal segments were infused with saline containing fluorescent dye and leakage pressure was defined as the peak pressure attained when visible leakage of saline solution occurred. The number of enterotomies that did or did not exhibit leakage at <40 mmHg intraluminal pressure was also recorded. RESULTS: Enterotomies closed using a combination of suture and tissue adhesive leaked at higher intraluminal pressure (58.2 (SD 4.7) mmHg) than those closed with suture alone (29.8 (SD 4.2) mmHg; p<0.001). The proportion of enterotomy closures in which the intraluminal pressure failed to reach 40 mmHg before leakage occurred was higher in enterotomies closed using suture alone (9/12, 75%) compared to those closed using both suture and tissue adhesive (3/12, 25%; p=0.002). CONCLUSIONS AND CLINICAL RELEVANCE: Use of tissue adhesive in addition to sutures increased the intraluminal pressure achieved before leakage occurred, compared to sutures alone, following enterotomy closure in a caprine cadaver model. In vivo studies are indicated to further assess the value of supplementing intestinal suture lines with tissue adhesive.

Mutation in codon 713 of the beta amyloid precursor protein gene presenting with schizophrenia.

Following reports of mutations of codon 717 in exon 17 of the amyloid precursor protein (APP) gene in early-onset familial Alzheimer's disease, we screened exon 17 for new mutations in presenile dementia. The majority of the 105 patients screened had definite or probable Alzheimer's disease, but we also included atypical cases and some chronic schizophrenics. We identified a single abnormal case--a chronic schizophrenic with cognitive defects. Sequencing revealed a C to T nucleotide substitution which produces an alanine to valine change at codon 713. We were unable to detect the mutation in the remaining members of the original cohort nor in a further 100 chronic schizophrenics and 100 non-demented controls. Nonetheless, the position of the mutation in a critical portion of the APP gene suggests that it may well prove to be pathogenic.

The role of the ecological scaffold in the origin and maintenance of whole-group trait altruism in microbial populations.

BACKGROUND: Kin and multilevel selection provide explanations for the existence of altruism based on traits or processes that enhance the inclusive fitness of an altruist individual. Kin selection is often based on individual-level traits, such as the ability to recognize other altruists, whereas multilevel selection requires a metapopulation structure and dispersal process. These theories are unified by the general principle that altruism can be fixed by positive selection provided the benefit of altruism is preferentially conferred to other altruists. Here we take a different explanatory approach based on the recently proposed concept of an "ecological scaffold". We demonstrate that ecological conditions consisting of a patchy nutrient supply that generates a metapopulation structure, episodic mixing of groups, and severe nutrient limitation, can support or "scaffold" the evolution of altruism in a population of microbes by amplifying drift. This contrasts with recent papers in which the ecological scaffold was shown to support selective processes and demonstrates the power of scaffolding even in the absence of selection. RESULTS: Using computer simulations motivated by a simple theoretical model, we show that, although an altruistic mutant can be fixed within a single population of non-altruists by drift when nutrients are severely limited, the resulting altruistic population remains vulnerable to non-altruistic mutants. We then show how the imposition of the "ecological scaffold" onto a population of non-altruists alters the balance between selection and drift in a way that supports the fixation and subsequent persistence of altruism despite the possibility of invasion by non-altruists. CONCLUSIONS: The fixation of an altruistic mutant by drift is possible when supported by ecological conditions that impose a metapopulation structure, episodic mixing of groups, and severe nutrient limitation. This is significant because it offers an alternative explanation for the evolution of altruism based on drift rather than selection. Given the ubiquity of low-nutrient "oligotrophic" environments in which microbes exist (e.g., the open ocean, deep subsurface soils, or under the polar ice caps) our results suggest that altruistic and cooperative behaviors may be highly prevalent among microbial populations.

Evolution of the connectivity and indispensability of a transferable gene: the simplicity hypothesis.

BACKGROUND: The number of interactions between a transferable gene or its protein product and genes or gene products native to its microbial host is referred to as connectivity. Such interactions impact the tendency of the gene to be retained by evolution following horizontal gene transfer (HGT) into a microbial population. The complexity hypothesis posits that the protein product of a transferable gene with lower connectivity is more likely to function in a way that is beneficial to a new microbial host compared to the protein product of a transferable gene with higher connectivity. A gene with lower connectivity is consequently more likely to be fixed in any microbial population it enters by HGT. The more recently proposed simplicity hypothesis posits that the connectivity of a transferable gene might increase over time within any single microbial population due to gene-host coevolution, but that differential rates of colonization of microbial populations by HGT in accordance with differences in connectivity might act to counter this and even reduce connectivity over time, comprising an evolutionary trade-off. RESULTS: We present a theoretical model that can be used to predict the conditions under which gene-host coevolution might increase or decrease the connectivity of a transferable gene over time. We show that the opportunity to enter new microbial populations by HGT can cause the connectivity of a transferable gene to evolve toward lower values, particularly in an environment that is unstable with respect to the function of the gene's protein product. We also show that a lack of such opportunity in a stable environment can cause the connectivity of a transferable gene to evolve toward higher values. CONCLUSION: Our theoretical model suggests that the connectivity of a transferable gene can change over time toward higher values corresponding to a more sessile state of lower transferability or lower values corresponding to a more itinerant state of higher transferability, depending on the ecological milieu in which the gene exists. We note, however, that a better understanding of gene-host coevolutionary dynamics in natural microbial systems is required before any further conclusions about the veracity of the simplicity hypothesis can be drawn.

A Mup promoter-thymidine kinase reporter gene shows relaxed tissue-specific expression and confers male sterility upon transgenic mice.

A hybrid gene was made by fusing the 2.2-kilobase 5' promoter region of a mouse group 1 major urinary protein (Mup) gene to the coding region of the herpes simplex virus type 1 thymidine kinase gene (HSV tk) and introduced into the genomes of mice by microinjection. Transgenic G0 males were sterile, or when fertile did not transmit the foreign gene, and the transgenic male descendants of G0 females were also sterile. Seven "lines" were established by breeding from G0 females and their transgenic female descendants. Six lines expressed HSV thymidine kinase activity in the liver, and activity correlated perfectly with the presence of HSV tk RNA. In three of four lines examined, expression was lower in female than in male liver, and in these lines the same sex difference was observed in the rate of run-on transcription of the foreign genes in liver nuclei. When females of one of the sexually dimorphic lines were treated with testosterone, the levels of HSV tk RNA and thymidine kinase activity were increased, although not to male levels. In these aspects of liver expression, and also in a lack of expression in seven other tissues, the hybrid gene exhibits many of the characteristics of an endogenous group 1 Mup gene. However, the gene was also expressed (at high levels) in the preputial gland and testis, two tissues in which Mup genes are not expressed. The gene, when introduced into five of the seven lines, carried a copy of the Escherichia coli supF gene attached beyond the 3' end of the HSV tk gene, but this did not affect the overall expression pattern. All of the lines were male sterile and expressed HSV thymidine kinase in the testis, but one line showed no activity in the liver, and another showed none in the preputial gland. Testicular expression is therefore the likely cause of sterility. Data are described which suggest that the causes of misexpression in the preputial gland and testis are different. Since expression in each tissue occurred in several lines, the structure of the hybrid gene must be responsible in each case. Five intensively studied lines showed at least four consistently different patterns of relative expression in preputial gland, testis, male liver, and female liver. These differences do not correlate in any way with the copy number of the foreign gene in the different lines and must be due to some other aspect of line specific integration.

Influence of the Walker 256 carcinosarcoma on muscle, tumor, and whole-body protein synthesis and growth rate in the cancer-bearing rat.

The in vivo rates of protein synthesis were assessed in tumor tissue, skeletal muscle, and whole body of rats bearing the Walker 256 carcinosarcoma. Estimates of protein synthesis in the nontumorous tissues were compared to tumor-free controls. Changes in size of the whole animal and tumor (i.e., growth) were measured, and fractional rates of growth, synthesis, and breakdown were estimated. Muscle protein synthesis and whole-body growth were significantly reduced in rats bearing larger tumors, and both were negatively correlated with tumor size (r = -0.723 and -0.825, respectively; P less than 0.01). Furthermore, whole-body and muscle protein synthesis were positively correlated with body growth (r = 0.380 and 0.563, respectively; P less than 0.05). Tumor growth followed first-order kinetics between days 7 and 13 following implantation, with a mean rate constant of 34.3%/day for the larger tumors and 27.7%/day for the small tumors. The difference in tumor growth became statistically significant over the final 3 days of tumor volume measurements. Fractional protein synthesis was significantly lower in the larger compared to the smaller tumors (48.6 versus 84.8%/day; P less than 0.05) as measured on day 14. This finding indicates a lower protein breakdown rate for the larger tumors (14.3 versus 59.0%/day; P less than 0.01) and suggests that the process of protein breakdown could play a significant role in determining tumor size, leading support to the theory of tumors acting as nitrogen traps.

Some effects of glucose concentration and anoxia on glycolysis and metabolite concentrations in the perfused liver of fetal guinea pig.

Effects of glucose concentration and anoxia upon the metabolite concentrations and rates of glycolysis and respiration have been investigated in the perfused liver of the fetal guinea pig. In most cases the metabolite concentrations in the perfused liver were similar to those observed in vivo. Between 50 days and term there was a fall in the respiratory rate and in the concentration of ATP and fructose 1,6-diphosphate and an increase in the concentration of glutamate, glycogen and glucose. Reducing the medium glucose concentration from 10 mM to 1 mM or 0.1 mM depressed lactate production and the concentration of most of the phosphorylated intermediates (except 6-phosphogluconate) in the liver of the 50-day fetus. This indicates a fall in glycolytic rate which is not in accord with the known kinetic properties of hexokinase in the fetal liver. Anoxia increased lactate production by, and the concentrations of, the hexose phosphates ADP and AMP in the 50-day to term fetal liver, while the concentration of ribulose 5-phosphate, ATP and some triose phosphates fell. These results are consistent with an activation of glycolysis, particularly at phosphofructokinase and of a reduction in pentose phosphate pathway activity, particularly at 6-phosphogluconate dehydrogenase. The calculated cytosolic NAD+/NADH ratio for the perfused liver was similar to that measured in vivo and evidence is presented to suggest that the dihydroxyacetone phosphate/glycerol 3-phosphate ratio gives a better indication of cytosolic redox than the lactate/pyruvate ratio. The present observations indicate that phosphofructokinase hexokinase and possibly pyruvate kinase control the glycolytic rate and that glyceraldehyde-3-phosphate dehydrogenase is at equilibrium in the perfused liver of the fetal guinea pig.

V3 interneuron subpopulations in the mouse spinal cord undergo distinctive postnatal maturation processes.

Mice develop weight-bearing locomotion within the first 2-3 weeks of birth, a period during which motoneurons (MNs) and interneurons (INs) that control locomotor activities undergo rapid maturation. In this study, we investigate the maturation of two subpopulations of V3 INs in the mouse spinal cord during this period. To do this, we conducted whole-cell patch-clamp recordings of tdTomato fluorescent protein-expressing spinal V3 INs from Sim1(Cre/+);tdTom mice at post-natal day (P) 0, P4, P9 and P14 and compared their properties to those at P21. Combining electrophysiology with computational analyses, we show that dorsal and ventral V3 subpopulations are physiologically distinct at birth, but the electrophysiological properties of V3 INs change significantly during the first three post-natal weeks. We further reveal that there are multiple developmental phases of both V3 subpopulations during the maturation process. The different developmental trajectories of physiological properties also coincide with changes in an animal's locomotor behavior. These properties likely reflect the differential functions of V3 subpopulations in maturing spinal locomotor circuits.

The clearance of ACTH from the plasma of adult and fetal sheep.

The disappearance of 125-I-ACTH from the circulation of 4 pregnant and fetal sheep has been followed after a single injection to the ewe or fetus. The mean metabolic clearance rate for the fetus and the ewe was 55 and 34 ml/min/kg respectively, giving a half-life in each case of about 1 min. The higher fetal than maternal arterial plasma ACTH concentration has been ascribed to a higher rate of secretion rather than a reduced rate of clearance compared with the ewe. There was no evidence of placental transfer of immunologically reactive ACTH.

Corticosteroid stimulation of phosphatidylcholine synthesis in cultured fetal rabbit lung: evidence for de novo protein synthesis mediated by glucocorticoid receptors.

To investigate further the mechanism whereby glucocorticoids accelerate the maturation of the pulmonary surfactant system, we studied both binding of glucocorticoids and their effect on phosphatidylcholine synthesis in organ cultures of fetal rabbit lung grown in serum-free medium. The greatest effect of dexamethasone (100 nM for 48 h) occurred at 24 days gestation when there was a 103% increase in the rate of choline incorporation into phosphatidylcholine and a 24% increase in the tissue content of disaturated phosphatidylcholine. Stimulation by corticosteroid was first observed after 12 h of exposure. Choline incorporation increased in a linear fashion for 36 h and then began to plateau; removal of the steroid after 24 h prevented any further increase in stimulation. The presence of other hormones in the culture medium was not a prerequisite for the corticosteroid action. Fetal sex had no influence on dexamethasone-induced phosphatidylcholine synthesis or on nuclear binding of dexamethasone. There was a striking similarity between the Kd values for specific nuclear binding of dexamethasone and cortisol (0.6 +/- 0.1 and 7.3 +/- 0.1 nM, respectively) and the concentrations for half-maximal stimulation of phosphatidylcholine synthesis (0.7 +/- 0.1 and 6.8 +/- 0.5 nM). The relative potencies of a number of steroids (100 nM) for both nuclear binding and stimulation of choline incorporation were the same: dexamethasone greater than cortisol greater than cortisone greater than corticosterone greater than dehydrocorticosterone, with no effect by progesterone, testosterone, or estradiol at this dose. Actinomycin D and cycloheximide blocked dexamethasone-induced phosphatidylcholine synthesis in a dose-dependent fashion. Actinomycin D had a marked effect if added at the initiation of hormone exposure, but little effect when added after 24 h, whereas cycloheximide was primarily effective between 24-48 h. These findings suggest that glucocorticoid stimulation of phosphatidylcholine synthesis in fetal lung is mediated by binding to specific receptors, with subsequent de novo synthesis of RNA and protein.

Effect of glucocorticoids on alpha 1-adrenergic receptor binding in rat vascular smooth muscle.

Glucocorticoids are known to have marked effects on blood pressure regulation, predominantly through altering cardiovascular sensitivity to noradrenaline. However, the molecular mechanisms underlying this action remain unclear. As part of our studies into these we have measured alpha 1-adrenergic receptor binding using the ligand [3H]prazosin in plasma membrane fractions of aortas prepared from control, adrenalectomized and dexamethasone-treated adrenalectomized rats. In controls there were 50 +/- 8 (S.E.M.; n = 6) fmol alpha 1-adrenergic receptors/mg membrane protein (Bmax) with a dissociation constant (Kd) of 0.52 +/- 0.10 nM (n = 6). Adrenalectomy 8 days before tissue preparation caused a 40% decrease in Bmax and a 60% decrease in Kd. Dexamethasone replacement after adrenalectomy returned these values close to those of controls. Noradrenaline competed for the [3H]prazosin-binding sites. Computer analysis by a non-linear curve-fitting program (LIGAND) showed that noradrenaline binding was to a heterogeneous population of high- and low-affinity receptors with Kd values of 1.87 +/- 0.73 microM and 0.48 +/- 0.12 mM (n = 5) respectively. Guanosine thiotriphosphate (GTP[S]) caused the conversion of high-affinity to low-affinity binding, consistent with the model of the high-affinity sites being coupled to a G protein. After adrenalectomy, noradrenaline binding was to a homogeneous population of low-affinity receptors; hence, the effect of GTP[S] was no longer apparent, suggesting that under these conditions the alpha 1-adrenergic receptors were unable to couple to a G protein. The two-site model of binding and GTP[S] effect was returned by dexamethasone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoids regulate the amount of G proteins in rat aorta.

Glucocorticoids are known to influence cardiovascular sensitivity to catecholamines but the molecular mechanisms are undefined. We recently showed that glucocorticoids control the coupling of adrenergic receptors to G protein. Alterations in the amount of G protein is one mechanism by which receptor-G protein coupling may be controlled. Therefore, we set out to measure the levels of G proteins in aorta from normal, adrenalectomized and dexamethasone-treated adrenalectomized rats. G proteins were measured in plasma membrane preparations by immunoblotting and horseradish peroxidase staining. After adrenalectomy there was 53% (n = 5) decrease in the density of staining for Gi (ANOVA; P less than 0.05 compared to controls). Conversely, there was a 210% (n = 5) increase in the density of staining for Gs. The levels of Go and the beta-subunit of G proteins were not changed by adrenalectomy. Dexamethasone-replacement treatment after adrenalectomy returned Gi and Gs close to control values. Go remained unaltered compared to controls but was 24% (n = 3) less than the adrenalectomized values (ANOVA; P less than 0.05). The levels of beta-subunit after dexamethasone replacement were significantly greater (ANOVA; P less than 0.05) than both the controls and adrenalectomized values. These results show that glucocorticoids can differentially regulate the amounts of G proteins in rat aorta as in other tissues. This may be an important mechanism by which steroids control receptor-G protein coupling and hence transmembrane signalling pathways in vascular smooth muscle.

Influence of pregnancy on G-protein coupling to adenylate cyclase activation in guinea-pig myometrium.

The regulatory factors controlling uterine activity during pregnancy remain unclear in many species. Since myometrial relaxants raise intracellular cyclic AMP, modulation of signalling pathways coupling cell-surface receptors to adenylate cyclase activation could be an important site for control. To assess the functional activity of the stimulatory GTP-binding protein Gs we have measured adenylate cyclase activation by GTP, its non-hydrolysable analogue guanosine 5'-(beta-gamma-imido)triphosphate (Gpp(NH)p), fluoride, forskolin and manganese in a 50,000 g membrane fraction prepared from the myometrium of non-pregnant, mid-pregnant (30-32 days) and late-pregnant (62-66 days) guinea-pigs (full term 67 +/- 2 days). While forskolin- and manganese-dependent enzyme activation was unaltered by pregnancy, maximal stimulation by Gpp(NH)p and fluoride was enhanced by up to 200%. Recovery of adenylate cyclase activity in the 50,000 g fraction was essentially constant at 20-24% of the total activity throughout pregnancy, and thus cannot explain the increases observed. Since guanine nucleotides and fluoride stimulate adenylate cyclase through activating Gs, and forskolin and manganese act at the level of the catalytic unit, these data are consistent with a pregnancy-related increase in Gs functional coupling while adenylate cyclase activity is unaltered. These observations suggest a physiological regulation of myometrial Gs activity during pregnancy which could facilitate hormonal stimulation of adenylate cyclase and contribute to uterine quiescence by increasing uterine sensitivity to relaxants.

Enhancement of noradrenaline-induced inositol polyphosphate formation by glucocorticoids in rat vascular smooth muscle cells.

Glucocorticoids are known to regulate the contractility of vascular smooth muscle by increasing its response to noradrenaline. The molecular mechanisms for achieving this remain unclear. Recent results in our laboratory have demonstrated that glucocorticoids affect both alpha 1-adrenoceptor number and coupling to G proteins. Whether this leads to an increase in second-messenger production has to be established. The present experiments, therefore, report the effects of dexamethasone on inositol polyphosphate production in vascular smooth muscle cells in culture. Noradrenaline induced the release of inositol polyphosphates from prelabelled [3H]inositol phosphoinositides in the membrane in a dose-dependent manner. The concentration of noradrenaline which caused half-maximal response was 1.26 mumol/l. Prazosin inhibited noradrenaline-induced inositol monophosphate formation to 10.26 +/- 3.67% (mean +/- S.E.M.; P less than 0.01, n = 5) of control value whereas yohimbine reduced it to only 61.74 +/- 11.82% (P less than 0.05, n = 5), suggesting an action primarily through alpha 1-adrenergic receptors. Dexamethasone (100 nmol/l, 48 h) enhanced noradrenaline-induced inositol monophosphate, bisphosphate and trisphosphate formation up to twofold (P less than 0.001, n = 5). The enhancement of the response occurred despite the fact that dexamethasone reduced [3H]inositol prelabelling of membrane phosphoinositides by 49.5 +/- 9.9% (P less than 0.05, n = 3). The present results suggest that the potential action of glucocorticoids on vascular smooth muscle contractility is, at least in part, through controlling alpha 1-adrenoceptor-mediated second-messenger production.

Changes in the concentration of adrenocorticotrophin and corticosteroid in the plasma of foetal sheep in the latter half of pregnancy and during labour.

The changes in plasma ACTH concentration of pregnant sheep and their foetuses during the latter half of pregnancy and during labour were studied. Before 140 days of gestation the mean concentration in foetal arterial plasma was 117+/-19 (S.E.M.) pg/ml which rose to a mean of 286+/-63 pg/ml. The rise in ACTH occurred at about the same time as, but not before, the rise in corticosteroid concentration in foetal plasma. The maternal plasma ACTH concentration did not change during the latter half of pregnancy and had a mean concentration of 64+/-9 pg/ml. During labour there was a progressive rise in the ACTH concentration in foetal plasma which was not associated with any corticosteroid changes. Ethanol did not suppress labour but reduced the ACTH concentration in foetal plasma.

Reduced adrenal cortical sensitivity to ACTH in lambs with cut splanchnic nerves.

The possibility that the sensitivity of the adrenal cortex to endogenous ACTH may be affected by splanchnic nerve activity has been investigated in conscious, weaned, 5- to 8-month-old lambs. The animals were atropinized (0.5 mg/kg) and tested with an i.v. infusion of noradrenaline (333 ng/kg per min for 10 min), which produced a significant rise in the mean concentration of both ACTH and cortisol in the arterial plasma. In lambs tested at least 7 days after section of both splanchnic nerves, just below the diaphragm, the rise in plasma ACTH concentration was significantly greater, and that in plasma cortisol significantly less, than in control lambs. The mean plasma ACTH and cortisol concentrations were linearly related to one another in both groups (r = 0.93 and 0.92) but the sensitivity of the adrenal cortex to the steroidogenic action of ACTH appeared to have been roughly halved 1 week after bilateral splanchnic nerve section.

Some experiments on the role of the foetal pituitary in the maturation of the foetal adrenal and the induction of parturition in sheep.

The effect of repeated increases in plasma ACTH on the production of corticosteroids and androstenedione in the sheep foetus has been investigated. Elevation of foetal plasma ACTH for up to 2 h every 24 h by repeated periods of hypoxia increased the output of cortisol. No consistent effects on foetal or maternal androstenedione concentrations or on maternal oestrogen levels were observed. Repeated short periods of increased foetal plasma ACTH concentration may promote maturation of the foetal adrenal, but there is no increase in androgen secretion by the gland nor is there an increase in oestrogen production by the placenta under such conditions.

Developmental changes in the responses of the adrenal glands of foetal sheep to endogenous adrenocorticotrophin, as indicated by hormone responses to hypoxaemia.

The change in plasma ACTH and corticosteroid concentrations in response to a 60 min period of hypoxaemia were studied in foetal and adult sheep during the latter half of pregnancy. Hypoxaemia consistently caused large rises in the concentration of ACTH in foetal plasma, the magnitude of which did not change with gestational age but was related to the physiological state of the foetus. Before 139 days small and slow rises in corticosteroid (predominantly cortisol) concentration in foetal plasma were observed during hypoxaemia, and these may have been of maternal origin. After 139 days, hypoxaemia caused a rapid and large rise in the concentration of cortisol and corticosterone in foetal plasma, which was largely of foetal origin. Hypoxaemia caused no consistent change in maternal plasma ACTH concentration but was associated with progressive increases in plasma cortisol concentrations. The cortisol: corticosterone ratio in foetal plasma was 1-5 before 139 days and increased to 4-1 several days before term which was lower than the value of 9 in maternal plasma. Small concentrations of 11-deoxycortisol and cortisone were detected in maternal and foetal plasma, the changes of which were small during hypoxaemia. The results indicate that a maturational change in the sensitivity of the foetal adrenal to endogenous ACTH occurs several days before term.

Control of adrenocorticotrophin secretion by catecholamines in the pregnant and foetal sheep.

The effect of adrenaline on the maternal and foetal plasma ACTH concentration of twelve pregnant sheep with chronically implanted vascular catheters has been studied. Adrenaline infused into the jugular vein of the ewe or foetus produced carotid arterial adrenaline concentrations of 1-9 ng/ml. The foetal plasma ACTH was 253 +/- 73 pg/ml and it showed a fivefold increase during adrenaline infusion; the ACTH concentration achieved was proportional to the plasma adrenaline. In the ewe plasma ACTH was 99 +/- 23 pg/ml. During adrenaline infusion to the ewe this rose by an amount dependent on the adrenaline concentration achieved and there was also a rise in foetal plasma ACTH but no consistent change in foetal plasma adrenaline. There was no reproducible change in plasma corticosteroid concentration during adrenaline infusion into the foetus but a rise in maternal plasma corticosteroid concentration during infusion into the ewes. Because the adrenaline concentrations achieved during the infusions were within the physiological range, the results indicate that circulating catecholamines may directly or indirectly influence the concentration of ACTH in the circulation. Also, physiological rises in plasma catecholamines in pregnant animals may stimulate the release of ACTH from the foetal pituitary.