Adrenocortical responses to adrenocorticotrophin in the hypophysectomized ovine fetus

Fetal adrenocortical responsiveness to ACTH declines during 90-120 days gestation and fetal pituitary peptides have been implicated in this refractoriness. In these studies the ACTH-induced cortisol responses were measured in 11 ovine fetuses of 114 days gestation. Five animals were hypophysectomized as evidenced by prolonged gestation, pituitary histology, TRH-testing, delayed maturation and decreasing fetal plasma prolactin concentrations (less than 1 ng.ml-1) (P less than 0.005). Resting cortisol concentrations decreased from 22.4 to 8.1 ng.ml-1 in the hypophysectomy group and were not different from the control group (19.6-14.9 ng.ml-1) over the 5 days of study. Responses measured as increments in plasma cortisol concentrations increased equally and successively in both groups. Since pituitary ablation fails to enhance fetal adrenal responsiveness to ACTH we conclude that refractoriness is unlikely to be caused by an inhibitor of pituitary origin.     

Latitude‐wide genetic patterns reveal historical effects and contrasting patterns of turnover and nestedness at the range peripheries of a tropical marine fish

Few studies have examined core–periphery genetic patterns in tropical marine taxa. The core–periphery hypothesis (CPH) predicts that core populations will have higher genetic diversity and lower genetic differentiation than peripheral populations as a consequence of greater population sizes and population connectivity in the core. However, the applicability of the CPH to many tropical marine taxa may be confounded by their complex population histories and/or high (asymmetric) population connectivity. In this study we investigated genetic patterns (based on mtDNA) across the latitudinal range of the neon damselfish Pomacentrus coelestis (36°N, Japan – 37°S, east Australia). We suggest a novel hypothetical framework for core–periphery genetic patterns and extend typical analyses to include genealogical analyses, partitioned β‐diversity measures (total β_SOR, turnover β_SIM, and nestedness‐resultant β_SNE), and analyses of nestedness. We found that the existence of two divergent lineages of the neon damselfish led levels of genetic diversity to deviate from CPH expectations. When focusing on the widespread lineage (Pacific clade) nucleotide diversity was higher in the core, supporting the CPH. However, genetic patterns differed toward the northern and southern peripheries of the Pacific clade. The turnover of haplotypes (pairwise‐β_sim) increased over distance in the north, indicative of historical colonization with little contemporary migration. In contrast, although turnover was still dominant in the south (β_SIM), there was no relationship to distance (pairwise‐β_sim), suggesting the influence of more contemporary processes. Moreover, the haplotype compositions of populations in the south were nested according to latitude, indicating immigration from lower latitudes toward the southern periphery. By extending the typical characterizations of core–periphery genetic patterns we were able to identify the effects of lineage sympatry on measures of genetic diversity and contrasting demographic histories toward the latitudinal peripheries of the neon damselfish's range.     

Enzymes of the Tryptophan Pathway in Acinetobacter calco-aceticus

All enzymes of the tryptophan synthetic pathway were detectable in extracts from wild-type Acinetobacter calco-aceticus. The levels of these enzymes were determined in extracts from a number of auxotrophs grown under limiting tryptophan. In each case only anthranilate synthetase was found to be present in increased amounts, whereas the specific activities of the remaining enzymes remained unchanged and unaffected by the tryptophan concentration. Derepression of anthranilate synthetase was found to occur as the concentration of tryptophan became limiting. Anthranilate synthetase and phosphoribosyl transferase activities are both feedback-inhibited by tryptophan. Molecular weight determination carried out by gel filtration and zonal centrifugation in sucrose revealed that all the enzymes are less than 100,000, and no molecular aggregates of these enzymes were detected. The data indicate that tryptophan synthesis in Acinetobacter is regulated both by feedback inhibition of the first two enzymes of the pathway and by repression control of anthranilate synthetase.     

Phospholipase A activity in human and ovine uterine tissues.

Phospholipase A was assayed in crude lysosomal fractions of human decidua, amnion, chorion and myometrium. Activity was present in all the tissues and was highest in decidua and amnion which contained enzymes with pH optima of 6.5-8.0 and 7.2 respectively. Comparison of the activities in tissues obtained before labor with others obtained during labor showed no differences. In sheep, the fetal membranes contained a greater activity of phospholipase A than placenta and myometrium. Stimulation of the fetal adrenals with corticotrophin caused a marked increase in activity in both amnion and chorioallantois. It is concluded that the human amnion and the ovine amnion and chorioallantois could participate in the biosynthesis of prostaglandins by releasing stored arachidonic acid.     

Oxytocin stimulates the release of arachidonic acid and prostaglandin F2 alpha from human decidual cells

Oxytocin at a physiological concentration stimulated the immediate release of free arachidonic acid from dispersed human decidual cells in a perfusion system. This indicates that oxytocin activates phospholipase(s) thus enhancing prostaglandin synthesis. The effect of oxytocin on the release of [3H]-arachidonic acid from decidual cells of women in labor was significantly greater (1036 +/- 207, mean dpm +/- SEM, n = 23) than from those of women not-in-labor (505 +/- 121 dpm, n = 12) or with endometrial cells of non-pregnant women (711 +/- 210 dpm, n = 18), and correlates well with reported oxytocin receptor concentrations in these tissues. These new findings are consistent with a role for endogenous oxytocin in stimulating prostaglandin synthesis at the onset of parturition.     

Synergistic hormonal effects on lung maturation in fetal sheep

Cortisol has minimal effects on lung maturation in fetal sheep before 130 days gestation. To test whether there is enhancement of cortisol action by other hormones, cortisol (F), triiodothyronine (T3), epinephrine (E), prolactin (PRL), and epidermal growth factor (EGF), alone or in combination, were infused into fetal sheep for 84 h between 124 and 128 days gestation. A mixture of F + T3 + PRL, but not any combination of two hormones, increased both distensibility [1.71 +/- 0.12 (SE) ml of air/g wet wt at 40 cmH2O, V40] and stability (1.16 +/- 0.09 ml of air per g wet wt at 5 cmH2O, V5) to near full-term values, above values resulting from treatment with F alone (0.91 +/- 0.12 and 0.43 +/- 0.09 ml/g, P less than 0.01). Only F had an effect when given alone, V40 increasing (P less than 0.05). Treatment with F + T3 (0.81 +/- 0.18 ml/g) and F + E (0.77 +/- 0.07 ml/g) increased V5 above values obtained with F alone (P less than 0.05). Alveolar saturated phosphatidylcholine (SPC) was higher after treatment with F + T3 (161 +/- 52 micrograms/g), F + T3 + PRL (156 +/- 53 micrograms/g, P less than 0.05), and F + E (113 +/- 40 micrograms/g, P = 0.07) than after F (12 +/- 3 micrograms/g). We conclude that F, T3, and PRL have a synergistic effect on the development of distensibility and stability of the ovine fetal lung.     

Prevention of muscle necrosis in an experimental neurovascular island muscle flap by a vasodilator drug--isoxsuprine.

We report an experiment that demonstrates one means to prevent necrosis in an experimental island muscle flap. The results imply that necrosis of skeletal muscle in a clinical flap could be prevented by treatment with isoxsuprine.     

Differential production of PGF and 6-keto-PGF1α by the rat endometrium and myometrium in response to oxytocin, catecholamines and calcium ionophore

Uterine horns from castrated, estrogen-treated rats were superfused for 6 hours in 95% O₂/5% CO₂ at 37°C. The method of superfusion in which medium flows separately over the inner and outer surfaces of the horn allows prostaglandin synthesis in the myometrium and endometrium to be measured independently while their anatomical relationship is undisturbed. Prostaglandins were measured by radioimmunoassay. The myometrium formed more 6-keto-PGF_1α than PGF whereas the opposite was true of the endometrium. Production rates of TxB₂ in both tissues were relatively low. The addition of ionophore A-23187, oxytocin or phenylephrine to the superfusion medium not only increased the myometrial production rates of both 6-keto-PGF_1α and PGF but also increased the ratio 6-keto-PGF_1α:PGF. Neither ionophore nor phenylephrine affected the rate of prostaglandin synthesis in the endometrium whereas oxytocin caused a significant increase in the production rate of PGF. We conclude that the large amounts of 6-keto-PGF_1α in the myometrial superfusate probably originate in both the smooth-muscle cells of the myometrium and the endothelium of the myometrial blood vessels. The differential responses to ionophore A-23187, phenylephrine and oxytocin suggest differences in the mode of their regulation of prostaglandin synthesis.     

The dopamine augmenter L-DOPA does not affect positive mood in healthy human volunteers

Dopamine neurotransmission influences approach toward rewards and reward-related cues. The best cited interpretation of this effect proposes that dopamine mediates the pleasure that commonly accompanies reward. This hypothesis has received support in some animal models and a few studies in humans. However, direct assessments of the effect of transiently increasing dopamine neurotransmission have been largely limited to the use of psychostimulant drugs, which elevate brain levels of multiple neurotransmitters in addition to dopamine. In the present study we tested the effect of more selectively elevating dopamine neurotransmission, as produced by administration of the immediate dopamine precursor, L-DOPA (0, 100/25, 200/50 mg, Sinemet), in healthy human volunteers. Neither dose altered positive mood. The results suggest that dopamine neurotransmission does not directly influence positive mood in humans.