Metabolism of glucose by fetus and placenta of sheep. The effects of normal fluctuations in uterine blood flow

The metabolism by the fetus and placenta of [2-3H, U-14C]glucose infused into fetal sheep has been studied. Uptake of glucose from the fetus by the placenta and transfer to the ewe, as well as placental metabolism of glucose to fructose and lactate have been quantified. About two-thirds of the glucose removed from the fetal circulation was taken up by placenta. Less than 15% of this passed back into the maternal circulation, the remainder was converted, at roughly equivalent rates, into lactate and fructose, most of which was transferred back to the fetus. It seems likely that little of this glucose is oxidised by the placenta. This data indicates that there are substrate cycles between the placenta and fetus, one possible function of which is to limit fetal glucose loss back to the mother; lactate and fructose have limited placental permeability. At uterine blood flow rates in the middle of the normal range net glucose uptake by the placenta from the maternal circulation was about 7-fold higher than that from the fetus. About 20% of this was transported to the fetus, 50% was oxidised and much of the remainder converted to lactate and transferred back to the ewe. Labelling patterns in fructose and lactate make it unlikely that this placental pool of glucose mixes freely with that derived from uptake from the fetus. Net movement of glucose across the placenta is markedly influenced by fluctuations in uterine blood flow over the normal range of 500-3000 ml/min. At low flow rates there is net output of glucose from the fetus to the placenta, and in some instances from the placenta to the ewe, i.e. there is evidence of net utero-placental production of glucose to the ewe separate from output by the fetus. There is a close linear relationship between uterine glucose supply (maternal arterial concentration x uterine blood flow) and net balance across the placenta. As uterine supply of glucose falls there is increased uptake by the placenta of glucose from the fetal circulation and corresponding enhanced recycling of fructose and lactate to the fetus. This production of fructose and lactate by the placenta may function to reduce glucose loss from the fetus to the ewe. Hence at high rates of placental uptake of glucose from the fetus placental production of lactate and particularly fructose may approach saturation and allow significant backflow of glucose from the fetus to the ewe. Under these conditions glucose uptake may in part sustain placental oxygen consumption.     

Localization of vanadium-containing particles in the lungs of uranium/vanadium miners

Several geological formations of the Utah-Colorado mining region mined for uranium ore during and after World War II had been mined earlier for vanadium. Therefore, most miners and millers from that region were exposed to those metals’ ores or tailings at one time or another. Preliminary investigation to determine uranium and vanadium retained in the lungs of a former uranium miner and miller from this region, who died of lung cancer (mesothelioma), showed a high nonuniform distribution of vanadium. This observation led to the hypothesis that the vanadium content in the lungs could be associated with inhaled particles. Further examination of spectra of characteristic X-rays obtained by scanning particle-induced X-ray emission (microPIXE) of an autopsy sample of this lung indicated that vanadium was indeed present in localized sites within the 20-μm spatial resolution of the proton beam. This work points out that the microPIXE-RBS (Rutherford backscattering) test for vanadium can be used for site localization of inhaled particles retained in the lungs. Further studies are in progress to: (i) locate uranium-bearing particles in lung tissues of former uranium miners and millers; and (ii) evaluate the local doses of alpha radiation received from these particles.     

Role of nuclear analytical probe techniques in biological trace-element research

Many biomedical experiments require the qualitative and quantitative localization of trace elements with high sensitivity and good spatial resolution. The feasibility of measuring the chemical form of the elements, the time course of trace element metabolism, and conducting experiments in living biological systems are also important requirements for biological trace element research. Nuclear analytical techniques that employ ion or photon beams have grown in importance in the past decade and have led to several new experimental approaches. Some of the important features of these methods are reviewed here along with their role in trace element research. Examples of their use are given to illustrate potential for new research directions. It is emphasized that the effective application of these methods necessitates a closely integrated multidisciplinary scientific team.     

The heritability of fitness: Bad news for 'good genes'?

Some models of sexual selection depend on a female preference for 'good genes': females choose conspicuous males as these are advertising their possession of genes for fitness characters which can be inherited by their offspring. In contrast, Fisher's fundamental theorem of natural selection - which underlies much of population genetics theory - predicts that in a population at equilibrium there can be no additive genetic variation in fitness. Recent work on collared flycatchers in the wild shows that characters influencing fitness do indeed have a relatively low heritability. However, other studies of the inheritance of fitness in the laboratory suggest that under some circumstances a population may retain considerable genetic diversity for fitness characters. Genetically based female choice might hence have the potential to control the evolution of male sexual ornaments. More work on natural populations is needed; and birds may be a good place to start looking.     

Preliminary studies of the effects of bromocriptine on testicular regression and the spring moult in a seasonal breeder, the male blue fox (Alopex lagopus)

Bromocriptine administration in the form of slow-release injections to male blue foxes during March-May abolished the normal spring rise in plasma prolactin concentrations seen in May and June. The spring moult was prevented and the treated animals retained a winter coat of varied quality and maturity until the end of the study in August. Plasma testosterone concentrations fell normally from March until August. Testicular regression was, however, delayed, although there were individual variations in response. Estimation by DNA flow cytometry in early July of the relative numbers of haploid, diploid and tetraploid cells in the testis showed that, in the treated animals, 74-80% of the cells were haploid (maturing germinal cells), 4-6% tetraploid (mainly primary spermatocytes) and the rest diploid cells (somatic cells and the remaining germinal cell types). In the control males, however, no haploid cells were detected and the majority of cells were diploid (93-99%). At castration in August, histological examination revealed various stages of testicular regression in the treated and control animals.     

Covalent labeling of opioid receptors with 3H-D-Ala2-Leu5-enkephalin chloromethyl ketone. I. Binding characteristics in rat brain membranes

The chloromethyl ketone derivative of D-Ala2-Leu5-enkephalin was synthesized in a radioactive form, and the resulting compound (3H-DALECK) was used to label opioid receptors. 3H-DALECK binds with high affinity, specificity and saturability to rat brain membranes. The number of sites labeled is 130 fmoles/mg protein. Unlabeled opioids inhibited the binding of 3H-DALECK; etorphine and DAGO being most potent. A 10-fold preference for mu sites over delta was seen in site-specific competition experiments; while DALECK displayed low affinity for kappa sites of rat brain. DALECK irreversibly blocked a certain population of sites. Approximately 40% of 3H-DALECK binding at 15 min, and 60% at 60 min association time did not dissociate in the presence of a large excess of unlabeled DALECK and was resistant to washing. Autoradiography performed after SDS-PAGE revealed specific alkylation of proteins with molecular weight of 74, 65, 56, 43 and 34 kD. These results demonstrate the applicability of using 3H-DALECK to covalently label opioid receptors.     

Presynaptic control of dopamine metabolism in the nucleus accumbens. Lack of effect of buspirone as demonstrated using in vivo voltammetry

Buspirone is a non-benzodiazepine drug with anxiolytic properties. It has been reported to induce a marked increase in the metabolism of dopamine in the striatum and the nucleus accumbens which is similar to that induced by neuroleptics. It has been suggested that the effect observed in the striatum reflects an action of buspirone on dopaminergic autoreceptors in both terminals and cell bodies. In the present study, presynaptic effects of buspirone on dopaminergic metabolism in the nucleus accumbens were investigated, and they were compared to the effects of the classical neuroleptic, haloperidol. Dopaminergic terminals were isolated by infusion of tetrodotoxin into the median forebrain bundle in order to evaluate the effects of buspirone and haloperidol on presynaptic receptors. Changes in dopamine metabolism were determined by in vivo voltammetry. Buspirone administered after interruption of the impulse flow did not affect dopamine metabolism. In contrast haloperidol treatment led to an increase in metabolism of dopamine. It is concluded that buspirone did not act at the presynaptic level and furthermore on dopaminergic autoreceptors.     

Effects of stress and beta-funal trexamine pretreatment on morphine analgesia and opioid binding in rats

This study was essentially an in vivo protection experiment designed to test further the hypothesis that stress induces release of endogenous opioids which then act at opioid receptors. Rats that were either subjected to restraint stress for 1 hr or unstressed were injected ICV with either saline or 2.5 micrograms of beta-funaltrexamine (beta-FNA), an irreversible opioid antagonist that alkylates the mu-opioid receptor. Twenty-four hours later, subjects were tested unstressed for morphine analgesia (tail-flick assay) or were sacrificed and opioid binding in brain was determined. [3H]D-Ala2NMePhe4-Gly5(ol)enkephalin (DAGO) served as a specific ligand for mu- opioid receptors, and [3H]-bremazocine as a general ligand for all opioid receptors. Rats injected with saline while stressed were significantly less sensitive to the analgesic action of morphine 24 hr later than were their unstressed counterparts. Beta-FNA pretreatment attenuated morphine analgesia in an insurmountable manner. Animals pretreated with beta-FNA while stressed were significantly more sensitive to the analgesic effect of morphine than were animals that received beta-FNA while unstressed, consistent with the hypothesis that stress induces release of endogenous opioids that would protect opioid receptors from alkylation by beta-FNA. beta-FNA caused small and similar decreases in [3H]-DAGO binding in brain of both stressed and unstressed animals. Stressed rats injected with saline tended to have increased levels of [3H]DAGO and [3H]-bremazocine binding compared to the other groups. This outcome may be relevant to the tolerance to morphine analgesia caused by stress.     

DNA-dependent RNA polymerase subunits encoded within the vaccinia virus genome.

Antiserum to a multisubunit DNA-dependent RNA polymerase from vaccinia virions was prepared to carry out genetic studies. This antiserum selectively inhibited the activity of the viral polymerase but had no effect on calf thymus RNA polymerase II. The specificity of the antiserum was further demonstrated by immunoprecipitation of RNA polymerase subunits from dissociated virus particles. The presence in vaccinia virus-infected cells of mRNA that encodes the polymerase subunits was determined by in vitro translation. Immunoprecipitable polypeptides with Mrs of about 135,000, 128,000, 36,000, 34,000, 31,000, 23,000, 21,000, 20,000, and 17,000 were made when early mRNA was added to reticulocyte extracts. The subunits were encoded within the vaccinia virus genome, as demonstrated by translation of early mRNA that hybridized to vaccinia virus DNA. The locations of the subunit genes were determined initially by hybridization of RNA to a series of overlapping 40-kilobase-pair DNA fragments that were cloned in a cosmid vector. Further mapping was achieved with cloned HindIII restriction fragments. Results of these studies indicated that RNA polymerase subunit genes are transcribed early in infection and are distributed within the highly conserved central portion of the poxvirus genome in HindIII fragments E, J, H, D, and A.     

Regulation of the elemental composition of the epididymal fluids in the tammar, Macropus eugenii

Micropuncture, microanalytical and microelectrode techniques were used to study electrochemical aspects of 7 elements and fluid in the ductuli efferents and ductus epididymidis of the tammar. Rete testis fluid was isosmotic with blood and had a lower pH. It also contained lower concentrations of bicarbonate, sodium, calcium, magnesium, phosphorus and sulphur and higher concentrations of potassium and chloride than blood. The luminal fluid was acidified further during passage through the sperm ducts and all of the elements which were studied moved in or out of the lumen, usually against an electrochemical gradient. The ductuli efferents reabsorbed 87% of the fluid leaving the testis without changing the intraluminal concentrations of sodium, potassium and calcium, but the concentrations of magnesium, phosphorus and sulphur increased. The caput epididymidis reabsorbed about half the fluid entering it: sodium concentrations decreased and those of potassium and phosphorus increased. There was also some fluid reabsorption and an increase in the values of potassium and phosphorus in the corpus epididymidis. There was little net transport of fluid in the cauda epididymidis; sodium, chloride, magnesium and phosphorus concentrations decreased and potassium values increased. Studies involving filtration through a dialysis membrane of blood and fluid from the rete testis and cauda epididymidis showed that, whilst some of the calcium, magnesium, phosphorus and sulphur was associated with high molecular weight compounds in blood, the association was not significant in the reproductive fluids.