AZFa Y gene, DDX3Y, evolved novel testis transcript variants in primates with proximal 3´UTR polyadenylation for germ cell specific translation

Translational control is a major level of gene expression regulation in the male germ line. DDX3Y located in the AZFa region of the human Y chromosome encodes a conserved RNA helicase important for translational control at the G1-S phase of the cell cycle. In human, DDX3Y protein is expressed only in premeiotic male germ cells. In primates, DDX3Y evolved a second promoter producing novel testis-specific transcripts. Here, we show primate species-specific use of alternative polyadenylation (APA) sites for these testis-specific DDX3Y transcript variants. They have evolved subsequently in the 3´UTRs of the primates´ DDX3Y transcripts. Whereas a distal APA site (PAS4) is still used for polyadenylation of most DDX3Y testis transcripts in Callithrix jacchus; two proximal APAs (PAS1; PAS2) are used predominantly in Macaca mulatta, in Pan trogloydates and in human. This shift corresponds with a significant increase of DDX3Y protein expression in the macaque testis tissue. In chimpanzee and human, shift to predominant use of the most proximal APA site (PAS1) is associated with translation of these DDX3Y transcripts in only premeiotic male germ cells. We therefore assume evolution of a positive selection process for functional DDX3Y testis transcripts in these primates which increase their stability and translation efficiency to promote its cell cycle balancing function in the human male germ line.

Quantitative measurement of udder oedema in dairy cows using ultrasound to monitor the effectiveness of diuretic treatment with furosemide

INTRODUCTION

The aim of this study was to record the course of peripartal udder oedema with ultrasonography in dairy cows and to investigate the therapeutic effects of diuretic furosemide. For this purpose, a device with a force sensor for the ultrasound probe was developed, which ensured the generation of data under similar pressure conditions and thereby repeatable and comparable results. In a pretrial with ten cows, ultrasonographic measurements were performed daily at four locations per udder quarter beginning 14 days ante partum until 14 d post partum. The main study included 50 dairy cows. The experimental group (n=25) received 500 mg furosemide intramuscularly on the day of calving, as well as on the first and second day post partum. The control group (n=25) was treated with 10 mL 0,9 % sodium chloride solution (NaCl) at the same timepoints. The experimental period was extended from 21 days ante partum until 21 days post partum and included 15 ultrasonographic measurements at three-day intervals. The measurements were performed at the teat base, which turned out to be the most suitable location in the pretrial. Quarter milk samples were collected on the day of calving, 7 and 14 days post partum. The average thickness of the udder oedema between the group treated with furosemide and the control group did not differ. In conclusion, a method for the ultrasonographic measurement of udder oedema under comparable applied forces was established. The teat base turned out to be a suitable location to monitor the characteristic temporal course of udder oedema. In the present study, treatment with furosemide did not have a measurable, positive effect on the severity of the udder oedema post partum in the study animals. Finally, further studies with a higher sample size are necessary to confirm this relationship.

Characterization of a non-human primate model for the study of testicular peritubular cells-comparison with human testicular peritubular cells

STUDY QUESTION

Are monkey testicular peritubular cells (MKTPCs) from the common marmoset monkey (Callithrix jacchus) a suitable translational model for the study of human testicular peritubular cells (HTPCs)?

SUMMARY ANSWER

MKTPCs can be isolated and propagated in vitro, retain characteristic markers for testicular peritubular cells and their proteome strongly (correlation coefficient of 0.78) overlaps with the proteome of HTPCs.

WHAT IS KNOWN ALREADY

Smooth-muscle-like peritubular cells form the wall of seminiferous tubules, transport sperm, are immunologically active, secrete a plethora of factors and may contribute to the spermatogonial stem cell niche. Mechanistic studies are hampered by heterogeneity of human samples.

STUDY DESIGN, SIZE, DURATION

We established a culture method for MKTPCs and characterized these cells from six young adult animals (2-3 years). To examine whether they qualify as a translational model we also examined HTPCs from seven men and compared the proteomes of both groups.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We used explant cultures to obtain MKTPCs, which express smooth muscle markers (calponin (CNN1), smooth muscle actin (ACTA2)), lack FSH-receptors (FSHR) and LH-receptors (LHCGR), but possess androgen receptors (AR). MKTPCs can be passaged at least up to eight times, without discernable phenotypic changes. Mass-spectrometry-based analyses of the MKTPC and HTPC proteomes were performed.

MAIN RESULTS AND THE ROLE OF CHANCE

We established a method for isolation and cultivation of MKTPCs, and provide a comprehensive analysis of their protein repertoire. The results let us conclude that MKTPCs are suitable as a non-human primate model to study peritubular cell functions.

LARGE SCALE DATA

List of identified proteins in MKTPCs by liquid chromatography-tandem mass spectrometry is accessible at the ProteomeXchange (identifier PXD009394).

LIMITATIONS, REASON FOR CAUTION

This is an in vitro cellular non-human primate model used to provide a window into the role of these cells in the human testis.

WIDER IMPLICATIONS OF THE FINDINGS

Previous studies with HTPCs from patients revealed a degree of heterogeneity, possibly due to age, lifestyle and medical history of the individual human donors. We anticipate that the new translational model, derived from young healthy non-human primates, may allow us to circumvent these issues and may lead to a better understanding of the role of peritubular cells.

STUDY FUNDING AND COMPETION OF INTEREST(S)

This work was supported by grants from the Deutsche Forschungsgemeinschaft (MA 1080/27-1; AR 362/9-1; BE 2296/8-1). The authors declare no competing financial interests.

Core body temperature is not a reliable parameter to follow the reproductive cycle in female marmoset monkey (<i>Callithrix jacchus</i>)

Abstract. Marmosets represent an attractive and widely used animal species in biomedical research, and the routine monitoring of female reproductive cycles is often mandatory in the fields of reproductive biology and stem cell research. Today, the established method for the reliable detection of ovulation is the determination of progesterone concentrations from blood samples. This method is based on relatively frequent handling and blood collections; therefore, less invasive alternatives would help to reduce stress on the animals. Here, we investigated whether the core body temperature of marmosets would show a correlation with cycle-dependent hormonal fluctuations, as has been described for humans and other primate species. In particular, the objective was to investigate whether the telemetric recording of core body temperature could replace progesterone measurements as a reliable, less invasive method for the detection of ovulation in these animals. Here we show that the core body temperature parameters in female marmosets were characterized by frequent variations, but they were not related to particular days or phases during the reproductive cycle. Therefore, the recording of core body temperature in our controlled standard experimental setting is not an appropriate method to monitor the reproductive cycle in female marmosets, and cannot replace serum progesterone measurement as a state-of-the-art method.

Primordial germ cell development in the marmoset monkey as revealed by pluripotency factor expression: suggestion of a novel model of embryonic germ cell translocation

Primordial germ cells (PGCs) are the embryonic progenitors of sperm and egg cells. Mammalian PGCs are thought to actively migrate from the yolk sac endoderm over long distances across the embryo to reach the somatic genital ridges. The general principles of mammalian PGC development were discovered in mice. In contrast, little is known about PGC development in primates due to extremely limited access to primate embryos. Here, we analyzed 12 well preserved marmoset monkey (Callithrix jacchus) embryos covering the phase from PGC emergence in the endoderm to the formation of the sexually differentiated gonad (embryonic day (E) 50 to E95). We show using immunohistochemistry that the pluripotency factors OCT4A and NANOG specifically mark PGCs throughout the period studied. In contrast, SALL4 and LIN28 were first expressed ubiquitously and only later down-regulated in somatic tissues. We further show, for the first time, that PGCs are located in the endoderm in E50 embryos in close spatial proximity to the prospective genital ridge, making a long-range migration of PGCs dispensable. At E65, PGCs are already present in the primitive gonad, while significantly later embryonic stages still exhibit PGCs at their original endodermal site, revealing a wide spatio-temporal window of PGC distribution. Our findings challenge the ‘dogma’ of active long-range PGC migration from the endoderm to the gonads. We therefore favor an alternative model based primarily on passive translocation of PGCs from the mesenchyme that surrounds the gut to the prospective gonad through the intercalar expansion of mesenchymal tissue which contains the PGCs. In summary, we (i) show differential pluripotency factor expression during primate embryo development and (ii) provide a schematic model for embryonic PGC translocation.

The neonatal marmoset monkey ovary is very primitive exhibiting many oogonia

Oogonia are characterized by diploidy and mitotic proliferation. Human and mouse oogonia express several factors such as OCT4, which are characteristic of pluripotent cells. In human, almost all oogonia enter meiosis between weeks 9 and 22 of prenatal development or undergo mitotic arrest and subsequent elimination from the ovary. As a consequence, neonatal human ovaries generally lack oogonia. The same was found in neonatal ovaries of the rhesus monkey, a representative of the old world monkeys (Catarrhini). By contrast, proliferating oogonia were found in adult prosimians (now called Strepsirrhini), which is a group of ‘lower’ primates. The common marmoset monkey (Callithrix jacchus) belongs to the new world monkeys (Platyrrhini) and is increasingly used in reproductive biology and stem cell research. However, ovarian development in the marmoset monkey has not been widely investigated. Herein, we show that the neonatal marmoset ovary has an extremely immature histological appearance compared with the human ovary. It contains numerous oogonia expressing the pluripotency factors OCT4A, SALL4, and LIN28A (LIN28). The pluripotency factor-positive germ cells also express the proliferation marker MKI67 (Ki-67), which has previously been shown in the human ovary to be restricted to premeiotic germ cells. Together, the data demonstrate the primitiveness of the neonatal marmoset ovary compared with human. This study may introduce the marmoset monkey as a non-human primate model to experimentally study the aspects of primate primitive gonad development, follicle assembly, and germ cell biology in vivo.

The pluripotency factor LIN28 in monkey and human testes: a marker for spermatogonial stem cells?

Mammalian spermatogenesis is maintained by spermatogonial stem cells (SSCs). However, since evidentiary assays and unequivocal markers are still missing in non-human primates (NHPs) and man, the identity of primate SSCs is unknown. In contrast, in mice, germ cell transplantation studies have functionally demonstrated the presence of SSCs. LIN28 is an RNA-binding pluripotent stem cell factor, which is also strongly expressed in undifferentiated mouse spermatogonia. By contrast, two recent reports indicated that LIN28 is completely absent from adult human testes. Here, we analyzed LIN28 expression in marmoset monkey (Callithrix jacchus) and human testes during development and adulthood and compared it with that in mice. In the marmoset, LIN28 was strongly expressed in migratory primordial germ cells and gonocytes. Strikingly, we found a rare LIN28-positive subpopulation of spermatogonia also in adult marmoset testis. This was corroborated by western blotting and quantitative RT–PCR. Importantly, in contrast to previous publications, we found LIN28-positive spermatogonia also in normal adult human and additional adult NHP testes. Some seasonal breeders exhibit a degenerated (involuted) germinal epithelium consisting only of Sertoli cells and SSCs during their non-breeding season. The latter re-initiate spermatogenesis prior to the next breeding-season. Fully involuted testes from a seasonal hamster and NHP (Lemur catta) exhibited numerous LIN28-positive spermatogonia, indicating an SSC identity of the labeled cells. We conclude that LIN28 is differentially expressed in mouse and NHP spermatogonia and might be a marker for a rare SSC population in NHPs and man. Further characterization of the LIN28-positive population is required.

Water immersion is associated with an increase in aquaporin-2 excretion in healthy volunteers

Here, we report the alterations in renal water handling in healthy volunteers during a 6 h thermoneutral water immersion at 34 to 36 degrees C. We found that water immersion is associated with a reversible increase in total urinary AQP2 excretion.

Nitrogen metabolism and bone metabolism markers in healthy adults during 16 weeks of bed rest

BACKGROUND

The associations between nitrogen metabolism and bone turnover during bed rest are still not completely understood.

METHODS

We measured nitrogen balance (nitrogen intake minus urinary nitrogen excretion) and biochemical metabolic markers of calcium and bone turnover in six males before head-down tilt bed rest (baseline), during 2, 10, and 14 weeks of immobilization, and after reambulation.

RESULTS

The changes in nitrogen balance were highest between baseline and week 2 (net change, -5.05 +/- 1.30 g/day; 3.6 +/- 0.6 g/day at baseline vs -1.45 +/- 1.3 g/day at week 2; P<0.05). In parallel, serum intact osteocalcin (a marker of bone formation) was already reduced and renal calcium and phosphorus excretions were increased at week 2 (P <0.05). Fasting serum calcium and phosphorus values and renal excretion of N-telopeptide (a bone resorption marker) were enhanced at weeks 10 and 14 (P <0.05-0.001), whereas serum concentrations of parathyroid hormone, calcitriol, and type I collagen propeptide (a marker of bone collagen formation) were decreased at week 14 (P <0.05-0.01). Significant associations were present between changes of serum intact osteocalcin and 24-h calcium excretion (P <0.001), nitrogen balance and 24-h phosphorus excretion (P <0.001), nitrogen balance and renal N-telopeptide excretion (P <0.05), and between serum osteocalcin and nitrogen balance (P <0.025).

CONCLUSIONS

Bone formation decreases rapidly during immobilization in parallel with a higher renal excretion of intestinally absorbed calcium. These changes appear in association with the onset of a negative nitrogen balance, but decreased bone collagen synthesis and enhanced collagen breakdown occur after a time lag of several weeks.

Body mass changes, energy, and protein metabolism in space

Most astronauts lose body mass during their stay in microgravity. The early hypothesis, which attributed this phenomenon to an increase in diuresis and natriuresis after entering microgravity, is now untenable. Although a fluid shift from the lower to the upper body occurs, it does not lead to a marked fluid loss in the first 2 days of space flight. The continuous day-by-day body mass measurement during the Euromir 94 mission showed that there was a gradual reduction over the entire mission instead of a rapid loss of 2 to 3 kg at the beginning of a mission. The daily energy intake during this mission and the negative energy balances found in the Skylab and LMS-Mission show that lowered body mass is very likely caused by an insufficient energy consumption and its accompanying effects. These include the metabolization of endogenous energy stores, ie, glycogen, protein, and fat. Mobilization of glycogen and protein buffers will also cause the water that is bound to both to be lost. Thus, a gradual decrease in body mass and a concomitant reduction in total body fluid occurs without a significant increase in urine flow or natriuresis. In conclusion, the body mass loss in microgravity is likely a result of undernutrition instead of diuresis and natriuresis caused by the fluid shift.

Renal and sympathoadrenal responses in space

According to a classic hypothesis, weightlessness should promote the renal excretion rate of sodium and water and lead to a fluid- and electrolyte-depleted state. This hypothesis is based on experiments in which weightlessness has been simulated in humans by head-down bed rest and water immersion. However, after 5 to 6 days of space mission, the diuretic and natriuretic responses to an intravenous isotonic saline load were attenuated and plasma norepinephrine and renin concentrations increased compared with those of the acute supine position before flight. Renal fluid excretion after an oral water load was also attenuated in space. Similar decreases were not observed during head-down bed rest. Sympathetic activity is of major importance in regulating blood volume and renal function. Studies in space have indicated that, compared with that while in a supine position on Earth, sympathoadrenal activity is increased during space flights as measured using plasma concentration and urinary excretion of norepinephrine and epinephrine. The space-induced activation of antinatriuretic mechanisms and sympathoadrenal activity could have been caused by early in-flight reduction in total and central blood volume. The decreased plasma volume may be explained by such factors as redistribution of plasma from the lower to the upper body (thin legs and puffy face), reduced food intake, and decreased muscle activity. The decrease in plasma volume and the subsequent increase in sympathetic activity is due, at least in part, to the abrupt cessation of activity in large muscle groups during microgravity, which normally counteracts the effects of gravity in the upright posture. This would lead to accumulation of albumin and fluid in the interstitial space.

Validity of microgravity simulation models on earth

Many studies have used water immersion and head-down bed rest as experimental models to simulate responses to microgravity. However, some data collected during space missions are at variance or in contrast with observations collected from experimental models. These discrepancies could reflect incomplete knowledge of the characteristics inherent to each model. During water immersion, the hydrostatic pressure lowers the peripheral vascular capacity and causes increased thoracic blood volume and high vascular perfusion. In turn, these changes lead to high urinary flow, low vasomotor tone, and a high rate of water exchange between interstitium and plasma. In contrast, the increase in thoracic blood volume during a space mission is combined with stimulated orthosympathetic tone and lowered urine flow. During bed rest, body tissues are compressed by pressure from gravity, whereas microgravity causes a negative pressure around the body. The differences in renal function between space and experimental models appear to be explained by the physical forces affecting tissues and hemodynamics as well as by the changes secondary to these forces. These differences may help in selecting experimental models to study possible effects of microgravity.

Revised hypothesis and future perspectives

Results from space have been unexpected and not predictable from the results of ground-based simulations. Therefore, the concept of how weightlessness and gravity modulates the regulation of body fluids must be revised and a new simulation model developed. The main questions to ask in the future are the following: Does weightlessness induce a diuresis and natriuresis during the initial hours of space flight leading to an extracellular and intravascular fluid volume deficit? Can sodium in excess be stored in a hitherto unknown way, particularly during space flight? Why are fluid and sodium retaining systems activated by spaceflight? Why are the renal responses to saline and water stimuli in space attenuated compared with those of ground simulations? How can the effects of weightlessness on fluid and electrolyte regulation be correctly simulated on the ground? The information obtained from space may be of relevance to fluid and electrolyte balance in edematous patients.

Water and sodium balance in space

We have previously shown that fluid balances and body fluid regulation in microgravity (microG) differ from those on Earth (Drummer et al, Eur J Physiol 441:R66-R72, 2000). Arriving in microG leads to a redistribution of body fluid-composed of a shift of fluid to the upper part of the body and an exaggerated extravasation very early in-flight. The mechanisms for the increased vascular permeability are not known. Evaporation, oral hydration, and urinary fluid excretion, the major components of water balance, are generally diminished during space flight compared with conditions on Earth. Nevertheless, cumulative water balance and total body water content are stable during flight if hydration, nutritional energy supply, and protection of muscle mass are at an acceptable level. Recent water balance data disclose that the phenomenon of an absolute water loss during space flight, which has often been reported in the past, is not a consequence of the variable microG. The handling of sodium, however, is considerably affected by microG. Sodium-retaining endocrine systems, such as renin-aldosterone and catecholamines, are much more activated during microG than on Earth. Despite a comparable oral sodium supply, urinary sodium excretion is diminished and a considerable amount of sodium is retained-without accumulating in the intravascular space. An enormous storage capacity for sodium in the extravascular space and a mechanism that allows the dissociation between water and sodium handling likely contribute to the fluid balance adaptation in weightlessness.

Involvement of the renal natriuretic peptide urodilatin in body fluid regulation

Urodilatin, a 32-aminoacid peptide, is expressed in distal tubular cells of the human kidney and presumably released into the luminal part of the nephron to exert its effect via activation of membrane-bound guanylyl cyclases (type A) at the medullary collecting duct. Thereby, the tubular reabsorption of sodium is inhibited and natriuresis is stimulated. The peptide is derived from the same gene and propeptide as the atrial natriuretic peptide (ANP), a more N-terminal cleavage in the human kidney than in other body tissues may be responsible for the existence of this renal natriuretic peptide and its increased stability in the extreme environment of the kidney and primary urine. The results of a sequence of human and animal physiology experiments has suggested that the renal natriuretic peptide, rather than its cardiac analog ANP, may play an essential role in mediating urinary sodium excretion. First observations are made suggesting a contribution of the renal natriuretic peptide also to disturbed sodium handling under pathophysiological conditions.

Nutrient supply during recent European missions

An inadequate nutrient intake during space flight may compromise the crewmembers' health status. In fact, during recent European missions (D-2, EuroMIR 94 and EuroMIR 95), monitoring of the astronauts' food intake revealed that they had a deficient energy, fluid, and calcium intake and an excessive sodium consumption compared to the dietary reference intakes for earthbound conditions. Inappropriate amounts of these nutrients have a considerable impact on body fluid regulation, the cardiovascular system and on calcium and bone metabolism, especially bone mineral density, which are all stressed by the microgravity environment. Provision of adequate nutrition especially when facing long-term space flights is therefore one of the foremost challenges. Therefore, for the German MIR 97 mission, we considered the data obtained from previous European missions to devise a constant and controlled nutrient intake that matched the earthbound dietary reference intake values in our experiments. Specific markers indicated that bone formation continually declined and bone resorption increased in the MIR 97 astronaut. This suggests that the nutritional criteria chosen for the subjects remaining on Earth may be inadequate for extended space missions. Therefore, more emphasis has to be placed on investigating the effects of a deficient nutrient intake on astronauts during exposure to microgravity, to manage their nutritional care appropriately during long-term missions.

Orthostatic stress is necessary to maintain the dynamic range of cardiovascular control in space

In the upright position, gravity fills the low-pressure systems of human circulation with blood and interstitial fluid in the sections below the diaphragm. Without gravity one pressure component in the vessels disappears and the relationship between hydrostatic pressure and oncotic pressure, which regulates fluid passage across the capillary endothelium in the terminal vascular bed, shifts constantly. The visible consequences of this are a puffy face and "bird" legs. The plasma volume shrinks in space and the range of cardiovascular control is reduced. When they stand up for the first time after landing, 30-50% of astronauts suffer from orthostatic intolerance. It remains unclear whether microgravity impairs cardiovascular reflexes, or whether it is the altered volume status that causes the cardiovascular instability following space flight. Lower body negative pressure was used in several space missions to stimulate the cardiovascular reflexes before, during and after a space flight. The results show that cardiovascular reflexes are maintained in microgravity. However, the astronauts' volume status changed in space, towards a volume-retracted state, as measurements of fluid-regulating hormones have shown. It can be hypothesized that the control of circulation and body fluid homeostasis in humans is adapted to their upright posture in the Earth's gravitational field. Autonomic control regulates fluid distribution to maintain the blood pressure in that posture, which most of us have to cope with for two-thirds of the day. A determined amount of interstitial volume is necessary to maintain the dynamic range of cardiovascular control in the upright posture; otherwise orthostatic intolerance may occur more often.

Body fluid regulation in micro-gravity differs from that on Earth: an overview

Similar to the response to central hypervolemic conditions on Earth, the shift of blood volume from the legs to the upper part of the body in astronauts entering micro-gravity should, in accordance with the Henry-Gauer mechanism, mediate diuresis and natriuresis. However, fluid balance and kidney function experiments during various space missions resulted in the surprising observation that the responses qualitatively differ from those observed during simulations of hypervolemia on Earth. There is some evidence that the attenuated responses of the kidney while entering weightlessness, and also later during space flight, may be caused by augmented fluid distribution to extravascular compartments compared to conditions on Earth. A functional decoupling of the kidney may also contribute to the observation that renal responses during exposure to micro-gravity are consistently weaker than those during simulation experiments before space flight. Deficits in body mass after landing have always been interpreted as an indication of absolute fluid loss early during space missions. However, recent data suggest that body mass changes during space flight are rather the consequences of hypocaloric nutrition and can be overcome by improved nutrition schemes. Finally, sodium-retaining humoral systems are activated during space flight and may contribute to a new steady-state of metabolic balances with a pronounced increase in body sodium compared to respective conditions on Earth. A revision of the classical "micro-gravity fluid shift" scheme is required.

Differential expression of functional guanylyl cyclases in melanocytes: absence of nitric-oxide-sensitive isoform in metastatic cells

Nitric oxide (NO) is a reactive endogenous molecule with multiple functions and its cellular signaling activity is mainly mediated by activation of the soluble isoform of guanylyl cyclase, a heterodimeric (alpha/beta) hemeprotein. The expression of the NO-sensitive soluble isoform of guanylyl cyclase was studied in various cultured melanocytic cells by measuring the accumulation of guanosine 3',5'-cyclic monophosphate in the presence and absence of NO donors. Here we report that 3-morpholino-sydnonimine, a donor of NO redox species, and (Z)-1-[2- (2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, a direct NO donor, induced a 20-fold increase in intracellular guanosine 3',5'-cyclic monophosphate in nonmetastatic melanoma cells and normal melanocytes in culture that could be related to cellular melanin content in a concentration-dependent manner. The increased intracellular guanosine 3',5'-cyclic monophosphate was due to stimulation of the activity of soluble guanylyl cyclase as such increase was completely abolished by using a specific inhibitor of soluble guanylyl cyclase. The involvement of functional soluble guanylyl cyclase was further confirmed by the presence of alpha1 and beta1 subunits in these cells at both mRNA and protein levels. In contrast, none of the NO donors induced guanosine 3',5'-cyclic monophosphate production in metastatic melanoma cells, which could be attributed to the absence of the beta1 subunit that is essential for catalytic activity of the soluble isoform of guanylyl cyclase. Metastatic melanoma cells produced higher levels of intracellular guanosine 3',5'-cyclic monophosphate in response to natriuretic peptides than other cell types, however, due to upregulation of membrane-bound guanylyl cyclase activities, but they are less pigmented or unpigmented. The present finding suggests that NO signaling in association with melanogenesis is dependent on the soluble isoform of guanylyl cyclase, whereas absence of soluble guanylyl cyclase but the presence of membrane-bound guanylyl cyclase correlates with the metastatic behavior of melanoma cells.

Microgravity inhibits intestinal calcium absorption as shown by a stable strontium test

BACKGROUND

Little is known about the onset and degree of biochemical and functional alterations in calcium metabolism during microgravity.

OBJECTIVE

To evaluate the effect of microgravity on intestinal calcium absorption and calcium-regulating hormones under metabolic ward conditions.

MATERIALS AND METHODS

Fractional calcium absorption (Fc240 in percentage of dose administered) was determined pre-flight, in-flight and post-flight, by use of a stable strontium test in one cosmonaut who spent 20 days in space. Moreover, a sequence of blood samples was collected for the determination of serum parathyroid hormone (PTH), 25-hydroxyvitamin D, calcitriol and serum C-telopeptide (CTx, biomarker of bone resorption) levels. During all periods of data collection, calcium intake was held constant at a minimum level of 1.000 mg day(-1) and a daily supplement of 16.6 microg vitamin D2 was given. Personal ultraviolet (UV) light exposure was measured during the whole mission using a biologically weighting UV dosimeter.

RESULTS

Fc240 was markedly reduced on flight day 19 (4.4%) as compared to pre-flight and post-flight data (13.4% and 17.2%, respectively). Serum calcitriol levels fell from 40.6 pg mL(-1) (mean pre-flight level) to 1.3 pg mL(-1) on flight day 18 and returned into the normal range after recovery. Serum CTx increased during the flight, while serum PTH and 25-hydroxyvitamin D levels did not change significantly.

CONCLUSIONS

Intestinal calcium absorption can be diminished after only three weeks of microgravity. Changes are associated with a severe suppression of circulating calcitriol levels, but are independent of exogenous vitamin D supply and serum PTH levels.

Cardiovascular response to lower body negative pressure stimulation before, during, and after space flight

BACKGROUND

It is well known that space travel cause post-flight orthostatic hypotension and it was assumed that autonomic cardiovascular control deteriorates in space. Lower body negative pressure (LBNP) was used to assess autonomic function of the cardiovascular system.

METHODS

LBNP tests were performed on six crew-members before and on the first days post-flight in a series of three space missions. Additionally, two of the subjects performed LBNP tests in-flight. LBNP mimics fluid distribution of upright posture in a gravity independent way. It causes an artificial sequestration of blood, reduces preload, and filtrates plasma into the lower part of the body. Fluid distribution was assessed by bioelectrical impedance and anthropometric measurements.

RESULTS

Heart rate, blood pressure, and total peripheral resistance increased significantly during LBNP experiments in-flight. The decrease in stroke volume, the increased pooling of blood, and the increased filtration of plasma into the lower limbs during LBNP indicated that a plasma volume reduction and a deficit of the interstitial volume of lower limbs rather than a change in cardiovascular control was responsible for the in-flight response. Post-flight LBNP showed no signs of cardiovascular deterioration. The still more pronounced haemodynamic changes during LBNP reflected the expected behaviour of cardiovascular control faced with less intravascular volume. In-flight, the status of an intra-and extravascular fluid deficit increases sympathetic activity, the release of vasoactive substances and consequently blood pressure. Post-flight, blood pressure decreases significantly below pre-flight values after restoration of volume deficits.

CONCLUSION

We conclude that the cardiovascular changes in-flight are a consequence of a fluid deficit rather than a consequence of changes in autonomic signal processing.

Water and sodium balances and their relation to body mass changes in microgravity

BACKGROUND

Since the very beginning of space physiology research, the deficit in body mass that is often observed after landing has always been interpreted as an indication of the absolute fluid loss early during space missions. However, in contrast to central hypervolemic conditions on Earth, the acute shift of blood volume from the legs to the upper part of the body in astronauts entering microgravity (microG) has neither stimulated diuresis and natriuresis nor resulted in negative water-and sodium-balances.

DESIGN

We therefore examined the kinetics of body mass changes in astronauts (n = 3) during their several weeks aboard the space station MIR. A continuous diet monitoring was performed during the first mission (EuroMIR94, 30 days). The second mission (MIR97, 19 days) comprised a 15-day metabolic ward period (including predefined constant energy and sodium intake). Water and sodium balances were calculated and the kinetic of changes in basal concentrations of fluid-balance-related hormones during flight were determined.

CONCLUSION

The data suggest firstly that loss of body mass during space flight is rather a consequence of hypocaloric nutrition. Secondly, microG provokes a sodium retaining hormonal status and may lead to sodium storage without an accompanying fluid retention.

Unexpected renal responses in space

Urine output in astronauts following ingestion of an oral water load was low in space on the Russian space station Mir and less than during simulation by 6 degrees head-down bed rest. This surprising observation shows that the effects of gravity and weightlessness on fluid volume regulation are not well understood and that the head-down bed-rest model does not simulate the effects of weightlessness on renal water handling.

Regulation and distribution of body fluid during a 6-day head-down tilt study in a randomized cross-over design

Head down tilt (-6 degrees HDT) examinations are commonly used simulation models for various microgravity induced changes in body functions. Body fluid distribution (by means of dye dilution and two independent multifrequency impedance techniques), water- and sodium-handling, and the plasma/serum concentrations of fluid balance related hormones have been determined in a randomized, controlled, cross-over study in 8 healthy test subjects. The comparison of responses to HDT and an upright control position with respective experiences from space shows some similarities but also various discrepancies between the terrestrial simulation and real microgravity.

Lactose does not enhance calcium bioavailability in lactose-tolerant, healthy adults

BACKGROUND

There is evidence from animal studies that lactose has a beneficial effect on intestinal calcium absorption. However, data concerning the effect of lactose on calcium absorption in lactose-tolerant adults are inconclusive.

OBJECTIVE

Our objective was to investigate the effect of lactose on calcium bioavailability in humans by the use of a stable-strontium test under controlled metabolic conditions.

DESIGN

Eleven healthy, lactose-tolerant subjects (8 women, 3 men) randomly received a bolus of 2.27 mmol strontium alone (load A), the bolus with 35 g lactose (load B), or the bolus with 17.5 g glucose and 17.5 g galactose (load C). Blood samples were drawn at 0, 15, 30, 60, 90, 180, 240, and 300 min. Urine specimens were collected during the time intervals -2 to 0, 0-2, 2-4, 4-6, and 6-24 h.

RESULTS

Pharmacokinetic parameters of strontium bioavailability were comparable for all 3 loads. In detail, fractional absorption at 240 min for loads A, B, and C was 12.1 +/- 0.7%, 13.0 +/- 1.1%, and 12.2 +/- 0.7%, respectively. Areas under the curve for 0-240 min were 70.8 +/- 6.3, 69.6 +/- 3.5, and 65.8 +/- 5.1 micromol*h/L for loads A, B, and C, respectively (NS). Moreover, fractional strontium excretion values of 5.1 +/- 0.8% (load A), 5.8 +/- 0.4% (load B), and 5.2 +/- 0.8% (load C) were not significantly different.

CONCLUSIONS

Lactose does not have a beneficial effect on calcium bioavailability in lactose-tolerant adults.

High dietary sodium chloride consumption may not induce body fluid retention in humans

A commonly accepted hypothesis is that a chronically high-sodium diet expands extracellular volume and finally reaches a steady state where sodium intake and output are balanced whereas extracellular volume is expanded. However, in a recent study where the main purpose was to investigate the role of natriuretic peptides under day-to-day sodium intake conditions (Heer M, Drummer C, Baisch F, and Gerzer R. Pflügers Arch 425: 390-394, 1993), our laboratory observed increases in plasma volume without any rise in extracellular volume. To scrutinize these results that were observed as a side effect, we performed a controlled, randomized study including 32 healthy male test subjects in a metabolic ward. The NaCl intake ranged from a low level of 50 meq NaCl/day to 200, 400, and 550 meq/day, respectively. Plasma volume dose dependently increased (P < 0.01), being elevated by 315 +/- 37 ml in the 550-meq-NaCl-intake group. However, in contrast to the increased plasma volume, comparable to study I, total body water did not increase. In parallel, body mass also did not increase. Mean corpuscular volume of erythrocytes, as an index for intracellular volume, was also unchanged. We conclude from the results of these two independently conducted studies that under the chosen study conditions, in contrast to present opinions, high sodium intake does not induce total body water storage but induces a relative fluid shift from the interstitial into the intravascular space.

Effects of an antihypertensive medication on functional capacity under simulated flight-typical stress-conditions

A model to investigate the functional capacity (psychomental performance) under stressful conditions was developed. Twenty eight patients with mild hypertension receiving Nitrendipine (20 mg) for 30 days were tested under hypoxic (16% oxygen) and/or orthostatic (-30 mmHg lower body negative pressure) conditions using a subset of the AGARD battery. The main effect was a decreasing performance of the grammatical reasoning task (GRT) under hypoxia or the combination of hypoxia and orthostasis. A simultaneous application of stressors while performing psychometric test batteries may be useful to reveal pharmaceutical influences on human performance and may help to recommend the use of drugs in occupational medicine.

Calcium metabolism in microgravity

Unloading of weight bearing bones as induced by microgravity or immobilization has significant impacts on the calcium and bone metabolism and is the most likely cause for space osteoporosis. During a 4.5 to 6 month stay in space most of the astronauts develop a reduction in bone mineral density in spine, femoral neck, trochanter, and pelvis of 1%-1.6% measured by Dual Energy X-ray Absorption (DEXA). Dependent on the mission length and the individual turnover rates of the astronauts it can even reach individual losses of up to 14% in the femoral neck. Osteoporosis itself is defined as the deterioration of bone tissue leading to enhanced bone fragility and to a consequent increase in fracture risk. Thinking of long-term missions to Mars or interplanetary missions for years, space osteoporosis is one of the major concerns for manned spaceflight. However, decrease in bone density can be initiated differently. It either can be caused by increases in bone formation and bone resorption resulting in a net bone loss, as obtained in fast looser postmenopausal osteoporosis. On the other hand decrease in bone formation and increase in bone resorption also leads to bone losses as obtained in slow looser postmenopausal osteoporosis or in Anorexia Nervosa patients. Biomarkers of bone turnover measured during several missions indicated that the pattern of space osteoporosis is very similar to the pattern of Anorexia Nervosa patients or slow looser postmenopausal osteoporosis. However, beside unloading, other risk factors for space osteoporosis exist such as stress, nutrition, fluid shifts, dehydration and bone perfusion. Especially nutritional factors may contribute considerably to the development of osteoporosis. From earthbound studies it is known that calcium supplementation in women and men can prevent bone loss of 1% bone per year. Based on these results we studied the calcium intake during several European missions and performed an experiment during the German MIR 97 mission where we investigated the effects of high calcium intake (>1000 mg/d) and vitamin D supplementation (650 IU/d) on the calcium and bone metabolism during 21 days in microgravity. In the MIR 97 mission high calcium intake and vitamin D supplementation led to high ionized calcium levels and a marked decrease in calcitriol levels together with decreased bone formation and increased bone resorption markers. Our conclusion from the MIR 97 mission is that an adequate calcium intake and vitamin D supplementation during space missions is mandatory but, in contrast to terrestrial conditions, does not efficiently counteract the development of space osteoporosis.

Regulation of natriuretic peptide (urodilatin) release in a human kidney cell line

BACKGROUND

To identify the molecular mechanisms underlying the release of a renal natriuretic peptide (NP) we selected a human kidney cell line (HEK 293) that displays several characteristics of distal tubular cells.

METHODS

Cells were exposed to different extracellular and intracellular stimuli, and the effect on NP release was measured with a specific urodilatin radioimmunoassay, as well as with an atrial NP (ANP) radioimmunoassay.

RESULTS

In the absence of stimuli, HEK 293 cells showed a basal release of urodilatin immunoreactivity and ANP immunoreactivity. Raising the osmolality of the secretion medium with sodium chloride and various other osmolytes rapidly increased cellular NP secretion. Elevation of intracellular cAMP levels by forskolin plus 3-isobutyl-1-methylxanthine and administration of phorbol-12-myristate-13-acetate together with the calcium-ionophore A23187 also resulted in respective increases in the amount of secreted peptide. HEK 293 cells exhibit the endogenous expression of both particulate and soluble guanylyl cyclases. In the presence of 8-Br-cGMP, cell cultures showed the enhanced secretion of an ANP immunoreactive peptide only, indicating that guanylyl cyclase activation provoked the secretion of ANP immunoreactivity but not of urodilatin immunoreactivity.

CONCLUSIONS

The human embryonic kidney cell line HEK 293 represents a renal cellular model system in which we have identified a rapid and regulated release of NPs in response to the osmotic effect of increased extracellular sodium chloride and various intracellular stimuli.

The renal natriuretic peptide urodilatin is present in human kidney

BACKGROUND

The natriuretic peptide urodilatin was first isolated from human urine and may be one of the important mediators of natriuresis, while the atrial natriuretic peptide alpha-ANP, the circulating member of the family, rather seems to play a role in cardiovascular regulation. Although the renal expression of the common propeptide for urodilatin and alpha-ANP has been detected in rat and pig, it is not yet shown that urodilatin is synthesized in human kidney.

METHODS

Immunohistochemically we localized urodilatin with an urodilatin-antibody, which does not cross-react with alpha-ANP, the ANP propeptide, brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). Radiolabelled urodilatin binding was examined autoradiographically.

RESULTS

We could demonstrate that urodilatin is present in human distal tubular cells, in which we could also localize propeptide immunoreactivity. The glomeruli, the cells of the proximal tubule, and the collecting duct did not show any urodilatin immunoreactivity. In human kidney homogenate the urodilatin content was 4600 + 520 fmol/g protein (n = 6). The renal concentration of BNP and CNP, mainly localized in the distal tubule, was much lower at 40 + 8 and 400+/-50 fmol/g protein (n=6) respectively. Furthermore the autoradiographic examinations showed that radiolabelled urodilatin binds to natriuretic peptide receptors in the glomeruli, blood vessels, and collecting ducts.

CONCLUSIONS

Our data suggest that urodilatin may be the predominant representative of natriuretic peptides in human kidneys. Urodilatin being synthesized in the distal tubular region may be transported as a paracrine factor to the collecting duct, where it exerts its suppressing effect on the sodium reabsorption by stimulating the guanylyl cyclase A.

Effects of elevated carbon dioxide environment on calcium metabolism in humans

BACKGROUND

Chronic respiratory acidosis induced by an elevated carbon dioxide (CO2) environment should provoke hypercalciuria with related total body and subsequent bone calcium losses. We examined this hypothesis in four healthy male volunteers, who were exposed during a 25-d period to an 0.7% CO2 environment within a deep diving isolation chamber. Three months later the same subjects were reexamined during a second campaign being exposed to a 1.2% CO2 atmosphere.

METHODS

The subjects received a constant calcium intake (1.4 g.d-1) and vitamin D supplement (1000 IU.d-1) during both campaigns. Calcium balance (oral calcium intake minus urinary and fecal calcium output) was evaluated. Serum calcium concentrations and biomarkers of bone metabolism were measured, in order to evaluate bone turnover. Additionally, the response to an acute oral calcium load was examined as a sensitive measure of changes in calcium metabolism.

RESULTS

Both, urinary calcium excretion (from 245 +/- 38 to 199 +/- 31 mg.d-1; mean +/- SE, 0.7% and 1.2%, respectively) and fecal calcium losses (from 1229 +/- 128 to 996 +/- 62 mg.d-1) were significantly reduced in the higher (1.2%) CO2 atmosphere. Although more calcium was retained in the body during the 1.2% than during the 0.7% CO2 campaign, serum calcium concentrations and biomarkers of bone formation were significantly lower in the higher CO2 campaign. Furthermore, bone resorption was slightly increased in the 1.2% experiment.

CONCLUSION

Elevated CO2 atmosphere may dose-dependently preserve body calcium without a parallel improvement of bone substance.

[Renal urodilatin secretion is associated with diuresis and natriuresis after spontaneous, supraventricular tachycardia]

Patients with paroxysmal supraventricular tachycardia (SVT) may have a polyuria after termination of tachycardia. There is increasing evidence that the renal peptide urodilatin (ANP (95-126))--and not plasma ANP (ANP (99-126))--is the member of the natriuretic peptide family mediating natriuresis and diuresis in man. In patients with SVT we, therefore, analyzed the relationship between diuresis, natriuresis, plasma ANP, urinary urodilatin excretion and renal excretion of cyclic GMP, the second messenger in the ANP system. During and after clinical presentation with spontaneously occurring SVT, two patients with AV-nodal and one patient with atrioventricular reentry tachycardia (heart rate 160 to 200 bpm) were studied. Urinary urodilatin excretion was correlated to diuresis (r = 0.73) and natriuresis (r = 0.93); similarly urinary cyclic GMP excretion was related to diuresis (r = 0.80) and natriuresis (r = 0.87; p < 0.001, respectively). In contrast, there was no significant correlation between plasma ANP concentrations and diuresis (r = 0.28, n.s.) or natriuresis (r = 0.11, n.s.). As an explorative analysis, stepwise multiple linear regression identified urinary urodilatin as the most important contributor to diuresis and natriuresis after SVT. These data on polyuria after spontaneous SVT further support the view that in man urodilatin is the member of the natriuretic peptide family participating in kidney physiology.

Increased renal natriuretic peptide (urodilatin) excretion in heart failure patients

Accumulating evidence suggests that urodilatin, a kidney-derived member of the natriuretic peptide family, contributes as a major mediator of sodium excretion to body fluid regulation in healthy men. In contrast to other members of the natriuretic peptide family, pathophysiological data for the renal natriuretic peptide have still been missing. The present study compares renal synthesis of urodilatin in patients with congestive heart failure (CHF) and healthy volunteers. Because urodilatin excretion, considerably increases with increasing nutritive sodium intake (p<0.004), the CHF patients (15 NYHA I/II, 8 NYHA III/IV) were kept on a 165 mmol/day sodium diet and 6 healthy volunteers on a identical nutritive sodium intake level were selected as proper controls. Although urodilatin excretion significantly increased (p<0.027) with increasing severity of CHF and was therefore significantly higher in mild CHF (40.7 +/- 2.5 fmol/min) and severe CHF (54.7 +/- 6.6 fmol/min) than in healthy controls (3.2 +/- 4.2 fmol/min), both groups of CHF patients retained sodium and had significantly lower sodium excretion rates (NYHA I/II 79.0 +/- 6.9 micromol/min, NYHA III/IV 97.9 +/- 12.7 micromol/min) than the healthy controls (139 +/- 3.4 micromol/min). Our data suggest that renal urodilatin synthesis, may not be involved in the etiology of sodium retention in CHF, but may rather be stimulated to counteract antinatriuresis during CHF.

Haematocrit, plasma volume and noradrenaline in humans during simulated weightlessness for 42 days

Previous results from our laboratory demonstrate that changes in haematocrit (Hct) and haemoglobin concentration (Hb) underestimate the relative (%) change in plasma volume (PV) in seated subjects during simulation of weightlessness by water immersion. Therefore, we examined whether changes in Hct and Hb would accurately reflect the changes in PV in seven subjects during simulation of weightlessness by another model, 6 degrees head-down tilted bed rest (HDBR), for 42 days. Since we have previously observed unexpectedly high plasma levels of noradrenaline (NA) in astronauts during space flight, we also took the opportunity to measure this variable. The measurements were compared with those of the supine horizontal position before and after HDBR. During HDBR, PV measured by the Evans blue dye dilution technique decreased by 6.1 +/- 2.8% (P < 0.05) on day 2 and 9.6 +/- 2.2% (P < 0.05) on the 42nd day compared with that of the supine, horizontal position. Based on changes in Hct and Hb, PV decreased similarly by 8.3 +/- 2.8 and 10.2 +/- 3.2% (P < 0.05) respectively. There were no differences comparing the results of the two methods (P > 0.05). Forearm venous plasma NA was unchanged during the whole course of HDBR compared with that of the pre-HDBR supine position. It is concluded that changes in Hct and Hb reliably reflect the changes in PV comparing prolonged HDBR with the pre- and post-HDBR horizontal, supine position. Thus, changes in Hct and Hb might accurately reflect the change in PV during weightlessness in humans provided that the horizontal supine position is used as the ground-based reference. Furthermore, the results of this study, as well as of previous studies from space, confirm that NA release is unchanged or even increased during weightlessness.

Body fluid metabolism at actual and simulated microgravity

Recent observations from space missions indicate that weightlessness does not induce an increase in diuresis and natriuresis in astronauts. Rather, both oral fluid and sodium intake as well as renal fluid and sodium output appear reduced compared with the preflight condition. In addition, influences of reduced energy intake may be more important for total body fluid content inflight than generally assumed. Decreases in plasma volume and observations of upper body edema formation inflight indicate, in addition, an increased extravasation as a result of the headward fluid shift in weightlessness. Current simulations models of microgravity for body fluid metabolism are valid for simulations of the central fluid shift occurring in microgravity. Since weightlessness appears to decrease central venous pressure and does not induce an increased renal fluid and sodium excretion, while simulations models have opposite effects, additional models to simulate adaptation of body fluid metabolism to weightlessness might be necessary.

Effect of organic nitrates on ex vivo platelet aggregation and fibrinolysis in man

Previous in vitro studies have suggested that nitric oxide-releasing agents can increase the fibrinolytic capacity while platelet aggregability is decreased. We have therefore directly compared the influence of organic nitrates on ex vivo platelet aggregation and the fibrinolytic system in 16 healthy volunteers. Each subject received glyceryl trinitrate (GTN, 2 x 32 mg patches), isosorbide-dinitrate (ISDN, 120 mg p.o.), isosorbide-5-mononitrate (ISMN, 50 mg p.o.), and placebo in a randomized double-blind manner. Ex vivo platelet aggregation, activities and concentrations of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) were measured before, 90 and 150 minutes after drug intake. GTN, ISDN, and ISMN were equipotent in respect to their hemodynamic responses. Platelet aggregation induced with a low (1 microM) but not with a high (4 microM) agonist concentration (adenosine diphosphate, ADP) was reduced after GTN and ISDN. ISMN had no influence on aggregation. An increase of t-PA activity was significantly reduced after GTN and ISDN (p<0.05), whereas t-PA concentrations were not affected by the nitrates. A decrease of PAI-1 activity after ISMN and placebo was not apparent after GTN and ISDN. In the case of GTN, the decrease of PAI-1 concentration was delayed. In conclusion, GTN and ISDN did not increase the fibrinolytic capacity but decreased the reversible phase of ADP-induced platelet aggregation, while ISMN had neither an effect on the fibrinolytic system nor on platelet aggregation.

Natriuresis caused by increased carotid Na+ concentration after renal denervation

The renal effects of a selective estimated 3 mM increase in the concentration of Na+ in blood perfusing the brain was investigated in conscious dogs with surgically denervated kidneys. In split-infusion experiments the concentration of Na+ in carotid plasma was increased by a bilateral carotid infusion of hypertonic NaCl combined with an infusion of distilled water into the caval vein. In control experiments the same load of NaCl and water was administered as an isotonic solution into the carotid and jugular vessels. Peak rate of Na+ excretion was significantly higher during split infusion (156 +/- 19 mumol/min) compared with control (89 +/- 14 mumol/min). Renal excretion of urodilatin increased in both series. Renal excretion of endothelin immunoreactivity increased significantly more during split infusion (20 +/- 6 pg/min) than during control (9 +/- 3 pg/min). It is concluded that the natriuretic response to minute increases in Na+ concentration of carotid plasma is intact after renal denervation. Furthermore, endothelin may be involved in the excess excretion observed.

Postprandial natriuresis in humans: further evidence that urodilatin, not ANP, modulates sodium excretion

We examined the effects of a high-salt (100 mmol NaCl) and a low-salt (5 mmol NaCl) meal on the renal excretion of sodium and chloride in 12 healthy male upright subjects. We also measured the urinary excretion of urodilatin [ANP-(95-126)], and the plasma or serum concentrations of atrial natriuretic peptide [ANP-(99-126)], aldosterone, and renin. The high-salt meal produced a postprandial natriuresis (urinary sodium excretion from 59.0 to a peak rate of 204.6 mumol/min in 3rd h after ingestion of meal) and chloride excretion. In parallel, the urinary excretion of urodilatin increased from 35.7 to a peak rate of 105 fmol/min. The effect of high-salt intake on urinary sodium, chloride, and urodilatin excretion was significant (analysis of variance, P < 0.01), and close significant correlations were observed between urodilatin and sodium excretion (mean R = 0.702) as well as between urodilatin and chloride excretion (mean R = 0.776). In contrast, plasma ANP, which was acutely elevated 15 min after high-salt intake, was already back to low-salt values 1 h later. It did not parallel the postprandial natriuretic profile, and no positive correlation between plasma ANP and sodium excretion was observed. These results provide further evidence that urodilatin, not ANP, is the member of this peptide family primarily involved in the regulation of the excretion of sodium and chloride.

Neutral endopeptidase 24.11 inhibition may not exhibit beneficial haemodynamic effects in patients with congestive heart failure

OBJECTIVES

Inhibition of neutral endopeptidase 24.11 (NEP) prevents degradation of plasma atrial natriuretic peptide (ANP), a substance with vasodilatory and natriuretic properties. The aim of the study was to investigate the haemodynamic and endocrine effects of the NEP inhibitor candoxatril in patients with congestive heart failure (CHF).

METHODS

In a randomized double-blind, parallel group study design, 24 patients with CHF received a 10-day oral drug treatment with candoxatril (25, 100 or 400 mg b.i.d.) or placebo. Invasive haemodynamics and laboratory parameters were measured on days 1 and 10.

RESULTS

On the first treatment day, candoxatril produced a dose-dependent increase in plasma cyclic GMP, the second messenger of ANP. At doses of 100 and 400 mg, candoxatril induced an increase (!) in systemic vascular resistance (SVR) and a decrease in cardiac index (CI), which was not observed with placebo and the lower candoxatril dose.

CONCLUSION

Despite significant activation of the ANP system, reflected by a dose-dependent increase in plasma cyclic GMP concentrations, high doses of candoxatril induced systemic vasoconstrictory rather than vasocilatory effects in patients with CHF. Therefore NEP inhibition by candoxatril may not exhibit beneficial haemodynamic effects in CHF.

The dihydropyridine calcium channel blocker BAY t 7207 attenuates the exercise induced increase in plasma ANF and cyclic GMP in patients with mildly impaired left ventricular function

In man, chronic antihypertensive calcium antagonist treatment improves cardiac function and reduces plasma ANF concentrations. Physical exercise increases cardiac workload and plasma ANF levels. In the present study, we investigated the effects of acute administration of the dihydropyridine calcium antagonist BAY t 7207 (BAY) during bicycle exercise on plasma ANF and plasma cyclic GMP levels, on mean arterial pressure (MAP), heart rate (HR), and on natriuresis and urinary urodilatin excretion. In a randomized, double-blind placebo controlled cross-over trial, 8 patients (age 56.8 +/- 2.5 y) with documented coronary artery disease and mildly impaired left ventricular function (EF 50.0 +/- 1.3%), received oral BAY (20 mg) or placebo. Forty-five minutes after medication, patients underwent a standardised exercise bicycle test in the supine position (6 min 25 W, 6 min 50 W). Before exercise, MAP was lower after BAY (88.8 +/- 4.1 mmHg) than after placebo (95.7 +/- 3.5 mmHg; p = 0.024), and HR was higher after BAY (76.8 +/- 3.5 bpm) than after placebo (69.5 +/- 3.6 bpm; p = 0.049). Plasma ANF tended to be higher after BAY (31.2 +/- 5.6 pg/ml) than after placebo (26.7 +/- 5.0 pg/ml), and plasma cGMP was not different (BAY 3.4 +/- 0.3, placebo 3.8 +/- 0.3 pmol/ml). During exercise, the relative increases in HR (+43%) and MAP (+17%) were identical after BAY and placebo. In contrast, ANF levels during exercise increased by 130 +/- 28% after placebo but only by 36 +/- 11% after BAY (p = 0.011). In parallel, plasma cyclic GMP increased by 61 +/- 13% after placebo and by 20 +/- 8% after BAY (p = 0.013). At the end of exercise, the BAY-induced reduction in plasma cyclic GMP reflected the reduction in diastolic arterial pressure (r = 0.717; p = 0.045). Compared to placebo, BAY treatment increased the fractional excretion rate of sodium from 0.46 +/- 0.11 to 0.90 +/- 0.22% (p = 0.016), without relation to urinary urodilatin excretion. Thus, the calcium antagonist BAY t 7207 attenuated the exercise-induced increase in plasma ANF and cyclic GMP probably due to its vasodilator effect. The relationship between blood pressure and the ANF system during exercise, which parallels findings during chronic antihypertensive treatment, may open a perspective for early evaluation of long-term therapy with calcium channel blockers.

Renal and endocrine responses in humans to isotonic saline infusion during microgravity

It was the purpose of this study to investigate how the endocrine and renal mechanisms of fluid volume control in humans (n = 4) adapt to microgravity by applying an intravenous isotonic saline infusion. The acute ground-based supine (Sup) and seated (Seat) positions were chosen as references. During microgravity, renal sodium excretion (UNaV) was doubled during the second and third hours after infusion compared with during Seat (P < 0.05) but blunted during the first hour after infusion compared with during Sup, leading to a reduction in cumulative UNaV (59 +/- 15 vs. 108 +/- 12 mmol/5 h; P < 0.05). Plasma norepinephrine (NE) attained the highest value 3 h after infusion during microgravity (31 +/- 5 x 10(-2) ng/ml vs. 19 +/- 1 and 13 +/- 3 x 10(-2) ng/ml for Seat and Sup, respectively; P < 0.05). Inflight levels of plasma renin and aldosterone were very similar to levels during Seat. In conclusion, 1) the microgravity-adapted renal responses to infusion reflected a condition in between that of ground-based Seat and Sup, respectively, and 2) the plasma levels of NE, renin, and aldosterone were elevated inflight and not related to the changes in UNaV and urinary flow rate. These observations are in contrast to results of ground-based simulation experiments and might partly have been caused by a prior inflight reduction in extracellular fluid volume. The high levels of NE during microgravity warrant further investigation.

Severe hypotension and bradycardia after continuous intravenous infusion of urodilatin (ANP 95-126) in a patient with congestive heart failure

The effects of a continuous i.v. infusion of urodilatin at a dose of 30 ng kg-1 min-1 were studied in a patient with congestive heart failure. After 30 min, urodilatin had induced a marked stimulation of plasma cyclic GMP concentrations. In parallel haematocrit increased. No significant diuresis and no change of invasive haemodynamics was observed. After 2 h the patient developed a profuse perspiration. Eighty minutes later he suffered from dizziness due to hypotension (blood pressure 80/40 mmHg) and a sudden bradycardia (50 bpm). Urodilatin was discontinued and symptoms were relieved by bed tilt and rapid infusion of isotonic saline solution. Mechanisms contributing to these adverse effects may be fluid extravasation to the third space and sympathoinhibitory effects known to occur with natriuretic peptide infusion.

The volume protective natriuretic peptide system in the inner ear. Comparison between vestibular and cochlear compartments

It has been suggested that the family of natriuretic peptides (NP) has a protective role in volume overloading. Specific binding sites for atrial natriuretic peptide (ANP) and the kidney analog urodilatin (URO) were identified and quantified with computerized autoradiography and biochemical assay in the cryosection in the cochlear and vestibular (utricle/ampulla) tissue. Immunohistochemistry was used to identify and localize NP-like immunoreactive cells. Different levels of specific receptors between and within the inner ear compartments were detected. The presence of specific receptors for NP, as well as unequal distribution of NP-immunoreactivity between the compartments (in certain parts of the cochlea and the endolymphatic sac), may indicate a local autocrine and/or paracrine action of these peptide systems (presumably as a result of the integration of the different peptide effects), independent of their action via the more conventional systemic route, in addition to differences in response of the inner ear compartments to the load. The present results on specific binding of ANP and URO in the inner ear tissue may suggest physiological homology between the inner ear and the kidney. Moreover, a similar role of NP in these organs is suggested.

Effect of water temperature on diuresis-natriuresis: AVP, ANP, and urodilatin during immersion in men

Effects of water temperature on diuresis, natriuresis, and associated endocrine responses during head-out immersion were studied in eight men (23.4 +/- 0.3 yr) during four 5-h experimental conditions: air control at 28 degrees C and immersion at 34.5 degrees C [thermoneutral (Tnt)], 36 degrees C [above Tnt (aTnt)], and 32 degrees C [below Tnt (bTnt)]. Esophageal temperature decreased by approximately 0.4 degrees C in bTnt and increased by approximately 0.5 degrees C in aTnt. Cardiac output increased by approximately 80% in aTnt and approximately 40% in bTnt while thoracic impedance, an index of central blood pooling, decreased by 7.5 omega in bTnt (NS vs. Tnt) and 8.8 omega in aTnt (P < 0.05 vs. Tnt and bTnt). Total peripheral resistance decreased at all temperatures (50% in aTnt, 20% in bTnt). Urine flow and Na+ excretion increased by sixfold in bTnt and Tnt but by only threefold in aTnt. Creatinine clearance was unchanged while osmolal clearance (but not free water clearance) increased two-fold with all immersions. Plasma atrial natriuretic peptide (ANP), urinary urodilatin, and urinary guanosine 3',5'-cyclic monophosphate increased while plasma renin activity, aldosterone, and arginine vasopressin (AVP) decreased similarly at all temperatures. bTnt did not potentiate diuresis by selective attenuation of AVP. The overall natriuretic response exhibited a higher correlation with urodilatin (r = 0.45, P < 0.001) than with ANP (r = 0.26, P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)