Neurohypophysial hormones and renal function in fish and mammals

The two major basic neurohypophysial peptides, arginine vasopressin (AVP) of mammals and arginine vasotocin (AVT) of all non-mammalian vertebrates, share common structure and major roles in regulating renal function. In this review the complexity of AVP actions within the mammalian kidney is discussed and comparisons are made with the emerging picture of AVT's renal effects in fish. It has become apparent that the antidiuretic action of the neurohypophysial hormones is an ancient phylogenetic phenomenon, although this is based upon reduced glomerular filtration in fish by comparison with predominant tubular effects in mammals. Nonetheless, there appears to be retention of AVP effects upon the functional heterogeneity of nephron populations in mammals. Preliminary evidence for the possible existence of V(2)-type (tubular) neurohypophysial hormone receptors in fish, implies possible AVT actions which parallel those in mammals on tubular ion transport. Further insight from recent mammalian tubule microperfusion studies suggests that in teleost fish both apical (tubular lumen) and basolateral (blood borne) AVT have the potential to modulate renal function, though this remains to be examined.     

Arginine Vasotocin: Structure-Activity Relationships and Influence on Gonadal Growth and Function

When AVT (arginine vasotocin) was given neonatally during theperiod when the brain is undergoing sexual differentiation,increased growth of the reproductive organs was observed inadulthood. Injection of AVT after this neonatal period in immatureanimals led to diminished growth of the accessory organs andin some cases the gonads themselves. The hypertrophic responseof the in situ ovary in adult mice following unilateral ovariectomy(UO) was inhibited in a dose-related manner by a single intraperitonealinjection of freshly prepared AVT. Much less AVT was requiredfor this response when injected into the third ventricle. Afterintraperitoneal injection, arginine vasopressin (AVP), lysinevasopressin (LVP), and 4-leucine vasotocin (4-leu-AVT) alsoinhibited compensatory ovarian hypertrophy whereas oxytocindid not. The commonality in die structure of these antigonadotrophicpeptides include a closed ring and a basic amino acid in position8. After opening the disulfide bond of these nonapeptides withmercaptoethanol, a single injection of the reduced AVT, AVP,LVP, or 4-leu-AVT into UO mice causes exaggerated hypertrophyof the remaining ovary. When added with leuteinizing hormone-releasinghormone (LRH) to culture medium containing hemipituitaries fromcastrated estrogen-progesterone primed female rats, AVT significantlyincreased the release of radioimmunoassayable LH above thatdue to LRH alone. AVT might interact at all levels of the hypothalamo-hypophysealgonadalaxis.     

Phylogenetic study of the arginine-vasotocin/arginine-vasopressin-like immunoreactive system in invertebrates

1. A phylogenetic study of arg-vasotocin (AVT)/arg-vasopressin (AVP)-like immunoreactive cells was performed by the PAP method in the central nervous system of invertebrates. 2. The immunoreactivity was detected in the nerve cells of Hydra magnipapillata of the Coelenterata; Neanthes japonica and Pheretima communissima of the Annelida; Pomacea canaliculata, Aplysia kurodai, Oncidium verrucosum, Bradybaena similaris, Achatina fulica, Limax marginatus and Meretrix lamarckii of the Mollusca; Gnorimosphaeroma rayi, Hemigrapsus sanguineus, Gryllus bimaculatus and Baratha brassicae of the Arthropoda; Asterina pectinifera of the Echinodermata; and Halocynthia roretzi of the Protochordata. 3. No immunoreactivity was detected in Bipalium sp. of the Platyhelminthes, or in Procambarus clarkii and Helice tridens of the Arthropoda. 4. From these results, it appears that AVT/AVP is a phylogenetically ancient peptide which is present in a wide variety of invertebrates. 5. The actions of AVT/AVP and its presence in invertebrates are discussed.     

A comparison of grooming behavior potencies of neurohypophyseal nonapeptides

We have previously demonstrated that intracerebroventricular (ICV) administration of oxytocin (OXY) enhanced grooming behaviors in male and female rats at a 1 microgram dose. In the present study female rats were injected ICV with 1 microgram OXY or equimolar doses of other peptides. At this dose arginine-vasopressin (AVP), arginine-vasotocin (AVT) and lysine-vasopressin (LVP), as well as alpha-MSH, were as effective as OXY in increasing grooming behavior. At equimolar doses, ACTH1-10, tocinoic acid (the ring structure of OXY) and Pro-Leu-Gly-NH2 (the tail structure of OXY) had no significant effect on grooming behavior. The potency of AVP and AVT was determined across a 0.05-5 microgram dose range. Grooming scores increased in an apparent linear manner across a similar OXY dose range. Both AVP and AVT, however, manifested an inverted U grooming response curve. Maximum grooming scores resulted from a 0.1 microgram dose of AVT or a 0.5 microgram AVP dose. Analyses of the aspects of grooming separately found that nonapeptides OXY, AVP and AVT all elevated body grooming, washing, and scratching. Because AVT and AVP administration resulted in grooming scores significantly higher than OXY at lower doses, we concluded that the CNS is more sensitive to the effects of AVT and AVP on grooming behavior than OXY.     

Arginine vasotocin mRNA revealed by in situ hybridization in bovine pineal gland cells

Arginine vasopressin (AVP) is the main antidiuretic hormone in mammals and arginine vasotocin (AVT) in submammalian vertebrates. The possibility that the genetic material encoding AVT is maintained in mammals is controversial. In this study, we investigated by radioactive in situ hybridization the possible presence of the mRNA encoding AVP and AVT, and using immunocytochemistry the presence of structures immunoreactive for AVP and AVT in the bovine pineal gland. In situ hybridization was performed by use of ³⁵S-labelled oligoprobes. Immunocytochemistry was performed using specific polyclonal rabbit antibodies and the avidin-biotin-complex method. In situ hybridization revealed positive signals for both AVP mRNA and AVT mRNA in a few cells scattered throughout the pineal body. Immunocytochemistry revealed thin AVP-immunoreactive fibres in the pineal stalk and the pineal gland. It also revealed staining of several AVT-immunoreactive nerve fibres in both the pineal stalk and the gland. In addition, polyhedral, neuron-like cell bodies from which two to three processes emerged were also AVT-immunoreactive. Thus, our investigation shows the presence of AVP/AVT-immunoreactive cellular structures in the bovine pineal gland. Our data further show the presence of mRNAs encoding both AVT and AVP. We therefore suggest that AVT mRNA is translated into an AVT-like peptide in the bovine pineal.     

Immunocytochemical evidence for the presence of an albumin-like substance in the rat pineal gland

Summary Two rabbits and two guinea pigs were immunized with arginine vasotocin (AVT) conjugated to bovine albumin with glutaraldehyde. Only one preparation of antiserum (anti-G 7) was of value. Anti-G 7 immunochemically defined the same rat pineal cells previously reported as presumptive AVT cells. However, absorption of anti-G 7 with bovine albumin inhibited the staining of the pineal cells demonstrating that they contained an albumin-like substance. Positive immunochemical staining of the rat pars nervosa suggested that anti-G 7 contained antibodies able to react with arginine vasopressin (AVP). Loss of a positive reaction in the posterior lobe on absorption of anti-G 7 with AVT or AVP confirmed this. However, the addition of AVT to anti-G 7 failed to inhibit the immunochemical staining of the pineal cells. This study reports the presence of an albumin-like substance in pineal cells previously described as presumptive AVT cells, and discusses possible explanations for the inability of anti-G 7 to recognize immunocytochemically the native AVT molecule. Confirmation of AVT in the pineal gland by immunocytochemistry must await the availability of more specific antisera.     

Effect of vasotocin on locomotor activity in bullfrogs varies with developmental stage and sex

Although neurohypophysial peptides are present in many regions of the developing and adult bullfrog (Rana catesbeiana) brain, the function of these peptides remains unclear. To investigate possible behavioral actions, we examined locomotor activity following peptide injection in bullfrogs at various developmental stages. An intraperitoneal (ip) injection of arginine vasotocin (AVT) in tadpoles (stages V, X, or XVII) produced an immediate and dose-dependent inhibition of locomotor activity. On the other hand, AVT stimulated activity when administered ip to juvenile or adult female bullfrogs, but did not influence activity in juvenile or adult males. The minimum effective dose of AVT, when injected directly into the brain of tadpoles, was 100-fold less than that observed when injected ip, suggesting a central nervous system site of action for this peptide. A vasopressin receptor antagonist (d(CH2)5[Tyr(Me)2]AVP administered ip or icv) significantly increased locomotor activity in tadpoles, compared to controls. Oxytocin, vasopressin, and AVP4-9 inhibited activity in tadpoles while mesotocin, des Gly(NH2)AVP, and pressinoic acid had no significant effect. Injection of PGF2 alpha also significantly decreased activity levels in tadpoles. However, pretreatment of tadpoles with indomethacin, a prostaglandin synthesis inhibitor, did not prevent the behavioral effects of AVT, suggesting that prostaglandin synthesis is not required for this response. In summary, AVT influenced locomotor activity in bullfrog tadpoles and female frogs. This effect shifted during development from an inhibitory action in tadpoles to a stimulatory effect in metamorphosed female frogs. The effect of AVT on juvenile and adult frog locomotion was sexually dimorphic, as this peptide altered female behavior but not male behavior.     

Oxytocin antagonist blocks the vasodepressor but not the vasopressor effect of neurohypophysial peptides in chickens

Cockerels with permanent cannulas in the brachial artery and vein were put into isolated slings. Arterial pressure and heart rate were continuously recorded. Following habituation, tests were initiated. In each cockerel 2 nmol/kg of the tested neurohypophysial peptide (NPs) or analogue was IV injected six times at 6-min intervals. Arginine vasotocin (AVT) caused an immediate vasodepressor (VDP) effect and tachycardia. These subsided within 20–30 s and were followed by a vasopressor (VP) response and bradycardia. On repeated injections of AVT, the VDP response declined and bradycardia intensified. Arginine vasopressin (AVP), oxytocin (OT), and mesotocin (MT) had short-lasting VDP effect in the following order of potency: OT = MT > AVT > AVP. Only AVT and, more effectively, AVP, caused a VP response. The VDP effect of MT and OT declined on repeated injections. When AVT was injected after three injections of MT, it had mostly an immediate VP effect. Although the V₁ agonist is VP in chickens, at the dose used the V₁ antagonist, [d(CH₂)₅,O-Me-Tyr²]AVP, had no effect on cardiovascular responses to AVT. Pretreatment with OT antagonist, [d(CH₂)₅-O-Me-Tyr^2,Thr^4,Tyr^9,Orn⁸]VT, abolished the VDP effect of all NPs. Thus, MT had no effect on blood pressure, whereas AVP and, more effectively, AVT, had a marked immediate VP action. In chickens the VDP effect of NPs is probably mediated by an OT/MT-like receptor, wherein the peptide's ring structure, shared by AVT, OT, and MT, is important. The VP effect is mediated by a receptor only partially similar to the mammalian V₁ receptor, where arginine in position 8, shared only by AVT and AVP, is necessary for action, and the native AVT is more effective than the mammalian AVP. This receptor reacts to the V₁ agonist but probably not to the V₁ antagonist.     

Osmotic threshold and sensitivity for vasopressin release and fos expression by hypertonic NaCl in ovine fetus

In adults, hyperosmolality stimulates central osmoreceptors, resulting in arginine vasopressin (AVP) secretion. Near-term fetal sheep have also developed mechanisms to respond to intravascular hypertonicity with stimulation of in utero AVP release. However, prior studies demonstrating fetal AVP secretion have utilized plasma tonicity changes greater than those required for adult osmotically induced AVP stimulation. We sought to examine near-term fetal plasma osmolality threshold and sensitivity for stimulation of AVP secretion and to correlate plasma hormone levels with central neuronal responsiveness. Chronically instrumented ovine fetuses (130 +/- 2 days) and maternal ewes simultaneously received either isotonic or hypertonic intravascular NaCl infusions. Maternal and fetal plasma AVP and angiotensin II (ANG II) levels were examined at progressively increasing levels of plasma hypertonicity. Intravenous hypertonic NaCl gradually elevated plasma osmolality and sodium levels. Both maternal and fetal plasma AVP increased during hypertonicity, whereas ANG II levels were not changed. Maternal AVP levels significantly increased with a 3% increase in plasma osmolality, whereas fetal plasma AVP significantly increased only at higher plasma osmolality levels (over 6%). Thus the slope of the regression of AVP vs. osmolality was greater for ewes than for fetuses (0.232 vs. 0.064), despite similar maternal and fetal plasma osmolality thresholds for AVP secretion (302 vs. 304 mosmol/kg). Hyperosmolality induced Fos immunoreactivity (FOS-ir) in the circumventricular organs of the fetal brain. FOS-ir was also demonstrated in the fetal supraoptic and paraventricular nuclei (SON and PVN), and double labeling demonstrated that AVP-containing neurons in the SON and PVN expressed Fos in response to intravenous NaCl. These results demonstrate that, in the ovine fetus at 130 days of gestation, neuroendocrine responses to cellular dehydration are functional, although they evidence a relatively reduced sensitivity for AVP secretion compared with the adult.     

Osmotic regulation of prolactin secretion in the fetal sheep

The functions of prolactin in the fetus remain speculative. No obvious physiological role has been found for the prolactin present in the fetal or maternal plasma and amniotic fluid compartments. The aim of the present study was to investigate changes in fetal plasma prolactin following intracerebroventricular (i.c.r.) administration to the fetus of artificial cerebrospinal fluid of different tonicities. A lateral ventricle catheter was placed in 11 fetuses at 107-128 days of gestation. Either isotonic artificial cerebrospinal fluid (300 mOsm.1(-1);n = 9), 15% polyethylene glycol (340 mOsm.1(-1);n = 5), or 7% distilled water in isotonic artificial cerebrospinal fluid (270 mOsm.1(-1);n = 9) was infused i.c.v. at 35 mu1.min-1 for 240 min. At 180 min thyrotropin releasing hormone (TRH) was administered through a fetal a fetal jugular catheter. Fetal carotid arterial blood gases, plasma osmolality and concentrations of prolactin, vasopressin (AVP), and norepinephrine (NE) were measured. Administration of hypotonic artificial cerebrospinal fluid produced an increase in fetal plasma prolactin from 46.6 +/- 36 ng.ml-1 at 0 min to 83.3 +/- 49 ng.ml-1 at 180 min (mean +/- SEM; P less than 0.05). No changes in either AVP or NE were observed. Administration of hypertonic artificial cerebrospinal fluid produced a decrease in plasma prolactin from 85 +/- 57 at time 0 to 49 +/- 35 at 180 min (P less than 0.05). No changes in either AVP or NE were observed. Fetal plasma prolactin, AVP, and NE did not change during control infusion of isotonic artificial cerebrospinal fluid.(ABSTRACT TRUNCATED AT 250 WORDS)     

Do circulating plasma AVT and/or cortisol levels control pulsatile urea excretion in the gulf toadfish (Opsanus beta)?

Previous work has shown that pulsatile urea excretion at the gills of the gulf toadfish is due to periodic activation of a facilitated diffusion transport system with molecular and pharmacological similarity to the UT-A transport system of the mammalian kidney. In mammals, AVP and glucocorticoids are two important endocrine regulators of this system. The present study focused on the potential role of circulating AVT (the teleost homologue of AVP) and cortisol levels as possible triggers for urea pulses. Long-term (34–84 h) monitoring of plasma levels by repetitive sampling at 2-h intervals from chronic cannulae in individual toadfish demonstrated that circulating AVT concentrations are low (10⁻¹²–10⁻¹¹ M), and show no relationship to the occurrence of natural urea pulses. In contrast, plasma cortisol levels decline greatly prior to natural pulses and rise rapidly thereafter. AVT injections into the caudal artery or ventral aorta elicited pulse events, but these were extremely small (1–10%) relative to natural pulses, and occurred only at unphysiological dose levels (10⁻⁹ M in the plasma). AVP was a partial agonist, but isotocin, insulin-like growth factor-1, and atrial natriuretic peptide were without effect at the same concentration. Artificially raising plasma cortisol levels by cortisol injection tended to reduce responsiveness to AVT. Pharmacological reduction of plasma cortisol levels by metyrapone injection elicited small pulses similar to those caused by AVT. Following such pulse events, AVT was ineffective in inducing pulses. We conclude that decreases in circulating cortisol play an important permissive role in urea pulsing, but that circulating AVT levels are not involved.     

Antipyretic effect of arginine vasotocin in toads

Arginine vasotocin (AVT) is a nonmammalian analog of the mammalian hormone arginine vasopressin (AVP). These peptides are known for their antidiuretic and pressor effects. More recently, AVP has been recognized as an important antipyretic molecule in mammals. However, no information exists about the role of AVT in febrile ectotherms. We tested the hypothesis that AVT is an antipyretic molecule in the toad Bufo paracnemis. Toads equipped with a temperature probe were placed in a thermal gradient, and preferred body temperature was recorded continuously. A behavioral fever was observed after lipopolysaccharide (LPS) was injected systemically (200 microg/kg). Systemically injected AVT (300 pmol/kg) alone caused no significant change in body temperature, but abolished LPS-induced fever. Moreover, a smaller dose of AVT (10 pmol/kg), which did not affect LPS-induced fever when injected peripherally, abolished fever when injected intracerebroventricularly. We therefore conclude that AVT plays an antipyretic role in the central nervous system, by means of behavior, in an ectotherm, a fact consistent with the notion that AVT/AVP elicits antipyresis by reducing the thermoregulatory set point.     

Excitatory Transmission in Insect Neuromuscular Systems

Many, but not all, visceral muscles in insects are innervatedby neurosecretory axons. The neurosecretory junctions with theheart muscle of the American cockroach, Periplaneta americana,show ultrastructural and electrophysiological evidence of chemicallytransmitting synapses, and cytochemical evidence for the presenceof monoamines. Electron microscopy of nerve terminals showsthat synaptic vesicles may be formed directly from electron-dense"neurosecretory" granules Neurotomy of motor axons to skeletal muscles in insects leadsto aggregation and clumping of synaptic vesicles after 48 hours.Treatment of in vitro nerve-muscle preparations with variousrespiratory poisons caused aggregation similar to that developedin neurotomized animals. This suggested that vesicle aggregationin both cases may have resulted from a decrease in availableadenosine triphosphate in the nerve terminal with subsequentalteration in the normal charge density which supports a repulsiveforce between the vesicles.     

Excitatory action of the bird antidiuretic hormone vasotocin on neurons in the subfornical organ

The responsiveness of spontaneously active neurons in the subfornical organ (SFO) of adult ducks to angiotensin II (ANGII) and the bird specific anti-diuretic hormone, arginine vasotocin (AVT), the analog of the mammalian arginine vasopressin (AVP), were investigated in brain slices with extracellular recording technique. 65% (n = 66) of the neurons increased their activity after superfusion with ANGII, the rest were unresponsive. Application of AVT activated 52% (n = 68) of the investigated neurons and like ANGII never caused an inhibition of the spontaneously active SFO neurons. A close correlation exists between the ANGII and AVT sensitivity of duck SFO neurons, because 29 out of 33 neurons were excited by AVT as well as ANGII. The relatively weak antagonistic effect of the V₁-type receptor antagonist Pmp-Tyr (Me)-Arg⁸-vasopressin on the AVT induced excitation suggests a different pharmacology of the bird AVT receptor as compared to the mammalian AVP receptor. The excitatory response of ANGII and AVT on the very same neurons suggest a similar function of both peptides on SFO mediated effects in vivo, such as an increase in water intake. However, peripheral AVT concentrations, unlike ANGII concentrations in the blood are not high enough to activate SFO neurons from the blood side of the blood brain barrier. Therefore AVT is presumably released from synapses of neurons originating within or projecting to the SFO. The identity of the ANGII and AVT reactive neurons suggests that synaptically released AVT should facilitate SFO mediated drinking.Abbreviations _a CSF artificial cerebrospinal fluid - ANGII angiotensin II - AVT arginine vasotocin - AVP arginine vasopressin - ADH antidiuretic hormone - SFO subfornical organ - AVP _4–9 arginine-vasopressin fragment 4–9 - BBB blood-brain barrier     

Continuous central vasopressin infusion increases peripheral fetal corticotropin and cortisol in the fetal sheep

In previous studies on regulation of fetal adrenocorticotropin (ACTH) secretion, corticotropin releasing factor (CRF) and arginine vasopressin (AVP) have been administered by peripheral intravascular infusion. In order to look at an alternate route of administration, we investigated the effect of continuous intracerebroventricular administration of AVP to the fetus on fetal plasma ACTH and fetal and maternal plasma cortisol concentrations. Sheep fetuses (n = 9) were instrumental with carotid artery and lateral cerebral ventricular catheters. Fetuses were given intracerebroventricular infusion from 125-134 days gestational age of artificial cerebrospinal fluid vehicle (n = 4), or AVP 250 mu U.min-1 continuously in artificial cerebrospinal fluid vehicle (n =5). Fetal blood was obtained daily between 09.00 and 12.00h and 20.00 and 23.00h. Over the infusion period, fetal plasma ACTH and cortisol concentrations in AVP infused fetuses increased (P less than 0.05) compared with the vehicle infused group. Gestation length for the fetuses in the AVP and vehicle infused groups were 139 +/- 4.9 (n =4) and 145 +/- 4.6 (n = 3) days respectively (n.s.). Fetal plasma AVP concentrations in the AVP infused group were not different from the vehicle infused group.     

Ontogeny of the bovine neurohypophysial hormone precursors. III. Identification of neurohormones, neurophysins and copeptin in the early bovine fetus

Neurohypophysial hormone precursors are small proteins processed into several fragments during axonal transport from hypothalamus to neurohypophysis. From 3-month-old fetal bovine pituitaries the three fragments of vasopressin precursor, arginine vasopressin, MSEL-neurophysin and copeptin, and the two fragments of oxytocin precursor, oxytocin and VLDV-neurophysin, have been isolated and characterized. These polypeptides are identical to those previously identified in the late fetus (7-9 months old) and in the adult. It is concluded that the same genes are expressed during fetal and adult lives, the vasopressin gene appearing roughly four times more active than the oxytocin gene in the early fetus. Vasotocin, mesotocin and additional neurophysin have not been detected in the early fetus.     

Casparian Strips in the Leaf Intrastelar Canals of Isoetes duriei Bory, a Mediterranean Terrestrial Species

Anatomical observations, using light and fluorescence microscopy,were made on leaves of Isoetes duriei to verify the presenceof casparian bands around the intrastelar canals. This peculiaranatomical feature, previously reported for some Isoetes species,is confirmed. The possible role of this endodermis-like structure,in the transport of water due to root pressure or in the accumulationof certain metabolites, is discussed in relation to the ecologicaland anatomical features of the species. Copyright 2000 Annalsof Botany Company Isoetes duriei, Lycopsida, Mediterranean, leaf anatomy, endodermis, casparian strips, fluorescence microscopy     

Effects of i.c.v. losartan on the angiotensin II-mediated vasopressin release and hypothalamic fos expression in near-term ovine fetuses

Our previous studies have shown that central administration of angiotensin (ANG II) causes arginine vasopressin (AVP) release in the fetus at 70-90% gestation. This is evidence that the hypothalamic-neurohypophysial system is relatively mature before birth. However, few data exist regarding central ANG receptor mechanisms-mediated AVP response during fetal life. To determine roles of brain ANG receptor subtypes in this response, AT1 and AT2 receptor antagonists, losartan and PD123319, were investigated in the brain in chronically prepared ovine fetuses at the last third of gestation. Application of losartan intracerebroventricularly (i.c.v.) at 0.5 mg/kg suppressed central ANG II-stimulated plasma AVP release. Losartan at 5 mg/kg (i.c.v.) demonstrated a significant enhancement of AVP increase to i.c.v. ANG II. Associated with the increase of plasma vasopressin levels, c-fos expression in the hypothalamic neurons was significantly different between the low and high doses of losartan. The low dose losartan markedly reduced the dual immunoreactivity for FOS and AVP in the supraoptic nuclei and paraventricular nuclei after i.c.v. ANG II, whereas the high dose losartan together with ANG II, significantly increased the co-localization of positive FOS in the AVP-containing neurons than that induced by i.c.v. ANG II alone. Central ANG II induced fetal plasma vasopressin increase was not altered by PD123319. The data suggest that losartan in the fetal brain has remarkably different effects based on the doses administrated on central ANG II-related neuroendocrine effects at the late gestation, and that the AT1 mechanism is critical in the regulation of fetal body fluid homeostasis related to plasma AVP levels.     

Induction time and reversibility of changes in Daphnia life history caused by the presence of fish

Two experiments were run, to demonstrate how Daphnia life historychanges in the response to fish kairomone, depending on at whichontogenetic stage the simulated presence of fish appears ordisappears. Exposures of Daphnia, starting from different ontogeneticstages, to the fish kairomone showed that the period betweenthe initiation of phenotypic changes induced by the presenceof fish and their adaptive expression in Daphnia varies fromone instar (2–3 days) in the case of size at first reproductionto five instars (about 7 days) in the case of age at first reproduction.Removing the fish kairomone in different ontogenetic stagesshowed, in turn, that if a proximal factor that induced an anti-predatormechanism disappears and is not detected for at least four instars,Daphnia may withdraw from former changes (e.g. maturation whenlarger). It is suggested that the moment of the final ‘decision’regarding size at first reproduction cannot be attributed toa specific instar, but rather to a given moment in the Daphnialife cycle that is not related to any particular developmentalinstar but rather to the instantaneous level of resources thatcan be allocated to the reproduction.     

Taurine transporter in fetal T lymphocytes and platelets: differential expression and functional activity

Transplacental transfer of taurine, a -amino acid essential for fetal and neonatal development, constitutes the primary source of taurine for the fetus. Placental transport of taurine is compromised in pregnancies complicated by intrauterine growth restriction, resulting in a reduced concentration of taurine in cord plasma. This could impact on fetal cellular metabolism as taurine represents the most abundant intracellular amino acid in many fetal cell types. In the present study, we have used pure isolates of fetal platelets and T lymphocytes from cord blood of placentas, from normal, term pregnancies, as fetal cell types to examine the cellular uptake mechanisms for taurine by the system transporter and have compared gene and protein expression for the taurine transporter protein (TAUT) in these two cell types. System activity in fetal platelets was 15-fold higher compared with fetal T lymphocytes (P < 0.005), mirroring greater TAUT mRNA expression in platelets than T lymphocytes (P < 0.005). Cell-specific differences in TAUT protein moieties were detected with a doublet of 75 and 80 kDa in fetal platelets compared with 114 and 120 kDa in fetal T lymphocytes, with relatively higher expression in platelets. We conclude that greater system activity in fetal platelets compared with T lymphocytes is the result of relatively greater TAUT mRNA and protein expression. This study represents the first characterization of amino acid transporters in fetal T lymphocytes. cord blood cells; amino acid; taurine transporter protein; system