Measurement of blood volume in the elasmobranch fish Scyliorhinus canicula following acute and long‐term salinity transfers

A technique using ⁵¹chromium‐labelled erythrocytes was used to measure blood volume in Scyliorhinus canicula following long‐term and acute salinity transfers. Basal whole‐blood volume was 5·6 ± 0·2 ml 100 g^?1 (mean ±s .e .), this increased (6·3 ± 0·2 ml 100 g^?1) following +14 day acclimation to 80% sea water (SW) and decreased (4·6 ± 0·2 ml 100 g^?1) following acclimation to 120% SW. These changes were shown to be primarily due to changes in plasma volume, with no significant changes in extrapolated red‐cell volume being demonstrated. Blood volume was also measured in the same animals during 10 h acute transfer to 100% SW. Plasma volume in S. canicula during acclimation from 80% SW was significantly reduced (4·5 ± 0·3 ml 100 g^?1) after 6 h of transfer to 100% SW. Blood volume in animals during acclimation from 120% SW was significantly increased (4·8 ± 0·2 ml 100 g^?1) after 4 h of acute transfer. The osmoregulatory implications of these different timeframes during hyposaline and hypersaline transfer are discussed, along with the importance of this in vivo technique as context for in vitro studies with haemo‐dynamic stimuli.     

Changes in chloride secretion rate and vascular perfusion in the rectal gland of the European lesser-spotted dogfish in response to environmental and hormonal stimuli

Chloride secretion rates of rectal glands taken from the European lesser-spotted dogfish Scyliorhinus canicula adapting to 70% and 120% sea water (SW) were significantly greater and less than, respectively, those in the control 100% SW group. C-type natriuretic peptide (CNP) significantly increased chloride secretion rates above basal values in 100% SW although angiotenisn II (ANG II) had no effect. Perfusion of the secretory epithelia in rectal glands from 70% SW lesser-spotted dogfish was significantly higher than in rectal glands from 100% and 120% SW lesser-spotted dogfish. Perfusion of rectal glands with ANG II had no effect on perfusion of the secretory epithelia, although CNP perfusion induced significantly greater perfusion of the secretory epithelia than all other treatments. It remains to be determined if a reduction in environmental salinity induces an increase in plasma concentration of CNP and hence an increase in rectal gland activity.     

Role of V1- and V2-receptors in mechanism of physiological paradox--an increase of reabsorption of the solute free water and simultaneous rise of diuresis

In experiments on non-anesthetized rats with administration into stomach of water (5 ml/100 g body mass) direct correlation has been found between an increase of diuresis and excretion of solute free water (r = 0.98, p < 0.01), while after injection to these animals of 5 x 10(-11) M arginine-vasotocin - between an increase of diuresis and simultaneous rise reabsorption of solute free water (r = 0.8, p < 0.01). The rise of diuresis after the vasotocin injection is due to inhibition of sodium re- absorption, with the solute excretion fraction increasing from 2.6 +/- 0.2 % to 11.9 +/- 1.2, p < 0.001. A similar physiological paradox - an increase of diuresis with the simultaneous increase of reabsorption of solute free water - has been revealed at night hours in children with tendency for nocturnal enuresis (r = 0.64, p < 0.01). Mechanism responsible for this phenomenon consists in a rise of diuresis due to a decrease of sodium ion reabsorption in the ascending Henle loop limb. A problem is discussed of the homeostatic significance of a decrease of sodium reabsorption combined with an increase of solute-free water reabsorption; it is suggested that this phenomenon is based on a redistribution of reabsorption inside the nephron - a decrease of ion and water reabsorption in the initial parts of the nephron distal segment and an increase of solute free water reabsorption with the antidiuretic hormone-stimulated high osmotic permeability of terminal parts of renal tubules. An intraperitoneal injection of V1-anatagonist (OPC-21268) decreased the natriuretic component of response to arginine-vasotocin, while injection of V2-antagonist (OPC-31260) eliminated the antidiuretic component.     

Development of an in situ perfused kidney preparation for elasmobranch fish: action of arginine vasotocin

Acclimation of the European lesser-spotted dogfish Scyliorhinus canicula to reduced environmental salinity [85-70% seawater (SW)] induced a significant diuresis in addition to a significant decrease in plasma osmolality in vivo. The threshold for this diuresis was determined to be 85% SW. Therefore, S. canicula acclimated to 85% SW was selected for further study as a diuretic model in the development of an in situ perfused kidney preparation. The renal role of arginine vasotocin (AVT) in the in situ perfused trunk preparation was investigated. In SW, perfusion of 10(-9) and 10(-10) M AVT resulted in a glomerular antidiuresis and decreases in tubular transport maxima for glucose and perfusate flow. In 85% SW, 10(-10) M AVT had no significant effect on these renal parameters with the exception of transport maxima for glucose and perfusate flow. Tubular parameters remained unchanged by either 10(-9) or 10(-10) M AVT. The results demonstrate that the perfused kidney preparation was a viable tool for the investigation of renal parameters in elasmobranch fish and that AVT induced a glomerular antidiuresis.     

Ciliated cells on the surface of embryos of Scyliorhinus canicula

Monociliated surface cells were found for the first time in an elasmobranch and were common on embryos of Scyliorhinus canicula . They occurred mainly near the anterior end, until Ballard stage 30, but disappeared soon thereafter. The functions of surface ciliated cells suggested in other embryos ( e.g. surface currents in lungfishes and amphibians, and determination of left–right patterns in amniotes) seem unlikely in elasmobranchs.     

Characteristics of the conditioned motor reactions of unrestrained elasmobranches and teleosts

In elasmobranch (Scyllium canicula, Galleus canis) and teleost (Migull capitocum) fishes it is possible to form motor food-searching conditioned reflexes to discrimination of light and darkness. Some differences were revealed in ecological and conditioned motor behavioural activities in higher and lower sharks. Elasmobranch and teleost fishes exhibit significant differences in ecological, feeding and conditioned reflex behaviour. Nervous activity in elasmobranchs is characterized by lower and primitive organization as compared to that in teleosts.     

VO2/power output relationship and the slow component of oxygen uptake kinetics during cycling at different pedaling rates: relationship to venous lactate accumulation and blood acid-base balance.

In this experiment we studied the effect of different pedalling rates during cycling at a constant power output (PO) 132+/-31 W (mean+/-S.D.), corresponding to 50% VO2 max, on the oxygen uptake and the magnitude of the slow component of VO2 kinetics in humans. The PO corresponded to 50% of VO2 max, established during incremental cycling at a pedalling rate of 70 rev.min(-1). Six healthy men aged 22.2+/-2.0 years with VO2 max 3.89+/-0.92 l.min(-1), performed on separate days constant PO cycling exercise lasting 6 min at pedalling rates 40, 60, 80, 100 and 120 rev.min(-1), in random order. Antecubital blood samples for plasma lactate [La]pl and blood acid-base balance variables were taken at 1 min intervals. Oxygen uptake was determined breath-by-breath. The total net oxygen consumed throughout the 6 min cycling period at pedalling rates of 40, 60, 80, 100 and 120 rev.min(-1) amounted to 7.727+/-1.197, 7.705+/-1.548, 8.679+/-1.262, 9.945+/-1.435 and 13.720+/-1.862 l, respectively for each pedalling rate. The VO2 during the 6 min of cycling only rose slowly by increasing the pedalling rate in the range of 40-100 rev.min(-1). This increase, was 0.142 l per 20 rev.min(-1) on the average. Plasma lactate concentration during the sixth minute of cycling changed little within this range of pedalling rates: the values were 1.83+/-0.70, 1.80+/-0.48, 2.33+/-0.88 and 2.52+/-0.33 mmol.l(-1). The values of [La]pl reached in the 6th minute of cycling were not significantly different from the pre-exercise levels. Blood pH was also not affected by the increase of pedalling rate in the range of 40-100 rev.min(-1). However, an increase of pedalling rate from 100 to 120 rev.min(-1) caused a sudden increase in the VO2 amounting to 0.747 l per 20 rev.min(-1), accompanied by a significant increase in [La]pl from 1.21+/-0.26 mmol.l(-1) in pre-exercise conditions to 5.92+/-2.46 mmol.l(-1) reached in the 6th minute of cycling (P<0.01). This was also accompanied by a significant drop of blood pH, from 7.355+/-0.039 in the pre-exercise period to 7.296+/-0.060 in the 6th minute of cycling (P < 0.01). The mechanical efficiency calculated on the basis of the net VO2 reached between the 4th and the 6th minute of cycling amounted to 26.6+/-2.7, 26.4+/-2.0, 23.4+/-3.4, 20.3+/-2.6 and 14.7+/-2.2%, respectively for pedalling rates of 40, 60, 80, 100 and 120 rev.min(-1). No significant increase in the VO2 from the 3rd to the 6th min (representing the magnitude of the slow component of VO2 kinetics) was observed at any of the pedalling rates (-0.022+/-0.056, -0.009+/-0.029, 0.012+/-0.073, 0.030+/-0.081 and 0.122+/-0.176 l.min(-1) for pedalling rates of 40, 60, 80, 100 and 120 rev.min(-1), respectively). Thus a significant increase in [La]pl and a decrease in blood pH do not play a major role in the mechanism(s) responsible for the slow component of VO2 kinetics in humans.     

Species, sex, size and male maturity composition of previously unreported elasmobranch landings in Kuwait, Qatar and Abu Dhabi Emirate

This paper presents data from the first major survey of the diversity, biology and fisheries of elasmobranchs in the Persian (Arabian) Gulf. Substantial landings of elasmobranchs, usually as gillnet by-catch, were recorded in Kuwait, Qatar and the Emirate of Abu Dhabi (part of the United Arab Emirates), although larger elasmobranchs from targeted line fisheries were landed in Abu Dhabi. The elasmobranch fauna recorded was distinctive and included species that are undescribed, rare and have a highly restricted known distribution. Numerical abundance was dominated by sharks (c. 80%), of which carcharhinids were by far the most important. The milk shark Rhizoprionodon acutus and whitecheek shark Carcharhinus dussumieri together comprised just under half of all recorded individuals. Around 90% of recorded sharks were small (50-90 cm total length, L(T) ) individuals, most of which were mature individuals of species with a small maximum size (<100 cm L(T) ), although immature individuals of larger species (e.g. Carcharhinus sorrah and other Carcharhinus spp.) were also important. The most frequently recorded batoid taxa were cownose rays Rhinoptera spp., an undescribed whipray, and the granulated guitarfish Rhinobatos granulatus. The first size, sex and maturity data for a wide range of Gulf elasmobranch species are presented (including L(T) at 50% maturity for males of four shark species) and include some notable differences from other locations in the Indo-West Pacific Ocean. A number of concerns regarding the sustainability of the fishery were highlighted by this study, notably that most of the batoid species recorded are classed by the IUCN Red List as vulnerable, endangered, data deficient or not evaluated. Despite their considerable elasmobranch landings, none of the three countries sampled have developed a 'Shark Plan' as encouraged to do so under the FAO International Plan of Action: Sharks. Furthermore, Kuwait and Qatar currently report zero or no elasmobranch landings to the FAO.     

Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans.

We tested the hypothesis that renal tubular Na(+) reabsorption increased during the first 24 h of exercise-induced plasma volume expansion. Renal function was assessed 1 day after no-exercise control (C) or intermittent cycle ergometer exercise (Ex, 85% of peak O(2) uptake) for 2 h before and 3 h after saline loading (12.5 ml/kg over 30 min) in seven subjects. Ex reduced renal blood flow (p-aminohippurate clearance) compared with C (0.83 +/- 0.12 vs. 1.49 +/- 0.24 l/min, P < 0.05) but did not influence glomerular filtration rates (97 +/- 10 ml/min, inulin clearance). Fractional tubular reabsorption of Na(+) in the proximal tubules was higher in Ex than in C (P < 0.05). Saline loading decreased fractional tubular reabsorption of Na(+) from 99.1 +/- 0.1 to 98.7 +/- 0.1% (P < 0.05) in C but not in Ex (99.3 +/- 0.1 to 99.4 +/- 0.1%). Saline loading reduced plasma renin activity and plasma arginine vasopressin levels in C and Ex, although the magnitude of decrease was greater in C (P < 0.05). These results indicate that, during the acute phase of exercise-induced plasma volume expansion, increased tubular Na(+) reabsorption is directed primarily to the proximal tubules and is associated with a decrease in renal blood flow. In addition, saline infusion caused a smaller reduction in fluid-regulating hormones in Ex. The attenuated volume-regulatory response acts to preserve distal tubular Na(+) reabsorption during saline infusion 24 h after exercise.     

Development of body oxygen stores in harbor seals: effects of age, mass, and body composition

Harbor seal pups are highly precocial and can swim and dive at birth. Such behavioral maturity suggests that they may be born with mature body oxygen stores or that stores develop quickly during the nursing period. To test this hypothesis, we compared the blood and muscle oxygen stores of harbor seal pups, yearlings, and adults. We found that pups had smaller oxygen stores than adults (neonates 57%, weaned pups 75%, and yearlings 90% those of adults), largely because neonatal myoglobin concentrations were low (1.6+/-0.2 g% vs. 3.8+/-0.3 g% for adults) and changed little during the nursing period. In contrast, blood oxygen stores were relatively mature, with nursing pups having hematocrit (55%+/-0.2%), hemoglobin (21.7+/-0.4 g%), and blood volume (12.3+/-0.5 mL/kg) only slightly lower than the corresponding values for adults (57%+/-0.2%, 23.8+/-0.3 g %, and 15.0+/-0.5 mL/kg). Because neonatal pups had relatively high metabolic rates (11.0 mL O2/kg min), their calculated aerobic dive limit was less than 50% that of adults. These results suggest that harbor seals' early aquatic activity is primarily supported by rapid development of blood, with immature muscle oxygen stores and elevated use rates limiting aerobic diving ability.     

Zea mays L. extracts modify glomerular function and potassium urinary excretion in conscious rats

Diuretic and uricosuric properties have traditionally been attributed to corn silk, stigma/style of Zea mays L. Although the diuretic effect was confirmed, studies of the plant's effects on renal function or solute excretion were lacking. Thus, we studied the effects of corn silk aqueous extract on the urinary excretion of water, Na+, K+, and uric acid. Glomerular and proximal tubular function and Na+ tubular handling were also studied. Conscious, unrestrained adult male rats were housed in individual metabolic cages (IMC) with continuous urine collection for 5 and 3 h, following two protocols. The effects of 25, 50, 200, 350, and 500 mg/kg body wt. corn silk extract on urine volume plus Na+ and K+ excretions were studied in water-loaded conscious rats (2.5 ml/100 g body wt.) in the IMC for 5 h (Protocol 1). Kaliuresis was observed with doses of 350 (100.42 +/- 22.32-120.28 +/- 19.70 microEq/5 h/100 g body wt.; n = 13) and 500 mg/kg body wt. (94.97+/- 29.30-134.32 +/- 39.98 microEq/5h/100 g body wt.; n = 12; p<0.01), and the latter dose resulted in diuresis as well (1.98 +/- 0.44-2.41 +/- 0.41 ml/5 h/100 g body wt.; n = 12; p<0.05). The effects of a 500 mg/kg body wt. dose of corn silk extract on urine volume, Na+, K+ and uric acid excretions, and glomerular and proximal tubular function, were measured respectively by creatinine (Cler) and Li+ (ClLi) clearances and Na+ tubular handling, in water-loaded rats (5 ml/100 g body wt.) in the IMC for 3 h (Protocol 2). Clcr (294.6 +/- 73.2, n = 12, to 241.7 +/- 48.0 microl/ min/100 g body wt.; n = 13; p<0.05) and the Na+ filtered load (41.9 +/- 10.3, n = 12, to 34.3 +/- .8, n = 13, p<0.05) decreased and ClLi and Na+ excretion were unchanged, while K+ excretion (0.1044 +/- 0.0458, n=12, to 0.2289 +/- 0.0583 microEq/min/100 body wt.; n = 13; p<0.001) increased. For Na+ tubular handling, the fractional proximal tubular reabsorption (91.5 +/- 3.5, n = 12, to 87.5 +/- 3.4%; n = 13; p<0.01) decreased, and both fractional distal reabsorptions--I and II--increased (96.5 +/- 1.5, n = 12, to 97.8 +/- 0.9%; n = 13; p<0.01; and 8.2 +/- 3.5, n = 12, to 12.2 +/- 3.4%, n = 13, p<0.01, respectively). To summarize, in water-loaded conscious rats (2.5 ml/100 body wt.), corn silk aqueous extract is diuretic at a dose of 500 mg/kg body wt. and kaliuretic at doses of 350 and 500 mg/kg body wt. In water-loaded conscious rats (5.0 ml/100 g body wt.), corn silk aqueous extract is kaliuretic at a dose of 500 mg/kg body wt., but glomerular filtration and filtered load decrease without affecting proximal tubular function, Na+, or uric acid excretion.     

An improved method for separation of leucocytes from peripheral blood of the little skate (Leucoraja erinacea)

Cartilaginous fish, especially sharks, rays and skates (elasmobranchs), hold interest as comparative models in immunology because they are thought to be among the organisms most closely related to the ancestor animal that first developed acquired immunity. The aim of this study was to improve methods used for the purification of viable leucocytes from peripheral blood of elasmobranchs. Here we describe modifications of density gradient centrifugation and medium formulation that improve isolation and analysis of highly purified leucocytes from peripheral blood of a model elasmobranch, Leucoraja erinacea, the little skate. These techniques contribute to the preparation of elasmobranch immune cells that can be reliably analyzed by a variety of means, including the study of immune function.     

Recovery potential and conservation options for elasmobranchs

Many elasmobranchs have experienced strong population declines, which have been largely attributed to the direct and indirect effects of exploitation. Recently, however, live elasmobranchs are being increasingly valued for their role in marine ecosystems, dive tourism and intrinsic worth. Thus, management plans have been implemented to slow and ultimately reverse negative trends, including shark-specific (e.g. anti-finning laws) to ecosystem-based (e.g. no-take marine reserves) strategies. Yet it is unclear how successful these measures are, or will be, given the degree of depletion and slow recovery potential of most elasmobranchs. Here, current understanding of elasmobranch population recoveries is reviewed. The potential and realized extent of population increases, including rates of increase, timelines and drivers are evaluated. Across 40 increasing populations, only 25% were attributed to decreased anthropogenic mortality, while the majority was attributed to predation release. It is also shown that even low exploitation rates (2-6% per year) can halt or reverse positive population trends in six populations currently managed under recovery plans. Management measures that help restore elasmobranch populations include enforcement or near-zero fishing mortality, protection of critical habitats, monitoring and education. These measures are highlighted in a case study from the south-eastern U.S.A., where some evidence of recovery is seen in Pristis pectinata, Galeocerdo cuvier and Sphyrna lewini populations. It is concluded that recovery of elasmobranchs is certainly possible but requires time and a combination of strong and dedicated management actions to be successful.     

Effects of L-alanine on membrane potential, potassium (86Rb) permeability and cell volume in hepatocytes from Raja erinacea

Isolated hepatocytes from the elasmobranch Raja erinacea were examined for their regulatory responses to a solute load following electrogenic uptake of L-alanine. The transmembrane potential (Vm) was measured with glass microelectrodes filled with 0.5 M KCl (75 to 208 M omega in elasmobranch Ringer's solution) and averaged -61 +/- 16 mV (S.D.; n = 68). L-Alanine decreased (depolarized) Vm by 7 +/- 3 and 18 +/- 2 mV at concentrations of 1 and 10 mM, respectively. Vm did not repolarize to control values during the 5-10 min impalements, unless the amino acid was washed away from the hepatocytes. The depolarizing effect of L-alanine was dependent on external Na+, and was specific for the L-isomer of alanine, as D- and beta-alanine had no effect. Hepatocyte Vm also depolarized on addition of KCN or ouabain, or when external K+ was increased. Rates of 86Rb+ uptake and efflux were measured to assess the effects of L-alanine on Na+/K+-ATPase activity and K+ permeability, respectively. Greater than 80% of the 86Rb+ uptake was inhibited by 2 mM ouabain, or by substitution of choline+ for Na+ in the incubation media. L-Alanine (10 mM) increased 86Rb+ uptake by 18-49%, consistent with an increase in Na+/K+ pump activity, but had no effect on rubidium efflux. L-Alanine, at concentrations up to 20 mM, also had no measurable effect on cell volume as determined by 3H2O and [14C]inulin distribution. These results indicate that Na+-coupled uptake of L-alanine by skate hepatocytes is rheogenic, as previously observed in other cell systems. However, in contrast to mammalian hepatocytes, Vm does not repolarize for at least 10 min after the administration of L-alanine, and changes in cell volume and potassium permeability are also not observed.     

Diuretic response to acute hypertension is blunted during angiotensin II clamp

Acute hypertension inhibits proximal tubule (PT) fluid reabsorption. The resultant increase in end proximal flow rate provides the error signal to mediate tubuloglomerular feedback autoregulation of renal blood flow and glomerular filtration rate and suppresses renal renin secretion. To test whether the suppression of the renin-angiotensin system during acute hypertension affects the magnitude of the inhibition of PT fluid and sodium reabsorption, plasma ANG II levels were clamped by infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril (12 microg/min) and ANG II after pretreatment with the bradykinin B(2) receptor blocker HOE-140 (100 microg/kg bolus). Because ACE also degrades bradykinin, HOE-140 was included to block effect of accumulating vasodilatory bradykinins during captopril infusion. HOE-140 increased the sensitivity of arterial blood pressure to ANG II: after captopril infusion without HOE-140, 20 ng x kg(-1) x min(-1) ANG II had no pressor effect, whereas with HOE-140, 20 ng x kg(-1) x min(-1) ANG II increased blood pressure from 104 +/- 4 to 140 +/- 6 mmHg. ANG II infused at 2 ng x kg(-1) x min(-1) had no pressor effect after captopril and HOE-140 infusion ("ANG II clamp"). When blood pressure was acutely increased 50-60 mmHg by arterial constriction without ANG II clamp, urine output and endogenous lithium clearance increased 4.0- and 6.7-fold, respectively. With ANG II clamp, the effects of acute hypertension were reduced 50%: urine output and endogenous lithium clearance increased two- and threefold, respectively. We conclude that HOE-140, an inhibitor of the B(2) receptor, potentiates the sensitivity of arterial pressure to ANG II and that clamping systemic ANG II levels during acute hypertension blunts the magnitude of the pressure diuretic response.     

The leucocytes of the elasmobranch Scyliorhinus canicula L.—a morphological study

The leucocytes of the peripheral blood of the elasmobranch Scyliorhinus canicula L. were examined by light, transmission and scanning electron microscopy and histochemistry. Seven distinct leucocytes were identified including lymphocytes, thrombocytes, monocytes and granulocytes. The major characteristics of these cells and their relative distribution is described.     

Urea based osmoregulation and endocrine control in elasmobranch fish with special reference to euryhalinity

Since the landmark contributions of Homer Smith and co-workers in the 1930s there has been a considerable advance in our knowledge regarding the osmoregulatory strategy of elasmobranch fish. Smith recognised that urea was retained in the body fluids as part of the ‘osmoregulatory ballast’ of elasmobranch fish so that body fluid osmolality is raised to a level that is iso- or slightly hyper-osmotic to that of the surrounding medium. From studies at that time he also postulated that many marine dwelling elasmobranchs were not capable of adaptation to dilute environments. However, more recent investigations have demonstrated that, at least in some species, this may not be the case. Gradual acclimation of marine dwelling elasmobranchs to varying environmental salinities under laboratory conditions has demonstrated that these fish do have the capacity to acclimate to changes in salinity through independent regulation of Na⁺, Cl⁻ and urea levels. This suggests that many of the presumed stenohaline marine elasmobranchs could in fact be described as partially euryhaline. The contributions of Thomas Thorson in the 1970s demonstrated the osmoregulatory strategy of a fully euryhaline elasmobranch, the bull shark, Carcharhinus leucas, and more recent investigations have examined the mechanisms behind this strategy in the euryhaline elasmobranch, Dasyatis sabina. Both partially euryhaline and fully euryhaline species utilise the same physiological processes to control urea, Na⁺ and Cl⁻ levels within the body fluids. The role of the gills, kidney, liver, rectal gland and drinking process is discussed in relation to the endocrine control of urea, Na⁺ and Cl⁻ levels as elasmobranchs acclimate to different environmental salinities.     

The relationships of cartilaginous fishes: an immunological study of serum transferrins of holocephalans and elasmobranchs

Serum transferrins from two holocephalan, five elasmobranch and three teleost species have been compared using quantitative microcomplement fixation. Calculated immunological distances emphasize the close relationship between the holocephalans and elasmobranchs and strongly support the view that they should be considered as part of a natural assemblage which is widely separated from the teleosts.
If the Holocephali and elasmobranchs have been separate since the beginning of the Carboniferous, this implies that transferrin has evolved at a rate approximating to 0-15-0-26 immunological units per million years involving some 9–15% substitution of amino acids. These values are extremely low and indicate that holocephalan and elasmobranch transferrins have evolved some 2–3–7 times more slowly than those known from any other group of vertebrates.     

Reduced plasma volume and mesenteric vascular reactivity in obese Zucker rats

Obese Zucker rats (OZR) are mildly hypertensive with an apparently elevated sympathetic vasomotor tone compared with lean Zucker rats (LZR). Studies have also suggested enhanced adrenergic pressor reactivity in OZR but assumed comparable baroreflexes, or blood volume-to-body weight ratio, to LZR. In 15-wk-old OZR and LZR, we measured plasma volume and vascular reactivity to norepinephrine (NE) and phenylephrine (PE) with doses evaluated by body weight and plasma volume. Plasma volume measured by dye dilution (Evans blue; 200 microl of 0.5%) showed that OZR had comparable blood volumes to LZR but lower blood volume-to-body weight ratio (3.4 +/- 0.2 ml/100 g) than LZR (5.7 +/- 0.2 ml/100 g, P < 0.05). Ganglionic blockade (mecamylamine, 4 mg/kg) in isoflurane-anesthetized rats produced larger decreases in arterial pressure in OZR compared with LZR (52 +/- 2 vs. 46 +/- 2 mmHg). Pressor responses to NE (0.01-10 microg/kg) were exaggerated with doses analyzed by body weight but not analyzed by drug quantity. Pressor responses to PE (1-24 microg/kg) showed no difference with doses analyzed by body weight, but, analyzed by drug quantity, OZR showed a slight decrease in pressor reactivity. PE-induced increases in vascular resistance were exaggerated in the hindlimb circulation of OZR, normal in the renal circulation, and attenuated in the mesenteric circulation. The timing of the peak pressor response to PE corresponded with the increase in mesenteric vascular resistance, followed by rises in hindlimb and renal resistance. These data suggest that systemic adrenergic pressor reactivity is not enhanced in OZR, despite exaggerated vascular reactivity in the hindlimb of the OZR.     

Molecular advantage of diferric transferrin in delivering iron to reticulocytes: a comparative study

Administration of aprotinin, a kallikrein inhibitor, to anesthetized rats infused with 0.9% saline solution to expand the extracellular fluid volume resulted in blunted natriuresis and diuresis. Urine flow declined from 27.1 +/- 2.6 to 8.0 +/- 0.9 microliter/min/100 g body wt while sodium and potassium excretion were reduced 63 and 45%, respectively (P less than 0.01). Mean blood pressure and glomerular filtration rate were not significantly altered by aprotinin. Acute or chronic pretreatment with DOCA, to enhance kinin synthesis, failed to modify the renal excretory response to aprotinin suggesting that saline loading alone was able to induce kinin generation fully in these rats. The results indicate that aprotinin enhanced the reabsorption of filtrate in rats expanded with isotonic saline and imply an influence of renal kinins on the tubular transport of salt and water.