Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, ³H₂0), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ · day⁻¹ of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0–0.2 U), while mammary LPL was elevated (1.8–2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U · animal⁻¹) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035). Accepted: 4 May 1999     

Energetics during nursing and early postweaning fasting in hooded seal (Cystophora cristata ) pups from the Gulf of St Lawrence, Canada

In this study we measured growth and milk intake and calculated energy intake and its allocation into metabolism and stored tissue for hooded seal (Cystophora cristata) pups. In addition, we measured mass loss, change in body composition and metabolic rate during the first days of the postweaning fast. The mean body mass of the hooded seal pups (n = 5) at the start of the experiments, when they were new-born, was 24.3 ± 1.3 kg (SD). They gained an average of 5.9 ± 1.1. kg · day⁻¹ of which 19% was water, 76% fat and 5% protein. This corresponds to an average daily energy deposition of 179.8 ± 16.0 MJ. The pups were weaned at an average body mass of 42.5 ± 1.0 kg 3.1 days after the experiment was initiated. During the first days of the postweaning fast the pups lost an average of 1.3 ± 0.5␣kg of body mass daily, of which 56% was water, 16% fat and 28% protein. During the nursing period the average daily water influx for the pups was 124.6 ± 25.8 ml · kg⁻¹. The average CO₂ production during this period was 1.10 ± 0.20 ml · g⁻¹ · h⁻¹, which corresponds to a field metabolic rate of 714 ± 130 kJ ·  kg⁻¹ · day⁻¹, or 5.8 ± 1.1 times the predicted basal metabolic rate according to Kleiber (1975). During the postweaning fast the average daily water influx was reduced to 16.1 ± 6.6 ml · kg⁻¹. The average CO₂ production in␣this period was 0.58 ± 0.17 ml · g⁻¹ · h⁻¹ which corresponds to a field metabolic rate of 375 ± 108 kJ · kg⁻¹ · day⁻¹ or 3.2 ± 0.9 times the predicted basal metabolic rate. Average values for milk composition were 33.5% water, 58.6% fat and 6.2% protein. The pups drank an average of 10.4 ± 1.8␣kg of milk daily, which represents an energy intake of 248.9 ± 39.1 MJ · day⁻¹. The pups were able to store 73.2 ± 7.7% of this energy as body tissue. Accepted: 15 August 1996     

Water and sodium balances and metabolic physiology of house mice (Mus domesticus) and short-tailed mice (Leggadina lakedownensis) under laboratory conditions

A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day⁻¹ and 1.2 ± 0.4 ml · day⁻¹, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day⁻¹ and 2.0 ± 0.3 ml · day⁻¹, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher in M. domesticus (1.1 ± 0.1 mg H₂O · g^−0.122 · h⁻¹) than in L. lakedownensis (0.6 ± 0.1 mg H₂O · g^−0.122 · h⁻¹). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations up to 1 mol · l⁻¹, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate was significantly higher in M. domesticus (3.3 ± 0.2 mg O₂ · g^−0.75 · h⁻¹) than in L. lakedownensis (2.5 ± 0.1 mg O₂ · g^−0.75 · h⁻¹). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose relatively high sodium fluxes may reflect sodium associated with available food. Accepted: 16 August 1999     

Mass transfer from mothers to pups and mass recovery by mothers during the post-breeding foraging period in southern elephant seals (Mirounga leonina) at King George Island

Mass transfer from mother to pup during the lactation period, and mass recovery for the same females during the foraging period were measured in the southern elephant seal at King George Island, Antarctica. During the 19.2 ± 0.9-day lactation period measured (which represented 87% of the entire nursing), females lost a mean mass of 10.56 ± 1.76 kg/day (n = 27), while their pups gained a mean mass of 5.27 ± 1.1 kg/day. There was a correlation between daily body weight gain in pups and daily weight loss by their mothers. Pup weaning mass was positively related to maternal post-partum mass. Serial samples showed that weight losses by females and gains by their pups were not linear over lactation, but showed lower values at the beginning and at the end of lactation. During the 60.5 ± 6.2-day foraging phase between the end of lactation and molt, females gained 2.21 ± 0.65 kg/day (n = 12), or 54% of the mass lost during nursing. Growth rates reported here are higher than those reported in other breeding sites. However, the ratio of body mass loss by females to gain by their pups was similar, suggesting that higher growth rates and greater weaning mass at South Shetland are due to a higher mean weight of females on arrival at this breeding site. The foraging period was shorter and the mass gained greater than those measured at South Georgia; this could be related to relatively shorter distances to foraging areas. Received: 20 September 1996 / Accepted: 28 April 1997     

Mass changes during their annual cycle in females of southern elephant seals at King George Island

Mass changes in female southern elephant seals, sampled sequentially at different points through their annual cycle, were measured at King George Island, South Shetland Islands, during the 1995/1996 and 1996/1997 field seasons. Females weighed after they had given birth showed an increase of 37 ± 36 kg (mean ± SD), which represented 6.2 ± 6.4% in relation to their mass in the first breeding season. During the first aquatic phase, between the end of lactation and the beginning of moult, females gained a mean of 128 ± 35 kg, (n = 18) (2.19 ± 0.65 kg day⁻¹), which represented between 27 and 83% of the mass they had lost during lactation. Nine females followed during moulting showed a mass loss rate of 5.0 ± 0.4 kg day⁻¹, which was half the rate during lactation. Total mass loss during moulting (129 ± 22 kg) was not significantly different from mass gain for the same females between lactation and moult (135 ± 37 kg). Furthermore, at the end of moulting, female mass was not significantly different from the mass at the end of lactation. These masses represented 65 ± 5% and 64 ± 5%, respectively, of their initial mass after parturition. During the second period at sea, from the end of the moult until females hauled out to give birth in the following breeding season, the estimated mass gain was 1.45 ± 0.24 kg day⁻¹ (n = 5), which was not significantly different to the rate of mass gain shown by the same females during the first period at sea (2.26 ± 0.70 kg day⁻¹). Total mass gain during the second aquatic phase (364 ± 63 kg) was not correlated with the mass at the end of moulting, but it was positively related to the mass loss experienced by females from parturition until the end of the moulting period in the first breeding season. Accepted: 5 September 1998     

Water influx and efflux in free-flying pigeons

We used tritium-labeled water to measure total body water, water influx (which approximated oxidative water production) and water efflux in free-flying tippler pigeons (Columba livia) during flights that lasted on average 4.2 h. At experimental air temperatures ranging from 18 to 27 °C, mean water efflux by evaporation and excretion [6.3 ± 1.3 (SD) ml · h⁻¹, n = 14] exceeded water influx from oxidative water and inspired air (1.4 ± 0.7 ml · h⁻¹, n = 14), and the birds dehydrated at 4.9 ± 0.9 ml · h⁻¹. This was not significantly different from gravimetrically measured mass loss of 6.2 ± 2.1 g · h⁻¹ (t = 1.902, n = 14, P>0.05). This flight-induced dehydration resulted in an increase in plasma osmolality of 4.3 ± 3.0 mosmol · kg⁻¹ · h⁻¹ during flights of 3–4 h. At 27 °C, the increase in plasma osmolality above pre-flight levels (ΔP _osm = 7.6±4.29 mosmol · kg⁻¹ · h⁻¹, n = 6) was significantly higher than that at 18 °C (ΔP _osm = 0.83±2.23 mosmol · kg⁻¹ · h⁻¹, (t = 3.43, n = 6, P < 0.05). Post-flight haematocrit values were on average 1.1% lower than pre-flight levels, suggesting plasma expansion. Water efflux values during free flight were within 9% of those in the one published field study (Gessaman et al. 1991), and within the range of values for net water loss determined from mass balance during wind tunnel experiments (Biesel and Nachtigall 1987). Our net water loss rates were substantially higher than those estimated by a simulation model (Carmi et al. 1992) suggesting some re-evaluation of the model assumptions is required. Accepted: 8 April 1997     

Effect of manipulation of the renin-angiotensin system in control of drinking in juvenile Atlantic salmon (Salmosalar L) in fresh water and after transfer to sea water

Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at a rate of 0.15 ± 0.03 ml · kg⁻¹ · h⁻¹ and administration of doses of 10 or 20 mg · kg⁻¹ of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn¹, Val⁵]-Angiotensin II (0.4 μmol · kg⁻¹) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril (50 mg · kg⁻¹) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg⁻¹ · h⁻¹, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg⁻¹) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg⁻¹ lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg⁻¹ · h⁻¹, respectively. All treatments were without effect on blood plasma levels of Na⁺ and Cl⁻ in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na⁺ and Cl⁻. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed. Accepted: 27 February 1997     

The use of amiloride to uncouple branchial sodium and proton fluxes in the brown trout, Salmo trutta

Resting proton, ammonium and sodium fluxes in Salmo trutta were 492.6 ± 19.5 (n = 29); 122.9 ± 34.2 (n = 28) and 277.1 ± 18.5 (n = 50) μmol · kg⁻¹ · h⁻¹, respectively. The resting transepithelial potential was found to be composed of three successive potentials, the outermost averaging −7.36 ± 0.19mV, the second, −14.3 ± 1.4 mV and the third −37 ± 1.7 mV. Amiloride inhibits the proton, ammonium and sodium fluxes in a dose-dependent manner at concentrations of 0.5 mmol · 1⁻¹ and 0.1 mmol · l⁻¹, but at 0.01 mmol · l⁻¹, proton and ammonium fluxes remained at control levels whilst the sodium was reduced to 70.59 ± 7.29 μmol · kg⁻¹ · h⁻¹. The trans-epithelial potential was effected in a bi-phasic manner by 0.5 mmol · l⁻¹ amiloride. An initial hyperpolarisation of ca. 6 mV was followed by a sustained depolarisation of ca. 14 mV (towards zero) which persisted until the amiloride was washed off the gill. The initial hyperpolarisation was thought to reflect a rapid inhibition of a positive inward sodium current and the subsequent depolarisation was due to the inhibition of a positive outward current (proton) which would abolish the transepithelial potential. However, at 0.01 mmol ·  l⁻¹ only the hyperpolarisation was seen, due to the inhibition of only the inward sodium current. Acetazolamide (0.1 mmol · l⁻¹) was found to have no significant effect on the proton, ammonium and sodium fluxes. These results indicate that the proton and sodium fluxes across the gill of the freshwater trout are not tightly linked. While this suggests that the trout gill resembles the model of Ehrenburg et al. (1985) of sodium uptake in frog skin, the apical potentials measured in the pavement epithelial cell(s) are too low to account for sodium uptake unless the activity of the sodium in the cells is very low. Accepted: 8 August 1996     

RNA turnover and protein synthesis in fish cells

Protein synthesis in fish has been previously correlated with RNA content. The present study investigates whether protein and RNA synthesis rates are similarly related. Protein and RNA synthesis rates were determined from ³H-phenylalanine and ³H-uridine incorporation, respectively, and expressed as % · day⁻¹ and half-lives, respectively. Three fibroblast cell lines were used: BF-2, RTP, CHSE 214, which are derived from the bluegill, rainbow trout and Chinook salmon, respectively. These cells contained similar RNA concentrations (∼175 μg RNA · mg⁻¹ cell protein). Therefore differences in protein synthesis rates, BF-2 (31.3 ± 1.8)>RTP (25.1 ± 1.7)>CHSE 214 (17.6 ± 1.1), were attributable to RNA translational efficiency. The most translationally efficient RNA (BF-2 cells), 1.8 mg protein synthesised · μg⁻¹ RNA · day⁻¹, corresponded to the lowest RNA half-life, 75.4 ± 6.4 h. Translationally efficient RNA was also energetically efficient with BF-2 cells exploiting the least costly route of nucleotide supply (i.e. exogenous salvage) 3.5–6.0 times more than the least translationally efficient RNA (CHSE 214 cells). These data suggest that differential nucleotide supply, between intracellular synthesis and exogenous salvage, constitutes the area of pre-translational flexibility exploited to maintain RNA synthesis as a fixed energetic cost component of protein synthesis. Accepted: 12 November 1999     

Field energetics and the estimation of pollen and nectar intake in the marsupial honey possum, Tarsipes rostratus, in heathland habitats of South-Western Australia

A method is described, based on the simultaneous turnover of both stable (¹⁸O) and radioactive isotopes (³H and ²²Na), whereby the daily nectar and pollen intake of free-ranging marsupial honey possums (Tarsipes rostratus) may be estimated. The field metabolic rate is measured using doubly labelled water and nectar intake is estimated independently from the measured water and sodium fluxes. The method assumes that free-water intake is negligible (but may be accounted for if not the case), that virtually all dietary sodium is derived from nectar rather than from pollen, and that the animals are in energetic balance over the period of measurement. These assumptions have been tested and found to be robust, except during periods of heavy rain when significant intakes of free-water were recorded. Leaching experiments with pollen grains suggest that less than 10% of the sodium ingested by honey possums is derived from pollen and calculations thus assumed a 90%:10% split between nectar and pollen. Nectar intake averaged 5.9 ± 0.6 ml · day⁻¹ and regressing nectar intake on daily change in body mass predicts an intake of approximately 7 ml · day⁻¹ nectar to maintain balance for a 9 g honey possum. Estimates of pollen intake averaged 660 ± 156 mg · day⁻¹ and a similar regression analysis of the data predicts that a daily intake of approximately 1 g pollen would be needed to maintain mass balance of honey possums. Estimated nectar and pollen intakes did not differ significantly between males and females, but nectar intake was higher in winter compared with dry periods of the year. The sugar content of nectar falls during winter, however, and the overall energy derived from nectar thus remains roughly constant. Estimates of pollen and nectar intake for individual animals were not significantly correlated, suggesting that honey possums forage selectively for these two food items. Accepted: 19 August 1999     

Energy gain and loss during lactation and postweaning in southern elephant seal pups (Mirounga leonina) at King George Island

Deuterium-labeled water was used to measure changes in the proximate body composition during the lactation period and after weaning in southern elephant seal pups at King George Island, South Shetland Islands, Antarctica. During the lactation period (23.0 ± 1.4 days) pups gained a mean of 4.9 ± 0.5 kg/day (n=7). Of the total mass gain (112 ± 8 kg), 38% was water, 48% was fat, and 11% was protein. This represented an increase in total body gross energy of 2437 ± 145 MJ. The proportion of body mass represented by fat was less than 2% at birth, increasing to 35 ± 2% at weaning. We followed the pups during a mean period of 36 ± 3 days after weaning. During this period, pups had a mean loss of 1.21 ± 0.10 kg/day (n=7) comprising 39% water, 48% fat, and 12% protein. The energy cost over this period was 952 ± 168 MJ, which represented, on average, 39% of the total energy gained during the suckling period. Accepted: 3 January 2000     

Catecholamine release in heat-stressed Antarctic fish causes proton extrusion by the red cells

Two species of Antarctic fish were stressed by moving them from seawater at −1 °C to seawater at 10 °C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 ± 54 nmol · l⁻¹ noradrenaline and 263 ± 131 nmol · l⁻¹ adrenaline at 10 min. Plasma noradrenaline concentrations rose to 47 ± 14 nmol · l⁻¹ and adrenaline to 73 ± 28 nmol · l⁻¹ in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na⁺/H⁺ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the β-adrenergic antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines. Accepted: 22 January 1998     

Ca2+ regulation of heart contractility in Octopus

Isometric force development of electrically paced preparations isolated from the systemic heart of Octopus vulgaris were utilized to examine the regulation of contractility by Ca²⁺. Increases in extracellular Ca²⁺, to the physiological level, resulted in enhancement of twitch force. For instance, at 36 beats · min⁻¹ an increase in Ca²⁺ from 3 to 9 mmol · l⁻¹ resulted in a threefold increase in twitch force development. When steady-state contraction at 12 beats · min⁻¹ was followed by a rest period of either 5 or 10 min, the first contraction always exhibited either an increase in twitch force or stayed unchanged such that post-rest twitch force was about 133% of the last value in the steady-state train. Ryanodine (12.5 μmol · l⁻¹), which is considered to be a specific inhibitor of the Ca²⁺ storage and release capabilities of the sarcoplasmic reticulum (SR), was applied to further assess Ca²⁺ handling. Twitch force fell to about 22% of the preteatment level in preparations paced at either 12 or 36 beats · min⁻¹. In all preparations the frequency transition from 12 to 36 beats · min⁻¹ was associated with an increase in resting tension. The␣increase␣was 37 ± 14% prior to ryanodine treatment and was significantly elevated to 127 ± 33% following treatment. When steady-state contraction at 36 beats · min⁻¹ was followed by a rest period of 10 s, the first contraction was not significantly different from the last beat in the train prior to ryanodine; however, with ryanodine treatment, post-rest twitch force development significantly decreased. Twitch force development was regular at pacing rates of up to 300 beats · min⁻¹. Twitch force was maintained up to rates of 84 beats · min⁻¹ but␣decreased thereafter and reached a value of about 10% at 300 beats · min⁻¹. Resting tension increased substantially as frequency was elevated from 12 to 36 beats · min⁻¹ and then gradually increased as frequency was further elevated to 180 beats · min⁻¹. In conclusion, the Octopus ventricle is dependent upon extracellular Ca²⁺ for contraction. A post-rest potentiation of force development, the negative impact of ryanodine, and the ability to respond regularly at high pacing rates imply a strong reliance on the SR in Ca²⁺ cycling based on criteria established for vertebrate hearts. Accepted: 19 January 1997     

The effect of exercise and restraint on pectoral muscle metabolism in pigeons

The effect of various activity regimes on metabolism of pigeon pectoralis was examined by measurement of blood lactate following exercise, total lactate dehydrogenase activity of pectoral muscle, and proportions of specific isoenzymes of pectoral muscle lactate dehydrogenase. Sprint-trained birds had the highest pectoral muscle lactate dehydrogenase activity (1409 IU · g⁻¹ wet tissue), while endurance-trained birds had the highest peak lactate levels (287 mg · dl⁻¹, extrapolated from decay curves) and fastest half-time of the lactate response (4.8 min) following exercise, but the lowest lactate dehydrogenase activity (115 IU · g⁻¹ wet tissue). Immobilization of one wing for 3 weeks following endurance training produced a marked increase in lactate dehydrogenase activity of the immobilized muscle, compared to that in the contralateral pectoralis and endurance-trained muscle. Aerobic forms of the lactate dehydrogenase enzyme (that favor conversion of lactate to pyruvate) predominated in pectoral muscle of endurance-trained birds, while cage-confined birds exhibited primarily the anaerobic isoenzymes. These results demonstrate that conversion of pectoral muscle lactate dehydrogenase isoenzymes, total lactate dehydrogenase activity, and half-time of lactate response after exercise is dependent on activity regime in pigeons. In this respect, pigeon pectoral muscle responds to training and disuse in a manner similar to that of mammalian skeletal muscle. Accepted: 10 September 1996     

Characteristics of dipeptide transport in pig jejunum in vitro

 Characteristics of dipeptide transport in pig jejunum were investigated in vitro by applying the Ussing-chamber technique and mucosal uptake studies. Addition of both glycyl-l-glutamine and glycyl-l-sarcosine (20 mmol · l⁻¹) to the mucosal buffer solution significantly increased the short-circuit current by 2.60 ± 0.15 and 1.57 ± 0.20 μeq · cm⁻² · h⁻¹, respectively. Concentration-dependent changes in short-circuit current followed Michaelis-Menten kinetics with similar affinity constants for both dipeptides. From unidirectional flux rates for radiolabelled glycyl-l-sarcosine, a net flux rate for glycyl-l-sarcosine of 49.8 ± 6.7 nmol · cm⁻² · h⁻¹ was calculated. In mucosal uptake experiments, the apical influx of ¹⁴C-labelled glycyl-l-sarcosine into isolated porcine mucosa was pH dependent and significantly inhibited by glycyl-l-glutamine. Moreover, RT-PCR studies with primers derived from rabbit PepT1 identified two PCR fragments of identical size to rabbit PepT1 from pig intestinal mRNA preparations. In conclusion, our studies revealed key features of mammalian intestinal peptide transporters and give evidence for a PepT1-like transporter in the pig jejunum that could significantly contribute to the overall amino acid absorption from the gut. Accepted: 30 June 1999     

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 ± 0.3 s, mean ± SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 ± 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 ± 0.19 breaths · min⁻¹) but with high tidal volumes (1.1 ± 0.01 l), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 ± 13.8 ml O₂ · min⁻¹) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O₂ values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 ± 1.0 ml · 100 ml⁻¹, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation. Accepted: 11 August 1999     

Energetics of lactation in harp seals (Phoca groenlandica) from the gulf of St. Lawrence,Canada

 This study reports the findings of an integrated, comprehensive analysis of lactation energetics in harp seals conducted using longitudinal measurements of mass, body composition and milk composition from mother-pup pairs in conjunction with water flux measurements in pups. The nursing period of harp seals is a short, intense and relatively efficient period of energy transfer from mothers to pups. The average daily milk intake for pups was 3.65±0.24 kg which is equivalent to 79.5 MJ of energy. Eighty-one per cent of the energy received in the milk was metabolisable and 66% of the energy was stored by the pups as body tissue. The field metabolic rate of pups was 3.9±0.4 time basal metabolic rate. The pups were growing at a rate of 2.2 kg per day during the nursing period. The distribution of this mass gain varied in terms of tissue composition, depending on the age of the pups, but over the whole nursing period approximately half of the tissue was stored as fat. Harp seal mothers lost an average of 3.1 kg per day during lactation which was composed of 37% water, 50% fat, 11% protein and 2% ash. Mothers spent half of their time during the lactation period actively diving and only one-third of their time on the surface of the ice. Milk compositional changes followed the normal phocid pattern with increasing fat content and decreasing water content as lactation progressed. The mean mass transfer efficiency was 73%. However, this value cannot be used without qualification because female harp seals in this study fed to varying degrees, consuming an estimated 0–4.8 kg of fish per day. Feeding does not appear to be required in order to achieve the energy requirements for lactation, given the energy stores possessed by females, and some females do fast through the entire period so feeding may be considered opportunistic in nature. Accepted: 25 April 1996     

Interprotein metal ion exchange between cadmium-carbonic anhydrase and apo- or zinc-metallothionein

 − 1  s^− 1 at 25 °C and pH 7.4 in Tris.HCl buffer and 0.1 M KCl. At 25 °C, Zn₇-metallothionein also exchanged metal ions with Cd-carbonic anhydrase with a rate constant of 0.33 ± 0.02 M^− 1 s^− 1 to reconstitute enzymatically active protein. Cd-carbonic anhydrase reacted within the time of mixing with the peptide sequence 49–61 of rabbit metallothionein 2 which contains four cysteinyl residues, leading to the exchange of most of the Cd²⁺ into the peptide. At pH 7.4 and 25 °C, Cd²⁺ has higher affinity for apometallothionein than for the apo-peptide. Received: 25 February 1999 / Accepted: 17 September 1999     

Dietary cholesterol enhances torpor in a rodent hibernator

Dietary cholesterol can affect both body lipid composition and steroid hormone concentration. We investigated whether a diet rich in cholesterol influences torpor patterns of hibernating chipmunks (Tamias amoenus) and, if so, whether these changes are better explained by diet-induced changes in body lipid composition or the concentration of testosterone, which at high levels inhibits torpor. Two groups of chipmunks were maintained either on a cholesterol diet (rodent chow containing 10% cholesterol) or a control diet (rodent chow) during pre-hibernation fattening and throughout the hibernation season. Torpid chipmunks on the cholesterol diet had significantly lower minimum body temperatures (−0.2 ± 0.2 vs +0.6 ± 0.2 °C), lower metabolic rates (0.029 ± 0.002 ml O₂ g⁻¹h⁻¹ vs 0.035 ± 0.001 ml O₂ g⁻¹h⁻¹), and longer torpor bouts at −1 °C (6.8 ± 0.5 vs 4.1 ± 1.0 days) than chipmunks on the control diet. Dietary cholesterol resulted in a significant increase in blood plasma cholesterol (sevenfold), liver cholesterol content (6.9-fold) and liver triglyceride content (3.5-fold) in comparison to controls. In contrast, dietary cholesterol had no detectable effect on the concentration of plasma testosterone, which was very low in both groups. Since torpor was deeper and longer in animals on the cholesterol diet our study suggests that torpor patterns of chipmunks were either directly affected by the dietary cholesterol or via changes in body lipid composition. Accepted: 22 January 1997     

Uptake of 3-O-methyl-D-[U-14C]glucose into brain of rainbow trout: possible effects of melatonin

The influx of glucose into the brain and plasma glucose disappearance were estimated in rainbow trout (Oncorhynchus mykiss) intravenously injected (1 ml · kg⁻¹ body weight) with a single dose (15 μCi · kg⁻¹ body weight) of 3-O-methyl-D-[U-¹⁴C]glucose ([U-¹⁴C]-3-OMG) at different times (2–160 min), and after intravenous injection at 15 min of increased doses (10–60 μCi · kg⁻¹ body weight) of [U-¹⁴C]-3-OMG. Brain and plasma radiotracer concentrations were measured, and several kinetic parameters were calculated. The apparent brain glucose influx showed a maximum after 15–20 min of injection then decreased to a plateau after 80 min. Brain distribution space of 3-OMG increased from 2 min to 20 min reaching equilibrium from that time onwards at a value of 0.14 ml · g⁻¹. The unidirectional clearance of glucose from blood to brain (k₁) and the fractional clearance of glucose from brain to blood (k₂) were estimated to be 0.093 ml · min⁻¹ · g⁻¹, and 0.867 min⁻¹, respectively. A linear increase was observed in brain and plasma radiotracer concentrations when increased doses of [U-¹⁴C]-3-OMG were used. All these findings support a facilitative transport of glucose through the blood-brain barrier of rainbow trout with characteristics similar to those observed in mammals. The injection of different doses of melatonin (0.25–1.0 mg · kg⁻¹) significantly increased brain glucose influx suggesting a possible role for melatonin in the regulation of glucose transport into the brain. Accepted: 26 January 2000