Muscle glycogen depletion and subsequent replenishment affect anaerobic capacity of horses.

The purpose of this study was to determine the effect of muscle glycogen depletion and subsequent replenishment on anaerobic capacity of horses. In a blinded crossover study, seven fit horses performed glycogen-depleting exercise on two occasions. Horses were infused after glycogen-depleting exercise with either 6 g/kg body wt of glucose as a 13.5% solution in 0.9% NaCl (Glu) or with 0.9% NaCl (Sal) of equivalent volume. Subsequently, horses performed a high-speed exercise test (120% of maximal rate of oxygen consumption) to estimate maximum accumulated oxygen deficit. Replenishment of muscle glycogen was greater (P < 0.05) in Glu [from 24.7 +/- 7.2 (SE) to 116.5 +/- 7 mmol/kg wet wt before and after infusion, respectively] than in Sal (from 23.4 +/- 7.2 to 47.8 +/- 5.7 mmol/kg wet wt before and after infusion, respectively). Run time to fatigue during the high-speed exercise test (97.3 +/- 8.2 and 70.8 +/- 8.3 s, P < 0.05), maximal accumulated oxygen deficit (105.7 +/- 9.3 and 82.4 +/- 10.3 ml O(2) equivalent/kg, P < 0.05), and blood lactate concentration at the end of the high-speed exercise test (11.1 +/- 1.4 and 9.2 +/- 3.7 mmol/l, P < 0.05) were greater for Glu than for Sal, respectively. We concluded that decreased availability of skeletal muscle glycogen stores diminishes anaerobic power generation and capacity for high-intensity exercise in horses.     

Volume and Twitch Tension Changes in Single Muscle Fibers in Hypertonic Solutions

Single muscle fibers were exposed to solutions made hypertonic (approximately 460 milliosmols/kg water) by addition of either NaCl, glycerol, urea, acetamide, ethylene glycol, or propylene glycol. The changes in either the fiber twitch tension or the volume were measured. In the case of NaCl both fiber volume and twitch tension fall rapidly to 64 and 27% of the respective initial value. These two values were maintained for the duration of the exposure. In the case of the other substances, the fiber volume and twitch tension also decreased but in these cases the effect was transient and the fibers recovered their initial volume and twitch tension. The rate of recovery in the different hypertonic media increased in the order: glycerol < urea < ethylene glycol < propylene glycol < acetamide. In the cases of the last three substances, the initial twitch value was recovered in less than 5 min and even surpassed. However, on returning to normal Ringer the fibers' ability to twitch or to develop potassium contractures was lost. The return of the fibers to normal Ringer after exposure to these hypertonic solutions causes a transient swelling of the fibers. However, when fibers were swelled by exposure to hypotonic media, they did not lose their ability to twitch on return to the normal Ringer.     

The Dual Effect of Lithium Ions on Sodium Efflux in Skeletal Muscle

Sartorius muscle cells from the frog were stored in a K-free Ringer solution at 3°C until their average sodium contents rose to around 23 mM/kg fiber (about 40 mM/liter fiber water). Such muscles, when placed in Ringer''s solution containing 60 mM LiCl and 50 mM NaCl at 20°C, extruded 9.8 mM/kg of sodium and gained an equivalent quantity of lithium in a 2 hr period. The presence of 10^-5 M strophanthidin in the 60 mM LiCl/50 mM NaCl Ringer solution prevented the net extrusion of sodium from the muscles. Lithium ions were found to enter muscles with a lowered internal sodium concentration at a rate about half that for entry into sodium-enriched muscles. When sodium-enriched muscles labeled with radioactive sodium ions were transferred from Ringer''s solution to a sodium-free lithium-substituted Ringer solution, an increase in the rate of tracer sodium output was observed. When the lithium-substituted Ringer solution contained 10^-5 M strophanthidin, a large decrease in the rate of tracer sodium output was observed upon transferring labeled sodium-enriched muscles from Ringer''s solution to the sodium-free medium. It is concluded that lithium ions have a direct stimulating action on the sodium pump in skeletal muscle cells and that a significantly large external sodium-dependent component of sodium efflux is present in muscles with an elevated sodium content. In the sodium-rich muscles, about 23% of the total sodium efflux was due to strophanthidin-insensitive Na-for-Na interchange, about 67% being due to strophanthidin-sensitive sodium pumping.     

Effects of changes in plasma hepatic-portal and systemic osmolality on plasma concentrations of arginine vasopressin in conscious newborn calves

Systemic plasma concentrations of arginine vasopressin (AVP) were studied in three groups of 10-15 day-old conscious newborn calves. Animals in the first group (control group) and in the second group (systemic-hypertonic-injected group) received respectively isotonic and hypertonic (8 mmol NaCl/kg body weight) saline injection into the right jugular vein. Animals in the third group were fitted with chronic mesenteric and hepatic-portal catheters and received a 1 h-hypertonic saline infusion (2 mmol NaCl/kg body weight) into the main mesenteric vein. In animals in the second group there were parallel increases in systemic plasma concentration of Na+ (from 148.0 +/- 2.6 to 177 +/- 8 mmol/l; P less than 0.01), osmolality (from 289 +/- 2 to 319 +/- 4 mOsmol/kg H2O; P less than 0.01) and systemic plasma concentrations of AVP (from 4.2 +/- 0.4 to 11.1 +/- 0.6 pmol/l; P less than 0.01) 10 min after the injection. There were no significant changes in control animals. Hypertonic saline infusion into the main mesenteric vein in the third group induced an increase in concentration of Na+ (from 147.3 +/- 2.0 to 165.0 +/- 5.0 mmol/l; P less than 0.01) and osmolality (from 288 +/- 5 to 315 +/- 10 mOsmol/kg H2O; P less than 0.01) in hepatic-portal vein plasma but did not alter systemic plasma osmolality or concentrations of Na+ and AVP. This study demonstrates that the relationship between plasma concentrations of AVP and systemic osmolality is operative in the newborn calf but does not support the hypothesis that hepatic portal osmo-receptors sensitive to hyperosmolality influence AVP release.     

Effect of extracellular osmolality on cell volume and resting metabolism in mammalian skeletal muscle

The purpose of the present investigation was to establish an in vitro mammalian skeletal muscle model to study acute alterations in resting skeletal muscle cell volume. Isolated, whole muscles [soleus and extensor digitorum longus (EDL)] were dissected from Long-Evans rats and incubated for 60 min in Sigma medium 199 (1 g of resting tension, bubbled with 95% O(2)-5% O(2), 30 +/- 2 degrees C, and pH 7.4). Medium osmolality was altered to simulate hyposmotic (190 +/- 10 mmol/kg) or hyperosmotic conditions (400 +/- 10 mmol/kg), whereas an isosmotic condition (290 +/- 10 mmol/kg) served as a control. After incubation, relative water content of the muscle decreased with hyperosmotic and increased with hyposmotic condition in both muscle types (P < 0.05). The cross-sectional area of soleus type I and type II fibers increased (P < 0.05) in hyposmotic, whereas hyperosmotic exposure led to no detectable changes. The EDL type II fiber area decreased in the hyperosmotic condition and increased after hyposmotic exposure, whereas no change was observed in EDL type I fibers. Furthermore, exposure to the hyperosmotic condition in both muscle types resulted in decreased muscle ATP and phosphocreatine (P < 0.05) contents and increased creatine and lactate contents (P < 0.05) compared with control and hyposmotic conditions. This isolated skeletal muscle model proved viable and demonstrated that altering extracellular osmolality could cause acute alterations in muscle water content and resting muscle metabolism.     

Intracellular pH recovery from lactic acidosis of single skeletal muscle fibers

Intracellular pH (pHi), measured with H+-selective microelectrodes, in quiescent frog sartorius muscle fibres was 7.29 +/- 0.09 (n = 13). Frog muscle fibres were superfused with a modified Ringer solution containing 30 mM HEPES buffer, at extracellular pH (pHo) 7.35. Intracellular pH decreased to 6.45 +/- 0.14 (n = 13) following replacement of 30 mM NaCl with sodium lactate (30 mM MES, pHo 6.20). Intracellular pH recovery, upon removal of external lactic acid, depended on the buffer concentration of the modified Ringer solution. The measured values of the pHi recovery rates was 0.06 +/- 0.01 delta pHi/min (n = 5) in 3 mM HEPES and was 0.18 +/- 0.06 delta pHi/min (n = 13) in 30 mM HEPES, pHo 7.35. The Na+-H+ exchange inhibitor amiloride (2 mM) slightly reduced pHi recovery rate. The results indicate that the net proton efflux from lactic acidotic frog skeletal muscle is mainly by lactic acid efflux and is limited by the transmembrane pH gradient which, in turn, depends on the extracellular buffer capacity in the diffusion limited space around the muscle fibres.     

Natriuresis induced by mild hypernatremia in humans

The hypothesis that increases in plasma sodium induce natriuresis independently of changes in body fluid volume was tested in six slightly dehydrated seated subjects on controlled sodium intake (150 mmol/day). NaCl (3.85 mmol/kg) was infused intravenously over 90 min as isotonic (Iso) or as hypertonic saline (Hyper, 855 mmol/l). After Hyper, plasma sodium increased by 3% (142.0 +/- 0.6 to 146.2 +/- 0.5 mmol/l). During Iso a small decrease occurred (142.3 +/- 0.6 to 140.3 +/- 0.7 mmol/l). Iso increased estimates of plasma volume significantly more than Hyper. However, renal sodium excretion increased significantly more with Hyper (291 +/- 25 vs. 199 +/- 24 micromol/min). This excess was not mediated by arterial pressure, which actually decreased slightly. Creatinine clearance did not change measurably. Plasma renin activity, ANG II, and aldosterone decreased very similarly in Iso and Hyper. Plasma atrial natriuretic peptide remained unchanged, whereas plasma vasopressin increased with Hyper (1.4 +/- 0.4 to 3.1 +/- 0.5 pg/ml) and decreased (1.3 +/- 0.4 to 0.6 +/- 0.1 pg/ml) after Iso. In conclusion, the natriuretic response to Hyper was 50% larger than to Iso, indicating that renal sodium excretion may be determined partly by plasma sodium concentration. The mechanism is uncertain but appears independent of changes in blood pressure, glomerular filtration rate, the renin system, and atrial natriuretic peptide.     

Osmotic and ionic regulation during hypoxia in the medicinal leech, Hirudo medicinalis L.

The concentrations of inorganic and organic ions and osmolality in the blood of the medicinal leech, Hirudo medicinalis, were determined during normoxia and hypercapnic and hypocapnic hypoxia. In normoxic animals, the blood sodium concentration was 124.5 +/- 4.2 mmol/l and the total cation concentration was 132.2 +/- 4.3 mEq/l (mean +/- S.D.). Major anionic compounds were chloride (40.8 +/- 1.6 mmol/l), bicarbonate (8.4 +/- 1.3 mmol/l), and organic anions (42.5 +/- 2.3 mEq/l). Among the latter, malate accounts for 30.4 +/- 2.2 mEq/l. The nature of the remaining anion fraction, which balances cation and anion concentrations in leech blood, remains unknown. Within 96 h of hypercapnic hypoxia, the amount of organic osmolytes in leech tissue increased from the control level of 56.6 +/- 9.1 to 158.3 +/- 19.5 mumol/g dry weight. An even higher amount of organic acids was accumulated within 96 h of hypocapnic hypoxia (218.0 +/- 53.7 mumol/g dry weight). A possible reason for this is that lactate, which is a major end-product of hypocapnic hypoxia, cannot be excreted to the external medium as easily as propionate. The accumulation of blood organic acids generating osmotic stress in the animals was compensated by an equimolar decrease in sodium and chloride ion concentrations. In hypercapnic animals these changes resulted in a constant osmotic concentration of the blood (200 mosmol/kg H2O) during the experimental period. Between 24 and 96 h of hypocapnic hypoxia, however, the increase in the osmotic gradient between animal and medium was correlated with further net water uptake and the obvious deterioration of the volume- and ion-regulatory mechanisms in these animals.     

Stereologic analysis of vacuolization of the T-system of frog muscle fibers, detected using confocal fluorescence microscopy

The confocal fluorescence microscopy has been used for quantitative evaluation of the T-system reversible vacuoles produced by efflux of 80-120 mM glycerol from frog skeletal muscle fibers. The fibers were stained by membrane probe RH414 and by water-soluble dye fluorescein dextran that marks the vacuolar lumen. Using morphometrical and stereological methods the volume and surface densities of vacuoles were measured on single optical sections and Z-series during a 30 min glycerol efflux. Various methods of measurements (three-dimensional reconstruction of vacuoles, computer morphometry, point counting method) applied to the same Z-series provide similar results. The vacuolar membranes stained by RH414 look like bright rings 0.3-0.4 micron in width. It is concluded that the real position of vacuolar membrane corresponds to the middle of the vacuolar envelope. The measurements of the external dimensions of the envelope overestimate the stereological parameters up to 50%. The volume density of vacuoles reaches 10% within 20-30 min of glycerol efflux. It means that the volume of the T-system may increase by 25-30 times compared to the control value (0.3-0.4%). The surface density of vacuoles during reversible vacuolation is equal to 0.20-0.35 micron-1 and does not exceed the surface density of normal T-system. The sufficiency of membrane material for the T-system reversible vacuolation is discussed in addition to the role of geometrical factor in this phenomenon.     

Physiological characterization and stress-induced metabolic responses of Dunaliella salina isolated from salt pan

A Dunaliella strain was isolated from salt crystals obtained from experimental salt farm of the institute (latitude 21.46 N, longitude 72.11 degrees E). The comparative homology study of amplified molecular signature 18S rRNA, proves the isolated strain as D. salina. The growth pattern and metabolic responses such as proline, glycine betaine, glycerol, total protein and total sugar content to different salinity (from 0.5 to 5.5 M NaCl) were studied. The optimum growth was observed at 1.0 M NaCl and thereafter it started to decline. Maximum growth was obtained on 17th day of inoculation in all salt concentrations except 0.5 M NaCl, whereas maximum growth was observed on 13th day. There were no significant differences (P < 0.01) in chlorophyll a/b contents (1.0-1.16 +/- 0.05 mug chl. a and 0.2-0.29 +/- 0.01 mug chl. b per 10(6) cells) up to 2.0 M NaCl, however at 3.0 M NaCl a significant increase (2.5 +/- 0.12 mug chl. a and 0.84 +/- 0.4 mug chl. b per 10(6) cells) was observed which declined again at 5.5 M NaCl concentration (2.0 +/- 0.1 mug chl. a and 0.52 +/- 0.03 mug chl. b per 10(6) cells). Stress metabolites such as proline, glycine betaine, glycerol and total sugar content increased concomitantly with salt concentration. Maximum increase in proline (1.4 +/- 0.07 mug), glycine betaine (5.7 +/- 0.28 mug), glycerol (3.7 +/- 0.18 ml) and total sugar (250 +/- 12.5 mug) per 10(5) cells was observed in 5.5 M NaCl. A decrease in total protein with reference to 0.5 M NaCl was observed up to 3.0 M NaCl, however, a significant increase (P < 0.01) was observed at 5.5 M NaCl (0.19 +/- 0.01 mug per 10(5) cells). Inductive coupled plasma (ICP) analysis shows that intracellular Na(+) remained unchanged up to 2.0 M NaCl concentration and thereafter a significant increase was observed. No relevant increase in the intracellular level of K(+) and Mg(++) was observed with increasing salt concentration. Evaluation of physiological and metabolic attributes of Dunaliella salina can be used to explore its biotechnological and industrial potential.     

Creatine phosphate in fiber types of skeletal muscle before and after exhaustive exercise

Percutaneous muscle biopsies were obtained from the vastus lateralis of physically active men (n = 12) 1) at rest, 2) immediately after an exercise bout consisting of 30 maximal voluntary knee extensions of constant angular velocity (3.14 rad/s), and 3) 60 s after termination of exercise. Creatine phosphate (CP) content was analyzed in pools of freeze-dried fast-twitch (FT) and slow-twitch (ST) muscle fiber fragments, and ATP, CP, creatine, and lactate content were assayed in mixed pools of FT and ST fibers. CP content at rest was 82.7 +/- 11.2 and 73.1 +/- 9.5 (SD) mmol/kg dry wt in FT and ST fibers (P less than 0.05). After exercise the corresponding values were 25.4 +/- 19.8 and 29.7 +/- 14.4 mmol/kg dry wt. After 60 s of recovery CP increased (P less than 0.01) to 41.3 +/- 12.6 and 49.6 +/- 11.7 mmol/kg dry wt in FT and ST fibers, respectively. CP content after recovery, relative to initial level, was higher in ST compared with FT fibers (P less than 0.05). ATP content decreased (P less than 0.05) and lactate content rose to 67.4 +/- 28.3 mmol/kg dry wt (P less than 0.001) in response to exercise. It is concluded that basal CP content is higher in FT fibers than in ST fibers. CP content also appears to be higher in ST fibers after a 60-s recovery period after maximal short-term exercise. These data are consistent with the different metabolic profiles of FT and ST fibers.     

Low glycogen and branched-chain amino acid ingestion do not impair anaplerosis during exercise in humans.

We examined the hypothesis that increasing the rate of branched-chain amino acid (BCAA) oxidation, during conditions of low glycogen availability, reduces the level of muscle tricarboxylic acid cycle intermediates (TCAI) by placing a carbon "drain" on the cycle at the level of 2-oxoglutarate. Six men cycled at approximately 70% of maximal oxygen uptake for 15 min under two conditions: 1) low preexercise muscle glycogen (placebo) and 2) low glycogen combined with BCAA ingestion. We have previously shown that BCAA ingestion increased the activity of branched-chain oxoacid dehydrogenase, the rate-limiting enzyme for BCAA oxidation in muscle, compared with low glycogen alone [M. L. Jackman, M. J. Gibala, E. Hultman, and T. E. Graham. Am. J. Physiol. 272 (Endocrinol. Metab. 35): E233-E238, 1997]. Muscle glycogen concentration was 185 +/- 22 and 206 +/- 22 mmol/kg dry wt at rest for the placebo and BCAA-supplemented trials, respectively, and decreased to 109 +/- 18 and 96 +/- 10 mmol/kg dry wt after exercise. The net increase in the total concentration of six measured TCAI ( approximately 95% of TCAI pool) during exercise was not different between trials (3.97 +/- 0. 34 vs. 3.88 +/- 0.34 mmol/kg dry wt for the placebo and BCAA trials, respectively). Muscle 2-oxoglutarate concentration decreased from approximately 0.05 at rest to approximately 0.03 mmol/kg dry wt after exercise in both trials. The magnitude of TCAI pool expansion in both trials was similar to that seen previously in subjects who performed an identical exercise bout after a normal mixed diet [M. J. Gibala, M. A. Tarnopolsky, and T. E. Graham. Am. J. Physiol. 272 (Endocrinol. Metab. 35): E239-E244, 1997]. These data suggest that increasing the rate of BCAA oxidation has no measurable effect on muscle TCAI during exercise with low glycogen in humans. Moreover, it appears that low resting glycogen per se does not impair the increase in TCAI during moderate exercise.     

Inositol 1,4,5-trisphosphate increases myoplasmic [Ca2+] in isolated muscle fibers. Depolarization enhances its effects

Inositol 1,4,5-trisphosphate (InsP3) has been proposed as an intracellular messenger which mobilizes calcium from the sarcoplasmic reticulum, during excitation-contraction coupling in skeletal muscle. We have measured the myoplasmic free calcium concentration ([Ca2+]i) by means of calcium selective microelectrodes in intact fibers isolated from Leptodactylus insularis microinjected with InsP3. In muscle fibers bathed in normal Ringer, the mean resting [Ca2+]i was 0.11 +/- 0.01 microM (M +/- SEM, n = 30). The microinjection of 0.3, 0.5 and 1 microM InsP3 induced transient increments in the [Ca2+]i to 0.35 +/- 0.02 microM (n = 9), to 0.53 +/- 0.03 microM (n = 11) and 0.94 +/- 0.06 microM (n = 10) respectively. Microinjection of 0.3, 0.5 and 1 microM InsP3 in muscle fibers incubated in low Ca2+ solution induced increments in [Ca2+]i similar to those observed in fibers bathed with normal Ringer. The microinjection of 0.3, 0.5 and 1 microM InsP3 in muscle fibers partially depolarized with 10 mM [K+]o induced transient enhancements of the resting [Ca2+]i that were greater than the transients observed in the normally polarized muscle. In partially depolarized fibers microinjected with 0.3, 0.5 and 1 microM InsP3, the [Ca2+]i was changed to 1.45 +/- 0.14 microM (n = 20), to 3.37 +/- 0.34 microM (n = 7) and to 7.43 +/- 0.70 microM (n = 6) respectively. In all partially depolarized fibers these increments in [Ca2+]i were associated with local contraction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epinephrine-induced changes in muscle carbohydrate metabolism during exercise in male subjects

Epinephrine increases glycogenolysis in resting skeletal muscle, but less is known about the effects of epinephrine on exercising muscle. To study this, epinephrine was given intraarterially to one leg during two-legged cycle exercise in nine healthy males. The epinephrine-stimulated (EPI) and non-stimulated (C) legs were compared with regard to glycogen, glucose, glucose 6-phosphate (G6P), alpha-glycerophosphate (alpha-GP), and lactate contents in muscle biopsies taken before and after the 45-min submaximal exercise, as well as brachial arterial-femoral venous (a-fv) differences for epinephrine, norepinephrine, lactate, glucose, and O2 during exercise. During exercise the arterial plasma epinephrine concentration was 4.8 +/- 0.8 nmol/l and the femoral venous epinephrine concentrations were 10.3 +/- 2.1 and 3.9 +/- 0.6 nmol/l, respectively, in the EPI and C leg. During exercise the a-fv difference for lactate was greater (-0.41 +/- 0.14 vs. -0.21 +/- 0.14 mmol/l; P less than 0.001), and the a-fv difference for glucose was smaller (0.07 +/- 0.12 vs. 0.24 +/- 0.12 mmol/l; P less than 0.01) in the EPI than in the C leg, but the a-fv differences for O2 were similar. Muscle glycogen depletion (137 +/- 63 vs. 99 +/- 43 mmol/kg dry muscle; P less than 0.1) and the muscle concentrations of glucose (P less than 0.05), alpha-GP (P less than 0.1), G6P (P greater than 0.1), and lactate (P greater than 0.1) tended to be higher in the EPI than the C leg after exercise. These findings suggest that physiological concentrations of epinephrine may enhance muscle glycogenolysis during submaximal exercise in male subjects.     

Stimulatory effect of CO2 on vagal bronchopulmonary C-fiber afferents during airway inflammation.

This study investigated 1) whether pulmonary C fibers are activated by a transient increase in the CO2 concentration of alveolar gas; and 2) if the CO2 sensitivity of these afferents is altered during airway inflammation. Single-unit pulmonary C-fiber activity was recorded in anesthetized, open-chest rats. Transient alveolar hypercapnia (HPC) was induced by administering a CO2-enriched gas mixture (25-30% CO2, 21% O2, balance N2) for five to eight breaths, which increased alveolar CO2 concentration progressively to near or above 13% for 3-5 s and lowered the arterial pH transiently to 7.10 +/- 0.05. Our results showed the following. 1) HPC evoked only a mild stimulation in a small fraction (4/47) of pulmonary C fibers, and there was no significant change in fiber activity (change in fiber activity = 0.22 +/- 0.16 imp/s; P > 0.1, n = 47). 2) In sharp contrast, after airway exposure to poly-L-lysine, a cationic protein known to induce mucosal injury, the same challenge of transient HPC activated 87.5% of the pulmonary C fibers tested and evoked a distinct stimulatory effect on these afferents (change in fiber activity = 6.59 +/- 1.78 imp/s; P < 0. 01, n = 8). 3) Similar potentiation of the C-fiber response to HPC was also observed after acute exposure to ozone (n = 6) and during a constant infusion of inflammatory mediators such as adenosine (n = 15) or prostaglandin E2 (n = 12). 4) The enhanced C-fiber sensitivity to CO2 after poly-L-lysine was completely abrogated by infusion of NaHCO3 (1.82 mmol.kg(-1).min(-1)) that prevented the reduction in pH during HPC (n = 6). In conclusion, only a small percentage (<10%) of the bronchopulmonary C fibers exhibit CO2 sensitivity under control conditions, but alveolar HPC exerts a consistent and pronounced stimulatory effect on the C-fiber endings during airway inflammation. This effect of CO2 is probably mediated through the action of hydrogen ions.     

Effect on maternal and fetal renal function and plasma renin activity of a high salt intake by the ewe

The effect on renal function of replacing maternal drinking water with a solution containing 0.17 M NaCl was studied in 9 ewes and their chronically catheterised fetuses over a period of 9 days. Maternal sodium intake increased from control values of 2.19 +/- 0.09 mmol/h to 44.3 +/- 7.4 (P less than 0.001) and 46.3 +/- 6.5 mmol/h (P less than 0.001) on the 3rd and 6th days of salt ingestion. Maternal plasma sodium levels were not affected, but the urinary sodium/potassium ratio increased from 0.15 +/- 0.07 to 2.26 +/- 0.34 (P less than 0.001) after 6 days and plasma renin activity fell from 2.87 +/- 0.76 to 1.00 +/- 0.25 ng/ml per h (P less than 0.05). The changes in maternal sodium intake had no effect on fetal plasma sodium levels nor on fetal plasma renin activity. Sodium excretion and fetal urinary sodium/potassium ratio did not change. However, 3 days after the ewes returned to drinking water fetal plasma renin activity was significantly higher than it was prior to maternal ingestion of 0.17 M NaCl. Fetal plasma renin activity was inversely related to fetal plasma sodium levels (P less than 0.01). The results show that changes in maternal sodium intake had no long term effect on fetal plasma sodium levels nor on fetal renal sodium excretion. The fall in maternal plasma renin activity in the absence of any change in the fetal renin activity, indicates that the fetal renin angiotensin system is controlled by factors other than those influencing the maternal renin angiotensin system. Since fetal urinary sodium/potassium ratios remained unchanged it would suggest that fetal sodium excretion is not influenced by maternal levels of aldosterone.     

Galanin in the porcine pancreas.

Galanin, a 29 amino acid neuropeptide, was recently isolated from pig intestine. We studied the localization, nature and effect of galanin in pig pancreas. Galanin immunoreactive nerve fibers were regularly found in the pancreas. A peptide chromatographically similar to synthetic galanin was identified in pancreas extracts. The effect of galanin on the endocrine and exocrine secretion was studied in isolated pancreases, perfused with a synthetic medium containing 3.5, 5 or 8 mmol/l glucose and synthetic galanin (10(-10)-10(-8) mol/l). There was no effect on the basal exocrine secretion. The output of insulin, glucagon, somatostatin and pancreatic polypeptide (PP) was measured in the effluent. There was no effect on PP secretion. At a perfusate glucose concentration of 5 mmol/l, galanin at 10(-9) mol/l increased insulin secretion by 55 +/- 14% (mean +/- S.E.M., n = 5) of basal secretion, and at 10(-8) mol/l by 58 +/- 27% (n = 6). At 8 mmol/l glucose, insulin secretion increased by 25 +/- 10% (n = 6) and 62 +/- 17% (n = 8). At 5 mmol/l glucose glucagon secretion was increased by 15 +/- 3% (n = 5) by galanin at 10(-9) mol/l and by 29 +/- 11% (n = 5) by galanin at 10(-8) mol/l, and at 8 mmol/l glucose by 66 +/- 27% and 41 +/- 25%. Somatostatin secretion was inhibited to 72 +/- 2% (n = 5) of basal secretion by galanin at 10(-9) mol/l and to 65 +/- 7% (n = 7) at galanin at 10(-8) mol/l, both at 5 mmol/l glucose. At 8 mmol/l the figures were 83 +/- 6% and 70 +/- 10%. Insulin secretion in response to square wave increases in glucose concentration from 3.5 to 11 mmol/l (n = 5) increased 2-fold during simultaneous perfusion with galanin (10(-8) mol/l).     

Regional differences in intramyocellular lipids in humans observed by in vivo 1H-MR spectroscopic imaging.

Regional differences in the content of intramyocellular lipids (IMCL), extramyocellular lipids, and total creatine (TCr) were quantified in soleus (S), tibialis posterior (TP), and tibialis anterior (TA) muscles in humans using in vivo 1H proton spectroscopic imaging at 4 T. Improved spatial resolution (0.25-ml nominal voxel resolution) made it feasible to measure IMCL in S, TP, and TA simultaneously in vivo. The most significant regional difference was found in the content of IMCL compared with extramyocellular lipids or TCr. The concentrations of TCr were found to be 29-32 mmol/kg, with little regional variation. IMCL content was measured to be 4.8 +/- 1.6 mmol/kg tissue wt in S, 2.8 +/- 1.3 mmol/kg tissue wt in TP, and 1.6 +/- 0.9 mmol/kg tissue wt in TA in the order of S > TP > TA (P < 0.05). It is likely that these IMCL values are consistent with the known fiber types of these muscles, with S having the greatest fraction of type I (slow-twitch, oxidative) fibers and TA having a large fraction of type IIb (fast-twitch, glycolytic) fibers.     

Elemental distribution in striated muscle and the effects of hypertonicity: Electron probe analysis of cryo sections

A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the "excess CI" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules.     

Glucose formation in human skeletal muscle. Influence of glycogen content.

Eight men exercised at 66% of their maximal isometric force to fatigue after prior decrease in the glycogen store in one leg (low-glycogen, LG). The exercise was repeated with the contralateral leg (control) at the same relative intensity and for the same duration. Muscle (quadriceps femoris) glycogen content decreased in the LG leg from 199 +/- 17 (mean +/- S.E.M.) to 163 +/- 16 mmol of glucosyl units/kg dry wt. (P less than 0.05), and in the control leg from 311 +/- 23 to 270 +/- 18 mmol/kg (P less than 0.05). The decrease in glycogen corresponded to a similar accumulation of glycolytic intermediates. Muscle glucose increased in the LG leg during the contraction, from 1.8 +/- 0.1 to 4.3 +/- 0.6 mmol/kg dry wt. (P less than 0.01), whereas no significant increase occurred in the control leg (P greater than 0.05). It is concluded that during exercise glucose is formed from glycogen through the debranching enzyme when muscle glycogen is decreased to values below about 200 mmol/kg dry wt.