Rat myoblast fusion requires exteriorized m-calpain activity.

Our previous studies demonstrated that fibronectin could be proteolyzed by m-calpain during muscle cell differentiation. Recent results indicated also that m-calpain could be exteriorized and more particularly associated to extracellular matrix components. To clarify one of the possible physiological functions of this proteinase during myogenesis, we have analyzed the incidence of added purified m-calpain and calpain inhibitors on the fusion kinetics of cultured myoblasts. Our results provided evidence that at low concentration (0.01 microgram/ml), added m-calpain induces precocious fusion and increases myoblast fusion by 78%. At high concentrations (10 micrograms/ml), the viability of the cells was not affected but the myoblasts were unable to fuse. Leupeptin and calpastatin--potent m-calpain inhibitors--added to the culture medium reduced myoblast fusion by 70%. On the other hand, the addition of monospecific m-calpain polyclonal antibodies to the culture medium induced a 76% decrease of myoblast fusion. In order to trap exteriorized m-calpain, myoblasts were incubated for 24 h with m-calpain antibodies. Following this treatment, nonpermeabilized myoblasts exposed to labeled secondary antibodies showed fluorescent spots scattered at the cell surface. These results strongly support that m-calpain which was involved in myoblast fusion was exteriorized and suggest therefore that this enzyme may play an important role extracellularly.

Renin-aldosterone axis and arginine-vasopressin responses to sodium depletion in camels.

Urinary output, urinary sodium and potassium excretion, plasma electrolyte concentrations and osmolality, plasma renin activity (PRA), and plasma aldosterone and arginine-vasopressin (AVP) concentrations were determined in eight camels in Tadla (Morocco). After administration of furosemide (2 mg.kg-1 body wt) urinary water, sodium and potassium excretions increased, inducing hypovolemia (as reflected by 14.6% increase in hematocrit), hyponatremia (142 +/- 1.0 vs 150 +/- 2.1 mmol.liter-1 in controls; P < 0.05), plasma hypo-osmolality (287.5 +/- 11.5 vs 307 +/- 1.4 mOsm.kg-1 H2O in controls; P < 0.05), and hypokalemia (3.7 +/- 0.2 vs 4.6 +/- 0.1 mmol.liter-1 in controls; P < 0.05). Such body fluid volume and composition changes were associated with parallel increases in PRA and plasma aldosterone concentrations (5.9 +/- 0.6 vs 0.9 +/- 0.2 ng AI.ml-1.hr-1 and 132.4 +/- 35.5 vs 25.1 +/- 6.5 pg.ml-1 in controls, respectively; P < 0.05). They were also associated with a fourfold increase in plasma arginine-vasopressin concentrations (0.8 +/- 0.2 vs 0.2 +/- 0.1 pg.ml-1; P < 0.05). In furosemide-treated animals, plasma aldosterone concentrations correlated positively with PRA (r = 0.85; n = 64; P < 0.01) and negatively with plasma sodium concentrations (r = -0.80; n = 64; P < 0.01), suggesting that in sodium-depleted camels the nexus between the renin-angiotensin system and aldosterone was restored.

Hormonal control of water and sodium in plasma and urine of camels during dehydration and rehydration.

Eight dromedary camels were studied for 24 days under control conditions (3 days), and during water deprivation (14 days) and rehydration (7 days) in Tadla (Morocco), during the summer. During dehydration, food intake gradually fell and was zero on the last day and animals lost about 30% of their body weight. However, most of this reduction in weight was attributed to water loss, since body weight of the animals returned to control values following rehydration. Dehydration was associated with a decrease in plasma volume (-42 +/- 3%) and a concomitant rise in plasma Na concentration (from 154 +/- 2 to 191 +/- 3 mM). These changes were accompanied by increased plasma arginine-vasopressin (from 0.2 +/- 0.1 to 5.7 +/- 2.2 pg ml-1) and plasma renin activity (from 1.2 +/- 0.2 to 20.0 +/- 5.2 ng Al ml-1 hr-1), without significantly changed plasma concentrations of aldosterone and atrial natriuretic peptide. Dehydration was associated with increased urine osmolality (from 952 +/- 515 to 1963 +/- 498 mosm kg-1 H2O), reduced urine production (from 4565 +/- 2230 to 817 +/- 178 ml day-1), and increased Na excretion. Most of these parameters returned to control values during initial rehydration, except for plasma renin activity, which remained elevated for 7 days, and diuresis, which rose to 12773 +/- 6707 ml day-1 on Day 7 of rehydration.

Renin-aldosterone system and arginine vasopressin in diarrhoeic calves.

Plasma renin activity, plasma aldosterone and arginine-vasopressin concentrations were determined in five diarrhoeic and five healthy newborn calves. In animals suffering from diarrhoea these three parameters were 10-15 times higher than those observed in controls. These results suggest that the hormonal systems that control fluid and electrolyte homeostasis are highly stimulated by dehydration and salt depletion induced by faecal losses of water and sodium in calves affected with diarrhoea.

Plasma adrenocorticotrophin, cortisol and aldosterone responses to ovine corticotrophin-releasing factor and vasopressin in sheep.

Ovine corticotrophin-releasing factor (oCRF) (1 microgram/kg) and arginine vasopressin (AVP) (1 microgram/kg) were injected iv in sheep, both separately and in combination. Plasma levels of immunoreactive ACTH (IR-ACTH), cortisol, and aldosterone were measured for 3 h after the injections. Mean levels before injections were 8 +/- 4 pmol/l for ACTH, 7 +/- 3 nmol/l for cortisol, and 28 +/- 9 pmol/l for aldosterone. CRF caused a rapid rise in IR-ACTH and a peak level of 125 +/- 52 pmol/l was obtained 15 min after injection. Highest values for cortisol and aldosterone levels were 40 +/- 9 nmol/l and 64 +/- 13 pmol/l, respectively, 30 min after injection. AVP also increased IR-ACTH (maximum level: 202 +/- 77 pmol/l at 5 min) and aldosterone (128 +/- 36 pmol/l at 15 min), whereas the cortisol increase was lower than after CRF. Simultaneous injection of CRF and AVP produced an addition of the IR-ACTH response (295 +/- 82 pmol/l at 15 min), but the changes in cortisol levels were similar to those obtained after CRF alone and those in aldosterone levels resembled those induced by AVP alone. Plasma Na and K, osmolality, and plasma renin activity (PRA) were not modified by either CRF or AVP. It is suggested that the increase in aldosterone levels after CRF could be mediated by ACTH and that after AVP by an IR-ACTH peptide with less effect on cortisol secretion.

Urinary sodium excretion and the renin-aldosterone system in new-born calves.

Urinary Na+ and K+ excretion, plasma aldosterone levels (PAL) and plasma renin activity (PRA) were measured in three groups of four 3-day-old calves infused with aldosterone, ethacrynic acid and hydrochlorothiazide or with vehicle. Aldosterone infusion (16.7 micrograms/kg body wt. given by rapid injection, followed by the infusion of 33.3 micrograms/kg body wt. during 6 h) decreased urinary Na+ concentration and excretion during the 6 h period of infusion. This effect disappeared during the following 18 h. Ethacrynic acid (2 mg/kg body wt. by rapid injection, followed by the infusion of 1.5 mg/kg body wt..h during 6 h) and hydrochlorothiazide (8 mg/kg body wt. by rapid injection, followed by the infusion of 6 mg/kg body wt..h during 6 h) increased urinary volume and urinary excretion of Na+, but decreased urinary K+ concentration without affecting urinary K+ excretion during the 6 h period of infusion. During the same time, the plasma Na+ concentration decreased, PRA increased rapidly and was followed by a significant rise in PAL. These results demonstrate that in very young healthy calves, the renal tubules are able to respond to aldosterone. The renin-aldosterone system is also operative in these animals since it responds to Na+ depletion induced by the combination of diuretics and inhibitors of tubular Na+ reabsorption.

Lack of effect of metoclopramide on plasma aldosterone concentrations in young calves.

In five 10-day-old Holstein X Friesian male calves, the intravenous injection of the dopamine blocker metoclopramide (1 mg/kg bwt) had no significant effect on plasma aldosterone concentration. Plasma sodium, potassium, cortisol, corticosterone concentrations and plasma renin activity measured in these animals during 120 min following metoclopramide injection were never significantly different from those simultaneously measured in 5 control calves.

Control of aldosterone secretion in domestic mammals during the perinatal period.

Aldosterone in ovine fetal circulation is mainly of fetal origin. Three of the renin-angiotensin system (RAS) parameters (renin, renin substrate and angiotensin II) originate in the fetus. The fetal RAS responds to stimulation (furosemide administration, hemorrhage, hypoxemia) or inhibition (phenylephrine or angiotensin II infusion) in a manner similar to that of the adult. The response of the fetal adrenal gland to angiotensin II is age-dependent and the near-term adrenal gland is not fully sensitive to angiotensin II and relatively insensitive to potassium (K+) as well as to adrenocorticotrophin hormone (ACTH) stimuli. In the newborn, the RAS is fully operative since it responds to diuretic stimulation in the lamb and the calf or to inhibition by angiotensin II administration in the lamb. Angiotensin II infusion, or angiotensin-converting enzyme blockade in the newborn lamb is followed by changes in plasma renin activity (PRA) or plasma aldosterone concentration (PAC) that suggest that angiotensin II regulates aldosterone secretion and that there is a negative feed back loop between angiotensin II and renin release. The newborn lamb adrenal gland is sensitive to potassium ions while in the newborn calf, ACTH stimulates cortisol secretion but fails to induce any change in PAC, suggesting that, in this species, the zona glomerulosa of the adrenal cortex is insensitive to ACTH.

Electrolyte balance, mode of delivery and plasma aldosterone levels in newborn lambs.

Plasma aldosterone, sodium (Na) and potassium (K) concentrations, daily Na and K intakes, and urinary and faecal excretion were measured during the first week of postnatal life in 9 lambs naturally born at term (145 days of gestation) and in 10 lambs delivered by caesarean section on day 145 (6 lambs) or on day 139 (4 lambs) of gestation. Plasma aldosterone, Na and K concentrations showed no significant variation during the experimental period in any group of lambs, and there was no significant difference concerning these parameters among the three groups. Na and K balances were always positive during the experimental period in naturally born lambs. It was negative on days 4 and 6 postdelivery in those delivered by caesarean section on days 145 and 139 of gestation, respectively. This was probably due to the lower daily Na and K intakes measured in these 10 lambs compared to the 9 control lambs: urinary output and urinary Na and K excretion were lower in the two groups of lambs delivered by caesarean section, while Na and K urinary concentrations were not different in any group.

ACTH and plasma corticosteroid levels in young calves.

1. Plasma sodium, potassium, aldosterone and cortisol levels were measured in seven 11-day-old calves after ACTH infusion and in five control animals. 2. During the 24 h following ACTH infusion the concentration of sodium and potassium in plasma and urine showed no significant variation either in treated or in control calves. 3. ACTH infusion induced a significant increase in plasma cortisol levels, which did not appear in control calves. Plasma aldosterone levels did not vary significantly in treated or in control calves.

Sodium and potassium balances and plasma aldosterone levels in newborn calves.

This paper describes a balance study, performed during the first 7 days of postnatal life on 10 male Holstein x Friesian calves born spontaneously at term. The relationship between sodium and potassium balances and plasma aldosterone levels were assessed during the postnatal period. The animals were put in metabolic cages immediately after birth for 7 days. Intakes of sodium and potassium and their plasma levels, as well as urinary and faecal excretion, were measured daily. Statistical (multiple regression) analysis of the results demonstrated that animal age accounted for 57 p. 100 of the variations observed in the plasma aldosterone levels. Neither intake nor faecal and urinary excretions of sodium and potassium were correlated with plasma aldosterone concentrations in newborn calves. The high plasma levels of this hormone at the time of birth might be a result of labor.

Sodium and potassium in blood and milk and plasma aldosterone levels in high-yield dairy cows.

Plasma sodium, potassium and aldosterone levels, daily milk production and milk sodium and potassium were measured in 10 Holstein X Friesian cows during a whole lactation period beginning in November and ending in November the following year. The milk production (4 p. 100 fat content) of these animals was 6 170 +/- 66 kg (mean +/- SEM). During the whole experimental period, the cows had free access to salt blocks and were thus always sodium-replete. Plasma sodium and potassium levels showed no significant variations during lactation. The daily excretion of sodium and potassium through milk paralleled that of daily milk production. Plasma aldosterone levels decreased sharply from 77.4 +/- 4.0 pg.ml-1 at calving to 13.2 +/- 3.6 pg.ml-1 (P less than 0.01) on day 7 of lactation, then remained stable until day 50 (16.4 +/- 4 pg.ml-1). They increased slightly on day 155 (60 days after mating: 36 +/- 5 pg.ml-1; P less than 0.05) and abruptly after spring grazing (54.9 +/- 11 pg.ml-1; P less than 0.01), then remained high until the end of lactation (48.5 +/- 12 pg.ml-1). Plasma aldosterone levels were 11.9 +/- 2.4 pg.ml-1 in seven 24-month old, non-pregnant heifers fed the same winter ration as the cows. No relationship could be demonstrated between sodium and potassium concentrations in blood and milk or between those parameters and plasma aldosterone levels. Thus, in high-yield dairy cows, aldosterone does not seem to play a major role in the regulation of sodium and potassium excretion through milk.

Plasma sodium, potassium and aldosterone levels in newborn calves.

1 Plasma sodium, potassium and aldosterone levels were measured in 11 calves during the first postnatal week. 2 Plasma sodium and potassium levels showed no significant variation between birth and the seventh day of postnatal life. 3 A sharp decrease in plasma aldosterone levels was observed between birth (119 +/- 7 pg/ml) and 12 hrs (25 +/- 8 pg/ml). The lowest values (13 +/- 5 pg/ml, similar to those measured in adult cows) were measured on day 7.