Biomedical subjects

Y Nys

Publications and source records attributed to Y Nys.

46 records · Page 3Linked to original sources

PubMed1986

Accumulation and specific cleavage of 5S RNA in the isthmus of laying hen oviduct. Evidence for three chicken 5S RNA.

RNA extracts from the isthmus of laying hen oviduct contain truncated 5S RNA molecules that were found to be shorter at their 5' terminus as compared to native 5S RNA I and II. Moreover one of the truncated species differs from 5S RNA I by the absence of the 3' end nucleotide. The truncated forms increase of about 70% the total 5S RNA (intact + truncated) in the isthmus, as compared to the other studied tissues. Furthermore 5S RNA I is heterogeneous: 25% have A instead of U at the 3' end, and some evidence was obtained for the existence of two 5S RNA I conformers.

Animals↗

PubMed1986

Effects of suppression and resumption of shell formation and parathyroid hormone on uterine calcium-binding protein, carbonic anhydrase activity, and intestinal calcium absorption in hens.

The calcium absorption and duodenal and uterine vitamin D-dependent calcium-binding protein (CaBP-28K) levels were decreased in hens when eggshell calcification was suppressed by premature expulsion of the egg. Nevertheless, these levels remained higher than those of immature pullets or pullets treated with estrogen. The resumption of shell formation by hens which had previously laid soft-shell eggs was associated during calcification of the first egg with increases in intestinal Ca absorption. CaBP concentration, and alkaline phosphatase activity. The increase in uterine CaBP concentration preceded the stage of rapid calcium deposition. Uterine carbonic anhydrase activity was increased by sexual maturity but not consistently by shell formation. Ablation of the parathyroids just before the resumption of shell formation suppressed the increases in duodenal calcium absorption and CaBP concentration elicited by egg calcification. In contrast, the increase in CaBP level was maintained in the uterus of parathyroidectomized hens, in spite of the decreased shell deposition. Previous studies indicated that increased uterine CaBP associated with eggshell calcification is not elicited by vitamin D. The present study confirms this observation and also shows that these changes are not elicited by either PTH or sex steroid hormones.

Animals↗

PubMed1986

Ontogeny and oestradiol dependence of vitamin D-binding protein blood levels in chickens.

The concentration of 25-hydroxyvitamin D3-binding protein (DBP) was measured, by immunodiffusion, in the blood of chickens from embryonic stages to sexual maturity. Low levels of DBP and 1,25-(OH)2D3 were detectable in the blood of chick embryos from the 12th and 17th day of incubation respectively and stayed at the same low levels until hatching. The blood concentration of DBP doubled between the 1st and 5th days of life, then increased slowly and reached the mean level of the adult male at 7-8 weeks of age. The concentration of DBP was independent of vitamin D status in growing chickens. A large increase was observed in DBP blood levels in hens just before sexual maturity. This change, and those observed in moulting hens, followed the variations in plasma concentrations of oestradiol more closely than those of progesterone or testosterone. Moreover, a large increase in plasma DBP levels was induced in immature chickens by oestradiol (0.5 mg/day), but not by testosterone or progesterone. Finally, the experimental suppression of egg shell formation and the associated decrease in 1,25-(OH)2D3 plasma levels had no effect on plasma DBP concentrations. However, 1,25-(OH)2D3 and DBP levels were higher in hens laying shell-less eggs than in immature pullets. The increases in DBP levels at hatching, in immature pullets treated with oestrogens, in hens laying uncalcified eggs and at the onset of egg production were associated with increases in 1,25-(OH)2D3, suggesting a relationship between the levels of DBP and 1,25-(OH)2D3 in the blood.

Animals↗

PubMed1986

Blood levels of ionized calcium, inorganic phosphorus, 1,25-dihydroxycholecalciferol and gonadal hormones in hens laying hard-shelled or shell-less eggs.

The production of shell-less eggs was induced in hens to measure the effects of the high demands made by shell formation on the blood minerals and hormones whose concentrations change during egg formation. In control hens laying hard-shelled eggs, the concentration of ionized calcium in plasma decreased at the onset of shell formation, but no change was found in hens laying shell-less eggs. Total calcium concentrations in plasma decreased slightly throughout the ovulation cycle in both groups. Concentrations of inorganic phosphorus in the plasma were increased in the control group during the period of shell formation and decreased when calcification was suppressed. Finally, the concentrations of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) in plasma were significantly increased 16 and 20 h following an ovulation compared with 4 h after ovulation, or compared with the concentrations observed in hens laying shell-less eggs. The variations in the plasma concentrations of ionized calcium, inorganic phosphorus and 1,25-(OH)2D3 associated with egg formation were therefore absent in hens laying shell-less eggs demonstrating their direct link with shell calcification. On the other hand, suppression of shell production had no influence on the changes in the plasma concentrations of progesterone, oestradiol and testosterone which are associated with the normal ovulatory cycle. It is concluded that the increases in intestinal and uterine calcium transport and in 1,25-(OH)2D3 production which occur at the onset of egg production in hens are mainly controlled by factors involved in maintaining calcium homeostasis rather than by gonadal hormones.

Animals↗

PubMed1984

Involvement of 1,25-dihydroxycholecalciferol in the short- and long-term increase of intestinal calcium absorption in laying hens: stimulation by gonadal hormones is partly independent of 1,25-dihydroxycholecalciferol.

The short- and long-term effects of 1,25-dihydroxycholecalciferol (1,25(OH)2D3) and its interactions with sexual steroids on Ca absorption were studied in hens. A single injection of 375 ng 1,25(OH)2D3 did not increase intestinal calcium transport in D-repleted hens within 24 hr of administration. However, five daily injections of 1 alpha-(OH)D3(0.5 micrograms/kg), a low Ca intake, or oestrogen-testosterone (O.T) did increase calcium absorption in D-repleted immature pullets (measured by in vivo perfusion), mainly by increasing the diffusional component of Ca transport. O.T. further increased the stimulation by 1 alpha-(OH)D3 of calcium absorption and of duodenal CaBP concentration. At higher doses the stimulation by 1 alpha-(OH)D3 of calcium transport estimated by in situ ligated loop procedure was dose dependent and was not saturable at daily doses of less than 3 micrograms/kg. When Ca transport was stimulated by 2 micrograms/kg of 1 alpha-(OH)D3, an additional effect of O.T. was observed again without any increase in plasma levels of 1,25(OH)2D3. Both oestrogen and testosterone were necessary for this effect on Ca transport. This is evidence for an indirect effect on Ca transport, as both steroids are also necessary to induce medullary bone. It is concluded that O.T. increased intestinal absorption of calcium, first by stimulating 25(OH)D3 1 alpha-hydroxylase activity but also by another mechanism which is independent of 1,25(OH)2D3 metabolism.

Animals↗

PubMed1984

Effects of suppression of eggshell calcification and of 1,25(OH)2D3 on Mg2+, Ca2+ and Mg2+HCO-3 ATPase, alkaline phosphatase, carbonic anhydrase and CaBP levels--I. The laying hen uterus.

Stimulation of Mg2+, Ca2+ and Mg2+HCO-3 dependent ATPase activity in mitochondrial and microsomal fractions from the uteri of laying hens is demonstrated. ATPase activity was greatest with 5 mM concentrations of Mg2+ at pH 8.5, and at pH 7.4-7.8 following the addition of bicarbonate. Suppression of eggshell calcification, induced by insertion of a thread into the uterus, did not alter Mg2+, Ca2+ and Mg2+HCO-3 ATPase activities. Alkaline phosphatase activity was generally low, and was unaffected by suppression of eggshell calcification. Levels of carbonic anhydrase and calcium binding protein were lower in the uteri of hens laying shell-less eggs. Injections of 1,25(OH)2D3 in hens laying shell-less eggs did not alter CaBP levels or enzyme activities. It is concluded that factors other than 1,25(OH)2D3 and gonadal hormones are involved in the regulation of uterine CaBP levels.

Adenosine Triphosphatases↗

PubMed1984

Effects of suppression of eggshell calcification and of 1,25(OH)2D3 on Mg2+, Ca2+ and Mg2+HCO-3 ATPase, alkaline phosphatase, carbonic anhydrase and CaBP levels--II. The laying hen intestine.

Activity of a HCO-3 stimulated Mg2+ dependent ATPase is demonstrated in mitochondrial fractions of the avian duodenum. Suppression of eggshell calcification resulted in a slight reduction in Mg2+, Ca2+ and Mg2+HCO-3 ATPase activities. Duodenal carbonic anhydrase activity was lower in birds laying soft-shelled eggs than in birds laying normal eggs. Alkaline phosphatase and calcium binding protein levels both decreased along the length of the small intestine, but the effect was more pronounced for alkaline phosphatase. Suppression of eggshell calcification and treatment of shell-less laying hens with 1,25(OH)2D3 influenced alkaline phosphatase activity only in the duodenal mucosa. Suppression of eggshell calcification reduced CaBP levels in all sections of the intestine. Treatment with 1,25(OH)2D3 restored CaBP levels. Regulation of intestinal CaBP levels by 1,25(OH)2D3 would therefore, seem to be controlled more directly by calcium requirements associated with eggshell calcification than by gonadal hormones.

Adenosine Triphosphatases↗

PubMed1983

[Increase in blood uric acid induced by indomethacin in hens or chickens].

Indomethacin (2.5 mg/kg) causes a rapid increase in plasma urate concentrations and at 5 mg/kg I.M. may cause death by deposition of urates in the viscera (visceral gout). This increase is probably a consequence of decreased renal tubular urate secretion. The sensitivity to indomethacin varies either according to the strain of Bird or the physiological status: Hens appear more sensitive during egg formation.

Animals↗

PubMed1982

Transport of electrolytes and water in the upper jejunum of the fowl in vivo perfusion.

The mechanism(s) of electrolytes (JNa, JC1, JCa and JK) and water transport (JV) were studied in the upper jejunum of the laying hen by an in vivo perfusion procedure. Water secretion is modified by the difference of osmotic pressure between the lumen and plasma and we have estimated the osmotic permeability coefficient (P osm = 17.4 microliter x h-1 x mosm-1 x g-1 DW) and the reflexion coefficient (0.72). At sodium concentrations of 0 and 80 mM x 1-1 in the lumen, there is a large secretion of Na. When the water flow is modified by osmotic pressure, this secretion is markedly influenced by JV. Similarly net chloride flux occurred mainly by solvent drag. Conversely water flow does not modify the large potassium absorption along the concentration gradient and only slightly affects the flux of calcium. Transport of calcium occurred along the gradient of concentration between lumen and plasma without saturation until a lumen concentration of 20 mM x 1-1. This driving force seemed to be the main one since JCa is close to zero when there is no gradient. This observation supports the hypothesis that the variations of net Ca absorption during the laying cycle is due to a modification of concentration of soluble calcium in the contents of the intestine.

Animals↗

PubMed1980

Jejunal calcium permeability in laying hens during egg formation.

The permeability of the upper jejunum to water, calcium, potassium, sodium and chloride was measured in the immature pullet and then in the laying hen before and during egg-shell calcification by an in vivo perfusion procedure. Jejunal calcium permeability was constant throughout egg formation. Thus, the increase of net absorption during shell calcification was not due to enhanced mucosal capacity for calcium translocation, but rather to a better solubilization of calcium carbonate in the upper digestive tract. However, this capacity increased at the onset of egg production, as shown by the difference between immature and mature birds.

Animals↗