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Biomedical subjects

N L First

Publications and source records attributed to N L First.

At least 145 records · Page 8Linked to original sources
PubMed1980

Effect of prostaglandin F-2 alpha on steroidogenesis by porcine corpora lutea.

The relationship between luteal cholesterol bound to cytochrome P450scc enzyme and progesterone production was studied in the pig. Luteal progesterone peaked on Day 10 of the oestrous cycle, declined slowly until Day 13 and then precipitously between Days 13 and 14. The P450scc was nearly saturated with cholesterol between Days 4 and 13, but changed abruptly by Day 14 to a partly depleted state which persisted until Day 16. Total P450scc did not decline significantly until Day 17. There was no change in cholesterol esterase activity in a 105 000 g supernatant or in total mitochondrial cholesterol esterase activity in a 105 000 g supernatant or in total mitochondrial cholesterol during this period. Intravenous administration of PGF-2 alpha to hysterectomized gilts resulted in a rapid depletion of cholesterol from P450scc with a half-life of about 2 h. The new level of cholesterol-P450scc interaction (less than 45% of cytochrome) persisted for at least 36 h after treatment. This was paralleled by declines in plasma and luteal progesterone. These results are compatible with the hypothesis that PGF-2 alpha provokes a decline in progesterone secretion around Day 13 by first decreasing the supply of cholesterol to P450scc.

Animals↗
PubMed1979

Effects of divalent cations on in vitro maturation of bovine oocytes.

Lowering the external concentrations of both Mg+2 and Ca+2 caused failure of meiotic resumption in vitro of bovine, oocyte-cumulus complexes. Lowering of external Ca+2 levels singly had no effect on either meiotic resumption or completion of the first meiotic division. Lowering of external Mg+2 concentrations alone, although having no effect on meiotic resumption in vitro when Ca+2 was present, did interfere with the completion of the first meiotic division. The result was arrest of oocyte maturation between germinal vesicle breakdown and formation of the first metaphase plate.

Animals↗
PubMed1979

Effect of age and parity on litter size in pigs.

Litter size increased (P less than 0.01) as the age of the dam at farrowing increased. However, previous reproductive experience (parity) had no direct effect on litter size of dams of the same age.

Animals↗
PubMed1977

Inhibition of sperm migration through cervical mucus in vitro.

The effectiveness of inhibiting bovine sperm migration through cervical mucus in vitro by prior treatment of semen with 45 to 150 micrograms of soybean trypsin inhibitor, univalent (papain-digested, nonagglutinating) and bivalent (undigested) rabbit anti-bovine sperm immunoglobulin, and heat-treated heifer serum was studied. Sperm head-to-head agglutination resulted from treatment of semen with bivalent immune antibody and heat-treated heifer serum. Migration through cervical mucus was inhibited only by treatment resulting in spermagglutination. It is postulated that in vivo inhibition of sperm migration may be influenced by secretory immunoglobulins from the cervix.

Animals↗
PubMed1976

Action of ionophore A23187 at the cellular level. Separation of effects at the plasma and mitochondrial membranes.

Bovine epididymal spermatozoa incubated aerobically in vitro in the presence of 0.1 to 0.2 mM CaCl2 accumulate 25 to 50 nmol of calcium/10(8) cells. The addition of low concentrations of the ionophore A23187 (0.01 to 0.5 nmol/mg of sperm protein) induces efflux of this accumulated calcium. At high ionophore concentrations (0.5 to 5.0 nmol/mg of sperm protein), calcium release is followed by an influx of up to 25 nmol of calcium/10(8) cells that is not dependent on mitochondrial energization. A selective increase in the permeability of the sperm plasma membrane produced by treatment with the polyene antibiotic, filipin, results in the release of that calcium which is accumulated in the presence of high concentrations of A23187. Sperm first treated with filipin possess the ability to accumulate and retain calcium (in the presence of an oxidizable substrate) but release Ca2+ without subsequent reaccumulation after the addition of 3 nmol of A23187/mg of protein. These observations are explained by the existence of competing calcium pumps operating within the mitochondrial and plasma membranes of the spermatozoan. Treatment with high concentrations of A23187 allows calcium influx into a non-mitochondrial compartment of the sperm cell as a consequence of the equilibration of this cation across both mitochondrial and plasma membranes. The amount of calcium uptake and its sensitivity to filipin indicate that calcium binding to soluble, intracellular components is also involved. The ability of low concentrations of A23187 to induce calcium efflux is explained as a result of the continued operation of the plasma membrane pump coincident with ionophore-induced decay of the concentration gradient across the mitochondrial membrane. This hypothetical action of low levels of the ionophore on the mitochondria is supported by the observation of net movements of calcium with filipin-treated cells and the respiratory responses and movements of phosphate and membrane-associated calcium with intact sperm. It is suggested that the basis of this apparent selectivity of ionophore action lies in the relative activities and kinetic properties of the competing calcium pumps in the plasma and mitochondrial membranes of these cells. Ionophore-induced influx of calcium into the extramitochondrial space results in a stimulation of respiration and kinetic activity of the sperm. This activation of motility is observed also with cells made entirely dependent upon glycolysis (by treatment with respiratory inhibitors) and suggests a direct involvement of calcium in the regulation of flagellar function.

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