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C J Wilde

Publications and source records attributed to C J Wilde.

86 records · Page 5Linked to original sources
PubMed1987

Mammary growth during lactation: implications for increasing milk yield.

Milk yield is greatly influenced by the size of the mammary secretory cell population. In rats, proliferation of cells during early lactation may account for as much as three-quarters of the increase in daily milk yield between parturition and peak lactation; the remainder is due to increased activity of existing cells. Conversely, in goats, all the initial decline in milk yield after peak lactation can be attributed to loss of secretory cells. Increased frequency of milking enhances milk yield and reduces secretory cell loss, whereas goats hemimastectomized at peak lactation undergo compensatory changes in the remaining gland, which include a complete maintenance of cell number for at least 18 wk. Cell proliferation is increased in both cases, showing that mammary growth can occur during established lactation. The significance of this observation is discussed in relation to ways in which the milk yield of dairy animals might be increased.

Animals↗
PubMed1986

Degradation of newly-synthesised casein in mammary explants from pregnant and lactating goats.

Casein degradation was measured by a pulse-chase method in explants from freshly-prepared from goat mammary tissue. An initial increase in L-[5-3H]proline radioactivity incorporated in casein during the chase period was followed in some conditions by a decrease resulting from intracellular degradation of the major casein polypeptides. Differences in the proportion of casein degraded in explants cultured with or without prolactin suggested that the process was under hormonal control. Greater degradation of casein by explants obtained in late pregnancy and early lactation suggested that the process may affect net casein production in vivo.

Animals↗
PubMed1986

Metabolic adaptations in goat mammary tissue during pregnancy and lactation.

Metabolic adaptations of goat mammary tissue during pregnancy and lactation were monitored in serial biopsies of the tissue. Changes in the synthetic capacity of secretory cells were studied by combining measurements of enzyme activities with short-term culture of mammary explants to measure lactose, casein and total protein synthesis. By these criteria, the main phase of mammary differentiation began in late pregnancy and was essentially complete by Week 5 of lactation, coinciding with the achievement of peak milk yield. While milk yield declined after Week 5, the activities of key enzymes expressed per mg DNA and the rates of lactose and casein synthesis in mammary explants were maintained over a considerable period. The results suggest that changes in the synthetic capacity of epithelial cells may account for much of the rise in milk yield in early lactation, but are not responsible for the declining phase of milk production characteristic of lactation in ruminants.

Acetyl-CoA Carboxylase↗
PubMed1984

Comparison of collagen gels and mammary extracellular matrix as substrata for study of terminal differentiation in rabbit mammary epithelial cells.

Mammary epithelial cells were prepared by collagenase digestion of tissue from mid-pregnant rabbits and cultured for up to 6 days on either collagen gels or an extracellular matrix prepared from the same tissue. The behaviour of the cells in serum-supplemented medium containing combinations of insulin, prolactin, hydrocortisone, estradiol and progesterone were monitored by measuring rates of casein synthesis, lactose synthesis, DNA synthesis and protein degradation. After 6 days, epithelial cells on floating collagen gels showed substantial increases in casein synthesis and DNA synthesis over freshly-prepared cells, following a decline during the first 3 days when the collagen gels are contracting. The optimum hormone combination for casein synthesis was insulin + prolactin + hydrocortisone, whereas for optimum DNA synthesis the additional presence of estradiol and progesterone was required. Cells on extracellular matrix showed increased rates of both casein synthesis and DNA synthesis by day 6 in the presence of insulin + prolactin + hydrocortisone, with additional estradiol + progesterone having an inhibitory effect. Whereas on day 2 rates of intracellular protein degradation were generally lower in cells on extracellular matrix, by day 6 rates of protein degradation were lowest in cells cultured on collagen gels with insulin + prolactin + hydrocortisone. In all cases, rates of lactose synthesis fell to low levels as the culture proceeded. Pulse-chase labelling of freshly-prepared cells with [32P]orthophosphate in medium containing serum and insulin + prolactin + hydrocortisone demonstrated that newly-synthesized casein was degraded during its passage through the epithelial cell. The influences of the collagen gels and extracellular matrix and of the hormone combinations on epithelial cell differentiation and secretory activity are discussed.

Animals↗
PubMed1982

Protein degradation in mammary gland explants. Evidence for limited heterogeneity of protein degradation rates.

Mammary gland explants in organ culture were subjected to hormonal manipulation, and rates of protein degradation during 1 and 2 day periods were measured by a double-isotope method. Isotope ratios for protein subunits in subcellular fractions were measured after resolution by two-dimensional polyacrylamide gel electrophoresis. Frequency distribution analysis shows that isotope ratios for each fraction are grouped predominantly in exponential distributions corresponding to populations of protein subunits with different mean degradation rates. The results also suggest that heterogeneity of protein degradation rates within each population is limited. There is no consistent correlation of degradation rate with protein isoelectric point or subunit molecular weight either overall or within any population of degradation rates. Therefore, the similarity of protein degradation rates within each population is clearly related to these molecular properties of the proteins.

Animals↗
PubMed1981

Characteristics of protein degradation in liver and mammary gland.

There is no correlation of protein degradation rate (measured by double isotope methods) with protein subunit molecular weight or isoelectric point in liver subcellular and suborganelle fractions and mammary cytosolic fractions. Most isotope ratios in each fraction fall in exponential distributions corresponding to populations of protein degradation rates; there is no statistically significant difference between protein degradation rates within several populations. The prime determinant for the degradation of proteins in these populations may be the morphological localization of the proteins. Pulse-chase labelling profiles indicate that a considerable proportion of newly-synthesised casein is rapidly degraded in mammary explants from mid-pregnant rabbits. This casein degradation is not co-translational; it appears to be a lysosomally-mediated event. In mammary tissue, the intracellular calcium concentration may acutely regulate synthesis and degradation of intracellular proteins, and the synthesis of casein.

Animals↗
PubMed1980

Protein degradation during terminal cytodifferentiation. Studies on mammary gland in organ culture.

1. In mammary gland explants subjected to experimental manipulation, average rates (during 24 h periods) of degradation of fatty acid synthase, casein and cytosol-fraction proteins were measured by a double-isotope method. Rates of degradation of fatty acid synthase were also computed from measurements of changing enzyme amount and rate of synthesis. 2. During the period of most rapid enzyme accumulation there is a transient decrease in the computed rate of degradation of fatty acid synthase. Removal of hormones produces a rapid increase in the computed rate of degradation of the enzyme. 3. The average rate of degradation of fatty acid synthase measured by the double-isotope method is low in the presence of hormones, and increases on hormone removal. This increase in degradation rate is inhibited by adrenaline and further blocked by insulin. NH4Cl (10 mM) also partially inhibits the increase in protein degradation on hormone removal. 4. The pattern of changes in the average rate of degradation of cytosol-fraction proteins is similar to that for fatty acid synthase alone. There is no relationship between subunit molecular weight and rate of degradation under all experimental conditions. 5. Isotope ratios for resolved cytosol protein mixtures are transformed logarithmically to make the standard deviations an estimate of heterogeneity of degradation rates. By this analysis, in some conditions there appears to be significant measureable heterogeneity of degradation rates. 6. Little degradation of casein is measured in the presence of hormones, but a marked increase in the rate of degradation can be measured when hormones are removed. Whereas at 24-48h NH4Cl (10 mM) has little effect on this enhanced rate of degradation, at 48-72h it causes a large decrease in degradation rate. 7. Results are discussed in terms of a two-component degradation system in mammary gland explants.

Animals↗
PubMed1980

Lactose synthesis: the possibilities of regulation.

Elucidation of the details of lactose synthesis, in particular its dependence upon alpha-lactalbumin and its location within the lumen of the Golgi apparatus, now allows one to ask useful questions pertaining to its regulation. Attention is directed towards galactosyltransferase itself (EC 2.4.1.22), which appears to be rate-limiting in the uridine nucleotide cycle that supports lactose synthesis, and to those factors that may affect its activity. In laboratory animals alpha-lactalbumin appears to be the major agent of regulation during lactogenesis but is not necessarily limiting at other times, whereas the increase in amount of galactosyltransferase seems largely to account for the rising yield of lactose during lactation. Studies with pinched-off Golgi membrane vesicles, together with measurements of intracellular chemical concentrations, suggest that beta-glucose and uridine diphosphategalactose do not saturate lactose synthesis and are, therefore potentially regulatory features of this process. Further aspects of lactose synthesis that may offer points of regulation include calcium ions, generation of protons within the Golgi lumen, and the generally rate-limiting nature of the Golgi membrane.

Animals↗
PubMed1979

Lactose synthesis in the rat, and the effects of litter size and malnutrition.

1. The rate of lactose synthesis per g of mammary tissue, measured in vivo by a radioisotopic technique, rose 13-fold between parturition and day 16 of lactation in the rat, but was unaffected by wide variation in litter size. 2. The increase reflected a greater tissue content of galactosyltransferase (EC 2.4.1.22), and was augmented by a rise in the total weight of mammary tissue. Superimposed on this were unpredictable changes in the functional efficiency of the enzyme. 3. Lactose synthesis in 14-day-lactating rats, permitted only 76% of the food intake of paired control rats over the previous 3 weeks, showed a pronounced diurnal variation at an overall rate markedly below that in control rats. 4. Such nutritional deficiency did not affect the tissue content of galactosyltransferase, but impaired its functional efficiency in a manner reversed by renewed feeding or by the preparation and incubation of acini in vitro. 5. Plasma insulin concentrations decreased at parturition and with increasing litter size, and remained relatively unchanged during lactation and malnutrition.

Animals↗
PubMed1979

Coordination of protein synthesis and degradation.

The degree of coordination between protein synthesis and protein degradation in developing and mature cels is considered. Studies on specific enzyme and general protein turnover in developing liver and differentiating mammary gland are presented. In the mature liver mitochondrion average protein degradation rates are higher for outer membrane and intermembrane space proteins than for matrix and inner membrane proteins. Significant heterogeneity of protein degradation rates was observed only in the outer mitochondrial membrane. During postnatal development the rates of degradation of proteins in many liver cellular fractions are increased. In the mitochondrion only the average rates of degradation of proteins in the outer membrane and intermembrane space fractions increase during development. Evidence for hormonally regulated changes in both protein synthesis and degradation during mammary cell differentiation is given. The data indicate that a transitory decrease in protein degradation accompanies the increase in protein synthesis on hormonal stimulation of the tissue. The results from the two model systems are collated and used to formulate a phenomenological hypothesis of protein degradation and its integration with protein synthesis in steady-state and non-steady-state conditions.

Animals↗