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Biomedical subjects

M Peaker

Publications and source records attributed to M Peaker.

At least 55 records · Page 3Linked to original sources
PubMed1984

The effects of colchicine and vincristine on the concentrations of glucose and related metabolites in goat's milk.

The effects of colchicine and vincristine on the concentration of glucose and its metabolites in milk were studied following intramammary injection of the alkaloids into one mammary gland of lactating goats. Both alkaloids decreased the rate of milk secretion from the treated gland and produced similar changes in the concentrations of various metabolites in milk. The concentrations of glucose, UDP-galactose, galactose, pyruvate and lactate increased, while those of glucose 6-phosphate and phosphoenolpyruvate decreased in milk from treated glands. The rate of milk secretion from the untreated gland increased, along with the concentrations of glucose in the milk. The changes in the concentrations of the metabolites in milk are discussed in relation to possible biochemical changes occurring in the mammary gland during the suppression of milk secretion by the alkaloids. It is suggested that, before alkaloid treatment, the rate of milk secretion was limited by intracellular glucose supply.

Animals↗
PubMed1984

Cyclic nucleotides in goats' milk: changes with physiological state.

Concentrations of cAMP and cGMP were measured in mammary secretions of goats. [cAMP] and [cGMP] increased during late pregnancy. At the onset of copious milk secretion, [cGMP] decreased while [cAMP] increased further. After the cessation of milking in late lactation, [cGMP] increased and [cAMP] tended to decrease. During withdrawal of food for 48 hr, the rate of milk secretion fell, [cGMP] increased and [cAMP] decreased; the changes were reversed on re-feeding. During temporary inhibition of milk secretion by intramammary treatment with colchicine, [cGMP] increased while [cAMP] decreased. It is concluded that cyclic nucleotide concentrations in milk change with physiological state.

Animals↗
PubMed1984

Milk yield in rats in relation to activity and size of the mammary secretory cell population.

An attempt was made to partition changes in milk yield during lactation in the rat between changes in the size of the secretory cell population and changes in cellular activity. Groups of rats were studied on d 2, 7, 14, 21 and 28 of lactation. Milk yield increased between d 2 and 7, less markedly between d 7 and 14 and decreased between d 14 and 21. Milk secretion had apparently ceased on d 28. Total mammary DNA (DNAt) and RNA (RNAt) increased from d 2 to 14. It is concluded that of the increase in milk yield between d 2 and 14, an increase in cell population accounted for 75% and an increase in cellular activity for 25%. A decrease in activity appeared to be entirely responsible for the decrease in yield between d 14 and 21.

Animals↗
PubMed1984

Effects of frequent milking on milk secretion and mammary blood flow in the goat.

When goats were milked every hour for 8 h without the use of exogenous oxytocin, milk ejection each hour appeared to be more complete than had previously been reported. Moreover, the rate of milk secretion increased by 15% over the period of hourly milking. There were no major changes in the composition of the aqueous phase of milk. Mammary blood flow was not apparently changed when goats were milked hourly: there was no significant effect of time of day (between 09.00 and 17.00 h) on blood flow. These results are discussed in relation to the mechanism by which frequent milking increases the rate of milk secretion.

Animals↗
PubMed1984

Mammary development and regression during lactation in goats in relation to milk secretion.

Mammary development was assessed in lactating goats using a combination of biopsy (for analysis of nucleic acids) and udder volumes (for determination of gross size). Single biopsies were shown to be highly representative of the composition of the whole gland provided that they were taken from carefully selected sites. Results indicated an increase in both milk yield and the size of the mammary cell population ( DNAt ) over the first three weeks of lactation. Yield, but not DNAt , continued to increase until peak lactation at around week eight. As milk yield fell between weeks eight and twenty-three the size of the cell population also decreased; beyond week twenty-three and until week thirty-six DNAt stabilized but yield continued to fall. It is concluded that the first part of the increase in milk yield during ascending (early) lactation in goats can be attributed to proliferation of secretory cells, but subsequently there is an increase in the amount produced by each cell. Likewise, declining lactation is initially characterized by a loss of cells, and yield per cell falls later.

Animals↗
PubMed1984

Feed-back control of milk secretion in the goat by a chemical in milk.

In order to investigate the nature of the inhibition of milk secretion during a long milking interval, goats were treated in three possible ways: (i) milked twice daily at 08.00 h and 16.00 h or (ii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, or (iii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, but at 00.00 h the milk removed was replaced with an equal volume of isosmotic sucrose solution. The latter treatment was carried out in order to subject the gland to a degree of physical distension equivalent to that on treatment (i). On either thrice-daily milking or thrice-daily milking with sucrose replacement, milk secretion rate over the 16.00-08.00 h period was significantly higher (by about 10% in both cases) than on twice-daily milking. Secretion rates of lactose, milk protein, citrate and calcium during the 00.00-08.00 h period were similar on either thrice-daily milking or thrice-daily milking with sucrose replacement; the secretion rate of fat was significantly higher on thrice-daily milking with sucrose replacement. Secretion rates of Na+, K+ and Cl- were significantly higher on thrice-daily milking with sucrose replacement. In the case of Na+, the increased Na+ secretion rate was sufficient to create a normal Na+ concentration in the milk/sucrose mixture removed at the next milking. In the cases of K+ and Cl-, their secretion rates were not sufficient to restore their concentrations to normal by the next milking.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Arterial plasma composition during compensatory increase in milk secretion in the goat: relation to rate limitation.

Colchicine was injected into one mammary gland of goats at peak lactation. Milk secretion in the treated gland decreased to 40% of the previous level while that in the other gland increased to reach 126% of its previous level. The concentrations of tyrosine and glucose in arterial plasma increased while those of lysine, arginine asparagine, glycine, alanine and ornithine decreased; the concentrations of other amino acids and of acetate did not change significantly. The results are discussed in relation to factors which normally limit the rate of milk secretion and to the mechanism by which compensatory increases occur in one gland during the inhibition of secretion in the other. These and previous results are not compatible with the view that arterial plasma concentrations of essential amino acids are rate-limiting for milk secretion.

Amino Acids↗
PubMed1983

Effect of decreased feed intake on the response of milk secretion to frequent milking in goats.

During declining lactation in goats, dietary intake was decreased and the animals switched from positive to negative energy balance. Milk yield and empty udder volume decreased. Goats on the reduced diet were milked hourly with the aid of oxytocin for 8 h. No stimulatory effect of hourly milking was observed. The results are discussed in relation to the factors which limit the rate of milk secretion in the declining phase of lactation.

Animals↗
PubMed1983

The effects of milking thrice instead of twice daily on milk secretion in the goat.

Milk yields of goats milked twice daily at 16/8 h intervals or 12/12 h intervals were equal. In goats normally milked twice daily at 16/8 h intervals, one mammary gland was milked thrice daily for one week while the other continued to be milked twice daily. This was done at 3, 7, 16, 24 and 33 weeks of lactation. Feeding level was maintained during these experiments. At every stage of lactation, thrice-daily milking increased milk yield (by about 8%). Stage of lactation had no effect on the size of the response. Yields of each gland increased by as much in an experiment involving thrice-daily milking both glands. Milk yield increased as soon as thrice-daily milking was started, and decreased towards normal values as soon as twice-daily milking was resumed. Milk composition during thrice-daily milking was unaffected with respect to concentrations of Na+, K+, Cl-, lactose, protein, fat and citrate. There was no change in milk yield of the gland which continued to be milked twice daily. The stimulatory effect was entirely local to the gland receiving the extra milking. Milk secretion rate during the 16 h period which included the extra milking was significantly higher during thrice-daily than during twice-daily milking; secretion rate during the rest of the day was unaffected. There were significant diurnal variations in secretion rate during thrice-daily milking such that the secretion rate during the 23.00-07.00 h period was highest and the secretion rate during the 07.00-15.00 h period was the lowest.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Compensatory increases in milk secretion in response to unilateral inhibition by colchicine during lactation in the goat.

1. Milk secretion in one mammary gland of goats was temporarily inhibited by intramammary treatment with colchicine at weeks 6, 12, 18, 24 and 30 of lactation. The magnitude of the inhibition was similar at all stages when compared with milk yield before the experiment. 2. The untreated gland partially compensated for the decreased rate of milk secretion by significantly increasing its own rate of secretion. There was no significant effect of stage of lactation on this response. 3. The rapidity of the compensatory response suggests that existing secretory cells increased their rate of secretion, and therefore that the mammary secretory cells are not secreting at their intrinsic maximum at any stage of lactation. 4. In later stages of lactation (weeks 18, 24 and 30) the increases in the untreated gland were more pronounced in afternoon milkings (8 h milking interval) than in morning milkings (16 h interval. At week 30 only, the rate of secretion before treatment was similarly lower in the 16 h period. It is proposed that an additional limitation is imposed on secretion during the relatively long period of milk accumulation as lactation advances and declines. 5. The results are discussed in relation to rate-limitations on milk secretion with respect to substrate supply and possible systemically active mammary factors.

Animals↗
PubMed1983

Mammary uptake and metabolism of progesterone in goats and its effect on milk progesterone concentrations during the oestrous cycle and early pregnancy.

Following the observation that the concentration of progesterone in goats' milk differs appreciably according to the specificity of the antiserum used in a non-extraction (direct) radioimmunoassay, experiments were carried out to find an explanation for these results. Milk and plasma samples were collected during the oestrous cycle and during an equivalent period of pregnancy after a fertile mating. Samples were analyzed by a direct radioimmunoassay using two antisera, 18/3 which is highly specific for progesterone and 465/6 which is less specific, and by radioimmunoassay of fractions isolated by thin-layer chromatography (TLC). Values obtained for milk and plasma samples collected during the oestrous cycle and early pregnancy were similar, except that values for milk samples measured with antiserum 465/6 were higher in pregnancy compared to those obtained during the oestrous cycle. Values obtained for milk and plasma with antiserum 465/6 were significantly higher than those obtained with 18/3 (P less than 0.001). After TLC this difference was found to be due principally to the presence of compound(s) with chromatographic properties identical to 5-pregnanedione(s). A comparison of the concentration measured in arterial and mammary venous plasma and in milk showed that about 25% of progesterone (5.7 nmol/min) was extracted by the mammary gland, and that substantial amounts of immunoreactive metabolites of progesterone are secreted into milk with only small quantities being transferred into mammary vein plasma.

Animals↗
PubMed1983

Effects of exogenous glucose on glucose metabolism in the lactating goat in vivo.

1. Glucose turnover in fed and 48 h-starved lactating goats was determined during a glucose load of 500 mumol/min using a continuous infusion of [U-14C]- and [3-3H]glucose. 2. Endogenous rates of irreversible glucose turnover (i.e. total rates of irreversible glucose turnover minus the rate of exogenous glucose supply) were depressed during glucose loading by 14 and 62% in the fed and starved animals respectively. 3. Plasma glucose concentrations increased significantly by 57 and 88% in the fed and starved goats respectively. Plasma insulin concentrations increased by 108 and 128% in the fed and starved animals respectively. 4. Milk yields increased significantly (41%) in the starved animals during glucose loading, but were unaffected in fed animals. 5. In both the fed and 48 h-starved goats, mammary glucose metabolism via glycolysis and the pentose phosphate pathway appeared to be stimulated by glucose loading.

Animals↗
PubMed1982

Blood flow and catecholamine concentration in bovine and caprine skin during thermal sweating.

1. Blood flow and the concentrations of noradrenaline, adrenaline and dopamine were determined in the skins of cattle and goats, before, at the onset of and 3 hr after commencement of sweating induced by heat exposure (40 degrees C). 2. The onset of sweating in both cattle and goats was associated with a rise in cutaneous blood flow, which was thus independent of sweat pattern. Cutaneous blood flow was also higher at 40 degrees C than at 15 degrees C. 3. The predominant catecholamine in the skin of both species was dopamine, which in the goat increased in concentration in the warm environment. 4. There was no clear evidence of a change in the amount of any of the cutaneous catecholamines during exposure to 40 degrees C, although there was a consistent tendency for the concentrations of adrenaline in the calf and noradrenaline in the goat, to fall during the onset of sweating.

Animals↗
PubMed1982

Effects of fasting during mid pregnancy or early lactation on mammary development and milk yield in mice.

Mice were fasted during pregnancy or early lactation and the effects on mammary development and milk yield studied on d 13 and d 18 of pregnancy and on d 7 of lactation. Fasting during pregnancy reduced body weight and mammary weight on d 13 of pregnancy but not on d 18. Mammary concentrations and total contents of DNA and RNA ([DNA], [RNA], DNAt, RNAt) were increased or unchanged on d 13 but significantly decreased on d 18. Fasting had no effect on fetal number or weight at either stage of pregnancy. Fasting on d 1 of lactation reduced mammary weight, DNAt and RNAt (but not [DNA] or [RNA]) and the incorporation of tritiated thymidine into DNA or d 2 of lactation. Mammary gland weight and composition on d 7 of lactation were not significantly affected by fasting for 24 h on d 1 of lactation or for 40 h on d 11-13 of pregnancy, except that DNAt was decreased slightly by the latter treatment. Milk yield (litter weight gain) was depressed markedly during fasting on d 1 of lactation, but thereafter recovered so that it was the same as controls between d 3 and 13 of lactation; after d 13 it fell once more. A 40 h fast on d 11-13 of pregnancy had no effect on milk yield. Thus, although normal mammary development was inhibited by starvation, the gland was subsequently able to compensate so that milk yield was not reduced.

Animals↗
PubMed1982

Glucose metabolism in vivo in fed and 48 h starved goats during pregnancy and lactation.

1. Glucose turnover (i.e. glucose entry and utilization rates) in fed and 48 h starved goats during pregnancy and lactation was determined using a continuous infusion of [U-14C)- and [3-3H]glucose. 2. Glucose synthesis and utilization increased during pregnancy and lactation in fed but not in starved goats. 3. Recycling of glucose-C was approximately 10% in fed animals and 15-20% in starved animals and was unaffected by the stage of pregnancy or lactation. 4. Plasma glucose concentrations were maintained during pregnancy and lactation in fed goats but decreased during 48 h starvation in pregnant goats. Little change was seen in the plasma concentration of lipids and their metabolites during pregnancy and lactation in fed goats, but increases were observed after 48 h starvation. 5. The control of glucose metabolism in ruminants during pregnancy and lactation is discussed.

Animals↗