Originals Basic The Onset of Mammary Extraction of Plasma Triglycerides and Circulating Levels of Progesterone During Lactogenesis in the Cow and Goat G. E. Thompson Hannah Research Institute, Ayr, United Kingdom
In untreated cows and goats, the onset of mammary extraction of plasma triglyceride was sometimes detected several hours before parturition, prior to removal of secretion from the mammary glands by offspring and when circulating progesterone concentrations were low. In cows and goats that had secretion regularly removed from the mammary glands late in gestation, the onset of triglyceride extraction occurred up to several days before parturition, when circulating progesterone concentrations were moderately high (up to 3.9 ng/ml in the cow and 6.2 ng/ml in the goat). Key words Cow—Goat—Lactogenesis
Introduction The lactating mammary gland extracts triglyceride from the circulating blood plasma to support secretion of long-chain triglyceride fatty acids in milk (Annison, Linzell, Fazakerley and Nichols 1967). This extraction most likely depends on lipoprotein lipase activity at the luminal surface of the mammary capillary endothelium, and lipoprotein lipase activity in mammary tissue of cows is increased during lactation (Shirley, Emery, Convey and Oxender 1973). An early onset of lipoprotein lipase activity in mammary tissue of latepregnant rats has been brought about by injecting them with prostaglandin F2a, but this treatment simultaneously reduced plasma progesterone levels; replacement with exogenous progesterone during prostaglandin F20a treatment prevented the increase of lipoprotein lipase activity suggesting that it is normally brought about by falling progesterone levels in the circulation at parturition (Spooner, Garrison and Scow 1977). The onset of mammary extraction of plasma triglyceride occurs abruptly at parturition in the cow (Thompson 1989) and goat (Thompson, unpublished) and the experiments reported here examine the relationship between the onset of triglyceride extraction and circulating levels of endogenous progesterone in these animals. Regular manual removal of mammary secre-
Horm.metab.Res.23(1991) 101-103 © GeorgThieme Verlag Stuttgart-New York
tion before parturition can make the onset of secretion of longchain triglyceride fatty acids (Thompson 1988) and mammary extraction of triglyceride from the circulation (Thompson 1989) several days early and plasma progesterone levels have also been estimated during this treatment. Materials and Methods
Goats A total of 10 late-pregnant British Saanen goats were used. A group of 5 untreated animals had blood samples (approximately 5 ml) taken daily from a carotid artery, previously exteriorised in a skin loop, or from the right side of the heart, through a catheter previously inserted in a jugular vein, and from a subcutaneous abdominal ("milk") vein (Linzell 1960). Sampling, at approximately 10 am each day, began at least 5 days before parturition and ended 2 days after parturition. Another group of 5 goats had as much secretion as possible manually removed from the mammary glands daily, and blood samples taken, as above, beginning on day 143 of gestation and ending 2 days after parturition. In the last 2 days of experiments, kids sucked their dams. Cows A total of 10 late-pregnant Friesian cows were used. A group of 5 untreated animals had blood samples (approximately 10 ml) taken from the coccygeal artery and from a subcutaneous abdominal vein, at approximately 10 am, at intervals of 1 or 2 days beginning on day 266 of gestation and ending 2 days after parturition. Another group of 5 cows had as much secretion as possible removed from their mammary glands daily, beginning on day 266 of gestation, and blood samples taken as above. After parturition, in both groups, calves sucked their dams for about 12 hours then cows were milked twice daily by machine. Analyses Samples of blood plasma were stored at — 18 °C until analysed. The concentration of triglyceride in plasma was estimated using a fluorimetric method to measure the glycerol content before and after enzymatic hydrolysis (Gleeson and Maughan 1986); the initial dilution of the sample was adjusted to take account of the relatively low levels of triglyceride in ruminant plasma. The progesterone in plasma was extracted with petroleum ether and its concentration estimated by liquid-phase radioimmunoassay (Chard 1978) using an antiserum with cross-reactivities progesterone 100%, pregnenolone 5.6%, 11-deoxyCortisol, corticosterone, 11-deoxycorticosterone and Cortisol all < 2%. Received: 20 Apr. 1990
Accepted: 24 July 1990
Downloaded by: Universite Laval. Copyrighted material.
Summary
102 Horm. metab. Res. 23 (1991)
Statistics The significance of change in a series of measurements made over a period of time within a group of animals was estimated using analysis of variance (Snedecor and Cochran 1956). Results Goats In 5 untreated goats, the difference of triglyceride concentration between arterial (or mixed venous) and mammary venous plasma did not change in the period between 5 and 2 days before parturition (P > 0.05). In the period between 2 days before parturition and 2 days after parturition, the arterial-venous difference increased (P < 0.05) and the concentration of triglyceride in arterial plasma fell (P < 0.001). An increase of arterial-venous difference, with hypotriglyceridaemia, was apparent before parturition and sucking of the mammary glands by the offspring in 4 of the 5 goats when they were sampled at times ranging from 2 to 20 hours pre-partum. The mean changes of triglyceride concentration in the group are shown with mean changes of progesterone concentration in arterial plasma in Figure 1. Examination of values for individual animals showed that the prevailing concentrations of progesterone in arterial plasma at the time when increases of arterial-venous difference of triglyceride concentration were first apparent ranged from 0.3 to 2.2 ng/ml in individual goats. In 5 goats that had as much secretion as possible removed from the mammary glands daily beginning on day 143 of gestation, the increase of arterial-venous difference of triglyceride concentration first became apparent at times ranging from 8 days to 1 day before parturition, when arterial progesterone concentrations ranged from 0.4 to 6.2 ng/ml.
Fig. 2 Concentrations of triglyceride (TG) in arterial (A) and mammary venous (V) plasma, and concentrations of progesterone (P4) in arterial plasma of an individual cow that had as much secretion as possible removed from the mammary glands daily beginning on day 266 of gestation. P = day of parturition.
Cows In 5 untreated cows, the difference of triglyceride concentration between arterial and mammary venous plasma (P > 0.05) and arterial plasma triglyceride concentration (P > 0.05) did not change in the period between 5 days and 1 day before parturition. In the period between 1 day before parturition and 2 days after parturition, the arterialvenous difference increased (P < 0.05) and the concentration of triglyceride in arterial plasma fell (P < 0.001). In 2 animals that were fortuitously sampled approximately 2 and 4 hours before parturition, there was an obvious increase of arterialvenous difference of triglyceride concentration, and hypotriglyceridaemia, before the mammary glands were sucked by the calf. Arterial plasma progesterone concentrations ranged from 0.7 to 1.5 ng/ml at the time when the increase of arterial-venous triglyceride difference was first detected. In 5 cows that had as much secretion as possible removed from the mammary glands daily beginning on day 266 of gestation, an increased arterial-venous difference of triglyceride concentration first became apparent at times ranging from 4 days (Fig. 2) to 1 day before parturition. Arterial plasma progesterone concentrations ranged from 1.2 to 3.9 ng/ml at the time when the increase of arterial-venous difference was first detected. Discussion The changes of triglyceride concentration in arterial and mammary venous plasma observed in the present experiment confirm previous observations of an abrupt increase of mammary extraction of circulating triglycerides during lactogenesis (Thompson 1989). This phenomenon presumably reflects an onset of lipoprotein lipase activity at the mammary capillary endothelium. The results of concurrent measurements of circulating progesterone concentrations made on untreated cows and goats are consistent with the proposition that the onset of lipoprotein lipase activity is triggered by falling levels of progesterone in the circulation. However, this conclusion is contradicted by the observations on those cows and goats that had secretion regularly removed
Downloaded by: Universite Laval. Copyrighted material.
Fig. 1 Mean concentrations of triglyceride (TG) in arterial (A) and mammary venous (V) plasma in 5 untreated goats before and after parturition (P), and concurrent concentrations of progesterone (P4) in arterial plasma. Bars represent one standard error of the mean above and below the mean.
G. E. Thompson
Mammary Triglyceride
Horm. metab. Res. 23 (1991)
103
Linzell, J. L.: Mammary gland blood flow and oxygen, glucose and volatile fatty acid uptake in the conscious goat. J. Physiol. 153: 492-509(1960) Maule Walker, F. M., M. Peaker: Local production of prostaglandins in relation to mammary function at the onset of lactation in the goat. J. Physiol. 309:65-79 (1980) Peaker, M., C. J. Wilde: Milk secretion: autocrine control. News in Physiological Science 2:124-126 (1987) Shirley, J. E., R. S. Emery, E. M. Convey, W. D. Oxender: Enzymic changes in bovine adipose and mammary tissue; serum and mammary tissue hormonal changes with initiation of lactation. J. Dairy Sci. 56:569-574(1973) Acknowledgements Snedecor, G. W., W. G. Cochran: Statistical methods. Iowa State University Press, Ames, IA (1956) I thank Margaret McClelland and John Munro for Spooner, P. M., M. M. Garrison, R. O. Scow: Regulation of mammary their assistance. and adipose tissue lipoprotein lipase and blood triacylglycerol in rats during late pregnancy. J. Clin. Invest. 60:702-708 (1977) Thompson, G. E.: Mammary secretion of triglycerides in the cow preReferences partum. Comp. Biochem. Physiol. 90B: 163 -166 (1988) Annison, E. F., J. L. Linzell, S. Fazakerley, B. W. Nichols The oxidationThompson, G. E.: Mammary extraction of plasma triglycerides in the cow during lactogenesis. Comp. Biochem. Physiol. 94B: 411—413 and utilisation of palmitate, stearate, oleate and acetate by the (1989) mammary gland of the fed goat in relation to their overall metabolism and the role of plasma phospholipids and neutral lipids in milkfat synthesis. Biochem. J. 102:637-647 (1967) Chard, T.: An introduction to radioimmunoassay and related techRequests for reprints should be addressed to: niques. In Laboratory Techniques in Biochemistry and Molecular Biology; T. S. Work, E. Work, Ed. North Holland Publishing Dr. G. E. Thompson Company, Amsterdam/New York/Oxford (1978), pp. 301-531 Gleeson, M., R. J. Maughan: A simple enzymatic fluorimetric method Hannah Research Institute for the determination of triglycerides in 10 ul of serum. Clin. Chim. Ayr (United Kingdom) Actal56:97-104(1986)
Downloaded by: Universite Laval. Copyrighted material.
from the mammary glands before parturition: removal of secretion presumably removes an inhibitor of lactogenesis in the gland (Maule Walker and Peaker 1980; Peaker and Wilde 1987). It is not known how natural this stimulus is, because the onset of triglyceride extraction preceded sucking by the offspring in some untreated animals at least. Nevertheless, it is clear that the early onset of triglyceride extraction produced by removal of secretion was not inhibited by moderately high circulating progesterone levels.
In untreated cows and goats, the onset of mammary extraction of plasma triglyceride was sometimes detected several hours before parturition, prior to removal of secretion from the mammary glands by offspring and when circulating progesterone concentrations were low. In cows and goats that had secretion regularly removed from the mammary glands late in gestation, the onset of triglyceride extraction occurred up to several days before parturition, when circulating progesterone concentrations were moderately high (up to 3.9 ng/ml in the cow and 6.2 ng/ml in the goat). Key words Cow—Goat—Lactogenesis
Introduction The lactating mammary gland extracts triglyceride from the circulating blood plasma to support secretion of long-chain triglyceride fatty acids in milk (Annison, Linzell, Fazakerley and Nichols 1967). This extraction most likely depends on lipoprotein lipase activity at the luminal surface of the mammary capillary endothelium, and lipoprotein lipase activity in mammary tissue of cows is increased during lactation (Shirley, Emery, Convey and Oxender 1973). An early onset of lipoprotein lipase activity in mammary tissue of latepregnant rats has been brought about by injecting them with prostaglandin F2a, but this treatment simultaneously reduced plasma progesterone levels; replacement with exogenous progesterone during prostaglandin F20a treatment prevented the increase of lipoprotein lipase activity suggesting that it is normally brought about by falling progesterone levels in the circulation at parturition (Spooner, Garrison and Scow 1977). The onset of mammary extraction of plasma triglyceride occurs abruptly at parturition in the cow (Thompson 1989) and goat (Thompson, unpublished) and the experiments reported here examine the relationship between the onset of triglyceride extraction and circulating levels of endogenous progesterone in these animals. Regular manual removal of mammary secre-
Horm.metab.Res.23(1991) 101-103 © GeorgThieme Verlag Stuttgart-New York
tion before parturition can make the onset of secretion of longchain triglyceride fatty acids (Thompson 1988) and mammary extraction of triglyceride from the circulation (Thompson 1989) several days early and plasma progesterone levels have also been estimated during this treatment. Materials and Methods
Goats A total of 10 late-pregnant British Saanen goats were used. A group of 5 untreated animals had blood samples (approximately 5 ml) taken daily from a carotid artery, previously exteriorised in a skin loop, or from the right side of the heart, through a catheter previously inserted in a jugular vein, and from a subcutaneous abdominal ("milk") vein (Linzell 1960). Sampling, at approximately 10 am each day, began at least 5 days before parturition and ended 2 days after parturition. Another group of 5 goats had as much secretion as possible manually removed from the mammary glands daily, and blood samples taken, as above, beginning on day 143 of gestation and ending 2 days after parturition. In the last 2 days of experiments, kids sucked their dams. Cows A total of 10 late-pregnant Friesian cows were used. A group of 5 untreated animals had blood samples (approximately 10 ml) taken from the coccygeal artery and from a subcutaneous abdominal vein, at approximately 10 am, at intervals of 1 or 2 days beginning on day 266 of gestation and ending 2 days after parturition. Another group of 5 cows had as much secretion as possible removed from their mammary glands daily, beginning on day 266 of gestation, and blood samples taken as above. After parturition, in both groups, calves sucked their dams for about 12 hours then cows were milked twice daily by machine. Analyses Samples of blood plasma were stored at — 18 °C until analysed. The concentration of triglyceride in plasma was estimated using a fluorimetric method to measure the glycerol content before and after enzymatic hydrolysis (Gleeson and Maughan 1986); the initial dilution of the sample was adjusted to take account of the relatively low levels of triglyceride in ruminant plasma. The progesterone in plasma was extracted with petroleum ether and its concentration estimated by liquid-phase radioimmunoassay (Chard 1978) using an antiserum with cross-reactivities progesterone 100%, pregnenolone 5.6%, 11-deoxyCortisol, corticosterone, 11-deoxycorticosterone and Cortisol all < 2%. Received: 20 Apr. 1990
Accepted: 24 July 1990
Downloaded by: Universite Laval. Copyrighted material.
Summary
102 Horm. metab. Res. 23 (1991)
Statistics The significance of change in a series of measurements made over a period of time within a group of animals was estimated using analysis of variance (Snedecor and Cochran 1956). Results Goats In 5 untreated goats, the difference of triglyceride concentration between arterial (or mixed venous) and mammary venous plasma did not change in the period between 5 and 2 days before parturition (P > 0.05). In the period between 2 days before parturition and 2 days after parturition, the arterial-venous difference increased (P < 0.05) and the concentration of triglyceride in arterial plasma fell (P < 0.001). An increase of arterial-venous difference, with hypotriglyceridaemia, was apparent before parturition and sucking of the mammary glands by the offspring in 4 of the 5 goats when they were sampled at times ranging from 2 to 20 hours pre-partum. The mean changes of triglyceride concentration in the group are shown with mean changes of progesterone concentration in arterial plasma in Figure 1. Examination of values for individual animals showed that the prevailing concentrations of progesterone in arterial plasma at the time when increases of arterial-venous difference of triglyceride concentration were first apparent ranged from 0.3 to 2.2 ng/ml in individual goats. In 5 goats that had as much secretion as possible removed from the mammary glands daily beginning on day 143 of gestation, the increase of arterial-venous difference of triglyceride concentration first became apparent at times ranging from 8 days to 1 day before parturition, when arterial progesterone concentrations ranged from 0.4 to 6.2 ng/ml.
Fig. 2 Concentrations of triglyceride (TG) in arterial (A) and mammary venous (V) plasma, and concentrations of progesterone (P4) in arterial plasma of an individual cow that had as much secretion as possible removed from the mammary glands daily beginning on day 266 of gestation. P = day of parturition.
Cows In 5 untreated cows, the difference of triglyceride concentration between arterial and mammary venous plasma (P > 0.05) and arterial plasma triglyceride concentration (P > 0.05) did not change in the period between 5 days and 1 day before parturition. In the period between 1 day before parturition and 2 days after parturition, the arterialvenous difference increased (P < 0.05) and the concentration of triglyceride in arterial plasma fell (P < 0.001). In 2 animals that were fortuitously sampled approximately 2 and 4 hours before parturition, there was an obvious increase of arterialvenous difference of triglyceride concentration, and hypotriglyceridaemia, before the mammary glands were sucked by the calf. Arterial plasma progesterone concentrations ranged from 0.7 to 1.5 ng/ml at the time when the increase of arterial-venous triglyceride difference was first detected. In 5 cows that had as much secretion as possible removed from the mammary glands daily beginning on day 266 of gestation, an increased arterial-venous difference of triglyceride concentration first became apparent at times ranging from 4 days (Fig. 2) to 1 day before parturition. Arterial plasma progesterone concentrations ranged from 1.2 to 3.9 ng/ml at the time when the increase of arterial-venous difference was first detected. Discussion The changes of triglyceride concentration in arterial and mammary venous plasma observed in the present experiment confirm previous observations of an abrupt increase of mammary extraction of circulating triglycerides during lactogenesis (Thompson 1989). This phenomenon presumably reflects an onset of lipoprotein lipase activity at the mammary capillary endothelium. The results of concurrent measurements of circulating progesterone concentrations made on untreated cows and goats are consistent with the proposition that the onset of lipoprotein lipase activity is triggered by falling levels of progesterone in the circulation. However, this conclusion is contradicted by the observations on those cows and goats that had secretion regularly removed
Downloaded by: Universite Laval. Copyrighted material.
Fig. 1 Mean concentrations of triglyceride (TG) in arterial (A) and mammary venous (V) plasma in 5 untreated goats before and after parturition (P), and concurrent concentrations of progesterone (P4) in arterial plasma. Bars represent one standard error of the mean above and below the mean.
G. E. Thompson
Mammary Triglyceride
Horm. metab. Res. 23 (1991)
103
Linzell, J. L.: Mammary gland blood flow and oxygen, glucose and volatile fatty acid uptake in the conscious goat. J. Physiol. 153: 492-509(1960) Maule Walker, F. M., M. Peaker: Local production of prostaglandins in relation to mammary function at the onset of lactation in the goat. J. Physiol. 309:65-79 (1980) Peaker, M., C. J. Wilde: Milk secretion: autocrine control. News in Physiological Science 2:124-126 (1987) Shirley, J. E., R. S. Emery, E. M. Convey, W. D. Oxender: Enzymic changes in bovine adipose and mammary tissue; serum and mammary tissue hormonal changes with initiation of lactation. J. Dairy Sci. 56:569-574(1973) Acknowledgements Snedecor, G. W., W. G. Cochran: Statistical methods. Iowa State University Press, Ames, IA (1956) I thank Margaret McClelland and John Munro for Spooner, P. M., M. M. Garrison, R. O. Scow: Regulation of mammary their assistance. and adipose tissue lipoprotein lipase and blood triacylglycerol in rats during late pregnancy. J. Clin. Invest. 60:702-708 (1977) Thompson, G. E.: Mammary secretion of triglycerides in the cow preReferences partum. Comp. Biochem. Physiol. 90B: 163 -166 (1988) Annison, E. F., J. L. Linzell, S. Fazakerley, B. W. Nichols The oxidationThompson, G. E.: Mammary extraction of plasma triglycerides in the cow during lactogenesis. Comp. Biochem. Physiol. 94B: 411—413 and utilisation of palmitate, stearate, oleate and acetate by the (1989) mammary gland of the fed goat in relation to their overall metabolism and the role of plasma phospholipids and neutral lipids in milkfat synthesis. Biochem. J. 102:637-647 (1967) Chard, T.: An introduction to radioimmunoassay and related techRequests for reprints should be addressed to: niques. In Laboratory Techniques in Biochemistry and Molecular Biology; T. S. Work, E. Work, Ed. North Holland Publishing Dr. G. E. Thompson Company, Amsterdam/New York/Oxford (1978), pp. 301-531 Gleeson, M., R. J. Maughan: A simple enzymatic fluorimetric method Hannah Research Institute for the determination of triglycerides in 10 ul of serum. Clin. Chim. Ayr (United Kingdom) Actal56:97-104(1986)
Downloaded by: Universite Laval. Copyrighted material.
from the mammary glands before parturition: removal of secretion presumably removes an inhibitor of lactogenesis in the gland (Maule Walker and Peaker 1980; Peaker and Wilde 1987). It is not known how natural this stimulus is, because the onset of triglyceride extraction preceded sucking by the offspring in some untreated animals at least. Nevertheless, it is clear that the early onset of triglyceride extraction produced by removal of secretion was not inhibited by moderately high circulating progesterone levels.
