Suppression by perchlorate of technetium-99m and iodine-123 secretion in milk of lactating goats.

Lactating goats were infused with either technetium-99m (99mTc) or iodine-123 (123I) together with chlorine-36 (36Cl) through an indwelling catheter previously placed in an external pudic mammary artery. The radioisotope infusions were repeated together with 100 mg of sodium perchlorate. There was a rapid transfer of 99mTc and 123I into milk, reaching a peak concentration 30 min after a 15-min infusion. The fractional secretion of 99mTc and 123I in milk was reduced by 70%-80% and 60%-66%, respectively, by perchlorate. The fractional secretion of 36Cl was not affected by perchlorate, and the shape of the 36Cl secretion curve differed from those of 99mTc and 123I, which were similar. It is probable, therefore, that the latter nuclides were secreted by a transport route different from that of chloride. Available data describing the secretion of 99mTc in human milk after pertechnetate administration was reviewed, and it was concluded that perchlorate pretreatment significantly reduced the secretion of 99mTc in human breast milk.

Transport of oestrone sulphate by the mammary gland in the goat.

During pregnancy in goats the concentration of endogenous oestrone sulphate in milk increased more than twofold, and that in arterial and mammary venous plasma 10- and 20-fold respectively. The concentration in milk was higher than that in arterial plasma, particularly in lactating goats during mid-gestation. This was partly related to mammary production of oestrone sulphate (or of a closely related steroid which cross-reacted in the radioimmunoassay) since in tracer infusion studies the specific activity of oestrone sulphate in milk was significantly lower than that in arterial or mammary venous plasma. It was also related to the existence of a mechanism within the gland which concentrates oestrone sulphate in milk since when infused close-arterially into the mammary gland of a non-pregnant goat with undetectable levels of the endogenous compound in the circulation, a concentration ratio of 7.4:1.0 was reached for oestrone sulphate in milk:arterial plasma. Tracer kinetic studies showed that mammary extraction of [3H]oestrone sulphate was variable (up to 41.3 +/- 30.6%, mean +/- S.E.M.). During intravenous or close-arterial infusion, radioactivity in arterial and mammary venous plasma at steady state was mainly in the form of [3H]oestrone sulphate (range, 64 +/- 10.6 to 80.2 +/- 5.9% of total radioactivity in plasma). The remainder was in the form of compounds chromatographically similar to oestradiol-17 beta-3-monosulphate, oestradiol-17 alpha-3-monosulphate and unconjugated oestrogens. The distribution of radioactivity between these different steriods was similar in arterial mammary venous plasma indicating a low level of selective mammary metabolism or extraction. The amount of labelled oestrone sulphate transferred into milk was low, and it was significantly less in pregnant (range, 0.11 +/- 0.07 to 0.27 +/- 0.16% of total infusate) than in non-pregnant animals (3.23 +/- 0.50%). Studies of the rate of transfer of [3H]oestrone sulphate from blood to milk indicated the presence of a transcellular route with peak activity in milk occurring about 110 min after the start of the infusion.

Blood prolactin concentrations affect prolactin transfer into goat milk: implications for maintenance of lactation.

125I-Labelled ovine prolactin was infused for 15 min into a pudic artery supplying one mammary gland of lactating goats (n = 17). Between 0 and 4.25 h significantly more total (P < 0.01) and trichloroacetic acid (TCA)-precipitable (P < 0.001) radioactivity appeared in the milk of the infused compared with the non-infused gland. Gel chromatography and antibody precipitation indicated the presence of undegraded 125I-labelled prolactin in milk whey. Maximum transfer occurred 60-80 min after the end of infusion suggesting passage via a transcellular route. High plasma prolactin concentrations, resulting from infusion of cold prolactin with labelled prolactin in late lactation or from seasonally elevated prolactin at peak lactation, reduced the specific activity of infused prolactin and depressed the difference in secretion of 125I-labelled prolactin into milk of infused and non-infused glands. This suggests the operation of a competitive and saturable mechanism. Together with the increase in the milk to blood ratio of prolactin in goats given long-term (3 week) bromocriptine treatment, the results suggest that the goat mammary gland has a high avidity for prolactin especially when circulating prolactin is low. There was also evidence from TCA precipitation that prolactin may be protected from degradation in these circumstances. These mechanisms may contribute to the resistance of ruminant lactation to reduction in plasma prolactin and protect lactation from seasonal prolactin fluctuations.

The local differential effect of prostacyclin, prostaglandin E2 and prostaglandin F2 alpha on mammary blood flow of lactating goats.

Mammary blood flow (MBF) and milk yield are closely related in dairy ruminants, but little is known about the regulation of MBF in vivo. The local effects on MBF of injections or continuous infusions into the mammary artery of prostaglandins (PG) or indomethacin (an inhibitor of prostaglandins) respectively, were investigated in surgically prepared conscious goats. Prostacyclin (PGI2) was found to be a potent stimulator of MBF which increased linearly over the dose range 50-1000 ng. PGE2 was almost as potent as PGI2 at low doses, but tachyphylaxis occurred at doses at and above 100 ng. The response to repeated injections of PGE2 quickly declined depending on the dose. PGF2 alpha had no effect on MBF. During infusion of indomethacin into the mammary artery MBF was reduced markedly, showing that endogenous mammary prostaglandins are involved in the regulation of vasodilatation. The results indicate that PGI2 (and to a lesser extent PGE2) has an important role in the local regulation of vascular tone in the mammary gland.

The galactopoietic effect of bovine growth hormone in goats is associated with increased concentrations of insulin-like growth factor-I in milk and mammary tissue.

Lactating goats exhibiting widely divergent responses to short-term (4 days) treatment with bovine GH (bGH) were retrospectively divided into two groups based on the magnitude of this response. There was no difference between groups in terms of the pretreatment milk yield, but by day 4 of treatment milk secretion had increased by 4.99 +/- 2.5 (S.E.M.) ml/h (P greater than 0.05 compared with pretreatment) for group 1 and 22.9 +/- 2.4 ml/h (P less than 0.001) for group 2. Plasma GH increased in both groups, but concentrations were significantly higher both before and during treatment in group 1 compared with group 2. Plasma concentrations of insulin-like growth factor-I (IGF-I) increased significantly during bGH treatment for both groups and there was no significant difference between the two until day 4 of treatment when levels of IGF-I in group 1 began to decline, whereas those from group 2 were maintained. Concentrations of IGF-I in milk from goats in group 1 were not significantly altered by GH administration, whereas those in goats in group 2 were increased by 40% (P less than 0.01 compared with pretreatment). Levels of IGF-I in mammary secretory tissue from four animals from group 1 were not altered by bGH (2.8 +/- 0.2 and 2.77 +/- 0.08 nmol/kg tissue before and after treatment respectively), but were significantly (P less than 0.05) increased in four animals from group 2 (2.80 +/- 0.2 and 9.9 +/- 1.1 nmol/kg tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetics of transfer of 125I-labelled epidermal growth factor from blood into mammary secretions of goats.

125I-Labelled mouse epidermal growth factor (125I-EGF) was transferred intact and undegraded from circulating blood into milk in conscious lactating goats. Greater than 90% of the total radioactivity present in milk from the infused gland was in the aqueous phase and more than 72% was acid-precipitable. This radiolabelled material co-eluted with authentic EGF through gel filtration and was immunoprecipitable by a specific rabbit anti-mouse EGF immunoglobulin. Mammary uptake of 125I-EGF infused into mammary arterial blood (close-arterial infusion) for 1 h varied from 20 to 83% at different stages of the reproductive cycle. Only 0.5-2.9% of the infused 125I-EGF was transferred into milk during the first 3 h after the start of the infusion, which represents 0.7-6.3% of mammary uptake of EGF. The kinetics of transfer of 125I-EGF were followed in two lactating goats. Radioactivity reached peak levels in milk about 120 min after the start of a 1 h close-arterial infusion into the mammary gland, with an initial lag of about 30 min when little transfer occurred. Transfer was slower in two non-lactating goats with maximal levels of activity in milk being reached after about 180 min. The results are consistent with a transcellular transfer, whereby the factor is bound to receptors on the baso-lateral membrane, internalized by epithelial cells and subsequently secreted across the apical membrane into the alveolar lumen. The low level of degraded labelled EGF in milk (and mammary vein blood) suggests a modification of the normal pathway of EGF degradation such that the delivery of internalized factor to lysosomes is avoided.

Mechanism of secretion of plasma insulin-like growth factor-I into milk of lactating goats.

125I-Labelled insulin-like growth factor-I (IGF-I) was infused as the free form directly into the pudic artery supplying one gland of lactating goats (n = 6). The infusion was for 60 min and 0.4 +/- 0.09% (S.E.M.) of the infusate was secreted into milk from the infused gland during its first passage through that gland. A large proportion of the 125I-labelled IGF-I escaped into the systematic circulation and was secreted into milk of both glands. A total of 5.2 +/- 0.4% of infused radioactivity was recovered in milk from both glands from 0 to 720 min. Radioactivity consisted of trichloroacetic acid (TCA)-precipitable and -soluble counts which were shown by gel filtration to be authentic IGF-I and degraded products of the peptide. The amount and time course of TCA-soluble radioactivity in milk from both glands was similar, suggesting degradation of 125I-labelled IGF-I at extramammary sites. Maximum specific activity for 125I-labelled IGF-I in milk from the infused gland was reached 80-120 min after the start of infusion and was 2.5-fold greater than milk from the non-infused gland. The time course of appearance of 125I-labelled IGF-I in milk suggests that transfer was via the transcellular pathway and this was further supported by comparing the pattern of transfer of [14C]sucrose and [14C]amino acids. When excess unlabelled IGF-I was included in the infusate, specific activity in milk from the infused gland was reduced to that of the non-infused gland, indicating a competitive and saturable mechanism of secretion for 125I-labelled IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in milk secretion and mammary blood flow by intra-arterial infusion of insulin-like growth factor-I into the mammary gland of the goat.

The close-arterial infusion of free insulin-like growth factor-I (IGF-I; 1.1 nmol/min) for 6 h into the pudic artery supplying one mammary gland of lactating goats caused a 25 +/- 6% (mean +/- S.E.M., n = 6) increase in the rate of milk secretion of that gland. The increase in the rate of milk secretion in the adjacent noninfused gland (14 +/- 4%) was not significantly different from that observed during saline infusion (4 +/- 5%). Blood flow to the infused gland was increased from 378 +/- 26 ml/min 1 h before to 487 +/- 56 ml/min approximately 5 h after the start of the infusion of IGF-I, declining to 420 +/- 44 ml/min approximately 2 h after the end of the infusion. The total concentration of IGF-I (free and bound) in milk of the infused gland was significantly higher than that of the non-infused gland. The concentrations of IGF-I in carotid arterial plasma samples increased during IGF-I infusion from a mean value of 32 +/- 2 nmol/l before to a maximum of 49 +/- 3 nmol/l 5 h after the infusion commenced. Circulating concentrations of total IGF-I declined slowly after the infusion with an estimated half-life of 5 h. Infusion of saline alone did not alter mammary blood flow or the concentration of total IGF-I in milk or plasma. The results indicate that the infusion of free IGF-I into the mammary arterial supply enhances milk secretion and mammary blood flow in intact, conscious goats.(ABSTRACT TRUNCATED AT 250 WORDS)

Oestrogen metabolism in the endometrium, corpus luteum and ovarian residual tissue of the rabbit.

Reproductive tissues (uterine endometrium, corpus luteum and ovarian residual tissues) from pregnant and pseudopregnant rabbits were incubated with equimolar concentrations of [3H]oestrone and [3H]oestrone sulphate (0.375 pmol) to monitor the changes in oestrogen metabolism during the early stages of pregnancy (days 0, and 3-8 post coitum) and to investigate the embyonic effect upon maternal oestrogen metabolism. Oestradiol-17 beta was the major metabolite formed from oestrone and sulphoconjugation occurred in all tissues studied. Oestrone sulphate was converted primarily to oestradiol-17 beta-3-monosulphate. Endometrial 17 beta-oxidoreductase significantly decreased and sulphotransferase increased in activity during the preimplantation period, but no differences were noted between gravid and non-gravid horns in unilaterally pregnant animals, nor between pregnant or pseudopregnant animals. Significant decreases occurred in 17 beta-oxidoreductase and sulphotransferase activity in luteal tissue, but these were more than offset by increases in tissue weight. No differences in the activities in luteal tissues were detected between pregnant or pseudopregnant animals, nor between ovarian tissue adjacent to gravid or non-gravid uterine horns. The results show that significant changes occur in oestrogen metabolism in the rabbit endometrium and corpus luteum within 8 days after ovulation, and that these changes result from maternal factors expressed systemically rather than by the effects of the developing conceptus expressed locally.

Neurotransmitters and lymphatic-vascular transfer of prostaglandin F2 alpha stimulate ovarian oxytocin output in sheep.

The mechanisms of lymphatic-vascular transfer across the ovarian vascular pedicle were studied in anaesthetized sheep 8-15 days after ovulation. [3H]Prostaglandin F2 alpha (PGF2 alpha), [14C]mannitol and [36Cl]Na were infused continuously into either a uterine lymphatic or a uterine vein and the kinetics of transfer into the adjacent utero-ovarian vein or ovarian plasma were studied. Transfer occurred according to the sequence [36Cl] greater than [14C] greater than [3H] indicating that PGF2 alpha is not transferred by rapid diffusion, as with [36Cl]Na, nor by a paracellular route, as with [14C]mannitol, but by a slower process probably involving facilitated diffusion. Transfer into the adjacent utero-ovarian vein or ovarian blood was greater when compounds were infused into a uterine lymphatic than into a uterine vein. Substantially more [3H]PGF2 alpha occurred in the adjacent corpus luteum than either of the other compounds after a lymphatic infusion. Intra-lymphatic infusion of PGF2 alpha stimulated the release of ovarian oxytocin but the effect was not confined to the adjacent ovary. Intravenous (jugular) infusion of PGF2 alpha failed to stimulate ovarian oxytocin secretion whereas close-arterial infusion into the ovaries was effective, and the possibility was investigated that any systemic effect of PGF2 alpha was mediated through neural mechanisms. Noradrenaline and acetylcholine were both effective in causing the release of ovarian oxytocin when infused close-arterially into the ovary. With infusions of acetylcholine, ovarian oxytocin secretion rate was increased over fivefold without any change in posterior pituitary release. Noradrenaline and acetylcholine produced a concomitant fall in ovarian blood flow, and neurotransmitter-induced ischaemia may have played a role in ovarian oxytocin release. The finding that PGF2 alpha infused into a uterine lymphatic stimulates ovarian secretion of oxytocin, and that the effect is bilateral whereas PGF2 alpha accumulation in ovarian tissue is unilateral, implies that its mechanism of action may not be solely directed at the luteal cell.

Mammary uptake and excretion of prostanoids in relation to mammary blood flow and milk yield during pregnancy-lactation and somatotropin treatment in dairy goats.

Mammary arterious-venous differences (A-V) and excretion into milk of four prostanoids were related to changes in milk yield and milk vein blood velocity (MBV) in goats at different stages of pregnancy and lactation, and during somatotropin (ST) treatment in mid-lactation. Arterial concentrations and mammary A-V for the vasodilators prostacyclin (PGI(2)) and prostaglandin (PG) E(2) (measured as 6-keto-PGF(1 alpha) and bicyclic PGE(2), respectively) decreased from late pregnancy to lactation. A-V were negatively correlated to MBV (r = -0.32 to -0.34). Arterial concentrations of the vasoconstrictors PGF(2 alpha) and TXA(2) (measured as TXB(2)) changed similarly, but no A-V across the mammary gland were found. The vasodilator to vasoconstrictor ratio in plasma was around 1:1, and in skimmed milk around 0.29-0.49 due to significantly higher TXB(2) levels in milk compared to plasma. Close linear correlations were established between milk yield and excretion of TXB(2) into milk (r = 0.80, P < 0.001), and between MBV and PGE(2) excretion into milk (r = 0.69, P < 0.001). ST treatment stimulated MBV and mammary prostanoid supply, and decreased prostanoid concentration in milk vein plasma. The high arterial levels of prostaglandins during pregnancy most likely reflected uterine synthesis. Our results support a role for PGI(2) and PGE(2) in local mammary blood flow regulation during lactation. Increased mammary uptake of these two prostanoids may be involved in the mammary blood flow response to ST. TXA(2) may be synthesized by mammary epithelial as well as vascular cells, and TXA(2) may be an important factor in regulation of mammary function.

Mammary uptake of amino acids and glucose throughout lactation in Friesland sheep.

Changes in mammary blood flow, arterial and venous plasma concentrations of glucose and individual amino acids, udder volume, and milk yield and composition were measured at intervals throughout lactation in four Friesland ewes. Milk yields peaked 50-80 d post partum and declined by 40% within 3 months. Neither mammary blood flow (43.3 +/- 5.8 (s.e.m.) ml/100 cm3 X min) nor udder volume changed significantly throughout the period of study, but for three ewes the 'mammary blood flow: milk yield' ratio increased from 300 (peak yield) to 570 (late lactation). Mammary glucose uptake remained essentially constant throughout lactation despite a 50% decline in lactose output. Arterial concentrations of glucose were much lower at peak yield than in late lactation. Mammary amino acid uptake conformed quite closely to 'essential' and 'non essential' categories previously defined for goats and cows, the degree of balance with output in milk protein being similar at all stages of lactation. For several amino acids arterial concentrations and arteriovenous differences were significantly positively correlated: the changes in arterial concentrations with lactation stage were also correlated for some amino acids. Apart from the intrinsic value of such studies on a breed of ewe increasingly used for dairy purposes, the Friesland ewe appears well suited for use in quantitative metabolic studies on lactation.

Secretion of insulin-like growth factor II into milk.

125I-labeled insulin-like growth factor II (IGF-II) was infused directly into the pudic artery supplying one gland of lactating goats (n = 4). Maximum specific activity for [125I]IGF-II transferred into milk from the infused gland was reached 60 min after that in plasma and was 2.5 fold greater than in milk from the non-infused gland. Inclusion of either 67.5 nmoles unlabeled IGF-II or IGF-I had no influence on the amount or pattern of secretion of [125I]IGF-II into milk from either gland. While the temporal pattern of secretion of [125I]IGF-II into milk was consistent with a transcellular mechanism of transfer, the lack of competition by unlabeled IGF-II or IGF-I suggests a non-specific mechanism is operable, which contrasts to secretion of IGF-I.

Mammary function and its control at the cessation of lactation in the goat.

1. The changes in mammary function following cessation of milking during declining lactation have been studied in conscious goats. 2. No significant changes in the rate of milk secretion, mammary blood flow or metabolism occurred in the first 24 h after cessation of milking. After then, secretory rate, mammary blood flow, oxygen consumption, glucose uptake and acetate uptake decreased markedly over the next 3 days. Up to the time of maximum udder distension on day 3, there were no major changes in milk composition. 3. It was found that the rate of milk secretion declined when the calculated pressure within the alveoli became positive. 4. After 3 days, mammary volume and intramammary pressure decreased, and the composition of milk changed slowly to resemble that of extracellular fluid, i.e. [Na+], [Cl-], [HCO3-] and pH increased while [K+], [lactose] and [citrate] decreased. During this time [lactose] and [K+] were positively correlated, and [lactose] and [Na+], and [lactose] and [Cl-] negatively correlated. 5. It is suggested that the changes in milk composition, the decreases in mammary volume and in intramammary pressure after day 3 are due to the loss of integrity of the mammary epithelium. 6. By about 7 weeks after the cessation of milking the udder volume was less than the empty udder volume before milking was stopped, indicating a loss of mammary tissue as well as the resorption of fluid. 7. When milking of an autotransplanted gland was stopped, while milking of the control gland in situ was continued, the rate of secretion in the transplant fell while that of the control did not change. 8. In goats milked normally but in which a volume of isosmotic lactose equal to the volume of milk removed at that milking was injected into the lumen of one gland at each milking, the rate of secretion of that gland, but not that of the other, decreased.

Autotransplantation of the goat mammary gland.

The modified technique for transplanting one mammary gland of a lactating goat to the neck, with the mammary (pudic) artery and vein anastomosed to the carotid artery and jugular vein respectively, is described. This technique was successful in 6 operations and there were no significant differences between the milk yield of the transplanted and control (in situ) glands at any stage after operation. These results are compared with those from an earlier series in which no special provision was made for lymphatic drainage and in which anticoagulant therapy and treatment of the gland prior to attachment were not standardized.

Prostaglandin F-2 alpha is transferred from the uterus to the ovary in the sheep by lymphatic and blood vascular pathways.

[3H]Prostaglandin F-2 alpha (PGF-2 alpha) was infused into a uterine lymphatic vessel or a uterine vein for up to 1 h, or injected into the uterine lumen of anaesthetized non-pregnant sheep 7-15 days after oestrus. After an intraluminal injection, labelled PGF-2 alpha was recovered in uterine lymph and peak radioactivity was reached 50 min after injection. [3H]PGF-2 alpha infused at a constant rate into a uterine lymphatic vessel resulted in a maximum concentration of radioactivity in plasma which was 5.6- and 1.7-fold higher in the adjacent utero-ovarian and ovarian vein, respectively, than in carotid arterial plasma. Estimation of the amount of infusate transferred from a lymphatic into ovarian venous blood gave a value (0.4%) similar to that for transfer from a uterine vein (0.3%). Evidence for local transfer was substantiated by the presence of significantly higher concentrations of 3H-labelled compounds in the ovary and corpus luteum adjacent to the site of intra-lymphatic infusion compared with those in the opposite organs. The concentrations in the adjacent ovary and corpus luteum were significantly greater when an intra-lymphatic rather than intra-uterine vein infusion was adopted. The results show that [3H]PGF-2 alpha is transferred locally from uterine lymphatic vessels into the adjacent ovary, corpus luteum and ovarian vein.

Transfer of insulin-like growth factors I and II from plasma to lymph in young goats.

The plasma clearance of intravenously injected 125I-labelled insulin-like growth factor I (IGF-I, n = 13) and IGF-II (n = 12) and their transfer into lymph draining the foreleg of 3.5- to 8-week-old British Saanen goats was studied. Both peptides were initially distributed into a volume equivalent to the plasma volume, while the final distribution spaces for IGF-I and IGF-II were 90 +/- 9.8 and 125 +/- 12 ml/kg live weight respectively. There were two phases to the plasma clearance of both IGF-I and IGF-II, with the half-lives of both phases for IGF-I (9.6 +/- 0.9 and 287 +/- 23 min, first and second phase respectively) being significantly (P less than 0.001) longer than those of IGF-II (4.2 +/- 0.6 and 172 +/- 18 min, respectively). The radioactivity transferred into lymph originated from intact IGF-I and IGF-II as well as degraded products of these compounds, as assessed by precipitation with trichloroacetic acid and gel filtration. Levels of undegraded IGF-I in lymph were 50% greater than IGF-II. While more than 90% of either peptide was bound to specific IGF-binding proteins in plasma, in lymph 34 +/- 2% of IGF-I and 23 +/- 3% of IGF-II remained in the free form 60-80 min after injection. The plasma: lymph ratio for free IGF-I was 2:1 and for bound IGF-I, 8:1. The corresponding values for IGF-II were 3:2 and 8:1 respectively. These results provide direct experimental evidence for transfer of undegraded IGF-I and IGF-II from blood into lymph of the foreleg, consistent with the ability of these factors to act in an endocrine role in growing tissues. Differences between plasma clearance and transfer of IGF-II into lymph compared with IGF-I may be due to its greater cellular uptake and/or degradation in vivo.

Increased secretion of insulin-like growth factor I into milk of cows treated with recombinantly derived bovine growth hormone.

Six lactating, non-pregnant Jersey cows were given subcutaneous injections of recombinantly derived bovine growth hormone for 7 d. Milk yield was increased by 4.5 kg/d on d 7, compared with the average yield of 10.7 +/- 0.4 kg/d (mean +/- s.e.m.) for the 7 d preceding treatment. Concentrations of insulin-like growth factor I (IGF-I) in the milk increased from 0.44 +/- 0.04 nmol/l (mean +/- s.e.m.) during the 7 d preceding treatment to 1.6 +/- 0.2 nmol/l on d 7 of treatment. Taking the increase in milk yield into account the total increase in the secretion of IGF-I into milk of one udder half was 6-fold. Plasma concentrations of total IGF-I rose from 15.5 +/- 1.3 nmol/l (mean +/- s.e.m.) on the day preceding treatment to 56.9 +/- 3.6 nmol/l (mean +/- s.e.m.) on d 7 of treatment. Mammary plasma flow increased from 1.6 +/- 0.09 to 2.2 +/- 0.06 l/min.udder half over the same time. Estimates of the amount of IGF-I that reached the mammary gland gave values of 24 and 116 nmol/min.udder half before and during treatment respectively. IGF-I in milk of treated cows was associated predominantly with proteins ranging from 40,000 to 150,000 mol.wt, but a significant proportion (19%) of the total IGF-I was present in the free unbound form. IGF-I crosslinking studies revealed the presence in milk of one specifically labelled band at 31,000 mol.wt.

Protein synthesis and degradation in the mammary gland of lactating goats.

Lactating goats were given a close arterial infusion of [1-14C]leucine and [4,5-3H]4-methyl-2-oxopentanoic acid into one half of the mammary gland at 2-3 weeks and 34-39 weeks after kidding. Rates of protein synthesis, degradation and net output were determined from measurements of arteriovenous difference and blood flow using a model of leucine metabolism previously developed for muscle (Oddy & Lindsay, 1986). Protein leucine output in milk (Y mumol/min) correlated well with the difference between synthesis and degradation (X mumol/min) derived from the model: Y = 1.30 + 1.24X (r2 = 0.9; n = 9, P less than 0.01). There was substantial synthesis and degradation of protein within the mammary gland. Although only an approximate value could be obtained for the partitioning of protein synthesis and degradation between tissue and milk proteins, there was evidence of appreciable turnover of both. There was no significant difference between mammary leucine and protein metabolism in early and late lactation other than that imparted by a greater mass of mammary tissue in early lactation, although there was a tendency for greater oxidation of leucine in late lactation.

Residual milk in Friesland sheep and the galactopoietic effect associated with oxytocin treatment.

Mature lactating Friesland ewes had a mean lactation yield of 293 +/- 26 kg during a lactation period of 35 +/- 2 weeks giving an average daily milk yield of 1.2 kg/d. Ewes were injected intravenously after normal milking with either saline (sham) or oxytocin and then remilked to determine the volume of residual (alveolar) milk. After a long milking interval of 16 h oxytocin treatment gave a significantly greater total daily milk yield than the sham treatment (oxytocin minus saline, morning milking, 0.199 +/- 0.038 kg, mean +/- s.e.m., P less than 0.01) Oxytocin had a small significant reverse effect after a short milking interval of 8 h (afternoon milking, -0.065 +/- 0.022 kg, P less than 0.05). The average increase in total daily yield over four stages of lactation was 0.133 +/- 0.029 kg (P less than 0.01), or 11% of the average daily milk yield. The galactopoietic effect of oxytocin was associated with the efficient removal of residual (alveolar) milk. Residual milk accounted for 7.4 and 27.2% of the total daily milk yield in ewes treated with saline or oxytocin respectively. Residual milk expressed as a proportion of daily total milk yield remained steady in ewes studied between April and July, but declined in September when yields were less than 1 kg/d.