Effects of 2-Br- -ergocryptine on plasma prolactin level and milk yield in cows

Synthetic Alkaloid Treatment Influences the Intestinal Epithelium and Mesenteric Adipose Transcriptome in Holstein Steers

Holstein steers (n = 16) were used to determine if a synthetic alkaloid, bromocriptine, would alter the transcriptome of the small intestine and adjacent mesenteric adipose. On d 0, steers were assigned to one of two treatments: control (CON; saline only) or bromocriptine (BROMO; 0.1 mg/kg BW bromocriptine mesylate injected intramuscularly every 3 d for 30 d). Steers were slaughtered and midpoint sections of jejunal epithelium and associated mesenteric fat were collected for RNA isolation. Transcriptome analysis was completed via RNA-Seq to determine if BROMO differed compared with CON within intestinal epithelium or mesenteric adipose mRNA isolates. Differential expression thresholds were set at a significant P-value (P < 0.05) and a fold change ≥ 1.5. Only two genes were differentially expressed within the intestinal epithelium but there were 20 differentially expressed genes in the mesenteric adipose tissue (six up regulated and 14 down regulated). Functions related to cell movement, cell development, cell growth and proliferation, cell death, and overall cellular function and maintenance were the top five functional molecular categories influenced by BROMO treatment within the intestinal epithelium. The top molecular categories within mesenteric adipose were antigen presentation, protein synthesis, cell death, cell movement, and cell to cell signaling and interaction. In conclusion, BROMO treatment influenced the intestinal epithelium and mesenteric adipose transcriptome and identified genes and pathways influential to the effects associated with alkaloid exposure which are important to beef production.

Dopamine Agonists: From the 1970s to Today

The discovery of dopamine inhibitory effects on prolactin secretion has led to an era of successful dopaminergic therapy for prolactinomas. Herein we provide an overview of the evolution of dopamine agonists and their use in patients with PRL-secreting pituitary tumors, starting from the 1970s up to today, highlighting that normalization of PRL levels, restoration of eugonadism, and reduction of tumor mass can be achieved in the majority of patients by treatment with dopamine agonists.

Arterial Responses to Acute Low-Level Ergot Exposure in Hereford Cows

Ergot alkaloids are toxic secondary metabolites produced by the fungus Claviceps purpurea that contaminate cereal grains. Current Canadian standards allow 2 to 3 parts per million of ergot alkaloids in animal feed. The purpose of this study was to determine whether hemodynamic parameters were altered when beef cows were fed permissible levels of ergot alkaloids (i.e., <3 ppm) on a short-term basis. A dose-response relationship between ergot alkaloid concentration and hemodynamic changes in caudal (coccygeal), median sacral, and internal iliac arteries was hypothesized. Beef cows were randomly allocated to: Control (<15 μg total ergot alkaloids/kg dry matter), Low (132 μg/kg), Medium (529 μg/kg), and High (2115 μg/kg) groups (n = 4 per group). Animals were fed 8.8 kg of dry matter daily for 4 days (pre-treatment), 7 days (treatment), and 4 days (post-treatment). The caudal, median sacral, and internal iliac arteries were examined daily using ultrasonography in B-mode and Doppler (color and spectral) mode and hemodynamics endpoints were analyzed by repeated measures mixed model analyses. Caudal artery diameter decreased in the Medium (p = 0.004) and High (p < 0.001) groups compared to pre-treatment values and the pulsatility index increased (p ≤ 0.033) in all ergot treatments during the post-exposure period compared to the Control group. Blood volume per pulse (mL) and blood flow (mL/min) through the caudal artery during the treatment period were reduced in the Medium (-1.0 mL reduction; p ≤ 0.004) and High (-1.1 mL p ≤ 0.006) groups compared to pre-treatment values. The median sacral artery diameter decreased in the Medium (p = 0.006) and High (p = 0.017) treatments compared to the Control group. No differences were detected in any hemodynamic endpoints for the internal iliac artery except changes in pulse rate (p = 0.011). There was no treatment (p > 0.554) or Treatment^*Time interaction (p > 0.471) for plasma prolactin concentration or body temperature. In conclusion, alterations in caudal artery hemodynamics were detected when cows were fed 529 and 2115 μg ergot alkaloids per kg dry matter per day for 1 week. The caudal artery was more sensitive to ergot alkaloids than the median sacral and internal iliac arteries. Our results partially support the hypothesis of a dose-response effect of ergot alkaloids in feed on hemodynamics.

New developments on the galactopoietic role of prolactin in dairy ruminants

In most mammals, prolactin (PRL) is essential for maintaining lactation and its suppression strongly inhibits lactation. However, the involvement of PRL in the control of ruminant lactation is less clear because inconsistent effects on milk yield have been observed with short-term suppression of PRL by bromocriptine. By contrast, in vitro studies have provided evidence that PRL helps to maintain the differentiation state and act as a survival factor for mammary epithelial cells. Therefore, a series of experiments were conducted to assess the galactopoietic role of PRL. In a first experiment, daily injections of the PRL inhibitor quinagolide reduced milking-induced PRL release and induced a faster decline in milk production. Milk production was correlated with PRL released at milking. Quinagolide reduced mammary cell activity, survival, and proliferation. During the last week of treatments, differential milking (1× vs 2×) was applied. The inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the udder half milked 1×, suggesting that the response to PRL is modulated at the gland level. In a second experiment, cows were injected with quinagolide, quinagolide + injection of bovine PRL at milking time, or water. As in the first experiment, quinagolide reduced milk, protein, and lactose yields. Although PRL injections at milking time were not sufficient to restore milk yield, they tended to increase milk protein and lactose yields and increased the viability of milk-purified mammary epithelial cells. Recently, we investigated the use of quinagolide at drying off. Treating late-lactation cows with quinagolide decreased milk production within the first day of treatment and induced faster increases in somatic cells and bovine serum albumin content in mammary secretions after drying off, which indicates an acceleration of mammary gland involution. In conclusion, these data, combined with data from other studies, provide a good body of evidence indicating that PRL is galactopoietic in dairy cows. However, the response to PRL appears to be modulated at the mammary gland level.

Effect of the prolactin-release inhibitor quinagolide on lactating dairy cows

In most mammals, prolactin (PRL) is essential for maintaining lactation, and yet the short-term suppression of PRL during established lactation by bromocriptine has produced inconsistent effects on milk yield in cows and goats. To assess the effect of the long-term inhibition of PRL release in lactating dairy cows, 5 Holstein cows in early lactation received daily intramuscular injections of 1mg of the PRL-release inhibitor quinagolide for 9 wk. Four control cows received the vehicle (water) only. During the last week of the treatments, one udder half was milked once a day (1×) and the other twice a day (2×). Blood samples were harvested at milking in wk -1, 1, 4, and 8. The daily injections of quinagolide reduced milking-induced PRL release but not the basal PRL concentration. Quinagolide induced a faster decline in milk production, which was about 5.3 kg/d lower in the quinagolide-treated cows during the last 4 wk of treatment. During wk 9, the inhibition of milk production by quinagolide was maintained in the udder half that was milked 2× but not in the half milked 1×. Milk production was significantly correlated with the quantity of PRL released at milking. Quinagolide did not affect the release of oxytocin at milking. Serum concentration of insulin-like growth factor-1 was not affected by treatment or correlated with milk production. Serum concentrations of leptin and the calciotropic hormone stanniocalcin were not affected by the treatment. In conclusion, the chronic administration of the PRL-release inhibitor quinagolide decreases milk production in dairy cows. The effect is likely the result of the reduced release of milking-induced PRL and is modulated at the level of the gland by milking frequency.

Interactions of prolactin and growth hormone (GH) in the regulation of mammary gland function and epithelial cell survival

The relative importance of GH and prolactin in mammary gland function varies between species with prolactin playing a major role in rodents and GH taking lead role in ruminants. In rodents, however, GH appears to play a vital role in maintaining a high-fat/low volume milk in the absence of prolactin and a similar finding has been demonstrated in goats where prolactin deficiency causes a more modest (15%) decrease in milk yield. Surprisingly GH-deficiency in goats induced no further decline in milk yield whereas exogenous GH or prolactin both stimulated milk output considerably. Although direct effects of prolactin on mammary epithelial cells are well-documented effects of GH are believed to be mediated indirectly via IGF-1 production from the liver. We have been unable to confirm this hypothesis in rats and believe this to be because it is too simplistic. By considering prolactin and GH to be survival factors for the mammary gland we now propose a mechanism by which they interact through the IGF system. Involution of the mammary gland involves apoptosis and, in rats, it is induced by prolactin-deficiency or milk accumulation. Coincidentally with this process mammary epithelial cells synthesize and secrete and IGF binding protein, IGFBP-5. We hypothesize that GH stimulates IGF-1 production, possibly from the mammary parenchyma. IGF-1 then acts as a survival factor for the mammary gland. Prolactin plays an essential role since it suppresses the secretion of IGFBP-5 which would otherwise inhibit IGF-1 action and lead to the induction of cell death.

Animal models for the study of milk secretion

Milk secretion is regulated by a complex interaction of galactopoietic hormones which is not yet fully understood. Recent studies have demonstrated that this systemic control is modulated within the mammary gland by local mechanisms responsive to the frequency and completeness of milk removal. New insights into the endocrine and local (paracrine and autocrine) regulation of milk secretion have come from the adaptation of traditional endocrinological techniques to take advantage of new molecular tools, and from technical advances in other fields. This paper reviews recently developed animal models for the study of milk secretion and describes their application to provide new information into the roles of two key galactopoietic hormones, growth hormone and prolactin, and the modulation of their actions by local, intramammary mechanisms.

Effect of plane of nutrition before and during gestation on the concentration of hormones in dairy heifers

Forty heifers (1 yr of age; 313 +/- 27 kg of BW) were assigned to one of four treatments in a 2 x 2 factorial design. Main effects were plane of nutrition (ad libitum vs. moderate feeding) during the second isometric phase (1 yr of age to 3 mo of gestation) and during the second allometric phase (3 mo of gestation to 14 d before calving) of mammary development. Jugular blood samples were collected from 16 heifers before the onset of treatment, at the end of the isometric phase, and at the end of the allometric phase. Additional daily blood samples were collected from 32 heifers from 14 d before expected calving to 10 d postpartum and then thrice weekly until 70 d postpartum. High plane of nutrition reduced average growth hormone concentrations during the isometric and allometric phases. Serum concentrations of prolactin tended to be higher in heifers on ad libitum intake during the isometric phase and were higher during the allometric phase. Prolactin was positively correlated with BW and average daily gain during allometric phase. Plasma IGF-I concentrations were not affected by plane of nutrition. No effect was found for previous plane of nutrition on concentrations of growth hormone, prolactin, IGF-I, and progesterone during either prepartum or postpartum periods. Average postpartum IGF-I concentrations were negatively correlated with milk production. A positive relationship existed between mean postpartum concentrations of growth hormone and both peak milk production and feed intake during lactation.

Negative cooperativity in the prolactin-receptor interaction in the rabbit mammary gland: action of high prolactin concentration

The concentration of serum prolactin in the lactating mother is elevated by milking, and the dissociation of prolactin from the receptor is accelerated by the presence of prolactin in vitro. The interaction of prolactin at high concentrations with the receptor was examined using lactating rabbit mammary microsomes. At low concentrations of prolactin, the Scatchard plots were linear. At concentrations > 30 ng/ml, however, the slope of the Scatchard plot line changed. The Hill coefficient decreased from 1.09 to .77 or from .80 to .65 as prolactin concentrations increased. When a receptor preloaded with prolactin was utilized, prolactin at concentrations > 20 ng/ml associated with the receptor in a concentration-dependent manner. The Hill coefficient of this reaction was .70. The receptor remained intact for re-association after prolactin-induced dissociation. These data indicate that, because of the presence of negative cooperativity, prolactin at exceedingly high concentrations greatly accelerates the prolactin-binding reaction. The elevation of serum prolactin induced by milking may be important in the maintenance of active milk synthesis.

Bromocriptine treatment of periparturient goats: long-term suppression of prolactin and lack of effect on lactation

British Saanen dairy goats (n = 10) were treated with bromocriptine or vehicle from day 147 of pregnancy to day 4 post partum, a treatment duration of 8.8 +/- 1.7 d (mean +/- SEM). The periparturient prolactin surge was abolished by this treatment, but there were no significant effects on plasma growth hormone or insulin concentrations. Lactogenesis was delayed in the bromocriptine-treated goats, milk yields being significantly depressed (P < 0.01) for the first week of lactation. Yields had recovered to control values by day 10 when prolactin concentrations were still significantly depressed. Mammary gland biopsies were taken on day 4 post partum from five animals in each group. Using this tissue, no significant differences could be shown in mammary morphology or DNA synthesis, but the RNA:DNA ratio was significantly reduced (P < 0.05). After week 1, there were no significant differences between bromocriptine-treated and control goats in milk yield, milk composition, udder volume, time of peak yield or persistence. The goats given short-term bromocriptine treatment at parturition showed prolonged effects on prolactin secretion, their seasonal prolactin rise being severely blunted (P < 0.001). A normal lactation is therefore not prevented in goats by a delay in lactogenesis, suppression of prolactin at parturition or the resulting prolonged depression of circulating prolactin. Goats in established lactation given bromocriptine for 8 d showed, by contrast, a rapid recovery of plasma prolactin concentrations within 5 d post treatment. Milk yield declined significantly (P < 0.03) compared with pretreatment values during and for 1 week after bromocriptine but then began to recover, with no significant change in vehicle-treated goats.

Endocrine responses in cows milked by hand and machine

Plasma concentrations of oxytocin, prolactin, and cortisol were compared in five Swedish Red and White cows milked by hand versus machine. Cows were divided into two groups. One group was hand-milked; the other group was machine-milked. Treatments were switched every other day. The experiment was carried out for 6 d. Blood samples were taken prior to, during, and after milking and were assayed for hormones. More oxytocin and prolactin were released in hand-milked cows. There were no significant diurnal differences between the total amount of oxytocin released for the different treatments, but prolactin tended to be higher during hand-milking in the evening than in the morning milking. Cortisol concentrations were greater during hand-milking than during machine-milking. There were no significant treatment differences with regard to the total amount of cortisol released. During morning milking, cortisol concentrations were higher during hand-milking than during machine-milking. Our data show that hand-milking results in a pronounced and prolonged release of oxytocin and prolactin.

Effect of gestational mastectomy on postpartum gonadotropin releasing hormone and thyrotropin releasing hormone-induced luteinizing hormone and prolactin response in first lactation Holstein cattle

First lactation Holstein cows were divided into two treatment groups to evaluate thyrotropin releasing hormone (TRH, 0.25 microgram/kg body weight) and gonadotropin releasing hormone (GnRH; 200 micrograms) induced secretion of prolactin (PRL) and luteinizing hormone (LH) on days 7 and 16 postpartum. Disregarding treatment, LH response was greater (p less than 0.01) on day 16 than day 7 postpartum (7.5 +/- 0.3 ng/ml on day 7 vs 10.2 +/- 0.3 ng/ml serum on day 16). Mastectomized cattle had similar time for initiation of LH increase, but peak concentrations were achieved later. Peak PRL concentrations were reached 12 to 15 min after injection and returned to baseline within 2.5 h in both groups. However, intact cows had higher (p less than 0.01) mean serum PRL than the mastectomized cows for 1 h following injection. Peak PRL concentration was 83.3 +/- 17.6 ng/ml for mastectomized cows vs 128.0 +/- 24.7 ng/ml for intact cows. It appears that udder removal allows for greater pituitary responsiveness to GnRH but diminishes PRL response to TRH suggesting the mammary gland differentially affects pituitary secretion of LH and PRL.

Physiological responses to intramammary or intravenous treatment with endotoxin in lactating dairy cows

Twenty-one, middle to late lactation Holstein cows were assigned to one of three treatments in a completely randomized design to examine physiological changes associated with intramammary or intravenous administration of Escherichia coli endotoxin. Treatments were 1) Hank's balanced salt solution infusion in two contralateral quarters (control), 2) E. coli endotoxin infusion in two contralateral quarters, and 3) intravenous infusion of E. coli endotoxin. Blood was sampled and rectal temperature was measured at 30-min intervals. Endotoxin treatment was at 0900 h and sampling continued until 1700 h. Serum prolactin, cortisol, and 13,14-dihydro-15-keto-prostaglandin F2 alpha were measured. A pyretic response was observed in intravenous and intramammary treatment groups after endotoxin treatment. Response peak was higher (41.1 vs. 40.3 degrees C) and occurred later (6 vs. 4.5 h posttreatment) in the intramammary than the intravenous treatment group. Significant prolactin peaks were observed also in intravenous and intramammary endotoxin treatment groups. Prolactin peaked higher (288 vs. 112 ng/ml) and occurred sooner (1 vs. 4 h posttreatment) in the intravenous than in the intramammary treatment group. Cortisol followed a trend similar to prolactin. Cortisol peaked higher (100 vs. 82 ng/ml) and sooner (2.5 vs. 4.5 h posttreatment) in the intravenous than in the intramammary treatment group. Concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha increased rapidly posttreatment in the intravenous group only.

Approaches to the manipulation of mammary involution

Mammary involution is a gradual process that occurs following cessation of milking. Regression of mammary secretory tissue accompanies dramatic changes in secretion composition during the transition from lactation to involution. Conversely, rapid differentiation of secretory tissue and copious accumulation of colostrum occur as parturition approaches. The duration of the nonlactating period, mammary gland health, and secretory cell response to hormones influence subsequent lactational performance in most species. Manipulation of the bovine mammary gland in an attempt to hasten involution has been studied. The primary objective of these studies was to determine if hastened involution would decrease new intramammary infections during the early nonlactating period. Results of these studies have also led to a more fundamental understanding of events that occur during physiological transition of the mammary gland. Adequate regression, proliferation, and differentiation of mammary secretory epithelium during the nonlactating period of ruminants appear to be essential for maximal milk production during lactation. Factors that interfere with these mechanisms can adversely affect mammary function during the impending lactation. A greater understanding of these processes may provide new approaches for increasing milk production in dairy cattle.

Effects of abomasal or intravenous administration of arginine on milk production, milk composition, and concentrations of somatotropin and insulin in plasma of dairy cows

Holstein cows just past peak lactation were used in a 3 x 3 Latin square design to determine the effects of arginine infusion on concentrations of somatotropin and insulin in plasma, milk production, and milk composition. Treatments were: 1) control; 2) arginine injection into jugular vein, and 3) arginine infusion into abomasum. Concentrations of arginine and ornithine in plasma were increased by injection of arginine into the jugular vein compared with the control. The concentration of ornithine in plasma was increased shortly after injection of arginine into the jugular vein, and both arginine and ornithine concentrations in plasma decreased rapidly. Abomasal infusion of arginine significantly increased concentrations of arginine, ornithine, and urea in plasma compared with concentrations in the control treatment. Injection of arginine into the jugular vein increased concentrations of somatotropin and insulin in plasma, but the increase did not persist for more than 30 min. A secondary peak in plasma somatotropin concentration occurred approximately 1 h after the initial peak. Arginine infusion into the abomasum did not alter plasma concentrations of either somatotropin or insulin. Dry matter intake, milk production, and milk composition were not affected by treatments. Lack of changes in milk production and milk composition suggest that acute increases in somatotropin with concomitant increases in insulin are not sufficient to stimulate synthesis of milk and milk components by cows during established lactation.

Effect of exogenous prolactin administration on lactational performance of dairy cows

Eight Holstein cows were utilized to examine the effect of prolactin on lactational performance prior to peak milk production (day 21-34 postpartum) and after peak milk production (day 60-73 postpartum). During each 14 day period, cows received daily intramuscular injections of pituitary-derived bovine prolactin (120 mg; 13.0 IU/mg protein) or excipient. Cows were housed in a controlled environment at 18.1C, 47.8% relative humidity and a 15 hr light: 9 hr dark cycle. In cows administered exogenous prolactin, circulating prolactin concentrations increased within one-half hr post injection, peaked within 2 to 6 hours and declined through the remainder of the day. Average prolactin concentration in the plasma was increased 2 to 5 fold over the 24 hr period in response to prolactin treatment. Yields of milk and milk components (fat, lactose and protein) were not affected by prolactin treatment in either period but the concentration of alpha-lactalbumin in milk was significantly increased (P less than .10) in both periods. Circulating concentrations of somatotropin, triiodothyronine, thyroxine, glucagon, nonesterified fatty acids and glucose were not altered. In prolactin-treated cows, the milking-stimulated prolactin release was decreased at both the PM milking, when circulating concentrations of prolactin were high, and the AM milking, when prolactin concentrations had returned to baseline. Concentration of prolactin in milk tended to increase but was not significantly altered by administration of exogenous prolactin. However, prolactin concentrations in plasma were correlated (r = .56) with milk concentrations. It is clear that postpartum administration of exogenous prolactin during the period of lactation prior to peak milk yield or after peak milk yield does not alter lactational performance in high producing dairy cows.

Concentration of thyroid hormones and prolactin in dairy cattle serum and milk at three stages of lactation

Eighteen lactating Holstein cows were used with six each in early, mid, and late lactation. Blood samples were obtained on 7 successive d. Blood serum and milk were measured by radioimmunoassay for thyroxine, 3,5,3'-triiodothyronine, and 3,3',5'-triiodothyronine. Prolactin was also measured in serum by radioimmunoassay. Serum thyroxine increased as lactation progressed and milk production declined (50, 55, and 62 ng/ml). Serum concentrations of triiodothyronine and reverse triiodothyronine were unchanged throughout lactation. Prolactin in serum declined as lactation advanced linearly (14.4, 11.8, and 10.5 ng/ml). Concentrations of thyroxine and triiodothyronine in milk declined significantly between early and mid but not mid and late lactation. Reverse triiodothyronine in milk did not change over the lactation. Serum triiodothyronine contained 1200 to 1300 pg/ml, whereas that in milk was 200 to 300 pg/ml. Reverse triiodothyronine was over 300 pg/ml in serum and only 80 to 90 pg/ml in milk. Amounts of thyroxine and triiodothyronine available to offspring from milk were calculated to be minor sources (4 to 5%) of total requirements for maintenance of metabolic function.

Variation among species in the endocrine control of mammary growth and function: the roles of prolactin, growth hormone, and placental lactogen

Prolactin, growth hormone, and placental lactogen form a family of structurally related hormones, which may have evolved from a common ancestral peptide. Prolactin and growth hormone are present in all mammals, but the biological activity associated with placental lactogen has been detected in only some groups. Attempts to detect placental lactogen using bioassay and radioreceptor assay are reported and have been unsuccessful in an insectivore (the shrew), a bat, an edentate (the armadillo), a lagomorph (the rabbit), several carnivores (dog, cat, ferret), perissodactyls (horse, zebra, rhino), and, within the artiodactyls, pigs. Placental lactogenic activity has been detected in primates (chimpanzee, orangutan), rodents (voles, Pinon mouse, guinea-pig, mara), and in numerous artiodactyls (llama, giraffe, several species of deer, antelope, gnu, gazelle, musk ox, cape buffalo, Barbary sheep, several sheep of the genus Ovis, goat, and cow). These results confirm and extend the work of others and are discussed in relation to the evolution of these hormones. In synergism with steroid and thyroid hormones, protein hormones of the prolactin and growth hormone family play a crucial role in stimulating the development of the mammary gland, the differentiation and function of mammary cells to secrete milk, and in the systemic adjustments in maternal metabolism in pregnancy and lactation. Studies in vitro have shown that mammary tissues from several species synthesize milk components in response to insulin plus adrenal corticoid plus prolactin. However, there are also species differences in minimal hormonal requirements for lactogenesis. In vivo, for example, rabbits will initiate or sustain lactation in response to prolactin alone, whereas sheep and goats require prolactin plus growth hormone plus adrenal corticoid plus thyroid hormone. Measurement of hormone concentrations in the plasma of pregnant animals shows considerable differences among species in the pattern of secretion of lactogenic hormones to bring about mammary development. A surge of prolactin secretion occurs at parturition but may not be essential in the initiation of lactation. The timing of progesterone withdrawal correlates well with lactogenesis in eutherian mammals, but species differ in the mechanisms at parturition which bring this about. Marsupials show a quite different pattern of suckling-induced lactation. In maintaining lactation the greatest contrast is between ruminants, in which growth hormone is of particular importance, and other mammals, in which reduction of prolactin secretion with bromocriptine rapidly suppresses milk synthesis and secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Lactogenic hormones: binding sites, mammary growth, secretory cell differentiation, and milk biosynthesis in ruminants

Roles of the lactogenic hormones prolactin and placental lactogen in mammary development in ruminants were reviewed. In contrast with other ruminants, failure to detect lactogenic activity in the serum of pregnant cows (in excess of that attributed to prolactin) suggests that placental lactogen may have little direct effect on mammary growth or lactogenesis. However, replacement and ablation experiments using ergocryptine provide definitive evidence that increased periparturient secretion of prolactin is necessary for maximal milk production in cattle. Quantitative microscopy indicates a relative failure of mammary cells in cows with inhibited secretion of prolactin to differentiate structurally. Prolactin induces synthesis and secretion of alpha-lactalbumin in prepartum bovine mammary tissue. Temporary disruption of mammary microtubules immediately prepartum in pregnant heifers reduced subsequent milk production, biosynthetic capacity, and cellular differentiation. For maximal milk production, mammary secretory cells apparently must respond to lactogenic hormone stimulation during the immediate periparturient period. Colchicine may desensitize the mammary epithelium to prolactin action. Membrane binding of radiolabeled human growth hormone to ruminant mammary gland provides a measure of lactogenic hormone binding sites. Specific binding to 600 micrograms of mammary membrane protein was 296% greater in lactating, compared with nonlactating, pregnant (65 days of gestation) ewes. Binding capacity (fmol/mg membrane protein) averaged 275 +/- 57 in mammary membranes from nonlactating, pregnant ewes (100 days gestation, n = 2) and 2,325 +/- 521 in mammary membranes from lactating ewes (n = 6, 14 to 21 days postpartum). Greater understanding of hormonal regulation of the ruminant mammary gland likely will result in development of techniques to produce milk more efficiently and perhaps capability to evaluate production potential of young animals.

Seasonal patterns of circulating progesterone and prolactin and response to bromocriptine in the female tammar Macropus eugenii

Concentrations of prolactin and progesterone in the plasma of female tammars (Macropus eugenii) were measured during lactational quiescence and seasonal quiescence and during the period of natural resumption of reproduction after the summer solstice in December. Prolactin concentrations were consistently low (less than 40 ng/ml) during the period of declining day length and consistently elevated (greater than 40 ng/ml) during the period of increasing day length. Basal levels of progesterone were lowest (118.9 +/- 9.1 pg/ml) at the winter solstice and highest (244.1 +/- 21.0 pg/ml) at the summer solstice. Treatment with bromocriptine (CB154) did not depress prolactin levels at either time of the year but during February to June a single injection of 5 mg/kg body wt induced development of the quiescent corpus luteum (CL) and the diapausing embryo was reactivated. In February and March the level of progesterone increased in association with the developing CL, but after treatment at the winter solstice in June plasma progesterone did not increase although pregnancy was successfully completed. From September through November only 1 of 50 females responded to bromocriptine. None responded to bromocriptine given at the summer solstice in December, but all these animals spontaneously reactivated 2 weeks later. The difference in response of female tammars to bromocriptine treatment in the two halves of the year suggests that different endocrine controls operate in lactational and seasonal quiescence and that the latter is more complex.

Hormonal control of casein synthesis in organ culture of the bovine lactating mammary gland

Explants from lactating bovine mammary gland were cultured in vitro in serum-free medium though 1-9 d. casein synthesis was determined by [32P] incorporation into newly synthesized Ca rennin precipitable fraction. High correlation (r = 0.98) was found between incorporation of [32P] and [3H]amino acids in explants cultured under different hormonal regimes, thus indicating that post-translational phosphorylation is not a rate-limiting step in casein synthesis. Hormonal effects on casein synthesis were studied by supplementing the incubating medium with insulin (I), prolactin (PRL), cortisol (F), thyroxine (T4) and triiodothyronine (T3). It was found that both PRL and I were required absolutely for maximal synthesis and almost maximal effect was achieved with 50 ng/ml. The effect of F was less clear, but some increase was achieved at the 200-1000 ng/ml range. T4 and T3 did not affect casein synthesis at a range of 10(-11)-10(-7) M while a significant inhibition was observed at 2 X 10(-5) M. A time-course study of casein synthesis further substantiated the dominant role of PRL in maintenance or even elevation of the initial rate of casein synthesis in the explants, through the first 4 d of incubation.

The lactation-blocking drug bromocriptine and its application to studies of weaning and behavioral development

An experimental method for blocking maternal lactation is reviewed and the possible application of this technique for experimentally manipulating weaning is considered. Maternal milk production can be inhibited using the prolactin-suppressing drug bromocriptine. The suitability of bromocriptine for use in behavioural experiments is considered. The pharmacology of bromocriptine (CB 154) is briefly outlined and a compilation of the reported lactation-inhibiting doses for various species is presented. The possible endocrine and behavioral side-effects and the toxicity of the drug are discussed. It is concluded that, in most species studied so far, the drug is relatively free from significant side-effects at the low doses needed to suppress lactation. Guidelines for the practical use of bromocriptine are suggested. Finally, some ideas about the possible application of the drug to the study of behavioral development and parent-offspring relationships are discussed.

The prophylaxis of rat and mouse mammary gland tumorigenesis by suppression of prolactin secretion: a reappraisal

The purpose of this study was to evaluate the effect of early and temporal CB-154 induced suppression of prolactin secretion on the genesis of mammary tumors in female Sprague-Dawley rats treated i.g. with 3 doses of 7,12-dimethylbenzanthracene (DMBA); doses which yield a high (20 mg), moderate (5 mg) and low (1.25 mg) mammary carcinoma incidence. In addition, the effect of prolactin suppression on the genesis of mammary tumors in strains of rodents which, when treated with maximally tolerated doses of DMBA, develop a moderate (female Lewis rats) and a low (female Long-Evans rats and female Balb/c mice) mammary carcinoma incidence was also evaluated. Daily suppression of prolactin secretion during DMBA treatment (30 days before, during and 30 days after) (series 1) or commencing 30 days after DMBA treatment (for 60-81 days) (series 2) significantly (P less than 0.05) reduced the number of mammary carcinomas in Sprague-Dawley rats treated with 20 and 5 mg DMBA and in Lewis rats (series 2); treatment with CB-154 did not significantly lower mammary carcinoma incidence in Sprague-Dawley rats treated with 1.25 mg DMBA, nor in Lewis rats (series 1), Long-Evans rats and Balb/c mice. These results provide evidence that the effectiveness of prolactin suppression in the prophylaxis of chemical carcinogenesis of the rodent mammary gland is enhanced when a moderate or large dose of the carcinogen is used, or a strain of rodent is used which is moderately or highly susceptible to the mammary oncogenic effects of the carcinogen. Low doses of the carcinogen or use of a rodent strain relatively resistant to the carcinogen nullifies the chemopreventive activities of early prolactin suppression.

Role of prolactin in the transcription of beta-casein and 28-S ribosomal genes in the rabbit mammary gland

Isolated mammary nuclei were incubated in the presence of HgCTP and the neosynthesized RNA was isolated with a SH-Sepharose column. The concentration of beta-casein mRNA and 28-S ribosomal RNA in the neosynthesized RNA fractions was evaluated using [3H]DNA probes complementary to beta-casein mRNA and 28-S rRNA respectively. In the unstimulated pseudopregnant rabbit, the transcription of both genes was easily detectable. Injections of prolactin progressively enhanced the transcription rate of both genes and preferentially the beta-casein gene. A comparison between the transcription rates and the accumulation of the corresponding gene products in the cell revealed that there is a good correlation between these two parameters for the 28-S rRNA gene. By contrast, the acceleration of beta-casein gene transcription by prolactin is unable to account for the simultaneous accumulation of beta-casein mRNA, indicating that prolactin is a potent stabilizer of casein mRNA. Injections of CB154 into lactating rabbits (a drug which suppresses the secretion of prolactin by hypophysis), induced a rapid drop of beta-casein mRNA concentration and a slow decline of beta-casein gene transcription. Simultaneously the drug was responsible for a marked and rapid decrease of 28-S rRNA gene transcription, while the concentration of the rRNA remained elevated. During weaning the transcription of the beta-casein gene and, to a lower degree, the transcripton of the 28-S rRNA gene proceeded more slowly and this phenomenon was accompanied by a progressive decline of the RNA concentrations.

Partitioning of nutrients during pregnancy and lactation: a review of mechanisms involving homeostasis and homeorhesis

Control of metabolism during pregnancy and lactation involves two types of regulation-homeostasis and homeorhesis. Homeostasis control involves maintenance of physiological equilibrium or constancy of environmental conditions within the animal. Homeorhesis is the orchestrated or coordinated control in metabolism of body tissues necessary to support a physiological state. Regulation of nutrient partitioning during pregnancy involves homeorhetic controls arising from the conceptus. This assures growth of the conceptus (fetus and fetal membranes) and gravid uterus as well as development of the mammary gland. With the onset of lactation many--perhaps even most--maternal tissues undergo further adaptations to support rates of lipogenesis and lipolysis in adipose tissue are examples of important homeorhetic controls of nutrient partitioning that are necessary to supply mammary needs for milk synthesis. The interactions between homeorhesis and homeostasis during pregnancy and lactation and possible endocrine control are discussed. While not definitively established, roles for placental lactogen and prolactin are attractive possibilities in homeorhetic regulation of maternal tissues to support pregnancy and the initiation of lactaion, respectively.

Inhibition of mammary tumorigenesis in GR mice with 2-bromo-alpha-ergocryptine

A high incidence of mammary tumors is found in multiparous GR mice during the 2nd and 3rd pregnancies and in nulliparous GR mice treated with estrone/progesterone. The purpose of this study was to determine if prolactin is a contributing hormone in the genesis of these neoplasms. In one series of experiments, 238 15-week-old nulliparous GR mice were treated with estrone (drinking water, 0.5 mg/liter) plus progesterone (30 mg progesterone pellet with cholesterol, implanted SC once monthly) for a period of 13 weeks. Half of these mice were injected SC once daily with 100 micrograms of the prolactin-suppressing drug 2-bromo-alpha-ergocryptine (CB-154) for the duration of hormone treatment, and the other half were injected SC once daily with 0.9% NaCl solution (controls). In another series of experiments, 87 pregnant GR mice were divided into two groups and injected SC once daily from day 7 to 21 of pregnancy with 0.9% NaCl solution (controls) or CB-154 (100 micrograms/mouse). In the first series, the numbers of mice with mammary tumors and total number of mammary tumors were: controls, 58/119 (49%) and 73; CB-154 treatment, 34/119 (29%) and 37, respectively. In the second series, the numbers were: controls, 39/44 (89%) and 73; CB-154 treatment, 24/43 (56%) and 43, respectively. In both studies, CB-154 treatment significantly (p less than 0.05-0.005) reduced the percentage of mice with mammary tumors and total number of mammary tumors. These results provide evidence that prolactin is a contributing hormone in the genesis of estrone/progesterone and pregnancy-induced mammary tumors in female GR mice.

Endocrine control of energy metabolism in the cow: correlations of hormones and metabolites in high and low yielding cows for stages of lactation

Measures of hormones and metabolites in blood plasma of high and low yielding cattle matched for diet and stage of lactation were investigated for relationships between milk yield, body weight, and concentrations of hormones (prolactin, growth hormone, insulin, and thyroxine) and metabolites (glucose, nonesterified fatty acids, beta-hydroxybutyric acid, and L-lactic acid) for stages of lactation. A first approach correlated total milk yields of 15 cows with average constituents during the four 24-h blood samplings through the first 27 wk of lactation. The second examined associations of changes with sampling periods in milk yield or body weight with changes in hormones and metabolites. Total milk yield of the high yielding group was correlated positively with ratios of growth hormone/thyroxine and glucose/thyroxine and correlated negatively with thyroxine. Changes in growth hormone and its ratio to insulin, and changes in yield were correlated positively for groups combined. Changes in thyroxine were correlated negatively with changes in yield. Changes in liveweight gain were related positively to insulin and lactic acid and negatively with changes in growth hormone. Changes in growth hormone were related positively to changes in nonesterified fatty acids.

Investigations on the influence of prolactin suppression on reproductive function in bulls

In 3 mature bulls 2 injections (i.m.) of 150 mg 2-Br-alpha-ergocryptine (CB-154, Sandoz) within 48 hrs. decreased the plasma prolactin concentrations significantly for about 14 days (first experiment). In a second experiment, where treatment was repeated after 2 weeks, the period of maximal prolaction deficiency could be extended to a length of about 4 weeks. However, intensity of prolactin inhibition was less pronounced. This is attributed to seasonal factors. Neither during the shorter nor during the longer period of prolactin suppression were apparent changes of the LH and testosterone levels observed. Apart from a minor increase in the rate of morphologically abnormal sperm cells, reproductive function as libido, mating behaviour, semen quality, secretory activity of the accessory glands (concentration of fructose, GPC and chloride in seminal plasma and pre-sperm fraction resp.) were not significantly affected. It seems questionable, therefore, whether under physiological conditions prolactin is essential for the regulation of sexual functions in mature bulls.

17beta-oestradiol and Enovid mammary tumorigenesis in C3H/HeJ female mice: counteraction by concurrent 2-bromo-alpha-ergocryptine

Chronic administration of 17beta-oestradiol (via drinking water) or the oral contraceptive Enovid (norethynodrel and mestranol) (0-1 mg injected s.c. twice weekly) to nulliparous C3H/HeJ female mice, beginning at one month of age and terminating at 20 months (17beta-oestradiol) or 22 months (Enovid), significantly increased the incidence of mammary tumours over solvent-treated controls. Concurrent treatment of the steroid-treated mice with 2-bromo-alpha-ergocryptine (CB-154) (0-1 mg s.c. injected daily) significantly reduced mammary tumour incidence and mammary hyperplastic nodule development to the control level. CB-154 is an efficacious inhibitor of pituitary prolactin secretion. These results demonstrate that steroid-induced mammary gland dysplasias can be sharply reduced by chronic CB-154 treatment, and suggest that some of the mammary tumorigenic activities of oestrogenic steroids in C3H mice are mediated via an increased secretion of pituitary prolactin.