Th.--Méd.--Nancy 1, 1983. N°: 227.

Th.--Méd.--Reims, 1981. N°: 51.

Thesis (doctoral)--Rijksuniversiteit te Utrecht.

A series of trials was carried out to examine the role of prolactin (PRL) in the control of lactogenesis in New Zealand Romney x Border Leicester ewes. In addition, a study was made of differences in milk yields and plasma PRL concentrations between spring- and autumn-lambing ewes.Daily subcutaneous injections of 2 mg CB154 inhibited PRL secretion and delayed lactogenesis. There were no consistent effects on plasma progesterone or insulin concentrations. CB154 treatment was more effective in reducing milk yield in twin-bearing than in single-bearing ewes when used for 20 days than for 9 days prepartum. The differential effects on milk yield cannot be explained by corresponding effects on plasma PRL or insulin concentrations. Circulating PRL during the period 20 to 10 days prepartum may have an important effect on milk yield in twin- but not single-bearing ewes.Subcutaneous injections of 0.5 mg/kg live weight oPRL, administered on 2 consecutive days peripartum, to ewes treated with CB154 for 7 days prepartum, resulted in milk yields similar to those in control ewes and significantly (P<0.01) greater than those in ewes treated with CB154 alone. This indicated that oPRL prevented the CB154-induced reduction of milk yields and has established that the effect of CB154 on lactogenesis is mediated through suppression of PRL secretion and not by effects on some other hormone.Injection of 10 mg oPRL directly into one mammary gland (via the teat duct) increased milk yields relative to the contralateral, bicarbonate-treated gland in CB154-treated ewes. The intramammary oPRL injection did not raise circulating PRL concentrations. Furthermore, the milk yields of bicarbonate-treated glands in ewes treated with bicarbonate only, did not differ from those of bicarbonate-treated glands in ewes treated with oPRL in the contralateral gland, demonstrating that there were no effects of oPRL, transferred via the circulation from the treated gland, on the contralateral gland. Glands treated with oPRL produced 15% (P<0.05) more milk than the bicarbonate-treated glands during the first 8 days of lactation and the difference was maintained throughout the 8-week lactation period, indicating that the oPRL had effected a permanent change in the ability of the gland to produce milk. It is concluded that PRL acts directly on the mammary gland without the need for a putative intermediate hormone, and that intramammary PRL concentrations during lactogenesis may have long-lasting effects on lactation.The possibility was examined that dietary differences were responsible for seasonal differences in plasma PRL concentrations, milk yields, milk composition, lamb birthweight and lamb growth rate, observed in earlier trials. Mean plasma PRL levels were significantly (P<0.01) higher in spring- (192±38 ng/ml) than in autumn- (71±17 ng/ml) lambing ewes housed indoors under constant photoperiod (18L:6D) and fed the same diet. Milk yields were also significantly (P<0.05) higher in the spring- (2041±114 g/d) than in the autumn- (1563±109 g/d) lambing ewes over the 8 day lactation. Lamb growth rates (adjusted for birthweight, birthrank and sex of lamb) from birth to 8 weeks of age were significantly (P<0.001) higher in spring (282±12 g/d) than in autumn (225±15 g/d). The seasonal differences were confounded with corresponding differences in ewe live weight and it was not possible to determine whether dietary differences contributed significantly to the differences observed.Two routes of oPRL supplementation were used to test the effectiveness of elevating peripheral or local levels of PRL in autumn-lambing ewes which, based on previous results, were expected to have low plasma PRL concentrations and milk yields relative to spring-lambing ewes. Administration of 10 mg supplementary oPRL directly into the gland or subcutaneous injection of 0.5 mg/kg oPRL did not increase the milk yields, or change the composition of milk, compared to controls. These results suggest that the circulating level of PRL, and the intramammary concentration of PRL, in autumn-lambing ewes are not limiting lactogenesis. Because the plasma prolactin concentration in the ewes was unexpectedly high, it was not possible to reach firm conclusions regarding possible effects of supplementary oPRL in ewes with naturally low plasma PRL concentrations. Nevertheless, the results indicate that raising the intramammary concentration of PRL around the time of parturition, in ewes with circulating PRL levels characteristic of normal spring-lambing ewes, does not enhance lactogenesis.It is concluded that PRL is important to the complete initiation of lactogenesis in ewes, that it acts directly on the gland and that it is necessary for establishing the maximum potential of the gland to secrete milk.

Consumption of endophyte-infected (E+) grasses has long been associated with health problems in animals. In cattle E+ tall fescue consumption leads to fescue toxicosis, and in horses it leads reproductive problems. The health-related issues associated with endophyte consumption have been attributed to the effects caused by the ergot alkaloids produced by the fungus. These ergot alkaloids are considered D2-like receptor agonists, and 5-HT2 serotonin and α-adrenergic receptor partial agonists. Many studies in humans, swine, cattle, and horses have identified that ergopeptines cause a decrease in prolactin production due to their dopaminergic activities. Additionally, these molecules have been found to cause vasoconstriction in cattle and horses through their other agonistic activities. Furthermore, dopamine agonists are currently being used to treat pituitary pars intermedia dysfunction (PPID) in horses, a condition in which the horse lacks sufficient dopamine. However, the ergot alkaloids found in E+ tall fescue had not previously been investigated for their potential benefits in treating PPID horses. Moreover, little research has investigated the effects of ergot alkaloids and dopamine agonists on the immune system of horses, even though many health problems associated with E+ tall fescue consumption suggest there to be an elicited inflammatory response. Thus, the primary objective of this study was to establish an understanding of immune and hormone responses to ergot alkaloids and dopamine agonists in the horse. The hypothesis of this body of research was that ergot alkaloids and bromocriptine both would elicit inflammatory and hormone responses in the horse. Specifically, this research was conducted to determine the effects of E+ tall fescue seed consumption on immune, hormone, and vasoconstrictive responses, in both non-PPID and PPID horses. In addition, both the in vitro and in vivo effects of bromocriptine on cytokine production from equine peripheral blood mononuclear cells (PBMCs) were investigated. In the first study, there were no significant changes in body morphometrics, vasoconstriction, hormone responses or cytokine expression due to the consumption of ergot alkaloids in non-PPID and PPID horses. The second study was an in vitrostudy in which PBMCs were exposed to varying concentrations of either bromocriptine, a D2-like receptor agonist that is used as a model for ergot alkaloid consumption, or dopamine. This experiment demonstrated that exposure to dopamine or a dopamine agonist at a concentration greater than 10-5M is toxic to PBMCs, and that bromocriptine elicits an anti-inflammatory effect at concentrations less than 10-5M. Concentrations of dopamine less than 10-5M, on the other hand, did not cause any significant changes in cytokine expression. A third study was conducted that evaluated the effects of an intravenous injection of bromocriptine on hormone and immune responses in the aged mare. This study identified that bromocriptine maximally reduced prolactin levels 12 hours post-injection and prolactin returned to baseline levels approximately 56 hours post-injection. Additionally, only a significant increase in IL-1β was detected 12 hours post-injection, which suggests bromocriptine was activating an innate immune response. Overall, the body weights and rectal temperatures of horses did not significantly change in any of the experiments, which indicated that aged non-pregnant horses are able to tolerate E+ tall fescue. In addition, this body of research identified that intravenous delivery of a semi-synthetic dopamine agonist, bromocriptine, and not an oral delivery of an E+ tall fescue seed derived dopamine agonist, caused a decrease in prolactin concentrations, but revealed conflicting results regarding inflammatory responses. In summary, further research is warranted to determine the mechanism of action that dopamine agonists have on the immune system of horses.

Made available in DSpace on 2015-03-26T13:47:20Z (GMT). No. of bitstreams: 1 texto completo.pdf: 235255 bytes, checksum: e59ffc4b4d93eb2387e5b1f9aaefaf2a (MD5) Previous issue date: 2003-12-16 / With the goal of evaluating the efficacity of bromocriptine and dexametazone, 30 mongrel bitches, with more than 35 days of pregnancy confirmed by ultrasonography, clinicaly healthy, with weights varying between 10 and 30 kgs, were divided in three groups: Group 1 - Underwent treatment with bromocriptine for 6 days with a dosage of 0,03 mg/kg every 12 hours; Group 2 Underwent treatment with dexametasone for 10 days with a dosage of 0,2 mg/kg every 12 hours; Group 3 control. The results demonstrated that both the animals treated with bromocriptine as well as those treated with dexametasone had their pregnancies interrupted in 90% of the cases. In the conditions in which the present experiment was made, no serious endometrial alterations, with endangerment of uterine phisiology, were observed. It was verified that the abortion happens later in the group treated with dexametasone, where the phoetus expulsion may occur up to the 10th day after the treatment. / Objetivando avaliar o efeito abortivo de bromocriptina e da dexametasona, 30 cadelas sem raça definida, com mais de 35 dias de gestação, confirmada por ultrasonografia, clinicamente sadias, com peso variando entre 10 e 30 kg foram separadas em três grupos, a saber: Grupo 1 - Submetidas ao tratamento com bromocriptina durante 6 dias na dose de 0,01 mg/kg a cada 12 horas; Grupo 2 - Tratadas com dexametasona durante 10 dias na dose de 0,02 mg/kg a cada 12 horas; Grupo 3- Controle. Os resultados demonstraram que tanto os animais tratados com bromocriptina, como aqueles tratados com dexametasona tiveram suas gestações interrompidas em 90% dos casos. Na condição em que foi realizado o presente experimento, não foram observadas alterações endometriais graves, que pudessem comprometer a fisiologia uterina. Verificou-se que o abortamento é mais tardio no grupo tratado com dexametasona com a expulsão do feto pode ocorrer até o 10o dia após o início do tratamento.

Atualmente, é crescente o interesse em estudar o potencial do Sistema Nervoso Central (SNC) como alvo de medicamentos antidiabéticos, uma vez que ele possui receptores de insulina e desempenha papel crítico na regulação da homeostase glicêmica. Nesse sentido, o Cycloset® (mesilato de bromocriptina de liberação rápida), um medicamento de ação central aprovado nos Estados Unidos para o tratamento do DMT2, atende a essa tendência atual. Trabalhos prévios mostram efeitos benéficos da bromocriptina (Bromo) sobre a hiperglicemia e hiperlipidemia em modelos de animais obesos tratados com essa droga. Por ser um agonista dopaminérgico, um dos possíveis mecanismos de ação dessa droga pode ser bloqueando a liberação e produção de prolactina (Prl). Níveis elevados de prolactina na circulação sanguínea, observados tanto em indivíduos com prolactinomas como em pessoas tratadas com medicamentos que causam hiperprolactinemia, geram anormalidades no metabolismo de carboidratos e lipídeos, o que pode levar a um quadro de síndrome metabólica. Na presente tese, testamos a hipótese de que ao menos parte dos efeitos antidiabéticos da Bromo seja mediada pela inibição da secreção de prolactina. Avaliamos os efeitos do tratamento com Bromo em camundongos machos e fêmeas geneticamente obesos e resistentes à insulina (ob/ob), bem como testamos se os efeitos benéficos do medicamento seriam revertidos com a reposição de Prl. Machos tratados com Bromo apresentaram maior sensibilidade à insulina, enquanto que a reposição de Prl manteve os animais menos sensíveis, tais como os animais do grupo controle. As fêmeas tratadas com Bromo apresentaram tendência à melhora de sensibilidade à insulina, bem como foram mais tolerantes à glicose, sendo que a reposição de Prl em animais tratados com Bromo também reverteu o efeito benéfico do medicamento. Dessa forma, demonstramos que ao menos parte dos efeitos antidiabéticos da Bromo é mediada pela inibição da secreção basal de Prl. Em um segundo conjunto de experimentos, testamos se a administração de antagonistas de prolactina (G129R-hPrlR) em machos ob/ob, por vias centrais ou periféricas, produziria efeito antidiabético. Observamos que tanto o tratamento periférico como o central diminui a curva glicêmica dos animais em testes de tolerância à glicose e melhoram a sensibilidade à insulina, embora ainda não tenhamos obtido valores significativos devido a nossa amostragem. Por fim, investigamos se a ação da Prl sobre o metabolismo ocorre por meio da interação com o receptor de estrógeno alfa (ER&#945;). Verificamos que receptores de prolactina e de ER&#945; são expressos em áreas comuns no SNC e que variações nos níveis circulantes de estrógeno causam mudanças na sensibilidade à prolactina. Portanto, no presente trabalho, identificamos o possível mecanismo pelo qual a Bromocriptina promove melhorias no controle glicêmico e, de forma inédita, produzimos evidências que o uso de antagonistas de prolactina pode ter potencial no tratamento do DMT2. / Type 2 Diabetes mellitus (T2DM) is a syndrome characterized by dysfunctions in the metabolism of glucose, amino acids and free fat acids. Although most of the drugs currently used to treat T2DM targets peripheral organs, a growing interest in studying the Central Nervous System (CNS) as a potential target of antidiabetic drugs is appearing. The CNS possesses insulin receptors and plays a critical role in regulating glucose homeostasis. In this sense, Cycloset® (quick release bromocriptine mesylate) a drug that acts on CNS, was recently approved in United States to treat T2DM. Previous studies have shown beneficial effects of bromocriptine (Bromo) on hyperglycemia and hyperlipidemia in obese animal models. As a dopaminergic agonist, a possible mechanism of action of this drug could be caused by a decreased prolactin (Prl) production and release. High serum prolactin levels, as observed in patients bearing prolactinomas or individuals using drugs that induce hyperprolactinemia, generate abnormalities in carbohydrate and lipid metabolism, which can lead to metabolic syndrome. In the current thesis, we tested the hypothesis that part of bromocriptine antidiabetic effects is due to an inhibition of prolactin secretion. We evaluated Bromo effects in genetically obese and insulin resistant male and female mouse (ob/ob), as well as we tested whether replacing Prl could reverse the beneficial effects of Bromo. Males treated with Bromo showed lower insulin resistence, whereas Prl replacement decreased insulin sensitivity. Females treated with Bromo showed tendency towards an improvement in their insulin sensitivity and glucose tolerance. Prl replacement also reversed the beneficial effects of Bromo in this group. Thus, we demonstrated that at least part of the antidiabetic effects of Bromo is due to inhibition of Prl secretion. In another set of experiments, we tested whether central or peripheral treatment with prolactin antagonists (G129R-hPrlR) causes antidiabetic effects in ob/ob male mice. Both peripheral and central treatment decreased the glycemic curve during glucose and insulin tolerance tests, although we still did not obtain statistically significant values with our sample size. Lastly, we investigated whether metabolic Prl action occurs due to a putative interaction with estrogen receptor alpha (ER&#945;). We found a wide co-expression between Prl receptor and ER&#945; in the CNS. Additionally, changes in estrogen levels decrease prolactin sensitivity. Therefore, in the present study we identified the possible mechanism by which bromocriptine promotes improvements in glycemic control, and for the first time, we obtained evidence that the use of prolactin antagonists can have a potential effect in the treatment of T2DM.

Atualmente, é crescente o interesse em estudar o potencial do Sistema Nervoso Central (SNC) como alvo de medicamentos antidiabéticos, uma vez que ele possui receptores de insulina e desempenha papel crítico na regulação da homeostase glicêmica. Nesse sentido, o Cycloset® (mesilato de bromocriptina de liberação rápida), um medicamento de ação central aprovado nos Estados Unidos para o tratamento do DMT2, atende a essa tendência atual. Trabalhos prévios mostram efeitos benéficos da bromocriptina (Bromo) sobre a hiperglicemia e hiperlipidemia em modelos de animais obesos tratados com essa droga. Por ser um agonista dopaminérgico, um dos possíveis mecanismos de ação dessa droga pode ser bloqueando a liberação e produção de prolactina (Prl). Níveis elevados de prolactina na circulação sanguínea, observados tanto em indivíduos com prolactinomas como em pessoas tratadas com medicamentos que causam hiperprolactinemia, geram anormalidades no metabolismo de carboidratos e lipídeos, o que pode levar a um quadro de síndrome metabólica. Na presente tese, testamos a hipótese de que ao menos parte dos efeitos antidiabéticos da Bromo seja mediada pela inibição da secreção de prolactina. Avaliamos os efeitos do tratamento com Bromo em camundongos machos e fêmeas geneticamente obesos e resistentes à insulina (ob/ob), bem como testamos se os efeitos benéficos do medicamento seriam revertidos com a reposição de Prl. Machos tratados com Bromo apresentaram maior sensibilidade à insulina, enquanto que a reposição de Prl manteve os animais menos sensíveis, tais como os animais do grupo controle. As fêmeas tratadas com Bromo apresentaram tendência à melhora de sensibilidade à insulina, bem como foram mais tolerantes à glicose, sendo que a reposição de Prl em animais tratados com Bromo também reverteu o efeito benéfico do medicamento. Dessa forma, demonstramos que ao menos parte dos efeitos antidiabéticos da Bromo é mediada pela inibição da secreção basal de Prl. Em um segundo conjunto de experimentos, testamos se a administração de antagonistas de prolactina (G129R-hPrlR) em machos ob/ob, por vias centrais ou periféricas, produziria efeito antidiabético. Observamos que tanto o tratamento periférico como o central diminui a curva glicêmica dos animais em testes de tolerância à glicose e melhoram a sensibilidade à insulina, embora ainda não tenhamos obtido valores significativos devido a nossa amostragem. Por fim, investigamos se a ação da Prl sobre o metabolismo ocorre por meio da interação com o receptor de estrógeno alfa (ER&#945;). Verificamos que receptores de prolactina e de ER&#945; são expressos em áreas comuns no SNC e que variações nos níveis circulantes de estrógeno causam mudanças na sensibilidade à prolactina. Portanto, no presente trabalho, identificamos o possível mecanismo pelo qual a Bromocriptina promove melhorias no controle glicêmico e, de forma inédita, produzimos evidências que o uso de antagonistas de prolactina pode ter potencial no tratamento do DMT2. / Type 2 Diabetes mellitus (T2DM) is a syndrome characterized by dysfunctions in the metabolism of glucose, amino acids and free fat acids. Although most of the drugs currently used to treat T2DM targets peripheral organs, a growing interest in studying the Central Nervous System (CNS) as a potential target of antidiabetic drugs is appearing. The CNS possesses insulin receptors and plays a critical role in regulating glucose homeostasis. In this sense, Cycloset® (quick release bromocriptine mesylate) a drug that acts on CNS, was recently approved in United States to treat T2DM. Previous studies have shown beneficial effects of bromocriptine (Bromo) on hyperglycemia and hyperlipidemia in obese animal models. As a dopaminergic agonist, a possible mechanism of action of this drug could be caused by a decreased prolactin (Prl) production and release. High serum prolactin levels, as observed in patients bearing prolactinomas or individuals using drugs that induce hyperprolactinemia, generate abnormalities in carbohydrate and lipid metabolism, which can lead to metabolic syndrome. In the current thesis, we tested the hypothesis that part of bromocriptine antidiabetic effects is due to an inhibition of prolactin secretion. We evaluated Bromo effects in genetically obese and insulin resistant male and female mouse (ob/ob), as well as we tested whether replacing Prl could reverse the beneficial effects of Bromo. Males treated with Bromo showed lower insulin resistence, whereas Prl replacement decreased insulin sensitivity. Females treated with Bromo showed tendency towards an improvement in their insulin sensitivity and glucose tolerance. Prl replacement also reversed the beneficial effects of Bromo in this group. Thus, we demonstrated that at least part of the antidiabetic effects of Bromo is due to inhibition of Prl secretion. In another set of experiments, we tested whether central or peripheral treatment with prolactin antagonists (G129R-hPrlR) causes antidiabetic effects in ob/ob male mice. Both peripheral and central treatment decreased the glycemic curve during glucose and insulin tolerance tests, although we still did not obtain statistically significant values with our sample size. Lastly, we investigated whether metabolic Prl action occurs due to a putative interaction with estrogen receptor alpha (ER&#945;). We found a wide co-expression between Prl receptor and ER&#945; in the CNS. Additionally, changes in estrogen levels decrease prolactin sensitivity. Therefore, in the present study we identified the possible mechanism by which bromocriptine promotes improvements in glycemic control, and for the first time, we obtained evidence that the use of prolactin antagonists can have a potential effect in the treatment of T2DM.