In vivo investigation of luteal function in dogs: Effects of cabergoline,a dopamine agonist,and prolactin on progesterone secretion during mid-pregnancy and -diestrus |
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| Institution: | 1. Clinic of Small Animal Surgery and Reproduction, Center for Clinical Veterinary Medicine, Faculty of Veterinary Medicine, Ludwig Maximilian University, Munich, Germany;2. Institute of Veterinary Pathology, Ludwig Maximilians University, Munich, Germany;3. Institute of Veterinary Anatomy, University of Munich, Munich, Germany;1. Laboratory of Animal Reproduction, Department of Animal Production, Faculty of Veterinary Sciences, University of Chile, Santa Rosa 11735, La Pintana, Santiago, Chile;2. Laboratory of Animal Physiology, Department of Biological Sciences, Faculty of Veterinary Sciences, University of Chile, Santa Rosa, 11735, La Pintana, Santiago, Chile;1. Department of Animal Medicine Production and Health-University of Padova, via dell’Università 16, 35020 Legnaro, PD, Italy;2. Department of Obstetrics and Gynaecology, Faculty of Veterinary Medicine, Istanbul, Turkey;1. Cardiology Service, Faculty of Veterinary Sciences. National University of La Plata, 60 y 118, La Plata, 1900, Argentina;2. Laboratory of Reproductive Physiology, FVS-NULP, La Plata, Argentina;3. CONICET, Argentina;1. Sooam Biotech Research Foundation, 64 Kyungin-ro, Guro-gu, Seoul, Republic of Korea;2. Laboratory of Veterinary Embryology and Biotechnology, College of Veterinary Medicine, Chungbuk National University, Cheongju, Republic of Korea;3. Department of Animal Sciences, Chungbuk National University, Cheongju, Republic of Korea;1. Institute of Veterinary Anatomy, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland;2. Department of Reproductive Immunology and Pathology, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, Poland;3. Department of Animal Reproduction, University of Warmia and Mazury, Olsztyn, Poland;4. Clinic for Obstetrics, Gynaecology and Andrology of Large and Small Animals, Faculty of Veterinary Medicine, Justus-Liebig-University Giessen, Giessen, Germany |
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| Abstract: | The role of prolactin on luteal function in dogs was investigated in vivo. The function of prolactin in mid-luteal phase was compared in pregnant and nonpregnant dogs. A dopamine agonist, cabergoline, known for its prolactin secretion inhibitory effects, was injected subcutaneously at a dose of 5 μg/kg body weight in five pregnant and five nonpregnant Beagle bitches. Mean plasma prolactin and progesterone were dramatically suppressed for 4 to 5 days after injection in both groups when compared with control pregnant and non-pregnant animals, whereas no effect on luteinizing hormone (LH) secretion was observed. The decline in plasma progesterone occurred after that in prolactin, suggesting plasma progesterone was impaired by inhibition of prolactin secretion. These results confirm the luteotropic importance of prolactin in pregnant bitches, and also demonstrate its importance in luteal phase of the nonpregnant dog.Second, to demonstrate that the effects of cabergoline were mediated by prolactin inhibition and not by a direct action on the corpus luteum, concomitant administration on Day 30 of cabergoline and prolactin (375 μg IV twice daily on Days 30 and 31) or cabergoline and LH (750 μg IV twice daily on Days 30 and 31) was affected in two groups of five pregnant animals each. Results showed that only prolactin was able to reverse the negative effects of cabergoline on circulating progesterone. This confirms the indirect mode of action of the dopamine agonist, cabergoline on corpus luteum function.Third, further investigation on the precise luteotropic role of prolactin was made by IV injection of 375 μg pure canine prolactin twice daily in five pregnant bitches on Days 30 and 31, and in five pregnant bitches on Days 40 and 41. No direct stimulatory effect of prolactin on plasma progesterone secretion occurred. Nor was there a noticeable effect on plasma LH secretion. These results suggest that prolactin is unable to directly stimulate progesterone secretion by the corpus luteum of pregnancy.The results of this study suggest that prolactin is an essential luteotropin in the dog from mid-luteal phase in both pregnant and nonpregnant animals. However, it appears to act by sustaining corpus luteum lifespan and function rather than by direct stimulatory effects on progesterone secretion. |
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