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      Human Placental Lactogen Decreases Regional Blood Flow in Anesthetized Pigs


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          In 22 pigs anesthetized with sodium pentobarbitone, changes in blood flow caused by infusion of human placental lactogen into the left renal, external iliac, and anterior descending coronary arteries were assessed using electromagnetic flowmeters. In 17 pigs, infusion of human placental lactogen whilst keeping the heart rate and arterial pressure constant decreased coronary, renal and iliac flow. In 5 additional pigs, increasing the dose of human placental lactogen produced a dose-related decrease in regional blood flow. The mechanisms of the above response were studied in 15 of the 17 pigs by repeating the experiment of infusion. The human placental lactogen-induced decrease in regional blood flow was not affected by blockade of cholinergic receptors (5 pigs) or of α-adrenergic receptors (5 pigs), but it was abolished by blockade of β<sub>2</sub>-adrenergic receptors (5 pigs). The present study showed that intra-arterial infusion of human placental lactogen primarily decreased coronary, renal and iliac blood flow. The mechanism of this response was shown to be due to the inhibition of a vasodilatory β<sub>2</sub>-adrenergic receptor-mediated effect.

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          Most cited references 23

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          Roles of prolactin and related members of the prolactin/growth hormone/placental lactogen family in angiogenesis.

          Prolactin, growth hormone and placental lactogen are members of a family of polypeptide hormones which share structural similarities and biological activities. Numerous functions have been attributed to these hormones, among which stand out their recently discovered effects on angiogenesis, the process by which new blood vessels are formed from the pre-existing microvasculature. Prolactin, growth hormone and placental lactogen, along with two non-classical members of the family, proliferin and proliferin-related protein, can act both as circulating hormones and as paracrine/autocrine factors to either stimulate or inhibit various stages of the formation and remodeling of new blood vessels, including endothelial cell proliferation, migration, protease production and apoptosis. Such opposing actions can reside in similar but independent molecules, as is the case of proliferin and proliferin-related protein, which stimulate and inhibit angiogenesis respectively. The potential to exert opposing effects on angiogenesis can also reside within the same molecule as the parent protein can promote angiogenesis (i.e. prolactin, growth hormone and placental lactogen), but after proteolytic processing the resulting peptide fragment acquires anti-angiogenic properties (i.e. 16 kDa prolactin, 16 kDa growth hormone and 16 kDa placental lactogen). The unique properties of the peptide fragments versus the full-length molecules, the regulation of the protease responsible for specific protein cleavage, the selective expression of specific receptors and their associated signal transduction pathways are issues that are being investigated to further establish the precise contribution of these hormones to angiogenesis under both physiological and pathological situations. In this review article, we summarize the known and speculative issues underlying the effects of the prolactin, growth hormone and placental lactogen family of proteins on angiogenesis, and address important remaining enigmas in this field of research.
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            Sequence-function relationships within the expanding family of prolactin, growth hormone, placental lactogen, and related proteins in mammals

             V Goffin (1996)
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              Variation among species in the endocrine control of mammary growth and function: the roles of prolactin, growth hormone, and placental lactogen.

               P A Forsyth (1986)
              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)

                Author and article information

                J Vasc Res
                Journal of Vascular Research
                S. Karger AG
                February 2006
                16 February 2006
                : 43
                : 2
                : 205-213
                Laboratorio di Fisiologia, Dipartimento di Scienze Mediche, Facoltà di Medicina e Chirurgia, Università del Piemonte Orientale ‘A. Avogadro’, Novara, Italy
                90950 J Vasc Res 2006;43:205–213
                © 2006 S. Karger AG, Basel

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                Page count
                Figures: 4, Tables: 1, References: 34, Pages: 9
                Research Paper


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