The effect of relaxin infusion on prolactin and growth hormone secretion in monkeys

Cynthia Bethea, M. J. Cronin, G. J. Haluska, M. J. Novy

    Research output: Contribution to journalArticle

    36 Citations (Scopus)

    Abstract

    To test the hypothesis that relaxin may affect pituitary hormone secretion, synthetic human relaxin was infused into cycling and pregnant rhesus monkeys. Doses ranging from 0.154-1540 ng/kg · min were calculated to achieve circulating relaxin concentrations of 1 pM to 10 nM. Low (0.154 and 1.54 ng/kg · min), intermediate (15.4 and 154 ng/kg · min), and high (1540 ng/kg · min) doses of relaxin were infused for 15 min each hour into ovulating monkeys at the midluteal phase of the menstrual cycle in two separate experiments. Serum GH and PRL were measured by RIA, and serum relaxin was determined by enzyme-linked immunosorbent assay. Relaxin was undetectable in peripheral plasma during the control saline infusion and during infusion of the lowest dose of relaxin. Serum relaxin levels reached 0.011, 0.119, 0.965, and 13.0 nM with 1.54, 15.4, 154, and 1540 ng/kg · min, respectively. Serum GH was significantly elevated over basal levels upon infusion of relaxin from 1.54-1540 ng/kg · min; however, a plateau was observed with the intermediate doses, and a decrease in the magnitude of the response was observed at the highest dose. Serum PRL increased over basal levels with 15.4 and 154 ng/kg ·min, but there was no difference in the magnitude of the increase between these doses. PRL levels during infusion of the highest dose of relaxin were similar to control levels. These data suggest that relaxin can stimulate secretion of GH and PRL in cycling monkeys within a defined dose range, but that a decrease in pituitary responsiveness occurs at higher doses. One high dose of relaxin (2600 ng/kg · min) was infused for 1 h into the maternal and then the fetal circulations of chronically catheterized and tethered pregnant monkeys between 120-140 days gestation. Upon infusion of relaxin into the maternal circulation, ther was a significant elevation of PRL in the mother but not the fetus. Upon infusion of relaxin into the fetus, there was no consistent change in PRL secretion in either the mother or the fetus. In conclusion, relaxin may have a heretofore undescribed role in pituitary physiology during the menstrual cycle and in pregnancy.

    Original languageEnglish (US)
    Pages (from-to)956-962
    Number of pages7
    JournalJournal of Clinical Endocrinology and Metabolism
    Volume69
    Issue number5
    StatePublished - 1989

    Fingerprint

    Relaxin
    Prolactin
    Growth Hormone
    Haplorhini
    Serum
    Fetus
    Menstrual Cycle
    Mothers
    Pregnancy
    Immunosorbents
    Pituitary Hormones
    Level control
    Physiology

    ASJC Scopus subject areas

    • Biochemistry
    • Endocrinology, Diabetes and Metabolism

    Cite this

    The effect of relaxin infusion on prolactin and growth hormone secretion in monkeys. / Bethea, Cynthia; Cronin, M. J.; Haluska, G. J.; Novy, M. J.

    In: Journal of Clinical Endocrinology and Metabolism, Vol. 69, No. 5, 1989, p. 956-962.

    Research output: Contribution to journalArticle

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    N2 - To test the hypothesis that relaxin may affect pituitary hormone secretion, synthetic human relaxin was infused into cycling and pregnant rhesus monkeys. Doses ranging from 0.154-1540 ng/kg · min were calculated to achieve circulating relaxin concentrations of 1 pM to 10 nM. Low (0.154 and 1.54 ng/kg · min), intermediate (15.4 and 154 ng/kg · min), and high (1540 ng/kg · min) doses of relaxin were infused for 15 min each hour into ovulating monkeys at the midluteal phase of the menstrual cycle in two separate experiments. Serum GH and PRL were measured by RIA, and serum relaxin was determined by enzyme-linked immunosorbent assay. Relaxin was undetectable in peripheral plasma during the control saline infusion and during infusion of the lowest dose of relaxin. Serum relaxin levels reached 0.011, 0.119, 0.965, and 13.0 nM with 1.54, 15.4, 154, and 1540 ng/kg · min, respectively. Serum GH was significantly elevated over basal levels upon infusion of relaxin from 1.54-1540 ng/kg · min; however, a plateau was observed with the intermediate doses, and a decrease in the magnitude of the response was observed at the highest dose. Serum PRL increased over basal levels with 15.4 and 154 ng/kg ·min, but there was no difference in the magnitude of the increase between these doses. PRL levels during infusion of the highest dose of relaxin were similar to control levels. These data suggest that relaxin can stimulate secretion of GH and PRL in cycling monkeys within a defined dose range, but that a decrease in pituitary responsiveness occurs at higher doses. One high dose of relaxin (2600 ng/kg · min) was infused for 1 h into the maternal and then the fetal circulations of chronically catheterized and tethered pregnant monkeys between 120-140 days gestation. Upon infusion of relaxin into the maternal circulation, ther was a significant elevation of PRL in the mother but not the fetus. Upon infusion of relaxin into the fetus, there was no consistent change in PRL secretion in either the mother or the fetus. In conclusion, relaxin may have a heretofore undescribed role in pituitary physiology during the menstrual cycle and in pregnancy.

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