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Aspects of neurohypophysial physiology during fetal development and pregnancy in the fur seal Callorhinus ursinus Vizsolyi, Elizabeth

Abstract

The neurohypophyses of the fur seal, Callorhinus ursinus were studied in the control non-breeding animals, in the pregnant females at five stages of gestation, and in their fetuses at seven stages of intrauterine life. The neurohypophyses of the fur seal, a marine mammal, were found to be exceptionally potent in rat uterus and vasopressor activities. Purification procedures and amino acid analyses have shown the active neurohypophysial peptides of the seal, in common with the majority of mammalian species, to be arginine vasopressin and oxytocin. The neurohypophysial hormone levels of the pregnant females were found to be fluctuating from the control level with the advancement of gestation. The vasopressor activity showed an initial rise between 0.19 and 0.31 of term, but during the remainder of pregnancy it was found to fall below the control values. The oxytocic activities were found to be elevated from the control values all through pregnancy, but a fluctuation in the potencies was detected, which parallelled that found for vasopressor activities. Neurosecretory activity in the fetal neurohypophysial system was investigated at seven stages of gestation by histological, pharmacological and biochemical methods. The histological studies have shown the two hypothalamic nuclei, the supra-optic and the para-ventricular nucleus, as well as the neurohypophysis to contain neurosecretory material at 0.5 of term, or mid-gestation. However, biological activities as measured by rat uterus, vasopressor and frog bladder assays were detected at a much earlier stage, at 0.19 of term. In the vasopressor and rat uterus activities a steady accumulation of activities was recorded with the advancement of gestation, but in the third biological activity, the potency on the isolated frog bladder, the highest value was recorded at 0.68 of term, and declined from there until term. Since the neurohypophysial hormones of the fetal neurohypophysis have not been previously purified, the crude posterior pituitary extracts of fetuses were subjected to gel filtration and ion exchange chromatography. The pharmacological characteristics of the purified fetal principles, when assayed against synthetic standards, suggested that they were arginine vasopressin, oxytocin and arginine vasotocin. These findings were confirmed by amino acid analyses of the three active neurohypophysial peptides, and it was concluded that the fetal neurohypophysis contains arginine vasotocin, the antidiuretic hormone of sub-mammalian vertebrates, in addition to oxytocin and arginine vasopressin, the commonly occurring mammalian peptides. Preliminary experiments suggested that the embryonic membranes might constitute the possible target organs of the fetal neurohypophysial agents.

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