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Neurohypophysial principles of the western brook lamprey (Lampetra richardsoni) and the Pacific hagfish (Polistotrema stoutii). Rurak, Danny William

Abstract

Pharmacologic and chromatographic methods were employed to identify the neurohypophysial peptides present in, two species of cyslostomes, the western brook lamprey, Lampetra richardsoni, and the Pacific hagfish, Polistotrema stoutii. The evidence obtained indicated the presence of low amounts of 8-arginine -oxytocin or arginine vasotocin in both animals. No evidence was provided to suggest the existence of a second biologically active posterior pituitary principle in either species, and with the lamprey, it appeared unlikely that more than one percent of the total activity extracted from the neurohypophysial tissues could have been due to a second peptide without being detected. The results of the study thus supported previous claims that cyclo-stomes were unique amoung vertebrates in the possession of a single active neurohypophysial principle. The evolutionary significance of this feature of lamprey and hagfish is discussed, as well as the possibility of the existence, in the pituitary of lower vertebrates, of "intermediate" neurohypophysial peptides with low biological activity. Pharmacologic and chromatographic investigations of midbrain and hind-brain "control" material from the western brook lamprey suggested that small amounts of arginine vasotocin may have been present in these tissues. The possible explanations for this extra-hypothalamic location of a neurohypophysial peptide are discussed, in light of similar findings in other vertebrates. Subsequent to the demonstration of the presence of arginine vasotocin in Lampetra richardsoni, the levels of the peptide were studied in animals of various ages and in larvae kept under various photoperiods. Determinations of the amounts of AVT present in the lamprey during its life history were made in an attempt to corroborate published histological observations which suggested that in Lampetra planeri a marked depletion of the principle occurred at metamorphosis. Although the interpretation of results was complicated by the presence of substantial amounts of contaminating substances in the pituitary extracts, it appeared unlikely that the levels of AVT were drastically reduced at transformation in L. richardsoni. Rather, the data indicated that the amounts of the peptide, as well as the quantities of other active substances in both pituitary and hindbrain tissues, were augmented when larvae transformed into adults. This increase in rat uterus activity extracted from the tissues was correlated with an increase in dry weight of the brain, and it appeared likely that the two occurrences were causally linked. No significant deviations were noted in the rat uterus activity extracted from groups of larval lamprey kept under different photoperiods. The variations that occurred amoung the neurohypophysial tissues were paralleled by differences amoung the control tissues; this suggested that photoperiod had effects on other biologically active subatances in the central nervous system besides AVT.

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