Studies of atrial natriuretic peptide in the freshwater turtle Pseudemys scripta
Reinhart, Glenn Alan
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Permalink
https://hdl.handle.net/2142/19947
Description
Title
Studies of atrial natriuretic peptide in the freshwater turtle Pseudemys scripta
Author(s)
Reinhart, Glenn Alan
Issue Date
1990
Doctoral Committee Chair(s)
Zehr, John E.
Department of Study
Molecular and Integrative Physiology
Discipline
Molecular and Integrative Physiology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
Studies were carried out to verify the presence of a recently discovered mammalian cardiac hormone known as atrial natriuretic peptide (ANP), in a reptilian species, the freshwater turtle Pseudemys scripta. These studies demonstrate that unlike mammalian species, both the atria and ventricles of this ancient reptile contain extractable ANP-like materials. Injection of crude, desalted turtle atrial and ventricular extracts induced a potent natriuretic and diuretic response in rats, with atrial extracts being relatively more potent. This extract induced natriuresis was characterized by a rapid onset and relatively short duration, thus mimicking the natriuretic and diuretic effects of crude and purified forms of mammalian ANP. Other similarities between mammalian and reptilian ANP were demonstrated by the partially purified turtle atrial extract induced relaxation of isolated rat thoracic aortic ring segments precontracted with norepinephrine. This spasmolytic activity is similar to mammalian ANP and was not found in partially purified turtle skeletal muscle extracts.
These studies have also shown that ANP can exert physiologic effects in Pseudemys scripta. Both conscious and anesthetized turtles demonstrated reduced arterial blood pressures in response to bolus injections of synthetic rat ANP. This suggests the presence of peripheral receptors for ANP in this reptile and further, provides indirect support for the concept of ANP as a primitive and functional cardiac hormone in this reptile.
Other studies focused on the biochemical characterization of the putative turtle ANP. Partially purified turtle atrial extracts demonstrated dose-dependent inhibition of binding of labeled $\alpha$-ANP in a radioimmunoassay system using antisera raised against the mammalian peptide. Partially purified turtle atrial extracts also demonstrated a dose dependent inhibition of binding of labeled mammalian ANP in a radio-receptor assay system. In addition, size exclusion chromatography of partially purified turtle atrial extracts suggested a molecular weight of 3,000 to 5,000 for the natriuretic factor. The immunoreactivity and biological activities demonstrated for turtle atrial extracts suggest that turtle ANP is highly homologous to the mammalian peptide and further, that ANP is a highly conserved and primitive hormone.
Attempts to purify further the active component using reversed-phase HPLC techniques and the radio-receptor assay resulted in the isolation and sequencing of two ANP receptor-binding peptides. These peptides were not homologous to ANP but rather were homologous to the muscle protein fragments porcine desmin protein and human cardiac $\alpha$-myosin protein.
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