Characterization of angiotensin I-converting enzyme activity in the freshwater turtle, Amyda japonica

Prepubescent female rodents have enhanced hippocampal LTP and learning relative to males, reversing in adulthood as inhibition increases

Multiple studies indicate that adult male rodents perform better than females on spatial problems and have a lower threshold for long-term potentiation (LTP) of hippocampal CA3-to-CA1 synapses. We report here that, in rodents, prepubescent females rapidly encode spatial information and express low-threshold LTP, whereas age-matched males do not. The loss of low-threshold LTP across female puberty was associated with three inter-related changes: increased densities of α5 subunit-containing GABA_ARs at inhibitory synapses, greater shunting of burst responses used to induce LTP and a reduction of NMDAR-mediated synaptic responses. A negative allosteric modulator of α5-GABA_ARs increased burst responses to a greater degree in adult than in juvenile females and markedly enhanced both LTP and spatial memory in adults. The reasons for the gain of functions with male puberty do not involve these mechanisms. In all, puberty has opposite consequences for plasticity in the two sexes, albeit through different routes.

Angiotensin-converting enzyme C-terminal catalytic domain is the main site of angiotensin I cleavage in vivo

Angiotensin-converting enzyme (ACE) plays a central role in the production of the vasoconstrictor angiotensin II. ACE is a single polypeptide, but it contains 2 homologous and independent catalytic domains, each of which binds zinc. To understand the in vivo role of these 2 domains, we used gene targeting to create mice with point mutations in the ACE C-domain zinc-binding motif. Such mice, termed ACE13/13, produce a full-length ACE protein with tissue expression identical to wild-type mice. Analysis of ACE13/13 mice showed that they produce ACE having only N-domain catalytic activity, as determined by the hydrolysis of domain specific substrates and by chloride sensitivity. ACE13/13 mice have blood pressure and blood angiotensin II levels similar to wild-type mice. However, plasma renin concentration is increased 2.6-fold and blood angiotensin I levels are increased 7.5-fold. Bradykinin peptide levels are not different from wild-type levels. ACE13/13 mice have a reduced increase of blood pressure after intravenous infusion of angiotensin I. ACE13/13 mice have a normal renal structure, but they are not able to concentrate urine after dehydration as effectively as wild-type mice. This study shows that the C-domain of ACE is the predominant site of angiotensin I cleavage in vivo. Although mice lacking C-domain activity have normal physiology under laboratory conditions, they respond less well to the stress of dehydration.

Comparative renal physiology of exotic species

In this article the osmoregulatory, acid-base homeostasis, and excretory functions of the renal system of invertebrates and vertebrates are reviewed. The mammalian renal system is the most highly evolved in terms of the range of functions performed by the kidneys. Renal physiology in other animals can be very different, and a sound knowledge of these differences is important for understanding health and disease processes that involve the kidneys, as well as ion and water homeostasis. Many animals rely on multiple organs along with the kidneys to maintain osmotic, ionic, and pH balance. Some animals rely heavily on postrenal modification of urine to conserve water and salt balance; this can influence the interpretation of disease signs and treatment modalities.

Angiotensin I-converting enzyme-like activity in tissues from the Atlantic hagfish (Myxine glutinosa) and detection of immunoreactive plasma angiotensins

Using a highly sensitive fluorimetric assay, significant levels of angiotensin I -converting enzyme-like activity (ACELA) were detected in a range of tissues (branchial heart, gill, kidney with associated vasculature and archinephric duct, liver, whole brain and gut) from the Atlantic hagfish (Myxine glutinosa). The highest ACELA occurred in heart and gill (1.8 and 1.5 nmol His-Leu min(-1) mg protein(-1), respectively). The mammalian angiotensin I-converting enzyme (ACE) inhibitor, captopril, at 10(-5) M was a potent inhibitor of the ACELA found in all hagfish tissues. Radioimmunoassay showed that immunoreactive angiotensins (251.8+/-11.8 pM) were detectable in hagfish plasma. The validity of the assay for measurement of hagfish angiotensins was indicated by the parallelism of the angiotensin II standard curve against serially diluted hagfish plasma. Measurement of immunoreactive plasma angiotensins and detection of significant levels of ACELA in a wide range of tissues gives indirect evidence for the presence of a renin-angiotensin system in hagfishes, the earliest evolved group of craniates.

Effect of chloride and diamide on serum angiotensin I-converting enzyme activity from eight mammalian species

1. The effect of chloride on serum angiotensin I-converting enzyme (ACE) activity was characterized in eight mammalian species: dog, guinea pig, hamster, human, mouse, rabbit, rat, and sheep. 2. Optimum chloride concentrations varied from 300 mM for rabbit to 1700 mM for hamster. 3. The increments with these optimum concentrations with respect to 100 mM chloride concentration were from 1.4-fold in rabbit to 7.9-fold in hamster and dog. 4. There was no correlation between serum chloride concentration or serum ACE activity and optimum chloride concentration. 5. Serum ACE increased only in humans with diamide pretreatment suggesting the presence of endogenous inhibitors.

Angiotensin-converting enzyme distribution and hypoxia response in mammal, bird, and fish

Angiotensin I-converting enzyme activity was measured in homogenates of guinea pig (Cavia porcellus), chicken (Gallus domesticus), and carp (Cyprinus carpio) organs. The highest activity was found in guinea pig lung and chicken kidney. In carp the highest activity was found in heart and spleen, although gill arch also showed a high activity. Acute hypoxia decreased the angiotensin I-converting enzyme activity in guinea pig lung and carp gill arch, but the changes in chicken lung and kidney were considered nonsignificant.