Interaction between Angiotensinase Activities in Pituitary and Adrenal Glands of Wistar-Kyoto and Spontaneously Hypertensive Rats under Hypotensive or Hypertensive Treatments.

In the present study, we analyzed the activity of several aminopeptidases (angiotensinases) involved in the metabolism of various angiotensin peptides, in pituitary and adrenal glands of untreated Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) or treated with the antihypertensive drugs captopril and propranolol or with the L-Arginine hypertensive analogue L-NG-Nitroarginine Methyl Ester (L-NAME). Intra- and inter-gland correlations between angiotensinase activities were also calculated. Membrane-bound alanyl-, cystinyl-, and glutamyl-aminopeptidase activities were determined fluorometrically using aminoacyl-ß-naphthylamide as substrates. Depending on the type of angiotensinase analyzed, the results reflect a complex picture showing substantial differences between glands, strains, and treatments. Alanyl-aminopeptidase responsible for the metabolism of Ang III to Ang IV appears to be the most active angiotensinase in both pituitary and adrenals of WKY and particularly in SHR. Independently of treatment, most positive correlations are observed in the pituitary gland of WKY whereas such positive correlations are predominant in adrenals of SHR. Negative inter-gland correlations were observed in control SHR and L-NAME treated WKY. Positive inter-gland correlations were observed in captopril-treated SHR and propranolol-treated WKY. These results may reflect additional mechanisms for increasing or decreasing systolic blood pressure in WKY or SHR.

Enkephalinase activity is modified and correlates with fatty acids in frontal cortex depending on fish, olive or coconut oil used in the diet.

OBJECTIVE: Enkephalins are neuropeptides involved in functions such as pain modulation and/ or cognitive processes. It has been reported that dietary fat modifies enkephalins in the brain. Since enkephalins are hydrolyzed by enkephalinases, the study of the influence of dietary fats, differing in their degree of saturation, on brain fatty acids content and enkephalinase activity is important to understand its regulatory role on neuropeptides under different type of diets. METHODS: We analyzed enkephalinase activity, assayed with alanine-ß-naphthylamide as sub-strate, in frontal cortex of adult male rats fed diets supplemented with fish oil, olive oil or coconut oil, which markedly differed in the saturation of their fatty acids. RESULTS: Rats fed a diet enriched with coconut oil had lower soluble enkephalinase activity than the group fed olive oil (p<0.01) and fish oil (p<0.05) whereas rats fed a diet enriched with fish oil had lower membrane-bound enkephalinase activity than the group fed with olive (p<0.001) or coconut oil (p<0.05). Significant negative correlations were observed between certain fatty acids and enkephalinase activities in the groups fed with olive and coconut oils. No correlations were observed in the group fed with fish oil. CONCLUSIONS: Dietary fat modifies enkephalinase activity in the frontal cortex depending on the degree of saturation of the used oil. It is postulated that the functions, in which enkephalins are involved, such as pain modulation or cognitive functions, may also be affected according to the type of oil used in the diet.

Neuropeptidase activities in plasma after acute restraint stress. Interaction with cortico-limbic areas.

OBJECTIVE: To evaluate the influence of acute restraint stress (ARS) on plasma enkephalinase and oxytocinase activities. ARS modifies basal activities in cortico-limbic regions of rats and induces changes in the correlations observed between these regions. The interactions between plasma and cortico-limbic activities will be also evaluated. METHODS: Enkephalinase (AlaAP and LeuAP) and oxytocinase (P-LeuAP) activities were fluorometrically determined in plasma of control and stressed rats using aminoacyl-ß-naphthylamides (aaNNap), AlaNNap and LeuNNap as substrates. RESULTS: No differences in enzymatic activities were observed between control and stressed animals in plasma. In contrast, highly significant positive and negative correlations between plasma and cortico-limbic regions were demonstrated in controls. Stress conditions significantly alter the pattern of these correlations. CONCLUSION: The present results clearly support a connection between plasma and brain involving certain neuropeptidase activities that change under stress conditions.

Brain, heart and kidney correlate for the control of blood pressure and water balance: role of angiotensinases.

The renin-angiotensin system (RAS) plays a major role in the control of blood pressure (BP) and water balance by coordinating brain, heart and kidney functions, connected with each other by hormonal and neural mechanisms through the autonomic nervous system (ANS). RAS function may be monitored by the study of the enzymes (angiotensinases) involved in the metabolism of its active peptides. In order to study the relationship between the brain-heart-kidney axis and the control of BP and water balance, we analyzed the correlation of angiotensinase activities, assayed as arylamidase activities, between hypothalamus, left ventricle, renal cortex and renal medulla, collected from Wistar-Kyoto and spontaneously hypertensive rats, treated or not treated with L-NAME [N(G)-nitro-L-arginine methyl ester]. This compound not only inhibits the formation of nitric oxide but also disrupts the normal function of the ANS activating the sympathetic nervous system (SNS) to increase BP. In addition, to assess the influence of the SNS, we studied the effect of its blockade by treatment of both strains with propranolol. The present results support the notion that RAS function of the brain-heart-kidney axis, as reflected by the activities of angiotensinases, is reciprocally connected by afferent and efferent mechanisms between these locations, presumably through the ANS. These results reveal new aspects of neuroendocrine regulation possibly involving the ANS.

Asymmetric Interaction of Neuropeptidase Activities between Cortico-Limbic Structures, Plasma and Cardiovascular Function after Unilateral Dopamine Depletions of the Nigrostriatal System.

In emotional processing, dopamine (DA) plays an essential role, and its deterioration involves important consequences. Under physiological conditions, dopamine exhibits brain asymmetry and coexists with various neuropeptides that can coordinate the processing of brain functions. Brain asymmetry can extend into a broader concept of asymmetric neurovisceral integration, including behavior. The study of the activity of neuropeptide regulatory enzymes (neuropeptidases, NPs) is illustrative. We have observed that the left and right brain areas interact intra- and inter-hemispherically, as well as with peripheral tissues or with physiological parameters such as blood pressure or with behaviors such as turning preference. To obtain data that reflect this integrative behavior, we simultaneously analyzed the impact of left or right brain DA depletion on the activity of various NPs in corticolimbic regions of the left and right hemispheres, such as the medial prefrontal cortex, amygdala and hippocampus, as well as on the plasma activity of the same aminopeptidase activities (APs) and on systolic blood pressure (SBP). Intra- and inter-hemispheric interactions as well as the interactions of NPs from the left or right hemispheres were analyzed with the same plasma APs and the SBP obtained from sham and from left or right lesioned rats. The results demonstrate a complex profile depending on the hemisphere considered. They definitively confirm an asymmetric neurovisceral integration and reveal a higher level of inter-hemispheric corticolimbic interactions including with SBP after left dopamine depletion.

The Type of Fat in the Diet Influences the Behavior and the Relationship Between Cystinyl and Alanyl Aminopeptidase Activities in Frontal Cortex, Liver, and Plasma.

Insulin-regulated aminopeptidase (IRAP, cystinyl aminopeptidase, CysAP) and aminopeptidase M (alanyl aminopeptidase, AlaAP) are closely related enzymes involved in cognitive, metabolic, and cardiovascular functions. These functions may be modulated by the type of fat used in the diet. In order to analyze a possible coordinated response of both enzymes we determined simultaneously their activities in frontal cortex, liver, and plasma of adult male rats fed diets enriched with fats differing in their percentages of saturated, mono or polyunsaturated fatty acids such as sesame, sunflower, fish, olive, Iberian lard, and coconut. The systolic blood pressure, food intake, body and liver weight as well as glucose and total cholesterol levels in plasma were measured. The type of fat in the diet influences the enzymatic activities depending on the enzyme and its location. These results suggest cognitive improvement properties for diets with predominance of polyunsaturated fatty acids. Physiological parameters such as systolic blood pressure, food intake, and biochemical factors such as cholesterol and glucose in plasma were also modified depending on the type of diet, supporting beneficial properties for diets rich in mono and polyunsaturated fatty acids. Inter-tissue correlations between the analyzed parameters were also modified depending on the type of diet. If the type of fat used in the diet modifies the behavior and relationship between CysAP and AlaAP in and between frontal cortex, liver and plasma, the functions in which they are involved could also be modified.

Asymmetrical response of aminopeptidase A and nitric oxide in plasma of normotensive and hypertensive rats with experimental hemiparkinsonism.

Aminopeptidases and dopamine (DA) exhibit asymmetries in the brain that are reflected in the peripheral response to unilateral striatal DA depletions (experimental hemiparkinsonism). This might be due to asymmetries in the autonomic innervation of the peripheral vessels. Nitric oxide (NO) is released through vascular sympathetic activation. A similar pathway could be postulated for aminopeptidases. Angiotensin II, metabolized by aminopeptidase A (AP A), interacts with NO and dopamine in the control of blood pressure. Moreover, plasma AP A activity and NO concentrations are elevated in hypertensive rats in which sympathetic activity is increased. We hypothesize that plasma AP A activity and NO concentrations may reflect a central asymmetry of the sympathetic activity. Therefore, we analyzed the effect of unilateral depletions of brain DA by injecting 6-hydroxydopamine into the left or right striatum and measuring plasma AP A, NO and systolic blood pressure (SBP) in normotensive and hypertensive rats. Changes in plasma AP A and NO in opposite directions may reflect an asymmetry in the function of the nigrostriatal system. Our results also revealed an inverse correlation between AP A and NO, in normotensive rats lesioned or sham operated in the right side and hypertensive rats lesioned in the left one. We concluded that the observed changes in plasma NO and AP A after left or right striatal DA depletions may be due to asymmetries in the peripheral autonomic innervation of the vessels.

Stress influences brain enkephalinase, oxytocinase and angiotensinase activities: a new hypothesis.

Brain enkephalin and oxytocin are anxiolytic agents involved in the response mechanism to stress. Degrading enzymes such as enkephalinase and oxytocinase could also be associated with this response. The effect of acute immobilization stress on enkephalinase and oxytocinase activities was determined in the soluble and membrane fractions of the medial prefrontal cortex, hippocampus and amygdala using alanyl- and leucyl-beta-naphthylamide as substrates, the latter in the presence and absence of 20 mM L-methionine. No change in aminopeptidase activities was observed in the prefrontal cortex of stressed rats. In contrast, enkephalinase activity decreased in the soluble fraction of the hippocampus but increased in the membrane fraction. In the amygdala, soluble oxytocinase and membrane enkephalinase activities decreased in stressed animals. These results show that acute immobilization stress affects differentially enkephalinase and oxytocinase activities depending on the fraction and brain region analyzed. A reduction in the activity of soluble enkephalinase in the hippocampus and soluble oxytocinase as well as membrane enkephalinase in the amygdala may suggest higher availability/longer action of enkephalin and oxytocin at these locations. This may explain the relative importance of these enzymatic activities in the anxiolytic properties proposed for enkephalins and oxytocin in the hippocampus and amygdala during stress conditions. This interpretation is not applicable to membrane enkephalinase activity in the hippocampus. However, alanyl-beta-naphthylamide hydrolyzing activity not only measures enkephalinase activity, it also reflects the angiotensinase-induced metabolism of angiotensin III to angiotensin IV. Therefore, our results may also mirror an increase in the formation of Ang IV in hippocampus and a decrease in the amygdala in acute stress. In conclusion, aminopeptidase activities in the hippocampus and amygdala may affect enkephalin, oxytocin and angiotensin III metabolism during acute immobilization stress and therefore be involved in the anxiolytic response.

Enkephalinase regulation.

After millennia of knowledge of opium, it was only recently that endogenous substances called opioids with similar properties to opium and derivatives were discovered. The first to be discovered were enkephalins. In addition to the regulation of their synthesis and expression of receptors, an important mechanism for the regulation of their functions carried out by multiple proteolytic enzymes acting at all levels of their structure is described. The action of such enzymes, known as enkephalinases, is also regulated by endogenous and exogenous factors which ultimately affect the control of the enkephalins's action. For therapeutic purposes, it is not only necessary to develop specific inhibitors but also to acquire a deep knowledge of the influence that such factors exert on their activities. This knowledge could help us to establish adapted therapeutic strategies in the treatment of pain or other processes in which enkephalinases are involved. In this chapter, some of these regulatory factors are discussed, such as regional and subcellular distribution, developmental changes, diurnal variations, hormonal influences, stress, dietary factors or interactions with other neurotransmitters.

Neuropeptidase activity in the frontal cortex of Wistar-Kyoto and spontaneously hypertensive rats treated with vasoactive drugs: a bilateral study.

BACKGROUND AND OBJECTIVE: Hypertension can lead to mood disorders that may worsen or ameliorate depending on the type of antihypertensive prescribed. Depression is associated with modifications in basal brain asymmetry particularly that of the frontal cortex, which is involved in blood pressure control. Furthermore, different vasoactive drugs may change the brain's asymmetry in a manner that contributes to cognition status. We studied the bilateral activity of several neuropeptidases in frontal cortex as a reflect of the functional status of certain neuropeptides involved in mood. METHODS: Using arylamide derivatives as substrates, we fluorometrically analysed the activity of these enzymes in the left and right frontal cortex of control untreated Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs) and compared their activities with WKY or SHR treated with the antihypertensive drugs captopril (CAP) and propranolol (PRO) or with the hypertensive N (G)-nitro-L-arginine methyl ester. SBP was also measured in all WKY and SHR groups. RESULTS: Untreated WKY, WKY treated with CAP or PRO and SHR treated with CAP exhibited normotensive values of SBP. However, WKY treated with N (G)-nitro-L-arginine methyl ester as well as untreated SHR and SHR treated with PRO and N(G)-nitro-L-arginine methyl ester demonstrated hypertensive values of SBP. Changes in the bilateral distribution of neuropeptidases were depending on the strain, the enzyme analysed and the drug used. Normotensive WKY groups (WKY, CAP, PRO) revealed intrahemispheric correlations mainly in the left hemisphere. In contrast, WKY treated with N(G)-nitro-L-arginine methyl ester and SHR groups demonstrated intrahemispheric correlations mainly in the right hemisphere. Interhemispheric correlations were mostly observed in WKY as well as in SHR groups with antihypertensive treatments (CAP, PRO). CONCLUSION: Our results suggest specific brain bilateral patterns of neuropeptidase activities in WKY that change in SHR. This observation may be related to the cognitive disorders that have been described in these animals and that change under antihypertensive or hypertensive drug's treatments.

Functional and neurometabolic asymmetry in SHR and WKY rats following vasoactive treatments.

A lateralized distribution of neuropeptidase activities in the frontal cortex of normotensive and hypertensive rats has been described depending on the use of some vasoactive drugs and linked to certain mood disorders. Asymmetrical neuroperipheral connections involving neuropeptidases from the left or right hemisphere and aminopeptidases from the heart or plasma have been suggested to play a role in this asymmetry. We hypothesize that such asymmetries could be extended to the connection between the brain and physiologic parameters and metabolic factors from plasma and urine. To assess this hypothesis, we analyzed the possible correlation between neuropeptidases from the left and right frontal cortex with peripheral parameters in normotensive (Wistar Kyoto [WKY]) rats and hypertensive rats (spontaneously hypertensive rats [SHR]) untreated or treated with vasoactive drugs such as captopril, propranolol and L-nitro-arginine methyl ester. Neuropeptidase activities from the frontal cortex were analyzed fluorometrically using arylamide derivatives as substrates. Physiological parameters and metabolic factors from plasma and urine were determined using routine laboratory techniques. Vasoactive drug treatments differentially modified the asymmetrical neuroperipheral pattern by changing the predominance of the correlations between peripheral parameters and central neuropeptidase activities of the left and right frontal cortex. The response pattern also differed between SHR and WKY rats. These results support an asymmetric integrative function of the organism and suggest the possibility of a different neurometabolic response coupled to particular mood disorders, depending on the selected vasoactive drug.

Asymmetrical response of aminopeptidase A in the medial prefrontal cortex and striatum of 6-OHDA-unilaterally-lesioned Wistar Kyoto and spontaneously hypertensive rats.

Aminopeptidase A is responsible for the hydrolysis of angiotensin II and cholecystokinin. By measuring its activity we obtain a reflection of the functional status of its endogenous substrates. Dopamine coexists with these neuropeptides in striatum and prefrontal cortex. If the content of any of them is altered, the others and the functions they are involved in would also be affected. Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) are rat models with different motor behavior and mood. We hypothesized that aminopeptidase A activity could be modified in WKY or SHR affecting the brain dopamine. The results may provide new insights for the understanding of dopamine-related disorders such as schizophrenia, depression or Parkinson's disease. To analyze the influence of unilateral depletions of dopamine on the intra- and inter-hemispheric behavior of aminopeptidase A in striatum and prefrontal cortex of WKY and SHR, aminopeptidase A activity was measured fluorometrically, using an arylamide derivative as substrate, in the left and right sides of striatum and prefrontal cortex of WKY and SHR treated with saline (control groups) or following left or right intrastriatal injections of 6-hydroxydopamine (lesioned groups). Differential asymmetrical intra- and inter-hemispheric behaviors of aminopeptidase A were observed, depending on the lesioned hemisphere, the region and the strain analyzed. Results also demonstrated differential intra and inter-hemispheric correlations between striatum and prefrontal cortex and between both regions and motor behavior depending on the side of lesion. The changes mostly involved the left hemisphere. The functions in which the aminopeptidase A activity is involved could be modified depending on whether the dopamine depletion occurs on the left or right hemisphere.

Combination of the dipeptidyl peptidase IV inhibitor LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] with the angiotensin II type 1 receptor antagonist valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl]methyl]-L-valine] enhances pancreatic islet morphology and function in a mouse model of type 2 diabetes.

LAF237 [(S)-1-[(3-hydroxy-1-adamantyl)ammo]acetyl-2-cyanopyrrolidine] is an inhibitor of dipeptidyl peptidase IV that delays the degradation of glucagon-like peptide-1 (GLP-1). Valsartan [N-(1-oxopentyl)-N-[[2'-(1H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl]-l-valine] is an antagonist of the angiotensin II type 1 receptor (AT1R) that reduces the incidence of type 2 diabetes mellitus. LAF237 and valsartan act on a common target through separate pathways to improve pancreatic islet cell function. We hypothesize that the combination of these two drugs acts in a synergistic or additive manner on islet function and structure. To test this hypothesis, we performed in vitro and in vivo studies. To measure the acute effect of the treatment, pancreatic islets of db/db mice were isolated and stimulated in vitro with glucose in the presence of valsartan (1 microM) and exendin-4 (100 nM), a GLP-1 receptor agonist. Combination treatment with valsartan and exendin-4 significantly enhanced glucose-stimulated insulin secretion from isolated islets. For studies of chronic effect, db/db mice received LAF237 (1 mg/kg/day) and/or valsartan (10 mg/kg/day). Islet cell reactive oxygen species (ROS), proliferation, apoptosis, fibrosis, beta-cell area, and glucose homeostasis were evaluated after 8 weeks of treatment, which showed that combination treatment resulted in a significant increase in pancreatic islet beta-cell area compared with monotherapy. This beneficial effect correlated with an increase in beta-cell proliferation and a decrease in ROS-induced islet apoptosis and fibrosis. These in vitro and in vivo data indicate that combination treatment with LAF237 and valsartan has significant beneficial additive effects on pancreatic beta-cell structure and function compared with their respective monotherapeutic effects.

Role of aminopeptidases in the neuroendocrine control of blood pressure in experimental animals.

Control of blood pressure is partially accomplished by several proteolytic enzymes included in the renin-angiotensin system. These enzymes produce several peptides that form the active components of the system. Study of these enzymes is essential for a deep understanding of blood pressure control and could offer the possibility of controlling this system pharmacologically. Glutamylaminopeptidase converts angiotensin II into angiotensin III, which in turn is converted into angiotensin IV by an alanyl or arginyl aminopeptidase. Angiotensin I, through the action of aspartyl aminopeptidase, is converted into angiotensin 2-10, which may counteract the hypertensive actions of angiotensin II. Angiotensin III is the most active form of brain angiotensins and has a tonic stimulatory effect on blood pressure. Analysis of glutamyl-aminopeptidase inhibition has allowed the development of agents that effectively reduce blood pressure. Moreover, the development of aspartyl-aminopeptidase activators could be another goal, with a view to designing new antihypertensive agents. Our group has observed that unilateral lesions of the nigrostriatal pathway in rat brain produce simultaneous modifications in blood pressure and aminopeptidase activities, both in brain and plasma, curiously depending on the side of the lesion. This possible interaction among blood pressure, aminopeptidase activities and brain asymmetry, which could produce a differentiated neuroendocrine response on blood pressure control, may help us to understand the deep mechanism by which the brain is able to control blood pressure peripherally.

Divergent profile between hypothalamic and plasmatic aminopeptidase activities in WKY and SHR. Influence of beta-adrenergic blockade.

AIMS: Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) differ in their renin-angiotensin system function and sympathetic tone. The metabolism of angiotensins and vasopressin depends on the action of certain aminopeptidases whose activity may be influenced by the autonomic nervous system. Their regulation may differ between WKY and SHR in hypothalamus and plasma according to the sympathetic tone. We analyzed aminopeptidases responsible for the hydrolysis of certain angiotensins, vasopressin, cholecystokinin or enkephalins in hypothalamus and plasma of WKY and SHR in untreated controls rats and under beta-adrenoceptor blockade. Systolic blood pressure, food intake, water intake and diuresis were measured as parameters modulated by the autonomic nervous system and the above mentioned peptides. MAIN METHODS: Glutamyl-, aspartyl-, cystinyl- and alanyl-aminopeptidase activities were analyzed fluorimetrically in plasma and hypothalamus of control and propranolol-treated (100mg/kg/day administered in drinking water for 1month) WKY and SHR, using arylamide derivatives as substrates. KEY FINDINGS: An opposite response of aminopeptidases to propranolol treatment between plasma and hypothalamus was observed in either WKY and SHR. Furthermore, the behavior of aminopeptidases was inversed between WKY and SHR either in hypothalamus and plasma: while the activity increased in hypothalamus and decreased in plasma of WKY, it decreased in hypothalamus and increased in plasma of SHR. SIGNIFICANCE: These results revealed an inverse response of aminopeptidases between hypothalamus and plasma and also an opposite behavior of these enzymes between WKY and SHR in hypothalamus and plasma. These observations support the involvement of the sympathetic system in the modulation of aminopeptidase activities.

Thyroid Disorders Change the Pattern of Response of Angiotensinase Activities in the Hypothalamus-Pituitary-Adrenal Axis of Male Rats.

Thyroid disorders affect the hypothalamic-pituitary-adrenal axis with important consequences on the cardiovascular function in which the renin-angiotensin system plays a major role. Hypo and hyperthyroidism influence the classic main components of the renin-angiotensin system. However, the behavior of other elements of the renin-angiotensin system such as Ang III, Ang 2-10, Ang IV, or AT4, regulated by angiotensinase enzymes such as alanyl- (AlaAP), cystinyl- (CysAP), glutamyl- (GluAP), or aspartyl-aminopeptidase (AspAP), has not yet been described. In order to obtain a comprehensive view on the response of the renin-angiotensin system in the hypothalamic-pituitary-adrenal axis of animals with thyroid disorders, these enzyme activities were simultaneously analyzed fluorometrically, using arylamide derivatives as substrates in hypothalamus, anterior and posterior pituitary, adrenals and plasma of euthyroid, hypothyroid, and hyperthyroid rats, and their intra- and inter-tissue correlations were evaluated. The response is depending on the type of enzyme studied, its location and the thyroid status. Anterior pituitary, adrenals and plasma were mainly affected by the thyroid disorders. In the anterior pituitary, GluAP and AspAP increased in hypothyroid rats. In adrenals, AlaAP and CysAP decreased in hypothyroid whereas GluAP and AspAP decreased in hyperthyroid rats. In plasma, while AlaAP increased in hypo- and hyperthyroid rats, CysAP and GluAP decreased only in hyperthyroid. In comparison with euthyroid, intra-tissue correlations decreased in hypothyroid but inter-tissue correlations decreased mainly in hyperthyroid rats. Thyroid disorders also produced a disruption in the pattern of inter-tissue correlations observed in euthyroid. These results suggest that thyroid hormone levels hit components of the renin-angiotensin system and may influence the paracrine and endocrine cross talk between cells.

Diurnal opposite variation between angiotensinase activities in photo-neuro-endocrine tissues of rats.

Central and peripheral renin-angiotensin systems (RASs) act in a coordinated manner for the physiologic functions regulated by neuroendocrine events. However, whereas the diurnal rhythm of peripheral circulatory and tissue RASs is well known, the circadian behaviour of their components in central photo-neuro-endocrine structures, key elements for the control of circadian rhythms, has been barely studied. In the present study, we analysed the aspartyl- (AspAP) and glutamyl-aminopeptidase (GluAP) (aminopeptidase A) activities, the angiotensinases responsible for the metabolism of Ang I to Ang 2-10 and Ang II to Ang III, respectively, in the retina, anterior hypothalamus and pituitary at different light and dark time-points of a 12:12 h light:dark cycle (7-19 h light), using arylamide derivatives as substrates. The results demonstrated that while retina and pituitary exhibited their highest levels of AspAP activity in the light period and the lowest in the dark one, the contrary occurred in the hypothalamus - the lowest levels were observed in light conditions and the highest in darkness. The outcome for GluAP showed the highest levels in the light period and the lowest in the dark one in the three tissues analysed. In conclusion, changes in angiotensinase activities throughout the daytime may cause changes of their respective substrates and derived peptides and, consequently, in their functions. This observation may have implications for the treatment of hypertension.

Bilateral distribution of enkephalinase activity in the medial prefrontal cortex differs between WKY and SHR rats unilaterally lesioned with 6-hydroxydopamine.

Changes in the basal brain bilateral morphologic, neurochemical and/or functional patterns may be partly responsible for some brain disorders such as those involving mood. WKY and SHR strains as well as 6-hydroxydopamine (6-OHDA)-lesioned animals are validated models for the study of mood disorders. Because dopamine and enkephalins are involved in anxiety-related behaviors, the aim of our study was to analyze enkephalinase activity, assayed as aminopeptidase M activity, in the left and right medial prefrontal cortex (mPFC) of WKY and SHR treated with saline (sham group) or following left or right intrastriatal injections of the neurotoxic 6-OHDA. Sham left and sham right WKY exhibited a significant left predominance. Left 6-OHDA-lesioned rats inverted the left predominance of sham to right predominance. In right 6-OHDA-lesioned rats, the left predominance in sham right rats disappeared. Sham left as well as sham right SHR did not show any bilateral differences. In contrast, while the left lesion demonstrated a highly significant left predominance, the right lesion showed a slight but significant right predominance. A significant negative correlation between enkephalinase activity of the right mPFC and blood pressure and heart rate was observed only in left-lesioned SHR. Our results demonstrate that unilateral nigrostriatal injections of 6-OHDA influence the bilateral distribution of enkephalinase activity depending on both the side of the lesion and the strain analyzed. These results support the hypothesis that DA pathways may interact asymmetrically with enkephalins in the mPFC and that enkephalinase activity may play a role in the regulatory mechanisms underlying this interaction.

Brain aminopeptidases and hypertension.

The brain aminopeptidases that participate in the enzymatic cascade of the renin-angiotensin system play a major role in blood pressure (BP) control, and their study offers new perspectives for the understanding of central BP control and the treatment of hypertension. In this system, angiotensin II is converted to angiotensin III (Ang III) by glutamyl aminopeptidase (GluAP) and Ang III is further metabolised to angiotensin IV by alanyl aminopeptidase or arginine-aminopeptidase. It is now clear that Ang III is the key active form of the central angiotensins, exerting tonic stimulatory control over BP. Therefore, the development of GluAP inhibitors as potential antihypertensive agents offers new perspectives for therapy. Brain aspartyl aminopeptidase, which converts angiotensin I to angiotensin 2-10, is also a possible target for antihypertensive therapy because of its potential role in BP control. Finally, since changes in BP levels, that paralleled changes in brain and plasma aminopeptidase activities, were observed after unilateral lesions of the nigrostriatal system, brain asymmetry, aminopeptidase activities and BP control appear to be related, resulting their interplay in an asymmetrical neuroendocrine response that differentially affect BP control. The study of this interaction may contribute to our understanding of how the brain controls BP.

Effect of angiotensin II type 1 receptor blockade on cardiac remodeling in angiotensin II type 2 receptor null mice.

To clarify the possible involvement of uninhibited angiotensin II (Ang II) type 2 (AT(2)) receptor stimulation in the effects of an Ang II type 1 (AT(1)) receptor blocker, valsartan, we examined the cardiovascular remodeling induced by aortic banding with the use of wild-type (Agtr2+) and AT(2) receptor null (Agtr2-) mice. Aortic banding caused cardiac hypertrophy in Agtr2+ and Agtr2- mice to a similar degree 6 weeks after surgery, whereas coronary arterial thickening and perivascular fibrosis were more exaggerated in Agtr2- mice. The AT(2) receptor was observed predominantly in the coronary arteries and perivascular region of Agtr2+ mice. Valsartan at a dose of 1 mg/kg per day, which did not influence systolic blood pressure, suppressed cardiac hypertrophy similarly in both strains. Valsartan inhibited coronary arterial thickening and perivascular fibrosis in both groups; however, the inhibitory effects of valsartan were significantly weaker in Agtr2- mice. The inhibitory effects of a nonselective Ang II receptor antagonist, [Sar(1),Ile(8)]-Ang II, on cardiac hypertrophy, coronary artery thickening, and perivascular fibrosis were not significantly different in Agtr2+ and Agtr2- mice. These results suggest that the improvement by valsartan of coronary arterial thickening and perivascular fibrosis after pressure overload is caused by uninhibited AT(2) receptor stimulation in addition to AT(1) receptor blockade.