Ramírez Mj

Sex Differences and In Vitro Effects of Steroids on Serum Aminopeptidase Activities

We studied the possible existence of physiological sex differences in serum aminopeptidase activities in mice, by evaluating the effect of gonadectomy and the in vitro response to the presence in the medium of cholesterol or steroid hormones. Alanyl- and glutamyl-aminopeptidase activities were measured in sera from male, female, orchiectomized and ovariectomized mice, incubated with substrate solutions, and compared with the same groups of serum incubated with substrate solutions including cholesterol, 17-beta-estradiol, testosterone, progesterone or hydrocortisone. Our results demonstrated highly significant sex differences, and an influence of cholesterol and steroid hormones on aminopeptidase activity. Depending on the nature of the aminopeptidase, these enzymes responded in different ways to the presence of these substances and also responded differently to gonadectomy. For alanyl-aminopeptidase activity, but not for glutamyl-aminopeptidase activity, there was a clear difference in response between males and females to incubation of the serum with steroid hormones.

Sex differences and age-related changes in human serum aminopeptidase A activity

Given that aminopeptidase A is primarily responsible for cleaving aspartic acid and converting angiotensin II to angiotensin III, the purpose of the present study was to evaluate the activity of aminopeptidase A by determination of glutamate aminopeptidase activity (GluAP) and aspartate aminopeptidase activity (AspAP) (reported respectively as aminopeptidase A and angiotensinase A activities) in human serum during development and ageing, in an apparently healthy population of 139 male and 148 female subjects. To measure GluAP and AspAP we used glutamyl- and aspartyl-2-naphthylamide as substrates. Significant age-related increases were observed in GluAP activity in males and females and in AspAP activity in females. In males, there were no age-related differences in AspAP activity. A significant correlation was observed between age and GluAP activity in the population analysed as a whole or according to sex. No correlation was demonstrated between age and AspAP activity either in the whole population or according to sex. These results may reflect the evolution of the functional status of susceptible circulating substrates during development and ageing.

Aminopeptidase activities after water deprivation in male and female rats

Aminopeptidases (APs) play a major role in the metabolism of circulating and local peptides, such as angiotensins and vasopressin, substances involved in the control of blood pressure and water balance. In the present work, we studied the influence of dehydration on angiotensinases and vasopressin-degrading activity. Since sex differences may exist in the regulation of water balance by angiotensin II and differential sexual steroid modulation of vasopressin secretion, in response to osmotic stimulation have been reported, gonadotropin releasing hormone (GnRH)-degrading activity was also analysed in serum, neurohypophysis and adrenal glands of male and female rats. Our results did not suggest sex differences in the response to changes in osmolality. GnRH-degrading activity decreased in serum of dehydrated males and females, which suggests a longer action of the peptide under these conditions. In neurohypophysis, there was an increase in the activity of aminopeptidase A (APA), the enzyme responsible for the metabolism of angiotensin II to angiotensin III. This occurs with a decrease in alanyl aminopeptidase activity, which would lead to a prolonged action of angiotensin III by reduction of its metabolism. In adrenals of dehydrated animals, the results would imply a high degree of metabolism of angiotensin III and vasopressin.

Oral administration of losartan influences aminopeptidase activity in the frontal cortex

Although there is a brain renin-angiotensin system, its mechanisms of control are not fully understood. We studied the effect of oral administration of the AT(1) receptor antagonist losartan on brain aminopeptidase (AP) activity, which plays a major role in neuropeptide metabolism. Six AP activities, related and non-related with the angiotensin (Ang) metabolism, were measured in their soluble and membrane-bound forms in the frontal cortex of control animals and rats treated with losartan, chronically administered via the drinking water. The results demonstrate that soluble pGluAP and membrane-bound AspAP and GluAP increased significantly in losartan-treated animals, indicating that the blockade of the AT(1) receptor stimulates the activity of AP involved in the Ang metabolism. Moreover, the blockade of the AT(1) receptor induces changes not only in the brain angiotensin metabolism, but probably also in that of other neuropeptides.

Dietary supplementation with olive oil influences aminopeptidase activities in mice

Abstract We compared the effect of a low fat diet and an high fat diet containing olive oil (20% wt/wt) on soluble and membrane-bound aminopeptidase activities, in serum and selected tissues of male mice. After ten weeks of feeding, serum total cholesterol was determined colourimetrically. Alanyl-, arginyl- and cystinyl-aminopeptidase activities were measured fluorometrically using arylamide derivatives as substrates. Mice fed with the olive oil-supplemented diet had higher rates of weight gain than controls from the second week of feeding. Serum total cholesterol concentrations were higher after feeding the olive oil diet than after feeding the control diet. In serum, the olive oil-fed group had significantly higher arginyl-aminopeptidase activity levels than controls. Soluble alanyl- and arginyl-aminopeptidase activities increased significantly in the brain, adrenal gland and testis of olive oil-fed animals. Soluble cystinyl-aminopeptidase activity increased significantly in testes and liver and decreased in the adrenal glands of olive oil-fed mice. There was a significant decrease in membranebound cystinyl-aminopeptidase activity in the adrenal glands of olive oil-fed mice. These findings show that a diet supplemented with olive oil modifies certain aminopeptidase activities in specific tissues. The results may reflect functional modifications in susceptible endogenous substrates.

Lateralization of aminopeptidase A activity in substantia nigra, striatum and frontal cortex of rats ☆

Several brain aminopeptidase activities have been reported to be asymmetrical, but no direct correlation with lateralized functions has been proposed. Cholecystokinin (CCK) coexists with dopamine (DA) in the nigrostriatal system, which is involved in lateralized motor behaviors. Because aminopeptidase A activity is probably responsible for the hydrolysis of CCK, we studied the left-right distribution of glutamate- (GluAP) and aspartate-aminopeptidase (AspAP) activities in their soluble (Sol) and membrane-bound (M-B) forms in the substantia nigra, striatum and cortex of rats. Although there was a highly significant predominance of the left side in the substantia nigra and striatum for Sol GluAP and M-B AspAP respectively, in the frontal cortex predominance was on the right side for M-B AspAP. These results suggest a relationship between aminopeptidase A activity and lateralized nigro-striato-cortical functions involving CCK.

Changes in membrane‐bound leucine aminopeptidase activity during maturation and ageing of brain

Aminopeptidases are believed to be enzymes that regulate the activity of various neuropeptides. However, their physiological role, as well as their mechanisms of regulation, are not well understood. To analyze a part of the regulatory mechanisms that control the activity of these enzymes, the subcellular distribution of membrane‐bound leucyl aminopeptidase activity was studied in rat brain during development and ageing. Except in fetuses, the enzymic activity was greatest in the microsomal fraction in all ages tested. Except in microsomal and myelin fractions, compared with fetuses, leucyl aminopeptidase activity showed a decrease in 1‐week‐old rats and a subsequent increase to adult levels in 1‐month‐old rats. This profile differed in the microsomal fraction, where the activity increased steadily up to 1‐month‐old rats. After this age, the activity decreased progressively in 5‐month and 24‐month‐old rats. These results may reflect changes in the functional status of the susceptible substrates during development and ageing.