RESUMO
The activity of angiotensin I-converting enzyme (ACE) was determined in tubular fluid collected from several portions of the rat nephron and urine and in total and efferent arteriolar blood using hippuryl-L-His-Leu as substrate. ACE activity decreased 30% from the pre- to the postglomerular arterioles (P < 0.001), suggesting a role of the glomerulus in ACE clearance. The enzyme activity was found to be present throughout the rat nephron. However, the highest activities were found in the proximal tubule and urine (0.692 +/- 0.007 and 1.05 +/- 0.015 pmol x microl(-1) x min(-1), respectively). Compared with other segments, ACE activity decreased from the initial portion of the proximal tubule to the distal nephron and increased again in the urine. Along the proximal tubule, ACE was secreted and degraded and/or reabsorbed and then secreted again into the collecting duct; no ACE activity was found in the late distal tubule, but a high level was detected in the urine, indicating a potential physiological role in the inactivation of the kinins formed by kallikrein beyond the connecting tubules. Moreover, the possible role of mesangial cells (MC) in the decrease of intraglomerular ACE was also evaluated. The analysis of ACE gene showed that MC in culture are able to express ACE mRNA. Moreover, ACE is produced as an ectoenzyme and as a secreted form of the enzyme, indicating a potential effect of local angiotensin II production on MC function.
Assuntos
Mesângio Glomerular/enzimologia , Túbulos Renais/enzimologia , Néfrons/enzimologia , Peptidil Dipeptidase A/metabolismo , Animais , Sobrevivência Celular , Células Cultivadas , Mesângio Glomerular/citologia , Túbulos Renais Coletores/enzimologia , Túbulos Renais Proximais/enzimologia , Masculino , Oligopeptídeos , Peptidil Dipeptidase A/urina , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Especificidade por Substrato , Transcrição GênicaRESUMO
The response of juvenile cultivated Piaractus mesopotamicus to handling stress, without anesthesia, was determined over 3-5 min (T1), 1 h (T2) and 6 h (T3) after capture. Plasma cortisol, glucose and total cholesterol were measured. Hyperglycemia present at T2 continued to rise until T3 while plasma cortisol levels increased but were similar at T2 and T3. Total plasma cholesterol was altered only at T3. Hyperglycemic changes were greater in fish without than with stomach contents during the T2-T3 period. These differences in hyperglycemic changes may reflect the role of hormones other than cortisol in the regulation of glucose release in these fish.
