Biochemical aspects of the glomerular angiotensin ii formation

Biochemical

aspects

of kidney

xi

function

BIOCHEMICALASPECTS OF THE GLOMERULAR ANGIOTENSINII FORMATION Dept.

Herbert Dahlheim, Hans Schweisfurth, and Walter Rurghardt of Physiology, University of Munich, Pettenkoferstr. 12, D-8000 Munchen 2, West Germany.

The intrarenal renin angiotensin system (RAS) is postulated to participate in regulation of renal function. Little is known about renal angiotensin I converting enzyme (CE) which transforms the decapeptide angiotensin I (A I) into the octapeptide A II, the main biologically active component of the RAS. The investigations were performed to demonstrate the existence of glomerular CE activity (CEA), which has recently been questioned, and to study the A II formation in the glomerular area. Using our modification of the technique of Piquilloud et al., we were able to measure CEA of 10 microdissected rat glomeruli (CEA: 0.047+0.0045 M/glom.‘h; n=8). The existence of a glomerular A I iso-CE was demonstrated. Higher iso-CEA was found This enzyme had a pH optimum of about 6.0 in cortical tissue free of vasculature. (plasma CE: 8.0) for the synthetic CE substrate Z-Phe-His-Leu or about 6.5 (plasma CE: 8.2) for the natural substrate A I. Iso-CE could he blocked by the CE inhibitor SQ 20881. However, in contrast its to the plasma CE, neither EDTA nor NaCl affected activity. The KM value of iso-CE (23.2 PM) was significantly lower than that of plasma (70.5 PM). The highest renal A II immunoreactivity was found in microdissected glomeruli (>lO rig/g wet tissue) also implying the presence of glomerular CEA. However, up to now we cannot answer the question whether renin or CE is the rate limiting enzyme for glomerular A II formation. In preliminary experiments cortical iso-CEA was found to be influenced by several experimental conditions, such as renal artery stenosis, haemorrhage or NaCl intake. CORRELATIONBETWEEN RENALSODIUMTRANSPORT AND KIDNEYTISSUE LEVELS OF ATP AND ADENOSINE Abt.

Pharmokologie

H. Osswald and G. Nahakowski der RWTHAachen, Melatener Str.

213,

D-5100 Aachen

In this study we tested our working hypothesis of a metabolic control of glomerular filtration rate (GFR) via increased ATP utilization and increased production of the intrarenal vasoconstrictor adenosine. The work load of the kidney was elevated by infusions of hypertonic saline (HS) into the thoracic aorta. Transported sodium (T ) was calculated from GFR and sodium concentration in the femoral arterial bloodNgnd urine. Three groups of rats were studied; 1: controls, 2: HS-normal diet, 3: HS-low sodium diet. Adenine nucleotides were measured in tissue extracts from shock frozen kidneys using high pressure liquid chromatography, adenosine as previously described (Osswald et al., Pflug. Arch., -37: 45, 1977). The results are shown in the table. ATP

’

ADP nmol/g

ADO

AMP

T Na

-ATP ADO

vet weight

ueq/min

GROUP1 (n=6)

2550 +54

603 +86

248 +58

5.69 +1.2

536 +130

64.5 +4.7

GROUP2 (n=8) . .

1640 +99

465 +44

223 +47

7.69 +1 .n

307 +64

82.8 +5.9

GROUP3 (n=7)

1050 +259

434 l47

252 +47

16.2 +3.2

I

I expressed

I per

I

I

73 +22

I

109 +9

I

I

100 g body weight

It is obvious that tissue content of ATP is decreased when tubular sodium transport is markedly elevated, while adenosine tissue content is increased J-fold (Group 3). We conclude that our results support the concept of a metabolic control of GFR via increased formation of the intrarenal vasoconstrictor adenosine during periods of increased renal work. B.C. lop--o