BIOCHEMICAL

22, 264-265 ! 1979)

MEDICINE

LETTER Two Fractions

TO THE EDITOR

of Cryoactivable

Prorenin

in Human

Plasma

An inactive form of renin convertible into an enzymologically active renin by cryoactivation at -5°C and pH 7.4 for 4 days, has been identified in plasma of normal, hypertensive, and anephric subjects (l-6). This coldactivable substance termed “prorenin” (2.3) is measured as prorenin activity, resulting from the difference between values of plasma renin activity detected in cryoactivated plasma (total renin activity) and nonprocessed sample (endogenous renin activity). Results are reported here of studies on human plasma pool submitted to cryoactivation for more than 4 days. Plasma was obtained from blood samples collected at 9 AM in cooled vacutainers containing disodium ethylenediaminetetraacetic acid (Na, EDTA), from normal volunteers on random sodium intakes. The pool was divided into 0.4-ml aliquots and frozen at -40°C until the assay,

1 -.-.

r.5 E p” C*

Endogenous

renon

sctivaty r;

CD c z., g

3

., ii .5

5.0

i.

i 2

1

1.0 : 0.5 -

E 5 cz ci

E ii 2 1

Ol1 Days

5 10 of cold

15 activ*tion

20

25 at -5’C

1

30

Days

5

10

of cold

15 activation

20

25 at

30

-5’C

FIG. 2.

FIG. 1.

FIG. 1. Conversion in total renin activity during cold-activation period. Reproducibility of activation was obtained by measurements repeated 24 times in four distinct sets of radioimmunological assay. FIG. 2. Relationship between actual concentrations of prorenin and duration of cryoactivation. 264 0006-2944/79/050264-02$02,00/0 Copyright All rights

@I 1979 by Academic Press. Inc. of reproduction in any form reserved.

LETTER

TO THE EDITOR

265

Endogenous plasma renin activity was measured by radioimmunological determination of angiotensin I (AI) developed after incubation at 37°C and pH 5.7 for at least 90 min, using 2,3-dimercaptopropanol and Shydroxyquinolinsulfate to inhibit the converting enzymes and angiotensinases. Total renin activity in cryoactivated plasma was determined as plasma renin activity in the same radioimmunoassay. The AI measured at +4”C in nonpretreated plasma was used as reference blank in both determinations. The Fig. 1 illustrates the development of total renin activity in human plasma during the period of cryoactivation. Two points of equilibrium are visible. Figure 2 shows the calculated “concentrations” of prorenin. It can be seen that prolonging exposure to low temperature an additional peak of long-term convertible prorenin can be measured. On the basis of this bimodality in conversion it is plausible to suggest that two fractions of cold-sensitive prorenin are present in human plasma. REFERENCES 1. Osmond, D. H., Ross, L. J., and SciaiT, K. D., Canad. J. Physiol. Pharmucol. 51, 705 (lW3). 2. Sealey, J. E., and Laragh, J. H., Circ. Res. 36-37 (Suppl. I), 10 (1975). 3. kdey, J. E., Moon, C., Laragh, J. H., and Alderman, M., Amer. J. Med. 61,73 1 (1976). 4. Atlas, S. A., Sealey, J. E., Laragh, J. H., and Moon, C., Lancer 2, 785 (1977). 5. Leckie, B. J., McConnell, A., Grant, J., Morton, J. J., Tree, M., and Brown, J. J., Circ. Res. 40 (Suppl. I), 121 (1977). 6. Weimberger, M. H., Wade, M. B., Aoi, W., Usa, T., Dentino, M., Luft, F., and Grim, C. E., Circ. Res. 40 (Suppl. I), 1 (1977).

Cucmr PIETR0 SALANDI EGIDIO SCAVO DOMENICO

I Patologia Medica University of Rome Viale de1 Policlinico 00100 Rome, Italy Received March 13, 1979