Acta physiol. scand. 1976. 96. 134-136 From the Department of Physiology, College of Veterinary Medicine, Helsinki, Finland
A Comparison between the Central Effects of Angiotensin I1 and its Fragments, Desl-Angiotensin 11 and Dea,,-Angiotensin II BY
LEAERIKSONand F. FYHRQUIST
Angiotensin I1 is known to act centrally on fluid balance and blood pressure (cf. Severs and Daniels-Severs 1973). The natural fragment of angiotensin 11, 2-8 heptapeptide, so-called “angiotensin III”, has been found to increase adrenal aldosterone production effectively (Blair-West et al. 1971), whereas its action on vascular muscle cells is less (cf. Regoli, Park and Rioux 1974). Fitzsimons (1971) has studied the dipsogenic action of various angiotensin analogues by intracranial injections in the rat. He found that the 2-8 heptapeptide retained about 50% of the dipsogenic activity of the octapeptide, whereas the 3-8 hexapeptide was almost ineffective. This has made it of interest to study centrally mediated effects of these angiotensin analogues in the conscious goat. 6 adult female goats were used. The animals were routineously kept in metabolism cages where all experiments were conducted. The goats had free access to hay and water, and got 5 g NaCl in crushed oats each afternoon. They were provided with a permanent cannula in one of the lateral cerebral ventricles. Two of the goats had a polyvinyl catheter permanently implanted in the carotid artery. The blood pressure and heart rate were recorded on a “Beckmann-Offner” Dynograph via a “Statham” pressure transducer. The water diuresis was established by giving the goats about 100 ml of 38°C water/kg b.wt. into the rumen. Urine Na+ and K+ were determined with flame photomstry and urine osmolality was measured by a “Fiske” osmometer. Plasma osmolality 290 mosm/kg was used for calculation of renal free water clearance (CH~O). The angiotensin I 1 used was Hypertensin “Ciba”, whereas the fragments were des,-ileu6-angiotensin I1 and des,,,-ileuG-angiotensin11.
Comparison o f the effects of angiotensin II and III Prolonged intraventricular infusions. As expected from previous studies in the goat (Andersson et al. 1972) angiotensin I1 (at the concentration of 2.5 pg/ml at a rate of 20 pllrnin during 30 min) caused thirst, antidiuresis and conspicuous natriuresis. In contrast, infusions of “angiotensin 111” at equimolar concentration (2.2 pg/ml) did not induce any urge to drink or antidiuresis, and had no obvious influence on renal sodium excretion (3 expts., 3 goats). Erief infusions. When a more concentrated angiotensin I1 solution (10 pg/ml) was infused at a rate of 20 pl/min during 5 min, distinct antidiuresis and moderate natriuresis developed 134
135
CENTRAL EFFECTS OF ANGIOTENSIN FRAGMENTS RENAL
r
CH20 ml/min
x-x m--I
O--O
0
20
LO
60
80
100
ANGlO 11 “ANGIO 111’’ DES12-ANGIO II
120
140
160 MIN
Fig. 1 . The antidiuretic and natriuretic responses to short intraventricular infusions of angiotensin 11 and its fragments in the hydrated goat. Values given as means +S.E. Rate of infusion into the lateral ventricle 20 pl/min. The infusion of angiotensin 11 (10 pg/ml) caused distinct antidiuresis and moderate natriuresis (7 expts.. 5 goats). The infusion of des,-angiotensin I I (17.7 ,ug/ml, corresponding to 20 iLg/ml of angiotensin 11) induced a smaller antidiuretic response (8 expts., 6 goats). Similar infusion of des,,,-angiotensin 11 (14.6 ,ug/ml) had no effect on water balance (7 expts., 4 goats).
(Fig. 1). All but one of the infusions induced drinking (7 expts., 5 goats). In 5 expts. the goats would drink more than 500 ml, so that water had to be withheld in order to avoid overhydration. The infusions were compared to similar infusions of “angiotensin 111’ at the concentration of 17.7 pg/ml, corresponding to 20 ,ug/ml of angiotensin I1 (8 expts., 6 goats). Two of the animals drank (450 ml and 280 ml) and a third sipped small amounts of water. No urge to drink was observed in the other 5 expts. Some inhibition of the water diuresis was observed in 5 expts. (Fig. 1). Blood developed after every infusion, and negative CHIO pressure was recorded in 2 of the animals. In one goat blood pressure rose 10 to 15 mmHg after infusion of “angiotensin 111” at the concentration of 17.7 pg/ml (2 expts.), while a rise of 30 mmHg occured after infusion of angiotensin I1 at 10 pg/ml (1 exp.) and 45 mmHg at 20 pg/ml (1 exp.). In the other goat “angiotensin 111” (17.7 ,ug/ml) raised the blood pressure 5 mmHg as compared to the rise of 25 mmHg after angiotensin I1 at the concentration of 10 ,ug/ml. Znfusion of hexupeptide (desl,2-ungiotensin 11) at the concentration of 14.6 pg/ml (corresponding angiotensin I1 20 pg/ml) at a rate of 20 pl/min during 5 min had no effects on water balance (Fig. 1, 7 expts., 4 goats). Discussion. The various peptide analogues of angiotensin I1 have given valuable information on characteristics of angiotensin receptors. There is evidence for the idea that the receptors in the adrenal cortex are different from those of smooth muscle (Williams et al.
136
LEA ERIKSSON A N D F. FYHRQUIST
1974). The natural shorter peptide fragments derived from the parent octapeptide have been studied extensively in various experimental models. Desl-angiotensin 11 (angiotensin 111) has shown to be the most active fragment. It effectively stimulates aldosterone secretion (Blair-West e t a / . 1971), whereas its action on vascular muscle is lesser (cf. Regoli, Park and Rioux 1974). In the present study, “angiotensin 111” appeared dipsogenic, although to a lesser extent than when infused into the angiotensin-sensitive regions in the rat’s diencephalon (Fitzsimons 1971). However, the present data cannot be readily compared to those of Fitzsimons (1971), who, for instance, applied straight into the brain tissue des,-angiotensin I1 with valine at the position 5, while we used intraventricular infusion and des,-ileu5-angiotensin 11. In the goat the intraventricular infusion of “angiotensin 111” induced antidiuresis and rise in blood pressure, but these responses also were markedly smaller than after angiotensin I1 infusion. The same latency time was observed for the antidiuresis induced by angiotensin II and 111. This indicates that both polypeptides act on a common, presumably membrane located receptor, as has been shown for smooth muscle cells (Baudouin CI a/. 1972). Our data also indicate that the 2-8 heptapeptide of angiotensin, but not the 3-8 sequence, carries the minimum structural requirement needed to release antidiuretic hormone. This still has to be tested with specific measurements of ADH. This work was supported by the Finnish National Research Council for Medical Sciences (02003705- I ) . The gifts of Hypertensin from the Ciba-Geigy Company and of angiotensin fragments from SchwartzMann, Orangeburg, USA, are gratefully acknowledged.
References ANDERSSON, B., L. ERIKSSON, 0. FERNANDEZ, C.-G. KOLMODIN and R. OLTNER, Centrally mediated effects of sodium and angiotensin I I on arterial blood pressure and fluid balance. Acra physiol. scancl. 1972. 85. 398407. BAUDOUIN, M., P. MEYER,S. FERMANDJIAN and J.-L. MORGAT,Calcium release induced by interaction of angiotensin with its receptors in smooth muscle cell microsomes. Narure (Lond.) 1972. 235. 336-338. BLAIR-WEST, J . R., J. P. COGHLAN, D. A. DENTON, J. W. FUNDER, B. A. SCOGGINS and R. D. WRIGHT, The effect of the heptapeptide (2-8) and hexapeptide (3-8) fragments of angiotensin I1 on aldosterone secretion. J. clin. Endocr. Merab. 1971. 32. 575-578. FITZSIMONS. J . T., The effect on drinking of peptide precursors and of shorter chain peptide fragments of angiotensin I1 injected into the rat’s diencephalon. J. Physiol. (Lond.) 1971 214. 295-303. REGOLI,D., W. K. PARKand F. Rioux, Pharmacology of angiotensin. Pliarniacol. Reo. 1974. 26. 69-123. SEVERS, W. B. and A. E. DANIELS-SEVERS, Effects of angiotensin on the central nervous system. Pliarmacol. Reit. 1973. 25. 4 1 5 4 4 9 . WILLIAMS, G. H., L. M. MCDONNELL, M. C. RAUXand N. K. HOLLENBERG, Evidence for different angiotensin I 1 receptors in rat adrenal glomerulosa and rabbit vascular smooth muscle cells. Circular. Rrs. 1974. 34. 384-390.
A Comparison between the Central Effects of Angiotensin I1 and its Fragments, Desl-Angiotensin 11 and Dea,,-Angiotensin II BY
LEAERIKSONand F. FYHRQUIST
Angiotensin I1 is known to act centrally on fluid balance and blood pressure (cf. Severs and Daniels-Severs 1973). The natural fragment of angiotensin 11, 2-8 heptapeptide, so-called “angiotensin III”, has been found to increase adrenal aldosterone production effectively (Blair-West et al. 1971), whereas its action on vascular muscle cells is less (cf. Regoli, Park and Rioux 1974). Fitzsimons (1971) has studied the dipsogenic action of various angiotensin analogues by intracranial injections in the rat. He found that the 2-8 heptapeptide retained about 50% of the dipsogenic activity of the octapeptide, whereas the 3-8 hexapeptide was almost ineffective. This has made it of interest to study centrally mediated effects of these angiotensin analogues in the conscious goat. 6 adult female goats were used. The animals were routineously kept in metabolism cages where all experiments were conducted. The goats had free access to hay and water, and got 5 g NaCl in crushed oats each afternoon. They were provided with a permanent cannula in one of the lateral cerebral ventricles. Two of the goats had a polyvinyl catheter permanently implanted in the carotid artery. The blood pressure and heart rate were recorded on a “Beckmann-Offner” Dynograph via a “Statham” pressure transducer. The water diuresis was established by giving the goats about 100 ml of 38°C water/kg b.wt. into the rumen. Urine Na+ and K+ were determined with flame photomstry and urine osmolality was measured by a “Fiske” osmometer. Plasma osmolality 290 mosm/kg was used for calculation of renal free water clearance (CH~O). The angiotensin I 1 used was Hypertensin “Ciba”, whereas the fragments were des,-ileu6-angiotensin I1 and des,,,-ileuG-angiotensin11.
Comparison o f the effects of angiotensin II and III Prolonged intraventricular infusions. As expected from previous studies in the goat (Andersson et al. 1972) angiotensin I1 (at the concentration of 2.5 pg/ml at a rate of 20 pllrnin during 30 min) caused thirst, antidiuresis and conspicuous natriuresis. In contrast, infusions of “angiotensin 111” at equimolar concentration (2.2 pg/ml) did not induce any urge to drink or antidiuresis, and had no obvious influence on renal sodium excretion (3 expts., 3 goats). Erief infusions. When a more concentrated angiotensin I1 solution (10 pg/ml) was infused at a rate of 20 pl/min during 5 min, distinct antidiuresis and moderate natriuresis developed 134
135
CENTRAL EFFECTS OF ANGIOTENSIN FRAGMENTS RENAL
r
CH20 ml/min
x-x m--I
O--O
0
20
LO
60
80
100
ANGlO 11 “ANGIO 111’’ DES12-ANGIO II
120
140
160 MIN
Fig. 1 . The antidiuretic and natriuretic responses to short intraventricular infusions of angiotensin 11 and its fragments in the hydrated goat. Values given as means +S.E. Rate of infusion into the lateral ventricle 20 pl/min. The infusion of angiotensin 11 (10 pg/ml) caused distinct antidiuresis and moderate natriuresis (7 expts.. 5 goats). The infusion of des,-angiotensin I I (17.7 ,ug/ml, corresponding to 20 iLg/ml of angiotensin 11) induced a smaller antidiuretic response (8 expts., 6 goats). Similar infusion of des,,,-angiotensin 11 (14.6 ,ug/ml) had no effect on water balance (7 expts., 4 goats).
(Fig. 1). All but one of the infusions induced drinking (7 expts., 5 goats). In 5 expts. the goats would drink more than 500 ml, so that water had to be withheld in order to avoid overhydration. The infusions were compared to similar infusions of “angiotensin 111’ at the concentration of 17.7 pg/ml, corresponding to 20 ,ug/ml of angiotensin I1 (8 expts., 6 goats). Two of the animals drank (450 ml and 280 ml) and a third sipped small amounts of water. No urge to drink was observed in the other 5 expts. Some inhibition of the water diuresis was observed in 5 expts. (Fig. 1). Blood developed after every infusion, and negative CHIO pressure was recorded in 2 of the animals. In one goat blood pressure rose 10 to 15 mmHg after infusion of “angiotensin 111” at the concentration of 17.7 pg/ml (2 expts.), while a rise of 30 mmHg occured after infusion of angiotensin I1 at 10 pg/ml (1 exp.) and 45 mmHg at 20 pg/ml (1 exp.). In the other goat “angiotensin 111” (17.7 ,ug/ml) raised the blood pressure 5 mmHg as compared to the rise of 25 mmHg after angiotensin I1 at the concentration of 10 ,ug/ml. Znfusion of hexupeptide (desl,2-ungiotensin 11) at the concentration of 14.6 pg/ml (corresponding angiotensin I1 20 pg/ml) at a rate of 20 pl/min during 5 min had no effects on water balance (Fig. 1, 7 expts., 4 goats). Discussion. The various peptide analogues of angiotensin I1 have given valuable information on characteristics of angiotensin receptors. There is evidence for the idea that the receptors in the adrenal cortex are different from those of smooth muscle (Williams et al.
136
LEA ERIKSSON A N D F. FYHRQUIST
1974). The natural shorter peptide fragments derived from the parent octapeptide have been studied extensively in various experimental models. Desl-angiotensin 11 (angiotensin 111) has shown to be the most active fragment. It effectively stimulates aldosterone secretion (Blair-West e t a / . 1971), whereas its action on vascular muscle is lesser (cf. Regoli, Park and Rioux 1974). In the present study, “angiotensin 111” appeared dipsogenic, although to a lesser extent than when infused into the angiotensin-sensitive regions in the rat’s diencephalon (Fitzsimons 1971). However, the present data cannot be readily compared to those of Fitzsimons (1971), who, for instance, applied straight into the brain tissue des,-angiotensin I1 with valine at the position 5, while we used intraventricular infusion and des,-ileu5-angiotensin 11. In the goat the intraventricular infusion of “angiotensin 111” induced antidiuresis and rise in blood pressure, but these responses also were markedly smaller than after angiotensin I1 infusion. The same latency time was observed for the antidiuresis induced by angiotensin II and 111. This indicates that both polypeptides act on a common, presumably membrane located receptor, as has been shown for smooth muscle cells (Baudouin CI a/. 1972). Our data also indicate that the 2-8 heptapeptide of angiotensin, but not the 3-8 sequence, carries the minimum structural requirement needed to release antidiuretic hormone. This still has to be tested with specific measurements of ADH. This work was supported by the Finnish National Research Council for Medical Sciences (02003705- I ) . The gifts of Hypertensin from the Ciba-Geigy Company and of angiotensin fragments from SchwartzMann, Orangeburg, USA, are gratefully acknowledged.
References ANDERSSON, B., L. ERIKSSON, 0. FERNANDEZ, C.-G. KOLMODIN and R. OLTNER, Centrally mediated effects of sodium and angiotensin I I on arterial blood pressure and fluid balance. Acra physiol. scancl. 1972. 85. 398407. BAUDOUIN, M., P. MEYER,S. FERMANDJIAN and J.-L. MORGAT,Calcium release induced by interaction of angiotensin with its receptors in smooth muscle cell microsomes. Narure (Lond.) 1972. 235. 336-338. BLAIR-WEST, J . R., J. P. COGHLAN, D. A. DENTON, J. W. FUNDER, B. A. SCOGGINS and R. D. WRIGHT, The effect of the heptapeptide (2-8) and hexapeptide (3-8) fragments of angiotensin I1 on aldosterone secretion. J. clin. Endocr. Merab. 1971. 32. 575-578. FITZSIMONS. J . T., The effect on drinking of peptide precursors and of shorter chain peptide fragments of angiotensin I1 injected into the rat’s diencephalon. J. Physiol. (Lond.) 1971 214. 295-303. REGOLI,D., W. K. PARKand F. Rioux, Pharmacology of angiotensin. Pliarniacol. Reo. 1974. 26. 69-123. SEVERS, W. B. and A. E. DANIELS-SEVERS, Effects of angiotensin on the central nervous system. Pliarmacol. Reit. 1973. 25. 4 1 5 4 4 9 . WILLIAMS, G. H., L. M. MCDONNELL, M. C. RAUXand N. K. HOLLENBERG, Evidence for different angiotensin I 1 receptors in rat adrenal glomerulosa and rabbit vascular smooth muscle cells. Circular. Rrs. 1974. 34. 384-390.
