Prostaglandins & Medicine 7: 395-402, 1981

EFFECTS OF PROSTAGLANDIN INHIBITION ON RENAL FUNCTION IN DEOXYCORTICOSTERONE-ACETATE HYPERTENSIVE

YUCATAN MINIATURE SWINE

Charles D. Ciccone and Edward J. Zambraski

Department of Physiology Rutgers University

New Brunswick, New Jersey 08903

(reprint requests to EZ)

ABSTRACT

This study evaluated the effect of prostaglandin (PG) on renal function in normal and deoxycorticosterone-acetate (DOCA) hypertensive Yucatan minia- ture swine. Eight animals were implanted with DOCA impregnated silicone strips. MAP increased in the conscious DOCA animals from a normal pressure of 110-115 mmHg, to 148 + 4 mmBg. After 3-4 weeks, the DOCA hypertensive and eight normal (sham or non-tmplanted) animals were anesthetized with sodium pentobarbital which reduced MAP in the DOCA pigs to normotensive levels. Under anesthesia, PG inhibition (indomethacin or meclofenamate, 2 mg/kg i.v.) increased MAP only in the normal group (P < .05). PG inhibition caused a significant reduction in renal blood flow in both groups, but only decreased glomerular filtration rate in the DOCA animals (P < .05). Radioactive microsphere distribution to the outer cortex of the normal animals was significantly decreased with PG inhibition, (P < .05). No consistant changes in electrolyte excretion or urine flow rate was seen in either group following PG inhibition. These data indicate that PG may influence renal hemodynamics in both normal and DOCA hyper- tensive Yucatan miniature swine. The finding that PG inhibition selectively decreases GFR in the DOCA animals suggests a possible protective role of these hormones in this hypertensive animal model.

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INTRODUCTION

Chronic treatment of Yucatan miniature swine with deoxycorticosterone- acetate (DOCA) has proven to be a simple, effective method of creating a hypertensive animal model (10,ll). DOCA treated swine are currently being studied to assess the condition of low renin and presumably volume expanded hypertension. Studies from our lab have shown that certain changes in renal function such as decreased renal blood flow (RBF), glomerular filtration rate (GFR), and altered intrarenal blood distribution, occur in DOCA-hypertensive miniature pigs.

Prostaglandin (PG) synthesis has been shown to be elevated in DOCA- salt hypertension in the rat and the.dog (2,6). Since prostaglandins have been implicated in the control of certain aspects of renal function (l), we were interested in determining the role of these hormones in DOCA treated pigs. The purpose of this experiment was to examine the role of prostaglandins on renal function in DOCA hypertensive Yucatan miniature swine.

METHODS

Sixteen male Yucatan miniature swine, 20-34 kg, were used for this studyl. Under sterile conditions and halothane anesthesia, eight swine were implanted with DOCA impregnated silicone strips according to the procedure of Terris et al (9). A catheter was also placed in the carotid artery and exteriorized on the animal's back to allow for the measurement of mean arterial pressure (MAP). The normotensive group (n = 8) consisted of either non-treated or sham silicone implanted animals. Data from sham implanted and non-implanted animals were similar, consequently their results were combined. All animals were fed a swine diet which contained approximately 50 mEq of sodium per day. Water was provided ad libitum. -

MAP was measured in conscious control and DOCA animals 3-5 times per week following the surgery. The arterial catheter was connected to a Statham transducer while the animals were suspended in a hammock-type sling (7). Arterial pressure was meaned electronically and recorded on a direct- writing recorder. Seven of the eight DOCA-treated animals were studied 21- 31 days post-implant. Data from one animal, studied after 8 days of DORA treatment, were similar to those treated for the longer duration. Conse- quently, this animal's data were included in the results of the DOCA group. At the time of the study, the animals were anesthetized with ketamine hydrochloride (3.3 mg/kg) and sodium pentobarbital (33 mg/kg). Animals were intubated and mechanically ventilated. Catheters were placed in the jugular vein, aortic arch and abdominal aorta. The left kidney was approached via a flank incision. An electromagnetic flow probe (Biotronex) was placed around the left renal artery. A small catheter was placed in the left ureter. The bladder was approached via a mid-line incision and the right ureter was cannulated. Following the completion of surgery,

1 Buckshire Corporation, Perkasie, PA.

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animals were given a prime (62 mg/kg) and sustaining dose of inulin in 0.9% NaCl at 1 ml/minute to achieve plasma inulin levels of 0.2 mg/ml. After a 45 minute equilibration period, a 40-50 minute control urine collection was begun. Blood samples were obtained at the midpoint of the control period.

Following the control period, PG synthesis was inhibited by the intra- venous administration of either indomethacin (2 mg/kg) or meclofenamate (2 mglkg). These agents were infused over a ten minute period. Twenty minutes after the infusion of either indomethacin or meclofenamate, a 30 minute post PG inhibition urine collection was begun with blood samples taken at the mid oint of the period. imately l-2 x 108 Ceriuml4l

During the control period, approx- radiolabelled microspheres, 15~ in diameter

(New England Nuclear), of Scandium46

were injected into the aortic arch. A similar amount labelled microspheres were injected during the prostaglandin

inhibition period. During microsphere injection a reference flow was obtained by a timed withdrawal of blood from the abdominal aortic catheter. Left renal blood flow and MAP were recorded continuously on a Grass direct writing recorder.

At the end of the experiment, the flow probe was calibrated in situ -- by making timed blood flow collections through a catheter placed in the renal artery distal to the probe. The left kidney was then removed and sectioned according to the method of Stein et al (8) to determine -- intrarenal cortical blood flow distribution. Right kidney total blood flow was determined by the microsphere method (4). Reference blood samples and kidney sections were counted for Cerium141 and Scandium46 using a Beckman gamma radiation counter.

Serum and urine samples were analyzed for sodium and potassium via flame photometry. Glomerular filtration rate (GFR) was determined by inulin clearance. Inulin concentration was measured by the anthrone method.

Results are expressed as mean + SEM. Values from the control vs. PG inhibited period for either normal or DOCA-treated animals were compared using a paired student t test. All differences were considered significant at P < .05.

RESULTS

In the conscious DOCA-treated animals, MAP rose from approximately llO- 115 n@g to 148 + 4 u&g. After 3-4 weeks of DOCA treatment, pentobarbital anesthesia caused a reduction in MAP in the DOCA pigs; consequently, under anesthesia, MAP was similar between normal and DOCA animals. (Normal = 122 + 6 mmHg; DOCA = 113 + 8 nrmHg). Following PG inhibition, MAP increased signyficantly in the normal animals to 136 + 3 mmRg, (P < .05). MAP in the DOCA group increased slightly to 120 f. 13 mmHg. The effect of PG inhibition on RBF is shown in Figure 1. Left RBF decreased by 33 and 28% in the normal and DOCA animals, respectively, following PG inhibition. This decrement was significant.

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Figure 1. Left kidney renal blood flow (LRBF) In normal and DOCA animals during control and PG inhibited periods. Asterisks represent P < .05 vs. control period. Values are mean 2 SEX.

Although left kidney GFR increased slightly in the normal animals following PG inhibition (Figure 2), a significant decrease of over 50% occurred in the DOCA group (P < .05).

The effect of PG inhibition on fractional microsphere distribution is shown in Figure 3. In the normal animals, PG inhibition caused a decrease in outer cortical and an increase in inner cortical distribution, with the outer cortical decrement being significant (P < .05). DOCA animals showed trends in distribution similar to those seen in the normal group, i.e. a decrease in outer cortical and an increase in inner cortical distribution following PG inhibition. These differences, however, were not significant.

398

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Figure 2. Left kidney glomerular fi .tration (GFR) in control and DOCA animals pre- and post-PG inhibition. Values are mean 5 SEM (*P < .05>.

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Figure 3. Left kidney fractional renal blood flow, as determined by microsphere distribution pre- and post-PG inhibition. Values are mean + SEM (*P < .05).

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Electrolyte excretion rates are shown in Table 1. Fractional sodium excretion did not change significantly in either group with PG inhibition. Urinary potassium excretion was significantly lower after PG inhibition in the DOCA animals, while no change occurred in the normal group. Urine flow (Table 1) was not significantly different in either group following PG inhibition.

Table 1. Left kidney fractional sodium excretion (FENa), urinary potassium excretion (URV) and urine flow rate in normal and DOCA animals during control and PG-inhibited collections. Values are mean + SEM (*P < .05>.

NORMAL (n = 8) DOCA (n = 8)

Control PG-inhibited Control PG-inhibited

1.40 + .65 .91 + .39 1.24 + .32 1.36 + .30

UKV (pEq/min) 32.92 - f 5.56 31.28 2 3.80 38.52 + 6.72 17.23 + 5.60*

Urine Flow (ml/min) .47 + .16 .46 + .lO 1.01 + .30 .54 + .23

DISCUSSION

The results of this study indicate that PG inhibition causes several changes in renal function and hemodynamics in both normal and DOCA treated swine. As we have previously shown, the hypertension present in conscious DOCA-treated Yucatan miniature swine is normalized by anesthesia. The observation that PG inhibition caused an increase in MAP only in the normal animals may be related to the fact that DOCA-treated swine have very low levels of plasma renin activity in contrast to the normal animals (9). Since PG have been shown to have an attenuating effect on the vasoconstric- tor properties of angiotensin II, the removal of the inhibition of this potent vasoconstrictor may be responsible for the increase in MAP observed. It is also possible that PG may be influencing the release of circulating catecholamines or attenuating peripheral sympathetic nerve activity (3).

It has been shown that anesthesia and laparotomy tend to increase the renal hemodynamic alteration seen with indomethacin treatment (5). Since in this study the animals were anesthetized, some of the responses to indomethacin may have been caused by the anesthesia. However, since both the normal and DOCA animals were treated alike, differences in either the magnitude or direction of changes with indomethacin can be evaluated to assess the role of PG in this hypertensive animal model.

Renal blood flow decreased in both normal and DOCA animals. We have previously reported that in DOCA treated animals, RBF is lower than that observed in normals (11). It has been shown in several studies that PG may play an important compensatory role in attempting to maintain RBF during states of high renal vasoconstrictor activity. In the DOCA animals this may explain why PG inhibition caused a reduction in RBF. The fact that RBF was also reduced in the normal animals suggests that in this

400

animal, under these experimental conditions, that an appreciable amount of vasoconstrictor tone may exist.

In this study, after indomethacin or meclofenamate treatment there was a dissociation between RBF and GFR. RBF decreased in both the normal and DOCA animals, whereas GFR decreased in only the DOCA group. The reason why this occurred is unknown. One possibility may be a selective effect of PG on the ultrafiltration coefficient in DOCA hypertensive animals. This is unlikely because angiotension II levels in these pigs are extremely low (9) and PG are thought to influence the ultrafiltration coefficient through angiotensin II. Secondly, PG are believed to decrease the ultrafiltration coefficient, which should have resulted in an increase in GFR rather than a decrease following PG inhibition.

The decrease in outer cortical renal blood flow in the normal animals post PG inhibition may have been due to a removal of the inhibition of increased outer cortical vasoconstrictor activity. The reason for the accompanying increase in inner cortical flow post inhibition is unknown.

This study did not see a consistant effect of PG inhibition on elec- trolyte excretion in the normal or DOCA animals. Alterations in the renal handling of water or electrolytes with PG inhibition may be due more to the changes in GFR and/or filtered electrolyte load than to a direct influence on tubular reabsorption.

In summary, PG may play an important role in determining cardiovascular and renal hemodynamics in both normal and DOCA hypertensive Yucatan minia- ture swine. This study suggests that PG may be important in attenuating the augmented renal and perhaps systemic vasoconstrictor activity that has been observed in this DOCA hypertensive model.

ACKNOWLEDGEMENTS

This work was supported by a grant from the New Jersey Heart Asso- ciation and the National Institutes of Health (HL 25255).

We gratefully acknowledge the technical assistance of Constance Lakas.

REFERENCES

1. Dunn, M. J., Hood, V. L. Prostaglandins and the Kidney. Am. J. Physiol. 233: F169, 1977.

2. Dusing, R., Gill, J. R., Bartter, F. C. The Role of Prostaglandins in the Renal Response to Deoxycorticosterone (DOCA) in the Dog. Kidney Intern. 14: 693, 1978.

3. Gullner, H. G., Lake, C. R., Bartter, F. C., Kafka, M. S. Effect of Inhibition of Prostaglandin Synthesis on Sympathetic Nervous System Function in Man. J. Clin. Endocrinol. Metab. 49: 552, 1979.

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4.

5.

6.

7.

8.

9.

10.

11.

Laughlin, M. H., Witt, W. M., Whittaker, R. N. Regional Cerebral Blood Flow in Conscious Miniature Swine During High Sustained + Gg Acceleration Stress. Aviat. Space Environ. Med. 50: 1129, 1979.

Lonigro, A., Itskovitz, H. D., Crowshan, K., McGiff, J. C. Dependency of Renal Blood Flow on Prostaglandin Synthesis in the Dog. Circ. Res. 32: 712, 1973.

Nasjletti, A., McGiff, J. C., Colina-Chourio, J. Interrelations of the Renal Kallikrein-Kinin System and Renal Prostaglandins in the Conscious Rat. Circ. Res. 43: 799, 1978.

Panepinto, L. M., Phillips, R. W., Wheeler, L. R., Will, D. H. The Yucatan Miniature Swine as a Laboratory Animal. Lab. Anim. Sci. 28: 308, 1978.

Stein, J. H., Boonjarern, S., Wilson, C. B., Ferris, T. F. Alterations in Renal Blood Flow Distribution. Circ. Res. 32: 1161, 1973.

Terris, J. M., Berecek, K. H., Cohen, E. L., Stanley, J. C., Whitehouse, W. M., Bohr, D. F. Deoxycorticosterone Hypertension in the Pig. Clin. Sci. Mol. Med. 51: 303s, 1976.

Terris, J. M., Simmonds, R. C. Response of the Two-Kidney Yucatan Miniature Boar to DOCA and d-Aldosterone. Physiologist 22: 123, 1979,

Zambraski, E. J., Ciccone, C. D. Renal Function in Deoxycorticosterone- Acetate Hypertensive Yucatan Miniature Swine. Clin. Res. 29: 3628, 1981.

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