Clin Endocrinol Metab 45: 849, 1977 EFFECT OF FOOD INTAKE ON THE METABOLIC CLEARANCE RATE OF ALDOSTERONE A. Akesode, C.J. Migeon and A.A. Kowarski Harriet Lane Service, Children's Medical and Surgical Center, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205 ABSTRACT: The effect of eating on the metabolic clearance rate (MCR) of aldosterone was investigated in 10 adult individuals, %-aldosterone was infused continuously over a period of 5 h while the subjects remained supine. Three h after the start of the infusion, each subject ate a bowl of soup. The MCR of aldosterone, before and after the intake of food, was calculated by dividing the rate of infusion of ^H-aldosterone by the mean concentration of 3 H-aldosterone during these two periods. The MCR of 11 subjects was measured under the same conditions but without eating. The MCR of aldosterone (mean + 1 SD) was 1284 + 513 L/24 h before food intake and 2182 + 180 L/24 h after food intake in the 10 individuals who ate. The MCR in the 11 subjects who did not eat was 1363 + 446 and 1357 + 434 during the same periods (p>0.05). The 29% increase in the MCR induced by eating was highly significant (p< 0.001); it was similar in magnitude and duration to a previously reported effect of food intake on the hepatic blood flow (13). The plasma concentration of hormones depends on the rate at which they are secreted into the blood stream as well as on the rate at which they are removed from the plasma pool. This last parameter, the metabolic clearance rate (MCR), has been defined (1-3) as the volume of plasma containing an amount of hormone that is irreversibly cleared from the plasma pool during a unit of time. The MCR of aldosterone has been reported to be increased by administration of ACTH and of cortisol (58). This change was felt to be due to changes in binding of aldosterone to plasma proteins (7,8). Changes in posture have also been reported to influence the MCR of aldosterone (9, 10). In other reports the effect of posture was small (11,12). Another important factor influencing the MCR of aldosterone may be the hepatic blood flow. Aldosterone Submitted August 12, 1976. Supported by Grants R01 HD 06284, AM 00180, Tl AM 5219 and 5K06 AM 21855 12 of the NIH.
is extracted to a high degree by the liver (10) and most of its metabolism occurs in this organ (1,9). Since food intake was shown to increase the splanchnic blood flow (12), the ingestion of food should be considered among the possible factors influencing the rate at which aldosterone is cleared from the blood. This study was designed to test the effect of food intake on the MCR of aldosterone. MATERIALS AND METHODS Twenty-one healthy, volunteer subjects participated in this study. The project was reviewed and approved by the Committee on Clinical Investigation and the Committee on Radiation Control of the Johns Hopkins University. Informed consent was obtained. The subjects were admitted to the Clinical Research Center at 9a.m. on the day of the study, having been instructed not to eat after 8 p.m. on the preceding night. On arrival the subjects were asked to recline and to remain supine throughout the study. Ten ml of blood were drawn in a heparinized syringe from each subject at the beginning of the study. 5 pCi of 1,2-^H-aldosterone (specific ac-
849
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 03:17 For personal use only. No other uses without permission. . All rights reserved.
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JCE & M • 1977 Vol 45 • No 4
RAPID COMMUNICATIONS
tivity, 54 Ci/mM), diluted in 50 ml of 5% glucose, were infused into an antecubital vein, using a constant infusion pump. (Syringe Pump Model 355 Sage Instruments, Subsidiary of Orion Research, Inc.). The rate of infusion was 3-9 ml/min during the first min, and 0.145 ml/min for 5 h thereafter. Ten of the 21 subjects ate a bowl of soup 3 h after the beginning of the constant infusion. The remaining 11 subjects were not fed. While infusing ^H-aldosterone into one arm, blood samples were collected from the opposite arm. Five blood samples were drawn at 15 min intervals, beginning 2 h after the start of the experiment. Four samples of blood were taken subsequently at 30 min intervals. After removal of the IV catheter, 3 successive collections of 2 min efflux were transferred into counting vials. The amount of %-aldosterone in these vials was used to determine the rate of infusion. All plasma samples were frozen until analyzed. The concentration of •%-aldosterone in plasma was determined using a method reported in a previous publication (14). The main features of this method were: 5,000 cpm of 4- C-aldosterone were added to each plasma sample and to the 2 min effluxes from the constant infusion pump. The samples were then extracted twice with dichloromethane. The solvent was dried under a gentle stream of air at 37 C. The aldosterone was subsequently purified in a 2stage process. The extract was first applied to Whatman paper #2 and chromatographed in a system of benzene: methanol: water (100:50:50) for kh h. The aldosterone spot was identified under UV light and cut out. It was then eluted with methanol, dried down and acetylated with acetic anhydride and pyridine. The aldosterone diacetate was purified by paper chromatography (cyclohexane: diozane: methanol: water; 100:75:50:25) for 5 h. Each sample was counted in a liquid scintillation counter for 100 min and the 3 H/ 1 ^C ratio deter-
mined. Losses were corrected by determining the recovery of C as previously described (15). The MCR of aldosterone was determined from the rate of infusion of °H-aldosterone and its plasma concentration at equilibrium. Rate of infusion of 1,2- Haldosterone (cpm/h) MCR = Equilibrium concentration of l,2-3H-aldosterone (cpm/L) RESULTS AND DISCUSSION Figure 1 shows the mean (+ 1 SE plasma concentration of radioactive aldosterone, before and after the ingestion of food in the subjects who ate. An initial equilibrium concentration of 3fl-aldosterone was reached 120 min after the initiation of the constant infusion. A lower equilibrium concentraation was observed beginning 30 min
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is extracted to a high degree by the liver (10) and most of its metabolism occurs in this organ (1,9). Since food intake was shown to increase the splanchnic blood flow (12), the ingestion of food should be considered among the possible factors influencing the rate at which aldosterone is cleared from the blood. This study was designed to test the effect of food intake on the MCR of aldosterone. MATERIALS AND METHODS Twenty-one healthy, volunteer subjects participated in this study. The project was reviewed and approved by the Committee on Clinical Investigation and the Committee on Radiation Control of the Johns Hopkins University. Informed consent was obtained. The subjects were admitted to the Clinical Research Center at 9a.m. on the day of the study, having been instructed not to eat after 8 p.m. on the preceding night. On arrival the subjects were asked to recline and to remain supine throughout the study. Ten ml of blood were drawn in a heparinized syringe from each subject at the beginning of the study. 5 pCi of 1,2-^H-aldosterone (specific ac-
849
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 03:17 For personal use only. No other uses without permission. . All rights reserved.
850
JCE & M • 1977 Vol 45 • No 4
RAPID COMMUNICATIONS
tivity, 54 Ci/mM), diluted in 50 ml of 5% glucose, were infused into an antecubital vein, using a constant infusion pump. (Syringe Pump Model 355 Sage Instruments, Subsidiary of Orion Research, Inc.). The rate of infusion was 3-9 ml/min during the first min, and 0.145 ml/min for 5 h thereafter. Ten of the 21 subjects ate a bowl of soup 3 h after the beginning of the constant infusion. The remaining 11 subjects were not fed. While infusing ^H-aldosterone into one arm, blood samples were collected from the opposite arm. Five blood samples were drawn at 15 min intervals, beginning 2 h after the start of the experiment. Four samples of blood were taken subsequently at 30 min intervals. After removal of the IV catheter, 3 successive collections of 2 min efflux were transferred into counting vials. The amount of %-aldosterone in these vials was used to determine the rate of infusion. All plasma samples were frozen until analyzed. The concentration of •%-aldosterone in plasma was determined using a method reported in a previous publication (14). The main features of this method were: 5,000 cpm of 4- C-aldosterone were added to each plasma sample and to the 2 min effluxes from the constant infusion pump. The samples were then extracted twice with dichloromethane. The solvent was dried under a gentle stream of air at 37 C. The aldosterone was subsequently purified in a 2stage process. The extract was first applied to Whatman paper #2 and chromatographed in a system of benzene: methanol: water (100:50:50) for kh h. The aldosterone spot was identified under UV light and cut out. It was then eluted with methanol, dried down and acetylated with acetic anhydride and pyridine. The aldosterone diacetate was purified by paper chromatography (cyclohexane: diozane: methanol: water; 100:75:50:25) for 5 h. Each sample was counted in a liquid scintillation counter for 100 min and the 3 H/ 1 ^C ratio deter-
mined. Losses were corrected by determining the recovery of C as previously described (15). The MCR of aldosterone was determined from the rate of infusion of °H-aldosterone and its plasma concentration at equilibrium. Rate of infusion of 1,2- Haldosterone (cpm/h) MCR = Equilibrium concentration of l,2-3H-aldosterone (cpm/L) RESULTS AND DISCUSSION Figure 1 shows the mean (+ 1 SE plasma concentration of radioactive aldosterone, before and after the ingestion of food in the subjects who ate. An initial equilibrium concentration of 3fl-aldosterone was reached 120 min after the initiation of the constant infusion. A lower equilibrium concentraation was observed beginning 30 min
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