Psychosocial Stimuli and Human Plasma Renin Activity DENA M. CLAMAGE,* AB, ARTHUR J. VANDER, MD, AND DAVID R. MOUW, P H D
The effects of several types of acute psychosocial stimuli on plasma renin activity (PRA) were studied in normotensive healthy subjects. Puzzle-solving produced an increase in blood pressure but no significant change in PRA, although two of seven subjects did respond with large increases in PRA. Watching a disturbing movie also raised blood pressure, but did not alter PRA. In contrast, a combination of novelty, fear, and /or anticipation did constitute a significant stimulus for renin secretion; this was evidenced by the fact that naive subjects (who were not told in advance what to expect) had significantly higher PRAs on the first day of the 2-day puzzle-solving study. PRA on this day correlated strongly with anxiety proneness, as did the decrease from day 1 to day 2. We conclude that meaningful psychosocial stimuli can enhance renin secretion in susceptible individuals.
INTRODUCTION
Many investigators have hypothesized that psychosocial "stress," with its associated activation of the sympathetic nervous system, might be an important risk factor for the development of essential hypertension (1,5-7,9,14-16,18,20). Since the sympathetic nervous system is an important controller of renin secretion (8,12,25,26), it is possible that enhanced renin secretion contributes significantly to psychosocially induced elevations of blood pressure. Accordingly, it is important to determine whether psychosocial
From the Department of Physiology, University of Michigan Medical School, Ann Arbor, Michigan 48109. *Michigan Heart Association Fellow. Address reprint requests to: Arthur }. Vander, 6811 Medical Science n, University of Michigan, Ann Arbor, Michigan 48109. Received for publication November 29, 1976; final revision received May 5, 1977.
stimuli do, indeed, induce an increase in renin secretion. Several recent studies have demonstrated that acute psychosocial stimuli increase plasma renin activity (PRA) in rats (4) and baboons (3); analogous studies in human subjects have been few and inconsistent. Esler and Nestel (10) reported that forced problem-solving does not increase PRA in normotensive or hypertensive persons. In contrast, Baumann et al. (2) stated that repeated mental arithmetic under time pressure increases PRA; however, these authors reported no values for the variance of the response or its statistical significance. Syvalahti et al. (24) found that PRA is significantly higher for students taking examinations, compared to another group listening to lectures. In light of these conflicting results, we undertook the present studies to evaluate further the effects of acute psychosocial stimuli on plasma renin activity in normotensive people.
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977) Copyright® 1977 by the American Psychosomatic Society, Inc. Published by Elsevier North-Holland, Inc.
393
D.M. CLAMAGE, A.J. VANDER, AND D.R. MOUW METHOD
for 15 min, after which plasma was immediately removed and frozen. Blood pressure was measured just after each blood sampling by palpation of the radial artery, using a Propper aneroid sphygGeneral momanometer. The blood pressure cuff was left in Subjects were healthy unpaid volunteers, male place on the arm opposite the catheter throughout and female, 19-24 years old, who had responded to the experiment. either an advertisement posted or request to the Each subject filled out (prior to needle placement sophomore physiology class of the University of on day 1) the trait form of the State-Trait Anxiety Michigan Medical School. Both the advertisement Inventory (STAI) (23) as a measure of "trait anxiand the request described the experiment as a study ety" (anxiety proneness). A version of the Differenof "the effects of various psychosocial stimuli on tial Emotion Scale (DES-A), modified to include the plasma concentrations of several hormones." Vol- state form of the STAI (17), was used to monitor the unteers were told that a venipuncture for blood col- following subjective feelings at various times durlection would be required and that they would be ing the session: interest, joy, surprise, distress, disrequested to solve puzzles, perform physical tasks, gust, anger, guilt, shyness, fear, contempt, sleepior watch a movie. They were instructed not to disness, and anxiety. cuss the experiment with other subjects. Volunteers using birth control pills or with a personal or family history of hypertension or renal disProtocol 1 (Puzzle-Solving and ease were excluded. In addition, two subjects were "Initial-Experience" Effect) excluded at the time of experiment: one had a blood pressure reading of 152/66, the other a cardiac arSix subjects (three females and three males) parrhythmia and murmur. Subjects were instructed to ticipated in this study for two mornings each, one a eat their normal breakfast, but to refrain from drink- control session, the other an experimental (puzzleing coffee or tea or from smoking tobacco on the solving) session. A seventh subject (male) came in morning of the experiment. for the experimental session only. Of the six 2-day All experiments were performed in a quiet room subjects, four solved puzzles on their first day, the between 8:00 a.m. and 12:00 noon, with the subject other two being controls on the first day. However, in a sitting position. One experimenter and one sub- in light of the description of the experiment given ject were present at the test sessions. As far as was to the subjects when they volunteered (see above), possible, interactions between tester and subject all first-day subjects arrived expecting exposure to a were standardized by use of a script from which the "psychosocial stimulus"; they learned of the day's tester read. At the beginning of each session, the protocol only at the beginning of the session just day's protocol was explained, a consent form was prior to placement of the catheter. At the conclusigned, and the subject was given the opportunity sion of the first day, subjects were asked to return to empty his or her bladder. Blood pressure was for a second session; at this time, the second-day then measured by auscultation, the venous catheter protocol was described in detail. Thus, this protocol was placed, and the first blood sample was drawn made possible an evaluation of the possible role of immediately. The catheter was an in-dwelling novelty or anticipation ("initial-experience" effect) Butterfly-21 infusion catheter; it was inserted at the on PRA. antecubital fossa, and the arm was thereafter imOn control days, following the preliminaries demobilized on an armboard. Between samples, the scribed above, subjects sat quietly for 95 min, readcatheter tubing was filled with 1 ml of solution ing copies of National Geographic and Natural Hisfrom a "heparin lock," a plastic syringe containing tory. Seven 3-5-ml blood samples were collected as sterile heparin, 100 units /ml, in normal saline with follows: BS-0 at time zero (immediately after cathebenzyl alcohol. At the time of blood sampling, this ter placement), BS-1 at 30 min, BS-2 at 40 min, solution was removed from the tubing and dis- BS-3/4 at 55 min, BS-5 at 75 min, and BS-6 at 95 carded. Blood was then withdrawn into a 5- or min. 10-ml plastic syringe and immediately transferred Experimental sessions followed the same proceto chilled 15-ml plastic tubes containing 50 /AI of dure, with the exception that, following BS-2, sub(NH4)2EDTA solution, 7.5 g/100 ml. These tubes jects underwent the 20-min sequence of oral tests were kept in an ice-bath until the end of the exper- listed below. Following this, blood pressure was iment; at this time they were centrifuged in the cold immediately measured and BS-3 /4 taken. Subjects
394
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
RENIN AND PSYCHOSOCIAL STIMULI then sat quietly for the next 40 min, with blood pressure measured and a blood sample taken halfway through this period (BS-5) and again at the end (BS-6). Subjects filled out the DES-A state form at 55 and 95 min on both days (following BS-3 /4 and BS-6, respectively). On experimental days, subjects were told to fill out the first DES-A form (i.e., the one immediately following testing) based on the way they had felt during the testing. The following sequence of tests was used: (lj Rotated Letters (21) (3.5 min). Subjects examined pairs of printed letters, the first rotated with respect to the second mentally rotated the first letter, and then decided whether the two letters were the same or mirror images. (2) Stroop Color Test (21) (2.5-6 min). Subjects were shown the names of colors printed in contrasting shades of ink (for example, the word "red" printed in green) and read off the color ink used, not the printed color name. A metronome was used to set the pace, first at 120 /min, then at 144 /min. (3J Neisner Search Test (21) (3 minj. Subjects searched through groups of letters for specified target letters; 1, 2, or 4 targets were given for each trial. (4J GrammaticaJ Reasoning (21) (4 min). Subjects were given a series of statements, each followed by two letters (e.g., A is preceded by B—AB) and decided whether the statement correctly described the order of the two letters. (5) Mental Arithmetic (5) (4 minj. Subjects began with the number 1755 and sequentially subtracted 17 from this in time with a metronome set at 60 /min. The subjects had to answer all puzzles aloud; all testing was conducted by the same experimenter, who interrupted to point out wrong answers and to urge greater speed and accuracy. No deception was used. Performances were scored on the basis of total number of answers minus incorrect answers.
Protocol 2 (Movie) Six other subjects (three females and three males) participated in this study. Each had one or two initial "control" session(s) lasting 90 min, followed on another day by an experimental ("movie") session lasting 3a/2 hours; the "control" sessions were rela-
tively short because their primary purpose was to reduce novelty and anticipation on the movie day. In contrast to protocol 1, at the time of initial telephone contact subjects were told precisely what they would be doing at each session and were thoroughly reassured as to the innocuousness of the procedures. Control sessions followed the schedule described for the control groups in protocol 1. On experimental days, subjects followed this same initial procedure to time 40 min (BS-2), but were then shown a movie, "The Glass House" (Tomorrow Entertainment, LCA), lasting approximately 90 min. This movie portrays how a college professor, imprisoned in a state penitentiary on a manslaughter charge, is progressively brutalized by the prison environment and ultimately killed by a guard. Blood pressure was measured and a blood sample taken following each reel of the movie: BS-3 at 70 min, BS-4 at 110 min, and BS-5 at 140 min. Following this, subjects sat quietly for 40 min with blood pressure measured and a blood sample taken halfway through this period (BS-6, 160 min) and again at the end (BS-7, 180 min). On experimental days, subjects filled out the DES-A state form at times per-zero, 30 min (following BS-1), and 140 min (following BS-5, immediately after the movie). For the third DES-A form, subjects were instructed to complete the form on the basis of how they had felt during the movie.
Renin Assay Plasma renin activity was determined by a modification of the method of Haber et al. (13). Angiotensin was generated in vitro during a 1-hour incubation at a pH of 5.5 and a temperature of 37°; the incubation mixture contained 500 /xl test plasma, 100 /xl 2 M maleic acid buffer (ph adjusted to 5.5 with Nh4OH), 10 ^,1 BAL (1.7 g/100 ml), and 10 n 8-hydroxyquinoline (6.6 g /100 ml). The angiotensin generated was then measured using the I 12S radioimmunoassay kits supplied by New England Nuclear.
RESULTS Protocol 1 PRA values for individual subjects are shown in Fig. 1. In only two subjects (17 and 21) did PRA increase during the
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
395
D.M. CLAMAGE, A.J. VANDER, AND D.R. MOUW
EXPTL. DAY CONTROL DAY
A
/
\
/ — 07,/ | .Ml'-''
\
^
•(I6K
L 5
6
0
S A M P L E
I
2
NO.
0
I
2
3/4
SAMPLE NO.
Fig. 1. Effect of puzzle-solving on PRA in individual subjects. Panel A summarizes the findings for the experimental (puzzlesolving) day; puzzle-solving occurred between samples 2 and 3 /4 as indicated by the shaded area. Panel B presents the data for the control day. Numbers in parentheses identify the subjects; subject 14 was studied on only one day. See text for timing of samples.
puzzle-testing period (BS-3/4). Mean PRA and systolic blood pressure values for all subjects are summarized in Fig. 2A; at no sampling time did experimental-day group means differ significantly from those on the control day. Data were also analysed using paired-samples analysis, comparing each sample with the same-day BS-1 value for that subject (BS-1 was used as the "basal" sample, since it was taken 30 min after needle placement, during which time the subject sat quietly); as shown in Fig. 2B this analysis also failed to reveal a significant change in mean PRA during puzzle-solving. In contrast, there was a significant increase (P < 0.001) in systolic blood pressure for the group on the experimental day during puzzle-solving. There was no significant correlation between changes in PRA and blood pressure in individuals. 396
5
6
0
I
2
3A» 5
6
SAMPLE NO.
Fig. 2. (A)Summary of mean (± se) PRA and systolic blood pressure on control and experimental (puzzle-solving) days. Puzzlesolving occurred between samples 2 and 3 /4 on the experimental day, as indicated by the shaded area. See text for timing of samples. (B)Paired-samples analysis of changes during puzzle-solving day using BS-1 and BP-1 as "basal" (signified by o) in figure. BS-X and BP-X = any sample or blood pressure other than BS-1 or BP-1.
An "initial-experience" effect was also tested for by analysing the data in terms offirst-dayvs. second-day PRA values for each subject. For example, Fig. 3 summarizes day 1 and 2 values for each subject at the time of BS-0. The mean percent difference between these two days [(day 1 - day 2) /day 1] was 29 ± 9 (SE), P < 0.01, by paired-samples analysis. Figure 4 summarizes this analysis for each blood-sampling time; significant differences existed not only at time BS-0 but also at BS-1 and BS-3 /4 with BS-2 being of borderline significance. Comparison of the two days beyond sample BS-2 is not really justified since four subjects (12,16,17,21) solved puzzles on day 1 whereas two subjects (11 and 19) did so on day 2; the decreases in PRA for samples through BS-2 were similar for the two groups. There were no significant
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
RENIN AND PSYCHOSOCIAL STIMULI
I
6
The effects of several types of acute psychosocial stimuli on plasma renin activity (PRA) were studied in normotensive healthy subjects. Puzzle-solving produced an increase in blood pressure but no significant change in PRA, although two of seven subjects did respond with large increases in PRA. Watching a disturbing movie also raised blood pressure, but did not alter PRA. In contrast, a combination of novelty, fear, and /or anticipation did constitute a significant stimulus for renin secretion; this was evidenced by the fact that naive subjects (who were not told in advance what to expect) had significantly higher PRAs on the first day of the 2-day puzzle-solving study. PRA on this day correlated strongly with anxiety proneness, as did the decrease from day 1 to day 2. We conclude that meaningful psychosocial stimuli can enhance renin secretion in susceptible individuals.
INTRODUCTION
Many investigators have hypothesized that psychosocial "stress," with its associated activation of the sympathetic nervous system, might be an important risk factor for the development of essential hypertension (1,5-7,9,14-16,18,20). Since the sympathetic nervous system is an important controller of renin secretion (8,12,25,26), it is possible that enhanced renin secretion contributes significantly to psychosocially induced elevations of blood pressure. Accordingly, it is important to determine whether psychosocial
From the Department of Physiology, University of Michigan Medical School, Ann Arbor, Michigan 48109. *Michigan Heart Association Fellow. Address reprint requests to: Arthur }. Vander, 6811 Medical Science n, University of Michigan, Ann Arbor, Michigan 48109. Received for publication November 29, 1976; final revision received May 5, 1977.
stimuli do, indeed, induce an increase in renin secretion. Several recent studies have demonstrated that acute psychosocial stimuli increase plasma renin activity (PRA) in rats (4) and baboons (3); analogous studies in human subjects have been few and inconsistent. Esler and Nestel (10) reported that forced problem-solving does not increase PRA in normotensive or hypertensive persons. In contrast, Baumann et al. (2) stated that repeated mental arithmetic under time pressure increases PRA; however, these authors reported no values for the variance of the response or its statistical significance. Syvalahti et al. (24) found that PRA is significantly higher for students taking examinations, compared to another group listening to lectures. In light of these conflicting results, we undertook the present studies to evaluate further the effects of acute psychosocial stimuli on plasma renin activity in normotensive people.
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977) Copyright® 1977 by the American Psychosomatic Society, Inc. Published by Elsevier North-Holland, Inc.
393
D.M. CLAMAGE, A.J. VANDER, AND D.R. MOUW METHOD
for 15 min, after which plasma was immediately removed and frozen. Blood pressure was measured just after each blood sampling by palpation of the radial artery, using a Propper aneroid sphygGeneral momanometer. The blood pressure cuff was left in Subjects were healthy unpaid volunteers, male place on the arm opposite the catheter throughout and female, 19-24 years old, who had responded to the experiment. either an advertisement posted or request to the Each subject filled out (prior to needle placement sophomore physiology class of the University of on day 1) the trait form of the State-Trait Anxiety Michigan Medical School. Both the advertisement Inventory (STAI) (23) as a measure of "trait anxiand the request described the experiment as a study ety" (anxiety proneness). A version of the Differenof "the effects of various psychosocial stimuli on tial Emotion Scale (DES-A), modified to include the plasma concentrations of several hormones." Vol- state form of the STAI (17), was used to monitor the unteers were told that a venipuncture for blood col- following subjective feelings at various times durlection would be required and that they would be ing the session: interest, joy, surprise, distress, disrequested to solve puzzles, perform physical tasks, gust, anger, guilt, shyness, fear, contempt, sleepior watch a movie. They were instructed not to disness, and anxiety. cuss the experiment with other subjects. Volunteers using birth control pills or with a personal or family history of hypertension or renal disProtocol 1 (Puzzle-Solving and ease were excluded. In addition, two subjects were "Initial-Experience" Effect) excluded at the time of experiment: one had a blood pressure reading of 152/66, the other a cardiac arSix subjects (three females and three males) parrhythmia and murmur. Subjects were instructed to ticipated in this study for two mornings each, one a eat their normal breakfast, but to refrain from drink- control session, the other an experimental (puzzleing coffee or tea or from smoking tobacco on the solving) session. A seventh subject (male) came in morning of the experiment. for the experimental session only. Of the six 2-day All experiments were performed in a quiet room subjects, four solved puzzles on their first day, the between 8:00 a.m. and 12:00 noon, with the subject other two being controls on the first day. However, in a sitting position. One experimenter and one sub- in light of the description of the experiment given ject were present at the test sessions. As far as was to the subjects when they volunteered (see above), possible, interactions between tester and subject all first-day subjects arrived expecting exposure to a were standardized by use of a script from which the "psychosocial stimulus"; they learned of the day's tester read. At the beginning of each session, the protocol only at the beginning of the session just day's protocol was explained, a consent form was prior to placement of the catheter. At the conclusigned, and the subject was given the opportunity sion of the first day, subjects were asked to return to empty his or her bladder. Blood pressure was for a second session; at this time, the second-day then measured by auscultation, the venous catheter protocol was described in detail. Thus, this protocol was placed, and the first blood sample was drawn made possible an evaluation of the possible role of immediately. The catheter was an in-dwelling novelty or anticipation ("initial-experience" effect) Butterfly-21 infusion catheter; it was inserted at the on PRA. antecubital fossa, and the arm was thereafter imOn control days, following the preliminaries demobilized on an armboard. Between samples, the scribed above, subjects sat quietly for 95 min, readcatheter tubing was filled with 1 ml of solution ing copies of National Geographic and Natural Hisfrom a "heparin lock," a plastic syringe containing tory. Seven 3-5-ml blood samples were collected as sterile heparin, 100 units /ml, in normal saline with follows: BS-0 at time zero (immediately after cathebenzyl alcohol. At the time of blood sampling, this ter placement), BS-1 at 30 min, BS-2 at 40 min, solution was removed from the tubing and dis- BS-3/4 at 55 min, BS-5 at 75 min, and BS-6 at 95 carded. Blood was then withdrawn into a 5- or min. 10-ml plastic syringe and immediately transferred Experimental sessions followed the same proceto chilled 15-ml plastic tubes containing 50 /AI of dure, with the exception that, following BS-2, sub(NH4)2EDTA solution, 7.5 g/100 ml. These tubes jects underwent the 20-min sequence of oral tests were kept in an ice-bath until the end of the exper- listed below. Following this, blood pressure was iment; at this time they were centrifuged in the cold immediately measured and BS-3 /4 taken. Subjects
394
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
RENIN AND PSYCHOSOCIAL STIMULI then sat quietly for the next 40 min, with blood pressure measured and a blood sample taken halfway through this period (BS-5) and again at the end (BS-6). Subjects filled out the DES-A state form at 55 and 95 min on both days (following BS-3 /4 and BS-6, respectively). On experimental days, subjects were told to fill out the first DES-A form (i.e., the one immediately following testing) based on the way they had felt during the testing. The following sequence of tests was used: (lj Rotated Letters (21) (3.5 min). Subjects examined pairs of printed letters, the first rotated with respect to the second mentally rotated the first letter, and then decided whether the two letters were the same or mirror images. (2) Stroop Color Test (21) (2.5-6 min). Subjects were shown the names of colors printed in contrasting shades of ink (for example, the word "red" printed in green) and read off the color ink used, not the printed color name. A metronome was used to set the pace, first at 120 /min, then at 144 /min. (3J Neisner Search Test (21) (3 minj. Subjects searched through groups of letters for specified target letters; 1, 2, or 4 targets were given for each trial. (4J GrammaticaJ Reasoning (21) (4 min). Subjects were given a series of statements, each followed by two letters (e.g., A is preceded by B—AB) and decided whether the statement correctly described the order of the two letters. (5) Mental Arithmetic (5) (4 minj. Subjects began with the number 1755 and sequentially subtracted 17 from this in time with a metronome set at 60 /min. The subjects had to answer all puzzles aloud; all testing was conducted by the same experimenter, who interrupted to point out wrong answers and to urge greater speed and accuracy. No deception was used. Performances were scored on the basis of total number of answers minus incorrect answers.
Protocol 2 (Movie) Six other subjects (three females and three males) participated in this study. Each had one or two initial "control" session(s) lasting 90 min, followed on another day by an experimental ("movie") session lasting 3a/2 hours; the "control" sessions were rela-
tively short because their primary purpose was to reduce novelty and anticipation on the movie day. In contrast to protocol 1, at the time of initial telephone contact subjects were told precisely what they would be doing at each session and were thoroughly reassured as to the innocuousness of the procedures. Control sessions followed the schedule described for the control groups in protocol 1. On experimental days, subjects followed this same initial procedure to time 40 min (BS-2), but were then shown a movie, "The Glass House" (Tomorrow Entertainment, LCA), lasting approximately 90 min. This movie portrays how a college professor, imprisoned in a state penitentiary on a manslaughter charge, is progressively brutalized by the prison environment and ultimately killed by a guard. Blood pressure was measured and a blood sample taken following each reel of the movie: BS-3 at 70 min, BS-4 at 110 min, and BS-5 at 140 min. Following this, subjects sat quietly for 40 min with blood pressure measured and a blood sample taken halfway through this period (BS-6, 160 min) and again at the end (BS-7, 180 min). On experimental days, subjects filled out the DES-A state form at times per-zero, 30 min (following BS-1), and 140 min (following BS-5, immediately after the movie). For the third DES-A form, subjects were instructed to complete the form on the basis of how they had felt during the movie.
Renin Assay Plasma renin activity was determined by a modification of the method of Haber et al. (13). Angiotensin was generated in vitro during a 1-hour incubation at a pH of 5.5 and a temperature of 37°; the incubation mixture contained 500 /xl test plasma, 100 /xl 2 M maleic acid buffer (ph adjusted to 5.5 with Nh4OH), 10 ^,1 BAL (1.7 g/100 ml), and 10 n 8-hydroxyquinoline (6.6 g /100 ml). The angiotensin generated was then measured using the I 12S radioimmunoassay kits supplied by New England Nuclear.
RESULTS Protocol 1 PRA values for individual subjects are shown in Fig. 1. In only two subjects (17 and 21) did PRA increase during the
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
395
D.M. CLAMAGE, A.J. VANDER, AND D.R. MOUW
EXPTL. DAY CONTROL DAY
A
/
\
/ — 07,/ | .Ml'-''
\
^
•(I6K
L 5
6
0
S A M P L E
I
2
NO.
0
I
2
3/4
SAMPLE NO.
Fig. 1. Effect of puzzle-solving on PRA in individual subjects. Panel A summarizes the findings for the experimental (puzzlesolving) day; puzzle-solving occurred between samples 2 and 3 /4 as indicated by the shaded area. Panel B presents the data for the control day. Numbers in parentheses identify the subjects; subject 14 was studied on only one day. See text for timing of samples.
puzzle-testing period (BS-3/4). Mean PRA and systolic blood pressure values for all subjects are summarized in Fig. 2A; at no sampling time did experimental-day group means differ significantly from those on the control day. Data were also analysed using paired-samples analysis, comparing each sample with the same-day BS-1 value for that subject (BS-1 was used as the "basal" sample, since it was taken 30 min after needle placement, during which time the subject sat quietly); as shown in Fig. 2B this analysis also failed to reveal a significant change in mean PRA during puzzle-solving. In contrast, there was a significant increase (P < 0.001) in systolic blood pressure for the group on the experimental day during puzzle-solving. There was no significant correlation between changes in PRA and blood pressure in individuals. 396
5
6
0
I
2
3A» 5
6
SAMPLE NO.
Fig. 2. (A)Summary of mean (± se) PRA and systolic blood pressure on control and experimental (puzzle-solving) days. Puzzlesolving occurred between samples 2 and 3 /4 on the experimental day, as indicated by the shaded area. See text for timing of samples. (B)Paired-samples analysis of changes during puzzle-solving day using BS-1 and BP-1 as "basal" (signified by o) in figure. BS-X and BP-X = any sample or blood pressure other than BS-1 or BP-1.
An "initial-experience" effect was also tested for by analysing the data in terms offirst-dayvs. second-day PRA values for each subject. For example, Fig. 3 summarizes day 1 and 2 values for each subject at the time of BS-0. The mean percent difference between these two days [(day 1 - day 2) /day 1] was 29 ± 9 (SE), P < 0.01, by paired-samples analysis. Figure 4 summarizes this analysis for each blood-sampling time; significant differences existed not only at time BS-0 but also at BS-1 and BS-3 /4 with BS-2 being of borderline significance. Comparison of the two days beyond sample BS-2 is not really justified since four subjects (12,16,17,21) solved puzzles on day 1 whereas two subjects (11 and 19) did so on day 2; the decreases in PRA for samples through BS-2 were similar for the two groups. There were no significant
Psychosomatic Medicine Vol. 39, No. 6 (November-December 1977)
RENIN AND PSYCHOSOCIAL STIMULI
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6
