1. health and fitness
2. disease

Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
Circadian variations of plasma renin activity (PRA), aldosterone and
electrolyte concentrations in plasma in pregnant and non-pregnant
goats
Ewa Skotnicka*
Department of Animal Physiology, Agricultural University of Szczecin, Poland
Received 19 August 2002; received in revised form 11 January 2003; accepted 13 January 2003
Abstract
The aim of this study was to estimate and analyse circadian variations of the renin–angiotensin–aldosterone system
(RAA) activity in blood of goats and the influence of late pregnancy on the circadian variations of RAA system. The
study was carried out on a group of 17 non-pregnant and 9 pregnant goats. The animals were kept in uniform
environmental conditions, (9 h lighty15 h darkness). Blood samples were collected seven times over a period of 24 h,
every 4 h. Plasma renin activity (PRA), plasma aldosterone (PA), sodium, potassium and chloride concentrations were
determined. PRA and PA of both groups changed during 24 h, with the highest values in the dark phase and with higher
RAA system activity (especially during the night) in the pregnant goats. In the non-pregnant goats, no circadian changes
in PRA and PA were observed. The circadian changes in PRA and PA found in pregnant goats had acrophases at 06:27
h and 01:13 h, respectively. Plasma electrolyte concentrations in both groups of goats also changed during 24 h. These
results suggest that circadian changes of potassium concentration in plasma of goats during late pregnancy may be one
of the main factors affecting the RAA system.
䊚 2003 Elsevier Science Inc. All rights reserved.
Keywords: Biological rhythms; Circadian variations; Goats; Plasma aldosterone concentration; Plasma electrolyte concentrations;
PRA; Pregnant; RAA system
1. Introduction
Circadian variations are changes in the intensity
of physiological or biochemical processes over
approximately 24 h (approx. 1 solar day) (Mick
and Jouvet, 1994; Miller, 1993). The length of the
cycles and the timing of particular phases may be
Abbreviations: A I, angiotensin I; A II, angiotensin II; JG,
renal juxtaglomerular; PA, plasma aldosterone; PRA, plasma
renin activity; RAA, renin–angiotensin–aldosterone system
*Corresponding author. Present address: University of
Szczecin, Faculty of Natural Sciences, Department of Biochemistry, 3a Felczaka St., 71-412 Szczecin, Poland. Tel.: q
48-91-444-1550; fax: q48-91-444-1550.
E-mail address: ewaskot@univ.szczecin.pl (E. Skotnicka).
modified by the changes in daylight and in alternating phases of day-time activity and sleep of
animals (Miller, 1993).
Circadian variation has been observed in many
physiological variables. Renal excretion of salt and
water in various species of mammals is known to
show clear patterns over the 24-h cycle (Bultasova
et al., 1986; Muszczynski et al., 1996; Stoynev et
al., 1982; Voogel et al., 2001). One might also
expect to find parallel variations in the secretory
or plasma concentration pattern of the hormones
controlling water–electrolyte metabolism. Among
these hormones, the renin–angiotensin–aldosterone (RAA) system has a well-established role in
salt and water excretion, the volume of water
1532-0456/03/$ - see front matter 䊚 2003 Elsevier Science Inc. All rights reserved.
PII: S 1 5 3 2 - 0 4 5 6 Ž 0 3 . 0 0 0 0 7 - 3
386
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
spaces and acid–base balance (Goldfarb and Novich, 1994; Phillips et al., 1993; Murlow, 1999).
The activity of the RAA system is controlled
by protease renin produced in the renal juxtaglomerular (JG) cells (Della Bruna et al., 1996). Renin
interacts with angiotensinogen in the circulation to
form angiotensin I (Ang I)—a decapeptide with
the low biological activity (Goldfarb and Novich,
1994). After removal of dipeptide His–Leu from
Ang I in the lung by the action of kinase II (EC
3.4.15.1), i.e. angiotensin-converting enzyme
(ACE), angiotensin II (Ang II-octapeptide) is
formed (Erdos and Skidgel, 1990). Ang II is then
transported in the circulation to effector target sites
(blood vessels, kidney, adrenal gland), where it
interacts with specific receptors to exert its action
(Goldfarb and Novich, 1994), among other things
playing an important role in aldosteronogenesis.
Ang II interacts with the AT1 receptors type in
adrenal zona glomerulosa cells, which increases
synthesis and release of aldosterone (Bottari et al.,
1993). Aldosterone in turn, acts mainly on the
nephrone proximal tubules (Mutos, 1995), leading
an increase in sodium reabsorption and the excretion of potassium and hydrogen into the tubule
(Mutos, 1995; Todd-Turla et al., 1993).
Water-electrolyte metabolism undergoes significant modifications in pregnancy (Chapman et al.,
1999; Koehler, 1993; Sturgiss et al., 1996). It is
connected with the different activities of regulation
systems and the change in intensity of metabolic
processes (Sturgiss et al., 1996; Chapman et al.,
1999). We may assume that the RAA system
activity also undergoes certain changes in
pregnancy.
Circadian changes in the activity of the RAA
system are not well known, especially during
pregnancy. Except for reports in humans and
rodents, these changes have not been established
in mammals (Chiang et al., 1994; Kawasaki et al.,
1990; Lemmer et al., 2000; Voogel et al., 2001).
The circadian variation in the activity of the RAA
system is poorly known in ruminants, especially
in goats (quadruped animals with a permanent
horizontal posture).
The aim of the present study was to estimate
and analyse circadian variations in plasma renin
activity (PRA) and in plasma aldosterone (PA)—
parameters of the circulating renin–angiotensin–
aldosterone (RAA) system activity in goats—and
whether these findings are similar to those previously reported in other species. Moreover, the
influence of late pregnancy on the circadian variations of RAA system was examined.
2. Materials and methods
2.1. Animals
The study was carried out in January and February. The studies were performed on 26 healthy
goats (75% of the Polish White Breed) aged 2–3
years. The animals were divided into two study
groups, depending on their physiological state.
First group (ns17), non-pregnant, non-lactating
goats; and second group (ns9), goats in late
pregnancy, 2 weeks before parturition, first parturition. The animals of both groups were kept under
controlled environmental conditions (temperature
and lighting). The study was carried out in light
conditions natural for the season of the year: 9 h
lighty15 h darkness with lights off from 07.30 to
16.30 h. The period from 07.30 to 16.30 h will be
referred to as the day phase and that from 16.30
to 07.30 h as the light phase. For 10 days prior to
the studies and also during the studies, the animals
of particular study groups were kept in two separate parts of the room. They were fed according
to the standards (barley grain, 600 gyday; beetroot
pulp, 400 gyday; water, hay and salt-lick to taste).
The dry food was given at 09.00 h. Before the
experiment began, the external jugular vein of
animals was catheterized to enable blood sampling
without stress.
2.2. Analytical procedure
Blood was collected from the external jugular
vein, seven times in 24 h (at 16.00, 20.00, 24.00,
04.00, 08.00, 12.00 and 16.00 h). Then, the
scheme was repeated. While collecting blood in
the dark phase, a red spotlight was used (max.
wavelengths600 nm, 3 lux). Blood samples (5
ml) were collected into tubes containing heparine
(250 I.U. Heparine, Heparinum Jelfa, Poland, to
plasma electrolyte analysis) or EDTA (2 mgyml
of blood, to PRA and plasma aldosterone concentrations analysis), depending on the requirements
of the analytical methods. The samples centrifuged
at approximately 2000=g for 30 min in a refrigerated centrifuge to recover the plasma. Plasma
samples were stored at a temperature of y20 8C
until analysis.
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
2.3. Biochemical procedure
Plasma renin activity (PRA) was determined by
RIA Kit (code 12964, BIODATA Diagnostics
S.p.A., Italy) for angiotensin I generation. The
sensitivity of the PRA assay was 0.15 ngymlyh
and intra- and interassay coefficients of variations
were 7.8% and 8.2%, respectively.
Aldosterone was measured by RIA Kit (code
12254, BIODATA Diagnostics S.p.A, Italy), with
intra- and interassay coefficients of variation of
5.4% and 6.6%, respectively. The sensitivity of the
PRA assay was 6 pgyml. Plasma sodium and
potassium concentrations were measured by flame
photometry using a Flapho-40 photometer. Plasma
chloride concentration was determined by potentiometric titration using a Spexon-100 Chlorimeter.
2.4. Statistical analysis
The mean values and standard deviations were
calculated. The statistical analysis (in STATISTICA
for Windows PL v.5.1) was based on the model
for the assay with repeated measurements. The
calculation for the plasma renin activity and aldosterone concentration were performed on the transformed data w(ypslog (yq2)x. Also, the variation
analysis model with the repeatability of measurements was used. Two groups of goats (pregnant
and non-pregnant) and the time of the measurement as the repeatable factor were established. The
main effects (the group of goats and the time of
measurement) and the time of interaction were
tested. Also, the differences between the mean
values of the non-pregnant and pregnant animals
and the differences among the measurements within the groups were analysed. In order to confirm
the existence of circadian variations and to determine acrophases and rhythm periods, all the time
series were analysed in CHRONOS v.1.0, a program
used in an analysis of chronobiological experiments, in order to determine acrophases and
rhythm period. Acrophase (⭋) is phase equal
maximal function value in relation to midnight
(ts00.00 h); rhythm period (T) is the length of
time between the two subsequent maximal values
of a given function (in a circadian variations Ts
24"3 h). All the results were presented in tables
(Tables 1 and 2) and graphically (Fig. 1).
3. Results
In the non-pregnant group PRA ranged between
0.75 and 0.94 ngymlyh, reaching the highest val-
387
ues in the dark phase of the photoperiod (Table 1,
Fig. 1a). The difference between the maximum
(08.00 h) and the minimum value (20.00 h) was
statistically significant (PF0.01). PRA of the nonpregnant goats was not characteristic of circadian
variation. PRA of the pregnant goats varied during
the 24 h period and ranged from 0.96 to 1.21 ngy
mlyh) (Table 2, Fig. 1a). The highest PRA was
observed in the second half of the dark phase and
in the beginning of the light phase of the photoperiod (24.00, 04.00 and 08.00 h). The lowest
value was observed during the day and in the
beginning of the dark phase (12.00, 16.00 and
20.00 h). Significant differences were determined
between the PRA measured at 04.00 and 08.00 h,
and the levels at 12.00 (PF0.05), 16.00 (PF0.01)
and 20.00 h (PF0.05). PRA in the pregnant goats
was characteristic of circadian variations, with the
period of the rhythm 25.55 h and the acrophase at
06.27 h, in contrast with the changes during the
24 h period in PRA of the non-pregnant goats.
PRA of the pregnant goats was as also higher at
all measurement times, compared to PRA of the
non-pregnant goats (Fig. 1a).
The PA concentration in the non-pregnant goats
ranged from 21.40 pgyml (12.00 h) to 28.79 pgy
ml (24.00 h) (Table 1, Fig. 1b). PA concentration
of the non-pregnant goats had not characteristic of
circadian variation. The PA concentration in pregnant goats during the 24 h ranged from 21.06 to
38.25 pgyml, increased during the night, reaching
its maximum at 04.00 h, and decreased during the
day, reaching its minimum at 12.00 h. The
observed changes were statistically significant
(PF0.05) and were characteristic of circadian
variations (Table 2, Fig. 1b). The period of the
rhythm was 22.53 h and the acrophase was at
01.13 h. Moreover, the concentration of PA in the
pregnant goats was higher at night in comparison
with the non-pregnant goats (04.00 h, PF0.01).
During the day, however, the concentration of that
hormone was similar in both groups (Fig. 1b).
The concentration of sodium in plasma of the
non-pregnant goats ranged from 136.27 to 140.18
mmolyl (Table 1). The highest concentration of
this electrolyte was observed at 20.00 h, the lowest
at 12.00 h. The differences were statistically significant (PF0.01). In plasma of the pregnant goats
the concentration of sodium ranged from 130.11
to 137.44 mmolyl (Table 2). The highest concentration of this electrolyte was observed between
12.00 and 16.00 h. The differences in the values
388
Time
16:00
A
20:00
B
24:00
C
4:00
D
8:00
E
12:00
F
16:00
G
Significance
level
PF0.05
PRA
0.84"0.48
0.75"0.32
0.86"0.37
0.92"0.35
0.94"0.38
0.75"0.32
0.87"0.35
(ngymlyh)
Aldosterone
26.32"16.04 24.58"9.68 28.79"12.42 24.78"10.62 23.15"9.60 21.40"6.93 24.27"9.99 –
(pgyml)
Na (mmolyl) 138.38"4.36 140.18"3.99 138.09"4.92 138.53"2.90 138.88"4.61 136.27"2.70 137.03"1.41 B™A,C
D™F,G
K (mmolyl)
3.52"0.25
3.68"0.31
3.64"0.42
3.67"0.36
3.67"0.28
3.71"0.38
3.60"0.37 A™B,D,E,F
Cl (mmolyl) 105.65"2.94 107.03"3.92 106.00"4.42 108.91"5.34 107.86"3.25 106.56"3.24 106.00"2.91 A™B,D,E
D™C,G
Bold text represents the night period.
*
B™D, E significant differences between PRA at 20:00 (B) and PRA at 4:00 (D), 8:00 (E) at the significance level PF0.01.
Significance Rhythm
Acrophase
level
period (T) (Ø)
PF0.01
Hours
Time
B™D,E*
14.01
04.36
–
28.55
22.48
B™F,G
24.73
22.04
–
–
57.41
23.38
06.04
04.58
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
Table 1
Circadian variations of the plasma renin activity (PRA), aldosterone concentration, concentrations of sodium, potassium and chlorides in plasma of the non-pregnant goats (ns
17). Mean values (x), mean standard deviations ("S.D.), statistical significance of differences between the mean values at particular measurement times (A, B, C, D, E, F, G),
periods and acrophases of rhythms
Time
16:00
A
20:00
B
24:00
C
4:00
D
8:00
E
12:00
F
16:00
G
PRA
1.02"0.42
0.96"0.34
1.15"0.39
1.21"0.38
1.18"0.42
1.03"0.38
1.05"0.45
(ngymlyh)
Aldosterone
25.14"12.15 30.00"14.85 37.23"14.13 38.25"22.11 26.72"12.56 21.06"12.81 25.63"12.96
(pgyml)
Na (mmolyl) 130.67"5.87 131.44"5.43 130.11"5.27 131.44"3.83 131.44"5.70 135.78"2.35 137.44"3.04
K (mmolyl)
3.52"0.36
Cl (mmolyl) 105.78"5.44
3.73"0.23
106.89"4.67
Bold text represents the night period.
3.82"0.28
109.22"3.74
3.70"0.13
105.72"5.70
3.57"0.54
104.00"4.39
3.57"0.40
105.17"3.97
3.66"0.25
107.83"4.51
Significance Significance Rhythm Acrophase
level
level
period (⭋)
PF0.05
PF0.01
T)
Time
Hours
B™D,E
F™D,E
C™B,E
D™A,E,G
A,D,E™F,G
B™G
A™D,E
25.55
06.27
C™A,F,G
F™B,D
B™F
C™F,G
A™C
C™F
E™G
22.53
01.13
70.54
09.09
22.42
19.90
00.08
22.53
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
Table 2
Circadian variations of the plasma renin activity (PRA), aldosterone concentration, concentrations of sodium, potassium and chlorides in plasma of the pregnant goats (ns9). Mean
values (x), mean standard deviations ("S.D.), statistical significance of differences between the mean values at particular measurement times (A, B, C, D, E, F and G), periods
and acrophases of rhythms
389
390
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
Fig. 1. Circadian variations of PRA (a), aldosterone (b) and Kq (c) concentrations in blood plasma in pregnant (ns9) and non-pregnant (ns17) goats. Values are hourly means
("S.D.); (b) *significance of difference (PF0.05) between the mean values of plasma aldosterone concentration in both groups at the particular time.
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
were significant in comparison with the concentration of sodium at other times, but they did not
have the features of a circadian variation. The
differences between the Naq concentrations in
plasma of both groups were statistically significant
(PF0.01).
The concentration of potassium in plasma of the
non-pregnant goats was relatively stable during the
whole time of the present study, ranging from 3.52
to 3.71 mmolyl (Table 1, Fig. 1c). The observed
differences were not significant and they did not
have the character of the circadian variations. The
Kq concentration in plasma of the pregnant goats
during the 24 h ranged from 3.52 to 3.82 mmoly
l, with higher values at night and lower during the
day (Table 2, Fig. 1c). The significant differences
in concentration of this electrolyte (PF0.01) were
observed between 16.00 and 24.00 h. The changes
in the concentration of potassium in plasma of the
pregnant group had the character of the circadian
variations, with the period of the rhythm at 22.42
h and the acrophase at 00.08 h.
The concentration of chlorides in plasma of the
non-pregnant goats was relatively stable (Table 1).
An increase in concentration of that electrolyte
was observed between 04.00 and 08.00 h, with the
maximum value (108.91 mmolyl) at 04.00 h. The
lowest levels were observed at 16.00 h (105.65
mmolyl). The observed differences were significant (PF0.05) and they had the character of the
circadian variations (the period of rhythm was
23.38 h and the acrophase at 04.58 h). The
concentration of chlorides in plasma of the pregnant goats, during the 24 h, was the lowest between
04.00 and 12.00 h, with the minimum value at
08.00 h (104.00 mmolyl) (Table 2). The maximum
value was observed at 24.00 h (109.22 mmolyl).
The difference between those levels was statistically significant (PF0.01). The period of the
rhythm was 19.90 h with the acrophase at 22.53
h.
4. Discussion
In the present study, changes of the RAA system
activity and of the concentration of electrolytes
(Naq, Kq and Cly) in plasma during the 24 h
period were found in both groups of goats.
PRA in the non-pregnant goats changed significantly during the 24 h period. It increased at
night, and decreased during the day, with the
lowest value in the beginning of the dark phase.
391
The observed changes were not characteristic of
circadian variations. The increase in PRA could
be linked with the animals’ rest and the decrease
in the activity of the sympathetic–adrenal medullary system in the dark phase. It is proved by the
studies performed on man by Branderberger et al.
(1998), Eguchi et al. (2002) and Lapinski et al.
(1993) and Van Acker et al. (1993). These authors
show that PRA increases at night andyor when the
motoric activity phase decreases. The nocturnal
oscillations in the sympathetic nervous system and
decrease in blood pressure may also play a certain
role in 24-h PRA variations (Branderberger et al.,
1998; Sica, 1999; Van Acker et al., 1993). The
results of Branderberger et al. (1998) also demonstrate that the 24-h PRA variations are not
endogenous by nature, but are related to sleep
processes which create the nycthemeral rhythm by
increasing both the frequency and the amplitude
of the oscillations.
The PA concentration in the non-pregnant goats
during the 24-h period was relatively stable with
greater tendency at the time of rest. It was also
found by the studies in humans (Bernardi et al.,
1985; Janssen et al., 1992; Lapinski et al., 1993).
Tendencies in changes of both PRA and PA concentration in the non-pregnant goats during the 24h period were similar. Both of the hormone
concentrations in the non-pregnant goats did not
have the character of the circadian variations.
Circadian variation in both PRA and PA concentration has, however, occasionally been reported in humans (Chiang et al., 1994; Cugini et al.,
1992; Kawasaki et al., 1990; Voogel et al., 2001)
and in rats (Lemmer et al., 2000). The varying
results obtained for humans in both PRA and PA
concentration during the 24-h period have been
explained by different methodological approaches,
for example by differences in posture and activity
during the experiments. Postural changes, such as
head-down tilt and supine position, increase both
PRA and PA concentrations in diurnally active
subjects, following normal day activities and sleeping in supine position (Branderberger et al., 1998;
Eguchi et al., 2002; Lapinski et al., 1993; Van
Acker et al., 1993). In contrast, Chiang et al.
(1994), Koopman et al. (1989) and Voogel et al.
(2001) observed conversion of a daily pattern of
PRA and PA concentration in persons who
remained in recumbet position for 24 h. The goat
represents a species that lives in a horizontal
posture, and similar to other ruminants, lies down
392
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
in sternal recumbency to prevent aspiration of
regurgitated rumen contents (Kokkonen et al.,
2001). The results of the present study point to
absence of circadian variation in both PRA and
PA concentration in non-pregnant goats, supporting
the view that a sufficient stimulus is needed for
renin and aldosterone release. This stimulus could
be postural changes (Branderberger et al., 1998;
Lapinski et al., 1993; Van Acker et al., 1993),
which did not seem to occur in the goats which
were posturally and physically inactive.
In the present study both, PRA and PA concentration in pregnant goats also changed during the
24-h period. Moreover, the observed changes had
the character of circadian variations. The pattern
of PRA changes was relatively similar to the
changes in plasma potassium concentrations and it
is therefore possible that PRA circadian variations
were the result of the rhythm in the plasma Kq
concentration determining the secretion activity of
the juxtaglomerular apparatus in the pregnant
goats. The results of the present study suggest,
moreover, that in late pregnancy in goats the
circadian variation in the plasma Kq concentration
may by one of the main factors stimulating aldosteronogenesis andyor secretion of aldosterone.
Thomsen and Shalmi (1997) and Funder (1996)
observed in humans the effect of an increase in
the plasma Kq concentration on the secretion of
aldosterone. Bernardi et al. (1985) suggest that the
circadian variations in the concentration of this
electrolyte in human blood affect not only the
secretion of aldosterone but also secretion activity
of the macula densa, contributing to the increase
in PRA. The influence of natremia also cannot be
excluded, but Weir et al. (1975) suggest that in
human pregnancy the decrease in blood Naq
concentration is not the main factor in the secretion
of the aldosterone.
PRA in the pregnant goats observed in our study
was at each time point higher in comparison with
PRA in the non-pregnant goats. The increased
synthesis and secretion of renin in the pregnant
goats could be facilitated by a lower concentration
of sodium in plasma in pregnant goats. Many
authors suggest that there may be also other factors
responsible for higher PRA in pregnancy, as the
fetus prorenin andyor renin placental transfer
(Kalenga et al., 1991), estrogens (Chapman et al.,
1999; Sealey et al., 1994) and prostaglandins (Chu
and Beilin, 1993). It could be also due to the
decrease in the activity of adrenal receptors of
angiotensin II during pregnancy (Brooks and Keil,
1994; Chapman et al., 1999; Weir et al., 1975).
PA concentration in the pregnant goats was
higher (especially in the dark phase) in comparison
with the non-pregnant goats. The higher PA concentrations in pregnant sheep (Keller-Wood, 1995),
in pregnant rats (Brooks and Keil, 1994), in
pregnant guinea pigs (Kalenga et al., 1991), in
humans pregnancy (Chapman et al., 1999; Weir et
al., 1975) were also observed.
The results of the present study suggest that
goats have a relatively low level of the PA concentration compared to other species. The higher
values in PA concentration were observed in the
non-pregnant cows, mares, guinea pigs and mice
(Bardwel et al., 1978) and in humans (Bernardi et
al., 1985; Chiang et al., 1994; Janssen et al., 1992;
Lapinski et al., 1993; Steele et al., 1994).
In the present study, the RAA system activity
in the pregnant goats was higher in comparison
with the non-pregnant goats. It was also observed
by other authors in pregnant sheep (Gibson and
Lumbers, 1996; Keller-Wood, 1995), guinea pigs
(Kalenga et al., 1991) and humans (Chapman et
al., 1999; Sealey et al., 1994). It is difficult to
indicate the reason of the higher activity of the
circulating RAA system in pregnancy because it
clearly depends on many factors that do not
operate individually. As reported in the literature
in the case of sheep and humans, the higher
activity may be connected with the altered sodium
and water balance during pregnancy, and with the
change in blood pressure (Chapman et al., 1999;
Gibson and Lumbers, 1996; Keller-Wood, 1995).
In both groups of goats, the sodium, potassium
and chloride concentrations in blood were relatively stable. The changes within the 24 h period
ranged within the limits of the physiological norms
and in the case of some parameters manifested the
character of circadian variations.
The observed changes in the plasma Naq concentration in the non-pregnant goats were characteristic of circadian variations with the acrophase
in the dark phase. Similar results were found in
anoestrous goats (Kokkonen et al., 2001), calves
(Skotnicka et al., 1997) and in man (Kanabrocki
et al., 1973; Koopman et al., 1989; Sothern et al.,
1996). In the pregnant goats the Naq concentration
in plasma was lower than in non-pregnant goats.
The observed changes were not characteristic of
circadian variations. Muszczynski et al. (1996)
E. Skotnicka / Comparative Biochemistry and Physiology Part C 134 (2003) 385–395
also did not observed circadian variations in plasma sodium concentration in pregnant goats.
In the present study, no circadian variations in
the plasma Kq concentration in the non-pregnant
goats were found. Also, Kokkonen et al. (2001)
did not find circadian variations in plasma Kq
concentration in anoestrous goats. However, circadian variations in the plasma Kq concentration
were observed in calves (Skotnicka et al., 1997)
and in humans (Kanabrocki et al., 1973; Bernardi
et al., 1985). Moreover, Solomon et al. (1991)
observed the increase in the plasma Kq concentration during the day, with the acrophase at approximately noon. According to them, the decrease in
the plasma Kq concentration at night may result
in the decrease in its excretion. In the pregnant
goats, the circadian variations of the plasma Kq
concentration were observed, with the values higher at night and lower during the day. Kanabrocki
et al. (1973) observed similar results in man, with
the acrophase in dark phase. Circadian variations
were found in pregnant goats (Muszczynski et al.,
1996), calves (Skotnicka et al., 1997) and in
humans (Bernardi et al., 1985; Kanabrocki et al.,
1973; Solomon et al., 1991), but the acrophases
of the rhythms were in the light phase of the
photoperiod. Moreover, it is also interesting that
during pregnancy, there appeared circadian variations in plasma Kq concentration with similar
patterns to the changes in the activity of the
circulating RAA system. There is no doubt that
changes in potassium concentration can cause a
phase shift in vasopressin, and single unit rhythms
in vitro and behavioural rhythms in vivo (Rabinovitz et al., 1986; Miller, 1993). It is not known
whether such effects are due to membrane depolarisation or transmembrane transport of potassium
by ionic pumps (Laming, 1989).
In the present study, circadian variations in the
plasma Cly concentration in non-pregnant and
pregnant goats were found. The circadian variations in plasma Cly concentration was also
observed by Kanabrocki et al. (1973) and Sothern
et al. (1996) in man. But Muszczynski et al.
(1996) with pregnant goats and Skotnicka et al.
(1997) with calves did not find any circadian
variations in chloride concentrations.
In conclusion, the results of the present study
show that PRA and PA concentration change
during the 24-h study phase with achieved highest
values at night, and overall higher activity of the
RAA system in goats pregnant at this time. In the
393
non-pregnant goats no circadian variations were
observed. These results suggest that circadian
changes of potassium concentration in plasma
during late pregnancy in goats may be one of the
main factors affecting the RAA system.
Acknowledgments
The author wishes to thank Prof. W.F. Skrzypczak and Prof. K. Janus (Department of Animal
Physiology, Agricultural University of Szczecin)
for their help, stimulating discussions and precious
remarks. The author acknowledges Dr Zbigniew
Muszczynski for his technical assistance and M.
Biels for his help in translation.
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