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S Knardahl

Publications and source records attributed to S Knardahl.

At least 37 records · Page 2Linked to original sources
PubMed1995

Effect of in vivo corticosterone and acute food deprivation on rat resident peritoneal cell chemiluminescence after activation ex vivo.

Adrenoglucocorticoid regulation of rat peritoneal monocyte/macrophage function was studied by exposing rats to corticosterone (CS) in the drinking water, and to fast (48 h). Production of reactive oxygen metabolites was measured by luminol amplified chemiluminescence (CL) in preparations of peritoneal cells activated by serum treated zymosan (STZ). Administration of CS which led to an increase in plasma CS from 31 (controls) to 46 ng mL-1, reduced CL (per cell) by 31%. Fast, which did not change plasma CS or ACTH, also had an inhibitory effect on CL (-25%), while the combination of CS administration and fast strongly inhibited the CL (-89%), indicating that plasma CS and fast reduced CL in a synergistic way. Similar effects on cell number were observed: CS-administration, fast and the combination reduced macrophage numbers (-13, -19.7 and -55%), while no significant effect was observed on the number of monocytes. The effect of adrenalectomy (adx) was studied in another series of experiments; adx induced no significant change in peritoneal leucocyte number or composition, while cells from adx animals had significantly higher chemiluminescence reaction than cells from sham operated animals. CS substitution in adx animals reduced CL by 30% while sham operated animals had 49% lower CL in adx. The data from adx animals also suggest that endogenous levels of CS are inhibitory for CL, but the results are not conclusive for the effect of very low doses of CS since other mechanisms than elimination of CS could prime the chemiluminescence reaction after adx. In conclusion, a moderate elevation of CS after systemic administration in vivo reduced the total number of mononuclear phagocytes in rat peritoneum, reduced the relative number of macrophages compared with monocytes, and suppressed the function of monocytes/macrophages by reducing the production of reactive oxygen molecules in activated cells. Furthermore, the effect of corticosterone was also dependent on the physiological situation, since the effects of fast and corticosterone were synergistic.

Adrenalectomy↗
PubMed1995

A double-blind study of psychosocial factors in 40-year-old women with essential hypertension.

Most studies on essential hypertension have been performed in men. The aim of the present study was to describe psychosocial characteristics of 40-year-old women with never-treated essential hypertension. Psychosocial factors like childhood traumas, economy and education were studied, and psychological assessments of irritability, hostility, 'John Henryism' and type A behavior pattern carried out. Hypertensive premenopausal women (n = 29) were compared with healthy, age-matched, normotensive women (n = 18). Neither the women nor the examining physicians were aware of the subjects' blood pressure status, and the setting, thus, was double-blind. All women were investigated in the same phase of the menstrual cycle, and in a random order. The hypertensives' parents more often had hypotension than the normotensives'. The psychiatrist who conducted the interviews correctly classified the majority of subjects as either hypertensive or normotensive. Alexithymia and difficulties in coping with aggression were more prevalent among the hypertensives. Hypertensive and normotensive women did not differ in most of the psychosocial factors previously found to differ between hypertensive and normotensive men. Our data may imply that psychosocial as well as genetic factors may contribute differently to the etiology of essential hypertension in women than in men.

Adaptation, Psychological↗
PubMed1994

The role of the adrenal medulla in cardiovascular responses to hypertonic saline in haemorrhaged conscious rats.

The aim of this study was to determine if the adrenal medulla plays a role in mediating haemodynamic effects of hypertonic saline (HTS) resuscitation during haemorrhagic hypotension in conscious rats. Wistar-Kyoto rats were either adrenomedullectomized (ADMX, n = 11) or sham-operated (SHAM, n = 10) and implanted with intravascular catheters. Pre-haemorrhage resting mean arterial pressure (MAP) was lower in the ADMX than in the SHAM group. Haemorrhage was performed by withdrawal of blood through the venous catheter, and a MAP of 50 mmHg was maintained for 1 h by further withdrawal when necessary. Both groups responded to haemorrhage with marked bradycardia. Plasma adrenaline (A) rose 10-fold in response to hypotension in the SHAM group, while remaining at pre-haemorrhage levels in the ADMX group, indicating successful adrenal demedullation. Infusion of 2.0 ml kg-1 HTS (NaCl 8.0 mg ml-1 i.v.) produced an immediate increase in MAP and heart rate (HR) in both groups, to pre-haemorrhage values or higher. Plasma noradrenaline (NA) increased in both groups after HTS, while the high levels of A in the SHAM group slowly returned toward baseline. Plasma glucose and rate of haemodilution was higher in the SHAM group during and after hypotension. The maintenance of MAP above 60 mmHg was less effective in the SHAM group during the first 2 h after HTS, but after 24 h, prehaemorrhage MAP was established in both groups. In conclusion, the adrenal medulla does not play a major role in the response to HTS resuscitation.

Adrenal Medulla↗
PubMed1992

Behavior of hypertensive and hyperactive rat strains: hyperactivity is not unitarily determined.

The spontaneously hypertensive rat (SHR) is behaviorally hyperactive relative to the Wistar-Kyoto rat (WKY). By breeding SHR with WKY, followed by inbreeding, two new strains have been developed in which hypertension seems to be separated from hyperactivity to novel stimuli: the WKHT and the WKHA strains. The main purpose of the present study was to determine which behavioral characteristics of SHR have been dissociated from the hypertensive trait in the WKHA strain. Male SHR, WKY, WKHT, and WKHA were subjected to three protocols: 1) Two forced-exploration tests, where the results showed that both the SHR and the WKHA rats were hyperactive. 2) A free-exploration open field, where the SHR was more active than the other strains, showing shorter latencies to leave the home cage, spending more time in the field, ambulating and rearing more. Furthermore, the WKHT behavior was more similar to the SHR behavior than the WKHA behavior. 3) A two-component schedule of reinforcement, where one component (fixed-interval 2 min) was signaled by houselight on and the other (extinction, EXT) by houselight off. In this test, the SHR behavior was markedly different from that of the three other strains: the fixed-interval scallop, the accelerated responding towards the end of the interval, was steeper in SHR than in the other groups. The SHR emitted more responses during the extinction component of the schedule. The SHR hyperactivity was dependent upon the reinforcement value of the water deliveries and was increased even further by sensory-reinforcing respones feedback lights. Thus, the hyperactivity of the WKHA strain seems to be less pervasive than that of the SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Dam strain affects cardiovascular reactivity to acute stress in BHR.

The effect of maternal strain on reactivity to acute stress was studied in F1 reciprocals produced by crossing the spontaneously hypertensive rat (SHR) with its normotensive progenitor, the Wistar-Kyoto (WKY). This F1 generation, known as the borderline hypertensive rat (BHR), is genetically predisposed to develop hypertension in response to chronic stress or high dietary sodium. Reciprocals, considered to be genetically equivalent aside from sex-linked traits, differ in strain of dam during intrauterine and preweanling development. At 17 weeks of age, reciprocal F1 males did not differ in open-field behavior (squares crossed, rearings, and defecation measured over 3 days in 15-min sessions) or in home-cage measurements of mean arterial pressure (MAP) and heart rate (HR). However, different patterns of cardiovascular reactivity were displayed to transfer and footshock. While WKY-mothered rats reacted with graded pressor responses, SHR-mothered rats responded maximally to transfer, showed no additional increase to footshock, and maintained peak responding after footshock was terminated. Such reactivity differences may mediate the impact of environmental variables on the genetic disposition to hypertension.

Animals↗
PubMed1990

Association between cardiovascular reactivity to stress and hypertension or behavior.

The spontaneously hypertensive rat (SHR) exhibits increased cardiovascular reactivity (CVR) to environmental stress and behavioral hyperactivity relative to the Wistar-Kyoto rat (WKY). This study sought to determine whether enhanced CVR to stress in the SHR is related to hypertension or to behavioral hyperactivity. By breeding SHR with WKY, followed by inbreeding, E. D. Hendley has developed two strains in which the hypertensive trait seems to be separated from the hyperactivity trait: the Wistar-Kyoto hypertensive (WK-HT) and the Wistar-Kyoto hyperactive (WK-HA) strains. Male SHR, WKY, WK-HT, and WK-HA rats were implanted with intravascular catheters and Doppler flow-velocity probes to record arterial pressure, heart rate (HR), and changes in regional vascular resistances. Five days after surgery, the rats were subjected to air-jet stress and pharmacological interventions. The hyperactive strains (SHR and WK-HA) exhibited enhanced pressor, renal, and mesenteric responses to stress, and higher HRs under all conditions, even after autonomic blockade. Both hypertension and hyperactivity were associated with reduced baroreceptor sensitivity. These data indicate that CVR to stress is related to behavioral traits.

Adrenergic beta-Antagonists↗
PubMed1989

Plasma corticosterone and renin activity during two-way active avoidance learning in spontaneously hypertensive and Wistar-Kyoto rats.

The spontaneously hypertensive rat (SHR) exhibits increased sympathetic and behavioral responses to several types of environmental stress compared to its normotensive progenitor, the Wistar-Kyoto rat (WKY). The aim of the present study was to investigate response-dampening mechanisms in the SHR. This study examines whether learning to control a stressful environment reduces behavioral and neuroendocrine activation in the SHR. Twelve SHR and 12 WKY were subjected to daily sessions (S) of 20 trials of signaled two-way active avoidance. Another 12 SHR served as maturation controls. Blood samples were collected immediately after S 1, S 5, and S 14 and plasma level of corticosterone (p-CS) and plasma renin activity (PRA) were measured. There was an insignificant tendency for the SHR to exhibit larger increases in p-CS in response to stress than the WKY did. By S 5 both groups had attained the avoidance task. However, the level of p-CS was the same as after S 1, showing that activation is independent of the number of shock pulses received and performance. Postsession p-CS decreased between S 5 and 14, slightly more so in the SHR than in the WKY. The SHR exhibited lower PRA than the WKY, but there were no significant effects of exposure to the avoidance schedule. Behaviorally, the SHR exhibited shorter latency to escape in the first trial than the WKY did. The SHRs were hyperactive compared to the WKY, showing more ambulation and rearing behavior. The maturation control SHR reached the same mean arterial pressure as the SHRs which were tested. After S 14, signal duration was shortened from 10 to 3 s for six additional sessions. Both p-CS and PRA increased, while at the same time ambulation and rearing behavior decreased. These data show that the relationship between behavioral control and adrenocortical activation is normal in the SHR in spite of differences in behavior. The present results also confirm previous data on hyperreactivity to footshocks in two-way active avoidance tasks in the SHR.

Animals↗
PubMed1989

Haemodynamic responses to conflict stress in borderline hypertensive rats.

Chronic exposure to a shock-shock conflict paradigm (2 h/day, 5 days/week for 12 weeks [1]) produces hypertension in the borderline hypertensive rat (BHR), a cross between the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY). The purpose of the present study was to characterize the regional haemodynamic responses which take place during conflict-stress. A pulsed Doppler flowmeter and miniature probes implanted on the left renal and superior mesenteric arteries and the abdominal aorta were used to record changes in regional flow velocity. Recording of mean arterial pressure (MAP) allowed changes in regional resistance to be calculated. The first conflict session produced intense splanchnic and renal vasoconstriction and hindquarter vasodilation. Pressor responses were moderate. A second group of BHRs was studied during conflict sessions 17-18, prior to the development of hypertension. This group exhibited faster habituation to the stress than the group studied during the first conflict session: MAP and mesenteric resistance returned more rapidly towards pre-stress levels. Relative to naive control rats, this group exhibited a larger peak MAP and less tachycardia in response to a neutral stressor (air-jet stress) and a smaller reduction in renal resistance in response to ganglionic blockade. These data suggest that in this model, pressure load per se is moderate. More attention should be directed towards the role of trophic effects of the neurohumoral factors responsible for the pronounced constriction of splanchnic and renal vasculature in producing hypertension.

Analysis of Variance↗
PubMed1989

Lesions of the anteroventral third ventricle and development of stress-induce hypertension in the borderline hypertensive rat.

The anteroventral third ventricle (AV3V) region plays a critical role in the pathogenesis of many forms of experimental hypertension. The present study sought to determine whether the integrity of this area was necessary for the development of stress-induced hypertension in the borderline hypertensive rat (BHR). Male BHRs were assigned to three groups at 8 weeks of age: 1) AV3V lesion, 2) sham lesion, and 3) maturation control. BHRs with AV3V and sham lesions were exposed to 12 weeks of conflict stress (2 hr/day, 5 days/wk). At the end of the conflict protocol period, direct measurement of resting mean arterial pressure indicated that BHRs with sham lesions had significantly higher blood pressure (153 +/- 2.9 mm Hg) than rats with AV3V lesions (126 +/- 5.2 mm Hg) and maturation control rats (133 +/- 4.3 mm Hg). Although AV3V lesions prevented stress-induced hypertension in BHRs, these rats were still capable of transiently raising blood pressure. Specifically, the results also indicate that BHRs with AV3V lesions showed greater increase in blood pressure in response to an electric foot-shock paradigm. This study suggests a critical role for this forebrain region in the production of stress-induced hypertension in genetically predisposed animals.

Animals↗
PubMed1989

Selective central alpha-2 adrenoceptor control of regional haemodynamic responses to air jet stress in conscious spontaneously hypertensive rats.

The role of central nervous system alpha 2-adrenoceptors in the regulation of peripheral sympathetic outflow to regional vascular resistance beds during environmental stress was examined in conscious chronically instrumented spontaneously hypertensive rats (SHR). SHR were instrumented with pulsed Doppler flow probes on the renal and mesenteric arteries and the lower abdominal aorta. The mean arterial pressure (MAP), heart rate and regional vascular resistance responses to air jet stress were determined before and after cumulative administration of the alpha 2-adrenoceptor agonist, guanabenz, into the lateral cerebral ventricle in doses of 5 and 25 micrograms. Compared with intracerebroventricular (i.c.v.) administration of isotonic saline vehicle which did not affect baseline systemic and regional haemodynamic measurements, guanabenz produced significant decreases in baseline MAP and heart rate but did not affect regional vascular resistances. During air jet stress, the characteristic pattern of the classic defense reaction with an increase in MAP, heart rate, renal and mesenteric vascular resistances and a decrease in hindquarters vascular resistance was observed and was not affected by i.c.v. administration of isotonic saline vehicle. Guanabenz did not affect the MAP, heart rate or renal vascular resistance responses to air jet stress. The air jet stress-induced increase in mesenteric vascular resistance was reduced by 25 micrograms guanabenz. The air jet stress-induced decrease in hindquarters vascular resistance was converted to an increase by 25 micrograms guanabenz. These results demonstrate that the regulation of environmental stress-stimulated sympathetic neural outflow to different vascular beds may be independently controlled by central nervous system alpha 2-adrenoceptors.

Animals↗
PubMed1988

Effects of adrenal demedullation on stress-induced hypertension and cardiovascular responses to acute stress.

Because chronic infusions of adrenalin (A) produce hypertension in rats, it has been suggested that A is a mediator of stress-induced hypertension. In order to test the hypothesis that lowering A will attenuate stress-induced hypertension, rats who had their adrenal medullae removed (ADM) and sham-operated controls were subjected to chronic stress. All subjects were offspring of a cross between spontaneously hypertensive and Wistar-Kyoto rats. Prior to chronic stress, systolic pressures were the same in the two groups. The stress consisted of 60 2-h sessions of shock-shock conflict during 18 weeks. After conflict stress, the rats were implanted with arterial catheters and allowed two days to recover. The resting mean arterial pressure (MAP) was 141.2 mmHg in the ADM group and 142.3 mmHg in the Sham group. Cardiovascular responses to acute stress were then examined. The rats were transferred to a test-box and subjected to pulsed foot shocks (0.5-s duration, 5-s intervals) for 5 min. The MAP increase after transfer was 22.3% in the ADM and 4.2% in the Shams (P less than 0.001). After termination of the shocks, the MAP was elevated 22.2% above baseline in the ADM and 8.1% in the Shams (P less than 0.02). Five minutes after foot shocks the MAP increase was 21.6% in the ADM and 7.2% in the Shams (P less than 0.02). Adrenal demedullation was effective in attenuating plasma A during stress and reduced the plasma noradrenaline response. Therefore, the larger pressor responses of the ADM group seem to result from attenuation of beta-adrenoreceptor-mediated dilation of skeletal muscle vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Medulla↗
PubMed1984

Passive-avoidance behavior of spontaneously hypertensive rats.

Spontaneously hypertensive rate (SHR) generally exhibit higher performance in avoidance tasks than Wistar-Kyoto control rats (WKY) do. The SHR are more active than the WKY after transfer to a novel environment and after electric footshocks. The present study examined the performance, behavior, and plasma corticosterone of young male SHR and WKY in a passive-avoidance task in which high levels of locomotor activity do not facilitate performance. The effects of three levels of discriminability of the safe area were studied. Passive-avoidance performance was statistically significantly lower in the SHR, but the difference was small. There was no difference between the SHR and the WKY in post-test plasma-corticosterone levels, and there was no relationship between ambulation and plasma-corticosterone levels. The behavioral differences between the SHR and the WKY varied as a function of the discriminability of the safe area. Specifically, in the low-discriminability condition, ambulation, but not rearings, was equally suppressed in the SHR as in the WKY and there was no difference in immobility. In the high-discriminability condition the SHR exhibited more ambulation, more rearing, and less immobility than the WKY. These data confirm that the SHR exhibit an increased tendency for facilitation of locomotor activity during activation compared to the WKY. Because the passive-avoidance performance of the SHR was lower than that of the WKY, these data suggest that previous reports of superior avoidance learning in the SHR reflect their elevated level of locomotor activity rather than an improved ability to acquire conditioned responses. Ability to discriminate stimuli seems to be normal in the SHR since ambulation was modified according to stimulus parameters.

Animals↗
PubMed1984

Residential-maze behavior of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) exhibit elevated levels of ambulation after transfer to a novel environment compared to the Wistar-Kyoto rat (NR). The present experiment compared long-term activity of SHR and NR in a residential maze to determine whether the SHR exhibit elevated levels of locomotor activity under undisturbed, baseline conditions in addition to enhanced reactivity to stimuli. The SHR were much more active visiting more arms of the maze than the NR during the initial hours following transfer to the maze, and during hours around dark onset and light onset. However, the SHR also exhibited higher levels of activity than the NR under baseline conditions. While the NR visited the arm containing food more frequently than other arms, the SHR exhibited no such preference. These data show that both stimulus-induced and basal levels of ambulation are increased in the SHR compared to its normotensive genetical counterpart.

Animals↗