Official organ of the Association of Physiologist and Pharmacologists of India |
|
|
There was no significant change in the food intake after one day and 7 days of stress exposure (Table I). But forced swimming stress increased food intake after two weeks of stress exposure compared to control group for the same duration (P<0.05, Mann Whitney 'U' test). Food intake decreased significantly after 21 days stress exposure, compared to one-day stress subgroups (P<0.05, Mann Whitney 'U' test) (Table II). There was a significant decrease in the blood sugar level in all the subgroups, compared to control group (P<0.001, Mann Whitney 'U' test and Bonferroni 't' test) (Table I and II). More significant decrease was seen up to 7 days stress exposure. But from one day stress to 21-day stress, there was a gradual increase in blood sugar level (P<0.01, Mann-Whitney 'U' test), but this blood sugar level after 21st day was significantly less than control group for the same duration. A significant increase in the water
intake was observed after forced swimming stress, throughout
the duration of stress (P<0.001, Mann-Whitney 'U' test and
Bonferroni 't' test) (Table I and II). Control animals showed
gradual increase in water intake from day one to 21 days (P<0.001,
Bonferroni 't' test), compared to the stressed animals for the
same duration. Urine output also decreased significantly in
the initial period of' exposure to the stressor up to 7 days
(P<0.01, Mann-Whitney 'U' test), but later increased significantly
after 14 days stress exposure compared to one day stress subgroup
(P<0.05, Bonferroni 't' test) (Table I and II).
DISCUSSIONIngestive behavior undergoes significant changes when experimental animals like rats are exposed to different kinds of stress. The forced swimming stress involves immersing the rat in a tub of water from which it cannot escape. This test procedure itself is physiologically stressful because it results in increased serum corticosterone and prolactin levels (18, 19). The observed change in body weight after forced swimming stress is in accordance with other reports already published (12, 20). The effect of stress appeared to be more marked in the initial period of exposure to the stress up to a period of 7 days. The body weight regained gradually after 14 days stress and 21 days stress exposure. This recovery back to normalcy after two weeks of stress could be attributed to the habituation to the stressful stimulus when the stress period was prolonged. In the present study, we observed no change in the food intake in animals up to 7 days of stress exposure. In spite of having normal food intake, the body weight decreased in animals, up to 14 days of' stress. Control rats displayed a normal growth curve, where as the experimental animals showed a persistent decrease in their body weight, and this was in spite of improvement in food intake over a period of 14 days.
Stress is well known to trigger CRH secretion, which could exert suppressive effect on the food intake in animals (21). The forced swimming stress might have suppressed CRH secretion from hypothalamus, which might explain the normal food intake, observed in this study up to 14 days in stressed rats. However, stress is also known to increase protein catabolism. Normal rats subjected to food deprivation can still maintain growth and minimise weight loss by increasing the efficiency of utilization of whatever food was taken during the 24-hour period (21, 22). Stress may hamper this mechanism. Therefore rats subjected to forced swimming continued to lose weight initially, in spite of normal food intake.
Forced swimming produced a decrease in water intake in rats throughout the 21 day schedule of stress duration, But the urine volume decreased only in the initial period of exposure to stress. The urine volume did not change up to 21 days stress period after the initial decrease up to 7 days; but the water intake decreased throughout the swimming stress duration. This could be due to the possibility of dehydration after swimming stress in animals, which is in accordance with other reports already published (23). At the same time this observation is contradictory to certain other reports where there was increased water intake and urine output after stress in rats (15, 24). Stress induced decrease in urine volume may be because of stress induced decrease in water intake and also may be due to a possible antidiuretic effect of stress per se (14, 25). In the present study, food intake and urine output changed only slightly after stress whereas water intake was reduced significantly resulting in a state of mild dehydration after swimming stress.
Response to stress is highly contradictory with regard to blood sugar levels. Studies related to stressful events and fluctuations in blood sugar have shown responses ranging from slight decrease, relative increase and no change in blood sugar (26, 27). In the present study, it was observed that stress produced severe hypoglycemia. This observation confirms the previous reports by Rodnick et al., (28) who observed a decrease in blood sugar level after physical training by either swimming or running. Some stressful stimuli like swimming are known to enhance insulin sensitivity in rats (29). It is possible that the increased insulin sensitivity after forced swimming caused the lower level of blood sugar in rats.
The response to stress was maximally
observed after 7 days of stress exposure in the various parameters
studied. When the stress period was prolonged to 14-21 days,
there was a gradual recovery back to near normal in the body
weight, water intake and urine output. From the forgoing it
can be observed that an acute stress like swimming, produces
significant change in ingestive behavior where as when the stress
becomes chronic the changes induced became non significant.
This type of behavior of the animals to prolonged stress could
be attributed to habituation of the hypothalamo-pituitary-adrenal
axis (30). For a given stress, the habituation may depend upon
several factors such as, the intensity of stress, the inter-session
time interval, inter-individual variability etc. Since habituation
developed following exposure to the same stressor, it is likely
to result from behavioral familiarization to that particular
type of stress. On the contrary, no habituation response was
observed in the blood sugar level after forced swimming stress
possibly, because of variety of several other factors influencing
carbohydrate metabolism in situ. 1. McCarty R. Stress, behavior and the sympathetic adrenal medullary system. In L.A. Pohorecky, J. Brick eds. Stress and alcohol use, Elsevier Science Publishing Co. Inc. 1983: 7. 2. Pitman DL, Ottenweller JE, Natelson BH. Plasma corticosterone levels during repeated presentation of two intensities of restraint stress; chronic stress arid habituation. Physiol Behav 1988; 43: 47-56. 3. Van Dijken H H, Van der Heyden JAM, Mos J, Tilders FSH. Long lasting behavioral changes after a single foot shock stress session. A model of depression ? In Oliveir B, Mos J, Slangen J L eds. Animal models in psychopharmacology, Birkhauser Verlag, Basel 1991; 231-236. 4. Natelson BH, Ottenweller JE, Pitman DL, Cook JA, McCarty R, Tapp W N. Effect of stressor intensity on habituation of the adrenocortical stress response. Physiol Behav; 43: 41 – 46. 5. Sutanto W, De Kloet ER. The use of various animals models in the study of stress and stress related phenomenon. Laboratory Animals 1994; 28: 293. 6. Ramade F, Bayle JD. Adaptation of the adrenocortical response to chronic intermittent stress : Anticipatory conditioning. IRCS Med Sci 1985; 13: 219-220. 7. Tan N, Morimoto K, Sugiura T, Morimoto A and Murakami N. Effects if running training on the blood glucose and lactate in rats during rest and swimming. Physiol Behav 1992; 51: 927-931. 8. Greenen D, Buttrick P, Scheuer J. Cardiovascular and hormonal responses to swimming and running in the rat. J Appl Physiol 1988; 65: 116-123. 9. Kramer K, Dijkstra H, Bast A. Control of physical exercise of rats in a swimming basin. Physiol Behav 1993;53:271-276. 10. Levitsky DA, Faust I, Glassman M. The ingestion of food and the recovery of body weight following f',isting in the naive rat. Physiol Behav 1976; 17: 575-580. 11. Rodriguez Echandia EL, Gonzalez AS, Cabrera R, Fracchia LN. A further analysis of behavioral and endocrine effects of unpredictable chronic stress. Physiol Behav 1998; 43: 789-795. 12. Marti O, Gavalda A, Jolin T, Armario A. Effect of regulatory exposure to chronic immobilization stress on the circadian pattern of pituitary adrenal hormones, growth hormone and thyroid stimulating hormone in the adult male rat. Psychoneuroendocrinol 1993; 18: 67-77. 13. Abraham ME, Gogate MG. Effect of stress on behavior in rats. Ind J Physiol Pharmacol 1989; 3:3: 84-88. 14. Bensi N, Bertuzzi M, Armario A, Gauna HF. Chronic immobilization stress reduced sodium intake and renal sodium excretion in rats. Physiol Behav 1997; 62: 1391-1396. 15. Yoshida T, Okuno T, Kawalata T, Morimoto T. Salt consumption and body fluid balance during cold exposure in rats. Physiol Behav 1994; 55: 163 - 167. 16. Light KC, Koepke JP, Obrist PA, Willis PW. Psychological stress induces sodium and fluid retention in men at high risk for hypertension. Science 1983; 220: 429-431. 17. Abel EL. Physiological correlates of the forced swim test in rats. Physiol Behav 1993; 54: 309-317. 18. Manev H, Pericic D. Effects of the potential antidepressant dihydroergosine in rats forced to swim : Influence on plasma corticosterone. Psychoneuroendocrinol 1988; 13: 465-469. 19. Yelvington DB, Weiss GK, Ratner A. Habituation of the prolactin response in rats to psychological stress. Psychoneuroendocrinol 1985; 10: 95-102. 20. Nagaraja HS, Jeganathan PS. Effect of short term and long term restraint stress on some physiological and biochemical parameters in rats. Ind J Med Res 1999; 109: 76-80. 21. Levine AS, Rogers B, Kneip J. Effects of centrally administered corticotrophin releasing factor (CRF) on multiple feeding paradigms. Life Sci 1983; 22: 337-339. 22. Monteiro F, Abraham ME, Sahakari S D, Mascarenhas JF. Effect of immobilization stress oil food intake body weights and weights of various organs in rat. Ind J Physiol Pharmacol 1989; 33: 186-190. 23. Fregly MJ, Effect of exposure to cold on fluid and electrolyte exchange. In Claybaugli JR, Wade CE eds. Hormonal regulation of fluid and electrolytes, Plenum, New York 1989; 87: 116. 24. Rodriguez de Turco EB, Droy-Lefaix MT, Bazan NG, Egb-761 inhibits stress-induced polydipsia in rats. Physiol Behav 1993; 53: 1001-1002. 25. Koepke JP, Grignolo A, Light KC, Obrist PA, Central beta adrenoceptor inediation of the atitinatriuretic response to behavioral stress in conscious dogs. J Pharmacol Exp Ther 1983; 227: 73-77. 26. Gonder-Frederick LA, Carter WR, Cos D J, Clark(,, WL. Environmental stress and blood glucose change in insulin dependent diabetes mellitus. Health Psychol 1990; 9: 503-505. 27. Reis FM, Ribeiro-de-Oliveira A Jr., Guerra RM, Reis AM, Coimbra CC. Blood glucose and prolactin in hyperprolactinemic rats exposed to restraint and surgical stress. Life Sci 1996; 58: 155-161. 28. Hodnick KJ, Mondon CE, Haskel WL, Azhar S, Reaven GM. Differences in insulin-induced glucose uptake and enzyme activity in running rats. J Appl Physiol 1990; 68: 513-519. 29. Stallknecht B, Kjaer M, Mikines KJ, Maroun I,, Plough L, Ohkuwa T, Vinten J, Gallio H. Diminished epinephrine response to hypoglycemia despite enlarged adrenal medulla in trained rats. Am J Physiol 1990; 259: R998-R1003. 30. Terrazino S, Perego C, De Simoni MG.
Effect of development of habituation to restraint stress oil
hypothalamic noradrenaline release and adrenocorticotropin secretion.
J Neurochem 1995; 65:263-267. |
|
for more queries contact : Executive editor, Department of Physiology, All India Institute of Medical Sciences, N.Delhi - 29, mail id: exec_edit@ijpp.com |
© Copyright 2003 Allrights reserved to IJPP (indian journal of physiology and pharmacology) |
POWERED BY MIRROR ALLIANCE |