(Received 11 June 1979)

Transcription

1 J. Phymol. (1980), 304, pp With 2 text-fiure8 Printed in Great Britain TH FFCTS OF AMBINT TMPRATUR ON URINARY FLOW AND COMPOSITION IN TH FOWL BY. AZAHAN AND A. H. SYKS From Wye College, University of London, Ashford, Kent (Received 11 June 1979) SUMMARY 1. Urine flow and composition were determined in normally hydrated, waterloaded and hypotonic saline infused hens under various ambient temperatures (Ta). 2. At Ta 29 and normal urine flow was reduced and osmolality increased; at Ta 0 and urine flow increased and osmolality decreased. 3. In hydrated hens at Ta 32 0C antidiuresis occurred within 10 min and persisted for 2 hr without any significant change in rectal temperature (Tr). 4. At Ta 40 0C there was no antidiuresis but a tendency for urine flow to increase; Tr also rose. The antidiuresis shown by water-restricted hens at Ta was abolished at Ta 40 0C. 5. An antidiuresis, similar to that seen at Ta 32 0, could be produced at Ta 20 0C by moderate haemorrhage, exposure to infra-red heating or by vasopressin or vasotocin. Adrenaline and noradrenaline provoked a diuresis. 6. Hypothalamic heating failed to elicit an antidiuresis but hypothalamic cooling increased urine flow at Ta 20 0C and abolished the antidiuretic response at Ta 32 0C. 7. It is concluded that the antidiuresis seen at warm ambient temperatures is caused by the release of antidiuretic hormone possibly as a response to a rise in skin temperature. INTRODUCTION xposure to a high ambient temperature (Ta) decreases urine flow and raises plasma anti-diuretic hormone (ADH) activity in man (Segar & Moore, 1968), the pig (Forsling, Ingram & Stanier, 1976) and the rat (Itoh, 1954) although the severity of the climate, sometimes as high as 50 0C, must have caused a considerable degree of heat stress which complicates the interpretation of these results. It has also been shown in the rat (Grace & Stevenson, 1971) and fowl (Kechil, 1976) that drinking occurs as a direct response to moderately warm ambient temperatures. In the latter work it was noticed that thermogenic drinking was accompanied by a decrease in total water loss from the cloaca. Thus it is possible that the mechanisms which control water balance, both intake and excretion, may act in anticipation of the increased water loss brought about by exposure to hot climates. The aim of the present work was, therefore, to determine to what extent urine flow and composition in the fowl could be modified by ambient temperatures which were warm or hot but not extreme /80/ $ The Physiological Society

2 390. AZAHAN AND A. H. SYKS MTHODS Animals. Medium weight (2-2.5 kg) hybrid laying hens (Warrens) were used; they were normally kept at T. 20 0C with food and water freely available. xperimental procedure. A Perspex cannula, similar to that described by Bokori (1961), was inserted into the cloaca so as to allow ureteral urine to be collected directly, uncontaminated by faeces. The cannula was held in place by skin sutures, inserted under Procaine anaesthesia. Where possible only hens that had recently laid were used; otherwise an egg in the shell gland was removed manually. An hour after insertion of the cannula the hen was secured in a sitting position in a restraining frame. Hydration was achieved either by an oral dose of water equal to 3 % of body weight or by infusion of 0 45 % saline through a brachial vein at the rate of 0 85 ml./min following a priming injection equal to 2 % of body weight. TABL 1. Volume and composition of urine of the hen under various ambient temperatures Ambient temperature C 29 0C 32 0C C No. of observations Urine flow (ml. kg-'min-') ** 0.014** * ± ± Urine osmolality (m-osmole kg-1) * ± Na excretion (#equiv kg-l min-l) ** 1.51*** i0-16 i i0 33 K excretion (,uequiv kg-1 min-') ** 1* *21 ± ±012 +0o24 Mean values of mean. **, *** Significantly different from control values at 5, 1 and 0.1 % probability levels in this and succeeding Tables. Hypothalamic thermodes were inserted according to the procedure described by Richards (1970). The temperature at the tip of the thermode was measured by a thermistor incorporated into the assembly. Rectal temperatures (fi,) were taken with a clinical thermometer; respiration rate (f) was counted visually. The climatic chambers were accurate to 1 0C; humidity was uncontrolled but remained low at the warmer temperatures. vaporative water loss was estimated from body weight change corrected for the amount of urine and faeces collected under liquid paraffin during the period. Analytical methods. Urine was first centrifuged to remove precipited uric acid; sodium and potassium were determined with an L flow photometer and osmolality with a Knauer osmometer. Synthetic lysine vasopressin and arginine vasotocin (Ferring, Stockholm) were used. All the values for sodium and potassium excretion and other additional details are given by Azahan (1979). RSULTS Normal hydration and water restriction In this series of experiments one hour's collection of urine was made at Ta before exposing the hens to higher temperatures. There was no significant difference between these control values which have, therefore, been aggregated. At Ta 29 and there was a well marked anti-diuresis accompanied by an increase in osmolality and a decrease in sodium excretion. At Ta urine flow was similar to that of the control and at T there was a tendency for urine flow to increase (Table 1). Under control conditions (Ta 20 00) Tr was between 40-9 and ; respiration

3 THRMOGNIC ANTIDIURSIS 391 rate (f) was min-'. At Ta 29 or Tr had risen only by within 1 hr and there was no panting. At Ta 36 and 40 0 Tr rose quickly by I -0 ( within an hour, and the hens were panting within 15 min. When hens were deprived of water for 24 hr, in order to promote the release of endogenous ADH, the urine flow at Ta (0.017 ml. kg-1 min-") was almost the same as at Ta (0.018 ml. kg-' min') but at the flow increased significantly (0.023 ml. kg-' min-', P < 0.01). TABL 2. Renal excretion following water loading and exposure to different ambient temperatures for 1 hr Ambient temperature C -5 0C 32 0C Infra-red 40 OC No. of observations Urineflow (ml. kg-' min') *** 0.157** 0-081*** Urine osmolality (m-osmole kg-') 67 39** 140*** 108*** ±13 +3 ±21 Na excretion (equiv kg-' min-') * 3.57 ± *76 +0* K excretion (equiv kg-' min') ± Percentage water load excreted *** 16*** 52 Response to water loading The results of this series of experiments are summarized in Table 2. At Ta the hens had a T, of and f rate of min-'. On transfering to Ta urine flow was reduced with little or no change in Tr and f during the first hour. At Ta Tr rose quickly, panting commenced within 15 min and the birds were visibly heat stressed; under these conditions urine flow was similar to that seen at Ta 20 0C. It is clear that the ability to remove a given water load was reduced in a warm, but not in a hot, environment. At Ta 0 and -.5 C the urine flow of hydrated birds increased compared with that of the controls at Ta 20 0C. In another series of experiments water loaded birds at Ta were exposed to radiant heat from an infra-red lamp placed vertically above. There was no change in Tr during an hour's exposure but there was a well marked antidiuresis accompanied by an increase in osmolality. Finally it was shown with water-loaded birds that the antidiuresis normally seen at Ta 32 0C could be prevented when drinking was permitted during the experiment. Water intake during the hour's exposure increased despite the positive water balance that already existed from the water loading, thus confirming its thermogenic origin, but although urinary flow tended to decrease over the hour there were no significant differences in either volume or osmolality. Infusion of hypotonic saline At Ta 20 0C a fairly constant rate of urine flow ( ml. min-) was achieved within min. After transfering the hens to Ta the urine flow was signifi-

4 392. AZAHAN AND A. H. SYKS cantly reduced in the second and subsequent 15 min periods and this was accompanied by an increase in osmolality and a decrease in sodium excretion. At To 40 TC there was a moderate antidiuresis during the first 15 min (P < 0.05) but thereafter urine flow was similar to or greater than the control. A typical result on one hen is shown in Fig. 1. Ambient temperature C ' 32 '' ' 20 C *4 cm cr i 030 0>09 b 00 w. 0) :L- C- 0 -._ 0xQ II I Time (min) Fig. 1. Changes in renal function following exposure to ambient temperatures (P.) of 20 TC, 32 TC and 4 'C. One hen infused with hypotonic saline. Response to ADH, catecholamines and hemorrhage Arginine vasotocin (AVT), 10 ng kg-', or lysine vasopressin (LVP), 20 i.u., were injected intravenously into hens infused with hypotonic saline at Ta 20 0C (Table 3). The antidiuresis was almost immediate but of the same magnitude as that seen on exposure to Ta 32 'C. Osmolality increased, sodium excretion and free water clearance decreased, all significantly.

5 THRMOGNIC ANTIDIURSIS 393 Adrenaline and noradrenaline, 25 jtg kg-' intravenously into hypotonic-salineinfused hens, produced an immediate increase in urine flow and a decrease in osmolality lasting for about 15 min. Haemorrhage, a stimulus known to release ADH in mammals, was used here to indicate whether an antidiuresis could be produced comparable to the thermogenic response at Ta 32 0C. Blood (8-10 ml. kg-') was withdrawn from a brachial artery in water-loaded hens and it was seen that urine flow decreased and osmolality increased. TABL 3. Urine flow and osmolality in hens infused with hypotonic saline; the effect of ADH, catecholamines and haemorrhage (15 min periods) Urine flow Osmolality n (ml. kg-' min-1) (m-osmole kg-1) Control Arginine vasotocin *** *** Control Adrenaline *** *** Noradrenaline *** *** Control Haemorrhage ** 69± 9* Hypothalamic heating and cooling In three experiments on saline-infused hens at Ta 20 0C the temperature of the thermode located in the hypothalamus was raised by 5-8 0C for 30 min without change in urine volume or composition. When the hypothalamus was cooled by 8-10 'C there was a marked diuresis and a fall in urine osmolality. When cooling was repeated at Ta 32 0C there was also a diuresis, compared with Ta 20 0, but when hypothalamic cooling ceased urine flow fell and osmolality rose in a manner typical of thermogenic antidiuresis (Fig. 2). DISCUSSION In normal, water-loaded or saline-infused hens there was a clearly defined antidiuresis following sudden exposure to a warm environment which imposed little or no heat stress. This could be considered to be an anticipatory response in that it occurred at a time when water balance was not disturbed. Itoh (1954) also noted that greater amounts of plasma antidiuretic activity were present in rats when they were exposed to Ta C although he did not look for changes in urine flow directly. In man too this ability to excrete a given water load was reduced (Weiner, 1944) and an antidiuresis was observed (Segar & Moore, 1968) but here the conditions were more severe, up to 50 0C in the latter work. Similarly in the pig, Forsling et al. (1976) could not demonstrate any antidiuretic response until Ta as high as C was reached, by which time Tr had risen to 43 0C. There is, therefore, some doubt about whether the response in the pig and man is similar in origin to that seen in the fowl if it can be evoked only by extreme temperatures. At these higher temperatures (40 0C and above) antidiuresis was not observed in the fowl but there

6 394. AZAHAN AND A. H. SYKS was instead a tendency towards a diuresis which could be mimicked by injections of catecholamines. It had been observed earlier (Korr, 1939) that adrenaline was diuretic in the fowl, and since the fowls were clearly heat stressed it is likely that the sympathetico-adrenal system was stimulated. Plasma catecholamine levels have been shown to increase at Ta (den & Siegel, 1975) but not at Ta (Lin & Sturkie, 1968), the temperature at which antidiuresis occurred here. 20 0C C Ambient IHypothalamic H cooling cooling temperature (9t C) I coo 3,s 04 i _ > ~I I D -~ ''''~ 0. L35 + ~ ~ -,I U)~ Time (m2) Fig. 2. Changes in renal function following hypothalamic cooling at an ambient temperature (2^) of 32 C. One hen infused with hypotonic saline. There is much evidence to suggest that this thermogenic antidiuresis is of pituitary origin although final proof has yet to be obtained. The reduction in urine volume was accompanied by an increase in osmolality and in sodium concentration, and these effects could be reproduced in water-loaded fowls by AVT injected in amounts believed to be within the physiological range (Skadhauge, 1973) and by hemorrhage, a stimulus known to release ADH in mammals (Share, 1968). Clearly it would be desirable to measure changes in plasma AVT in the fowl following exposure to warm temperatures and also to use fowls

7 THRMOGNIC ANTIDIURSIS 395 with permanent diabetes insipidus, in which the thermogenic response should not be elicited. There is practically no information about the onset and course of experimental diabetes insipidus in the fowl. Koike & Lepkovsky (1967) placed hypothalamic lesions and found urine flows of 0 3 ml. kg-' minm- with an osmolality of 30 m-osmole/kg, values comparable to those found here following water loading or exposure to cold. Hypothalamic cooling in the fowl also produced a diuresis and inhibited the thermogenic response at Ta 32 'C. Simon-Oppermann, Hamel & Simon (1979) have shown in the duck that hypothalamic cooling induced a diuresis which could be suppressed by vasopressin, and similar findings on cold-induced duiresis have been made on the monkey (Hayward & Baker, 1968) but in the goat only an antidiuresis was elicited (Olsson, 1969; Simon-Oppermann & Jessen, 1977). The failure to evoke antidiuresis by hypothalamic heating may imply only that the stimulus to the response is either not central (the observations on infra-red heating suggest a peripheral component) or is not a direct response to temperature at all but, for example, to changes in body fluid redistribution. Forsling et al. (1976) could not alter plasma ADH in this way, unless the Ta was very hot (50 0C). On the other hand Szczepanska-Sadowska (1974) and Sadowski, Kruk & Chwalbinska- Moneta (1977) were able to increase plasma ADH by hypothalamic heating in the dog and the rabbit respectively. Renal function was recorded only in rabbits in which an antidiuresis occurred. Apart from possible species differences, it is known that other thermoregulatory responses, for example panting in fowls, can be evoked by direct thermal stimulation of the hypothalamus only when there is an adequate background of thermal signals from the periphery, including the spinal cord. Further work is obviously required to determine the mechanism of thermogenic antidiuresis in the fowl. Finally, an interaction between drinking and antidiuresis was observed. The thermal stimulus to both drinking and to antidiuresis was present when fowls were placed in a warm environment, but some further stimulus, consequent upon drinking, partially inhibited the antidiuretic response. Nicolaides (1969) has described, in the rat, a reflex inhibition of ADH release by the presence of water in the mouth and in the fowl Dicker & Haslam (1966) have shown that water entering the crop is associated with a prompt rise in urine flow, well before any absorption could have taken place. Thermogenic antidiuresis is obviously not appropriate in the presence of adequate amounts of water and it appears as though a mechanism exists to inhibit it. RFRNCS AzMA.N,. (1979). Ambient temperature as a factor modifying renal function in the fowl. M.Phil. thesis, University of London. BoKoRI, J. (1961). Neue methode zur Harngewinnung von Geflugel. Acta. vet. Med. hung. 11, DICKR, S.. & HASLAM, J. (1966). Water diuresis in the domestic fowl. J. Phy8iol. 183, DN, F. W. & SIGL, H. S. (1975). Adrenal responses in high and low ACTH response lines of chickens during acute heat stress. Gen. comp. ndocr. 25, FORSLING, M. L., INGRAM, D. L. & STANIR, M. W. (1976). ffects of various ambient temperatures and of heating and cooling the hypothalamus and cervical spinal cord on ADH secretion and urinary osmolality in pigs. J. Physiol. 257,

8 396. AZAHAN AND A. H. SYKS GRAC, J.. & STVNSON, J. A. F. (1971). Thermogenic drinking in the rat. Am. J. Phy8iol. 220, HAYWARD, J. N. & BLn, M. A. (1968). Diuretic and thermoregulatory responses to preoptic cooling in the monkey. Am. J. Physiol. 214, ITOH, S. (1954). The release of antidiuretic hormone from the posterior pituitary body on exposure to heat. Jap. J. Phy8iol. 4, KCHIL, A. A. (1976). A physiological investigation of thermogenic drinking in the domestic fowl. Ph.D. thesis, University of London. Koch, T. & LPKOVsKY, S. (1967). Hypothalamic lesions producing polyuria in chickens. Gen. comp. ndocr. 8, KORR, I. M. (1939). The osmotic function of the chicken kidney. J. cell. comp. Phyeiol. 13, LiN, Y. C. & STURIT, P. D. (1968). ffect of environmental temperatures on the catecholamines of chickens. Am. J. Physiol. 214, NIcOLMIDS, S. (1969). Systemic responses to orogastric stimulation in the regulation of food and water balance. Ann. N.Y. Acad. Sci. 157, OLSsoN, K. (1969). Studies on central regulation of secretion of ADH in the goat. Acta physiol. 8cand. 77, RICHARDS, S. A. (1970). The role of hypothalamic temperature in the control of panting in the chicken exposed to heat. J. Physiol. 211, SADOWSKI, J., KRuK, B. & CHWALBINSKA-MONTA, J. (1977). Renal function changes during preoptic-anterior hypothalamic heating in the rabbit. Pfluigers Arch. 370, SGAR, W.. & MOOR, W. W. (1968). The regulation of antidiuretic hormone release in man: effects of change in position and ambient temperature on blood ADH level. J. clin. Invest. 47, SHAR, L. (1968). Control of plasma ADH titer in haemorrhage. Role of atrial and arterial receptors. Am. J. Physiol. 215, SIMON-OPPRMANN, C., HAMML, H. T. & SIMON,. (1979). Hypothalamic temperature and osmoregulation in the Pekin duck. Pflugers Arch. 378, SimON-OPPRMANN, C. & JSSN, C. (1977). Antidiuretic responses to thermal stimulation of hypothalamus and spinal cord in the conscious goat. Pjfugers Arch. 368, SKADHAUG,. (1973). Renal and cloacal salt and water transport in the fowl (Galluw domestdius). Dan. med. Bull. 20, Suppl. I, SzczrAsKA-SAOwSxA, F. (1974). Plasma ADH increase and thirst suppression elicited by preoptic heating in the dog. Am. J. Physiol. 226, 1, WINR, J. S. (1944). The diuretic response of men working in hot and humid conditions. J. Physiol. 103, 36-37P.