GENERAL
Effects
AND
33,526-530
ENDOCRINOLOGY
(1977)
of Environmental Salinity and of Hormones on Urinary Bladder Function in the Euryhaline Teleost, Gillichthys mirabilis
ARNOLD Department
COMPARATIVE
OWENS, of Zoology
TREVOR and Cancer
WIGHAM,’ Research
BYRON
Laboratory,
DONEEN,~
University
AND HOWARD
of California,
Berkeley,
A. BERN~ California
94720
Accepted July 5, 1977
Gillichthys mirabilis was found to acclimate successfully to salinities varying from 5 to 200% seawater. Water permeability of the bladder increased with increased environmental salinity, but the rate of sodium transport did not change significantly. Bovine, porcine, and teleostean (Tilapia) growth hormones did not affect water movement by the bladders of Gillichthys adapted to 5% seawater. Human growth hormone reduced water permeability significantly, presumably owing to its inherent prolactin activity. Cortisol and triiodothyronine had no effect, alone or in combinations. Thus, hormones possibly involved in seawater adaptation failed to alter water movement in the Gillichthys bladder.
The urinary bladder has been used as a model for transporting epithelia in euryhahne teleosts to analyze effects of environmental salinity and hormonal treatment on water permeability and ion transport. Previous studies with the urinary bladder have been concerned with the endocrine control of adjustments resulting from transfer of seawater-adapted fish to fresh water or to dilute seawater (Johnson et al., 1972; Hirano et al., 1973; Doneen, 1976a). In the present study, effects on bladder function of a broader range of salinities, from 5 to 300% seawater, were examined.
Earlier studies have shown that the Gilbladder can respond to prolactin and to cortisol (reviewed by Bern, 1975b). In seawater-adapted fish, prolactin reduced bladder water permeability, whereas cortisol increased permeability and also stimulated sodium transport (Doneen, 1976a). A similar prolactin-cortisol antagonism has been reported for the bladder of the starry flounder (Johnson, 1973). The existence of this antagonism led us to investigate the effects of cortisol on bladder water movement as a possible endocrine mechanism favoring adaptation to seawater of fish previously adapted to 5% seawater. In view of the postulated role of the thyroid in seawater adaptation (Hoar, 1965) and of the evidence for a thyroid-prolactin antagonism in other systems (Bern, 1975a), the possible effects of triiodothyronine on bladder permeability were also examined. Cortisol and triiodothyronine were tested alone and in combination. The action of growth hormones was also investigated in view of in-
lichthys
1 Present address: Department of Applied Biology, University of Wales Institute of Science and Technology, Cardiff, CFl 3NU, Wales, United Kingdom. 2 Present address: Division of Biological Sciences, Natural Science Building, University of Michigan, Ann Arbor, Michigan 48109. 3 Author to whom reprint requests should be addressed.
526 Copyright Q 1977 by Academic Press, Inc. All rights of reproduction in any form reserved.
ISSN 00166480
HORMONES
AND
TELEOST
formation concerning their ability to improve survival of salmonids transferred to seawater (Smith, 1956; Komourdjian et al., 1976; Clarke et al., 1977). Purified bovine, porcine, human, and Sarotherodon (Tilupiu) mossambicus growth hormones were tested. MATERIALS
AND
METHODS
Male Gillichthys mirabilis (40-60 g), collected from San Francisco Bay, were obtained from a commercial supplier. The fish were kept in 100% seawater (SW) at 15” on a 12:12 light cycle. Some fish were transferred to 33% SW for 1 week, after which half of them were killed for examination of bladder function. The remainder were then placed in 5% SW for an additional week. Other groups of fish were transferred from 100 to 200% SW for 1 month. A group of 200% SW-adapted animals was transferred to 300% SW for 2 days. Concentrated SW was made by addition of artificial seawater salts to artificial SW. Hormones. The growth hormones used were: Tilapia GH (cf. Farmer et al., 1976), bovine CH (high dose from C.H. Li, Lot 13539A; low dose from NIH, Lot GH-B-17). porcine GH (NIH Lot P-391), and human GH (from C. H. Li). Bovine and porcine GH doses were selected to correspond approximately with the effective hGH dose. Tilapia GH was used at one-tenth of the mammalian GH doses because of the scarcity of the hormone and because of the expectation that the teleost hormone would be more potent than mammalian GH, in a teleost, as is true for Tilapia prolactin (cf. Farmer et a/.. 1977). Growth hormones and triiodothyronine were dissolved in 0.9% N&l. Cortisol acetate was prepared as a fine suspension in the same solvent. Fish adapted to 5% SW were injected intraperitoneally once daily for 2 or 3 days with 0.25 ml of hormone solution. Doses are given in Table 2. Control fish received 0.9% NaCl. Twenty-four hours after the final injection, blood samples were obtained from the caudal artery; the fish were then decapitated and the bladder was quickly removed for in vitro measurement of sodium (in adaptation experiments only) and water movements as previously described (Johnson et al.. 1972). Briefly, net sodium transport was determined from the difference in bladder Ringer sodium content at the beginning and end of a I-hr incubation in 100% Ringer. Osmotically driven water movement was determined from the weight change in bladders filled with 20% Ringer and incubated for 20 min in 100% Ringer. Plasma and Ringer sodium concentrations were measured by atomic absorption spectrophotometry (Perkin-Elmer 290-B). Experimental Salinity
adaptation.
527
BLADDER
results were compared with control values by the Student t test (two-tailed).
RESULTS
Table 1 summarizes the effects of environmental salinity on urinary bladder water movement, on net sodium uptake, and on plasma sodium concentration. In the first experiment (Table 1, Expt l-l), bladder water movement was significantly higher (P< 0.05) in 33% SW-adapted fish than in 5% SW-adapted animals. The water movement in the bladders of 33% SW-adapted fish was, however, substantially lower than that typically observed in 100% SW-acclimated fish bladders (60-80 ~1 cm-2 hr-I; Table 1, Expt 1-2 and l-3). Plasma sodium was significantly higher (P < 0.05) in 33% SWadapted fish than in 5% SW-adapted controls. Water and sodium movements in the bladders of 200% SW-adapted fish (Table 1, Expt l-2) did not differ significantly from those of 100% SW-acclimated fish, though the former displayed a tendency toward a higher rate of bladder sodium transport. In experiment 3 (Table 1, Expt l-3), bladders of 100% SW-adapted fish were compared with bladders of fish first acclimated to 200% SW (one week) and then placed in 300% SW. After 2 days in 300% SW, nearly half of the fish had died. The remaining fish were sacrificed for examination of the bladder, though they were definitely in osmoregulatory failure as indicated by a high plasma sodium value (mean, 266 meq/liter). Bladder water permeabilities in Giflichthys were no different in 100 and 300% SW; however, sodium transport was significantly elevated (P < 0.05) in the bladders of fish exposed to the higher salinity. Plasma sodium values did not differ between 100 and 200% SW-adapted fish. The effects of some growth hormones, triiodothyronine, and cortisol acetate on the bladder osmotic permeability of 5% SW-adapted Gillichthys are shown in Table 2. In experiment 2-1, human growth hormone treatment further reduced bladder
528
OWENS ET AL. TABLE EFFECTS
Environmental
Experiment
salinity (% SW)
l-l
5 (control) 33
l-2
l-3
1
OF ADAPTATIONAL SALINITY ON Gillichthys URINARY BLADDER SODIUM TRANSPORT AND ON PLASMA SODIUM CONCENTRATION
Adaptation time (days) 7 7
100 (control)
26
200
30
100 (control)
9
300
20
Net water movement (~I.cm-~.hr-‘)
WATER
AND
Net sodium movement (peq.cm-2.hr-L)
Plasma sodium concentration (meq .liter+)
8.4 + 0.9 (lo)* 17.7 k 1.6** (11)
0.79 2 0.11 (10) 0.92 2 0.14 (10)
138.4 2 3.3 (7) 151.7 + 2.9* (7)
56.0 -+ 6.6 (11) 65.6 % 4.5 (13)
0.86 t 0.16 (10) 1.35 k 0.24 (13)
162.1 f 0.9 (7) 167.2 f 1.9 (7)
78.0 ” 6.0 (10) 65.3 ? 7.1
1.07 f 0.08 (11) 1.79 * 0.39* (4)
158,7 k 2.1
(6)
(6) 266.0 k 3.8** (5)
a Values given as means + SEM. Numbers in parentheses are numbers of bladders or animals in each group. D After one week in 200% SW. * P < 0.05 (two-tailed Student t test). ** P c 0.001 (two-tailed Student t test).
water permeability below the relatively low level already achieved after 1 week of acclimation to 5% SW. In contrast, bovine (Table 2, Expt 2-2 and 2-3), porcine (Table 2, Expt 2-6), and Sarotherodon (Tilupiu) (Table 2, Expt 2-4 and 2-5) growth hormones had no effect on bladder osmotic permeability. Injection of 1 mg/day of cortisol acetate for 3 days failed to alter bladder osmotic permeability when cortisol was given alone (Table 2, Expt 2-6, 2-7) or in combination with porcine growth hormone (Table 2, Expt 2-6) or triiodothyronine (Table 2, Expt 2-7). DISCUSSION
Adaptation experiments (Table 1) show that Gillichthys display a wide salinity tolerance, living successfully in the laboratory in environments of 5% SW to at least 200% SW. The range of salinity tolerance for this species was apparently exceeded in 300% SW. Physiologically, water permeability in the Gillichthys urinary bladder can be pro-
portionally adjusted to the external salinity. At the one moderate salinity examined (33% SW), bladder water permeability and plasma sodium level were intermediate between the values observed in 100 and 5% SW (Table 1). As prolactin and cortisol appear to have opposite and antagonistic effects on bladder water movement (Johnson, 1973; Doneen, 1976a), the interaction between these hormones may determine a particular osmotic permeability. Alternatively, pituitary prolactin secretion may be regulated to a level appropriate to a particular environmental salinity (Nagahama et al., 1975). As previously observed (Doneen, 1976a), rates of bladder sodium movement did not differ in fish adapted to 100% SW and to more dilute salinities. However, fish exposed to salinities more concentrated than 100% SW displayed an elevated bladder sodium absorption (Table 1, Expt 1-2 and l-3). Bladder sodium transport has also been shown to increase after injection of cortisol acetate into 100%
HORMONES
EFFECT
Experiment 2-l 2-2 2-3 2-4 2-5 2-6
2-7
AND
TELEOST
529
BLADDER
TABLE 2 OF GROWTH HORMONES, CORTICAL ACETATE, AND TRIIODOTHYRONINE, COMBINATION, ON BLADDER WATER MOVEMENT IN 5% SW-ADAPTED
Hormonal treatment Saline Human growth hormone Saline Bovine growth hormone Saline Bovine growth hormone Saline Tdapia growth hormone Saline Tilapiu growth hormone Saline Cortisol acetate Porcine growth hormone Cortisol acetate + porcine growth hormone Saline Cortisol acetate Triiodothyronine Cortisol acetate + triiodothyronine
* P < 0.01 (two-tailed
GIVEN
ALONE
AND IN
Gillichthys
Number of days of treatment
n
0.35 0.3 0.7 0.035 0.07 1.0 0.25
2 2 3 3 3 3 2 2 2 2 3 3 3
8 6 7 8 7 6 4 9 9 8 9 9 5
18.8 10.7 14.7 15.6 15.2 15.4 17.3 17.1 18.4 14.4 19.8 17.1 18.0
k 2.2 2 1.6* c 1.8 ” 1.7 It 1.9 If: 2.5 * 1.2 ?I 1.9 f 2.9 2 1.5 t 3.1 t 2.7 -e 3.6
1.0 0.015
3 3 3 3
5 7 11 5
15.4 22.3 18.8 20.8
2 k 2 k
3
4
Dose (m&v)
Net water movement (~1. cm- *. hr- ‘)
4.1 7.7 3.6 4.9
14.9 2 5.6
Student t test).
SW-adapted Gillichthys (Doneen, 1976a). Thus, the elevated bladder sodium absorption in Gillichthys exposed to concentrated seawater may result from increased cortisol secretion. Whereas seawater adaptation is promoted by growth hormone in salmonids (Smith, 1956; Komourdjian et al., 1976; Clarke e$ al., 1977), three of the growth hormones tested, including a highly purified teleostean growth hormone, were inactive both on the 5% SW-adapted Gillichthys bladder in vivo and on the 100% SWadapted bladder maintained in organ culture (Doneen, 1976b). If these growth hormones had acted on the gobiid (Gillichthys) bladder in a fashion consistent with their apparent contribution to seawater adjustment in salmonids, increased permeability to water might have been expected, as oc-
curs when Gillichthys are transferred from dilute to more concentrated seawater. The Tilapia GH may not have been fully tested because of the low dosage we were compelled to use. Despite the greater potency that might be expected of a teleost GH acting on a teleost, growth of both Tilupiu and Oncorhynchus nerka were stimulated about equally by Tilupia GH and bovine GH (Clarke et al.; 1977). Human growth hormone further reduced bladder osmotic permeability (Table 2, Expt 2-l) in 5% SW-adapted animals. The inherent prolactin-like actions of human growth hormone have been previously noted in the Gillichthys bladder (Doneen, 1976b), and in other teleosts (Pickford et al., 1965; Clarke et al., 1973). The ability of cortisol to increase the water permeability of the 100% SW-
530
OWENS
adapted fish bladder (Doneen, 1976a) cannot be duplicated in fish adapted to 5% SW (Table 2, Expt 2-6 and 2-7). The inability of cortisol acetate to alter bladder osmotic permeability could result either from the presence of antagonizing levels of endogenous prolactin or from treatment periods (2-3 days) of insufficient duration to alter bladder function. Despite the postulated role of thyroid hormone in SW adaptation (Hoar, 1965), triiodothyronine failed to influence bladder water movement in Gillichthys. In general, then, three hormonal entities (cortisol, thyroid hormone, and growth hormone) that have been implicated in seawater adaptation do not affect the bladder of 5% seawater-adapted Gillichthys, at least at the dose levels administered, to favor water conservation by increased water reabsorption from bladder urine. ACKNOWLEDGMENTS Supported by National Science Foundation Grant BMS 75-16345. Tilapia growth hormone, and the bovine (high dose) and human growth hormones were generously provided by the Hormone Research Laboratory, University of California, San Francisco (from Dr. S. Farmer and Dr. H. Papkoff, and from Dr. C. H. Li, respectively). The porcine and bovine (low dose) growth hormones were provided by the National Institutes of Health. We are indebted to Nathan Collie for important assistance.
REFERENCES Bern, H. A. (1975a). On two possible primary activities of prolactins: osmoregulatory and developmental. Verb. Dem. Zool. Ges., 40-46. Bern, H. A. (1975b). Prolactin and osmoregulation. Amer.
Zool.
15, 937-949.
Clarke, W. C., Bern, H. A., Li, C. H., and Cohen, D. C. (1973). Somatotropic and sodium-retaining effects of human growth hormone and placental lactogen in lower vertebrates. Endocrinology 93, 960-964. Clarke, W. C., Farmer, S. W., and Hartwell, K. M. (1977). Effect of teleost pituitary growth hormone on growth of Tilapia mossambica and on growth
ET AL
and seawater adaptation of sockeye salmon (Oncorhynchus
nerka).
Gen.
Comp.
Endocrinol.
33,
174- 178. Doneen, B. A. (1976a). Water and ion movements in the urinary bladder of the gobiid teleost Gillichthys mirabilis in response to prolactins and to cortisol. Gen. Comp. Endocrinol. 28, 33-41. Doneen, B. A. (1976b). Biological activities of mammalian and teleostean prolactins and growth hormones on mouse mammary gland and teleost urinary bladder. Gen. Comp. Endocrinol. 30,34-42. Farmer, S. W., Papkoff, H., Hayashida, T., Bewley, T. A., Bern, H. A., and Li, C. H. (1976). Purification and properties of teleost growth hormone. Gen. Camp. Endocrinol. 30, 91-100. Farmer, S. W., Papkoff, H., Bewley, T. A., Hayashida, T., Nishioka, R. S., Bern, H. A., and Li, C. H. (1977). Isolation and properties of teleost prolactin. Gen. Comp. Endocrinol. 31,60-71. Hirano, T., Johnson, D. W., Bern, H. A., and Utida, S. (1973). Studies on water and ion movements in the isolated urinary bladder of selected freshwater, marine and euryhaline teleosts. Comp. Riothem.
Physiol.
45A,
529-540.
Hoar, W. S. (l%S). The endocrine system as a chemical link between the organism and its environment. Trans. Roy. Sot. Canada. Sect. 4, 3, 175200. Johnson, D. W. (1973). Endocrine control of hydromineral balance in teleosts. Amer. Zool. 13, 799-818. Johnson, D. W., Hirano, T., Bern, H. A., and Conte, F. P. (1972). Hormonal control of water and sodium movements in the urinary bladder of the starry flounder, Platichthys stellatus. Gen. Comp. Endocrinol. 19, 115-128. Komourdjian, M. P., Saunders, R. L., and Fenwick, J. C. (1976). The effect of porcine somatotropin on growth and survival in seawater of Atlantic salmon (Salmo salar) parr. Canad. 3. Zool. 54,531535. Nagahama, Y., Nishioka, R. S., Bern, H. A., and Gunther, R. L. (1975). Control of prolactin secretion in teleosts, with special reference to Gillichthys mirabilis and Tilapia mossambica. Gen. Camp. Endocrinol. 25, 166-180. Pickford, G. E., Robertson, E. E., and Sawyer, W. H. (1965). Hypophysectomy, replacement therapy, and the tolerance of the euryhaline killifish, Fundulus heteroclitus, to hypotonic media. Gen. Comp. Endocrinol. 5, 160-180. Smith, D. C. W. (1956). The role of the endocrine organs in the salinity tolerance of trout. Mem. Sot.
Endocrinol.
5, 83-98.
Effects
AND
33,526-530
ENDOCRINOLOGY
(1977)
of Environmental Salinity and of Hormones on Urinary Bladder Function in the Euryhaline Teleost, Gillichthys mirabilis
ARNOLD Department
COMPARATIVE
OWENS, of Zoology
TREVOR and Cancer
WIGHAM,’ Research
BYRON
Laboratory,
DONEEN,~
University
AND HOWARD
of California,
Berkeley,
A. BERN~ California
94720
Accepted July 5, 1977
Gillichthys mirabilis was found to acclimate successfully to salinities varying from 5 to 200% seawater. Water permeability of the bladder increased with increased environmental salinity, but the rate of sodium transport did not change significantly. Bovine, porcine, and teleostean (Tilapia) growth hormones did not affect water movement by the bladders of Gillichthys adapted to 5% seawater. Human growth hormone reduced water permeability significantly, presumably owing to its inherent prolactin activity. Cortisol and triiodothyronine had no effect, alone or in combinations. Thus, hormones possibly involved in seawater adaptation failed to alter water movement in the Gillichthys bladder.
The urinary bladder has been used as a model for transporting epithelia in euryhahne teleosts to analyze effects of environmental salinity and hormonal treatment on water permeability and ion transport. Previous studies with the urinary bladder have been concerned with the endocrine control of adjustments resulting from transfer of seawater-adapted fish to fresh water or to dilute seawater (Johnson et al., 1972; Hirano et al., 1973; Doneen, 1976a). In the present study, effects on bladder function of a broader range of salinities, from 5 to 300% seawater, were examined.
Earlier studies have shown that the Gilbladder can respond to prolactin and to cortisol (reviewed by Bern, 1975b). In seawater-adapted fish, prolactin reduced bladder water permeability, whereas cortisol increased permeability and also stimulated sodium transport (Doneen, 1976a). A similar prolactin-cortisol antagonism has been reported for the bladder of the starry flounder (Johnson, 1973). The existence of this antagonism led us to investigate the effects of cortisol on bladder water movement as a possible endocrine mechanism favoring adaptation to seawater of fish previously adapted to 5% seawater. In view of the postulated role of the thyroid in seawater adaptation (Hoar, 1965) and of the evidence for a thyroid-prolactin antagonism in other systems (Bern, 1975a), the possible effects of triiodothyronine on bladder permeability were also examined. Cortisol and triiodothyronine were tested alone and in combination. The action of growth hormones was also investigated in view of in-
lichthys
1 Present address: Department of Applied Biology, University of Wales Institute of Science and Technology, Cardiff, CFl 3NU, Wales, United Kingdom. 2 Present address: Division of Biological Sciences, Natural Science Building, University of Michigan, Ann Arbor, Michigan 48109. 3 Author to whom reprint requests should be addressed.
526 Copyright Q 1977 by Academic Press, Inc. All rights of reproduction in any form reserved.
ISSN 00166480
HORMONES
AND
TELEOST
formation concerning their ability to improve survival of salmonids transferred to seawater (Smith, 1956; Komourdjian et al., 1976; Clarke et al., 1977). Purified bovine, porcine, human, and Sarotherodon (Tilupiu) mossambicus growth hormones were tested. MATERIALS
AND
METHODS
Male Gillichthys mirabilis (40-60 g), collected from San Francisco Bay, were obtained from a commercial supplier. The fish were kept in 100% seawater (SW) at 15” on a 12:12 light cycle. Some fish were transferred to 33% SW for 1 week, after which half of them were killed for examination of bladder function. The remainder were then placed in 5% SW for an additional week. Other groups of fish were transferred from 100 to 200% SW for 1 month. A group of 200% SW-adapted animals was transferred to 300% SW for 2 days. Concentrated SW was made by addition of artificial seawater salts to artificial SW. Hormones. The growth hormones used were: Tilapia GH (cf. Farmer et al., 1976), bovine CH (high dose from C.H. Li, Lot 13539A; low dose from NIH, Lot GH-B-17). porcine GH (NIH Lot P-391), and human GH (from C. H. Li). Bovine and porcine GH doses were selected to correspond approximately with the effective hGH dose. Tilapia GH was used at one-tenth of the mammalian GH doses because of the scarcity of the hormone and because of the expectation that the teleost hormone would be more potent than mammalian GH, in a teleost, as is true for Tilapia prolactin (cf. Farmer et a/.. 1977). Growth hormones and triiodothyronine were dissolved in 0.9% N&l. Cortisol acetate was prepared as a fine suspension in the same solvent. Fish adapted to 5% SW were injected intraperitoneally once daily for 2 or 3 days with 0.25 ml of hormone solution. Doses are given in Table 2. Control fish received 0.9% NaCl. Twenty-four hours after the final injection, blood samples were obtained from the caudal artery; the fish were then decapitated and the bladder was quickly removed for in vitro measurement of sodium (in adaptation experiments only) and water movements as previously described (Johnson et al.. 1972). Briefly, net sodium transport was determined from the difference in bladder Ringer sodium content at the beginning and end of a I-hr incubation in 100% Ringer. Osmotically driven water movement was determined from the weight change in bladders filled with 20% Ringer and incubated for 20 min in 100% Ringer. Plasma and Ringer sodium concentrations were measured by atomic absorption spectrophotometry (Perkin-Elmer 290-B). Experimental Salinity
adaptation.
527
BLADDER
results were compared with control values by the Student t test (two-tailed).
RESULTS
Table 1 summarizes the effects of environmental salinity on urinary bladder water movement, on net sodium uptake, and on plasma sodium concentration. In the first experiment (Table 1, Expt l-l), bladder water movement was significantly higher (P< 0.05) in 33% SW-adapted fish than in 5% SW-adapted animals. The water movement in the bladders of 33% SW-adapted fish was, however, substantially lower than that typically observed in 100% SW-acclimated fish bladders (60-80 ~1 cm-2 hr-I; Table 1, Expt 1-2 and l-3). Plasma sodium was significantly higher (P < 0.05) in 33% SWadapted fish than in 5% SW-adapted controls. Water and sodium movements in the bladders of 200% SW-adapted fish (Table 1, Expt l-2) did not differ significantly from those of 100% SW-acclimated fish, though the former displayed a tendency toward a higher rate of bladder sodium transport. In experiment 3 (Table 1, Expt l-3), bladders of 100% SW-adapted fish were compared with bladders of fish first acclimated to 200% SW (one week) and then placed in 300% SW. After 2 days in 300% SW, nearly half of the fish had died. The remaining fish were sacrificed for examination of the bladder, though they were definitely in osmoregulatory failure as indicated by a high plasma sodium value (mean, 266 meq/liter). Bladder water permeabilities in Giflichthys were no different in 100 and 300% SW; however, sodium transport was significantly elevated (P < 0.05) in the bladders of fish exposed to the higher salinity. Plasma sodium values did not differ between 100 and 200% SW-adapted fish. The effects of some growth hormones, triiodothyronine, and cortisol acetate on the bladder osmotic permeability of 5% SW-adapted Gillichthys are shown in Table 2. In experiment 2-1, human growth hormone treatment further reduced bladder
528
OWENS ET AL. TABLE EFFECTS
Environmental
Experiment
salinity (% SW)
l-l
5 (control) 33
l-2
l-3
1
OF ADAPTATIONAL SALINITY ON Gillichthys URINARY BLADDER SODIUM TRANSPORT AND ON PLASMA SODIUM CONCENTRATION
Adaptation time (days) 7 7
100 (control)
26
200
30
100 (control)
9
300
20
Net water movement (~I.cm-~.hr-‘)
WATER
AND
Net sodium movement (peq.cm-2.hr-L)
Plasma sodium concentration (meq .liter+)
8.4 + 0.9 (lo)* 17.7 k 1.6** (11)
0.79 2 0.11 (10) 0.92 2 0.14 (10)
138.4 2 3.3 (7) 151.7 + 2.9* (7)
56.0 -+ 6.6 (11) 65.6 % 4.5 (13)
0.86 t 0.16 (10) 1.35 k 0.24 (13)
162.1 f 0.9 (7) 167.2 f 1.9 (7)
78.0 ” 6.0 (10) 65.3 ? 7.1
1.07 f 0.08 (11) 1.79 * 0.39* (4)
158,7 k 2.1
(6)
(6) 266.0 k 3.8** (5)
a Values given as means + SEM. Numbers in parentheses are numbers of bladders or animals in each group. D After one week in 200% SW. * P < 0.05 (two-tailed Student t test). ** P c 0.001 (two-tailed Student t test).
water permeability below the relatively low level already achieved after 1 week of acclimation to 5% SW. In contrast, bovine (Table 2, Expt 2-2 and 2-3), porcine (Table 2, Expt 2-6), and Sarotherodon (Tilupiu) (Table 2, Expt 2-4 and 2-5) growth hormones had no effect on bladder osmotic permeability. Injection of 1 mg/day of cortisol acetate for 3 days failed to alter bladder osmotic permeability when cortisol was given alone (Table 2, Expt 2-6, 2-7) or in combination with porcine growth hormone (Table 2, Expt 2-6) or triiodothyronine (Table 2, Expt 2-7). DISCUSSION
Adaptation experiments (Table 1) show that Gillichthys display a wide salinity tolerance, living successfully in the laboratory in environments of 5% SW to at least 200% SW. The range of salinity tolerance for this species was apparently exceeded in 300% SW. Physiologically, water permeability in the Gillichthys urinary bladder can be pro-
portionally adjusted to the external salinity. At the one moderate salinity examined (33% SW), bladder water permeability and plasma sodium level were intermediate between the values observed in 100 and 5% SW (Table 1). As prolactin and cortisol appear to have opposite and antagonistic effects on bladder water movement (Johnson, 1973; Doneen, 1976a), the interaction between these hormones may determine a particular osmotic permeability. Alternatively, pituitary prolactin secretion may be regulated to a level appropriate to a particular environmental salinity (Nagahama et al., 1975). As previously observed (Doneen, 1976a), rates of bladder sodium movement did not differ in fish adapted to 100% SW and to more dilute salinities. However, fish exposed to salinities more concentrated than 100% SW displayed an elevated bladder sodium absorption (Table 1, Expt 1-2 and l-3). Bladder sodium transport has also been shown to increase after injection of cortisol acetate into 100%
HORMONES
EFFECT
Experiment 2-l 2-2 2-3 2-4 2-5 2-6
2-7
AND
TELEOST
529
BLADDER
TABLE 2 OF GROWTH HORMONES, CORTICAL ACETATE, AND TRIIODOTHYRONINE, COMBINATION, ON BLADDER WATER MOVEMENT IN 5% SW-ADAPTED
Hormonal treatment Saline Human growth hormone Saline Bovine growth hormone Saline Bovine growth hormone Saline Tdapia growth hormone Saline Tilapiu growth hormone Saline Cortisol acetate Porcine growth hormone Cortisol acetate + porcine growth hormone Saline Cortisol acetate Triiodothyronine Cortisol acetate + triiodothyronine
* P < 0.01 (two-tailed
GIVEN
ALONE
AND IN
Gillichthys
Number of days of treatment
n
0.35 0.3 0.7 0.035 0.07 1.0 0.25
2 2 3 3 3 3 2 2 2 2 3 3 3
8 6 7 8 7 6 4 9 9 8 9 9 5
18.8 10.7 14.7 15.6 15.2 15.4 17.3 17.1 18.4 14.4 19.8 17.1 18.0
k 2.2 2 1.6* c 1.8 ” 1.7 It 1.9 If: 2.5 * 1.2 ?I 1.9 f 2.9 2 1.5 t 3.1 t 2.7 -e 3.6
1.0 0.015
3 3 3 3
5 7 11 5
15.4 22.3 18.8 20.8
2 k 2 k
3
4
Dose (m&v)
Net water movement (~1. cm- *. hr- ‘)
4.1 7.7 3.6 4.9
14.9 2 5.6
Student t test).
SW-adapted Gillichthys (Doneen, 1976a). Thus, the elevated bladder sodium absorption in Gillichthys exposed to concentrated seawater may result from increased cortisol secretion. Whereas seawater adaptation is promoted by growth hormone in salmonids (Smith, 1956; Komourdjian et al., 1976; Clarke e$ al., 1977), three of the growth hormones tested, including a highly purified teleostean growth hormone, were inactive both on the 5% SW-adapted Gillichthys bladder in vivo and on the 100% SWadapted bladder maintained in organ culture (Doneen, 1976b). If these growth hormones had acted on the gobiid (Gillichthys) bladder in a fashion consistent with their apparent contribution to seawater adjustment in salmonids, increased permeability to water might have been expected, as oc-
curs when Gillichthys are transferred from dilute to more concentrated seawater. The Tilapia GH may not have been fully tested because of the low dosage we were compelled to use. Despite the greater potency that might be expected of a teleost GH acting on a teleost, growth of both Tilupiu and Oncorhynchus nerka were stimulated about equally by Tilupia GH and bovine GH (Clarke et al.; 1977). Human growth hormone further reduced bladder osmotic permeability (Table 2, Expt 2-l) in 5% SW-adapted animals. The inherent prolactin-like actions of human growth hormone have been previously noted in the Gillichthys bladder (Doneen, 1976b), and in other teleosts (Pickford et al., 1965; Clarke et al., 1973). The ability of cortisol to increase the water permeability of the 100% SW-
530
OWENS
adapted fish bladder (Doneen, 1976a) cannot be duplicated in fish adapted to 5% SW (Table 2, Expt 2-6 and 2-7). The inability of cortisol acetate to alter bladder osmotic permeability could result either from the presence of antagonizing levels of endogenous prolactin or from treatment periods (2-3 days) of insufficient duration to alter bladder function. Despite the postulated role of thyroid hormone in SW adaptation (Hoar, 1965), triiodothyronine failed to influence bladder water movement in Gillichthys. In general, then, three hormonal entities (cortisol, thyroid hormone, and growth hormone) that have been implicated in seawater adaptation do not affect the bladder of 5% seawater-adapted Gillichthys, at least at the dose levels administered, to favor water conservation by increased water reabsorption from bladder urine. ACKNOWLEDGMENTS Supported by National Science Foundation Grant BMS 75-16345. Tilapia growth hormone, and the bovine (high dose) and human growth hormones were generously provided by the Hormone Research Laboratory, University of California, San Francisco (from Dr. S. Farmer and Dr. H. Papkoff, and from Dr. C. H. Li, respectively). The porcine and bovine (low dose) growth hormones were provided by the National Institutes of Health. We are indebted to Nathan Collie for important assistance.
REFERENCES Bern, H. A. (1975a). On two possible primary activities of prolactins: osmoregulatory and developmental. Verb. Dem. Zool. Ges., 40-46. Bern, H. A. (1975b). Prolactin and osmoregulation. Amer.
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