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Effects of recombinant human growth hormone in juvenile nile crocodiles (Crocodylus niloticus)
Camp. Biochem. Physiol. Great Britain
Vol. 97A,
OX@-9629/90 $3.00 + 0.00
No. 4, pp. 607-609, 1990
0 1990Pergamon Press plc
Printed in
EFFECTS OF RECOMBINANT HUMAN GROWTH HORMONE IN JUVENILE NILE CROCODILES (CROCODYLUS
NILOTICUS)
OIVIND ANDERSEN’, CHARLES KIMwELEt, ARNFINNAULIEand Trlus
ICmurt
Department of Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146, 0033 Oslo I, Norway. Telephone: (47) 994 8545, Fax: (47) 994 3789; TDepartment of Animal Physiology, College of Agriculture and Veterinary Sciences, University of Nairobi, Nairobi, Kenya (Received 23 April 1990)
Abstract-l. Recombinant human growth hormone (hGH) showed somatotropic activity in juvenile Nile crocodiles (Crocodylus niloticus). 2. Body weight of crocodiles receiving 3.25 pg hGH/g body weight twice a week was increased by 49% after five weeks of treatment, compared to 31% increase in controls. 3. Total length was increased by 15 and 5%, respectively, in the two groups. 4. Food conversion efficiency increased from 28% in the controls to 36% in the hormone injected animals. 5. Cessation of hormone treatment was followed by reduced appetite and decreasing body growth.
INTRODUCITON
estimated by weighing the crocodiles before and after each meal.
The general structure of growth hormone (GH) has been strongly conserved during evolution (Wallis, 1981; Miller and Eberhardt, 1983; Kawauchi and Yasuda, 1987). The scarce immunological and biochemical studies on reptilian GH also support this statement (Hayashida et al., 1975; Yasuda et al., 1989). Mammalian GH stimulated growth in lizards (Licht and Hoyer, 1968) and turtles (Nichols, 1973; Owens et al., 1979). Injection of radiolabelled human (h)GH in turtles indicated a specific uptake of the hormone in the liver and the presence of both somatogenic and lactogenic binding sites in this organ (Marques et al., 1979). No information concerning the somatotropic activity of mammalian GH in the crocodilians has so far been available. In the present study we have investigated the effects of recombinant hGH in juvenile Nile crocodiles.
Hormone source, preparation and administration
Recombinant hGH (3 IU/mg) was obtained from KabiGen AB, Sweden. The lyophilized hormone was dissolved in 0.01 M NaOH and diluted to the desired final concentration in 0.2 M phosphate buffered 0.9% saline, pH 7.4. The hormone nrenaration (5Otil) was in&ted intramuscularly in the tail iwice a week’ in a dosage of 3.25 pg/g body weight. Control crocodiles were given 50 ~1 buffered saline. Experimental procedure
Body growth was first recorded from the day of hatching (day 0) to day 28 (pretreatment period). The hormone injections started on day 28 and was continued for five weeks until day 60. The crocodiles were then observed for a further 59 days (post-treatment period). One animal in each group died during this period. Linear growth was estimated twice a week by measuring the total body length (tip of the snout to tip of the tail) and head length (tip of the snout to the median hind edge of the cranial platform). The crocodiles were weighed to the nearest 0.01 g on a Mettler balance.
MATERIALSAND METHODS Animals
Nile crocodile eggs, which were obtained from a crocodile farm in Mombasa, Kenya, were transported to the Norwegian College of Veterinary Medicine, Norway, and embedded in sand in a chicken incubator (Glarus 8750) kept at 30.0 k 0.5”C. Ten eggs hatched 99 days after laying. The hatchlings were randomly divided into two groups, marked by claw-clipping and transferred to two 80 1 aquaria. The aquaria, which contained sand and flat stones, were filled with 10 I of water that was changed three times a week. A 250 W infrared lamp placed above the sand kept the temperature in the water at 30.0 f 1.O”C. The crocodiles were fed ad libitum, initially five times a week, with pieces of raw calf meat or liver and fish meat. Later the feeding was reduced to three times a week. The food intake was
*Present address and correspondence should be sent to: Section for Biochemistry, Agricultural University of Norway, P.O. Box 36, N-1432 Aas-NLH, Norway.
RESULTS
All the crocodiles gained weight during the pretreatment period, and a steady increase in length of the body and the head was observed. No difference was found between the two groups prior to hormone injections. After five weeks of hormone treatment the body and the head were significantly longer in the hormone treated crocodiles (P < 0.05). The mean body length was increased by 15%, the head length by 18% and the body weight by 49%, compared to 5, 7 and 31%, respectively, in the controls (Table 1). Due to large differences in size between the individual animals in both groups, the effect of the hormone treatment is better visualized by expressing the growth parameters as percentage increase for each 607
608
ANDERSEN et al.
OIVIND
Table 1. Body weight, body length and head length (mean + ISD)
Days
hGH
0 4 28 60 II9
54.3 66.8 99.6 87.6
i f i_ k
Body weight (9)
Control
55.2 k-2.4 (10) 2.2 (5) 54.6 5.3 (5) 65.8 Il.0 (5) 86.0 14.9 (4) 100.3
+ + + *
of juvenile
hGH
2.3 (5) 7.4 (5) 13.86) 15.7 (4)
28.3 32.7 37.6 36.6
Nile crocodiles
Body length (cm)
before, during and after treatment
Control
3.88 i 0.09 (IO) 4.06+0.13(5) 4.01 f 0.17 (5) 4.56 + 0.10 (5) 4.52 + 0.22 (5) 5.36 + 0.13 iSj* 4.83 + 0.33 i5j 5.35 * 0.22 (4) 5.30 + 0.34 (4)
The treated animals were injected with 3.25 pg hGH twice a week between days 28 and 60, while the controls Numbers of animals are given in parenthesis. *Significant difference (P < 0.05).
100
were given buffered
saline.
respectively, for the controls. Thus, the calculated food conversion efficiency was increased from 28% (controls) to 36% following hormone treatment. Within a week after the last injection all the hormone treated crocodiles stopped eating, and the body growth was arrested during the rest of the observation period. Their body length even showed a tendency to decrease between days 60 and 119. A marked lightening of the skin was also observed after hormone treatment. In contrast, the control crocodiles ate and grew as normal during the posttreatment period with no change in skin colour.
. hGH 0 control
0
20
DISCUSSION
40
60
60
100
120
Age(days)
Fig. 1. Percentage increase (from day 4) in body weight of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. The treatment period is indicated by the horizontal bar. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 53 and 66.
Recombinant hGH was recently shown to stimulate body growth of juvenile brook trout (Salvelinus fontinalis) and toads (Bufo bufo) (Skyrud et al., 1989; Larsen and Andersen, 1990). This study demonstrates somatogenic activity of hGH in juvenile Nile crocodiles. The hormone treated crocodiles (7.5 pg hGH/g week) were 12% longer than the controls after 33 days of treatment. Juvenile lizards (Anolis carolinensis) daily injected with bovine GH (approximately 2pg/g week) were about 7% longer (snout-vent length) than the controls after 40 days (Licht and Hoyer, 1968). The lizards continued to grow at this rate when the dosage was increased up to ten times. In juvenile snapping turtles (Chefydra serpenfina) daily injections of ovine GH in a dosage of Spg/g week gave similar somatotropic effect as the dosage of 25 pg/g week (Nichols, 1973). 40
LO
s u 1 al .c;
Control
hGH
26.9 f 1.2 (IO) Il.1 (5) 27.4 k I .3 (5) + I .O (5) 31.9 + 2.1 (5) I I .3 (5j* 33.5 : 2.6 (5j f 2.1 (4) 35.8 f 2.5 (4)
animal. Figures l-3 show that during the treatment period the crocodiles receiving hGH showed similar growth rate as before treatment, whereas the controls grew at a lower rate in this period. During the treatment period the crocodiles receiving hGH ingested significantly more per meal, 5.1 f 3.3(SD) g (n = 90), than the controls, 4.1 f 3.O(SD) g (n = 90) (P < 0.02). The mean total food uptake was 91.5 g and the weight gain 32.8 g for the hormone group, while it was 73.1 g and 20.2 g,
with hGH
Head length (cm)
r-
30
-
20
-
. hGH 0
r .
hGH
control -0 p---o
Y8
L G 4
10
-
0’
05 0
20
40
60
60
100
120
Age (days)
Fig. 2. Percentage increase (from day 4) in body length of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 42 and 102.
’
0
a n 20
’ 40
I
I
n I
60
60
*
o 100
” 120
Age(days)
Fig. 3. Percentage increase (from day 4) in head length of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. The treatment period is indicated by the horizontal bar. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 53 and 88.
609
Effects of human GH in crocodiles Administration of ovine GH (24 ,ug/g week) greatly increased (up to 300%) the food consumption of juvenile lizards (Licht and Hoyer, 1968). The daily food intake of the crocodiles was not stimulated to the same degree, since the hGH treated animals ingested only about 25% more than the controls. When the difference in body weight is taken into account, the appetite was not significantly different between the two groups. However, the crocodiles receiving hGH seemed to be able to convert the food more efficiently into body tissue than the controls. The calculated food conversion efficiency of 36 and 28%, respectively, are underestimated values, since the food intake also includes water swallowed. More efficient food utilization was also observed in the lizard Anolis carolinensis and the sea turtle (Chelonia mydas) given bovine GH (DiMaggio, 1961; Owens et al., 1979). We did not kill the valuable crocodiles in order to analyse the body composition. However, exogenous GH did not increase the percentage water content of turtle liver and trout skeletal muscles (Nichois, 1973; Skyrud et al., 1989). Following the treatment period the hGH injected crocodiles did not eat at all, the body growth decreased and they were unusually lethargic. A reasonable explanation is that the previous high levels of exogenous hGH may have down regulated the GH receptors and/or suppressed the endogenous GH secretion. An alternative possibility is that administration of heterologous GH may have caused an allergenic response. Thus, the crocodiles were affected even worse when the hormone treatment was restarted at day 169 (data not shown), indicating a secondary immunological response. Turtles seem to recognize mammalian GH and prolactin as foreign proteins and produce antibodies to neutralize their effects (Nichols, 1973; Owens et al., 1979). Due to the small number of animals available, an untreated group was not included in this study. Therefore, it is not clear whether the hormone treatment improved growth over that which would have been observed in the absence of any treatment. The saline injected crocodiles grew at a slower rate during the treatment than before this period, indicating that injections alone may retard growth. However, Nichols (1973) demonstrated that saline injected turtles grew faster than uninjected controls. Breeding of crocodiles has become important, mostly due to their valuable skin. However, a genera1 low growth rate makes the skin production hardly profitable. This preliminary investigation shows that administration of mammalian GH stimulates growth; however, such therapy is not likely to be of practical use for crocodilian husbandry.
Acknowledgements-This
work was supported by a grant from the NORAD KEN 046 Project. The authors express
gratitude to KabiGen AB which kindly provided us with r~mb~nant hGH and to Dr M. A. Fazil for helping us in getting the eggs. Thanks are due also to Dr L. 0. Larsen for valuable comments on the manuscript.
REFERENCES
DiMaggio A. (1961) Hormonal Regulation of Growth in the Lizard, Rnolis carolinensis. Ph.D. Dissertation. Louisiana State University, Baton Rouge, LA. Hayashida T., Farmer S. W. and Papkoff H. (1975) Pituitary growth hormones: Further evidence for evolutionary conservatism based on immunochemical studies. Proc. Natl. Acad. Sci. USA 72, 4322-4326.
Kawauchi H. and Yasuda A. (1987) Evolutionary aspects of growth hormone from nonmammalian species. J. Endocrinol. Invest. 10 (Suppl. 4). Kawauchi H. and Yasuda A. (1989) Evolutionary aspects of growth hormones from nonmammalian species. In Advances in Growth Hormone and Growth Factor Research
(Edited by Miiller E. E., Cocchi D. and Locatelli V.). pp. 51-68. Pythagora Press, Berlin. Larsen L. 0. and Andersen 0. (1990) Skeletal growth in the toad, Bufo bufo, treated with bovine or human growth hormone. Program of the 15th Conference of European Comparative Endocrinologists, Leuven. Licht P. and Hoyer H. (1968) Somatotropic effects of exogenous prolactin and growth hormone in juvenile lizards (Lacerfa s. sicula). Gen. Comp. Endocrinol. II, 338-346.
Marques M., Silva R. S. M., Turyn D. and Dellacha J. M. (1979) Dist~bution and specific binding in uiuo of iodinated growth hormones in the turtle Chrysemys dorbigni. Gen. Comp. Endocrinol. 37, 487-492.
Miller W. L. and Eberhardt N. L. (1983) Structure and evolution of the growth hormone gene family. Endocr. Rev. 4, 97-130.
Nichols C. W. (1973) Somatotropic effects of prolactin and growth hormone in juvenile snapping turtles (Chelydra serpentina). Gen. Comp. Endocrinol. 21, 219-224.
Owens D. W., Hendrickson J. R. and Endres D. B. (1979) Somatic and immune responses to bovine growth hormone, bovine prolactin, and diethylstil~strol in the green sea turtle. cien. Comp. Endocrinol. 38, 53-61. Skyrud T., Andersen 0., Alestrem P. and Gautvik K. M. (1989) Effects of recombinant human growth hormone and insulin-like growth factor 1 on body growth and blood metabolites in brook trout (Salvelinus fontinalis). Gen. Comp. Endocrinol. 75, 247-255.
.
Yasuda A.. Yamaauchi K.. Paukoff H.. Yokoo Y. and Kawauchi H. (l&9) The complete ammo acid sequence of growth hormone from the sea turtle (Chelonia mydas). Gen. Comp. Endocrinof. 73, 242-251.
Wallis M. (1981) The molecular evolution of pituitary growth hormone, prolactin and placental lactogen: A protein family showing variable rates of evolution. J. Mol. Evol. 17, 10-18.
Vol. 97A,
OX@-9629/90 $3.00 + 0.00
No. 4, pp. 607-609, 1990
0 1990Pergamon Press plc
Printed in
EFFECTS OF RECOMBINANT HUMAN GROWTH HORMONE IN JUVENILE NILE CROCODILES (CROCODYLUS
NILOTICUS)
OIVIND ANDERSEN’, CHARLES KIMwELEt, ARNFINNAULIEand Trlus
ICmurt
Department of Physiology and Nutrition, Norwegian College of Veterinary Medicine, P.O. Box 8146, 0033 Oslo I, Norway. Telephone: (47) 994 8545, Fax: (47) 994 3789; TDepartment of Animal Physiology, College of Agriculture and Veterinary Sciences, University of Nairobi, Nairobi, Kenya (Received 23 April 1990)
Abstract-l. Recombinant human growth hormone (hGH) showed somatotropic activity in juvenile Nile crocodiles (Crocodylus niloticus). 2. Body weight of crocodiles receiving 3.25 pg hGH/g body weight twice a week was increased by 49% after five weeks of treatment, compared to 31% increase in controls. 3. Total length was increased by 15 and 5%, respectively, in the two groups. 4. Food conversion efficiency increased from 28% in the controls to 36% in the hormone injected animals. 5. Cessation of hormone treatment was followed by reduced appetite and decreasing body growth.
INTRODUCITON
estimated by weighing the crocodiles before and after each meal.
The general structure of growth hormone (GH) has been strongly conserved during evolution (Wallis, 1981; Miller and Eberhardt, 1983; Kawauchi and Yasuda, 1987). The scarce immunological and biochemical studies on reptilian GH also support this statement (Hayashida et al., 1975; Yasuda et al., 1989). Mammalian GH stimulated growth in lizards (Licht and Hoyer, 1968) and turtles (Nichols, 1973; Owens et al., 1979). Injection of radiolabelled human (h)GH in turtles indicated a specific uptake of the hormone in the liver and the presence of both somatogenic and lactogenic binding sites in this organ (Marques et al., 1979). No information concerning the somatotropic activity of mammalian GH in the crocodilians has so far been available. In the present study we have investigated the effects of recombinant hGH in juvenile Nile crocodiles.
Hormone source, preparation and administration
Recombinant hGH (3 IU/mg) was obtained from KabiGen AB, Sweden. The lyophilized hormone was dissolved in 0.01 M NaOH and diluted to the desired final concentration in 0.2 M phosphate buffered 0.9% saline, pH 7.4. The hormone nrenaration (5Otil) was in&ted intramuscularly in the tail iwice a week’ in a dosage of 3.25 pg/g body weight. Control crocodiles were given 50 ~1 buffered saline. Experimental procedure
Body growth was first recorded from the day of hatching (day 0) to day 28 (pretreatment period). The hormone injections started on day 28 and was continued for five weeks until day 60. The crocodiles were then observed for a further 59 days (post-treatment period). One animal in each group died during this period. Linear growth was estimated twice a week by measuring the total body length (tip of the snout to tip of the tail) and head length (tip of the snout to the median hind edge of the cranial platform). The crocodiles were weighed to the nearest 0.01 g on a Mettler balance.
MATERIALSAND METHODS Animals
Nile crocodile eggs, which were obtained from a crocodile farm in Mombasa, Kenya, were transported to the Norwegian College of Veterinary Medicine, Norway, and embedded in sand in a chicken incubator (Glarus 8750) kept at 30.0 k 0.5”C. Ten eggs hatched 99 days after laying. The hatchlings were randomly divided into two groups, marked by claw-clipping and transferred to two 80 1 aquaria. The aquaria, which contained sand and flat stones, were filled with 10 I of water that was changed three times a week. A 250 W infrared lamp placed above the sand kept the temperature in the water at 30.0 f 1.O”C. The crocodiles were fed ad libitum, initially five times a week, with pieces of raw calf meat or liver and fish meat. Later the feeding was reduced to three times a week. The food intake was
*Present address and correspondence should be sent to: Section for Biochemistry, Agricultural University of Norway, P.O. Box 36, N-1432 Aas-NLH, Norway.
RESULTS
All the crocodiles gained weight during the pretreatment period, and a steady increase in length of the body and the head was observed. No difference was found between the two groups prior to hormone injections. After five weeks of hormone treatment the body and the head were significantly longer in the hormone treated crocodiles (P < 0.05). The mean body length was increased by 15%, the head length by 18% and the body weight by 49%, compared to 5, 7 and 31%, respectively, in the controls (Table 1). Due to large differences in size between the individual animals in both groups, the effect of the hormone treatment is better visualized by expressing the growth parameters as percentage increase for each 607
608
ANDERSEN et al.
OIVIND
Table 1. Body weight, body length and head length (mean + ISD)
Days
hGH
0 4 28 60 II9
54.3 66.8 99.6 87.6
i f i_ k
Body weight (9)
Control
55.2 k-2.4 (10) 2.2 (5) 54.6 5.3 (5) 65.8 Il.0 (5) 86.0 14.9 (4) 100.3
+ + + *
of juvenile
hGH
2.3 (5) 7.4 (5) 13.86) 15.7 (4)
28.3 32.7 37.6 36.6
Nile crocodiles
Body length (cm)
before, during and after treatment
Control
3.88 i 0.09 (IO) 4.06+0.13(5) 4.01 f 0.17 (5) 4.56 + 0.10 (5) 4.52 + 0.22 (5) 5.36 + 0.13 iSj* 4.83 + 0.33 i5j 5.35 * 0.22 (4) 5.30 + 0.34 (4)
The treated animals were injected with 3.25 pg hGH twice a week between days 28 and 60, while the controls Numbers of animals are given in parenthesis. *Significant difference (P < 0.05).
100
were given buffered
saline.
respectively, for the controls. Thus, the calculated food conversion efficiency was increased from 28% (controls) to 36% following hormone treatment. Within a week after the last injection all the hormone treated crocodiles stopped eating, and the body growth was arrested during the rest of the observation period. Their body length even showed a tendency to decrease between days 60 and 119. A marked lightening of the skin was also observed after hormone treatment. In contrast, the control crocodiles ate and grew as normal during the posttreatment period with no change in skin colour.
. hGH 0 control
0
20
DISCUSSION
40
60
60
100
120
Age(days)
Fig. 1. Percentage increase (from day 4) in body weight of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. The treatment period is indicated by the horizontal bar. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 53 and 66.
Recombinant hGH was recently shown to stimulate body growth of juvenile brook trout (Salvelinus fontinalis) and toads (Bufo bufo) (Skyrud et al., 1989; Larsen and Andersen, 1990). This study demonstrates somatogenic activity of hGH in juvenile Nile crocodiles. The hormone treated crocodiles (7.5 pg hGH/g week) were 12% longer than the controls after 33 days of treatment. Juvenile lizards (Anolis carolinensis) daily injected with bovine GH (approximately 2pg/g week) were about 7% longer (snout-vent length) than the controls after 40 days (Licht and Hoyer, 1968). The lizards continued to grow at this rate when the dosage was increased up to ten times. In juvenile snapping turtles (Chefydra serpenfina) daily injections of ovine GH in a dosage of Spg/g week gave similar somatotropic effect as the dosage of 25 pg/g week (Nichols, 1973). 40
LO
s u 1 al .c;
Control
hGH
26.9 f 1.2 (IO) Il.1 (5) 27.4 k I .3 (5) + I .O (5) 31.9 + 2.1 (5) I I .3 (5j* 33.5 : 2.6 (5j f 2.1 (4) 35.8 f 2.5 (4)
animal. Figures l-3 show that during the treatment period the crocodiles receiving hGH showed similar growth rate as before treatment, whereas the controls grew at a lower rate in this period. During the treatment period the crocodiles receiving hGH ingested significantly more per meal, 5.1 f 3.3(SD) g (n = 90), than the controls, 4.1 f 3.O(SD) g (n = 90) (P < 0.02). The mean total food uptake was 91.5 g and the weight gain 32.8 g for the hormone group, while it was 73.1 g and 20.2 g,
with hGH
Head length (cm)
r-
30
-
20
-
. hGH 0
r .
hGH
control -0 p---o
Y8
L G 4
10
-
0’
05 0
20
40
60
60
100
120
Age (days)
Fig. 2. Percentage increase (from day 4) in body length of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 42 and 102.
’
0
a n 20
’ 40
I
I
n I
60
60
*
o 100
” 120
Age(days)
Fig. 3. Percentage increase (from day 4) in head length of juvenile Nile crocodiles before, during and after treatment with recombinant hGH. The treatment period is indicated by the horizontal bar. Each point represents a mean of 4-5 animals. The mean values were significantly different between days 53 and 88.
609
Effects of human GH in crocodiles Administration of ovine GH (24 ,ug/g week) greatly increased (up to 300%) the food consumption of juvenile lizards (Licht and Hoyer, 1968). The daily food intake of the crocodiles was not stimulated to the same degree, since the hGH treated animals ingested only about 25% more than the controls. When the difference in body weight is taken into account, the appetite was not significantly different between the two groups. However, the crocodiles receiving hGH seemed to be able to convert the food more efficiently into body tissue than the controls. The calculated food conversion efficiency of 36 and 28%, respectively, are underestimated values, since the food intake also includes water swallowed. More efficient food utilization was also observed in the lizard Anolis carolinensis and the sea turtle (Chelonia mydas) given bovine GH (DiMaggio, 1961; Owens et al., 1979). We did not kill the valuable crocodiles in order to analyse the body composition. However, exogenous GH did not increase the percentage water content of turtle liver and trout skeletal muscles (Nichois, 1973; Skyrud et al., 1989). Following the treatment period the hGH injected crocodiles did not eat at all, the body growth decreased and they were unusually lethargic. A reasonable explanation is that the previous high levels of exogenous hGH may have down regulated the GH receptors and/or suppressed the endogenous GH secretion. An alternative possibility is that administration of heterologous GH may have caused an allergenic response. Thus, the crocodiles were affected even worse when the hormone treatment was restarted at day 169 (data not shown), indicating a secondary immunological response. Turtles seem to recognize mammalian GH and prolactin as foreign proteins and produce antibodies to neutralize their effects (Nichols, 1973; Owens et al., 1979). Due to the small number of animals available, an untreated group was not included in this study. Therefore, it is not clear whether the hormone treatment improved growth over that which would have been observed in the absence of any treatment. The saline injected crocodiles grew at a slower rate during the treatment than before this period, indicating that injections alone may retard growth. However, Nichols (1973) demonstrated that saline injected turtles grew faster than uninjected controls. Breeding of crocodiles has become important, mostly due to their valuable skin. However, a genera1 low growth rate makes the skin production hardly profitable. This preliminary investigation shows that administration of mammalian GH stimulates growth; however, such therapy is not likely to be of practical use for crocodilian husbandry.
Acknowledgements-This
work was supported by a grant from the NORAD KEN 046 Project. The authors express
gratitude to KabiGen AB which kindly provided us with r~mb~nant hGH and to Dr M. A. Fazil for helping us in getting the eggs. Thanks are due also to Dr L. 0. Larsen for valuable comments on the manuscript.
REFERENCES
DiMaggio A. (1961) Hormonal Regulation of Growth in the Lizard, Rnolis carolinensis. Ph.D. Dissertation. Louisiana State University, Baton Rouge, LA. Hayashida T., Farmer S. W. and Papkoff H. (1975) Pituitary growth hormones: Further evidence for evolutionary conservatism based on immunochemical studies. Proc. Natl. Acad. Sci. USA 72, 4322-4326.
Kawauchi H. and Yasuda A. (1987) Evolutionary aspects of growth hormone from nonmammalian species. J. Endocrinol. Invest. 10 (Suppl. 4). Kawauchi H. and Yasuda A. (1989) Evolutionary aspects of growth hormones from nonmammalian species. In Advances in Growth Hormone and Growth Factor Research
(Edited by Miiller E. E., Cocchi D. and Locatelli V.). pp. 51-68. Pythagora Press, Berlin. Larsen L. 0. and Andersen 0. (1990) Skeletal growth in the toad, Bufo bufo, treated with bovine or human growth hormone. Program of the 15th Conference of European Comparative Endocrinologists, Leuven. Licht P. and Hoyer H. (1968) Somatotropic effects of exogenous prolactin and growth hormone in juvenile lizards (Lacerfa s. sicula). Gen. Comp. Endocrinol. II, 338-346.
Marques M., Silva R. S. M., Turyn D. and Dellacha J. M. (1979) Dist~bution and specific binding in uiuo of iodinated growth hormones in the turtle Chrysemys dorbigni. Gen. Comp. Endocrinol. 37, 487-492.
Miller W. L. and Eberhardt N. L. (1983) Structure and evolution of the growth hormone gene family. Endocr. Rev. 4, 97-130.
Nichols C. W. (1973) Somatotropic effects of prolactin and growth hormone in juvenile snapping turtles (Chelydra serpentina). Gen. Comp. Endocrinol. 21, 219-224.
Owens D. W., Hendrickson J. R. and Endres D. B. (1979) Somatic and immune responses to bovine growth hormone, bovine prolactin, and diethylstil~strol in the green sea turtle. cien. Comp. Endocrinol. 38, 53-61. Skyrud T., Andersen 0., Alestrem P. and Gautvik K. M. (1989) Effects of recombinant human growth hormone and insulin-like growth factor 1 on body growth and blood metabolites in brook trout (Salvelinus fontinalis). Gen. Comp. Endocrinol. 75, 247-255.
.
Yasuda A.. Yamaauchi K.. Paukoff H.. Yokoo Y. and Kawauchi H. (l&9) The complete ammo acid sequence of growth hormone from the sea turtle (Chelonia mydas). Gen. Comp. Endocrinof. 73, 242-251.
Wallis M. (1981) The molecular evolution of pituitary growth hormone, prolactin and placental lactogen: A protein family showing variable rates of evolution. J. Mol. Evol. 17, 10-18.