Comp. Biochem. Physiol., 1975, Vol. 50A, pp. 221 to 222. Pergamon Press. Printed in Great Britain
TEMPERATURE MAMMALIAN
DEPENDENCE OF THE ACTIONS OF AND REPTILIAN GONADOTROPINS IN A LIZARD PAUL
Department
LIGHT
of Zoology, University of California, Berkeley, California 94720, U.S.A. (Received 20 November 1973)
Abstract-l. The same marked temperature dependence is evident in the actions of both reptilian (snapping turtle) gonadotropin and mammalian gonadotropin (ovine FSH) when tested in the lizard Anolis carolinensis. 2. Steroidogenic processes
(androgen production) in the lizard testis is less temperature sensitive than is spermatogenesis. 3. The temperature dependence of the lizard’s response to gonadotropins is evidently a characteristic of the reptile’s gonadal system rather than a property of the hormone’s structure.
INTRODUCTION mammalian hormones inSTUDIES with purified dicated that some of the responses of reptiles to gonadotropins are highly temperature dependent (Licht & Pearson, 1969; Licht, 1972; Tsui & Licht, 1974). For example, a decrease in body temperature of only 10°C below normal preferred levels virtually abolished the stimulation of ovarian growth and spermatogenesis by exogenous hormones in lizards. However, in interpreting these results, the possibility must be considered that some of the thermal effects observed in reptiles may be “artifacts” of the chemistry of the mammalian hormones. Fontaine (1969) found that the thyroids of fish did not show the same temperature sensitivity with all thyrotropins (TSH); in particular, the actions of mammalian TSH were relatively more suppressed by low temperatures than were those of the piscine TSH molecule. Since thermal effects on gonadotropin action have important implications for understanding the reproductive biology of reptiles (Licht, 1972), tests were undertaken to determine whether the actions of reptilian gonadotropins were suppressed to the same extent as were the mammalian hormones at low body temperatures in the lizard Anolis carolinensis. MATERIALS
AND METHODS
The snapping turtle Chelydra serpentina served as the source for a reptilian pituitary gonadotropin. The nreparation used here (designated T-GTH) consisted of a mixture of FSH and ‘LH activities (see details for S-2 fraction from Batch II in Licht & Pankoff, 19741. In tests performed in male Anolis carolineks at 30-32”C, this hormone was found to be approximately equipotent with NIH-FSH-S9, based on responses in testis weight,
8
spermatogenesis and androgenesis. At this warm body temperature, a dose of 10 pg hormone every other day stimulates full testis enlargement, spermatogenic development and hypertrophy of accessory sexual structures within about 3 weeks during the non-breeding season (see especially Licht & Pearson, 1969; Licht & Papkoff, 1974). In the present study, the two hormones were administered at doses of either 2 or 10 pg every other day for 30 days (fifteen injections) in intact adult males maintained at 2O+l”C with a 12 hr photoperiod. Previous studies have shown that the sperrnatogenic actions of the mammalian FSH are greatly reduced at this temperature (Licht & Pearson, 1969). Treatment was started in early September when the gonads were fully regressed (see initial controls in Table 1). Reproductive responses were assessed from the weight of the testes and by histological examination of testes, epididymides and renal sexual segments (Licht & Pearson, 1969).
RESULTS
AND DISCUSSION
There was essentially no change in the reproductive condition of the saline-injected controls after 1 month at 20°C; testes and accessory sexual structures remained fully involuted, indicating the absence of endogenous gonadotropic activity (Table 1). All test groups showed approximately the same small but statistically significant (P< 0.02) increase in testis weight (Table 1). However, the germinal epithelium remained quiescent; tubules contained only Sertoli cells and a few resting spermatogonia. Increased testis weights appeared to be a result of hydration (see Fig. 18 in Licht & Pearson, 1969). At the high doses, both hormones stimulated some development of accessory sexual structures in almost all lizards, but this hypertrophy was definitely less 221
222
PAUL
Table 1. Response of male A. curolinensis to mammalian-FSH (NIH-FSH-S8) and turtle-gonadotropin (T-GTH) at 20°C
Hormone Initial control Saline control NIH-FSH-S9 NIH-FSH-S9 T-GTH T-GTH
Testis weight Dose (rag) (pg) N (x+S.E.) 2 10 2 10
10 6 7 8 6 8
4.1 kO.40 3.4kO.59 12.2+1,88 14.8T2.46 8.4*0.76 12.320.82
Accessory sexual structures* Epididy- Renal mis segment 0 0 0 1.5 (l-2) 0.83 (O-l) 1.4 (O-2)
0 0 0 0.63 (O-l) 0.33 (O-l) 0.75 (O-2)
* The degree of hypertrophy was judged qualitatively from the general appearance of the epithelium and the width of tubules: 0, atrophic; 1, marginal stimulation; 2, about half of normal maximum development; 3, fully hypertrophied. Values show the mean with range in parentheses. Treatment was performed for 1 month starting September 1. than that observed after comparable hormone treatment at 30°C (cf. Licht & Pearson, 1969). The T-GTH was slightly more potent than the ovine FSH at the low dose with regard to stimulation of accessory structures. When compared with previous results obtained at 30°C (see Materials and Methods), the data obtained at 20°C demonstrate that the lizard A. curolinensis shows the same marked thermal sensitivity in its response to both reptilian and mammalian gonadotropin molecules; i.e. the actions of the reptilian hormone closely parallel those of mammalian hormones at both 20 and 30°C. With both hormones, the steroidogenic responses of the testes (as judged by development of the androgen-dependent accessory structures) appear to be less temperature sensitive than are the spermatogenic processes. Thus, the primary actions of the hormone appear to vary as body temperature is changed. The snapping turtle is an aquatic species inhabiting ponds and rivers, and it probably rarely elevates
LIGHT
its body temperature above ambient levels since basking is uncomon. Pituitary glands were harvested from turtles collected in the northern United States, especially around Wisconsin. The hormones of such a species must be adapted to normally function at relatively low temperatures when compared to those of mammalian hormones. Nevertheless, there is no apparent improvement in the potency of the turtle gonadotropin relative to the mammalian molecule when tested at low body temperatures in the lizard. Thus, it seems reasonable to conclude that the marked thermal dependence of the responses to exogenous gonadotropins in the lizard is a characteristic of the saurian gonadal tissues rather than a property of the various hormones employed. These results support the view that temperature changes represent an important component in the lizard’s reproductive endocrinology. Acknowledgements-This work was supported in part by funds from the committee on research of the University of California, Berkeley, and by NSF Grant No. GB-35241X from the National Science Foundation. REFERENCES
FONTAINE Y. A. (1969) La specificite zoologique des proteines hypophysaires capables de stimuler la thyroide. Actu Endocr. Suppl. 136, 60, 1-154. LIGHTP. (1972) Physiology of breeding cycles in reptiles. Gen. & compar. Endocr. Suppl. 3,477-488. LIGHTP. & PAPKOFFH. (1974) Identification and separation of two distinct gonadotropins in the pituitary gland of the snapping turtle (Chelydra serpentina). Gen. & compar. Endocr. 22, 218-237. LICHT P. & PEARSONA. K. (1969) Effects of mammalian gonadotropin (FSH and LH) on the testes of the lizard Anolis carolinensis. Gen. & compar. Endocr. 13, 367-381. TSUI H. W. & LICHT P. (1974) Pituitary independence of winter sperm storage in snakes. Gen. & compar. Endocr. 22, 277-279. Key Word Index-Gonadotropins reptile; lizard; turtle hormone.
; temperature effects ;
TEMPERATURE MAMMALIAN
DEPENDENCE OF THE ACTIONS OF AND REPTILIAN GONADOTROPINS IN A LIZARD PAUL
Department
LIGHT
of Zoology, University of California, Berkeley, California 94720, U.S.A. (Received 20 November 1973)
Abstract-l. The same marked temperature dependence is evident in the actions of both reptilian (snapping turtle) gonadotropin and mammalian gonadotropin (ovine FSH) when tested in the lizard Anolis carolinensis. 2. Steroidogenic processes
(androgen production) in the lizard testis is less temperature sensitive than is spermatogenesis. 3. The temperature dependence of the lizard’s response to gonadotropins is evidently a characteristic of the reptile’s gonadal system rather than a property of the hormone’s structure.
INTRODUCTION mammalian hormones inSTUDIES with purified dicated that some of the responses of reptiles to gonadotropins are highly temperature dependent (Licht & Pearson, 1969; Licht, 1972; Tsui & Licht, 1974). For example, a decrease in body temperature of only 10°C below normal preferred levels virtually abolished the stimulation of ovarian growth and spermatogenesis by exogenous hormones in lizards. However, in interpreting these results, the possibility must be considered that some of the thermal effects observed in reptiles may be “artifacts” of the chemistry of the mammalian hormones. Fontaine (1969) found that the thyroids of fish did not show the same temperature sensitivity with all thyrotropins (TSH); in particular, the actions of mammalian TSH were relatively more suppressed by low temperatures than were those of the piscine TSH molecule. Since thermal effects on gonadotropin action have important implications for understanding the reproductive biology of reptiles (Licht, 1972), tests were undertaken to determine whether the actions of reptilian gonadotropins were suppressed to the same extent as were the mammalian hormones at low body temperatures in the lizard Anolis carolinensis. MATERIALS
AND METHODS
The snapping turtle Chelydra serpentina served as the source for a reptilian pituitary gonadotropin. The nreparation used here (designated T-GTH) consisted of a mixture of FSH and ‘LH activities (see details for S-2 fraction from Batch II in Licht & Pankoff, 19741. In tests performed in male Anolis carolineks at 30-32”C, this hormone was found to be approximately equipotent with NIH-FSH-S9, based on responses in testis weight,
8
spermatogenesis and androgenesis. At this warm body temperature, a dose of 10 pg hormone every other day stimulates full testis enlargement, spermatogenic development and hypertrophy of accessory sexual structures within about 3 weeks during the non-breeding season (see especially Licht & Pearson, 1969; Licht & Papkoff, 1974). In the present study, the two hormones were administered at doses of either 2 or 10 pg every other day for 30 days (fifteen injections) in intact adult males maintained at 2O+l”C with a 12 hr photoperiod. Previous studies have shown that the sperrnatogenic actions of the mammalian FSH are greatly reduced at this temperature (Licht & Pearson, 1969). Treatment was started in early September when the gonads were fully regressed (see initial controls in Table 1). Reproductive responses were assessed from the weight of the testes and by histological examination of testes, epididymides and renal sexual segments (Licht & Pearson, 1969).
RESULTS
AND DISCUSSION
There was essentially no change in the reproductive condition of the saline-injected controls after 1 month at 20°C; testes and accessory sexual structures remained fully involuted, indicating the absence of endogenous gonadotropic activity (Table 1). All test groups showed approximately the same small but statistically significant (P< 0.02) increase in testis weight (Table 1). However, the germinal epithelium remained quiescent; tubules contained only Sertoli cells and a few resting spermatogonia. Increased testis weights appeared to be a result of hydration (see Fig. 18 in Licht & Pearson, 1969). At the high doses, both hormones stimulated some development of accessory sexual structures in almost all lizards, but this hypertrophy was definitely less 221
222
PAUL
Table 1. Response of male A. curolinensis to mammalian-FSH (NIH-FSH-S8) and turtle-gonadotropin (T-GTH) at 20°C
Hormone Initial control Saline control NIH-FSH-S9 NIH-FSH-S9 T-GTH T-GTH
Testis weight Dose (rag) (pg) N (x+S.E.) 2 10 2 10
10 6 7 8 6 8
4.1 kO.40 3.4kO.59 12.2+1,88 14.8T2.46 8.4*0.76 12.320.82
Accessory sexual structures* Epididy- Renal mis segment 0 0 0 1.5 (l-2) 0.83 (O-l) 1.4 (O-2)
0 0 0 0.63 (O-l) 0.33 (O-l) 0.75 (O-2)
* The degree of hypertrophy was judged qualitatively from the general appearance of the epithelium and the width of tubules: 0, atrophic; 1, marginal stimulation; 2, about half of normal maximum development; 3, fully hypertrophied. Values show the mean with range in parentheses. Treatment was performed for 1 month starting September 1. than that observed after comparable hormone treatment at 30°C (cf. Licht & Pearson, 1969). The T-GTH was slightly more potent than the ovine FSH at the low dose with regard to stimulation of accessory structures. When compared with previous results obtained at 30°C (see Materials and Methods), the data obtained at 20°C demonstrate that the lizard A. curolinensis shows the same marked thermal sensitivity in its response to both reptilian and mammalian gonadotropin molecules; i.e. the actions of the reptilian hormone closely parallel those of mammalian hormones at both 20 and 30°C. With both hormones, the steroidogenic responses of the testes (as judged by development of the androgen-dependent accessory structures) appear to be less temperature sensitive than are the spermatogenic processes. Thus, the primary actions of the hormone appear to vary as body temperature is changed. The snapping turtle is an aquatic species inhabiting ponds and rivers, and it probably rarely elevates
LIGHT
its body temperature above ambient levels since basking is uncomon. Pituitary glands were harvested from turtles collected in the northern United States, especially around Wisconsin. The hormones of such a species must be adapted to normally function at relatively low temperatures when compared to those of mammalian hormones. Nevertheless, there is no apparent improvement in the potency of the turtle gonadotropin relative to the mammalian molecule when tested at low body temperatures in the lizard. Thus, it seems reasonable to conclude that the marked thermal dependence of the responses to exogenous gonadotropins in the lizard is a characteristic of the saurian gonadal tissues rather than a property of the various hormones employed. These results support the view that temperature changes represent an important component in the lizard’s reproductive endocrinology. Acknowledgements-This work was supported in part by funds from the committee on research of the University of California, Berkeley, and by NSF Grant No. GB-35241X from the National Science Foundation. REFERENCES
FONTAINE Y. A. (1969) La specificite zoologique des proteines hypophysaires capables de stimuler la thyroide. Actu Endocr. Suppl. 136, 60, 1-154. LIGHTP. (1972) Physiology of breeding cycles in reptiles. Gen. & compar. Endocr. Suppl. 3,477-488. LIGHTP. & PAPKOFFH. (1974) Identification and separation of two distinct gonadotropins in the pituitary gland of the snapping turtle (Chelydra serpentina). Gen. & compar. Endocr. 22, 218-237. LICHT P. & PEARSONA. K. (1969) Effects of mammalian gonadotropin (FSH and LH) on the testes of the lizard Anolis carolinensis. Gen. & compar. Endocr. 13, 367-381. TSUI H. W. & LICHT P. (1974) Pituitary independence of winter sperm storage in snakes. Gen. & compar. Endocr. 22, 277-279. Key Word Index-Gonadotropins reptile; lizard; turtle hormone.
; temperature effects ;
