GENERAL
AND
COMPARATIVE
Testosterone-LH
ENDOCRINOLOGY
(1992)
87,410-415
Response and Episodic Secretion Marsupial, Dasyurus viverrinus
in the Male
S. L. BRYANT Department
of Parks,
Wildlife,
and Heritage,
134 Macquarie
Street,
Hobart,
Tasmania,
7001
Accepted February 10, 1992 The pattern of testosterone-LH secretion, feedback mechanism, and periodicity of release were investigated in the male marsupial eastern quell. Testosterone secretion is controlled directly by LH and in the wild, the secretion of both are synchronous and show a major peak at breeding time. An inverse relationship between the secretion of LH and testosterone occurs after castration which supports the hypothesis that a negative feedback mechanism exists between the gonads and the pituitary gland as in other mammals. These hormones fluctuate in a cyclic manner over 24 hr. o lvvz Academic press, hc.
Plasma testosterone and Sol-dihydrotestosterone are produced in the testes of most Australian marsupials and monotremes and secreted at a rate comparable with eutherian species (Carrick and Cox, 1977; Sernia, 1978; McDonald et al., 1981; Curlewis and Stone, 1985). The hypothalamic secretion of luteinizing releasing hormone (LHRH) provides the mechanism between the anterior pituitary and the gonads controlling the secretion of LH and testosterone in marsupials (Catling and Sutherland, 1980 Evans et al., 1980; Inns, 1982; Irby et al., 1984). The release of these two hormones exhibits a diurnal and periodic variation in many animals and has been investigated in the brushtail possum, Trichosurus vulpecula (Than and McDonald, 1973; Allen and Bradshaw, 1980; Curlewis and Stone, 1985), and a number of macropodid marsupials (Lincoln 1978; Harder et al., 1985; Hinds and Tyndale-Biscoe, 1985). Lincoln collected serial blood samples over a period of 10 hr and found that although testosterone levels could be affected by “stress,” spontaneous rises represented a natural episodic secretory pattern. Curlewis and Stone (1985) found a progressive decline in androgen levels during 20-min sampling periods in the brushtail possum and argued
that this species did not show a pulsatile response but rather a marked capacity for changes in peripheral androgen concentration over short periods. McDonald (1986) found pulsatile changes in plasma testosterone in breeding male koalas, Phuscolurctos cinereus, ranging from 0.5 to 8.0 ng per milliliter. He considered these were unrelated to changes in plasma corticosteroids or the stress of capture and suggested the pulses were spontaneous. In the wild, eastern quo11 have a short synchronized breeding period during which time males experience a high peak in testosterone (Bryant, 1986). This work examines the relationship between testosterone and LH secretion in the male quoll and the variation in release over a 24-hr period. METHODS Male eastern quo11 were live trapped and released at a site south of Hobart (Bryant, 1986). For captive experiments, 12 male quo11 were obtained in the northeast of Tasmania and maintained as in Bryant (1988). Blood collection. Blood samples were obtained from a peripheral ear vein and collected in heparanized vials. Samples were centrifuged and the plasma was stored at -20” until assayed for testosterone and LH. During captive experiments animals were housed individually and handled in captivity for some weeks prior to the start of sampling. 410
0016~6480/92 $4.00 Copyright 0 1992 by Academic Press, Inc. AU rights of reproduction in any form reserved.
TESTOSTERONE-LH
RESPONSE AND RELEASE
Testosterone-LH feedback. Six mature males were castrated by complete removal of the scrotal sac. Animals were fully sedated using a mix of Halothane (Fluothane, ICI) and oxygen. A blood sample was collected immediately before surgery and then daily for 14 days after castration. Blood samples were collected periodically for up to 2 years. D&rnal cycles. Blood samples were obtained from six mature male quo11 every 3 to 4 hr over a 24-hr period. Animals were restrained in hessian sacks during daytime sampling to minimize the stress of capture and handling. Night samples were collected using a red light and animals released in their cages between sampling periods. The experiment was conducted during the nonbreeding season. Testosterone assay. Details of the testosterone assay including validations for the eastern quo11 have been described by Bryant (1986). The assay was sensitive to between 100 and 2.50 pg testosterone per milliliter. LH assay. The LH assay as described by Sutherland
IN THE MARSUPIAL
QUOLL
411
et al. (1980) has been used by Fletcher (1983) and Horn et al. (1985) on various marsupial species. Highly purified rat LH (NIADDK-rat-LH-I-6, National Rormone and Pituitary Program, Baltimore, MD) was iodinated using a gel column and chloramine-T method. Antibody 1 was rabbit anti-ovine LH GDN-15 and antibody 2 was sheep anti rabbit y-globulin (ARyG), raised in sheep No. 5968. The assay was validated for the quo11 using castrate samples, pituitary extracts, and male and female breeding samples. Quo11 plasmas were assayed as 2Otl- or lSO-~1 duplicates and the assay was sensitive to 200 pg LH per milliliter of plasma.
RESULTS Testosterone-LH
Secretion
in the Wild
The cycle of LH and testosterone secretion in adult and juvenile male eastern quo11 is shown in Figs. la and lb. During the non-
a
3
5
5
7
9
9
11
12
11
11
8
9
6
7
2
3
b
E t P
DJFMAMJ 6 6
5
6
15
JY 12
A 8
S 8
0 7
N 9
D 4
J 4
Month
FIG. 1. (a) Mean LH concentration (%SE) for adult male quell in the wild, (b) corresponding testosterone levels (*-SE) from Bryant (1986). Sample sizes indicated below month,
mean
412
S. L. BRYANT
breeding period adult males had basal levels of about 1 .O ng LH per milliliter. During the breeding season in June these increased topeaklevelsof 13.9 + l.SngLH(n = 11, *SE). One individual recorded a level of 23.4 ng LH per milliliter. In January, juvenile males had significantly higher mean LH levels than adult males (t = 4.07, df 12, P > 0.005) but thereafter LH values were similar. The pattern of LH and testosterone secretion appeared synchronous although monthly sampling periods prevented more specific analysis of timing. Testosterone-LH
Feedback
Prior to castration, intact males had mean plasma testosterone levels of 0.7 ng per milliliter + 0.1 (n = 6, +SE) and LH at 1.0 ng per milliliter or: 0.2 (n = 6, &SE), similar to intact males in the wild at this time. Two days after castration, testosterone levels decreased to 0.2 ng per milliliter where they remained for the duration of the experiment (Fig. 2). LH levels showed a steady increase from 1.0 to 9.8 ng per milliliter ? 2.6 (n = 6, *SE) 2 days after castration. LH continued to increase showing maximal mean levels of 67.9 ng about 2 weeks after castration. One animal recorded a level of 122.4 ng per milliliter on Day 7 after castration. After Day 14 LH concentrations fluctuated between 5.0 and 35.0 ng per milliliter for up to 400 days.
The weight of the six males fluctuated according to a seasonal cycle (Bryant, 1988). Two animals that were sacrificed 2 years after castration had prostate glands weighing 0.34 and 0.61 g. These contrast to prostate weights between 1.30 to 3.70 g in intact males of similar body weight at similar times of the year (Fletcher, 1985). Diurnal
Cycles
The secretion of LH and testosterone fluctuated in a cyclic manner over a 24-hr period but much individual variation occurred (Fig. 3). There was no significant variation between the concentrations of testosterone secreted during the day or night hours (day = 7 AM to 5 PM) (day, F,1,51 = 0.28, P > 0.25; night, F,, 5l = 1.20, P > 0.25) or between LH secretion during the day or night (day, FL,,,, = 1.78, 0.1 < P < 0.25; night, FL,,5l = 0.29, P > 0.25). Animal No. 216 was not included in these calculations because blood samples could not be obtained during night hours. DISCUSSION
A negative feedback loop between the gonads and the hypothalamo-hypophyseal axis appears to regulate LH and testosterone secretion in the eastern quell, in a manner similar to that reported for male mam-
0.0
0 0123457
10
Day
after
12
214
z-24
60
100
castration
FIG. 2. Mean LH and testosterone levels in six adult male quo11 after castration (‘SE).
TESTOSTERONE-LH
RESPONSE
AND
RELEASE
Time
F!G. 3. Fluctuations in LH (0) and testosterone(M) shown).
mals generally (Hearn, 1975; Lincoln, 1978; Catling and Sutherland, 1980; Stewart et al., 1981; Inns, 1982; h-by et al., 1984). Testosterone concentrations declined to the sensitivity of the assay within 2 days of castration whereas LH levels continued to increase to reach maximal levels around 2 weeks later. This pattern is similar in the tammar wallaby, Macropus eugenii, and kowari, Desyuroides bymei, where testosterone levels were undetectable 2 to 5 days after gonadectomy and LH concentrations
IN
THE
MARSUPIAL
QUOLL
41%
Time
over 24 hr in six adult male quo11 (male numberi
were maximal 10 to 14 days later (Catling and Sutherland, 1980; Fletcher, 1983.. The basal levels of testosterone detected iivere probably being produced at the adrenal cartex which is a source of androgenic steroids in other marsupial? (Vinson et al., 1974; Vinson and Renfree, 1975; Allen and &adshaw, 1980; McDonald and Taitt, 1982). The quo11 has a higher range of LH levels compared to the tammar wallaby (iO.to 90 ng per milliliter compared to 4 to 8 ng per milliliter in the tammar) but both species
414
S. L. BRYANT
have considerably lower ranges of LH compared to the kowari (350 to 500 ng per milliliter). It is likely much species variation in LH secretion occurs. Male quoll tended to produce a cyclic release of hormones with one to two peaks in testosterone and LH being detected over a 24-hr period. A. LH peak was coincident with a testosterone peak but whether the release was in the form of surges or spontaneous pulses could not be determined. This pattern is similar in the bandicoot, Isoodon macrourus, and blue fox, Alopex lagopus, which release a range of hormones in an episodic fashion (Gemmell et al., 1985; Smith et al., 198.5; McFarlane et al., 1986b). The koala, Phascolarctos cinereus, can produce spontaneous pulses of testosterone (McDonald, 1986) and secretion in the brushtail possum, Trichosurus vulpecula, and lesser mouse lemur, Microcebus murinus, can vary between morning and evening (Allen and Bradshaw, 1980; Pen-et, 1985; McFarlane and Carrick, 1987). While the amplitude and frequency of the cycles in relation to the breeding season in the quo11 were not determined, there was no evidence to suggest that repeated blood sampling caused a decline in testosterone concentration as has been found in some other marsupials (Lincoln, 1978). The observations of greatly reduced prostates in two castrate males suggests the prostate gland, as in some other marsupials, is under androgen control (Inns, 1982; Fletcher, 1983; Wilson and Bourne, 1984; Gemmell et al., 1986; McFarlane et al., 1986a). ACKNOWLEDGMENTS Sincere thanks to Drs. Lyn Hinds and Hugh Tyndale-Biscoe for assay advice and use of facilities at the CSIRO Rangelands, Canberra. The M.A. Ingram Trust kindly funded the study and the work was undertaken in the Zoology Department, University of Tasmania.
REFERENCES Allen, N. T., and Bradshaw, S. D. (1980). Diurnal variation in plasma concentrations of testoster-
one, Sa-dihydrotestosterone, and corticosteroids in the Australian brush-tailed possum, Trichosurus vulpeculu (Kerr). Gen. Comp. Endocrinol. 40, 455458. Bryant, S. L. (1986). Seasonal variation of plasma testosterone in a wild population of male eastern quoll, Dasyurus viverrinus (Marsupialia:Dasyuridae) from Tasmania. Gen. Comp. Endocrinol. 64, 75-79. Bryant, S. L. (1988). Maintenance and captive breeding of the marsupial eastern quoll, Dasyurus viverrinus. Int. Zoo. Yearb. 21, 119-124. Carrick, F. N., and Cox, R. 1. (1977). Testicular endocrinology of marsupials and monotremes. In “Reproduction and Evolution” (J. H. Calaby and C. H. Tyndale-Biscoe, Eds.), pp. 137-141. Australian Academy of Science, Canberra. Catling, P. C., and Sutherland, R. L. (1980). Effect of gonadectomy, season and the presence of female tammar wallabies (Macropus eugenii) on concentrations of testosterone, luteinizing hormone and follicle-stimulating hormone in the plasma of male tammar wallabies. J. Endocrinol. 86, 25-33. Curlewis, J. D., and Stone, G. M. (1985). Peripheral androgen levels in the male brush-tail possum (Trichosurus vulpecula). J. Endocrinol. 105, 6370. Evans, S. M., Tyndale-Biscoe, C. H., and Sutherland, R. L. (1980). Control of gonadotrophin secretion in the female tammar wallaby (Macropus eugenii). J. Endocrinol. 86, 13-23. Fletcher, T. P. (1983). “Endocrinology of Reproduction in the Dasyurid Marsupial Dasyuroides Byrnei (Spender).” Ph.D. Thesis, La Trobe University, Melbourne. Fletcher, T. P. (1985). Aspects of reproduction in the male eastern quoll, Dasyurus viverrinus (Shaw) (Marsupialia:Dasyuridae), with notes on polyoestry in the female. Aust. J. Zool. 33, 101-110. Gemmell, R. T., Cepon, G., and Barnes, A. (1986). Weekly variations in body weight and plasma testosterone concentrations in the captive male possum, Trichosurus vulpecula. Gen. Comp. Endocrinol. 62, 1-7. Gemmell, R. T., Johnston, G., and Barnes, A. (1985). Seasonal variations in plasma testosterone concentrations in the male marsupial bandicoot, Zsoodon.
Harder, J. D., Hinds, L. A., Horn, C. A., and Tyndale-Biscoe, C. H. (1985). Effects of removal in late pregnancy of the corpus luteum, Graafian follicle or ovaries on plasma progesterone, oestradiol, LH, parturition and post-partum oestrus in the tammar wallaby, Macropus eugenii. J. Reprod.
Fertil.
75, 449-459.
Heam, J. P. (1975). The role of the pituitary in the
TESTOSTERONE-LH
reproduction ropus
RESPONSE
AND
of the male tammar wallaby, Mac-
eugenii.
J. Reprod.
Fertil.
42, 399-402.
Hinds, L. A., and Tyndale-Biscoe, C. H. (1985). Seasonal and circadian patterns of circulating prolactin during lactation and seasonal quiescence in the tammar, Macropus eugenii. J. Reprod. Fertil. 74, 173-183. Horn, C. A., Fletcher, T. P., and Carpenter, R. S. (1985). Effects of oestradiol-17a on peripheral plasma concentrations of LH and FSH in ovariectomized tammars (Macropus eugenii). J. Reprod.
Fertil.
13, 585-592.
Inns, R. W. (1982). Seasonal changes in the accessory reproductive system and plasma testosterone levels of the male tammar wallaby, Mucropus eugenii, in the wild. J. Reprod. Fertil. 66, 675-680. Irby, D. C,, Kerr, J. B., Risbridger, G. P., and de Kretser, D. M. (1984). Seasonally and experimentally induced changes in testicular function of the Australian bush rat (Rattus fiscipes). J. Reprod. Fertil.
IQ, 657666.
Lincoln, G. A. (1978). Plasma testosterone profdes in male macropodid marsupials. J. Endocrinol. 77, 347-3.51. McDonald, I. R. (1986). Episodic steroid secretion in koalas Phascolarctos cinereus. Bull. Aust. Mammal Society (Abstrucf) 9(l), 6. McDonald, I. R., Lee, A. K., Bradley, A. J., and Than, K. A. (1981). Endocrine changes in dasyurid marsupials with differing mortality patterns. Gen.
Comp.
Endocrinol.
44,292-301.
McDonald, I. R., andTaitt, M. J. (1982). Steroid hormones in the blood plasma of Townsend’s vole (Microtus townsendii). Can. J. Zool.60(10), 22642269. McFarlane, J. R., and Carrick, F. N. (1987). Episodic secretion of androgens and cortisol in the brushtail possum (Trichosurus vulpecula). Abstract, Proceedings of the nineteenth annual conference, Australian Society for Reproductive ,Biology, p. 74. McFarlane, J. R., Carrick, F. N., and Brown, A. S. (1986a). Seasonal changes in the size of the prostate in the brushtail possum Trichosurus vulpecula.
56.
Bull.
Aust.
Mhmmai.
Sot.
(Abstract)
9(I),
RELEASE
IN
THE
MARSUPIAL
QUOLL
415
McFarlane, J. R., Canick, F. N., Gemmell, R. T., and MacDonald, G. (1986b). Androgen secretion in the male bandicoot. Bull. Aust. Mammal. Sot. (Abstract)
9(l),
16.
Perret, M. (1985). Diurnal variations in plasma testesterone concentrations in the male lesser mouse lemur (Microcebus murinus). J. Reprod. Fertil. 74, 205-213. Sernia, C. (1978). Steroid-binding proteins in the plasma of the echidna, Tachyglossus aculeatus, with comparative data for some marsupials and reptiles. Aust. Zool. 20, 87-98. Smith, A. J., Mondain-Monval, M., Moller, 0. MI., Scholler, R., and Hansson, V. (1985). Seaso& variations of LH, prolactin, androstenedione, testosterone and testicular FSH binding in the male blue fox (Alopex lagopus). J. Reprod. Fe&l. 74, 449-458. Stewart, F., Sutherland, R. L., and Tyndage-Biscoe, C. H. (1981). Macropodid marsupial testicular gonadotrophin receptors and their use in assays for marsupial gonadotrophins. J. Endocrinol. 89, 213-223. Sutherland, R. L., Evans, S. M., andTyndale-Biscoe, C. H. (1980). Macropodid marsupial luteinizing hormone: validation of assay procedures and changes in concentrations in plasma during the oestrous cycle in the female tammar wallaby (Macropus eugenii). J. Endocrinol. 86, l-12. Than, K. A., and McDonald, I. R. (1973). Adrcnocortical fimction in the Australian brush-tailed possum Trichosurus vulpecula (Kerr). J. Endocrinol. 58, 97L109. Vinsoq, G, P., and Reufree, M. G. (1975). Biosynthesis and secretion of testosterone by adrenal tissue in the North American possum Dideiphis virginiana and the effects of tropic stimulation. Cen. Camp.
Endocrinof.
21, 214-222.
Vinson, G. P., Phillips, J. G., Chester-Jones, I., and Tsang, W, N. (1971). Functional zonation of adrenalcoitical tissue in the brushpossum TrikhosgFus vulpecula. J. Endocrinol. 49, 131-140. Wilson, B. A., and Boume, A. R. (1984). Reprodoction in the male dasyurid Antechinus minimus mrrritimus (Marsupialia:Dasyuridae). A~st. Y. Zool. 32, 311-318.
AND
COMPARATIVE
Testosterone-LH
ENDOCRINOLOGY
(1992)
87,410-415
Response and Episodic Secretion Marsupial, Dasyurus viverrinus
in the Male
S. L. BRYANT Department
of Parks,
Wildlife,
and Heritage,
134 Macquarie
Street,
Hobart,
Tasmania,
7001
Accepted February 10, 1992 The pattern of testosterone-LH secretion, feedback mechanism, and periodicity of release were investigated in the male marsupial eastern quell. Testosterone secretion is controlled directly by LH and in the wild, the secretion of both are synchronous and show a major peak at breeding time. An inverse relationship between the secretion of LH and testosterone occurs after castration which supports the hypothesis that a negative feedback mechanism exists between the gonads and the pituitary gland as in other mammals. These hormones fluctuate in a cyclic manner over 24 hr. o lvvz Academic press, hc.
Plasma testosterone and Sol-dihydrotestosterone are produced in the testes of most Australian marsupials and monotremes and secreted at a rate comparable with eutherian species (Carrick and Cox, 1977; Sernia, 1978; McDonald et al., 1981; Curlewis and Stone, 1985). The hypothalamic secretion of luteinizing releasing hormone (LHRH) provides the mechanism between the anterior pituitary and the gonads controlling the secretion of LH and testosterone in marsupials (Catling and Sutherland, 1980 Evans et al., 1980; Inns, 1982; Irby et al., 1984). The release of these two hormones exhibits a diurnal and periodic variation in many animals and has been investigated in the brushtail possum, Trichosurus vulpecula (Than and McDonald, 1973; Allen and Bradshaw, 1980; Curlewis and Stone, 1985), and a number of macropodid marsupials (Lincoln 1978; Harder et al., 1985; Hinds and Tyndale-Biscoe, 1985). Lincoln collected serial blood samples over a period of 10 hr and found that although testosterone levels could be affected by “stress,” spontaneous rises represented a natural episodic secretory pattern. Curlewis and Stone (1985) found a progressive decline in androgen levels during 20-min sampling periods in the brushtail possum and argued
that this species did not show a pulsatile response but rather a marked capacity for changes in peripheral androgen concentration over short periods. McDonald (1986) found pulsatile changes in plasma testosterone in breeding male koalas, Phuscolurctos cinereus, ranging from 0.5 to 8.0 ng per milliliter. He considered these were unrelated to changes in plasma corticosteroids or the stress of capture and suggested the pulses were spontaneous. In the wild, eastern quo11 have a short synchronized breeding period during which time males experience a high peak in testosterone (Bryant, 1986). This work examines the relationship between testosterone and LH secretion in the male quoll and the variation in release over a 24-hr period. METHODS Male eastern quo11 were live trapped and released at a site south of Hobart (Bryant, 1986). For captive experiments, 12 male quo11 were obtained in the northeast of Tasmania and maintained as in Bryant (1988). Blood collection. Blood samples were obtained from a peripheral ear vein and collected in heparanized vials. Samples were centrifuged and the plasma was stored at -20” until assayed for testosterone and LH. During captive experiments animals were housed individually and handled in captivity for some weeks prior to the start of sampling. 410
0016~6480/92 $4.00 Copyright 0 1992 by Academic Press, Inc. AU rights of reproduction in any form reserved.
TESTOSTERONE-LH
RESPONSE AND RELEASE
Testosterone-LH feedback. Six mature males were castrated by complete removal of the scrotal sac. Animals were fully sedated using a mix of Halothane (Fluothane, ICI) and oxygen. A blood sample was collected immediately before surgery and then daily for 14 days after castration. Blood samples were collected periodically for up to 2 years. D&rnal cycles. Blood samples were obtained from six mature male quo11 every 3 to 4 hr over a 24-hr period. Animals were restrained in hessian sacks during daytime sampling to minimize the stress of capture and handling. Night samples were collected using a red light and animals released in their cages between sampling periods. The experiment was conducted during the nonbreeding season. Testosterone assay. Details of the testosterone assay including validations for the eastern quo11 have been described by Bryant (1986). The assay was sensitive to between 100 and 2.50 pg testosterone per milliliter. LH assay. The LH assay as described by Sutherland
IN THE MARSUPIAL
QUOLL
411
et al. (1980) has been used by Fletcher (1983) and Horn et al. (1985) on various marsupial species. Highly purified rat LH (NIADDK-rat-LH-I-6, National Rormone and Pituitary Program, Baltimore, MD) was iodinated using a gel column and chloramine-T method. Antibody 1 was rabbit anti-ovine LH GDN-15 and antibody 2 was sheep anti rabbit y-globulin (ARyG), raised in sheep No. 5968. The assay was validated for the quo11 using castrate samples, pituitary extracts, and male and female breeding samples. Quo11 plasmas were assayed as 2Otl- or lSO-~1 duplicates and the assay was sensitive to 200 pg LH per milliliter of plasma.
RESULTS Testosterone-LH
Secretion
in the Wild
The cycle of LH and testosterone secretion in adult and juvenile male eastern quo11 is shown in Figs. la and lb. During the non-
a
3
5
5
7
9
9
11
12
11
11
8
9
6
7
2
3
b
E t P
DJFMAMJ 6 6
5
6
15
JY 12
A 8
S 8
0 7
N 9
D 4
J 4
Month
FIG. 1. (a) Mean LH concentration (%SE) for adult male quell in the wild, (b) corresponding testosterone levels (*-SE) from Bryant (1986). Sample sizes indicated below month,
mean
412
S. L. BRYANT
breeding period adult males had basal levels of about 1 .O ng LH per milliliter. During the breeding season in June these increased topeaklevelsof 13.9 + l.SngLH(n = 11, *SE). One individual recorded a level of 23.4 ng LH per milliliter. In January, juvenile males had significantly higher mean LH levels than adult males (t = 4.07, df 12, P > 0.005) but thereafter LH values were similar. The pattern of LH and testosterone secretion appeared synchronous although monthly sampling periods prevented more specific analysis of timing. Testosterone-LH
Feedback
Prior to castration, intact males had mean plasma testosterone levels of 0.7 ng per milliliter + 0.1 (n = 6, +SE) and LH at 1.0 ng per milliliter or: 0.2 (n = 6, &SE), similar to intact males in the wild at this time. Two days after castration, testosterone levels decreased to 0.2 ng per milliliter where they remained for the duration of the experiment (Fig. 2). LH levels showed a steady increase from 1.0 to 9.8 ng per milliliter ? 2.6 (n = 6, *SE) 2 days after castration. LH continued to increase showing maximal mean levels of 67.9 ng about 2 weeks after castration. One animal recorded a level of 122.4 ng per milliliter on Day 7 after castration. After Day 14 LH concentrations fluctuated between 5.0 and 35.0 ng per milliliter for up to 400 days.
The weight of the six males fluctuated according to a seasonal cycle (Bryant, 1988). Two animals that were sacrificed 2 years after castration had prostate glands weighing 0.34 and 0.61 g. These contrast to prostate weights between 1.30 to 3.70 g in intact males of similar body weight at similar times of the year (Fletcher, 1985). Diurnal
Cycles
The secretion of LH and testosterone fluctuated in a cyclic manner over a 24-hr period but much individual variation occurred (Fig. 3). There was no significant variation between the concentrations of testosterone secreted during the day or night hours (day = 7 AM to 5 PM) (day, F,1,51 = 0.28, P > 0.25; night, F,, 5l = 1.20, P > 0.25) or between LH secretion during the day or night (day, FL,,,, = 1.78, 0.1 < P < 0.25; night, FL,,5l = 0.29, P > 0.25). Animal No. 216 was not included in these calculations because blood samples could not be obtained during night hours. DISCUSSION
A negative feedback loop between the gonads and the hypothalamo-hypophyseal axis appears to regulate LH and testosterone secretion in the eastern quell, in a manner similar to that reported for male mam-
0.0
0 0123457
10
Day
after
12
214
z-24
60
100
castration
FIG. 2. Mean LH and testosterone levels in six adult male quo11 after castration (‘SE).
TESTOSTERONE-LH
RESPONSE
AND
RELEASE
Time
F!G. 3. Fluctuations in LH (0) and testosterone(M) shown).
mals generally (Hearn, 1975; Lincoln, 1978; Catling and Sutherland, 1980; Stewart et al., 1981; Inns, 1982; h-by et al., 1984). Testosterone concentrations declined to the sensitivity of the assay within 2 days of castration whereas LH levels continued to increase to reach maximal levels around 2 weeks later. This pattern is similar in the tammar wallaby, Macropus eugenii, and kowari, Desyuroides bymei, where testosterone levels were undetectable 2 to 5 days after gonadectomy and LH concentrations
IN
THE
MARSUPIAL
QUOLL
41%
Time
over 24 hr in six adult male quo11 (male numberi
were maximal 10 to 14 days later (Catling and Sutherland, 1980; Fletcher, 1983.. The basal levels of testosterone detected iivere probably being produced at the adrenal cartex which is a source of androgenic steroids in other marsupial? (Vinson et al., 1974; Vinson and Renfree, 1975; Allen and &adshaw, 1980; McDonald and Taitt, 1982). The quo11 has a higher range of LH levels compared to the tammar wallaby (iO.to 90 ng per milliliter compared to 4 to 8 ng per milliliter in the tammar) but both species
414
S. L. BRYANT
have considerably lower ranges of LH compared to the kowari (350 to 500 ng per milliliter). It is likely much species variation in LH secretion occurs. Male quoll tended to produce a cyclic release of hormones with one to two peaks in testosterone and LH being detected over a 24-hr period. A. LH peak was coincident with a testosterone peak but whether the release was in the form of surges or spontaneous pulses could not be determined. This pattern is similar in the bandicoot, Isoodon macrourus, and blue fox, Alopex lagopus, which release a range of hormones in an episodic fashion (Gemmell et al., 1985; Smith et al., 198.5; McFarlane et al., 1986b). The koala, Phascolarctos cinereus, can produce spontaneous pulses of testosterone (McDonald, 1986) and secretion in the brushtail possum, Trichosurus vulpecula, and lesser mouse lemur, Microcebus murinus, can vary between morning and evening (Allen and Bradshaw, 1980; Pen-et, 1985; McFarlane and Carrick, 1987). While the amplitude and frequency of the cycles in relation to the breeding season in the quo11 were not determined, there was no evidence to suggest that repeated blood sampling caused a decline in testosterone concentration as has been found in some other marsupials (Lincoln, 1978). The observations of greatly reduced prostates in two castrate males suggests the prostate gland, as in some other marsupials, is under androgen control (Inns, 1982; Fletcher, 1983; Wilson and Bourne, 1984; Gemmell et al., 1986; McFarlane et al., 1986a). ACKNOWLEDGMENTS Sincere thanks to Drs. Lyn Hinds and Hugh Tyndale-Biscoe for assay advice and use of facilities at the CSIRO Rangelands, Canberra. The M.A. Ingram Trust kindly funded the study and the work was undertaken in the Zoology Department, University of Tasmania.
REFERENCES Allen, N. T., and Bradshaw, S. D. (1980). Diurnal variation in plasma concentrations of testoster-
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