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Gonadal hormones in experimental Ancylostoma caninum infections in male Swiss albino mice
GONADAL
HORMONES IN EXPERIMENTAL ANCYLOSTOb444 INFECTIONS IN MALE SWISS ALBINO MICE
CANINUM
ISMAIL BHAI and A. K. Endocrinology
Unit, School of Studies in Zoology,
PANDEY
Vikram
University,
Ujjain.
456010,
India
(Received ii August 1981; in revised form 29 June 1982) Abstract-IsMAn BHA~ and PANDEY A. K. 1982. Cionadai hormones in experimental Ancylostoma cuninum infections in male Swiss albmo mice. ~nfern~tio~ffI Jour~u~for Parasitofogy 12: 589-591. Orchtectomy in mice increased their resistance to Ancylostoma cuninum infection. Testosterone propionate increased the susceptibility of castrated animals to infection and also increased the survival of larvae in muscles, compared with sham-operated placebo-treated controls with intact testes. Estradioi benzoate increased the resistance of castrated mice as demonstrated by differential larval recoveries. The possible involvement of the small intestine as a barrier to infection and the influence of testosterone on host susceptibility to infection is discussed. INDEX KEY WORDS: ~~c~~o~~o~u cuninum; fiiariform larvae; larval recoveries; susceptibility; gonadechormones; orchiectomy; testosterone; estradioi; intestinal barrier; Swiss albino mice.
tomy; gonadai
INTRODUCTION
THE DWDENCE and intensity of parasitic infection has been related to the function of the gonads in the host and to their hormones (von Brand, 1952). Controlled studies dealing with gonadectomy and replacement of gonadal hormones has demonstrated that oestrogens increase and androgens decrease the level of resistance of the host to parasitic infections (Dobson, 1961, 1962, 1966; Solomon, 1966, 1969; Novak, 1974, 1975, 1977). However abnormal host-parasite systems have not been studied in depth and some earlier reports are at variance. The main object of the present investigation was to study the course of Ancylostoma cuninum infections in gonadectomized and sex hormone treated mice. MATERIALS
sterone propionate and 17-8 estradiol benzoate, 10 pgcg/g (E. Merck, Darmstadt) were injected subcutaneously in 0.1 ml olive oil. Hormonal therapy was started 1 day prior to infection and continued bi-weekly, till the end of the experiment. Olive oil in the same dosage was given to sham-operated controls. Mice of ail groups were inoculated with 1000 2 25 motile fiiariform larvae of Ancylostoma cuninum, directly into the oesophagus, and necropsied 3-40 days postinfection, after ether euthanasia. Animals which died during the experiments were discarded. The techniques of culture of A. cuninum larvae, infection procedures, and parasitological methods were described previously by ismaii Bhai & Pandey (1981). Probabilities of signi~cant differences in the mean larval recoveries were determined according to Student’s ftest. Confidence limits [Mean 2 S.E.M. In] were set at P= 0.05, where S.E.M. denotes the standard error of the mean and “tn” denotes the Student’s f-value at 5% level of significance for n degrees of freedom.
AND METHODS
Two hundred healthy, male Swiss albino mice of about 3 months (27 + 2 g), were obtained from a stock colony. They were kept in separate cages (4 mice per cage), on dry husk bedding changed every 72 h, fed mouse cakes and water ad libitum, and housed in a naturally lighted and ventilated room between 25 and 28°C. Mice were divided into 4 groups of 50 mice: (1) sham-operated placebo-treated controls, (2) orchiectomized, (3) orchjectomized + testosterone treated, and (4) orchiectomized + estradioi treated. Ail experimental mice were gonadectomized one month before infection to allow for recovery and elimination of sex hormones. They were anaesthetized with ether and the testes with epididymes removed through a small incision anteriorly to the pubis. The musculature was sutured with surgical silk thread and the skin incision closed with 2 or 3 Autoclips (Clay-Adams). which were removed in 7 days. Sham-controls were operated jn a similar manner except the testes were not excised. Testo-
RESULTS
Conadectomy Mortality was 2-6% in all the experimental and control mice. Between 4 and 31% fewer larvae were found in castrated as compared with sham-operated control mice. The difference became significant on 11 days after infection (P < 0.05) and from 15 days until the end of the experiment it was highly significant (O*OOl < P < O*OOl) (Table 1 & Fig. 1). Testosterone Castrated mice treated with testosterone propionate had 34-l%% more larvae than castrated mice (P > OG.)l). Moreover, 11.5-41*7% more larvae were recovered from testosterone treated mice compared to sham-operated placebo-treated controls. This dif-
590
BHAI and A. K. PANDEY
ISMAIL TABLE
I-EFFECT
OF GONADECTOMY
FROM MICE INFECTED
WITH
AND
GONADAL
1000 FILARIFORM
HORMONE
LARVAE
OF
EXPERIMENTAL Number
Day postinoculation
140
larvae
585 563 533 508 486 521 464 427
e-e
Orchiectomized
-
Testosterone
-
Estradiol
2 49 -+ 60 It 73 k 33 k 28 2 35 k 44 + 54
recovered
(5) (5) (5) (5) (5) (5) (5) (5)
562 528 461 435 373 401 337 294
f k k f k k f k
48 46 64 34 67 58 26 13
.\
._/‘m /
120 \ z
A’
I IO1
>; t> 100 8 LL
c
___-_--
go
________
--
____
Conlral ---______
‘-\._
*O /\
\_.
70
‘*I.
AA \
I 60
50 ./1
0
I
1 5
1
1
IO
I5
20
25
30
1
I
35
40
Day post -inoculation
FIG. 1. Mean
percentage
(5) (5) (5) (5) (5) (5) (5) (6)
UPON
caninum,
LARVAL
RECOVERIES
DURING
THE
40 DAY
PERIOD +
S.E.M. tn (d.f.)]
Orchiectomized + testosterone 753 711 673 674 625 581 556 605
t 49 (5) ?28(5) k 73 (5) k 61 (5) k 28 (5) 2 46 (5) t 34 (5) f 31 (4)
Orchiectomized + estradiol 441 472 393 350 286 295 244 209
f 42 k 42 2 61 k 18 f 27 + 27 -c 24 -c 22
(5) (5) (5) (5) (5) (5) (6) (6)
DISCUSSION
c 130
THERAPY
Ancylostoma
[Mean
Orchiectomized
Control
3 7 11 15 20 25 30 40
150
of
I.J.P. VOL. 12. 1982
recovery
of
Anc,vlostoma
caninum
larvae from male mice, after orchiectomy and replacement therapy with testosterone propionate or estradiol benzoate for 40 days after infection
with 1000 larvae.
ference was highly significant (P > 0401), except on 25 days after infection (P < 0.01). But no sign of growth and development of filariform larvae was observed during these experiments (Table 1 & Fig. 1).
Estradiol Between 10.6 and 29% fewer larvae were recovered from castrated mice treated with estradiol benzoate than from castrated mice. The difference was highly significant (P > OWl), except on 7 (P < 0.025), 11 (P < 0.05), and 20 (P < 0.01) days after infection. The larval recoveries from estradiol treated animals were also 16-51070 lower than those from the shamcontrols. This difference was also highly significant (P > OWl), except on 7 (P= 0.01) days after infection (Table 1 & Fig. 1).
Although it is difficult to compare different hostparasite systems, the conclusion that orchiectomy of adult male mice decreased their susceptibility to A. caninum infection is in general agreement with Dobson (1961) who worked with Nematospiroides dubius, Mathies (1959) with Aspicularis tetraptera infection in mice, and Solomon (1966) with Nippostrongylus brasiliensis in hamsters. However, Robinson (1959) and Novak (1977) noted increased susceptibility of orchiectomized mice, infected with Schistosoma mansoni and tetrathyridia of Mesocestoides corti respectively. The present research clearly demonstrated that replacement therapy of castrated mice with testosterone propionate, not only restored the levels of infection with A. caninum larvae to those of the intact male host, but also made these animals significantly more susceptible. Previous reports with different hostparasite models suggested (a) either an increase in the host susceptibility: N. dubius in orchiectomized rats (Dobson, 1961, 1962); N. brasiliensis in normal and gonadectomized hamsters (Solomon, 1966); Hymenolepis nana in castrated male mice (Bailenger & Larcher-Fourrier, 1973); M. corti tetrathyridia in normal and gonadectomized mice (Novak, 1974, 1975); (b) a decrease: S. mansoni in orchiectomized mice (Berg, 1957; Robinson, 1959); or (c) produced negligible effects: A. tetraptera in mice (Mathies, 1959); Amplicaecum robertsi in gonadectomized mice (Dobson, 1966); Raillietina tetragona in chickens (Nadakal, Mohandas, John & Simon, 1973). The present study dealing with A. caninum-Swiss mice system in relation to the estrogen action demonstrated a significant decrease in the host susceptibility as compared to the castrated mice. The earlier reports were conflicting: (a) some favoured these results: A. tetraptera in male mice (Mathies, 1959); N. dubius in gonadectomized rats (Dobson, 1961); Trichinella spiralis in normal and castrated male hooded rats (Mankau & Hamilton, 1972); (b) some demonstrated an increase in the host susceptibility: Trichostrongylus retortaeformis in grazing rabbits (Dunsmore, 1971); M. corti tetrathyridia in mice (Novak, 1974); (c) some
I.J.P. VOL. 12.
Gonadal hormones and Ancylostoma caninutn
1982
were without any detectable effects: A. tetrapteru in female mice (Mathies, 1959); N. brasiliensis in female hamsters (Solomon, 1966). Kono & Sawada (1961) reported the migration of A. cuninum larvae after oral inoculation in mice, the abnormal host. The larvae penetrated through the intestinal wall and migrated via the liver, heart, lungs, pharynx and subsequently to the trachea, musculature, where they were gradually destroyed. Banerjee, Prakash & Deo (1970) also observed that infected A. caninrtm juveniles started penetrating the intestinal wall of mice as early as 15 min after oral infection and were able to enter the liver from the intestine in about 2 h after infection. Thus the route of larval migration after oral inoculation would essentially involve the penetration through small intestine; and that intestine might act as a tissue barrier for the onward migration of larvae to the musculature. Hamilton & Montagna (1950) studied the effects of gonadectomy and testosterone on the integumentary structures, including dermis and muscle fibres. Solomon (1966) also suggested that androgens might act to condition the integument, so as to facilitate the penetration and migration of N. brusiliensis larvae. In the present experiments the action of testosterone on the intestinal tissue may be the same as on the integumentary structures, thereby facilitating the penetration and migration of infective stage filariform larvae of A. cuninum, through the intestinal tissue to the visceral organs and muscles. Once larvae reached the musculature a greater percentage of them remained viable for longer periods in the testosterone treated animals than in the shamcontrols. Whether testosterone directly acted upon the larvae during the migratory or muscle phase, or indirectly on the muscles to provide better environment for larval retention, is not known. No encystment of A. caninum larvae in the muscles has been reported. Orchiectomy would remove the major source of androgens and bring about changes in the intestinal tissue sufficient to slow down penetration of larvae in comparison to sham-controls and testosterone treated castrated male mice. Consequently, noncompetent larvae were either destroyed or expelled out of the body. This may be one of the reasons for lowered larval recoveries from orchiectomized animals. Therefore, a more detailed study of the mechanism of the “intestinal barrier” is needed. Acknowledgements-The authors are grateful to the late Professor H. Swarup for critical suggestions and the University assistance
Grants Commission, to one of us (I. B.).
New Delhi,
for financial
REFERENCES BAILENGER J. & LARCHER-FOURRIER M. F. 1973. Influence of androgen hormones on the parasitism of male mice by Hymenolepis nana. Il. Action of testosterone. Annales de Parasitologie Hutnaine et Cornparke 48: 661-666. BANERJEE D., PRAKASH 0. & DEO M. G. 1970. Studies on the early stage of infection of Ancylostoma caninum in
591
mice. Indian Journal of Medical Research 58: 13211327. BERG E. 1957. Effects of castration and testosterone in male mice on Schistosoma mansoni. Transactions of the Royal Society of Tropical Medicine and Hygiene 51: 353-358. BRAND T. VON 1952. Chemical Physiology of Endoparasitic Animals. Academic Press, New York. DOBSONC. 1961. Certain aspects of the host-parasite relationship of Nematospiroides dubius (Baylis). Il. The effect of sex on experimental infections in the rat (an abnormal host). Parasitology 51: 499-510. DOBSONC. 1962. Certain aspects of the host-parasite relationship of Nematospiroides dubius (Baylis), IV. The effect of the host’s age on experimental infections in the mouse and rat. Parasitology 52: 31-40. DOBSON C. 1966. The age and sex of the host as factors affecting the host-parasite relationship of the third-stage larva of Amplicaecum robertsi Sprent & Mines, 1960, in the laboratory mouse. Parasitology 56: 399-406. DUNSMORE J. D. 1971. Influence of host hormones on nematode parasitism in rabbits, Oryctolagus cuniculus (L). Australian Journal of Zoology 19: 121-128. HAMILTON J. B. & MONTAGNA W. 1950. The sebaceous glands of the hamster. 1. Morphological effects of androgens on integumentary structures. American Journal of Anatomy 86: 191-233. ISMAILBHAI & PANDEYA. K. 1981. The influence of thyroxine on the host-parasite relationship of Ancylostoma caninum in Swiss albino mice. International Journal for Parasitology 11: 377-379. KONO M. & SAWADA T. 1961. Studies on hookworm immunity (Ancylostoma caninum). Ill. The migration of larvae in the body of mice infected with larvae. Kitakanto Igaku 11: 432-438. MANKAU S. K. & HAMILTONR. 1972. The effect of sex and sex hormones on the infection of rats by Trichinella spiralis. Canadian Journal of Zoology 50: 597-602. MA~HIES A. W. 1959. Certain aspects of the host-parasite relationship of Aspicularis tetraptera, a mouse pinworm. Il. Sex resistance. Experimental Parasitology 8: 39-45. NADAKAL A. M., MOHANDAS A., JOHN K. 0. & SIMON M. 1973. Resistance potential of certain breeds of domestic fowl exposed to Raillietina tetragona infections. X. Influence of sex hormones on R. terragona infection. Zeitschrift fiir Parasitenkunde 41: 147-156. NOVAK M. 1974. Effect of sex hormones on the growth and multiplication of tetrathyridia of Mesocestoides corti (Cestoda : Cyclophyllidea) in mice. Infernational Journalfor Parasitology 4: 371-374. NOVAK M. 1975. Gonadectomy, sex hormones and the growth of tetrathyridial populations of Mesocesfoides corti (Cestoda : Cyclophyllidea) in mice. international Journal for Parasitology 5: 269-274. NOVAK M. 1977. Gonadectomy and the development of polycephalic tetrathyridia of Mesocestoides corti (Cestoda : Cyclophyllidea) in mice. International Journal for Parasitology 1: 47-50. ROBINSONE. J. 1959. Recovery of Schistosoma mansoni from hormonally imbalanced hosts. Experimental Parasitology 8: 236-243. SOLOMON G. B. 1966. Development of Nippostrongylus brasiliensis in gonadectomized and hormone-treated hamsters. Experimental Parasitology 18: 374-396. SOLOMON G. B. 1969. Host hormones and parasitic infection. International Review of Tropical Medicine 3: 101158.
HORMONES IN EXPERIMENTAL ANCYLOSTOb444 INFECTIONS IN MALE SWISS ALBINO MICE
CANINUM
ISMAIL BHAI and A. K. Endocrinology
Unit, School of Studies in Zoology,
PANDEY
Vikram
University,
Ujjain.
456010,
India
(Received ii August 1981; in revised form 29 June 1982) Abstract-IsMAn BHA~ and PANDEY A. K. 1982. Cionadai hormones in experimental Ancylostoma cuninum infections in male Swiss albmo mice. ~nfern~tio~ffI Jour~u~for Parasitofogy 12: 589-591. Orchtectomy in mice increased their resistance to Ancylostoma cuninum infection. Testosterone propionate increased the susceptibility of castrated animals to infection and also increased the survival of larvae in muscles, compared with sham-operated placebo-treated controls with intact testes. Estradioi benzoate increased the resistance of castrated mice as demonstrated by differential larval recoveries. The possible involvement of the small intestine as a barrier to infection and the influence of testosterone on host susceptibility to infection is discussed. INDEX KEY WORDS: ~~c~~o~~o~u cuninum; fiiariform larvae; larval recoveries; susceptibility; gonadechormones; orchiectomy; testosterone; estradioi; intestinal barrier; Swiss albino mice.
tomy; gonadai
INTRODUCTION
THE DWDENCE and intensity of parasitic infection has been related to the function of the gonads in the host and to their hormones (von Brand, 1952). Controlled studies dealing with gonadectomy and replacement of gonadal hormones has demonstrated that oestrogens increase and androgens decrease the level of resistance of the host to parasitic infections (Dobson, 1961, 1962, 1966; Solomon, 1966, 1969; Novak, 1974, 1975, 1977). However abnormal host-parasite systems have not been studied in depth and some earlier reports are at variance. The main object of the present investigation was to study the course of Ancylostoma cuninum infections in gonadectomized and sex hormone treated mice. MATERIALS
sterone propionate and 17-8 estradiol benzoate, 10 pgcg/g (E. Merck, Darmstadt) were injected subcutaneously in 0.1 ml olive oil. Hormonal therapy was started 1 day prior to infection and continued bi-weekly, till the end of the experiment. Olive oil in the same dosage was given to sham-operated controls. Mice of ail groups were inoculated with 1000 2 25 motile fiiariform larvae of Ancylostoma cuninum, directly into the oesophagus, and necropsied 3-40 days postinfection, after ether euthanasia. Animals which died during the experiments were discarded. The techniques of culture of A. cuninum larvae, infection procedures, and parasitological methods were described previously by ismaii Bhai & Pandey (1981). Probabilities of signi~cant differences in the mean larval recoveries were determined according to Student’s ftest. Confidence limits [Mean 2 S.E.M. In] were set at P= 0.05, where S.E.M. denotes the standard error of the mean and “tn” denotes the Student’s f-value at 5% level of significance for n degrees of freedom.
AND METHODS
Two hundred healthy, male Swiss albino mice of about 3 months (27 + 2 g), were obtained from a stock colony. They were kept in separate cages (4 mice per cage), on dry husk bedding changed every 72 h, fed mouse cakes and water ad libitum, and housed in a naturally lighted and ventilated room between 25 and 28°C. Mice were divided into 4 groups of 50 mice: (1) sham-operated placebo-treated controls, (2) orchiectomized, (3) orchjectomized + testosterone treated, and (4) orchiectomized + estradioi treated. Ail experimental mice were gonadectomized one month before infection to allow for recovery and elimination of sex hormones. They were anaesthetized with ether and the testes with epididymes removed through a small incision anteriorly to the pubis. The musculature was sutured with surgical silk thread and the skin incision closed with 2 or 3 Autoclips (Clay-Adams). which were removed in 7 days. Sham-controls were operated jn a similar manner except the testes were not excised. Testo-
RESULTS
Conadectomy Mortality was 2-6% in all the experimental and control mice. Between 4 and 31% fewer larvae were found in castrated as compared with sham-operated control mice. The difference became significant on 11 days after infection (P < 0.05) and from 15 days until the end of the experiment it was highly significant (O*OOl < P < O*OOl) (Table 1 & Fig. 1). Testosterone Castrated mice treated with testosterone propionate had 34-l%% more larvae than castrated mice (P > OG.)l). Moreover, 11.5-41*7% more larvae were recovered from testosterone treated mice compared to sham-operated placebo-treated controls. This dif-
590
BHAI and A. K. PANDEY
ISMAIL TABLE
I-EFFECT
OF GONADECTOMY
FROM MICE INFECTED
WITH
AND
GONADAL
1000 FILARIFORM
HORMONE
LARVAE
OF
EXPERIMENTAL Number
Day postinoculation
140
larvae
585 563 533 508 486 521 464 427
e-e
Orchiectomized
-
Testosterone
-
Estradiol
2 49 -+ 60 It 73 k 33 k 28 2 35 k 44 + 54
recovered
(5) (5) (5) (5) (5) (5) (5) (5)
562 528 461 435 373 401 337 294
f k k f k k f k
48 46 64 34 67 58 26 13
.\
._/‘m /
120 \ z
A’
I IO1
>; t> 100 8 LL
c
___-_--
go
________
--
____
Conlral ---______
‘-\._
*O /\
\_.
70
‘*I.
AA \
I 60
50 ./1
0
I
1 5
1
1
IO
I5
20
25
30
1
I
35
40
Day post -inoculation
FIG. 1. Mean
percentage
(5) (5) (5) (5) (5) (5) (5) (6)
UPON
caninum,
LARVAL
RECOVERIES
DURING
THE
40 DAY
PERIOD +
S.E.M. tn (d.f.)]
Orchiectomized + testosterone 753 711 673 674 625 581 556 605
t 49 (5) ?28(5) k 73 (5) k 61 (5) k 28 (5) 2 46 (5) t 34 (5) f 31 (4)
Orchiectomized + estradiol 441 472 393 350 286 295 244 209
f 42 k 42 2 61 k 18 f 27 + 27 -c 24 -c 22
(5) (5) (5) (5) (5) (5) (6) (6)
DISCUSSION
c 130
THERAPY
Ancylostoma
[Mean
Orchiectomized
Control
3 7 11 15 20 25 30 40
150
of
I.J.P. VOL. 12. 1982
recovery
of
Anc,vlostoma
caninum
larvae from male mice, after orchiectomy and replacement therapy with testosterone propionate or estradiol benzoate for 40 days after infection
with 1000 larvae.
ference was highly significant (P > 0401), except on 25 days after infection (P < 0.01). But no sign of growth and development of filariform larvae was observed during these experiments (Table 1 & Fig. 1).
Estradiol Between 10.6 and 29% fewer larvae were recovered from castrated mice treated with estradiol benzoate than from castrated mice. The difference was highly significant (P > OWl), except on 7 (P < 0.025), 11 (P < 0.05), and 20 (P < 0.01) days after infection. The larval recoveries from estradiol treated animals were also 16-51070 lower than those from the shamcontrols. This difference was also highly significant (P > OWl), except on 7 (P= 0.01) days after infection (Table 1 & Fig. 1).
Although it is difficult to compare different hostparasite systems, the conclusion that orchiectomy of adult male mice decreased their susceptibility to A. caninum infection is in general agreement with Dobson (1961) who worked with Nematospiroides dubius, Mathies (1959) with Aspicularis tetraptera infection in mice, and Solomon (1966) with Nippostrongylus brasiliensis in hamsters. However, Robinson (1959) and Novak (1977) noted increased susceptibility of orchiectomized mice, infected with Schistosoma mansoni and tetrathyridia of Mesocestoides corti respectively. The present research clearly demonstrated that replacement therapy of castrated mice with testosterone propionate, not only restored the levels of infection with A. caninum larvae to those of the intact male host, but also made these animals significantly more susceptible. Previous reports with different hostparasite models suggested (a) either an increase in the host susceptibility: N. dubius in orchiectomized rats (Dobson, 1961, 1962); N. brasiliensis in normal and gonadectomized hamsters (Solomon, 1966); Hymenolepis nana in castrated male mice (Bailenger & Larcher-Fourrier, 1973); M. corti tetrathyridia in normal and gonadectomized mice (Novak, 1974, 1975); (b) a decrease: S. mansoni in orchiectomized mice (Berg, 1957; Robinson, 1959); or (c) produced negligible effects: A. tetraptera in mice (Mathies, 1959); Amplicaecum robertsi in gonadectomized mice (Dobson, 1966); Raillietina tetragona in chickens (Nadakal, Mohandas, John & Simon, 1973). The present study dealing with A. caninum-Swiss mice system in relation to the estrogen action demonstrated a significant decrease in the host susceptibility as compared to the castrated mice. The earlier reports were conflicting: (a) some favoured these results: A. tetraptera in male mice (Mathies, 1959); N. dubius in gonadectomized rats (Dobson, 1961); Trichinella spiralis in normal and castrated male hooded rats (Mankau & Hamilton, 1972); (b) some demonstrated an increase in the host susceptibility: Trichostrongylus retortaeformis in grazing rabbits (Dunsmore, 1971); M. corti tetrathyridia in mice (Novak, 1974); (c) some
I.J.P. VOL. 12.
Gonadal hormones and Ancylostoma caninutn
1982
were without any detectable effects: A. tetrapteru in female mice (Mathies, 1959); N. brasiliensis in female hamsters (Solomon, 1966). Kono & Sawada (1961) reported the migration of A. cuninum larvae after oral inoculation in mice, the abnormal host. The larvae penetrated through the intestinal wall and migrated via the liver, heart, lungs, pharynx and subsequently to the trachea, musculature, where they were gradually destroyed. Banerjee, Prakash & Deo (1970) also observed that infected A. caninrtm juveniles started penetrating the intestinal wall of mice as early as 15 min after oral infection and were able to enter the liver from the intestine in about 2 h after infection. Thus the route of larval migration after oral inoculation would essentially involve the penetration through small intestine; and that intestine might act as a tissue barrier for the onward migration of larvae to the musculature. Hamilton & Montagna (1950) studied the effects of gonadectomy and testosterone on the integumentary structures, including dermis and muscle fibres. Solomon (1966) also suggested that androgens might act to condition the integument, so as to facilitate the penetration and migration of N. brusiliensis larvae. In the present experiments the action of testosterone on the intestinal tissue may be the same as on the integumentary structures, thereby facilitating the penetration and migration of infective stage filariform larvae of A. cuninum, through the intestinal tissue to the visceral organs and muscles. Once larvae reached the musculature a greater percentage of them remained viable for longer periods in the testosterone treated animals than in the shamcontrols. Whether testosterone directly acted upon the larvae during the migratory or muscle phase, or indirectly on the muscles to provide better environment for larval retention, is not known. No encystment of A. caninum larvae in the muscles has been reported. Orchiectomy would remove the major source of androgens and bring about changes in the intestinal tissue sufficient to slow down penetration of larvae in comparison to sham-controls and testosterone treated castrated male mice. Consequently, noncompetent larvae were either destroyed or expelled out of the body. This may be one of the reasons for lowered larval recoveries from orchiectomized animals. Therefore, a more detailed study of the mechanism of the “intestinal barrier” is needed. Acknowledgements-The authors are grateful to the late Professor H. Swarup for critical suggestions and the University assistance
Grants Commission, to one of us (I. B.).
New Delhi,
for financial
REFERENCES BAILENGER J. & LARCHER-FOURRIER M. F. 1973. Influence of androgen hormones on the parasitism of male mice by Hymenolepis nana. Il. Action of testosterone. Annales de Parasitologie Hutnaine et Cornparke 48: 661-666. BANERJEE D., PRAKASH 0. & DEO M. G. 1970. Studies on the early stage of infection of Ancylostoma caninum in
591
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