Bangalore I. Sundararaj

Circannual and circadian variations in plasma levels of steroids (cortisol, estradiol-17β estrone, and testosterone) correlated with the annual gonadal cycle in the catfish, Heteropneustes fossilis (Bloch)

Circannual and circadian variations in plasma levels of steroids were estimated by radioimmunoassay in the female and male catfish, Heteropneustes fossilis, over two consecutive annual reproductive cycles. In the female catfish, testosterone (T), estradiol-17 beta (E2), and estrone (E1) were detectable in the plasma only during the reproductively active (preparatory through spawning) period and their levels increased during vitellogenesis. In the fully gravid catfish, when vitellogenesis was nearly complete, levels of E2 declined but those of T continued to increase suggesting a product-precursor relationship between the two steroids. Plasma cortisol (F) was detectable throughout the year and exhibited three peaks coinciding with summer, monsoon, and winter; the first and second peaks coincided with vitellogenesis and spawning, respectively. In the male catfish, changes in plasma T and F levels closely paralleled the seasonal recrudescence and activity of testes and seminal vesicles. After spawning, gonads regressed and levels of sex steroids declined sharply. In the absence of natural spawning due to scanty monsoon rains, as during the second year of this study, gonadal regression was delayed and the sex steroids persisted in the plasma well beyond the normal spawning season. In addition, the first two peaks of F levels merged to form a plateau extending from the preparatory period until the late spawning period. The three sex steroids (T, E2, and E1) exhibited identical circadian rhythms; a major peak occurred at the onset of the dark phase (20:00 hr) and a minor peak was generally observed 4 hr after the onset of the light phase (12:00 hr). The amplitude of rhythms was greatest during the prespawning and the spawning periods. Cortisol peak levels generally alternated with those of sex steroids. Steroid rhythms show rather precise correlations with environmental factors such as photoperiod, temperature, and rainfall as well as with seasonal reproductive activity in both sexes of catfish.

Steroid-induced synthesis of vitellogenin in the catfish, Heteropneustes fossilis (Bloch)

Abstract The synthesis of vitellogenin, the egg-yolk precursor, was induced by estrogenic steroids (estrone, estradiol, and estriol) but not by testosterone, progesterone, or cortisol; estrogen treatment alone did not lead to formation of yolky oocytes in the hypophysectomized catfish. Amplification of vitellogenin synthesis was observed following three spaced injections of estradiol as primary, secondary, and tertiary responses in intact males or hypophysectomized females. The pattern of 32 P incorporation indicated that the label was first incorporated into the phosphoprotein fraction of the liver of estrogenized males or females and thereafter labeled vitellogenin appeared in blood. Thus, in the catfish, liver is the site of estrogen-induced synthesis of vitellogenin.

Hormonal regulation of in vivo and in vitro oocyte maturation in the catfish, Heteropneustes fossilis (bloch)☆

The hormonal regulation of in vivo and in vitro oocyte maturation in the catfish, Heteropneustes fossilis has been investigated. Both piscine and mammalian gonadotropins which are very effective in vivo maturation-inducing agents are virtually ineffective under in vitro conditions, whereas steroids, specially C21 adrenal steroids are effective both under in vivo and in vitro conditions. In the catfish, gonadotropin seems to stimulate the interrenal to produce corticosteroids which in turn act on the oocytes to induce maturation. The mechanism of steroid-induced maturation has been investigated.

Isolation and identification of female-specific serum lipophosphoprotein (vitellogenin) in the catfish, Heteropneustes fossilis (Bloch)

Abstract A female-specific serum lipophosphoprotein, vitellogenin, was identified in the female catfish during vitellogenesis, and its synthesis was induced in the female or male catfish following administration of estradiol. A crude preparation of vitellogenin was isolated from the serum of estradiol-treated male or female catfish following gel filtration on Ultrogel AcA 34. Estimation of alkali-labile protein phosphorus was found to be a reliable index of the presence of vitellogenin in the serum of the catfish. Polyacrylamide gel electrophoresis study showed that a new protein band was present in the serum of estradiol-treated female catfish.

‘Seminal vesicle’ response of intact, castrate, and hypophysectomized catfish, Heteropneustes fossilis (Bloch), to testosterone propionate, prolactin, and growth hormone☆

Abstract The effects of human chorionic gonadotropin (HCG), testosterone propionate (TP), ovine prolactin (LtH), and ovine growth hormone (STH) in stimulating the seminal vesicles of the catfish, Heteropneustes fossilis have been investigated. LtH or TP alone had no significant effect on the atrophic seminal vesicles of intact, castrate, or hypophysectomized catfish. Intact catfish pretreated with HCG and then administered LtH had heavier and secretory seminal vesicles. Prolactin induced significant weight increases as well as secretory activity in androgen-primed seiminal vesicles of castrate or hypophysectomized catfish. Growth hormone also induced significant weight increases and secretory activity in the androgen-primed seminal vesicles of hypophysectomized catfish. In the hypophysectomized catfish, maximum response was observed after simultaneous administration of TP, LtH, and STH. The data indicate that while an additive response is obtained by simultaneous administration of TP and LtH or TP and STH, treatment with all the three hormones at the same time resulted in marked synergism.

Effects of exogenous gonadotrophins and gonadal hormones on the testes and seminal vesicles of hypophysectomized catfish, Heteropneustes fossilis (Bloch)

Response of regressed testes and seminal vesicles was studied after 30-day treatment with testosterone propionate (TP) or estradiol benzoate (EB) in 136-day hypophysectomized catfish, and with ovine follicle-stimulating hormone (FSH), human chorionic gonadotrophin (HCG), and TP singly or in combination in 337-day hypophysectomized catfish, Heteropneustes fossilis . In 136- and 337-day hypophysectomized controls, the testes and seminal vesicles showed complete regression; spermatogenesis in the testes was arrested at the level of spermatogonia and the loculi of the seminal vesicles were atrophic and devoid of secretion. After treatment with various doses of TP, spermatogenesis in the testes and secretory activity in the seminal vesicles were restored. Olive oil or EB treatment induced neither spermatogenesis in testes nor secretory activity in the seminal vesicles. Treatment with FSH did not restore spermatogenesis in the testes or secretory activity in the seminal vesicles, but caused a slight improvement in testicular weights over untreated hypophysectomized controls. On the other hand, after treatment with various doses of HCG, spermatogenesis in the testes and secretory activity in the seminal vesicles resumed. Catfish given FSH plus HCG had testes and seminal vesicles heavier than those given either component alone. Simultaneous treatment with FSH and TP did not induce gravimetric or histological changes in testes and seminal vesicles different from those obtained with TP alone. The above results indicate that while TP or HCG can reinitiate and restore spermatogenesis in the testes and secretory activity in the seminal vesicles of hypophysectomized catfish, FSH singly is virtually ineffective although it can synergize with HCG. The possible mechanisms involved are discussed.

Effects of melatonin and prolactin treatment on the hypophysial-ovarian system in the catfish, Heteropneustes fossilis (Bloch)

Abstract The effects of daily administration of melatonin or ovine prolactin for 20 days were evaluated with respect to the response of the hypophysial-ovarian system in the catfish. Heteropneustes fossilis, during the prespawning and spawning periods. In the prespawning period, daily treatment with melatonin (20 or 100 μg/fish) or prolactin (100 or 250 μg/fish) significantly inhibited vitellogenesis and induced follicular atresia in the ovary, whereas at the level of the pituitary, only the higher dose of melatonin (100 μg/fish) brought about a significant reduction in the number of gonadotrophs. In the spawning period, melatonin (20 or 100 μg/fish) and prolactin (100 or 250 μg/fish) treatment induced significant ovarian regression, and the higher doses of melatonin (100 μg/fish) and prolactin (250 μg/fish) alone significantly reduced the number of pituitary gonadotrophs. Cessation of treatment with melatonin or prolactin resulted in restoration of activity in the pituitary and ovaries. Evidence is presented to show that the inhibition exerted by melatonin or prolactin is tentative and that this inhibitory influence is abolished following withdrawal of treatment.

Effects of C18, C19, and C21 steroids on in vitro maturation of oocytes of the catfish, Heteropneustes fossilis (Bloch)

Abstract Eleven steroidal compounds were tested for their ability to induce in vitro maturation of Heteropneustes fossilis oocytes. C 18 estrogenic steroids (estradiol-17α and -17β) were totally ineffective in inducing oocyte maturation, while androgenic steroids (19-nortestosterone and 11-ketotestosterone) were only marginally effective. Significant maturational ability was confined to C 21 steroids; the most potent among them were 11-deoxycortisol, 11-deoxycorticosterone, and 21-deoxycortisol.

Effects of salmon pituitary gonadotropin, ovine luteinizing hormone, and testosterone on the testes and seminal vesicles of hypophysectomized catfish, Heteropneustes fossilis (Bloch) ☆

Abstract Response of the regressed testes and seminal vesicles was studied after 30-day treatment with partially purified salmon gonadotropin (SG), ovine luteinizing hormone (LH), and testosterone in 237-day hypophysectomized catfish. Daily treatment with SG (0.1, 1, 10, and 100 μg) and LH (1, 10, and 50 μg) produced a dose-dependent response in the testes and seminal vesicles. A dose of 1 μg of SG reinitiated spermatogenesis, whereas a dose of 100 μg of SG not only fully restored spermatogenesis but also induced spermiation. Treatment with 10 μg of LH produced a spermatogenic response in the testes and secretory activity in the seminal vesicles comparable to those induced by 1 μg of SG. A dose of 50 μg of SG and 100 μg of testosterone were equipotent in inducing spermatogenesis in the testes and secretory activity in the seminal vesicles. LH and testosterone at the dose levels used did not induce spermiation. The possibility of one functional gonadotropin regulating the whole maturation phenomenon in the male catfish is discussed.

Effects of partially purified salmon pituitary gonadotropin on ovarian maintenance, ovulation, and vitellogenesis in the hypophysectomized catfish, Heteropneustes fossilis (Bloch).

Salmon pituitary gonadotropin (SG-G100) was tested for its gonadotropic activity in the female catfish, Heteropneustes fossilis, by evaluating ovarian maintenance and ovulation in the hypophysectomized gravid catfish in the spawning season (July–August), and the induction of oogenesis and vitellogenesis in the regressed ovaries of the hypophysectomized catfish during the preparatory (February) and the postspawning (November) periods. Daily treatment with SG-G100 (1 or 5 μg/day) maintained the yolky oocytes in the gravid ovaries by preventing follicular atresia. Ovulation and spawning were induced in both the intact and hypophysectomized gravid catfish by a single dose of SG-G100 (50–100 μg). Daily treatment with SG-G100 (1, 10, 100, or 250 μg) produced a dose-dependent response in the regressed ovaries. Doses of 100 or 250 μg/day reinitiated and restored oogenesis and vitellogenesis, whereas lower doses (1 or 10 μg/day) were ineffective. The possibility of one pituitary gonadotropin regulating the whole maturation phenomenon in the female catfish is discussed.