Shashi V. Goswami

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.

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.

‘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 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.

Role of interrenal in luteinizing hormone-induced ovulation and spawning in the catfish Heteropneustes fossilis (Bloch) ☆

Abstract Experiments were conducted to evaluate the effects of mammalian hypophyseal hormones, gonadal steroids, and adrenal corticosteroids on ovulation and spawning in 3-day hypophysectomized gravid catfish. Of the several hormones tested, luteinizing hormone (LH) and adrenal corticosteroids proved to be potent ovulating agents indicating the involvement of both the gonadotropic and adrenocortical systems in ovulation and spawning. In order to assess the relative importance of gonadotropins and corticosteroids in ovulation and spawning, hypophysectomized catfish “chemically interrenalectomized” by treatment with high doses of Metopiron were used. Pretreatment of hypophysectomized gravid females with Metopiron greatly attenuated the ovulatory capacity of LH, whereas DOCA induced ovulation and spawning regardless of pretreatment. These findings suggest that LH may not act directly on the ovary, but via the interrenal. Studies on in vitro corticosteroidogenesis show that the catfish interrenal slices produce hydrocortisone (F) and deoxycorticosterone (DOC), the former being the major corticosteroid. Incubation of interrenal slices with ACTH resulted in a 2-fold increase in the yield of the two corticosteroids without change in the ratio of F to DOC. In contrast, incubation of interrenal slices with LH not only produced both F and DOC in quantities greater than those obtained with ACTH, but also altered the ratio of F to DOC in favor of the latter. The results, and their bearing on ovulation and spawning in the catfish, are discussed.

Effects of gonadotropins and adrenocorticotropin on plasmatic steroids of the catfish, Heteropneustes fossilis (Bloch) ☆ ☆☆

Abstract The levels of some steroids in the plasma of female catfish were estimated following a single injection of porcine ACTH, ovine LH, or partially purified salmon gonadotropin (SG-G100) during the spawning and postspawning seasons. In the regressed catfish, injection of either LH or SG-G100 resulted in a three- to fourfold increase, compared to uninjected controls, in plasmatic cortisol for at least 1 hr. Injection of LH and ACTH resulted in two- and fourfold increases, respectively, of plasma cortisol levels as compared to saline-injected controls for both regressed and gravid fish. The concentration of plasma cortisol after ACTH treatment was higher than after LH or SG-G100. Gonadectomy did not influence the effect of LH on plasma cortisol concentration, and 20 min after injection, the cortisol concentration was identical to that of the intact fish. These results show that in the gravid catfish, as in the regressed ones, the increase in plasmatic cortisol after injection of LH or SG-G100 results principally from the activation of the interrenal. The concentrations of 11-deoxycortisol, 11-deoxycorticosterone, and 17α-hydroxy-20β-dihydroprogesterone were low in all samples and there was no evidence of an effect related to the injected hormone. Testosterone concentrations in the plasma of gravid fish injected with LH increased over the 1-hr sampling time and all values were higher than those recorded for saline- or ACTH-injected fish. Since the levels of cortisol and testosterone in the plasma of gravid catfish increase following gonadotropin administration, they may either singly or synergistically play a role in oocyte maturation.

Formation of 3α-hydroxy-5β-pregnan-20-one in the ovaries of catfish, Heteropneustes fossilis (bloch)

Abstract Labeled pregnenolone was incubated with minced and homogenized tissue obtained from the ovaries and kidney or head kidney of two varieties of catfish, Heteropneustes fossilis and Ictalurus punctatus. No 21-hydroxylated steroids such as DOC were found as conversion products with ovarian tissue. The major ovarian steroid produced by H. fossilis was 3α-hydroxy-5β-pregnan-20-one. After extensive chromatography it was identified by recrystallization to constant specific activity. A second steroid was isolated and tentatively assigned the structure 5β-pregnane-3α-20α-diol based on chromatographic mobilities. In vivo pretreatment with salmon gonadotropin but not ACTH enhanced the conversion rate to 3α-hydroxy-5β-pregnan-20-one in ovarian tissue in H. fossilis. No conversion products were identified in the ovarian tissue of the channel catfish, Ictalurus punctatus. Extensive conversion of precursor to corticosteroid products was observed with interranal tissue in both species. In vivo pretreatment with ACTH enhanced the formation of adrenocorticosteroid products by interrenal tissue.

Role of testosterone, estradiol-17β, and cortisol during vitellogenin synthesis in the catfish, Heteropneustes fossilis (Bloch)

Abstract Incubation of ovarian tissue obtained from vitellogenic catfish with labeled testosterone (T) resulted in the formation of labeled estrogens in the incubation medium. The amount of label recovered in the estrogen fraction increased with the duration of incubation as well as with T concentration in the medium, suggesting a precursor-product relationship between T and estrogens. Alkali-labile phosphorus (vitellogenin) was estimated in the plasma of hypophysectomized female catfish following administration of cortisol (10 or 20 μg/100 g body wt) or estradiol-17β (1 μg/100 g body wt) alone or in combination. Estradiol-17β administration significantly increased plasma vitellogenin levels; cortisol, which by itself did not bring about any increase in circulating vitellogenin levels, significantly potentiated the effect of estradiol-17β. Thus T, present in plasma of vitellogenic catfish, serves as a precursor for estrogen synthesis, and cortisol, whose levels in the plasma are high during ovarian recrudescence, enhances estrogen-induced vitellogenin synthesis in the catfish.

Some aspects of oocyte maturation in catfish

Abstract Plasma levels of cortisol, testosterone and oestradiol increase in the gravid catfish and reach peak values at 15, 90 and 120min, respectively, following administration of ovine luteinizing hormone (LH) or partially-purified salmon gonadotropin (SG-G100). Of the three steroids, cortisol is of interrenal origin, whereas testosterone and oestradiol are contributed by the ovaries. Further, the ovarian tissue of the gravid catfish, under the influence of gonadotropin, can also synthesize pregnanolone (3α-hydroxy-5β-pregnan-20-one). These findings suggest that the injected gonadotropin stimulates the interrenal to produce cortisol and also promotes steroidogenesis in the ovary of the gravid catfish. Experiments were designed to evaluate the interactions between gonadotropin, cortisol and ovarian steroids during oocyte maturation. In vitro culture of catfish oocytes with cortisol acetate or LH alone and in various combinations revealed that not only is cortisol acetate a much more potent maturation-inducing agent than LH but that the two hormones act synergistically over a wide range of dosages. Prior exposure of oocytes to LH or pregnanolone for as short a duration as 90 min sensitized them to subsequent cortisol action on maturation, thereby indicating that possibly LH sensitizes oocytes through the formation of pregnanolone. Addition of testosterone or oestradiol to the culture medium simultaneously with cortisol, LH or pregnanolone markedly inhibited oocyte maturation. On the basis of our data a new hypothesis has been proposed to explain the hormonal regulation of oocyte maturation in the catfish. The gonadotropin injected to induce ovulation, or released spontaneously in the gravid catfish at the time of ovulation, acts at two sites, the ovarian tissue and the interrenal; the former produces pregnanolone, testosterone and oestradiol, while the latter produces cortisol. Pregnanolone sensitizes oocytes so that the maturation response to cortisol is enhanced. The significance of the increase in the plasma levels of testosterone and oestradiol is not properly understood. Further work will be necessary to elucidate this problem.

Effects of prolactin, adrenocorticotrophin, neurohypophysial peptides, cortisol, and androgens on some osmoregulatory parameters of the hypophysectomized catfish, Heteropneustes fossilis (Bloch)

Daily injections of ovine prolactin (PRL), cortisol acetate (FA), arginine vasotocin (AVT), and adrenocorticotrophic hormone (ACTH), at doses ranging from 0.1 to 500 mU/g, 0.2 to 25 micrograms/g, 0.01 to 0.02 micrograms/g, and 5 to 10 mU/g respectively, for 5 days elevated plasma osmolarity and plasma sodium levels in the 3-day hypophysectomized catfish, Heteropneustes fossilis maintained in tap water. PRL enhanced urine production and decreased urine osmolarity and sodium concentration. Administration of FA and AVT increased urine output as well as urine osmolarity and sodium concentration, thereby resulting in severe natriuresis. Simultaneous administration of PRL and FA to hypophysectomized catfish restored plasma osmolarity and sodium concentration to normal levels even in the presence of increased urinary salt loss. However, if the fishes were maintained in deionized water, administration of PRL and FA had no effect on plasma osmolarity or plasma sodium levels suggesting that these hormones increase plasma osmotic pressure by stimulating active uptake of salts from the external medium. Neither PRL nor AVT evoked any increase in plasma cortisol level indicating that their effects on catfish osmoregulation are not mediated through cortisol production. Isotocin, testosterone, and delta 4-androstenedione had no effect on any of the plasmatic or urinary parameters. It is concluded that prolactin, cortisol, and AVT are the principal hormones for osmoionic homeostasis in this catfish and that they act through independent mechanisms.