Recrudescence Phase Research Articles

In vitro effects of catecholamines and catecholestrogens on brain tyrosine hydroxylase activity and kinetics in the female catfish Heteropneustes fossilis.

Effects of catecholamines and catecholestrogens on tyrosine hydroxylase (TH) activity and kinetics were investigated in the telencephalon and hypothalamus of female Heteropneustes fossilis in gonad quiescent (resting) and recrudescent (preparatory) phases. Dopamine, noradrenaline and adrenaline and the catecholestrogen, 2-hydroxyestradiol-17 beta inhibited TH activity in a concentration-dependent manner in both resting and preparatory phases, with a higher effect in the resting phase. Two- methoxyestradiol-17 beta did not alter TH activity in any season. The catecholamines inhibited TH in a competitive manner increasing apparent K(m) values significantly without altering the apparent V(max). Two-hydroxyestradiol-17 beta inhibited significantly the enzyme in a noncompetitive manner and decreased apparent V(max) without altering apparent K(m) values. The apparent K(i) is higher for dopamine than noradrenaline or adrenaline. The apparent K(i) for 2-hydroxyestradiol-17 beta is not significantly different from that of noradrenaline. The present results suggest an interaction between oestradiol-17beta (E2) and catecholamine metabolism at the level of tyrosine hydroxylation and E2 effects on catecholamines may be mediated through its 2-hydroxylation.

Stress inhibits seasonal and FSH-induced ovarian recrudescence in the lizard,Mabuya carinata.

Stressors (handling, chasing, and noise) applied randomly five times per day for one month to lizards during the recrudescence phase of the ovarian cycle caused a significant reduction in mean number of oocytes and primordial follicles when compared to those of controls. Further, vitellogenic follicles were absent in the ovary of lizards subjected to stressors. Administration of bovine FSH during post-breeding regression phase of the ovarian cycle induced ovarian recrudescence as shown by significant increases in the mean number of oogonia, oocytes, and primordial follicles compared to controls, as well as vitellogenic growth of follicles. However, lizards treated with FSH and exposed to stressors did not exhibit ovarian recrudescence. Furthermore, FSH administration during the post-breeding regression phase caused a significant increase in serum levels of estradiol compared to controls, which was accompanied by significant increases in the relative weight of the liver and oviduct, as well as vitellogenic growth of follicles. Despite administration of FSH to lizards subjected to stressors, there was neither any increase in serum levels of estradiol and weight of the liver nor vitellogenic growth of follicles. The results indicate that repeated application of stressors inhibits vitellogenic growth of follicles by suppression of steroidogenic activity in M. carinata. This is the first report revealing that the ovary does not respond to gonadotrophin treatment under stressful conditions in reptiles.

Corticotropin-Releasing Factor Antagonist Attenuates Stress-Induced Inhibition of Seasonal Ovarian Recrudescence in the Lizard Mabuya carinata

Whether administration of the corticotropin-releasing factor (CRF) antagonist α-helical CRF9–41 (hCRF) prevents stress response of the ovary, the oviduct, the adrenals, and the spleen was studied in the lizard Mabuya carinata. Stressors (handling, chasing, and noise) applied randomly, five times a day, for 1 month to lizards during the recrudescence phase of the ovarian cycle caused a significant increase in mean nuclear diameter of the adrenal cortical cells and a significant reduction in mean number of islands of white pulp in the spleen. These results, albeit indirectly, indicated an activation of the adrenal gland and immune suppression. There was a significant decrease in the mean relative weight of the ovary and the oviduct and in the mean number of oocytes and the primordial follicles compared to those of controls. Furthermore, vitellogenic follicles were absent in the ovary of lizards exposed to stressors in contrast to their presence in controls. However, administration of hCRF to the lizards exposed to stressors (stress + hCRF) resulted in vitellogenesis and follicular growth. The mean relative weight of the ovary and the oviduct and the mean number of oocytes and the primordial follicles in stress + hCRF-treated lizards were significantly higher than those in the lizards exposed to stressors, whereas they did not significantly differ from those of controls. The results indicate that hCRF attenuates stress-induced inhibition of ovarian follicular and oviductal development in M. carinata. To the best of our knowledge, this is the first report revealing that CRF antagonist can prevent ovarian stress response in lower vertebrates.

Morphological and Biochemical Changes of Pituitary Gonadotropes in Male Golden Hamsters Submitted to Short and Long Photoperiods

Golden hamsters are seasonal breeders, and a pattern of regression-recrudescence in their hypothalamic-pituitary axis is observed when adult animals are exposed to less than 12.5 h daylight for a prolonged period of time. The purpose of the present work was to investigate the possible morphological and biochemical changes of gonadotrope cell population in male golden hamsters submitted to both short (SP) and long photoperiods (LP). Thus, adult male golden hamsters were exposed to SP (6 h light, 18 h darkness) for 8, 16, 22 and 28 weeks or maintained under LP (14 h light, 10 h darkness). Pituitaries were processed using both light and electron microscopy, and serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were assessed by heterologous radioimmunoassay. Volume density [VD = Σ cell area/reference area (RA)] and cell density (CD = number of cells/RA) of gonadotropes were measured with an image analysis system (Imaging Technology, Software Optimas 5.2). When analyzing the gonadotrope population from animals submitted either to SP or LP, no significant differences were found. At the ultrastructural level, we found a decrease (p < 0.05) in the exocytotic profiles and the individual mean area of secretory granules of both gonadotropes in hamsters maintained under SP for 16 and 22 weeks. Exposure to short days resulted in a decline in serum levels showing a nadir after 16 weeks (p < 0.05). Gonadotropin levels of the hamsters under prolonged exposure to short cycles spontaneously returned to normal values after 22 weeks. In summary, we found a decrease in the ultrastructural and biochemical parameters suggesting an altered release of FSH and LH in male golden hamsters submitted to SP, with a spontaneous recrudescence phase appearing at the end of the study.

Seasonal variation in plasma lipids, lipoproteins, apolipoprotein A-I and vitellogenin in the freshwater turtle, Chrysemys picta

An analysis of plasma lipids and lipoprotein fractions was performed over the course of the annual ovarian cycle of the female turtle, Chrysemys picta. Determinations of total plasma triglycerides, cholesterol, vitellogenin and apolipoprotein A-I (apoA-I) were made. The lipid and protein composition of the lipoprotein fractions [very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) and very high density lipoprotein (VHDL)] were also observed over the same period. Plasma triglyceride and vitellogenin levels were significantly increased in the spring preovulatory period and fall recrudescent phase. Total plasma cholesterol levels were significantly elevated only at the onset of the fall recrudescent phase and apoA-I levels were highest during the postoviposition/ovarian arrest phase. The triglyceride content of VLDL was highest in preovulatory animals and there were apparent seasonal changes in the expression of apoA-I and apoE of HDL/VHDL. We conclude that the coordinate regulation of lipids and protein contributes to seasonal ovarian growth and clearance of lipids from plasma, both of which are most likely under hormonal control.

Regulation of plasma gonadotropin II secretion by sex steroids, aromatase inhibitors, and antiestrogens in the protandrous black porgy, Acanthopagrus schlegeli Bleeker

Plasma gonadotropin II (GTH II) concentrations were significantly higher (approx. 15–20-fold) in estradiol-17β (E2) treated (1.0 μg or 2.5 μg g−1 body weight) female black porgy from days 4 to 12 compared with the control. E2 (1 μg g−1 wt.) had a stronger stimulation on plasma GTH II in early recrudescent phase (low GSI) males (11-fold) than in high GSI and late spermiating males (2.6-fold, P<0.05). No effect of androgens (testosterone, T; 5α-dihydrotestosterone, DHT) on plasma GTH II levels was observed either sex. The levels of plasma GTH II were stimulated in 1,4,6-androstatriene-3,17-dione (ATD, 1 μg g−1, 2 μg g−1 body wt.) and fadrozole-treated (1 μg g−1, 3 μg g−1 body wt.) groups compared to control. Tamoxifen (1 μg g−1, 3 μg g−1 body wt.) but not enclomiphene could stimulate high GTH II levels in plasma. In another experiment of ATD in combination with T, T treatment further attenuated the ATD stimulation of plasma GTH II levels. We concluded that GTH II secretion is positively regulated by an estrogen-specific effect in female and male black porgy. Gonadal stage had significant effects on the responsiveness of GTH II to E2 stimulation in males. A negative aromatase-dependent feedback control of plasma GTH II levels was also suggested in the protandrous black porgy, Acanthopagrus schlegeli.

Alterations in the GnRH–LH system in relation to gonadal stage and Aroclor 1254 exposure in Atlantic croaker

Exposure of Atlantic croaker (Micropogonias undulatus) to the polychlorinated biphenyl mixture (Aroclor 1254, PCB; 1 mg/kg body wt/day for 30 days) during the early-recrudescence phase of the gonadal cycle results in the impairment of LH secretion and gonadal growth. In order to determine whether impairment was due to disruption of the stimulatory GnRH neuroendocrine pathway, we compared various parameters of the GnRH-LH system in early recrudescing vs. spermiating (mature) fish. Seabream GnRH (GnRH) content in the preoptic anterior hypothalamic area (POAH) and pituitary, pituitary GnRH receptor concentrations, and basal and GnRH analog (GnRHa)-induced LH secretion were significantly higher in gonadally mature croaker compared to early-recrudescing fish. In a subsequent experiment, the effects of PCB on the same neuroendocrine indices were investigated during the gonadal recrudescence phase of croaker. PCB exposure during the period of testicular maturation prevented the natural increase in GnRH content in the POAH but not in the pituitary. This finding suggests that PCB may impair GnRH synthesis in the POAH. The number of pituitary GnRH receptors also remained significantly lower in the PCB-exposed group, which was likely due to an impairment of GnRH release. The GnRH content in the POAH, number of pituitary GnRH receptors, and LH secretion in the PCB-exposed group were comparable to those in early-recrudescing fish, suggesting an impairment of normal maturation of the GnRH-LH system during the gonadal recrudescence phase. This impairment may be due to a direct action of PCB on GnRH neurons and/or indirectly via interference with other neurotransmitter pathways that modulate GnRH function.

Annual cyclic variations in some biochemical constituents of seminal vesicle and testis of the catfish Heteropneustes fossilis (Bloch): A study correlating plasma testosterone level

In Heteropneustes fossilis, significant annual variations were observed in seminal vesicle-somatic index (SVSI), gonadosomatic index (GSI), concentrations of total proteins, hexosamines, fructose and glucose in both SV and testis, and in plasma testosterone with high values in late prespawning-early spawning phases (June-July) and low or undetectable levels in resting phase (December-January) except for glucose. There is an inverse relationship between the annual patterns of fructose and glucose with fructose dominant in the prespawning and early spawning phases (June-July), and glucose in the resting phase (November-January). The increase in the concentrations of SV and testicular protein, hexosamine and fructose can be correlated with the increase in testosterone concentration on one hand and with the increase of SVSI and GSI, on the other. The decrease in glucose level in the recrudescent phase may be due to its increased conversion into fructose, the main seminal sugar in this species.

Gonadal stage-dependent effects of gonadal steroids on gonadotropin II secretion in the Atlantic croaker (Micropogonias undulatus).

Involvement of gonadal steroids in the control of gonadotropin II (GTH II) (homologous to LH) secretion was investigated in the Atlantic croaker (Micropogonias undulatus) using gonadectomy (Gx) and steroid replacement paradigms. Gonadectomy in males and females during the late gonadal recrudescence phase elicited significant increases in the gonadotropin response to stimulation by an LHRH analog (LHRHa), without altering basal GTH II secretion. Slow-release silicone elastomer implants of testosterone or estradiol significantly inhibited LHRHa-induced GTH II secretion in gonad-intact and Gx males, and in Gx females, whereas 5alpha-dihydrotestosterone, a nonaromatizable androgen, was ineffective. Pretreatment of fish with an aromatase inhibitor, 1,4, 6-androstatrien-3,17-dione, 2 days before the administration of testosterone implants, completely blocked the negative effect of testosterone on LHRHa-induced GTH II secretion in males, but only partially restored it in females. This suggests that the negative feedback of testosterone in males is primarily mediated by its conversion to estradiol at the level of the hypothalamus and/or pituitary gland, while in females the androgen may also exert a direct inhibitory effect on GTH II secretion, probably mediated via an androgen receptor. In addition, estradiol and testosterone exerted positive effects on basal and LHRHa-induced GTH II secretion during the early-recrudescence phase of the gonadal cycle. The steroids switched to a negative effect on LHRHa-induced GTH II secretion once the fish had fully developed gonads, possibly as a mechanism that prevents a precocious surge in GTH II secretion and final gamete maturation until gametogenesis is complete and the environmental conditions are appropriate for spawning.

Distribution of γ-aminobutyric acid in catfish ( Heteropneustes fossilis) forebrain in relation to season, ovariectomy and E 2 replacement, and effects of GABA administration on plasma Gonadotropin-II level

In the catfish Heteropneustes fossilis, the hypothalamus and telencephalon showed seasonal variations in γ-aminobutyric acid (GABA) with high levels in prespawning and spawning phases and low levels in preparatory and postspawning phases. Ovariectomy for 4 and 5 weeks reduced significantly the GABA contents only in the hypothalamus. Replacement with E 2 (1 μg/g BW) restored the levels to that of sham ovariectomized or parallel control group. Treatment with GABA (i.p.; 10 or 50 μg/g body weight (BW)) alone did not produce any significant effect on plasma gonadotropin-II (GTH-II) level in any of the seasons. Injection of GABA, but not baclofen (a GABA B agonist), stimulated GTH-II secretion in pimozide or GnRH analogue-pimozide pretreated fish at both 0.5 and 2 h in early prespawning phase except at 0.5 h in the pimozide—GABA (10 μg) group. This stimulatory effect was not evident in other seasons. The results of the present study suggest that Estradiol-17β (E 2) seems to stimulate GABA which may account for its high level in the recrudescent phase. GABA seems to have a permissive role in GTH-II secretion when dopamine receptor function is inhibited.

Estradiol-17β and o,p′-DDT stimulate gonadotropin release in Atlantic croaker

Xenobiotic estrogens have the potential to act at a variety of estrogen-responsive target tissues on the hypothalamic-pituitary-gonadal axis. However, to date most studies in fish have focused on stimulation of vitellogenin synthesis by the liver. In the present study the effects of the xenoestrogen o,p′-DDT and estradiol-17β on the neuroendocrine control of gonadotropin secretion were compared. Atlantic croaker ( Micropogonias undulatus) were exposed to o,p′-DDT (0.02 and 0.1 μgg −1 body weight day −1) in the diet for 3 and 7 weeks during the gonadal recrudescence phase. The o,p′-DDT exposure elicited a significant increase in plasma gonadotropin levels after both 3 and 7 weeks of exposure. The stimulatory effect of o,p′-DDT on basal (spontaneous) gonadotropin release was accompanied by a slight increase in ovarian growth as evidenced by the increase in gonadosomatic index. It appears that the stimulation of gonadotropin release by o,p′-DDT during early-recrudescence phase results in enhanced ovarian growth. A comparable stimulatory effect was observed with estradiol-17β treatment during early- and late-recrudescence phases of the ovarian cycle using three injections on alternate days and slow release silastic implants (five days). The present study provides the first evidence for an estrogen-like action of o,p′-DDT on gonadotropin release in a teleost model.

The annual testicular cycle of the domestic quail (Coturnix coturnix japonica).

A morphometric study was conducted on the testis of the domestic quail Coturnix coturnix japonica to determine testicular kinetics. We investigated the variability along the year of testicular parameters such as seminiferous tubule diameter, germinal epithelium height and amount of meiotic figures of maturing spermatids in the seminiferous epithelium and of sperm in the tubular lumen. The results of morphometric analysis showed the occurrence of an annual testicular cycle defined by four distinct phases: a resting phase (at the end of summer), a recrudescence phase (in the fall), a proliferative phase (at the end of winter and beginning of spring), and a regression phase (spring and summer). We also observed that the testes of adult quails present elevated and maximal spermatogenic activity in fall-winter (short-day period) and at the beginning of spring, respectively, and lower values in spring and summer (long-day periods), with minimum values at the end of summer.

Pituitary adrenocorticotrophic (ACTH) cells during reproductive cycle in a Vespertilionid bat, Scotophilus heathi

Present study described the pituitary adrenocorticotropic (ACTH)-cells during different phases of reproductive cycle of Indian Vespertilionid bat, S. heathi. ACTH-cells were identified by histochemical, immunocytochemical and electron microscopic techniques. These cells shows round to polygonal in shape and be easily distinguished by histochemical staining. The body weight attains peak during recrudescence phase due to accumulation of fat. The mean areal fraction occupied by ACTH-cells were higher in recrudescence and winter dormancy as compared with other reproductive phases. The size and granulation pattern of these cells showed variation in relation with the seasonal fat cycle. The possible significance of ACTH-cells during periods of recrudescence and winter dormancy, which is also coincided with period of delayed ovulation in this species, were discussed.

Glycogen accumulation in the ovarian follicle of Indian vespertilionid bat, Scotophilus heathi during the period of delayed ovulation.

Massive accumulation of glycogen in the follicles of Scotophilus heathi during the period of delayed ovulation was noticed. The follicles which survive for prolonged periods are morphologically specialized. The accumulation of glycogen was noticed in the granulosa cells. The egg cytoplasm, thecal cells and interstitial cells were almost devoid of glycogen. The first sign of a glycogen deposit in the ovary was noticed during the recrudescence phase (October) in late pre-antral follicles. Most of the morphologically healthy late pre-antral and antral follicles showed a positive reaction with PAS and Best carmine from October to early February. Morphologically atretic follicles showed only a mild glycogen accumulation. Little or no glycogen accumulation was noticed in some of the healthy late-antral follicles before ovulation during late February and early March. HCG-induced antral follicles during quiescence also did not show any accumulation of glycogen. The study suggests that glycogen laden follicles are not suitable for ovulation and may be the reason for the occurrence of delayed ovulation in S. heathi.

Effects of pineal indoles and parachlorophenylalanine on seasonal reproduction in the pigeon

The effect of melatonin, methoxytryptophol (ML), methoxytryptamine (MT) and parachlorophenylalanine (p-CPA) on the mass and histology of the testes and the adrenal and thyroid glands and on serum thyroid hormone levels have been studied in the recrudescent phase of the feral pigeon Columba livia. All the pineal indoles showed a common anti-gonadal effect, resulting in the arrest of spermatogenesis and the degeneration of germ cells. Treatment with melatonin resulted in adreno-cortical enlargement and medullary hypertrophy, whereas ML, MT and p-CPA induced medullary enlargement and hypertrophy without having much influence on the cortex. Treatment with melatonin and ML brought about colloid retention in the thyroid follicles, while MT and p-CPA induced colloid depletion and hypertrophy of the follicular epithelium. From the present study, it can be concluded that both pineal indoles and p-CPA induce testicular regression in the breeding phase but do so by different mechanisms.

Long-Term Effects of Ovariectomy on Abdominal Fat Body and Body Masses in the Frog Rana tigrina during the Recrudescent Phase

Long-Term Effects of Ovariectomy on Abdominal Fat Body and Body Masses in the Frog Rana tigrina during the Recrudescent Phase

Seasonal pattern of ovarian growth and interrelated changes in plasma steroid levels, vitellogenesis, and oviductal function in the adult female soft-shelled turtleLissemys punctata punctata

The female reproductive cycle of the freshwater soft-shelled turtle Lissemys punctata punctata was studied by correlating ovarian growth with changes in plasma levels of steroids (17β-estradiol and progesterone), vitellogenic indices (calcium, lipid, protein, and cholesterol), and oviductal changes (growth, glycogen, and peroxidase levels). Ovarian growth starts after winter hibernation, proceeds slowly during the preparatory phase (March–June), becomes rapid in the recrudescent phase (July), and peaks in the breeding phase (August–September). Subsequently, the follicles undergo atresia in the regressive phase (October–November), which is followed by the quiescent phase (December–February) marked by negligible ovarian growth. Plasma levels of 17β-estradiol and vitellogenic indices reflect the same pattern of change as ovarian growth. The plasma progesterone concentration remains low throughout the reproductive cycle, except that the titre reaches a postovulatory peak and then declines prior to oviposition. Oviductal mass and glycogen and peroxidase concentrations correspond to changes in plasma estradiol concentration. The findings indicate that the seasonal reproductive cycle of L. p. punctata is characterized by a single annual peak of ovarian growth and estrogen secretion compared with a double peak recorded in other single-clutch turtles.

Photothermal effects on ovarian growth and function in the soft-shelled turtleLissemys punctata punctata

Investigations were carried out to find out the role of higher and lower ambient temperatures together with short and long photoperiods on ovarian growth and secretion of steroids (estradiol-17 beta and progesterone) in the adult female soft-shelled turtle Lissemys punctata punctata during the preparatory, recrudescent, and quiescent phases of its seasonal reproductive cycle. In each phase, females were treated with 3 degrees C higher and 3 degrees C lower than the mean highest and lowest ambient temperatures in association with short and long photoperiods for short-term (4 week) and long-term (8 weeks or more) durations. Short-term high-temperature treatment significantly stimulated ovarian growth and secretion of estradiol-17 beta during the preparatory phase. Eight-week treatment failed to exercise further stimulation over 4-week treatment, whereas 10-week treatment caused regressive changes of ovary (atresia of follicles). Both short- and long-term high-temperature treatments caused degeneration of ovarian follicles during the recrudescent phase. Low-temperature treatment slowed down ovarian growth and secretion in both the preparatory and recrudescent phases. In the quiescent phase, low- as well as high-temperature treatments exercised little influence over the refractory ovarian growth and secretion. Photoperiod appeared to have no effect on female reproduction in any phase. Thus, high temperature is suggested to have a triggering role on ovarian growth and secretion of estrogen at the early preparatory phase, but once the ovarian function sets in, high temperature seems to have a regressive rather than stimulatory effect on ovarian growth and function.

Effect of photoperiod and temperature on ovarian cycle of the frogRana tigrina (Daud.)

The effect of varying photoperiod regimes (LD: 20,4; 4,20; 6,18; 18,6 and 12,12) on ovarian follicular development was analysed in the frogRana tigrina maintained at ambient and constant 30° ± l°C for 3 months. The experiments were conducted in early recrudescent and quiescent phases. The frogs were fed guppiesad libitum on alternate day. None of the photoperiod regimes had any effect on the ovaries or the fat bodies, whereas exposure to constant high temperature (regardless of photoperiod) during recrudescent phase induced production of greater number of eggs (∼ 18000 vs 13000 in controls) of ovulatory sizes (> 1400 μm) compared to the corresponding controls maintained at ambient temperature. Hence, ovarian mass also increased in these frogs. In the quiescent phase, high temperature merely enhanced growth of previtellogenic oocytes. In both the phases high temperature caused a reduction in the fat bodies over the respective controls, possibly due to increased metabolic activity.

Histological and functional changes of oviductal endometrium during seasonal reproductive cycle of the soft-shelled turtle, Lissemys punctata punctata.

Scanning electron and light microscopic studies reveal significant changes in the endometrial histophysiology of the soft-shelled turtle Lissemys punctata punctata during its seasonal reproductive cycle. Scanning electron microscopy shows the entire oviductal mucosa to be only slightly folded throughout the non-breeding period (regressive, quiescent, preparatory and recrudescent phases). With the onset of the breeding phase, the mucosa shows extensive foldings and convolutions. The adluminal mucosal lining of the non-breeding oviduct is covered by a tall, dense ciliary bed, interrupted by a few fissures and pits. Microvilli-bordered secretory cells only appear amongst the ciliated cells during the breeding phase. Light microscopic study reveals the mucosal epithelium to be low pseudostratified columnar throghout the non-breeding period. The breeding epithelium, on the other hand, is tall columnar and does contain clearly distinguishable ciliated and secretory cell types. Submucosal glands only appear for a short period (ovulation to oviposition) in the infundibulum and isthmus regions of the oviduct, but these glands are observed throughout the reproductive cycle in the tube and uterus. The secretory activity of the submucosal glands, which occur only during the peak breeding stages, involves release of vesicular secretory materials through the gland openings. The stimulated endometrial histology and activity during the breeding phase coincide with increased levels of serum estrogen and progesterone, whereas the regressed and inactive state of the endometrium is paralleled by decreased levels of these ovarian steroids. © 1995 Wiley-Liss, Inc.