Short- and long-term effects of hypophysectomy and unilateral ovariectomy on ovarian follicular populations in sheep

The effects of hypophysectomy and unilateral ovariectomy on the total number of follicles with greater than 3 layers of granulosa cells were determined at 4 and 70 days following treatment. The population of preantral follicles (less than 0.23 min diam.) was found to be under the control of gonadotrophins but such control was only evident on a long-term basis. At 70 days after unilateral ovariectomy there was a large increase in the number of preantral follicles but at 70 days after hypophysectomy there was a large decrease. The population of antral follicles (greater than 0.23 mm diam.) was under the immediate control of gonadotrophins. By 4 days after hypophysectomy all large antral follicles had become atretic and the number of antral follicles was further decreased at 70 days after treatment. At 70 days after unilateral ovariectomy there was an increase in the number of antral follicles. The follicular growth rates at 70 days following treatment were decreased in hypophysectomized ewes but increased in ewes after unilateral ovariectomy.     

Compensatory responses after unilateral ovariectomy in rabbits

Compensatory ovarian and gonadotropic responses to unilateral ovariectomy (ULO) were examined in the rabbit doe, an induced ovulator. On Days 2, 4, 5, 6, 8, 10, 15 and 20 after ULO, ovaries from 3 hemiovariectomized does and 1 sham-hemiovariectomized doe were examined macro- and microscopically for number, size and signs of atresia of follicles. The number of surface follicles increased initially to 7 or 8 follicles 2 days after ULO, followed by an increase to 10 or more follicles by Day 15 (control ovaries had 5.7 +/- 0.4 follicles). Total numbers of antral follicles and the proportion of follicles which were atretic did not vary relative to day after ULO. However, distributions of antral follicles in classes of 0.2-mm increments were significantly different between sham-ovariectomized and hemiovariectomized does after Day 2 due to shifts of follicles into larger size classes. Peripheral serum concentrations of follicle-stimulating hormone (FSH), but not luteinizing hormone (LH), increased temporarily during the 48 h after ULO. Follicular compensation after ULO in the doe entailed nonlinear increases in numbers of preovulatory follicles, due to increased growth within the antral population of follicles, probably the result of an acute surge of FSH. A period of more than 10 days was necessary to restore the number of preovulatory follicles after ULO. Exogenous human chorionic gonadotropin (hCG) induced ovulation of recruited follicles.     

Changes in gonadotrophin secretion and ovarian antral follicular activity in seasonally breeding sheep throughout the year

Overall, significantly more antral follicles greater than or equal to 1 mm diameter were present in Romney ewes during anoestrus than in the breeding season (anoestrus, 35 +/- 3 (mean +/- s.e.m.) follicles per ewe, 23 sheep; Day 9-10 of oestrous cycle, 24 +/- 1 follicles per ewe, 22 sheep; P less than 0.01), although the mean numbers of preovulatory-sized follicles (greater than or equal to 5 mm diam.) were similar (anoestrus, 1.3 +/- 0.2 per ewe; oestrous cycle, 1.0 +/- 0.1 per ewe). The ability of ovarian follicles to synthesize oestradiol did not differ between anoestrus and the breeding season as assessed from the levels of extant aromatase enzyme activity in granulosa cells and steroid concentrations in follicular fluid. Although the mean plasma concentration of LH did not differ between anoestrus and the luteal phase of the breeding season, the pattern of LH secretion differed markedly; on Day 9-10 of the oestrous cycle there were significantly more (P less than 0.001) high-amplitude LH peaks (i.e. greater than or equal to 1 ng/ml) in plasma and significantly fewer (P less than 0.001) low amplitude peaks (less than 1 ng/ml) than in anoestrous ewes. Moreover, the mean concentrations of FSH and prolactin were significantly lower during the luteal phase of the cycle than during anoestrus (FSH, P less than 0.05, prolactin, P less than 0.001). It is concluded that, in Romney ewes, the levels of antral follicular activity change throughout the year in synchrony with the circannual patterns of prolactin and day-length. Also, these data support the notion that anovulation during seasonal anoestrus is due to a reduced frequency of high-amplitude LH discharges from the pituitary gland.     

Short- and long-term effects of unilateral ovariectomy in sheep: causative mechanisms

The mechanisms of ovulatory compensation following unilateral ovariectomy (ULO) are still not understood. In the present study, we investigated the short- and long-term effects of ULO in sheep using transrectal ovarian ultrasonography and hormone estimations made during the estrous cycle in which surgery was done, the estrous cycle 2 mo after surgery, and the 17-day period during the subsequent anestrus. The ULOs were done when a follicle in the first follicular wave of the cycle reached a diameter > or =5 mm, leaving at least one corpus luteum and one ovulatory-sized follicle in the remaining ovary. Ovulation rate per ewe was 50% higher in the ULO ewes compared with the control ewes at the end of the cycle during which surgery was performed, but it did not differ between groups at the end of the cycle, 2 mo later. This compensation of ovulation rate in ULO ewes was due to ovulation of follicles from the penultimate follicular wave in addition to those from the final wave of the cycle. Ovulation from multiple follicular waves appeared to be due to a prolongation of the static phase of the largest follicle of the penultimate wave of the cycle. Interestingly, the length of the static phase of waves was prolonged in ULO ewes compared with control ewes in every instance where the length of the static phase could be determined. Changes in follicular dynamics due to ULO were not associated with alterations in FSH and LH secretion. In conclusion, ovulatory compensation in ULO sheep involves ovulation from multiple follicular waves due to the lengthened static phase of ovulatory-sized follicles. These altered antral follicular dynamics do not appear to be FSH or LH dependent. Further studies are required to examine the potential role of the nervous system in the enhancement of the life span of the ovulatory-sized follicles leading to ovulatory compensation by the unpaired ovary in ULO sheep.     

Effect of unilateral ovariectomy on compensatory ovarian hypertrophy, peripheral concentrations of follicle-stimulating hormone and luteinizing hormone, and ovarian venous concentrations of estradiol-17 beta in prepuberal gilts

A study was designed to characterize the compensatory ovarian response to unilateral ovariectomy (ULO) in prepuberal gilts and to investigate further the mechanisms involved in compensatory ovarian hypertrophy (COH). Forty-eight crossbred gilts were sham ovariectomized (Sham) or unilaterally ovariectomized at 130 days of age (Day 0). Remaining ovaries in ULO gilts were removed and Sham gilts were bilaterally ovariectomized 2, 4 or 8 days later. A peripheral blood sample was taken before surgery and ovarian venous blood samples were taken before removal of each ovary. Serum estradiol-17 beta (E2) concentrations were determined. Mean wet and dry ovarian weights per ovary on Day 2 for ULO and Sham gilts were 3.4 versus 2.8 and 0.26 versus 0.24 g, respectively. Those weights on Days 4 and 8 were greater (P less than 0.01) for ULO than Sham gilts. Follicular fluid weight per ovary was greater (P less than 0.05) for ULO than Sham gilts on Days 2, 4 and 8. Ovarian venous E2 concentrations were greater (P less than 0.01) for ULO than for Sham gilts on Days 2 and 4 but were similar on Day 8. In a second experiment, 42 prepuberal gilts 130 days of-age were subjected to Sham (n = 18), ULO (n = 18) or bilateral ovariectomy (BLO; n = 6) to evaluate follicle-stimulating hormone (FSH) and luteinizing hormone (LH) secretion immediately after surgical treatment. Release of FSH within the first 24 h was greater for BLO than ULO and for ULO than Sham gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine profiles and reproductive output in European ground squirrels after unilateral ovariectomy

In the course of a long-term study on reproductive physiology and behaviour in female European ground squirrels (Spermophilus citellus) we investigated interactions among reproductive timing, maternal effort and hibernation. To gain information on the state of follicular development shortly before hibernation, histological investigations of ovaries were carried out. To collect the ovaries, unilateral ovariectomy was chosen as the least invasive method. The aim of this study was to monitor patterns of hormone secretion, behavioural parameters and reproductive output in females after unilateral ovariectomy, and compare them with intact individuals to assess potential effects of the treatment. Reproductive performance including duration of gestation and lactation, litter size, and offspring mass at natal emergence were similar in treated and untreated individuals. Before weaning, plasma estradiol levels were higher in the hemicastrated group than in intact females. Progesterone concentrations tended to be lower in unilaterally ovariectomized females during gestation and postlactation. In both groups we measured cortisol metabolites in fecal samples to estimate basal adrenal activity. Untreated individuals had significantly higher cortisol levels than hemicastrated females during lactation. In all other phases no significant differences in patterns of cortisol excretion were found between the two groups. Prehibernatory body-mass did not differ between treated and untreated females. These results indicate that unilateral ovariectomy had no significant negative effects on reproductive timing and output in female European ground squirrels. Compensatory activity of the remaining ovary does occur, concerning estradiol secretion even a kind of overcompensation was reported. These elevated estradiol levels in unilaterally ovariectomized females could play a role in limiting the degree of follicular compensation.     

Mechanisms regulating the ovarian cycle in the frog Rana cyanophlyctis: effect of unilateral ovariectomy, season, feeding, human chorionic gonadotrophin, and estradiol-17 beta

Effects of 30-day unilateral ovariectomy (ULO) on compensatory ovarian hypertrophy (COH) was studied in adult frog Rana cyanophlyctis in relation to reproductive phase/season, feeding, and treatment with human chorionic gonadotrophin (HCG) or estradiol-17 beta. Compensatory growth of the remaining ovary was assessed in terms of weight as well as changes in the dynamics of the pool sizes of different oocytes viz., first growth phase (FGP), medium-sized second growth phase (MSGP), large-sized second growth phase (LSGP), and atretic oocytes. The frogs were fed with live guppies 6 days a week. The effect of underfeeding on COH was studied in the frogs fed once a week. The ovaries removed at operation and those of the sham-operated frogs were used for comparison (controls). COH occurred in both pre- and postbreeding phases (February and November, respectively). In both instances follicular atresia was greatly reduced. In February, COH was due to recruitment of both MSGP and LSGP oocytes. The number of these oocytes increased significantly over controls, and the ovarian weight nearly doubled. However, in November COH occurred because of an increase in FGP oocytes and therefore total oocytes, but there were no changes in the ovarian weights. Administration of 20 IU HCG (6 days a week) had no influence on the basic pattern of COH-response exhibited by the remaining ovary in relation to reproductive phase/season, but it increased the recruitment of oocytes, i.e., FGP oocytes in November and SGP oocytes in February. Follicular atresia was drastically reduced with HCG. Underfeeding or treatment with estradiol-17 beta abolished the COH in both February and November.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in rat testicular adenylate cyclase activities and gonadotrophin binding during unilateral experimental cryptorchidism

Unilaterally cryptorchid rats were examined at 3, 8, 15, 22 and 28 days after operation. There was a selective decrease in the adenylate cyclase (ATP pyrophosphate--lyase (cyclizing), EC 4.6.1.1) responses to gonadotrophin stimulation in the abdominal testis. This was associated with a parallel decrease in specific FSH and LH binding. There was no reduction in the response of testicular adenylate cyclases to prostaglandin (PG) E-1 or fluoride stimulation, indicating that both the GTP binding protein (N-component) and the catalytic subunit of the adenylate cyclase complexes were intact. The reduction in FSH-responsive adenylate cyclase activity in the abdominal testis was not due to a change in the Km for adenylate cyclase activation, but was due to a reduction in maximal velocities. Unilateral cryptorchidism was also associated with a rapid decline in soluble Mn2+-dependent adenylate cyclase activity in germ cells (spermatids). By 3 days after operation there was an 82% decrease in germ cell adenylate cyclase activity. The loss of soluble Mn2+-dependent adenylate cyclase activity was associated with a parallel decrease in Sertoli cell secretion of androgen binding protein, indicating that Sertoli cell factors may be important for the maintenance of germ cell adenylate cyclase activity. The desensitization of the gonadotrophin--responsive adenylate cyclases and the loss of gonadotrophin receptors in Leydig and Sertoli cells were not due to changes in plasma gonadotrophin values because LH concentrations were within normal limits and plasma FSH was only marginally elevated in the cryptorchid rats. No significant alterations of any of these parameters were seen in the scrotal testis of unilaterally cryptorchid rats when compared to values for intact controls.     

Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Concentrations of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion. Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R2 = 0.77; FSH, R2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 +/- 0.04). Maximal concentrations of LH (20.58 +/- 1.97 ng/mL, Day 34.8 +/- 3.2) were attained approximately 2 wk before the peak in FSH (16.99 +/- 1.97 ng/mL, Day 49.7 +/- 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.     

Communities of arbuscular mycorrhizal fungi in arable soils are not necessarily low in diversity

Communities of arbuscular mycorrhizal fungi (AMF) in five agricultural field sites of different management intensities were studied. Variable regions of the ribosomal RNA genes were used to detect and identify AMF directly within colonized roots. Roots from a continuous maize monoculture showed low AMF diversity, in agreement with previous reports on molecular diversity of AMF in agricultural soils. In contrast, a substantially higher diversity of AMF was found throughout the long term 'DOK' field experiment, where organic and conventional agricultural practices have been compared side by side since 1978. In this experiment, a 7-year crop rotation is performed under lower levels of inorganic fertilizer input and chemical pest control. These results are in good agreement with analyses of the spore community previously conducted in these field sites. In a third site, an organically managed leek field with soil of very high phosphate content reflecting the highly intensive conventional field history and intensive tillage, we detected a low-diversity community comparable to the maize monoculture. In addition to fungi from Glomus group A, which have previously been reported to dominate arable soils, we regularly found members of the genera Scutellospora, Paraglomus and Acaulospora. The genus Acaulospora was shown to occur more frequently early in the growing season, suggesting that the life history strategy of AMF may influence the active community at a given time. These data show that the diversity of AMF is not always low in arable soils. Furthermore, low-input agriculture involving crop rotation may provide better conditions to preserve AMF diversity, by preventing the selection for the few AMF taxa tolerating high nutrient levels.     

Circulating insulin-like growth factor-I and -II concentrations are not dependent on pituitary influences in the midgestation fetal sheep

Studies were performed to investigate the possible role of pituitary factors on the regulation of circulating concentrations of insulin-like growth factor-I and -II in the midgestation sheep fetus. Four fetuses were decapitated at 59-64 days of gestation and fetal serum obtained at sacrifice at 90-102 days of gestation. Insulin-like growth factor-I and -II concentrations were similar in these samples to those from 6 control fetuses (83-102 days). A further 4 fetuses were studied following electrolytic destruction of the median eminence of the hypothalamus at 108-110 days of gestation. Four sham operated controls were also studied. Circulating growth hormone concentrations were markedly reduced (P less than 0.01) by destruction of the median eminence. However neither insulin-like growth factor-I nor -II levels differed from those of sham operated fetuses. We conclude that, in the midgestation fetal sheep, growth hormone is not essential for the maintenance of circulating concentrations of insulin-like growth factor-I or -II.     

Changes in rabbit corpus luteum progesterone secretion and cellular morphology following unilateral luteectomy or ovariectomy.

The objective of this study was to determine whether removal of corpora lutea (CL) from one ovary (unilateral luteectomy; ULL) or removal of the entire ovary (unilateral ovariectomy; ULO) of pseudopregnant rabbits would cause compensatory growth and progesterone production by the contralateral ovary. Pseudopregnancy was induced in rabbits with hCG (Day 0). On the first day of pseudopregnancy, one group of rabbits received a sham operation (controls), another group underwent ULL, and a third group underwent ULO. On Day 11 of pseudopregnancy, each rabbit underwent laparotomy, the ovarian artery and vein were cannulated, and the ovary(ies) was removed and perfused in vitro for 6 h. The mean CL weight increased by 33% in the ULL group and by 28% in the ULO group as compared to sham-operated controls. Peripheral estradiol and progesterone levels in sham-operated control, ULL, and ULO groups were similar. Ovarian venous estradiol levels were similar in the control and ULL groups, but were significantly increased in the remaining ovary of the ULO group. Both ovarian venous progesterone in vivo and progesterone secretion in vitro increased significantly in contralateral ovaries from ULL and ULO rabbits as compared to sham-operated controls. Progesterone secretion by ovaries perfused in vitro increased significantly in the contralateral ovary of the ULL and ULO groups. Mean number of luteal cells per CL increased significantly in the ULL group, but not in the ULO group. In contrast, luteal cell volume increased significantly in the ULO, but not in the ULL group. The stimuli responsible for increased progesterone production following ULL and ULO result in morphological changes in the remaining CL.(ABSTRACT TRUNCATED AT 250 WORDS)     

Free-radical-induced inactivation of lysozyme and carbonyl residue generation in protein are not necessarily associated

The 2,2'-azobis(2-amidinopropane) (AAPH)-induced inactivation and oxidative modification of lysozyme, as determined by the loss of tryptophan-associated fluorescence (TAF) and the increase in dinitrophenylhydrazine-reactive carbonyl groups (CO), were studied in the absence and in the presence of antioxidants. AAPH induced a progressive inactivation of the enzyme and a parallel decrease of its TAF. Both changes were closely correlated (R2 = 0.97); however, the inactivation was only partially associated with an increase in CO. The latter reached maximal values at times half those needed to attain maximal losses in both lysozyme activity and TAF. A stoichiometric comparison reveals that whereas over 74% of the enzyme molecules had lost their activity, only 5% exhibited an increment in CO. CO formation was affected differentially by boldine and trolox. Both antioxidants fully protected against the early inactivation and loss of TAF; however, the increase in CO was completely unaffected by trolox. Exposure of lysozyme to Fe3+/ascorbate induced no loss of activity or TAF, but it led to an accumulation of CO similar to that induced by AAPH. Results indicate that CO formation and lysozyme inactivation are two mechanistically dissociable events and that changes in the former parameter can perfectly occur in the absence of changes in the latter.     

Changes in pulsatile LH secretion after ovariectomy in Ile-de-France ewes in two seasons

Two experiments were conducted in Ile-de-France ewes to study changes in pulsatile LH secretion in ewes ovariectomized during anoestrus or during the midluteal phase of the oestrous cycle. In Exp. 1, blood samples were taken every 20 min for 12 h the day before ovariectomy (Day 0). After ovariectomy, samples were taken every 10 min for 6 h (10 ewes per group), on Days 1, 3, 7 and 15. In Exp. 2 samples were taken every 10 min for 6 h (10 ewes per group) on Days 7, 15, 30, 60, 90, 120, 150 and 180 after ovariectomy. Further samples were taken (5 ewes per group) at 9 and 12 months after ovariectomy. There were significant interactions between season and day of sampling for the interval between LH pulses in both experiments. LH pulse frequency increased within 1 day of ovariectomy and the increase was more rapid during the breeding season. There were clear seasonal differences in pulse frequency in Exp. 2. Compared with ewes ovariectomized in anoestrus, pulse frequency was significantly higher for ewes ovariectomized in the breeding season, from Day 7 until Day 120. Once pulse frequency had increased in ewes about the time of the normal breeding season, pulse frequency remained high and subsequent seasonal changes were greatly reduced. Pulse amplitude increased immediately after ovariectomy to reach a maximum on Day 7 and there were no differences between season of ovariectomy in the initial changes in amplitude. In Exp. 2, changes in amplitude followed changes in pulse interval and there was a significant interaction between season and day of sampling. There were no significant effects of season on nadir LH concentrations which increased throughout the duration of the experiments. These results show that, in ovariectomized ewes, LH pulse frequency observed on a given day depends on time after ovariectomy, season at the time of sampling and on previous exposure of ewes to stimulatory effects of season. The direct effects of season on LH pulse frequency and seasonal changes in sensitivity to steroid feedback may contribute to control of the breeding season and their relative contributions to the beginning and end of the breeding season may differ.