Long-term effects of a single cadmium chloride injection on the ovulation, ovarian progesterone and estradiol-17 beta secretion in rats

On the day of dioestrus II rats were given 5, 10 or 15 mg/kg of cadmium chloride (CdCl2), or 1, 0 ml/kg of 0.9% NaCl solution. Then ovarian cycle was checked daily for a period of 12 cycle length. On the day of oestrus or expected oestrus in the 13th cycle the animals were anaesthetized with pentobarbital and cannulas were inserted in one of the femoral arteries and veins and in one of the utero-ovarian veins. Five-minute blood fractions were collected for 40 minutes and following the first blood samples 10 IU of hCG were injected iv. Ovarian venous outflow and blood pressure were continuously recorded. From the blood fractions progesterone (P) and oestradiol-17 beta (E2) were determined with RIA and the P and E2 secretion rates of ovary were calculated. Ovaries were excised and oviducts were flushed for counting oocytes. CdCl2 shortly after its administration induced a (dose-dependent) anoestrous period which turned into regular or irregular cycles depending on the dose. Part (28-32%) of the oestrous animals (14% that of the controls) remained unovulatory, when ovulation occurred normal number of ova was found. None of the doses of CdCl2 has influenced the blood pressure of animals and blood flow of the ovary. The basal secretion rate of P and E2 was not changed in the ovary compared to the controls. The hCG induced rise of P secretion, however, in the animals treated with 5 and 10 mg/kg bw CdCl2 was diminished and delayed, while in the animals treated with the 15 mg/kg Cd dose a complete lack of response was observed.     

Zinc protection against cadmium-induced infertility in female rats. Effect of zinc and cadmium on the progesterone production of cultured granulosa cells

Adult female rats were treated subcutaneously (sc) with zinc chloride (ZnCl, 10 or 20 mg kg body weight, bw) four times during two ovarian cycles. The third injection was accompanied by cadmium chloride (CdCl) administration sc (2.5, 5 and 10 mg kg bw). The fourth zinc (Zn) treatment was followed by mating.ZnCl (20 mg kg) itself impaired fertility by 20%, while CdCl dose-dependently blocked the receptivity of female rats. In combination with 2.5 and 5 mg kg CdCl the metal salts decreased fertility in an additive fashion, whereas at the highest CdCl dose (10 mg kg) a marked ameliorating effect of ZnCl (10 and 20 mg kg) on cadmium (Cd)-caused sterility was observed.In the pregnant animals apart from the higher Cd-induced blood progesterone levels and reduced body weight gain of dams, no significant treatment-related maternal and fetal effects could be observed. ZnCl (10 to 80 m) and CdCl (10 to 80 m) were added to the culture medium of ovarian granulosa cells. CdCl suppressed follicle-stimulating-hormone- (FSH-) and cAMP-stimulated progesterone accumulation. No protective effect of Zn against Cd-induced drop in progesterone production could be seen, while Zn by itself induced a significant increase in FSH-supported progesterone synthesis.In conclusion, while Zn protected against Cd-induced sterility in vivo, it failed to counteract the direct effect of Cd on steroid biosynthesis. The data indicate that Zn protection does not take place at the level of ovary. Moreover, Zn and Cd seem to affect FSH-stimulated progesterone production by different mechanisms.     

Effects of beta 2-adrenergic stimulants on the progesterone and oestradiol-17 beta serum levels in pseudopregnant rats.

In CFY rats pseudopregnancy (PSP) was induced by mechanical stimulation of cervix uteri. On the days 1 or 7 of PSP indvelling catheter was built in one of the jugular veins and blood was collected daily until 7th or 14th days of PSP respectively, meanwhile the animals were daily injected with clenbuterol (0.1 mg/kg bw), fenoterol (0.5 mg/kg bw), ritodrin (1.0 mg/kg bw), propranolol (2.0 mg/kg bw) or 1.0 ml/kg bw 0.9% NaCl subcutaneously. From the blood samples progesterone (P) and oestradiol-17 beta (E2) were determined by RIA. beta 2-adrenergic agonists did not influence the serum levels of P either in the first or in the second half of PSP and the propranolol failed to alter also the serum levels of P during the PSP. Clenbuterol and ritodrin, however, decreased the serum levels of E2 in the first half of PSP, while in the second half of PSP fenoterol and ritodrin elevated, the propranolol diminished it. It was supposed that in PSP rats beta 2-adrenergic mechanism has a more pronounced effects on the theca-interstitial cells than that of the luteal cells.     

Effects of sodium N-methyl-N-dithiocarboxyglucamine on cadmium distribution and excretion

Sodium N-methyl-N-dithiocarboxyglucamine (MDCG) was evaluated for its efficacy in mobilizing and promoting excretion of metallothionein-bound 109Cd using mice which had received 0.03 mg of CdCl2 . 2 . 5H2O along with 1.0 muCi of 109CdCl2 three weeks earlier. The MDCG-induced change in the fecal excretion of Cd ranged from a 15-fold increase over the control rate at the lowest dose level used (2.2 mmol/kg; 684 mg/kg) up to a 72-fold increase at the highest dose (8.8 mmol/kg; 2736 mg/kg) following three daily injections. The latter treatment regimen resulted in a fecal excretion of almost 30% of the administered Cd over a 3-day period of observation. Urinary Cd excretion was insignificant in both the control and treated groups. The whole body burden of Cd was reduced by over 50% following seven thrice-weekly i.p. injections of MDCG at 8.8 mmol/kg. There was a 60-65% reduction in both the liver and kidney Cd levels following the same treatment regimen. Radioassay of ten other organs and tissues revealed only modest changes. Testicular Cd was decreased slightly at the highest dose level, and heart tissue from each treated group contained slightly more Cd than controls. Results indicated a rather marked specificity of MDCG in lowering the Cd content of two organs most susceptible to Cd-induced toxicity.     

Effects of cadmium chloride on ovulation and on induction of sterility in the female golden hamster

The effects of single subcutaneous injections of cadmium chloride (CdCl2) on ovulation, egg transport and early pregnancy in the golden hamster were studied. While a single dose of 1.25 or 2.5 mg/kg of CdCl2 imposed none to marginal effects, hamsters treated with 5 or 10 mg/kg CdCl2 experienced a period of sterility ranging from 11-69 (5 mg/kg) or 46-71 (10 mg/kg) days, followed by a normal pregnancy. Administration of CdCl2 also induced ovulation inhibition which was dose-and time-dependent. A minimum dose of 5 mg/kg CdCl2 was needed to inhibit ovulation. When CdCl2 was given closer to the time of the luteinizing hormone (LH) surge on the day of proestrus, a more pronounced effect on ovulation was recorded. The incidence of failure of ovulation was associated with decreased progesterone levels in serum and inflammation, hemorrhages and necrosis in the ovary. However, the ovarian lesions lasted less than 4 days. The results indicate that CdCl2 inhibits ovulation when administered close to the time of ovulation, whereas its influence on pregnancy is pronounced but temporary.     

Comparative Effects of Repeated Administration of Cadmium Chloride During Pregnancy and Lactation and Selenium Protection Against Cadmium Toxicity on some Organs in Immature Rats' Offsprings

This research comprises studies on the transfer of cadmium (CdCl(2)) from the lactating dam to the pup via milk and absorbed in the suckling, showing that cadmium is transferred to the testes, ovary, cerebellum, and thyroid gland during development. The present studies were carried out in order to assess the protective effects of selenium against cadmium toxicity in pregnant rats. On the sixth day of gestation, the females were dosed subcutaneously either with cadmium or with cadmium and selenium in the following doses (mg/kg of body weight): 0, 1 Cd, 1 Cd?+?1 Se, 2 Cd, 2 Cd?+?2 Se. In groups treated with cadmium, no maternal or embryonic toxicities were observed; however, an increase in testes diameters of seminiferous tubules, a progressive sloughing of germ cells, vacuolization of Sertoli cells, and Leydig cells hyperplasia were noted. The reduction in the ovary size and inhibited folliculogenesis resulted in diminution of the numbers of primordial, growing, and tertiary follicles. The pathological change in the cerebellum, the migration of granular cells from the external germinal layer to the internal granular layer, was strongly retarded. Also, the formation of many microfollicles in the thyroid gland which mimic the changes was seen in thyrotoxicosis. It also appears that selenium used at a low-enough dose could be a very effective protection against cadmium-induced developmental toxicity in the testes, ovary, cerebellum, and thyroid gland but not in the higher dose in the ovary and cerebellum.     

Ovarian Toxicity Induced by Dietary Cadmium in Hen

To investigate the toxicity of cadmium (Cd) on female reproduction in birds, this study was conducted to determine the changes in biochemical parameters of serum and ovary tissue caused by dietary cadmium in hens. Ninety 50-day-old hyline white hens were randomly divided into three groups (30 hens per group): a control group was fed with basal diet, a low dose group was fed with basal diet containing 140 mg/kg CdCl(2) and a high dose group was fed with basal diet containing 210 mg/kg CdCl2. After being treated with Cd for 20, 40 and 60 days, ovary and serum samples were collected and examined for Cd content, histological evaluations, malondialdehyde (MDA) content, glutathione peroxidase (GPx) content, activities of superoxide dismutase (SOD), nitric oxide (NO) content, nitric oxide synthase (NOS) activity, and serum estradiol and progestogen levels. The results showed that the content of Cd, MDA, NO and the activity of NOS in ovary and serum were increased (P < 0.05), while the level of GPx and the activity of SOD were decreased (P < 0.05) in low dose and high dose groups. A time- and dose-dependent correlation was observed between serum and ovary tissue cadmium levels. The number of apoptotic cells in the ovary was increased in the Cd treatment group (P < 0.05). Extensive damage was observed in the ovary. The level of estradiol and progestogen in the serum of low dose and high dose groups was decreased significantly (P < 0.05). It indicated that Cd exposure resulted in oxidative damage of hens' ovary tissue by altering antioxidant defense enzyme systems, lipid peroxidation, apoptosis and endocrine disturbance which may be possible underlying reproductive toxicity mechanisms induced by Cd.     

Oestrogen and progesterone concentrations in plasma and oviductal tissue of ewes exhibiting a natural or induced oestrus

Synchronisation of oestrus in Karagouniki ewes by administration of the standard dose of progesterone results in lower fertility than observed when these ewes ovulate naturally. This suggests that the optimum dose of progesterone may be breed dependent. The exogenous progesterone may perturb the concentrations of oestradiol-17beta and progesterone in blood plasma and the oviductal wall. This possibility was investigated using Karagouniki ewes allocated at random to three treatments (n=4 per treatment). Ewes were allowed to exhibit natural oestrus (N) or oestrus was synchronised by administration of 250 mg (LP) or 375 mg (HP) progesterone (subcutaneous implants) followed by PMSG at 8 mg/kg live weight i.m. 14 days later. Oestrus was observed using teaser rams. Blood samples were collected for plasma oestradiol-17beta and progesterone assay from the onset to the end of oestrus at 2 h intervals. The uterus of each ewe was recovered at the end of oestrus and samples of the oviductal wall were taken from both oviducts and prepared, separately, for progesterone and oestradiol-17beta assay. Statistical analysis was performed using univariate analysis of variance. Plasma oestradiol-17beta concentrations from the onset to the end of oestrus were highest for N ewes and lowest for HP ewes with the values for LP ewes occupying an intermediate position. The differences were significant (P<0.05) between HP and the other two treatments from 4 to 12 h after the onset of oestrus and then between all treatments until the end of oestrus. Plasma progesterone levels were similar and fairly constant from the onset to the end of oestrus for N and LP. The plasma progesterone levels for HP were significantly (P<0.05) higher than for the other two treatments throughout oestrus. In oviductal wall samples, the oestradiol-17beta concentration was significantly (P<0.05) higher for N ewes than for synchronised ewes and the levels were similar for LP and HP ewes. The concentration of oestradiol-17beta differed (P<0.05) between right and left oviducts for N ewes but not for ewes of either of the synchronised oestrus treatments. Progesterone concentrations in oviductal wall samples were highest (P<0.05) for HP ewes and the values for N and LP ewes were similar. The concentration of progesterone did not differ between right and left oviductal wall samples within treatments. It was concluded that the higher dose of exogenous progesterone perturbed the levels of oestradiol-17beta and progesterone in blood plasma and the oviductal wall, and this could explain the lower levels of fertility (relative to naturally occurring oestrus) observed when this protocol is used for Karagouniki ewes in practice.     

Direct effects of oestradiol-17 beta and prostaglandin E-2 in protecting pig corpora lutea from a luteolytic dose of prostaglandin F-2 alpha

Implants containing vehicle or oestradiol-17 beta (10 mg) were placed into pairs of corpora lutea (CL) with and without prostaglandin F-2 alpha (PGF-2 alpha) (100 micrograms) on Day 11 and CL were collected on Day 19, in cyclic gilts (Exp. 1). The results demonstrated that CL implanted with PGF-2 alpha with or without oestradiol-17 beta had a markedly lower (P less than 0.01) weight (mg) and progesterone concentration (ng/mg) than CL with vehicle-or oestradiol-17 beta-implanted or unimplanted CL, which were similar (149 and 7.2 vs. 304 and 49.6, respectively). In Exp. 2, CL implanted with vehicle, oestradiol-17 beta or PGE-2 remained fully functional until Day 19, whereas CL implanted with oestradiol-17 beta +/- PGF-2 alpha and PGE-2 + PGF-2 alpha exhibited lower (P less than 0.05) weight and progesterone concentrations; CL implanted with PGE-2 + PGF-2 alpha were heavier (P less than 0.05) and tended (P less than 0.10) to have greater progesterone concentrations than CL implanted with oestradiol-17 beta + PGF-2 alpha. In Exp. 3, a dose-dependent (P less than 0.05) effect of PGE-2 on preventing regression induced by PGF-2 alpha was observed on Day 19. These data demonstrate a direct effect of PGE-2, but not of oestradiol-17 beta in protecting the CL against luteolysis induced by PGF-2 alpha.     

Acute stimulatory effects of an LH-RH agonist on the ovary in pseudopregnant rats

Pseudopregnant rats were anaesthetized on day 5 of pseudopregnancy with pentobarbital and hypophysectomy or sham operation was performed. Polyethylene cannulas were inserted into one of the femoral arteries and utero-ovarian veins. Five-minute blood samples were collected from the ovary for 40 minutes. Following the first five minute blood fraction LH-RH, an agonistic analogue (D-Phe6, des Gly-NH10(2)-LH-RH-ethylamide) or an antagonistic analogue (Formyl-D-Tryp1,3, D-pCl-Ph2, D-Phe6LH-RH) were superfused into the ovarian bursa for 5 minutes in a volume of 50 microliters. Blood pressure, ovarian venous outflow and haematocrit were continuously measured. From the blood samples progesterone and oestradiol-17 beta were determined by RIA and the secretion rate was calculated. It was found, that LH-RH and its antagonistic analogue has no effect on the blood flow, progesterone (P) and oestradiol-17 beta (E2) secretion of ovary. However, an agonistic analogue of LH-RH induced a rapid elevation of blood flow, diminished vascular resistance in the ovary, and in a dose of 50 ng increased the secretion rate of E2. In sham operated animals the effects of agonistic analogue was similar to the effects of 1.0 IU of hCG.     

Hormonal control of uteroglobin secretion in rabbit uterus. Inhibition of uteroglobin synthesis and messenger ribonucleic acid accumulation by oestrogen and anti-oestrogen administration

Investigations were conducted to quantify activity of uteroglobin mRNA and secretion of uteroglobin in rabbit uterus after administration of progesterone and 5alpha-dihydrotestosterone, either alone or concomitantly with oestradiol-17beta and tamoxifen, a non-steroidal anti-oestrogen. Poly(A)-containing mRNA was isolated from the uterine tissue by extraction with phenol/chloroform, precipitation with ethanol and chromatography on oligo(dT)-cellulose. Cell-free translation in vitro of the poly(A)-containing mRNA was carried out in a wheat-germ lysate, and the product isolated by specific immuno-precipitation with anti-uteroglobin antiserum purified by affinity chromatography. Radioimmunoassay was utilized to determine uteroglobin content in the uterine flushings and tissue preparations. When given for 5 days, both progesterone (1mg/kg per day) and 5alpha-dihydrotestosterone (25mg/kg per day) elicited a marked induction of uteroglobin secretion, which was accompanied with accumulation of uteroglobin mRNA in the tissue. Concomitant administration of oestradiol-17beta (50mug/kg per day) or tamoxifen (12.5mg/kg per day) significantly decreased both progesterone- and 5alpha-dihydrotestosterone-induced uteroglobin secretion, with a parallel decrease in the uteroglobin-mRNA activity. The decline in the uteroglobin content of the uterine flushes brought about by oestradiol-17beta or tamoxifen administration was not due to inhibition of secretion of this protein by the endometrial cells, since a simultaneous decrease occurred in the tissue uteroglobin content. After a 5-day pretreatment with progesterone (1mg/kg per day), administration of oestradiol-17beta (50mug/kg per day) during the ensuing 4 days greatly accelerated the decay of the uteroglobin content in the uterine fluid.     

The Retention of Cadmium and Selenium Influence in Fowl and Chickens of F1 Generation

The retention of cadmium and selenium influence on Cd retention in the muscle, liver and kidneys of hens, chickens and in eggs was studied. Cadmium (Cd) as cadmium chloride (CdCl(2)) and selenium (Se) as sodium selenite (Na(2)SeO(3)) were added to feed at dosages: group 0-control, group 1-20 mg/kg Cd, group 2-30 mg/kg Cd + 4 mg/kg Se. The birds were exposed to Cd for 8 weeks. Cadmium level in hens and cocks was found highest in the kidneys, followed by the liver and muscle. Se supplementation resulted in Cd increase in the muscle tissue and in the reduction of Cd content in the liver and in significant decrease in the kidneys (p < 0.05). A higher Cd level in the yolk and lower in the white was noted in both experimental groups. Nonsignificant increase of Cd in eggs was noted in experimental groups with Se supplementation. Level of cadmium in organs of 7-day-old chicks hatched from Cd-treated hens in both experimental groups was low but the tendency to accumulate preferentially the Cd in the liver and kidneys was recorded. Supplementation of selenium in hens and cocks was not reflected in the decrease of Cd in these two organs of F(1) chickens but was reflected in increase in the muscle. In spite of relatively high Cd levels in the organs of layers no layer-egg-chickens transfer was observed. It was confirm that kidneys and liver are organs more attacked by dietary cadmium than muscle. Supplementation of low dose of Se resulted in decrease of cadmium deposition in analyzed organs.     

Initiation of follicular maturation during mid-pregnancy by the administration of LH in the rat

Pregnant rats were injected twice daily for 1-3 days (Days 13-16 of pregnancy) with various doses of ovine LH. Follicular maturation was determined by the ability of the follicles to ovulate in response to 10 i.u. hCG as well as by endogenous production of oestradiol-17 beta and inhibin. In control animals, no ovulation was induced by hCG given on Day 16 of pregnancy. An injection of hCG on Day 16 of pregnancy, however, induced ovulation in LH-treated animals (6.25-50.0 micrograms LH per injection, s.c. at 12-h intervals from Days 13 to 16). Concentrations of oestradiol-17 beta and inhibin activity in ovarian venous plasma increased after the administration of LH, indicating that development of ovulatory follicles had been induced. Abolishing the decline in plasma LH values therefore induced maturation of a new set of follicles or prevented the atresia of large antral follicles usually seen at this time of pregnancy. Plasma and pituitary concentrations of FSH decreased in LH-treated animals compared with those in control animals. Concentrations of progesterone, testosterone and oestradiol-17 beta in the peripheral plasma were not significantly different between the two groups. These results suggest that the increase in inhibin secretion from the ovary containing maturing follicles after LH treatment may suppress the secretion of FSH from the pituitary gland. These findings indicate that (1) the development of ovulatory follicles can be induced by the administration of exogenous LH during mid-pregnancy in the rat and (2) basal concentrations of FSH are enough to initiate follicular maturation even in the presence of active corpora lutea of pregnancy, when appropriate amounts of plasma LH are present.     

Immunotoxicological investigation of subacute combined exposure with low doses of Pb, Hg and Cd in rats

Detectable interactions between NOEL (No Observed Effect Level) doses of Pb, Hg and Cd in general toxicological, hematological, and immune function parameters were investigated. The metals (Pb-acetate, 20 mg/kg; HgCl2, 0.40 mg/kg; CdCl2, 1.61 mg/kg) were combined. First, the rats received the combination Pb + Hg + Cd for 4 weeks per os. Significant difference vs. control was found only in the weight of lung and popliteal lymph node (PLN). The Pb + Hg and Pb + Cd combinations significantly decreased the PLN to 100 g body weight and PLN to brain weight ratio, and Pb+Hg also decreased the relative adrenal weight. After 12 weeks treatment with the same doses, effects on the thymus, kidney, and adrenal weights in the Pb + Hg, and thymus weight in the Pb + Cd, combination were seen. Pb + Cd also affected the white and red blood cell count and hematocrit. Combined with Hg or Cd, NOEL dose Pb showed toxicity, indicating that exposure limits may be inefficient in combined exposure situations.     

Prolonged interovulatory interval after oestradiol treatment in mares.

This study was designed to test if oestradiol treatment would prevent or delay luteolysis in mares. Mares (5/group) received 0, 0.1, 1.0 or 10.0 mg oestradiol-17 beta daily from the day of ovulation until the next ovulation or for a maximum of 32 days. This treatment did not prevent luteolysis which occurred 15.8, 16.8, 15.8 and 17.3 days after the previous ovulation for the mares treated with 0, 0.1, 1.0 and 10.0 mg oestradiol respectively. Although oestradiol treatment failed to alter oestrous behaviour after luteolysis, daily treatment with 10.0 mg oestradiol prevented follicular growth and inhibited ovulation.     

The vascular architecture of the developing organum vasculosum of the lamina terminalis (OVLT) in the rat

The pituitary gland of the red grouper, Epinephelus akaara, was studied by histochemical techniques, and the prolactin cells, corticotrops, somatotrops, gonadotrops, thyrotrops, pars intermedia cells and neurohypophyseal cells, were identified. Oestradiol-17 beta treatment caused PAS-positive cells in the proximal pars distalis, presumably a mixture of gonadotrops and thyrotrops, to undergo hypertrophy, vacuolation and degranulation of cytoplasmic glycoprotein granules. Disappearance of cytoplasmic granules was also evident in the PAS-positive pars intermedia cells. Oestrogen-treated fish also showed an increase in the hepatosomatic index, and hepatocytes enlarged in size, their nuclear diameter increased and large vacuoles were formed in the cytoplasm. These changes in the liver were paralleled by a secretion of vitellogenin into the serum and an increased production of mucus by the thickened skin epithelium. Testosterone injections did not affect such changes, neither in the pituitary nor liver cells, but a proliferation of skin epithelial cells was noted. Neither oestradiol-17 beta nor testosterone stimulated ovarian incorporation of vitellogenin, but treatment with high doses (5 mg/kg) of oestradiol-17 beta or testosterone brought about a slight increase in the gonadosomatic index and atresia of some of the primary oocytes. The oogonial population size decreased in response to treatment with high doses of oestradiol-17 beta.     

Depression of estrogen-induced uterine peroxidase in alloxan-diabetic rats

The influence of alloxan diabetes on reproductive function and the estradiol-stimulated increase in uterine peroxidase was investigated. Alloxan monohydrate in a dose of 75 mg/kg body weight effectively produced permanent diabetes. In adult rats, 20 days of diabetes resulted in cessation of the estrous cycle and a significant reduction in the gain of body weight, the weights of anterior pituitary gland, ovary, uterus, the level of serum progesterone and the activity of the estradiol-stimulated uterine peroxidase (P less than 0.05). After 10 days of insulin treatment, the ovarian weight, the estrous cycle and the level of ovarian hormones were restored to normal whereas the uterine weight and the estradiol-stimulated uterine peroxidase activity were only partially recovered. Persistent depression of the uterine response in the insulin-treated diabetic rats to both endogenous and exogenous ovarian hormone stimulation suggests that the uterus was directly affected by diabetes. The direct effect of diabetes upon the uterus was further demonstrated in the ovariectomized immature rat in which diabetes depressed the stimulatory action of estradiol on both uterine weight and uterine peroxidase activity.     

Selenium in the anterior pituitary of the rat after a single injection of75Se sodium selenite

In order to investigate the selenite metabolism in the anterior pituitary and compare it with other endocrine organs, rats were injected intraperitoneally with⁷⁵Se sodium selenite (5 mg/kg). The rats were whole body counted shortly after injection and recounted just before sacrifice, which was performed 2, 24, 48 h, and 4, 10, 20, 30, 40, 60, and 80 d after injection. Besides the anterior pituitary, the selenium content was also estimated in the thyroid gland, testis, adrenals, liver, kidney, and blood. The maximum selenium content was observed in all organs 2 h after injection, at which time the anterior pituitary contained 2.9 μg/g wet wt, compared to 13.5 μ/g wet wt in liver and .6 μg/mg wet wt in testis. The excretion of selenite from the anterior pituitary resembled that seen in most other organs investigated, i.e., an initial rapid excretion and a slower secondary phase resembling a first order reaction. Practically all selenium was excreted by 60 d after injection.     

Plasma progesterone concentrations, ovarian and endocrinological response and sperm transport in ewes with synchronized oestrus

Two experiments involving 24 and 54 Australian Merino ewes were conducted in which the establishment of a cervical population of spermatozoa and several endocrinological events were studied after several regimens for the synchronization of oestrus. Intravaginal sponges impregnated with 500 mg (Exp. 1) or 200, 400 or 600 mg (Exp. 2) progesterone resulted in the maintenance of plasma progesterone concentrations of 1.5-4.9 ng/ml over a 12-day insertion period compared with 1.9-6.9 ng/ml during dioestrus in control ewes. In Exp. 1 basal concentrations of less than or equal to 0.25 ng/ml plasma were attained by 4 h after sponge withdrawal and this decline was much more rapid than in normal luteolysis. This was associated with fewer spermatozoa recovered from the cervix 2 h after insemination, and PMSG had no significant effect. In Exp. 2 injection of a supplementary dose of progesterone at sponge withdrawal resulted in a rapid increase in plasma progesterone concentrations followed by an equally rapid decrease and an attenuation of the rise in plasma oestradiol-17 beta, the LH surge, and the onset of oestrus. The numbers of spermatozoa recovered 4 h after insemination were not increased, and PMSG had no significant effect. Two factors were significant, namely the dose of progesterone in the sponge (600 mg greater than 400 or 200 mg, P less than 0.05) and stage of oestrus when inseminated (mid- or late oestrus greater than early). The data demonstrated that an adequate dose of progesterone/progestagen incorporated into intravaginal sponges and accurate timing of insemination relative to the LH surge are the most important factors involved in penetration of the cervix by spermatozoa.     

Ovarian steroid hormone involvement in endogenous opioid modulation of LH secretion in mature ewes during the breeding and non-breeding seasons

The opioid antagonist WIN-44441-3 (WIN-3, Sterling-Winthrop) caused significant increases in LH secretion in ovariectomized ewes treated with progesterone but not in ovariectomized animals treated with oestradiol-17 beta. In the non-breeding season, plasma LH concentrations in ovariectomized ewes without steroid therapy, given oestradiol-17 beta or oestradiol-17 beta and progesterone together were not affected by treatment with WIN-3 on Day 6 after ovariectomy (there was a significant increase in LH as a result of WIN-3 treatment 13 days after ovariectomy in sheep given no steroid therapy). However, WIN-3 treatment of ovariectomized sheep given progesterone resulted in a significant increase in plasma LH. WIN-3 was ineffective when given to intact ewes treated with progesterone during the non-breeding season. With ovariectomized sheep during the breeding season there was again no response to WIN-3 at 6 days after ovariectomy in sheep given oestradiol-17 beta, but significant LH elevations in animals given no steroid, those given progesterone and those given progesterone + oestradiol-17 beta. The lack of an LH response to WIN-3 in ovariectomized sheep treated with oestradiol-17 beta did not result from a reduced pituitary response to GnRH since such animals responded normally to exogenous GnRH treatment. Overall, these results are consistent with the idea that, irrespective of the time of year, progesterone exerts negative feedback upon LH release at least in part through an opioidergic mechanism, whereas oestradiol-17 beta exerts negative feedback through steps unlikely to involve opioids. Progesterone can override the effect of oestradiol-17 beta during the breeding season only. Further, there appears to be a steroid-independent opioid involvement in LH suppression, operating at both times of year.