Effect of cyproterone acetate,d-norgestrel and progesterone on cells of the pars distalis of the adenohypophysis in the beagle bitch

Summary The effects of short-term (8 weeks) treatment with different doses of cyproterone acetate (CPA), d-norgestrel (d-N) and progesterone on cells of the pars distalis, as revealed by the immunoperoxidase technique, were studied in cycle-synchronized beagle bitches (first anoestrus). Pituitary glands from non-treated primiparous beagle bitches at the 6th and 9th week of pregnancy were also included. For immunochemical staining specific antisera to the following hormones were used: canine GH, canine PRL, porcine ACTH, bovine TSH, bovine LH and human FSH. Morphological features of high secretory activity in GH cells were evident even after the human oral contraceptive doses of CPA and d-N, and after a dose as low as 0.1 mg/kg/day subcutaneously (s.c.) of progesterone. In contrast, PRL cells did not show any significant treatment-related effects except in those animals which received the highest dose of d-N (0.5 mg/kg/day per os). In this group, as well as in all pregnant bitches, hyperplasia and hypertrophy of PRL cells were found. In the animals treated with the highest doses of CPA (4.0 mg/kg/day per os) and progesterone (42.5 mg/kg/day s.c.) as well as in pregnant bitches, ACTH/MSH and TSH cells showed marked atrophy and regressive changes. Similar morphological signs of depressed secretory activity were also observed in the cells shown to contain FSH and/or LH as a result of treatment with the highest dose of progesterone and at the 9th week of pregnancy. These structural responses indicate that quantitative and/or qualitative differences may exist between progesterone, the synthetic progesterone derivative CPA and the nortestosterone type progestagen d-N with regard to their effect on pituitary hormone secretion in the beagle bitch.Abbreviations ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - CRH Corticotropin Releasing Hormone - TRH Thyrotropin Releasing Hormone The authors are grateful to Dr. Christel Schöbel and Mrs. P. Kurth for carrying out the experimental work on animals, to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistance, and to Dr. P. Günzel for his advice and encouragement     

Effect of cyproterone acetate,d-norgestrel and progesterone on the canine mammary gland

Summary The effects of short-term (8 weeks) treatment with different doses of cyproterone acetate (CPA), d-norgestrel (d-N) and progesterone (PRO) on the mammary gland were studied in cycle-synchronized beagle bitches (first anoestrus). Mammary glands from non-treated primiparous beagle bitches in the 6th and 9th weeks of pregnancy were also included. The results were evaluated using the whole-mount technique, histologic, histochemical and biochemical methods. CPA, d-N and PRO were shown to cause dose-dependent mammary growth accompanied by an increase in the mammary weight, DNA content and activity of several histochemically demonstrable dehydrogenases. These changes resembled in some aspects mammary development observed in the last third of pregnancy. A single human oral contraceptive dose (HCD) of CPA as well as a dose as low as 1.0mg/kg/day subcutaneously of PRO was capable of stimulating complete mammary development. A comparable effect was first observed as a result of treatment with as much as 100 times the HCD of d-N. However, d-N and CPA were shown to be more effective than PRO in stimulating ductal proliferative activity. These structural and biochemical responses indicate that quantitative and/or qualitative differences may exist between PRO, the synthetic progesterone derivative CPA and the synthetic nortestosterone progestagen d-N with regard to their growth-promoting effect on the canine mammary gland. This may be explained by possible differences in their potency and range of biological activity, pharmacodynamics and effects on pituitary hormone secretion.The authors are grateful to Dr. Christel Schöbel and Mrs. P. Kurth for carrying out the experimental work on animals, to Dr. Y. Nishino and Mr. M. Leidecker for biochemical determination of DNA, to Dr. J. Kaufmann for statistical analysis, to Miss E. Fallenbacher, Mrs. B. Schilk, Mrs. G. Soulioti and Miss. U. Tüshaus for their excellent technical assistance, and to Dr. P. Günzel for his advice and encouragement     

Effect of cyproterone acetate on cells of the pars distalis of the adenohypophysis in the Beagle Bitch

Summary The effects of oral administration of 100 mg per kg per day cyproterone acetate (CPA) for four weeks on cells of the pars distalis, as revealed by the immunoperoxidase technique and chemical staining, were studied in the ovariectomized beagle bitch. For immunochemical staining antisera to the following hormones were used: canine GH, canine PRL, porcine ACTH, bovine TSH, bovine LH and human FSH¹. The most striking effects of the treatment were an overall increase in the relative proportion of GH cells and a marked morphological indication of high secretory activity in these cells. In contrast, PRL cells were not affected significantly. In all ovariectomized control bitches a marked atrophy of the cells stained for FSH (FSH cells) and hypertrophy of the cells shown to contain LH(LH cells) were observed. FSH cells became enlarged, while LH cells appeared reduced in size by administration of CPA. In some treated bitches ACTH/MSH cells showed atrophy and regressive changes, whereas TSH cells seemed to become enlarged and were more densely arranged. These structural responses indicate that, in addition to its partial antigonadotropic properties, CPA as a synthetic progesterone derivative may stimulate GH secretion and possibly suppress CRH-ACTH activity in the ovariectomized beagle bitch.Abbreviations of Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - CRH Corticotropin Releasing Hormone The authors are grateful to Dr. Christel Schoebel and Mrs. P. Kurth for carrying out the experimental work on animals, to Dr. H. Wiemann for the statistical analysis, to Mrs. B. Schilk, G. Soulioti and Miss U. Tüshaus for their excellent technical assistance, and to Dr. P. Guenzel for his advice and encouragementRecipient of a Research Scholarship from the Arabic Republic of Egypt     

Effect of 17β-estradiol on cells stained for FSHβ and/or LHβ in the dog pituitary gland

Summary The effect of long-term treatment (52 weeks) with high doses of 17-estradiol (1.28 mg/kg/week intramuscularly) on gonadotrophs was studied in the pituitary gland of the beagle bitch. For immunochemical staining the immunoperoxidase technique and antisera to the specific beta () subunits of FSH and LH were employed. For control purposes antisera to the following hormones were also used: bovine TSH, canine GH, canine PRL and porcine ACTH¹. In the pars distalis and pars tuberalis of control bitches, in addition to the cells which react solely with antisera to either LH or FSH, most cells were reactive to both antisera. The cells stained for FSH were less numerous than those shown to contain LH. TSH, PRL, GH and ACTH/MSH were localized in distinctly different cell types in the pars distalis of all control animals. In the treated bitches, almost complete regression of cells classically identified as gonadotrophs and stained for LH was observed. On the other hand, using the antiserum to FSH, selective immunochemical staining was localized in cells fitting the morphological characteristics of TSH cells. All these cells were also stained for TSH. However, a few cells were also shown to react solely with the antiserum to TSH. These cells, which seem to contain both TSH and FSH, were further clearly differentiated from PRL, GH and ACTH/MSH cells on the basis of their cytological features, intraglandular distribution and by immunochemical double staining. These observations support the concept that the one cell-one hormone theory may not necessarily apply to the glycoprotein hormones of the dog pituitary gland.Abbreviations of Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin The authors are grateful to Mrs. K. Oertel for carrying out the experimental work on animals, to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistance, and to Dr. P. Günzel for his advice and encouragement     

Localization of thyrotropin (TSH) in the dog pituitary gland

Summary Using the immunoperoxidase technique and antisera to the specific beta () subunits of bovine and rat TSH¹, selective immunocytochemical staining was localized in a specific cell population in the pars distalis of the dog pituitary gland. These TSH cells were found to be positive to aldehyde fuchsin, alcian blue, periodic acid-Schiff (PAS) and aniline blue. With the performic acidalcian blue (pH 0.2) -PAS-orange G procedure these cells stained blue-purple, demonstrating FSH/LH cells (blue or turquoise), ACTH/MSH cells (redpurple) and PRL cells (orange-red). The TSH cells were further differentiated from other functional cell types of the pars distalis on the basis of their typical cytological features, intraglandular distribution and by immunocytochemical double staining. In the pars distalis of adult male dogs the TSH cells were mostly shown to be smaller in size and less numerous than in bitches in the anestrous phase of the sexual cycle. Moreover, cytological alterations in the immunoreactive thyrotrophs in the pituitary of male and female dogs generally paralleled the spontaneous changes in thyroid function associated with thyroid atrophy and/or pituitary insufficiency, and thyroid hyperplasia or goiter. In conclusion, because of their specificity and high potency, the antisera to the -subunits of bovine and rat TSH represent an effective tool for the selective immunocytochemical localization of TSH in the dog pituitary. This allows the study of the morphology and function of TSH cells under different physiological, pathological and experimental conditions.Abbreviations for Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin - TRH TSH Releasing Hormone - CG Chorionic Gonadotropin The authors are grateful to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistance     

Termination of pregnancy and induction of premature luteolysis by the antiprogestagen, mifepristone, in dogs

Five pregnant beagle bitches were treated with 2.5 mg mifepristone/kg body weight, twice a day, for 4.5 days starting at Day 32 of gestation. Results of fetal ultrasonography and assay of serum progesterone concentrations every 2-4 days were compared to those in 5 control bitches. Mifepristone resulted in a premature (P less than 0.01) termination of pregnancy (36 +/- 1 vs 65 +/- 1 days), without side effects. The antiprogestagen also caused progesterone to decline to less than 1 ng/ml by Day 40-45 after the preovulatory LH peak (vs 64-67 days in controls) and reduced (P less than 0.05) mean concentrations on Days 34-50 (2.2 +/- 0.5 vs 6.3 +/- 0.3 ng/ml). The results suggest that antiprogestagen therapy is a safe means to terminate unwanted pregnancy in dogs, and that luteal function in pregnant bitches is dependent on luteotrophic support that is blocked by antiprogestagen treatment, directly or indirectly, due to termination of pregnancy.     

Localization of gonadotrophic hormones in the dog pituitary gland

Summary Using the immunoperoxidase technique and antisera to the specific beta () subunits of FSH and LH¹, selective immunochemical staining was localized mostly in the same cell type in the pars distalis and pars tuberalis of the dog pituitary gland. However, some cells were consistently shown to react solely with antisera to either LH or FSH. The cells stained for FSH were at least 1.5 times less numerous than those shown to contain LH. In the pars distalis of adult male dogs the immunoreactive gonadotrophs varied greatly in their relative proportion and were mostly shown to be much less numerous than in bitches in the anestrus phase of the sexual cycle. These cells were found to be positive to aldehyde fuchsin, alcian blue, periodic acid-Schiff (PAS) and aniline blue. The performic acid-alcian blue (pH 0.2)-PAS-orange G procedure stained the FSH/LH cells blue or turquoise, demonstrating TSH cells (blue-purple), ACTH/MSH cells (red-purple) and PRL cells (orange-red). The FSH/LH cells were further differentiated from other functional cell types of the pars distalis on the basis of their typical cytological features, intraglandular distribution and by immunochemical double staining. These observations support the concept that the one cell-one hormone theory may not apply to gonadotrophic hormones, although some cells seem to be the source of either FSH or LH.Abbreviations for Pituitary Hormones cited in this Paper ACTH Adrenocorticotropin - FSH Follicle Stimulating Hormone - GH Growth Hormone - LH Luteinizing Hormone - MSH Melanocyte Stimulating Hormone - PRL Prolactin - TSH Thyrotropin The authors are grateful to Dr. H. Wiemann for the statistical evaluation and to Mrs. B. Schilk and Miss U. Tüshaus for their excellent technical assistanceRecipient of a Research Scholarship from the Arabic Republic of Egypt     

Structural studies of the adrenal zona glomerulosa and renal juxtaglomerular apparatus in pregnant sheep

The ultrastructural changes in the adrenal zona glomerulosa and renal juxtaglomerular apparatus have been examined during normal pregnancy in sheep. As pregnancy progressed, increasing numbers of cells in the adrenal zona glomerulosa displayed mitochondria with straight tubular "rod-like" structures replacing their normal lamelliform cristae; groups of cells showing these mitochondrial changes were predominantly located in the middle and superficial regions of the zona glomerulosa, but at all stages remained interspersed with cells with apparently normal mitochondria. In the same animals, the renal juxtaglomerular index was raised, reflecting an increase in renin storage, and juxtaglomerular myoepithelioid cells showed increased numbers of cytoplasmic granules, but no apparent increase in granular endoplasmic reticulum and Golgi profiles; there were no distinguishing morphological changes in juxtaglomerular peripolar cells. These findings provide morphologic evidence of stimulation of the adrenal zona glomerulosa in association with increased juxtaglomerular renin storage during pregnancy. The mitochondrial changes observed in an increasing proportion of cells in the zona glomerulosa closely resemble those seen in sodium-depleted animals, and may reflect the altered steroidogenic capacity of the adrenal gland in pregnant sheep. The finding of groups of cells displaying altered mitochondria lying next to cells with normal mitochondria suggests the presence of cells with different sensitivities to stimuli for aldosterone production or may indicate the presence of different cell types in the zona glomerulosa responding to different stimuli.     

金色中仓鼠不存在布鲁斯效应

布鲁斯效应是一种由非配偶雄性的化学信号所诱发的雌性妊娠终止现象,曾被认为是雌性对抗雄性杀婴行为的一种进化策略。布鲁斯效应最初在实验小鼠中发现。后续的研究证明了在实验室条件下多种啮齿类动物中存在布鲁斯效应。布鲁斯效应是否为实验室啮齿类动物中存在的普遍规律,目前尚无定论。本实验首先探讨了布鲁斯效应在金色中仓鼠中是否存在。在交配之后给予实验组雌鼠陌生雄鼠的非直接接触刺激,对照组雌鼠接受配偶雄鼠的非直接接触刺激。同时还测定了雌鼠的体重、胚胎质量以及生理器官(肾上腺、脾脏、卵巢和子宫)质量。结果显示,实验组雌鼠的流产率、体重、胚胎质量、生理器官(肾上腺、脾脏、卵巢、子宫)质量与对照组不存在显著差异。本实验结果表明:陌生雄鼠的化学信号对雌性金色中仓鼠的怀孕状态没有影响,实验室条件下的金色中仓鼠不存在布鲁斯效应。     

Radiographic contrast medium for uterine insemination in the bitch, and its effect upon the quality and fertility of fresh dog semen

Four ejaculates were collected from each of 6 adult male beagle dogs. The second fraction was divided into 3 aliquants which were then diluted with physiological saline, an isoosmolar solution of sodium/meglumine diatroate, and an iso-osmolar solution of iohexol. The diluted samples were incubated at 39 degrees C and evaluated at 0, 60, 90, 120, 240 and 360 min after dilution. A variety of assessments was made, including, spermatozoal motility, spermatozoal morphology, and acrosorne status. The practicality of using 1.0 ml of iso-osmolar contrast medium combined with radiographic examination was evaluated as a method of confirming accurate placement of a transcervical uterine catheter by injecting contrast after positioning the catheter in 4 beagle bitches. The effect of the procedure on fertility was assessed using 5 greyhound bitches which were inseminated with fresh semen and in which pregnancy was monitored using diagnostic B-mode ultrasound imaging. There was no significant difference between physiological saline and the sodium/meglumine diatroate solution upon semen quality, while the iohexol solution produced a significant reduction in spermatozoal motility and morphology. No adverse clinical effects were observed when contrast medium was administered into the uterus to either group of bitches. A subjective assessment of radiographic quality showed that the sodium/meglumine diatroate solution, which contained twice the iodine concentration of the iohexol solution, produced significantly greater radiopacity and was radiographically more useful than the iohexol solution. The sodium/meglurnine diatroate solution had no adverse effect upon the fertility of dog semen, and all bitches that were inseminated with this technique conceived and maintained the pregnancy to term. Litter size was considered to be normal for the breed. Small volumes of an iso-osmolar solution of sodium/meglumine diatroate may be useful for ensuring correct placement of transcervical catheters prior to artificial insemination in the bitch.     

Intercellular junctions in the uterine epithelium of Salamandra salamandra (L.) (Amphibia,Urodela)

Summary Intercellular junctions in the uterine epithelium of the ovoviviparous urodele Salamandra salamandra were studied in pregnant and non-pregnant females by freeze-fracture technique. Junctional complexes consist of zonulae occludentes (tight junctions) and numerous maculae adhaerentes (desmosomes); z. adhaerentes and nexuses (gap junctions) could not be identified. Tight junctions are of the flexible type exhibiting loosely interconnected fibrils. The fibrillary network appears stretched more often in pregnant females possibly due to the mechanical stress of pregnancy. The structure and occurrence of the junctions identified, especially that of the tight junctions, is discussed with regard to the functions of the uterus during pregnancy.Zusammenfassung Mit Hilfe der Gefrierbruchtechnik wurden im Uterus-epithel trächtiger und nichtträchtiger Feuersalamanderweibchen (Salamandra salamandra) Zonulae occludentes und Maculae adhaerentes, jedoch keine Z. adhaerentes sowie Nexus identifiziert. Die Z. occludentes sind flexibel. Ihr fibrilläres Netzwerk ist bei trächtigen Weibchen öfter gestreckt; das ist möglicherweise auf die stärkere Ausdehnung des Uterusgewebes während der Trächtigkeit zurückzuführen. Das Vorkommen der verschiedenen Kontakt-strukturen, namentlich das der Z. occludentes, wird im Hinblick auf die Funktionen des Uterus während der Trächtigkeit diskutiert.We are indebted to Mrs. K. Ott for excellent technical assistance and to Miss Dr. U. Beigel for linguistic help     

Erythrocytic parameters as indicators for differentiating between the pregnant and pseudopregnant bitches in Nigeria

The erythrocytic parameters during pregnancy and pseudopregnancy in bitches were studied and compared in 8 bitches aged 2 -3 years and weighing 10-12 kg. Blood samples were collected from the bitches before mating, during the three trimesters of pregnancy and the post partum period. The packed cell volume (PCV %), haemoglobin concentration (Hb gm/dl), red blood cell count(x106/μl) were determined using standard methods. The mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC) were then calculated. Six of the bitches were pregnant and 2 were pseudopregnant. The results showed that in pregnant bitches, the PCV decreased significantly from the premating values of 51.37+0.94% to 34.00+8.04% during the third trimester of pregnancy (P.     

Nucleolar alterations induced by 4-aminopyrazolo(3,4-d)pyrimidine in adrenal cortex and liver cells of rat

Summary The nucleolar ultrastructural changes produced in adrenal zona fasciculata cells and hepatocytes of rats by 4-aminopyrazolo(3,4-d) pyrimidine (4-APP), an inhibitor of the lipoprotein synthesis, are described. Male rats were injected intraperitoneally for three consecutive days with 4-APP in sodium phosphate buffer (50 mg/Kg/day). On the 4th day, the animals were sacrificed and their adrenals and liver were processed for EM. The nucleoli of the adrenal zona fasciculata cells showed nucleolar fragmentation with loss of their normal reticular appearance, separation of fibrillar and granular components, extensive vacuolization and evidence of fibrillar centers. The hepatocyte nucleoli also exhibited fragmentation. These changes seem to be the morphological counterpart of alterations in rRNA synthesis and processing, since 4-APP inhibits de novo purine synthesis and thus interferes with its incorporation into RNA and DNA.     

The use of epostane, a 3(beta)-hydroxysteroid dehydrogenase delta 4-5 isomerase enzyme inhibitor, in oil suspension as a mismating agent in the dog

Administration of epostane as a single subcutaneous injection in sesame oil prevented or terminated pregnancy in bred beagle bitches (P = 0.002). Doses of 15 and 20 mg/kg prevented or terminated pregnancy in all of 14 bred beagle bitches studied but demonstrated a high rate of serious abscess formation at the injection site. A dose of 10 mg/kg was partially effective in 3 of 12 subjects whelping live pups, and a dose of 2.5 mg/kg was completely ineffective in 12 of 12 subjects whelping live pups. Plasma progesterone levels were lowered in dose-related fashion with respect to both depth of depression (P < 0.01) and length of time (P < 0.05). Subjects in which pregnancy was maintained had significant differences (P < 0.01) in progesterone patterns compared with nonpregnant subjects, as measured by area under the curve. No clinically significant differences were seen between treated and control females with respect to return to estrus, subsequent fertility, or in a battery of serum electrolytes, blood parameters and serum enzymes.     

Decrease of body temperature after aglepristone treatment in bitches

Body temperature responses and the timing of abortions were evaluated in pregnant bitches with the anti-progestin aglepristone. Fifteen purebred and crossbred, 25-45 days pregnant, were included in this study and seven untreated bitches at the same stage of pregnancy served as controls. Treated bitches were administered two applications of aglepristone (10 mg/kg SC) 24 h apart for pregnancy termination. Pregnancy termination was confirmed by ultrasonographic assessment. Body temperature was rectally measured three times a day for 6 days beginning 24 h before treatment or pregnancy diagnosis in the treated and control bitches, respectively. Additionally, serum progesterone concentrations were assessed at time points during the study in the treated bitches. Pregnancy was terminated in 14 treated bitches in a mean+/-S.E.M. of 4.3+/-0.7 days after treatment. Control bitches remained pregnant. In the treated bitches, but not in the controls, body temperature significantly decreased 24 h after the beginning of the treatments (P < 0.01) and then gradually returned to pre-treatment values. Correlation between the day of mean minimum body temperature and the day of pregnancy termination was low (0.07; > 0.05). Progesterone did not show significant change throughout the study. Body temperature does not seem to be a suitable variable to clinically monitor the aborting effect of aglepristone. Decrease of body temperature after aglepristone treatment could represent further evidence of its hypothalamic effects.     

Fertility after vaginal or uterine deposition of dog semen frozen in a tris extender with or without Equex STM paste

Twenty-five bitches were artificially inseminated with semen that was frozen-thawed using an egg yolk-Tris-glucose-citrate extender containing 5% glycerol with, or without the addition of 0.5% Equex STM Paste. Semen was collected on 2 occasions from 11 dogs, pooled, and evaluated for sperm motility, morphology and plasma membrane integrity. Each pool was then divided in 2 parts, diluted with 1 of the 2 extenders, and frozen in 0.5-mL straws. In the bitches, plasma progesterone was assayed daily during late proestrus and estrus. Artificial insemination (AI) was performed twice on Days 3 and 5 after the estimated LH peak. For each insemination, 200x10(6) spermatozoa were used. Ten bitches were inseminated with semen frozen without Equex: In 5 females, semen was deposited transcervically into the uterus with the aid of a fiberoptic endoscope and a urethral catheter, while the remaining 5 bitches were inseminated in the cranial vagina using a Norwegian catheter. Fifteen bitches were inseminated with semen frozen-thawed with Equex: Two groups of 5 bitches were inseminated according to the techniques described above, while 5 bitches were inseminated vaginally using the Osiris catheter. Pregnancy was diagnosed and the number of fetuses counted by ultrasound examination. Post-thaw, spermatozoa frozen with Equex tended to have higher total and progressive motility and to survive longer in vitro than when the extender without Equex was used. Spermatozoal concentration, age of the bitches, duration of heat and estrus, and progesterone concentration at LH peak and at the first and second AI did not differ among the 5 groups. The overall pregnancy rate of 84% (21/25) was close to what can be expected from well controlled natural matings. For both freezing extenders tested, 5/5 bitches were pregnant after uterine deposition of semen and 4/5 were pregnant when semen was deposited in the anterior vagina using the Norwegian catheter. With the Osiris catheter, 3/5 inseminations resulted in a pregnancy. No significant differences in pregnancy rate or number of fetuses were found between groups, site of deposition or freezing extender.     

Reproductive cycles of the domestic bitch

Domestic dogs are monoestrous, typically non-seasonal, polytocous, spontaneous ovulators and have a spontaneous luteal phase slightly longer (by approx 5 day) than the 64±1day luteal phases of a 65±1day pregnancy, a phase followed by an obligate anestrus before the next 2-3 week "heat" (proestrus-estrus). The resulting inter-estrus intervals of 5-12 months are variable among bitches, commonly 6-7 months, and range from highly variable to regular (to perhaps within±5-10 day of sequential 7 month cycle, for instance) within bitches, and across studies and do not vary significantly between pregnant and non-pregnant cycles. Hormone levels reported are those observed in this laboratory using previously reported assays and canine gonadotropin standards unless stated otherwise. Endocrine sequences for dog cycles are not unlike those of many other mammals, including selection of ovulatory follicles by increased LH pulsatility, the occurrence of estrus behavior and LH surge during a decline in the estrogen: progestin ratio, a pronounced preovulatory luteinization as in humans and rodents, and luteotrophic roles for both LH and prolactin. Non-pregnant bitches have a spontaneously prolonged luteal phase, often longer and with a more protracted decline in serum progesterone than in pregnancy as there is no uterine luteolytic mechanism. The obligate anestrus of 8-40 weeks is terminated by poorly understood interactions of environment (e.g. pheromones, possibly photoperiod) and a potential endogenous circannual cycle in sensitivities of hypothalamic dopaminergic, serotonergic and/or opioid pathways.     

In vitro effects of L-arginine on spontaneous and homocysteine-induced contractility of pregnant canine uteri

The L-Arginine-Nitric Oxide Synthase-Nitric Oxide (L-Arg-NOS-NO) system exerts a pivotal role in the maintenance of uterine quiescence during pregnancy, whereas Homocysteine (Hcy) promotes uterine contractility. The aim of this study was to test the in vitro effects of L-Arg on spontaneous and Hcy-induced contractions of uteri excised from pregnant bitches. 104 strips cut from pregnant uteri were mounted in an organ bath. 40 out of 104 strips (16 from mid-gestation uteri and 24 from close to term uteri, respectively) were exposed to cumulative doses of L-Arg; 40 strips (16 from mid-gestation-uteri and 24 from close to term-uteri, respectively) were exposed to N-nitro-L-arginine methyl ester (L-NAME), a NOS antagonist; the remaining 24 strips (from close-to-term uteri) were first exposed to a single dose of Hcy and then to increasing doses of L-Arg. L-Arg showed no effects on spontaneous contractility both in mid-gestation- and close to term-uterine strips, whereas it promoted a relaxant effect on Hcy-induced contractility. On the contrary, L-NAME increased amplitude of contraction both in mid-gestation and close to term strips. These findings suggest that the L-Arg-NO system is present in the uterus of pregnant bitches and that Hcy is able to modulate its actions. Further investigation of this system may provide the basis of future obstetrical therapies in bitches.     

Progesterone concentration and reproduction: An evaluation in pregnant, heat-acclimated, white rats

1. 1.|Progresterone concentrations in peripheral plasma, corpus luteum, uterus and placenta were determined by radioimmunoassay, in pregnant heat-acclimated (HA) and control (C) rats.

2. 2.|Concentration of progesterone in plasma and uterus of HA rats were lower than C from day 5 to 18 and day 5 to mid-gestation respectively.

3. 3.|Number and weight of pups born to HA rats were lower than C by 11.1% and 12.3% respectively.

4. 4.|It is concluded that aberration in pregnancy development observed in HA rats is associated with lower progesterone concentration in plasma and uterus from day of implantation to mid-pregnancy.