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Summary. In studies of five hysterectomized and five control dogs, hysterectomy shortened the anoestrous interval (96·6 ± 28·0 versus 149·4 ± 50·9 days, P < 0·05). No differences in hormone concentrations (progesterone, oestradiol, prolactin and growth hormone) were observed between the control and hysterectomized dogs except for a brief fall in progesterone concentrations over 8 days immediately after surgery, between days 35 and 40 after onset of pro-oestrous bleeding; only these animals developed symptoms of overt pseudopregnancy. It is concluded that, in dogs, luteal regression occurs independently of a uterine luteolysin, but that the uterus may play a role in control of duration of anoestrus. Pseudopregnancy seems to be initiated by a fall in progesterone concentrations rather than by other hormonal changes.

Keywords: dog; hysterectomy; ovary; growth hormone; prolactin

Summary.

Levels of lh were determined by radioimmunoassay and those of progesterone by a competitive protein-binding technique. Blood samples from eight cows, representing two complete pregnancies (including post-partum periods), and from one cow in the first trimester and another around the time of parturition, were collected. The samples were withdrawn at intervals of 6 hr for lh and every 4 to 5 days for progesterone determination. Levels of lh were consistently low (1·0 to 1·6 ng/ml plasma) with a few single peaks occurring irregularly in individuals during the first 110 days. Distinct lh peaks were observed between Days 7 and 20 post partum. The decrease of progesterone from high levels during pregnancy (plateau between 5 and 9 ng/ml plasma with individual differences) before parturition and the low level following was not reflected in the lh concentration. In an experiment with one animal, an injection of 5 mg flumethasone near term caused a partial decrease in the progesterone concentration, and a larger dose of 10 mg induced parturition. This was preceded by a marked decrease of progesterone similar to that observed before a normal delivery.

No definitive information is yet available on the steroidogenic capacity of the two morphologically distinct cell types forming the bovine trophoblast, the uninucleated trophoblast cells (UTCs) and the trophoblast giant cells (TGCs). Hence, in order to localise 17α-hydroxylase-C17,20-lyase (P450c17) on a cellular level and to monitor its expression as a function of gestational age, placentomes from pregnant (days 80–284; n = 19), prepartal (days 273–282; 24–36 h prior to the onset of labour; n = 3) and parturient cows (n = 5) were immunostained for P450c17 using an antiserum against the recombinant bovine enzyme. At all stages investigated, P450c17 was exclusively found in the UTCs of chorionic villi (CV), where staining was ubiquitous between days 80 and 160, but was largely restricted to primary CV and the branching sites of secondary CV between days 160 and 240. Thereafter, a distinct ubiquitous staining reoccurred in the UTCs of all CV in late pregnant, prepartal and parturient animals. Using an antiserum against human aromatase cytochrome P450 (P450arom), specific cytoplasmic staining was observed in TGCs. In placentomes from pregnant cows, staining intensity was higher in mature compared with immature TGCs and was more pronounced in the trophoblast covering big stem villi compared with the trophoblast at other sites of the villous tree. In placentomes of a parturient cow, specific staining was only found in mature TGCs that survived the normal, but substantial, prepartal decline in TGC numbers. These results clearly showed that bovine UTCs and TGCs exhibit different steroidogenic capacities, constituting a ‘two-cell’ organisation for oestrogen synthesis. P450c17 expression appears to be quickly down-regulated and P450arom is up-regulated when UTCs enter the TGC differentiation pathway.

Under natural and artificial conditions, Alpine marmots (Marmota marmota) are true hibernators with a single breeding season starting immediately upon emergence from hibernation. Over three mating and breeding seasons, hormonal and mating patterns of colony-housed reproductive female marmots were investigated after exit from hibernation. Blood samples were taken for progesterone, oestrogen and relaxin assays with parallel ultrasound investigations. Copulations were observed from the first day after exit from hibernation until the end of pregnancy and reached a maximum number on day 37 before parturition. Mating behaviour was observed between the dominant animals as well as between dominant and subdominant group members. In the first week after exit from hibernation, plasma progesterone was detected in half of the animals. During the third week, progesterone concentrations were significantly higher in pregnant than in non-pregnant animals or animals that had aborted. Immediately after emerging from hibernation, all successfully mated females showed higher serum relaxin values than non-successfully mated animals and this increase in relaxin concentration lasted until the end of pregnancy. The total concentration of oestrogen did not differ between pregnant and non-pregnant animals. The results of this study indicate that progesterone and relaxin might be useful indicators of early pregnancy in Alpine marmots.

Testicular function in the dog was down-regulated using two different GNRH agonist implants, with adult and juvenile testes serving as controls. Treatment resulted in an increased percentage of the interstitial area and decreased area of Leydig cell nuclei. Expression of StAR and the steroidogenic enzymes cytochrome P450 side-chain cleavage enzyme (P450scc, CYP11A1) and cytochrome P450 17α-hydroxylase-17,20-lyase (P450c17, CYP17A1) in Leydig cells was blocked at the mRNA and protein level, showing no differences between the two agonists. Staining for androgen receptor (AR) by immunohistochemistry was positive in Sertoli, Leydig and peritubular cells and some spermatogonia, with in situ hybridization confirming expression in Sertoli cells. At the mRNA level, expression of AR was not affected; however, translation was blocked (reduced percentage of AR-positive Sertoli cells), with the number of nuclei in basal position being decreased. In the juvenile testes, mRNA expression of StAR, CYP11A1 and CYP17A1 was higher compared with the other groups but distinctly lower for the AR. At the protein level, the expression was at the limit of detection for StAR; AR-positive Sertoli cells were not detected. Our observations show that the down-regulated testis is different from the juvenile one rather resembling the testicular status in seasonal breeders out of season.

Summary.

The luteotrophic properties of endogenously secreted LH and prolactin were studied by measuring CL function after neutralization of circulating LH and prolactin by the administration of highly specific antisera against these hormones on the 11th and 12th day of the oestrous cycle. In addition, the effect of a prolactin inhibitor (CB-154), which reduced prolactin concentration in peripheral blood by 80 to 90% was studied. A hysterectomized heifer carrying a persistent CL was treated with CB-154, a combination of CB-154 and prolactin antiserum and then with LH antiserum. In all animals treated with the LH antiserum, CL function ceased or was quantitatively inhibited. No change in circulating progesterone was seen after treatment with the prolactin antiserum or the prolactin inhibitor. It is concluded that LH is the dominant luteotrophic factor in the bovine species while prolactin has little or no activity.

Sulfated steroids have been traditionally regarded as inactive metabolites. However, they may also serve as precursors for the production of active free steroids in target cells. In this study, we used the boar as a model to study the metabolism, transport, and function of steroid sulfates due to their high production in the porcine testicular–epididymal compartment, of which the role is unknown. To characterize the secretion of free and sulfated steroids, plasma samples were collected from six postpubertal boars over 6 h every 20 min from the jugular vein. Long-term secretion profiles were also established in seven boars stimulated with human chorionic gonadotropin. To directly characterize the testicular output, samples were collected from superficial testicular arterial and venous blood vessels. Testosterone, androstenedione and sulfated pregnenolone, DHEA, estrone (E₁), and estradiol-17β (E₂) were determined by liquid chromatography–tandem mass spectrometry. Free E₁ and E₂ were measured by RIA. Irrespective of a high variability between individuals, the results suggest that i) all steroids assessed are primarily produced in the testis, ii) they exhibit similar profiles pointing to a pulsatile secretion with low frequency (three to five pulses per day), and iii) after synthesis at least a major proportion is immediately released into peripheral circulation. The fact that all steroid sulfates assessed are original testicular products and their high correlations with one another suggest their role as being intermediates of testicular steroidogenesis rather than as being inactivated end products. Moreover, a substantial use of sulfated steroids in porcine testicular steroidogenesis would assign a crucial regulatory role to steroid sulfatase, which is highly expressed in Leydig cells.