Comparative aspects of oxytocin in baboon (Papio hamadryus anubis) and human corpora lutea

Expression of oxytocin, progesterone, and estrogen receptors in the reproductive tract of bitches with pyometra

Canine pyometra is considered a serious and life-threatening condition. Due to the relationship among sex steroid hormones, oxytocin receptor (OTR) expression, and canine pyometra pathogenesis, this study aimed to investigate the expression of oxytocin, progesterone, and estrogen receptors in the reproductive tissues of canines with pyometra by real-time PCR and immunohistochemistry. A total of 27 pyometra bitches were classified into open- and closed-cervix pyometra groups based on the presence of vaginal discharge. Moreover, 15 normal bitches in the luteal phase served as a control group. The results showed that OTR gene expression in the ovary of pyometra bitches was higher than that of normal bitches, whereas the level of OTR gene expression in the cervix of pyometra bitches was less than that of normal bitches (P < 0.05). Conversely, a lower OTR H-score in ovarian follicles was observed in pyometra bitches compared with normal bitches, whereas a higher percentage of OTR-positive immunostaining in uteri and cervices were found in pyometra bitches compared with normal bitches (P < 0.05). Moreover, the H-scores of estrogen receptor alpha in uteri and cervices of pyometra bitches were less than that of normal bitches (P < 0.05). However, the localization of the OTR and sex steroid receptors between groups of pyometra bitches was not different. Our findings suggest that pyometra pathogenesis is associated with a change in expression of OTR and sex steroid receptors in the canine reproductive tract. However, cervical dilation in bitches with pyometra was not influenced by the expression of OTR and sex steroid receptors.

Granulosa cells are refractory to FSH action in individuals with a low antral follicle count

The reason ovarian function and fertility are diminished in women with a low antral follicle count (AFC), despite significant numbers of follicles remaining in ovaries, is unknown. The bovine model is unique to address this question because cattle and women with a low AFC exhibit similar phenotypic characteristics including a diminished ovarian reserve, reduced circulating concentrations of anti-Müllerian hormone (AMH) but heightened FSH secretion during reproductive cycles. Because women and cattle with a low AFC respond minimally to gonadotropin stimulation during IVF cycles or superovulation, granulosa cells in individuals with a low AFC are hypothesised to be refractory to FSH. The present study evaluates this hypothesis by testing whether capacity of granulosa cells to respond to FSH differs between cattle with a low and a high AFC. Granulosa cells from cattle with a low (≤15 follicles ≥3 mm in diameter) or a high (≥25 follicles) AFC were cultured with different doses of FSH. Treatments were evaluated by measurement of oestradiol (E), progesterone (P) and AMH in media and abundance of mRNAs for aromatase (CYP19A1), AMH, FSH receptor (FSHR) and oxytocin (OXT). Progesterone and OXT mRNA are well-established markers of granulosa cell luteinisation. Although high doses of FSH induced granulosa cell luteinisation, basal and FSH-induced increases in E and AMH production and expression of mRNAs for CYP19A1, FSHR and AMH in granulosa cells were much lower, while P production and OXT mRNA expression were higher in non-luteinised and luteinised granulosa cells from the low than the high AFC group. Granulosa cells in cattle with a low AFC are refractory to FSH action, which could explain why ovarian function, responsiveness to gonadotropin stimulation and fertility are diminished in individuals with a low versus a high AFC.

Baboon corpus luteum: size and sex steroid secretion throughout the luteal phase

OBJECTIVE

To determine the size of the baboon corpus luteum (CL) and levels of plasma P, 17alpha-hydroxyprogesterone (17-OHP), and E2 in the ovarian vein draining it, the contralateral ovarian vein, and peripheral blood throughout the luteal phase of the menstrual cycle.

DESIGN

Prospective study.

SETTING

Academic department of obstetrics and gynecology in a US medical school.

ANIMAL(S)

Corpora lutea from a cohort of 27 adult cycling baboons (Papio anubis).

INTERVENTION(S)

Timed luteectomy.

MAIN OUTCOME MEASURE(S)

The authors weighed 166 CL and measured plasma P, 17-OHP, and E(2) in the blood samples obtained at luteectomy.

RESULT(S)

Early luteal phase corpora lutea weighed 189.1 +/- 12.3 mg (mean +/- SEM); their weight significantly increased to 239.4 +/- 8.4 mg at mid luteal phase and significantly declined to 188.3 +/- 14.0 mg in late luteal phase. Plasma P draining the CL (134.4 +/- 20.5 ng/mL in early, 167.4 +/- 18.7 ng/mL in mid, and 126.4 +/- 23.4 ng/mL in late luteal phase) was significantly higher than that in contralateral ovarian (11.0 +/- 1.4 ng/mL) and peripheral plasma (7.1 +/- 0.9 ng/mL). Similarly, levels of both plasma 17-OHP (10.9 +/- 1.5 to 15.9 +/- 2.4 ng/mL) and E2 (1.6 +/- 0.2 to 2.6 +/- 0.6 ng/mL) draining the CL were significantly higher than those from the contralateral ovary and peripheral blood (17-OHP, 1.1 +/- 0.2 ng/mL; E2, 0.2 +/- 0.05 ng/mL).

CONCLUSION(S)

Largest in mid luteal phase, the baboon CL secretes P, 17-OHP, and E2 throughout the luteal phase, with the highest levels seen in the ovarian vein draining the CL in the mid compared with the early and late luteal phases.

Mammalian mesotocin: cDNA sequence and expression of an oxytocin-like gene in a macropodid marsupial, the tammar wallaby

The oxytocin (OT)-like peptide of most Australian marsupials is mesotocin (MT), which differs from OT by substitution of isoleucine for leucine at position 8. To date, the only information on the evolution of the OT peptide in marsupials is based on the sequence of the 9-amino acid peptide itself. The main objective of this study was to obtain the nucleotide and derived amino acid sequences of a marsupial MT precursor for comparison with known OT and MT precursors of eutherians and nonmammalian vertebrates. The structural organization and sequence of the MT gene and its specific transcript were established in a macropodid marsupial, the tammar wallaby, using PCR strategies with a combination of genomic DNA and reverse-transcribed hypothalamic RNA. A consensus genomic sequence of 1221 bp was produced which, by comparison with the expressed cDNA sequence, included two intron sequences of 480 and 188 bp. The tammar MT precursor molecule consists of a 32-amino acid signal peptide, followed by the MT-encoding region and the Gly-Lys-Arg carboxy-terminal cleavage and amidation signal which separates the nonapeptide from the 92-amino acid neurophysin. At the amino acid level, the MT precursor is more similar to eutherian OT precursors than to nonmammalian MT, isotocin, or vasotocin precursors. Northern analysis demonstrated a single transcript of approximately 0.6 kB in the hypothalamus. Mesotocin mRNA is also present in several tissues of the reproductive tract, including the corpus luteum, follicle, uterus, and placenta. Within the ovary, MT transcripts are localized predominantly in the granulosa cells of antral follicles with some positive hybridization signals in cells of the theca interna. This pattern of MT gene expression in marsupials is very similar to that of OT in eutherians and suggests a conserved physiology in the mammalian ovary.

Cell proliferation and vascular morphology in the marmoset corpus luteum

Luteal formation is associated with angiogenesis and low progesterone production. Maximal mid-luteal phase progesterone production is concurrent with extensive vascularization, and luteolysis occurs when steroidogenesis decreases. Angiogenic cell proliferation and vascular changes have not been examined in the marmoset. The aim of this study was to examine vascular morphology throughout the luteal phase by identifying: (i) von Willebrand factor VIII antigen (vW)-immunopositive endothelial cells; (ii) Ki67-positive proliferating cells; and (iii) bromodeoxyuridine-positive proliferating cells. Marmoset corpora lutea were examined throughout the cycle, and natural regression was compared with induced luteolysis after administration of a prostaglandin F(2alpha) analogue or gonadotrophin-releasing hormone (GnRH) antagonist. Steroidogenic and endothelial cells were positive for proliferation markers. Endothelial cell proliferation was highest during luteal formation, then decreased and remained low during the luteal phase and functional regression, however endothelial cell proliferation increased during structural regression. Endothelial cell proliferation was unchanged by induced regression. The area of vW immunostaining was highest during luteal formation, decreased thereafter and remained constant during the luteal phase and regression. Distribution of immunostaining indicated the presence of an extensive capillary network, but during structural regression the numbers of capillaries decreased and numbers of microvessels increased. These results suggest that vascular changes are concurrent with changes in the functional status of the marmoset corpus luteum.