Hormonal concentrations in bitches with primary uterine inertia

Insights into the role of PGF2α in canine periparturient myometrium

Parturition in dogs is subjected to complex hormonal regulation, with the involvement of prostaglandin F2α (PGF2α) still not fully understood. To investigate uterine inertia (UI), the most prevalent maternal reason for dystocia in the bitch, a better understanding of undisturbed uterine, especially myometrial function, is crucial. Our aim was to gain deeper insights into the role of PGF2α in the canine parturient myometrium. Uterine biopsies were obtained during medically indicated cesarean sections. To test for stimulatory effects of PGF2α in vitro, circular and longitudinal myometrial layer tissue strips were challenged with 50 pM, 0.5 µM, and 50 µM PGF2α. Prostaglandin-endoperoxide synthase 2 (PTGS2) and PGF2α-receptor (PTGFR) mRNA expressions were compared between primary UI (PUI) and obstructive dystocia (OD) samples in isolated parturient myometrium. PTGFR protein expression was assessed in full thickness uterine samples. PGF2α concentrations were analyzed in canine interplacental tissue around term. In the organ bath, the contractile response to PGF2α was limited to the circular layer at the highest dosage. Correspondingly, PTGFR immunohistochemical staining was significantly stronger in the circular layer (p ≤ 0.01). PTGS2 gene expression did not differ between PUI and OD, whereas PTGFR gene expression could not be quantified. Local uterine PGF2α concentrations correlated negatively with serum P4 levels and were the highest during prepartum luteolysis while being significantly lower in PUI. Conclusively, despite the significant increase in local PGF2α concentrations at birth, confirming the interplacental tissue as a production site, our results suggest that PGF2α might affect uterine contractility during labor, mainly indirectly.

Etiology behind canine uterine inertia: Role of uterine expression of MLCK4, MYH2, and PKC genes

Dystocia is an obstetrical emergency, and primary uterine inertia (PUI) is the major etiological reason among the more prevalent maternal causes in dogs. The present study involved the relative expression analysis of genes associated with myometrial contraction in medium-sized dog breeds with uterine inertia. Dogs without any progress in the parturition process even after four hours of the onset of labor and the absence of uterine contractions were considered to have complete primary uterine inertia (CPUI, n = 9). Dogs that had expelled at least one fetus and made no further progress in parturition in the absence of active uterine contraction were considered to be experiencing partial primary uterine inertia (PPUI, n = 6). Dogs with the fetal cause of dystocia (FCD), i.e., obstructive dystocia, were taken as the third (n = 7) group. Uterine tissue samples were collected during cesarean section in each group, RNA was isolated, and the relative expression of myometrial ACTA2, ACTG2, MLCK4, MYH2, and PKC genes was analyzed. The MLCK4 gene expression was downregulated in CPUI (P ≤ 0.05) and PPUI (P ≤ 0.01) when compared to FCD. The MYH2 gene expression was downregulated in PPUI in comparison to CPUI (P ≤ 0.01) and FCD (P ≤ 0.05). The PKC gene expression was upregulated in PPUI in comparison to FCD and CPUI (P ≤ 0.05). The downregulation of MLCK4 and MYH2 gene expressions recorded in PPUI indicated the possibility of myometrial defects. The possibility of myometrial defects was also observed in CPUI, but to a lesser degree, suggesting other etiologies.

The In Vitro Contractile Response of Canine Pregnant Myometrium to Oxytocin and Denaverine Hydrochloride

In pregnant bitches, the response to oxytocin and denaverine hydrochloride in dystocia management is usually poor. To better understand the effect of both drugs on myometrial contractility, the circular and longitudinal muscle layers were examined in an organ bath. For each layer, three myometrial strips were stimulated twice, each with one of three oxytocin concentrations. The effect of denaverine hydrochloride was studied once in direct combination with oxytocin and alone with subsequent oxytocin administration. Contractions were recorded and evaluated for average amplitude, mean force, area under the curve (AUC), and frequency. Effects of different treatments were analyzed and compared within and between layers. In the circular layer, oxytocin significantly increased amplitude and mean force compared to untreated controls regardless of stimulation cycles or concentrations. In both layers, high oxytocin concentrations caused tonic contractions, while the lowest concentration created regular rhythmic contractions. Longitudinal layer tissue responded to oxytocin with a significantly decreased contractility when stimulated twice, presumably a sign of desensitization. Denaverine hydrochloride neither affected oxytocin induced contractions nor showed a priming effect to subsequent oxytocin. Thus, no benefit of denaverine hydrochloride on myometrial contractility was found in the organ bath. Our results suggest a better efficiency of low-dose oxytocin in canine dystocia management.

[Real-time analysis of parturition in bitches of a medium-sized breed]

OBJECTIVE

Observation of the birth processes in healthy bitches under controlled conditions. The primary aim was to gain more insight into the natural birth process. Additional goal was to determine under which circumstances caregivers seek veterinary assistance.

MATERIAL AND METHODS

Data regarding length of gestation, the course of the parturition process, litter size, as well as neonatal characteristics were collected from 345 Boxer bitches. A real-time evaluation supplied the data concerning the birth process itself. Statistical analysis included single- and multi-factor variance analyses, as well as correlation, regression, and rank correlation analyses.

RESULTS

Mother dogs with fewer fetuses were gravid for a significantly longer period than those with a high number (p=0.0012). The proportion of live neonates decreased significantly from the 5th litter onwards (p=0.0072). Female neonates exhibited a lower birth weight than male neonates (p<0.0001). Diurnal influences on the onset of stage II were not found. Birth processes could be divided into 3 groups based on the recorded progression: group 1 - eutocia (54.6%), group II - eutocia with prophylactic measures by the caregiver (20.5%), and group III - dystocia (24.9%). Bitches of group 1 were slightly younger than those of groups 2 and 3. In groups 2 and 3, the proportion of older primiparae (≥4 years) was significantly higher than in group 1 (p<0.05). The total duration of labor differed significantly between groups 1 and 2 (p<0.0001). Significant differences were seen between the groups in labor activity. In group 3, the proportion of bitches with a type I (=primary) weakness in labor was strikingly high (45.2%). In 83.8% of the births (groups 1 and 2), one or more pauses in labor (>60 min) occurred during the expulsive phase. This was correlated with litter size (p=0.0025), but not with age or birth number. The rate of stillbirth was positively correlated with duration of the birth process. Reasons for veterinary intervention primarily pertained to conditions of type II and III labor weakness (inadequate contractions of the uterus during parturition). The average time span between identification of a birth disorder and presentation of the bitch to a practice/clinic was 4.8±3.3 hours.

CONCLUSION AND CLINICAL RELEVANCE

In pre-partum-counselling, special attention should be paid to conditions of hyperfetia (>20% above the mean) as well as uniparous and biparous gravidity and these dams should be classified as risk patients with regard to the course of parturition. In the case of birth complications, rapid veterinary intervention is warranted in order to minimize the development of maternal inanition and fetal vitality depression.

Involvement of Oxytocin and Progesterone Receptor Expression in the Etiology of Canine Uterine Inertia

An altered oxytocin and progesterone receptor (OXTR and PGR, respectively) expression was postulated in canine uterine inertia (UI), which is the lack of functional myometrial contractions. OXTR and PGR expressions were compared in uterine tissue obtained during C-section due to primary UI (PUI; n = 12) and obstructive dystocia (OD, n = 8). In PUI, the influence of litter size was studied (small/normal/large litter: PUI-S/N/L: n = 5/4/3). Staining intensity in immunohistochemistry was scored for the longitudinal and circular myometrial layer and summarized per dog (IP-Myoscore). Mean P4 did not differ significantly between PUI (n = 9) and OD (n = 7). OXTR and PGR expressions (ratios) were significantly higher in PUI (OXTR: p = 0.0019; PGR: p = 0.0339), also for OXTR in PUI-N versus OD (p = 0.0034). A trend for a higher PGR IP-Myoscore was identified (PUI-N vs. OD, p = 0.0626) as well as an influence of litter size (lowest PGR-Myoscore in PUI-L, p = 0.0391). In conclusion, PUI was not related to higher P4, but potentially increased PGR availability compared to OD. It remains to be clarified whether OXTR is upregulated in PUI due to a counterregulatory mechanism to overcome myometrial quiescence or downregulated in OD due to physiological slow OXTR desensitization associated with an advanced duration of labor. Identified OXTR differences between myometrial layers indicate the need for further research.

Incidence and concomitant factors of cesarean sections in the bitch: A questionnaire study

Dystocia in the canine species is a common problem, and elective cesarean sections (C-sections) have become more frequent in breeds that are at risk. The aim of this study was to evaluate the incidence of C-section and contributing factors and to compare data on elective and emergency C-sections (e.g., regarding stillbirth). Using a questionnaire, a total of 423 bitches of 80 breeds and their 899 litters were included. The mean number of litters per bitch was 2.1 ± 1.1 litters. The overall rate of stillbirth was 6.7%. Of all litters, 194 were born via C-sections (21.6%), of which 35 were declared as elective and 159 as emergency due to dystocia. Significantly more C-sections were performed in either small litters (1-2 pups) or large litters (&gt;12 pups) (p &lt; 0.001). Bitches that have had prior C-sections had a 4-fold increase in the risk of successive C-sections (RR = 4.54 (95%CI 2.56–7.70; p &lt; 0.001). Furthermore, primiparous bitches of advanced age had a significantly higher incidence of emergency C-sections (p = 0.004). Stillbirth was significantly higher in emergency C-sections compared with that in elective C-sections (p = 0.003). Also, timing of intervention had a significant impact on stillbirth in emergency C-sections (p = 0.025). Within a breed-specific evaluation, significant differences were observed between breeds regarding incidence of C-section and stillbirth. Lesser-known breeds were represented in the population, and the results showed that the Norwich Terrier had the highest (51.6%) and the Gordon Setter had the lowest (4.8%) incidence of C-section (p &lt; 0.001). The inclusion and evaluation of lesser-known breeds regarding incidence of C-section is of importance as it shows that certain breeds without phenotypical traits such as brachycephaly may also have an increased incidence of emergency C-section and stillbirth. We further conclude that more importance may be given to the age at first parturition concerning the occurrence of dystocia and the decision making regarding possible elective C-sections.

Early Blood Analysis and Gas Exchange Monitoring in the Canine Neonate: Effect of Dam’s Size and Birth Order

Simple Summary

The complications that are observed during parturition are events that affect the vitality of the newborn and can also compromise their health by predisposing them to fetal hypoxia, increasing newborn mortality. Blood gas analysis to measure the main biomarkers associated with hypoxia evaluates the physiological and metabolic alterations derived from this state, and these could help identify if said markers respond to maternal or neonatal causes. This study aimed to assess the effect of the dam’s size, the birth order, and the presentation of blood gas alterations. Recognizing if these elements are intertwined may enhance newborns’ life expectancy by enabling the planning of a perinatal protocol to avoid serious metabolic consequences that are derived from prolonged hypoxia.

Abstract

In canines, size at birth is determined by the dam’s weight, which would probably affect the newborn’s viability due to litter size and birth order. Fetal hypoxia causes distress and acidemia. Identifying physiological blood alterations in the puppy during the first minute of life through the blood gas exchange of the umbilical cord could determine the puppy’s risk of suffering asphyxiation during labor. This study aimed to evaluate the effect of the birth order and dam’s size during spontaneous labor and the alterations during the first minute of life. The results indicate that the dam’s size and the birth order have considerable physiological and metabolic effects in the puppies, mainly in birth order 1 (BO1) in small-size dogs, while in the medium size, the last puppy presented more alterations, probably because of a prolonged whelping which could have fostered hypoxic processes and death. Likewise, with large-size dogs, intrapartum asphyxiation processes were registered during the first minute of life in any birth order.

Canine parturition: what is known about the hormonal setting?

Parturition is a challenging physiological process with perfect timing dictated by the events leading to the end of pregnancy in the female, and by the maturation of the fetus(es). The process of parturition remains an intricate interaction of hormones in a fine-tuned timing that remains to be better elucidated in the dog. In the dog pregnancy is maintained by the progesterone production by the corpora lutea, in which some hormones play a luteotrophic action. At term of pregnancy, the pre-parturient luteolytic cascade is the most apparent event, characterized by a rapid decline in plasma progesterone concentrations and useful in predicting the onset of spontaneous parturition. In contrast, cortisol plasma concentrations measurement showed high variability and suggested to be related to the stress condition instead of the onset of parturition. Both prostaglandin F2α and E2 concur in the process of parturition in the dog. The measurement of oxytocin plasma concentrations, also very variable, is implicated in uterine contractions. The measurement of plasma oxytocin concentrations showed to be useful to distinguish between normal and disturbed parturition, allowing the prompt recognition of dystocia and the immediate obstetrical intervention. In contrast to other species, no significant roles of estrogens for the initiating of parturition were demonstrated. Relaxin, the main pregnancy hormonal marker in the dog, beside an endocrine action, is also supposed to play a paracrine/autocrine role at the utero-placental unit and to support the maintenance of high plasma progesterone concentrations through a luteotrophic action, concurring to the main action of prolactin. Although important information has been provided, some aspects in the understanding the hormonal interactions and action timing implications in the process of parturition in the dog remains to be better investigated and represent intriguing topic for basic knowledge and applied research.

Investigations on the potential role of prostaglandin E2 in canine uterine inertia

Prostaglandin (PG) E2 plays a crucial role in the endocrine network of canine parturition and we hypothesized that PGE2, 15-hydroxyprostaglandin dehydrogenase (HPGD) and PG-transporter (PGT) might be involved in the development of primary uterine inertia (PUI). We investigated PTGE synthase (PTGES), PTGE receptors 2/4 (PTGER2/4), HPGD and PGT expression on the mRNA- and protein-level in interplacental (IP) and uteroplacental (UP) tissues of bitches presented with dystocia undergoing emergency caesarean section. Groups were formed retrospectively based on strict criteria: PUI (n = 12; small/normal/large litter - PUI-S/N/L: n = 5/4/3), and obstructive dystocia (OD, n = 8). Respective mRNA expressions (ratio) between PUI and OD in IP and UP, between PUI dogs with different litter sizes, between PUI-N and OD in IP, and overall between IP and UP were compared. PTGES, PTGER2, PTGER4, HPGD and PGT mRNA expressions did not differ significantly between PUI and OD in IP or UP. PUI-N PTGES mRNA expression was higher than PUI-S/L (P = 0.0203/P = 0.0186) and OD (P = 0.0314). Higher PTGES (P = 0.0112) and a tendency for higher PTGER2 (P = 0.059) mRNA-expressions were detected in UP versus IP. Other than hypothesized, we did not find a difference in PGE2 production and signaling between PUI and OD, indicating that altered uterine PTGES, PTGER2, PTGER4, HPGD and PGT expression was likely not causative for PUI. However, higher PTGES expression in PUI-N compared to OD might point to a possible role of PGE2 during the course of parturition. Higher PTGES expression in PUI-N compared to PUI-S/L indicates an influence of litter size, the underlying cause and biological relevance of which remain to be clarified.

Do uterine PTGS2, PGFS, and PTGFR expression play a role in canine uterine inertia?

The aetiology of primary uterine inertia (PUI), which is the most common cause of canine dystocia, is still not elucidated. Prostaglandins (PGs) play a crucial role in parturition. We hypothesized that the expression of prostaglandin endoperoxidase synthase 2 (PTGS2), PGF2α synthase (PGFS), and corresponding receptor (PTGFR) is altered in PUI. We investigated PTGS2, PGFS, and PTGFR mRNA expression, and PTGS2 and PGFS protein expression in interplacental (IP) and uteroplacental sites (UP) in bitches with PUI, obstructive dystocia (OD), and prepartum (PC). PTGS2, PGFS, and PTGFR mRNA expression did not differ significantly between PUI and OD (IP/UP). PTGFR ratio in UP was higher in PC than in OD (p = 0.014). PTGS2 immunopositivity was noted in foetal trophoblasts, luminal and superficial glandular epithelial cells, smooth muscle cells of both myometrial layers, and weakly and sporadically in deep uterine glands. PGFS was localized in luminal epithelial cells and in the epithelium of superficial uterine glands. PTGS2 and PGFS staining was similar between PUI and OD, while PGFS protein expression differed between OD and PC (p = 0.0215). For PTGS2, the longitudinal myometrial layer of IP stained significantly stronger than the circular layer, independent of groups. These results do not support a role for PTGS2, PGFS, and PTGFR in PUI. Reduced PGFS expression in IP during parturition compared with PC and the overall lack of placental PGFS expression confirm that PGFS is not the main source of prepartal PGF2alpha increase. The difference in PTGS2 expression between IP myometrial layers warrants further investigation into its physiological relevance.

Uterine expression of smooth muscle alpha- and gamma-actin and smooth muscle myosin in bitches diagnosed with uterine inertia and obstructive dystocia

Primary uterine inertia (PUI) is the most common type of dystocia in dogs. We hypothesized that PUI develops because of lower than normal expression of the basic contractile elements in the uterus, i.e., smooth muscle (SM) α- and γ-actin and SM-myosin, and that the expression of these proteins is influenced by the number of fetuses present in utero. Full-thickness inter-placental uterine biopsies were collected during Cesarean sections from dogs with PUI (n = 11), and from bitches with obstructive dystocia (OD) still presenting strong labor contractions (designated as the control group, n = 7). Relative gene expression was determined by semi-quantitative real-time (TaqMan) PCR, and protein localization by immunohistochemistry. Gene expression between PUI and OD bitches, and between PUI bitches carrying small, large, or average number of fetuses according to their breed, were compared. Uterine SM-γ-actin and SM-myosin mRNA levels were significantly higher in PUI than in OD dogs, while SM-α-actin did not differ. PUI bitches carrying large litters had lower uterine SM-γ-actin gene expression than those with small litters (P = 0.008). Immunostaining for SM-actin isoforms and SM-myosin was present in the myometrium, and localization pattern and staining intensity appeared similar in the PUI and OD groups. All proteins stained in blood vessels, and SM-γ-actin was also present in endometrial luminal and glandular epithelium. In conclusion, higher uterine SM-γ-actin and SM-myosin gene expression in PUI bitches, compared with OD dogs, might be an indication of abnormal progression with labor. Whether this is the cause of PUI due to an intrinsic error of the myometrium not becoming committed to labor, or the consequence of inadequate endocrine or mechanical stimuli, is not clear. Litter size was previously shown to be one of the risk factors for the development of uterine inertia in dogs, and our findings suggest possible differing uterine pathophysiology of PUI with respect to litter size.

Expression of uterine oxytocin receptors and blood progesterone, 13,14-dihydro-15-Keto-Prostaglandin F2α, and ionized calcium levels in dystocic bitches

This study aimed to examine the etiology of canine dystocia by measuring the relative expression of oxytocin receptor (OXTR) mRNA and the concentration of serum progesterone, plasma PGF_2α metabolite (PGFM), and blood ionized calcium (iCa) near term and in dystocia. Altogether 58 bitches were included in this study, 41 of which underwent cesarean section (CS). The four CS groups were based on history: complete uterine inertia (CUI; n = 7), partial uterine inertia (PUI; n = 13), obstructive dystocia (OD; n = 10), and elective cesarean section (ECS; n = 11). An additional group of medically treated dystocia without CS (MD; n = 8) and a control group (C; n = 9) with normal parturition (without CS and medical treatment) were also formed. Blood samples were taken prior to CS or medical treatment. Progesterone concentrations were highest in the ECS and a significant difference (p < 0.05) was observed between the ECS and the OD and between the ECS and the combined dystocia (CUI, PUI, OD, MD) groups (COMB). Highest concentrations of PGFM was observed in the C, the difference being significant (p < 0.05) between the C and the ECS and between the C and the COMB group. The progesterone:PGFM ratio was significantly (p < 0.05) higher in the ECS than in the C and the COMB group. No significant difference (p > 0.05) was observed in iCa concentrations between the groups. Relative OXTR mRNA expression was evaluated with real-time PCR from full-thickness uterine samples taken from the incision site during CS. The expression was highest in the ECS and the difference in expression was significant (p < 0.05) between the ECS and the OD and between ECS and the combined dystocia (CUI, PUI, OD) groups (COMB2). The study supports previous reports of decreasing progesterone and increasing PGFM during prepartum luteolysis. Upregulation of OXTR occurs near term. In obstructive dystocia, a prolonged influence of oxytocin and uterine exhaustion may lead to downregulation of OXTR. Complete primary uterine inertia may have a different etiology as no clear decrease in OXTR was observed in CUI as in OD. It remains unclear if parturition ceases because of uterine inertia or if uterine inertia occurs because of ceased parturition and desensitization of receptors.

Blood calcium, glucose and haematology profiles of parturient bitches diagnosed with uterine inertia or obstructive dystocia

Bitches with dystocia most often present with clinical signs of uterine inertia (UI). The aetiology of myometrial dysfunction in most of these cases is still not elucidated. We compared blood ionized calcium (iCa) and glucose concentrations in bitches diagnosed with primary UI (PUI, n = 14), secondary UI (SUI, n = 6) or obstructive dystocia (OD, n = 6), and we described their haematology profiles. Bitches diagnosed with UI had a patent birth canal and delivered no puppies yet (PUI) or only part of the whole litter (SUI). The OD group had no UI and showed strong abdominal contractions. Blood iCa did not differ between the PUI, SUI and OD groups and was not influenced by litter size. There was a significant positive relationship (R²  = .241, p = .013) between iCa concentrations and the dam's body weight. Glucose concentrations were also not significantly different between dystocia groups or influenced by body weight and litter size. Hypocalcaemia was detected in 11 bitches, and hypoglycaemia in two bitches. Pregnancy-associated anaemia was seen in about one-third of the bitches. Eight of 12 dogs had increased platelet counts, and ten had leukocytosis with mature neutrophilia. Although iCa did not differ between dystocia groups, low concentrations may have contributed to the development of UI in some of the small size bitches. Hypoglycaemia was uncommon, and therefore, we consider low glucose concentrations not to have played an important role in the pathogenesis of UI in our study population. Pregnancy-associated anaemia, thrombocytosis, leukocytosis and mature neutrophilia were common findings in otherwise healthy bitches diagnosed with different forms of dystocia.

Hormonal, Electrolytic, and Electrocardiographic Evaluations in Bitches With Eutocia and Dystocia

The objective of the study was to assess clinical alterations, electrocardiographic, hematological, biochemical, hemogasometric, electrolytic, and hormone plasma concentrations in bitches with eutocia and dystocia. Overall, 28 bitches (dystocia, n = 22 and eutocia, n = 6) were assessed. The evaluations were performed at 2 time points, M1 (1 hour prepartum-eutocia group and cesarean or clinical intervention-dystocia group) and M2 (postpartum-eutocia or dystocia group and anesthetic recovery-dystocia group). The main clinical finding was the hypothermia (mean: 36.9°C dystocia vs. 36.8°C eutocia). Sinus arrhythmia and tachycardia were the electrocardiographic parameters predominant in eutocia and sinus rhythm in dystocia group. The P wave amplitude, heart rate, creatinine concentration, hematocrit, and hemoglobin were increased in M1 (P < .05), whereas the concentration of TCO₂ was higher in M2. There was an increase in P₄ concentration in dystocia and total T₃ concentrations were increased in M1 in both groups. Total T₄ was higher in dystocia during M1 and in dystocia during M2 in eutocia than in dystocia. We concluded that at 1 hour prepartum or pre-cesarean, there is an increase in heart rate in bitches with eutocia or dystocia, and this finding was correlated to thyroid hormone concentration. P₄ concentrations remained high during dystocia, and hematological and biochemical changes returned to normal after parturition. The evaluation of these parameters in pregnancy can be used as tool to prevent dystocia and consequent fetal death.