Itt írjon a(z) Pseudopregnancy-ról/ről

Canine Pseudopregnancy

Introduction

Canine Pseudopregnancy (PSPG), also known as pseudocyesis, nervous lactation, copycat pregnancy or phantom pregnancy, is a normal self-limiting physiological syndrome that occurs in female dogs in their late diestrual phase. Signs of pregnancy will be shown in the postpartum period, however, in reality, the bitch is not pregnant (Feldman and Nelson 1996; Gobello et al, 2001b). Behavioural and physical changes occur. These may be covert i.e. without any clinical signs, or overt i.e. with clinical signs and are seen between 6-8 weeks after estrus (Gobello et al. 2002).

Although its exact prevalence is not known, it has been estimated that its incidence rate is as high as 50-75% in certain breeds, using a broad definition of the condition (Johnston, 1980). Voith (1980) and Jochle (1987) shared the opinion through their work that PSPG evolved through families because of the need for non-mated wolves to lactate and feed other female wolves’ litters. This is called alloparental care in mammal species that live in groups, where submissive individuals care for the dominants’ offspring without reproducing themselves (Paul et al., 2014).

The purpose of this essay is to present the most relevant aspects of the physiology, clinical signs, diagnosis, treatment and prevention of clinical pseudopregnancy while also highlighting information regarding this syndrome in humans and goats.

a) Pseudopregnancy in Goats

b) Pseudopregnancy in Humans

The Canine Estrous Cycle

A good understanding of the canine estrous cycle and endocrinology is needed to fully grasp the concept of PSPG and the hormonal changes that cause it. The bitch is said to be monoestrous and has the onset of the first estrus between 6-10 months of age and goes through estrus every 6 months thereafter (Concannon, 2011; Gobello et al., 2001b).

The anestrus phase is marked by ovarian inactivity, endometrial repair and uterine involution and lasts about 6 months. Its termination is marked by the secretion of pituitary gonadotropins, follicle-stimulating hormone (FSH), luteinizing hormone (LH) induced by gonadotropin-releasing hormone (GnRH). The release of LH results in proestrus folliculogenesis (Blendinger, 2007).

This phase is then followed by proestrus, a phase averaging about 9 days where the vulva becomes enlarged and serosanguineous discharge can be seen. A prominent hormonal change of this phase is the LH peak which causes estrogen to decrease and subsequently increases progesterone steadily (Concannon et al., 1977). These changes result in the luteal phase of the ovarian cycle and therefore estrus is reached.

Estrus lasts about 9 days on average and is the part of the cycle where primary oocytes ovulate after 2 days of LH peak and then matures 2-3 days later, secondary oocytes lasts 2-3 days (Concannon et al. 1977). Lastly, diestrus is reached. Characterised by diminishing attraction of male dogs and resolving of vulvar oedema discharge, dioestrus is the stage of refraction from breeding and our point of interest regarding PSPG as this is where it occurs as an exaggerated response (Blendinger, 2007).

It is also important to point out that the canine is unique in that, the state of pregnancy or non-pregnancy has no difference in the duration of reproductive cycle stages, development of the mammary gland and values of serum estradiol and progesterone concentrations (Romagnoli, 2009). In addition, Stefano Romagnoli (2009) also pointed out that there will be considerable differences in hormonal values as seen in the data in Figure 1.

Figure 1: Aspects of the estrous cycle in the bitch.Adapted from Blendinger (2007); Concannon (1986); Root Kustritz (2012).

Causes

Although not everything is known about what causes PSPG, It has been suggested that sensitivity of the endometrium and mammary glands to progesterone (P4), the increase in prolactin due to progesterone’s abrupt decrease and other hormones are the culprits behind pseudocyesis occurring in the late luteal phase of diestrous (Grunau et al. 1996).

Since PSPG is normally seen around 6-12 weeks after heat, at the expected whelping time, and the anti-prolactin agents were successful in the treatment of this syndrome, it is clear why these theories bear weight (Jochle et al. 1989).

What is known for sure, is that all the hormonal changes in the estrous cycle are normal and required in order to prepare for pregnancy, and because they are in circulation for a few weeks even if unfertilised these changes deceive the body into thinking it is pregnant. In addition, the non-pregnant dog has a corpus luteum lifespan that exceeds that in pregnant dogs (Gobello et al., 2001b). Moreover, factors including nutrition, breed type, age and number of prior pregnancies also play a role (Johnston, 1980; Gobello et al, 2002).

a) Physiology of Progesterone

Progesterone, whose structure can be seen in figure 2, is a steroid hormone that regulates ovulation and menstruation. It is produced in the corpus luteum of the ovaries which remains functional in the non-pregnant bitch for an extended period after ovulation (Gobello et al. 2001).

Due to the fact that its secretion is induced by LH, progesterone peaks at the late luteal phase and its concentration is equal in pregnant and non-pregnant bitches since they have no maternal recognition of pregnancy (Gobello et al. 2002; Concannon, 2011).

The effects of progesterone on the female sexual cycle are the following:

1. Promotes implantation and maintains a healthy pregnancy

2. Thickens the vaginal epithelium and cervical mucus making it impenetrable to sperm cells

3. Inhibits lactation during pregnancy

4. Blocks central Estrogen effect as it is the physiological antagonist of oestrogen (Gobello et al., 2001c)

A study found that serum progesterone concentration was higher in pseudopregnant than pregnant labradors during weeks 1 to 6 of gestation or pseudopregnancy. It was also recorded that mean serum estradiol concentrations in dogs experiencing pseudopregnancy was drastically higher than those of gestating individuals through week 3 and the lowest values were only observed at week 5 (Chakraborty, 1987).

This shows that the reduction in progesterone coupled with its reversely proportional relationship to prolactin, which is illustrated in Figure 4, are noteworthy when it comes to the causes of PSPG. Moreover, Dogs who have been spayed during a time in their heat cycle where progesterone levels are high has been found to cause false pregnancy when progesterone rapidly drops after surgery (Johnston, 1986; Lee WM, 2006).

b) Physiology of Prolactin

Prolactin is a peptide hormone produced in the pituitary gland with its structure shown in figure 3. Secreted by lactotroph cells, it is an important hormone for the initiation and maintenance of lactation. Therefore, it is responsible for the enlargement of the mammary glands and activation of their ductal and glandular tissues (Gobello et al., 2001).

Increased prolactin serum concentrations, which occur when progesterone levels fall in the late luteal phase, inhibit the release of GnRH from the hypothalamus thereby decreasing the secretion of gonadotropins (Jochle, 1997). Its secretion is regulated by FSH and LH and cortical stimuli during lactation, while dopamine is said to be Prolactin’s antagonist as it acts on D2 type dopamine receptors on the lactotroph cells (Egli et al., 2010).

However, Gobello et al (2001) and Tsutsui et al (2007) both reported a lack of relationship between plasma prolactin and clinical PSPG, which is why studies suggest that individual sensitivity to prolactin, its association to progesterone decrease depicted in figure 4, as well as molecular variations of canine prolactin which exhibit different bioactivity from one another may help clarify the etiopathology of pseudopregnancy (Gobello et al, 2002).

c) Causes of Pseudopregnancy in Goats

d) Causes of Pseudopregnancy in Humans

Clinical Signs

All non-pregnant bitches in mid and late diestrus can either show no clinical signs i.e. covert pseudopregnancy, or have a wide range of observable clinical signs i.e. overt pseudopregnancy. Firstly, this syndrome usually manifests itself in behavioural changes, that include restlessness, decreased activity, anorexia, aggression and licking of the abdomen (Gobello et al. 2001).

In addition, Romagnoli (2009) highlighted maternal behaviour that include carrying of inanimate objects and puppies that don’t belong to her and also a nesting habit (Romagnoli, 2009). Later, physical signs such as mammary enlargement accompanied by milk secretion, weight gain and contractions of the abdomen that copy those of parturition can be observed (Mialot et al. 1984; Feldman and Nelson, 1996).

Romagnoli (2009) also pointed out ancillary signs such as diarrhoea, polyuria (excessive urine production) and polyphagia (increased appetite and feeding). Furthermore, mastitis and mammary dermatitis are known for being uncommon clinical complications of pseudopregnancy. However, if these do not appear, clinical signs of pseudopregnancy usually stop after 2-4 weeks (Johnston, 1986).

It was also found that susceptible bitches have a high recurrence rate in successive oestrus cycles (Feldman and Nelson, 1996). The risk of mammary tumours development related to the frequency of pseudopregnancies is illustrated in Figure 5 (Donnay et al., 1994).

Figure 5: Odds ratio for the risk of mammary tumours development related to the frequency of pseudopregnancies (Donnay et al 1994)

a) Clinical Signs of Pseudopregnancy in Goats