Luteal regression vs. prepartum luteolysis: Regulatory mechanisms governing canine corpus luteum function

Abstract

Canine reproductive physiology exhibits several unusual features. Among the most interesting of these are the lack of an acute luteolytic mechanism, coinciding with the apparent luteal independency of a uterine luteolysin in absence of pregnancy, contrasting with the acute prepartum luteolysis observed in pregnant animals. These features indicate the existence of mechanisms different from those in other species for regulating the extended luteal regression observed in non-pregnant dogs, and the actively regulated termination of luteal function observed prepartum as a prerequisite for parturition. Nevertheless, the supply of progesterone (P4) depends on corpora lutea (CL) as its primary source in both conditions, resulting in P4 levels that are similar in pregnant and non-pregnant bitches during almost the entire luteal life span prior to the prepartum luteolysis. Consequently, the duration of the prolonged luteal phase in non-pregnant bitches frequently exceeds that of pregnant ones, which is a peculiarity when compared with other domestic animal species. Both LH and prolactin (PRL) are endocrine luteotrophic factors in the dog, the latter being the predominant one. In spite of increased availability of these hormones, luteal regression/luteolysis still takes place. Recently, possible mechanisms regulating the expression and function of PRL receptor have been implicated in the local, i.e., intraluteal regulation of PRL bioavailability and thus its steroidogenic potential. Similar mechanisms may relate to the luteal LH receptor. Most recently, evidence has been provided for an autocrine/paracrine role of prostaglandin E2 (PGE2) as a luteotrophic factor in the canine CL acting at the level of steroidogenic acute regulatory (STAR)-protein mediated supply of steroidogenic substrate, without having a significant impact on the enzymatic activity of the respective steroidogenic enzymes, 3-hydroxysteroid-dehydrogenase (3HSD, HSD3B2) and cytochrome P450 side-chain cleavage enzyme (P450scc, CYP11A1). Together with the strongly time-dependent expression of prostaglandin transporter, luteal prostaglandins seem to be involved more in the process of luteal formation than in termination of CL function in the dog. The possible roles of other factors such as vasoactive compounds, growth factors or cytokines have not been extensively studied but should not be neglected. Abstract: Canine reproductive physiology exhibits several unusual features. Among the most interesting of these are the lack of an acute luteolytic mechanism, coinciding with the apparent luteal independency of a uterine luteolysin in absence of pregnancy, contrasting with the acute prepartum luteolysis observed in pregnant animals. These features indicate the existence of mechanisms different from those in other species for regulating the extended luteal regression observed in non-pregnant dogs, and the actively regulated termination of luteal function observed prepartum as a prerequisite for parturition. Nevertheless, the supply of progesterone (P4) de...

Expression and functional implications of luteal endothelins in pregnant and non-pregnant dogs

“…From this, it has been concluded that the reduction of vascular network density does not seem to be the major factor regulating luteal regression in dogs (Hoffmann et al 2004a,b). Corroborating these results, expression of the vascular endothelial growth factor (VEGF) system also remained unaffected during prepartum luteolysis (Kowalewski 2014). The initially increased vasculogenic and angiogenic activities are evidenced by the expression of members of the VEGF system in steroidogenic and non-steroidogenic cells (Mariani et al 2006, Papa Pde et al 2013.…”

“…As in other species, following ovulation and formation of the corpus hemorrhagicum, the canine CL is rapidly vascularized (see review in Kowalewski (2014)). During this time, PGs, especially PGE2, are among the most potent luteotropic factors regulating CL functions (Kowalewski et al 2015).…”

Biología Gestacional y Predicción del Parto en la Perra

“…Esto ha sido demostrado en hembras histerectomizadas donde la regresión luteal ocurrió sin necesidad de la secreción de PGF 2α uterina (Hoffmann et al, 1992). Dada la similitud en la duración y comportamiento de la producción de P 4 entre perras en diestro y perras preñadas, se puede seña-lar que la vida útil fisiológica y los mecanismos de control endocrino de los cuerpos lúteos caninos son similares (Kowalewski, 2014).…”

“…Desde un punto de vista endocrinológico, existe evidencia de que el útero canino es capaz de sintetizar prostaglandinas que probablemente contribuyen a la contractibilidad del miometrio durante el parto (Kowalewski, 2014), sugiriéndose, además, que los receptores oxitócicos estarían involucrados en la cascada de señalización para la síntesis de las mismas en el útero gestante (Gram et al, 2014). Además, se ha descrito un descenso en las concentraciones séricas de leptina hacia el final de la gestación (Cardinali et al, 2017), así como también la expresión de genes de leptina (Lep) y de receptores Lep en úte-ro y placenta canina (Balogh et al, 2015), postulándose que el sistema de señalización de Lep tendría un rol en el mecanismo de parto de esta especie.…”

The immunohistochemical presence and distribution of ghrelin, apelin and their receptors in dog ovaries

“…[1][2][3][4][5] Many studies in humans and laboratory and domestic animals have shown that these molecules have a ubiquitous distribution: they are not limited to the digestive and nervous systems, but also extend to organs and systems not anatomically and functionally related to appetite control, such as the reproductive system. 6 Moreover and also for this reason, their functional activity is not only limited to the food intake control but it is extended to the control of the functional activity of the organs where they were evidenced.…”